The Review of Waste Stream Management Using Composting
within the Irish Agri-Business Sector
Environmental Science & Technology, Year 4
SUBMITTED TO:
Dr. M.A.Broaders
PRESENTED BY:
Diarmuid Neilan
John Durcan
Michael Fielding
Table of Contents
1.0
Page Number
Introduction
3
1.1
What is Composting?
3
1.2
Characteristics and benefits
4
1.3
Composting Technology
5
1.4
Composting Processes & Practices
9
1.5
Composting standards & Legislation
15
1.6
Composting in Ireland in Relation to the Rest of Europe
17
2.0
Microbiological Composting Processes
2.1
The Three Stages of Composting
2.2
Functions of Micro-organisms
2.3
Optimum Conditions
2.4
The Biochemistry of Composting
18
18
20
22
28
3.0
Composting in the Agri-Business Sector
3.1
Organic Waste Streams in the Irish Agri-Business Sector
3.2
Manure as a Composted Material
3.3
Mushroom Composting/Spent Mushroom Composting
3.4
Pesticides & Composting
3.5
Manure-A Compostable Product in Ireland?
29
29
38
42
45
51
4.0
Case Studies
4.1
Cork Waste Shredder Scheme
4.2
International Case Study
53
53
54
5.0
Health Hazards & Mitigation Measures
5.1
Bioaerosols/Dust
5.2
Odour
5.3
Pathogens
58
58
60
62
6.0
Discussion and conclusion
66
7.0
Calculations of the Adjustments Required to Find the Optimum
C:N Ratios for Both Cattle Manure and Spent Mushroom Compost
67
8.0
References
69
9.0
Appendices
73-84
2
1.0
Introduction
1.1
What is Composting?
USEPA (1994) describes composting as a natural process that begins with the first
plants on earth and has been going on ever since. As vegetation falls to the ground, it
slowly decays, providing minerals and nutrients needed for plants, animals and microorganisms. Composting is often used synonymously with biological decomposition.
However composting generally refers to the controlled decomposition of organic (or
carbon-containing) matter by micro-organisms (mainly bacteria and fungi) into stable
humus material that is dark brown or black and has an earthly smell. Satriana (1974)
states composting is distinguished from digestion or fermentation in that the
decomposing material is primarily discrete solids with open pore spaces rather then
solids in a liquid or semi-liquid environment. Composting processes vary from
anaerobic to aerobic and from mesophilic to thermophilic decomposition. However,
aerobic thermophilic composting is generally believed to provide the most rapid, and
complete decomposition of the readily oxidizable matter. Forester and Wase ((1987)
states during the process degradable organic substances undergo chemical and
physical transformations to give a stable humidified stable end product. The product
is of value in agriculture both as an organic fertilizer and as a soil improver.
Brady and Weil (2002) describe the composting process as the practice of creating
humus like organic materials outside of the soil by mixing, piling or otherwise storing
organic materials under conditions conducive to aerobic decomposition and nutrient
conservation. The aerobic decomposition in a compost pile can conserve nutrients,
while avoiding certain problems such as noxious odours and the presence of either
excessive or deficient quantities of nitrogen, which can occur if fresh organic wastes
are applied directly to soils.
USEPA (1994) states composting programmes can be designed to handle yard
trimmings (e.g., leaves, grass clippings, tree trimmings) or the compostable portion of
a mixed solid waste stream (e.g., yard trimmings, food scraps, scrap paper products
and other decomposable organics). These materials are the feedstock for the
composting process.
3
Composting Unit Operational Model
Source: http://tmecc.org/tmecc/Table_of_Contents.html
1.2
Characteristics and Benefits of Composting
Brady and Weil (2002) outline seven distinct advantages of composting:
Safe storage: Composting provides a means of safely storing organic materials worth
a minimum of odour release until it is convenient to release until it is convenient to
apply them to soils.
Easier handling: As a result of CO2 losses and settling, the volume of composted
organic materials decreases by about 30 to 50% during the composting process. The
smaller volume and greater uniformity of the resulting material may greatly ease and
the eventual use of the organic matter as a soil amendment or potting medium.
Nitrogen competition avoidance: For residues with a high initial C/N ratio, proper
composting ensures that any nitrate depression period will occur in the compost pile,
not in the soil thereby avoiding induced plant nitrogen deficiency.
Nitrogen stabilization: When applied to the soil the composted materials generally
decompose and mineralize much more slowly then un-composted organic materials.
Composting low C/N ratio materials (such as livestock manure and sewage sludge)
with high C/N ratios materials (such as sawdust, wood chips, senescent tree leaves, or
municipal solid waste), provides sufficient carbon for microbes to immobilize the
excessive nitrogen and minimize any nitrate leaching hazard from low C/N materials.
It also provides sufficient nitrogen to speed the decomposition of the high C/N
materials.
4
Partial sterilization: High temperature during the thermophilic stage in well managed
compost piles ills most of weed seeds and pathogenic organisms in a matter of a few
days. Under less ideal conditions, temperatures in parts of the pile may not exceed 40
to 50 oC, so weeks or months are required to achieve the same results.
Detoxification: Most toxic compounds that may be in organic wastes (pesticides,
natural phototoxic chemicals, etc) are destroyed by the time the compost is considered
mature and ready for use. Composting is therefore often used as a method of
biological treatment of polluted soils and wastes.
Disease suppression: some composts can affectivity suppress soil borne plant diseases
by encouraging microbial antagonisms.
The U.S EPA states compost is a valuable soil amendment. Some of the
improvements in soil properties that can result from using compost are:





Improved soil porosity
Improved water retention
Improved soil filtration
Improved resistance to erosion
Enhanced storage and release of nutrients
 Decreased soil crusting
 Improved soil tilth
 Plant disease suppression
Due mainly to its organic matter and humus content, compost helps to reduce erosion
and improve plant growth, which can substantially reduce nutrient transport in runoff
to surface waters. Therefore, the addition of compost to soil not only reduces erosion
and recycles nutrients, but also provides important water quality benefits.
1.3 Composting Technology (Processes and practices)
Tchobanoglous and Kreith (2002) state the rationale underlying compost system
design is twofold: (1) provide optimum conditions for composting in an
environmentally and economically acceptable manner: and (2) determine the type and
size of the compost system and other aspects of the technology by the type, volume,
nature of waste, and the size of the available buffer zone.
The U.S EPA (1994) defines composting into three stages (pre-processing, processing
and post-processing). The technologies and methods used at each stage will depend
on a number of factors. These can range from simple low-technology systems that
require minimal attention and maintenance to complex systems that use sophisticated
machinery and require daily monitoring and adjustment. The design and complexity
of a composting programme is determined by the volume, composition and size
distribution of the feedstock; the availability of equipment and the capital and the
operating funds; and the end use specification of the product
5
Process Parameters
The breakdown of organic wastes during the composting process is a dynamic and
complex ecological process in which temperature and food availability is constantly
changing. The subsequent composting process involving microbiological processes
will be dealt with in section 2.0. But the rate of progress towards a mature end product
is dependent on several interrelated process parameters. Forester and Wase (1987).
These include the following:
Nutrient supply, Particle size, Moisture level, Structural strength, Aeration, pH and
size of heap.
Therefore, the choice of technology used at all stages of the composting process must
also consider these process parameters in order to have a successful composting
process.
Composting processing Methods
Pre-processing processes
U.S.EPA (1994) states pre-composting has a significant impact on the quality of the
finished compost product and the speed at which composting can be conducted. In
general the more effective the pre-processing stage, the higher the quality of the
compost and the greater the efficiency of processing. Pr-composting process can be
divided into the following:
1/sorting and removing materials that are difficult to compost
2/reducing particle size of the feedstock materials
3/treating feedstock to optimize composting conditions –mixing
(bulking agents – adequate porosity etc.)
1/ Sorting The USEPA (1994) describes the level of effort required to sort and remove unwanted
material from the composting feedstock depends on several factors. Including the
source of the feedstock, the end use of the product, and the operations and technology
involved. The more diverse the feedstock material, the more sorting and removal will
be required.
2/Reducing particle size and feedstock material.
Skitt.J, (1972), discusses the importance of having an initial small particle size to aid
rapid decomposition by providing greater surface area for microbial attack. It also
reduces the depth of oxygen diffusion and microbial advance within the particle, aids
the homogenizing of an initially heterogeneous material and improves insulation. On
the other hand, too fine a particle size will involve very small inter-particle voids.
These will impede the diffusion of 02 and CO2 from the sites being attacked,
especially during the thermophilic stage of composting when oxygen consumption is
the highest. This consideration is particularly important in heaps and windrows
relying on natural aeration, rather then on forced air supply.
Forester and Wase (1987) state a compromise of particle size is therefore necessary.
For mechanical plants with agitation and forced aeration the particle size may be as
low as 12.5 mm after shredding. For the naturally aerated static heaps and windrows a
6
particle size of approximately 50 mm is appropriate. In some publications the
minimum particle size is quoted as being as low as 3.5mmm for forced aeration
systems to 25mm for windrows. Other factors such as agitation are important also
here.
3/treating feedstock to optimize composting conditions –mixing
Skitt (2002) states it is reasonable to assume that the composting process can be
speeded up by the judicious use of agitation. Movement of the material aids,
especially in heaps and windrows, introducing a fresh air supply into the middle of
large masses where diffusion alone has been insufficient to maintain high O2 and low
CO2 levels. Agitation aids homogeneity of the composting mass, aiding an even
spread of organic material and nutrients. It will also cause particles to rub together
leading to abrasion, size reduction and exposure of the unattacked material. Also it
assists the uniformity of temperature, prevents overheating in the centre of large
masses, and cooling at the exposed surfaces.
USEPA (1994) state the mixing process is often required to achieve optimum
composting conditions. Mixing entails blending certain ingredients with feedstock
materials together.
For example bulking agents are often added to feedstock materials that have fine
particle size. Bulking agents have the structural integrity to maintain adequate
porosity and help to maintain aerobic conditions in the compost pile.
Forester and Wase (1987) also describe the process of ‘bulking’ which is normally
necessary to ensure an open matrix for air diffusion when composting finely divided
organic solids such as sewage sludge animal manure slurries. Wood chip have been
favoured as the bulking agent in aerated pile systems for sewage sludge.
Processing Technologies
The criteria for composting systems can be divided into two types as outlined by
Polprassert (1996) who describes both on-site and off-site systems. On-site refers to
composting organic waste in the place of generation. i.e., farm yard composting. Offsite systems involves collection and transportation of organic waste to be composted
at central plants; the composting process is either controlled manually or
mechanically. Off-site composting usually refers to composting of large qualities of
organic wastes and requires large scale industrialized processes.
Therefore composting systems can be divided into in two main categories (1)
Windrows and (2) In-vessel. Reflecting their mechanism of aeration, Windrows may
the turned type, forced aeration (static pile) type, or a combination of turned and
forced aeration.
Reactors in in-vessel systems have one of the following configurations: horizontal
drum, which is rotated slowly and which may be compartmentalized; vertical silo; and
open tank equipped with a stirring or an agitation device. All designs of in-vessel
systems have provisions for forced aeration. Tchobanoglous and Kreith (2002)
7
Figure 1 Simple flow diagram of processing methods
Source: U.S EPA 530/ R-94-003
Sorting
Process
selection
Passive piles
Aerated static piles
Turned
windrow
Suction
system
Positive
Pressure
System
In-vessel
Systems
Rotating
Drum
Tank
system
Curing/Storage
Aeration mechanisms
The provision of satisfactory aeration is an essential feature of almost all existing
compost systems. Tchobanoglous and Kreith (2002) describe the aeration mechanisms
involved in providing atmospheric oxygen fall into three broad groups, namely,
agitation, forced aeration, and turning. A particular system may incorporate one or a
combination of mechanisms. Agitation is accomplished by tumbling, stirring, and/or
the act of mixing, the composting mass. In forced aeration, air is either pushed or
pulled through the composting mass. Most in-vessel systems rely on a combination of
the three mechanisms. In windrow composting, milling and stacking the raw waste
accomplishes the initial aeration.
Forester and Wase (1987) state where the technology of forced aeration is applied
moisture loss can be excessive and it may be necessary to supply additional water to
the composting mass. Also, in natural aeration composting systems the lower central
regions of the composting mass becomes anaerobic because the rate of diffusion of
oxygen into the mass is too low for metabolic requirements. In such cases turning the
pile by hand or by machine allows air to reach these deficient regions.
8
1.4
Composting (Processes & Practices)
Processing Methods
Windrow systems
Polprasert (1996) states this process involves periodic turning of the compost piles,
manually about once a week or mechanically about once a day. The purpose of pile
turning is to provide aeration and mix the composting materials.
Construction
Tchobanoglous and Kreith (2002) describes a windrow is constructed by stacking the
prepared feedstock in the form of elongated pile. The procedure of packing the
material is influenced by the volume and nature of the feedstock, the design and
capacity of the available materials handling equipment, and the physical layout of the
windrow pad.
Windrow dimensions (height and width)
Forming windrows of the appropriate size helps maintain the appropriate temperature
and oxygen levels. Polprasert (1996) outlines the approximate size of the pile to be
13× 3 × 1.5 metres (length by width by height) but other size may also be employed.
Tchobanoglous and Kreith (2002) offers a more elaborate approach to determining
windrow dimensions describing three key factors that enter into the determination of
windrow dimensions include (1) aeration equipment, (2) efficient utilization of land
area, and (3) the structural strength and size of the feedstock particles. Structural
strength, in turn, is a key factor in the maintenance of the interstitial integrity needed
to ensure a sufficient oxygen supply.
Other factors outlined by the U.S EPA (1995) include type of feedstock, season, the
region in which the composting operation is being conducted and the tendency of the
materials to compact.
Windrow Geometry
Tchobanoglous and Kreith (2002) outlines that windrow geometry should be geared
towards climatic conditions and efficient use of pad area. In regions in which rains are
frequent or heavy and the windrows are not sheltered the cross sectional configuration
should be conical in order to shed water.
The USEPA states windrows with concave crests are appropriate during dry periods
when the moisture content when the moisture content of the composting material is
low to allow precipitation to be trapped more easily.
9
Figure 2 Diagram of windrow
The amount of moisture content in the windrow is a crucial factor for a healthy
microbial composition. The shape of the windrow is therefore influenced by climatic
conditions.
In areas of high precipitation the windrow should have a peak shape to help water
run-off. The absorption of too much moisture at this stage can have adverse effects on
the composting process.
Turning equipment used
The turning equipment used will determine the size, shape and space between the
windrows.
Figure 3 Method of turning a windrow
Likely Environmental problems
The US EPA states Leachate can be a problem in the windrow composting process.
However, problems can be minimized by constructing windrows on firm surfaces
surrounded by vegetative filters or trenches to collect the run off. Run off controls are
also helpful. The problems with odour will be dealt with in section 5 health hazards
and mitigation
10
Pollution of surface waters (lakes, streams) is the other major concern with leachate.
While leachate from leaf composting is generally not toxic, it may deplete the
dissolved oxygen in the water, possibly even to the point where fish kills could occur.
Because of its dark color, it might also lead to a discoloration of the water. In order to
prevent this potential pollution, leachate should not be allowed to enter surface waters
without prior treatment. http://www.state.nj.us/dep/dshw/rrtp/compost/problem.htm
Forced-air aeration composting
Aerated static Piles
In order to increase the rate of decomposition and reduce and remove the need for
turning Forester and Wase (1987) states some windrow processes force-aerate the
heaps from air channels or pipes beneath the windrows.
Polprasert (1996) discusses forced-air aeration composting as an efficient composting
method which ensures temperatures in the upper thermophilic range and provides an
effective inactivation of pathogens. Tchobanoglous and Kreith (2002) states this could
actually be an effective means of aeration as a prime savings would be in the
elimination of expensive turning equipment used in windrow composting. Although
in practice this savings may not actually materialize because some turning is
inevitably necessary for the satisfactory remedying of localized problem zones, for
ensuring the uniformity of decomposition, and for adequate destruction of pathogens.
Figure 4 Diagram of an Aerated static pile
Source: U.S.EPA (1996)
11
Construction
US EPA (1994) outlines that in this method piles or windrows are placed on top of a
grid of perforated pipes. Fans or blowers pump or pull air through the pipes and
consequently through the composting material. This maintains aeration in the
composting pile and minimizes or eliminates the need for turning. Woodchips (or
other porous materials) are poured over the perforation pipes at the base of the pile.
The feedstock is then added on top of the woodchips. A layer of finished compost or
bulking material is then layered over the feedstock, protecting the surface of the
feedstock from drying, insulates it from heat loss, and protects it from drying.
One innovations and advantage of the aerated static pile system as outlined by
Tchobanoglous and Kreith (2002) who describes - tying airflow rate and timing with
temperature control. The underlying rationale is to use windrow ventilation as a
means of cooling the interior of the windrow. The temperature control approach
attempts to control the optimum temperature (e.g., 130 to 140oF or 54.4 to 60oC).
Because temperature directly indicates the status of the process, electronic
temperature sensors, such as thermocouples or thermisters, provide a means to control
airflow as well as monitor the temperature.
Environmental problems
In the suction method being drawn through the composting material condensate
drawn from the pile also needs to be removed before the air reaches the blower. It is
important to use an additional system to contain the exhaust gases being drawn from
the pile. Therefore a filter is required to filter the odour and bioaerosols. No systems
indicated the use of the forced aeration system to collect the leachate .
In-vessel systems
In vessel systems are high technology methods in which composting is conducted
within a fully enclosed system. All critically environmental conditions are
mechanically controlled with this method, and with most in-vessel systems they are
fully automated.
Tchobanoglous and Kreith (2002) states the primary objective of the design of the invessel systems is to provide the best environmental conditions, particularly aeration,
temperature, and moisture. Nearly all in-vessel systems are forced aeration in
combination with stirring, tumbling or both.
The four basic configurations are as follows: Vertical silos, the horizontal silos, the
horizontal drum (usually rotating), and the horizontal open tank (rectangular or
circular).
12
Figure 5 Flow diagram of a typical in-vessel composting system
Source: U.S.EPA (2000)
Representative systems
Plug-flow vertical reactors
Forester and Wase (1987) describe the vertical silo systems as a circular or
rectangular in cross-section and may have more then one floor. The material passes
through on a continuous batch principle. The air is supplied through a perforated
floor. Agitation may be either by vertical screw or auger device, or by horizontal
rotating arms or ploughs.
Plug-flow vertical reactors is a tubular reactor that typically consists of along
cylindrical pipe where the reactants are fed into one end and the products are are
withdrawn from the other. Experiences with the plug-flow vertical reactor has
revealed difficulty in adequately aerating the contents throughout the column.
Rotating horizontal drum
US EPA (1994) state the rotating drum system relies on the tumbling action to
continuous mix the feedstock materials. Oxygen is forced into the drum through
nozzles through exterior air pumping systems. The tumbling of the materials allows
oxygen to be maintained at high and relatively even level throughout the drum.
Forester and Wase (1987) states rotating drum units basically consist of a cylinder up
to 4m in diameter and 40m long, inclined slightly to the horizontal, the feedstock is
physically broken down by attrition and abrasion as the drum rotates continuously.
Figure 6 Diagram of a rotating drum
13
Open Horizontal, Rectangle Tank
This method of in-vessel composting is a combination of forced aeration and
tumbling. It involves the use of a long horizontal bin. Tchobanoglous and Kreith
(2002) outline that in the operation of the system; properly prepared waste is placed in
the bin. Tumbling is accomplished by way of a travelling endless belt, and air is
forced through the perforated plates that make up the bottom of the bin and into the
composting mass in the bin. The belt is passed through the composting material
periodically. The open horizontal rectangular tank is one of the most successful invessel units. This is probably related to the aeration and adequate retention time.
Figure 7 Diagram of Open Horizontal Rectangular Tank
Vertical mixed reactor
This tank is equipped with a set of augers supported by a bridge attached to the central
pivoting structure. The bridge with its set of hollow augers, is slowly rotated. The
augers are turned as the arm rotates. The hollow augers are perforated and air is
forced through the perforations and into the composting material. Tchobanoglous and
Kreith (2002)
14
Environmental Considerations of In-vessel systems
Table1 Comparisons of composting processes
Source: http://www.epa.gov/owm/mtb/combioman.pdf (Sept.2002)
1.5
Composting Standards and Legislation
Both Quality and Marketing have been established as being critical to the composting
industry. In order for the industry to progress, the concept of common standards has
to be embraced by all. Across Europe, and where they exist, standards for
composting may vary significantly. In countries such as Germany and Austria,
regulations exist that owe much to decades of experiences, research and advances.
(Barth, 2003)
In Ireland, there is no direct legislation in place to cover composting and the recent
growth in the industry in this country has largely been driven indirectly by a number
of directives from the European Union.
Under the European directive on the landfill of waste (99/31/EC), each member state
must reduce the amount of biodegradable waste sent to landfill by 25%, 50% and 65%
by 2006, 2009 and 2016 respectfully. Reductions are relative to volumes recorded in
1995. Composting is generally been seen as a cost effective method of achieving
these targets.
15
Under the Waste Management Act, 1996-01, and the subsequent Waste management
(Licensing) Regulations 2004, facilities composting waste amounts greater than 5000
tonnes per annum must obtain a waste licence and perform quality analysis subject to
the terms of licence. (Herity, 2005)
In a waste licence application, compost facilities are referred to in the 4th schedule of
the Waste Management Act, 1996-01 – Recovery Activities, Class 2 and 13, and in
the 3rd schedule of the Waste Management Act, 1996-01 – Disposal Activities, Class
6 and 13.
Compost facilities may also come under the terms of the Air Pollution Act, 1987,
regarding dust and bioaerosol emissions; however it is more likely that these
parameters would be referred to in a Waste licence.
In those countries where standards do exist for composting, they may vary
considerably across borders. This is particularly so in relation for heavy metal content
and can be seen in table 1.
The working document ‘Biological Treatment of Biowaste’, second draft, commonly
referred to as the ‘Biowaste Directive’ aims to establish the requirement of member
states to perform compost quality testing according to specific parameters and to
establish separate collection schemes for Biowaste in order to reduce contamination.
It sets limits for the presence of heavy metals, certain micro-organisms and also
foreign matter. (Appendix1)
It also divides compost into classes; Class I compost, Class II compost and stabilised
Biowaste. It is intended that Class I compost be available for use without restriction,
Class II compost-where it is spread on agricultural land-must not exceed 30 tonnes
dry matter/hectare on a 3 year average.
Stabilised biowaste must not be used where food production is concerned and is
therefore likely to suitable for landfill restoration. (Herity, 2005)
As of November 2005, the European Parliament has abandoned the idea of legislation
specifically designed for biowaste and instead, they intend to focus solely on the
setting of quality standards.
16
Table 2 European Quality Standards
Country
Quality of Standard
Austria
Belgium
(Flanders)
Denmark
Germany
Ireland
Cd
Cr
Cu
Hg
Ni
Pb
Zn
Biowaste Ordinance Class
1
A
70
150 0.7
60
120
500
Agricultural Ministry
70
90
20
120
300
-
100
0.8
0
30
120
4000
100 100 1
50
150
400
1.5
100 100 1
50
150
350
1.5
100 100 1
50
150
400
20
100
200
1.5
Agricultural Ministry
0.4
II
Biowaste Ordinance Type
1.5
II
Draft
Luxembourg Environmental Ministry
1
Netherlands
“Second Class Compost”
1
50
Spain
(Catalonia)
Class A (draft)
2
100 100 1
60
150
400
Sweden
Quality
organisation
1
100 100 1
50
100
300
United
Kingdom
TCA Quality Label
1.5
100 200 1
50
150
400
1.6
assurance
60
0.3
Composting in Ireland in relation to the rest of Europe
The European Union prior to the 2005 enlargement can be divided into categories
based on their development of organic waste activities.
Figure 8
17
Austria, Belgium (Flanders), Germany, Switzerland, Luxembourg, Italy, Spain
(Catalonia), Sweden and the Netherlands fall into category I as they have fully
implemented waste strategies and separately recover 80% of their organic waste most
of which is composted.
Denmark, United Kingdom and Norway make up Category II as these nations have
established the correct political, quality and organisation framework for separate
collection and composting.
Finland and France fall into category III. These two nations have developed a
strategy and are at the initial stages as regards separate collection and recovery of
their organic waste stream.
In the fourth category are countries where no organised effort has been established for
the composting of source separated organic waste. These countries include Ireland,
Greece, Portugal and parts of Spain.
It is estimated by the Environmental Protection Agency that 85% of the waste stream
in Ireland is organic and that up to 33 million tonnes of farm waste currently being
disposed of on land could be treated by a combination of composting and anaerobic
digestion.
At present there are 27 composting facilities throughout Ireland with several more
proposed, however obtaining planning permission remains a stumbling block.
(http://www.compostnetwork.info/biowaste/biowaste.htm)
2.0
Microbiological composting processes.
When observing the actions of micro-organisms within the composting process, one
may look at the life cycles and metabolisms of various individual micro-organisms, or
one may look at the overall product of their cumulative actions.
In the interest of simplicity this section will first describe the three commonly
recognised stages of composting, giving further detail when mentioning specific
functions of micro-organisms.
2.1
The three stages of composting:
The Initial Stage.
The Initial stage occurs in the first few weeks of the composting process. In this stage
the compost heap is colonised by common genera of mesophillic bacteria. Their rapid
rate of metabolism and carbohydrate utilisation begins to heat up the compost heap.
Presuming the absence of any major impingement on the mesophile’s metabolism or
habitat, as well as a helping hand from man (pH and C: N Ration adjustment), they
will continue to feed and reproduce. The sheer numbers and rapid rate of metabolism
within the compost causes the temperature to rise, which in turn creates difficulties
and opportunities for various species of micro-organisms. The heat produced by the
metabolism of the mesophiles will eventually cause the temperature of the compost to
exceed 40°C, and become a more habitable environment for thermophillic species.
18
The Active Stage.
Once the temperature has risen above 40°C the compost is now said to be in the
second phase or the active stage, as the majority of the degradation processes take
place by thermophillic (>40°C) bacteria. The main factor leading to the majority of
degradation taking place at this stage is largely due to the fact that these bacteria
produce active cellulolytic enzymes. It is important to note that all species of bacteria
may be present throughout all stages, but lie dormant through the action of cyst
formation or other spore formations.
The active phase of composting produces heat itself, and the thermophiles which
dominate here heat the compost to temperatures sufficient to kill of any potentially
pathogenic micro-organisms. Pathogens generally require temperatures surrounding
mammalian temperature (37°C) for survival and in an unventilated compost pile the
temperature
can
reach
in
excess
of
160°F,
(71°C)
(http://www.ciwmb.ca.gov/publications/organics/44200013.doc).
However, a well maintained compost heap is not allowed to reach temperatures in
excess of 65°C, as this is detrimental to the survival of many of the thermophiles and
dormant mesophiles themselves.
The temperature of the compost pile is managed at this stage by periodic turning of
the pile. As well as keeping the temperature in check, this also incorporates oxygen
into the system and increases the pore space.
The active stage of the composting process breaks down a great deal of the proteins
and fats present, as well as some complex carbohydrates. Due to the nature of the
bacteria these energy sources will eventually become scarce, and as thermophillic
bacteria become scarce themselves, the temperature of the pile will descend to
temperatures below 40°C again. This is regarded as the third and final stage of the
composting process.
The Curing Stage.
This third stage of the process is often referred to as the curing or maturation phase. It
differs significantly to the other two phases as it is dominated not by unicellular
bacteria, but by fungi and actinomycete degraders. The populations of these microorganisms rise as environmental conditions are invariably favourable for them in
older composts.
The temperature has dropped somewhat and there remains a carbon source in the form
of the non-water soluble carbohydrates (Lignin, hemicellulose and humic material). It
is extra-cellular degradation which gives these groups the upper hand once the readily
degradable organics are depleted.
19
2.2
Functions of micro-organisms
Colonisation of the compost material.
Colonisation of compost material may be primarily accredited to mesophillic freeliving bacteria. These bacteria are omnipresent in municipal and agricultural wastes,
and also enter the compost heap through the feedstock and exposure to the air.
During the initial stage of composting these bacteria will first utilise the most readily
degradable hydrocarbons, and reproduce rapidly.
Many different communities of bacteria will proliferate during this stage, the diversity
of which is comparable to that of topsoil, with bacillus and clostridia among the most
predominant genera. There is generally no requirement for inoculation of the
feedstock due to the nature and source of the material, especially in the agricultural
sector.
The rate at which bacteria grow in the initial stage is subject to many varying factors
such as the oxygen content of the compost, the pore space within the compost, water
content, carbon – nitrogen ratio and the range and volume of organics and toxins
present etcetera. These conditions which vary enormously will be dealt with in section
2.3 Optimum conditions. It can be presumed, however, that the growth of bacterial
populations is rapid here unless high concentrations of pesticides or toxins are
present.
Carbohydrate Stabilisation and Humification.
The process of biodegradation is at play throughout all stages of the composting
process. In the initial stage the most readily available organics are broken down by the
mesophiles, and in the active stage these and even more complex organics are
degraded by thermophillic micro-organisms. The final stage of curing, in which fungi
and actinomycete populations predominate, can even reduce complex organics such
ad celluloses and hemi-celluloses. These are broken down by extra-cellular
degradation as the long chains and high molecular weights of the compounds are too
large to be ingested by the bacterial species present.
Bacteria are the most numerous living organisms in any compost. They can reach
numbers in excess of one billion per gram and make up 80 – 90 % of the billions of
micro-organisms
found
in
a
typical
gram
of
compost.
(http://compost.css.cornell.edu/microorg.html ). However due to their size they do not
contribute as much to the overall microbial mass as fungi. The bulk of decomposition
within a compost system is still carried out by bacteria due to the sheer ferocity of a
thriving colony’s collective metabolism.
(http://www.ciwmb.ca.gov/publications/organics/44200013.doc).
The composting process of any material is relatively simple to predict. When nutrient
levels (including the carbohydrate sources) and oxygen are available bacteria will be
first to colonise the pile (See section 2.5 Colonisation process). All waste organics
from agriculture, by their very nature, will contain large numbers of micro-organisms,
20
and the bacterial populations are by far the most predominant in utilising the soluble
and readily degradable compounds (http://compost.css.cornell.edu/microorg.html). It
is for this reason that the initial stage of composting, or initial degradation, is
dominated by mesophilic (0-40°C) bacteria.
Principals of Biodegradation/Recalcitrance.
1. Compounds which are substituted (e.g. Chlorinated), insoluble or of a high
molecular weight are more resistant to enzymatic attack and degradation.
2. Carbon-Hydrogen bonds are stable and require an energy input to be broken.
3. Many substances (e.g. Pesticides) are engineered to be stable. This is not
desirable from an ecological/Environmental perspective due to their
persistence.
4. Cyclic structures, Aromatic compounds, Cycloalkanes and heterocyclic
compounds are more resistant to linear ones.
5. Generally the more complex a compound, the more resistant it is. (e.g.
Polymers are more resistant to their large size and insolubility.)
6. Some compounds do not induce the synthesis of specific enzymes.
7. Some compounds are too large to enter the cell, and therefore are resistant to
intracellular degradation.
8. Compounds which are insoluble in water are more recalcitrant.
9. Compounds with excess toxicity, or products of degradation with excess
toxicity are more recalcitrant.
Pathogen destruction.
As mentioned in section 2.1.2, Colonisation of the compost material, a typical pile
will contain whichever species the pile comes into contact with. And due to the large
microbial biomass which is encouraged within the system, the risk of pathogen
growth must be considered. It is fortunate that the vast majority of the risk is averted
by the process and microbial populations themselves.
The active phase of composting produces heat itself, and the thermophiles which
dominate here heat the compost to temperatures sufficient to kill of any potentially
pathogenic micro-organisms. Pathogens generally require temperatures surrounding
mammalian temperature (37°C) for survival and in an unventilated compost pile, the
temperature
can
reach
in
excess
of
160°F,
(71°C)
(http://www.ciwmb.ca.gov/publications/organics/44200013.doc).
However a well maintained compost heap is not allowed to reach temperatures in
excess of 65°C, as this is detrimental to the survival of many of the thermophiles
themselves.
The temperature of the compost pile is managed at this stage by periodic turning of
the pile. As well as keeping the temperature in check, this also incorporates oxygen
into the system and increases the pore space.
It is generally recognised that a turned windrow system must be maintained at 55°C
or higher for a period of 15 days, and turned at least five times during this time for a
satisfactory level of pathogen removal. (See section on pathogen removal).
21
Nutrient management.
Micro-organisms within a compost system are the main biological material within that
system, and therefore follow the same biological principles within another area of the
biosphere. Microbes multiply rapidly during the initial and active phases and in doing
so they remove nitrogen, as well as many other organic nutrients from that portion
which is bio-available. This reduction in the proportion which is bio-available does
restrict the growth of the microbial biomass, but it also has much greater advantages.
In the preparation phase of composting, where feedstock is added, the primary
considerations include the carbon-nitrogen ratio (C: N Ratio). This is due to the fact
that they are the two principle elements at play during biodegradation of organic
matter.
If the carbon content of a pre-compost material was too high, then there would be a
deficiency in the nitrogen, which would restrict microbial growth. This would
eliminate the active phase of composting as there would not be sufficient heat
generated. The composting process, if possible, would take many extra months/years
to complete, and this would cost a direct factor in the financial viability of a
commercial composting facility.
If on the other hand the carbon content was not great enough, then microbial growth
would exceed that which is required for stable degradation, and there would be
residual nitrogenous material.
Curing of the compost material.
This process takes place at the end stage of the process, and is defined as the
degradation of the remaining carbohydrates by actinomycete and fungal species
through extra-cellular degradation.
Insoluble carbohydrates such as Cellulose and hemi-cellulose are not broken down to
a great extent in the earlier stages due to the availability of more readily degraded
materials, and subsequent proliferation of bacteria. Once these materials become short
in supply new species of micro-organisms, which now have the advantage, begin to
advance.
Degradation of insoluble carbohydrates is often described as one of the most
important chemical reactions on earth, as if the reactions could not take place, the
carbon would effectively be lost from the biosphere.
2.3
Optimum Conditions/ Factors influencing composting
Micro-organisms are essential to the composting process. The environmental
conditions that maximize microbial activity will maximize the rate of composting.
Microbial activity is influenced by the following: Temperature, oxygen level, Nutrient
level and balance, pH of the materials, C/N ratios and moisture content.
Any changes in these parameters are interdependent; a change in one parameter can
often result in changes in others.
22
Table 3 Desired characteristics of raw material mixes
Characteristics
Reasonable Range
Carbon to Nitrogen
20:1 – 40:1
(C:N) Ratio
Moisture Content
40-65%
pH
5.5 - 9
Bulk Density
Less then 1100a
U.S (pounds per cubic
yard)
a = 40 pounds per cubic yard
Source:
2000)
Preferred Range
25:1 – 30:1
50 – 60%
6.5 – 8.5
http://compost.css.cornell.edu/OnFarmHandbook/ch3.p15.html
(updated
Temperature
At any time, the temperature of a pile of organic waste reflects the balance between
microbial heat generation and the loss of heat to the surroundings. Cheremisinoff
(2003) states the rate of heat generation is a function of factors such as temperature,
oxygen, water, nutrients, and the remaining concentration of easily biodegradable
organic materials. The rate of heat loss is a function of factors such as ambient
temperature, wind velocity, and pile size and shape. Temperature is a powerful
determinant of the rate of decomposition.
Composting will generally take place within two temperature ranges known as
mesophilic (50-105oF) and thermophilic (over 105oF). Although mesophilic
temperatures allow effective composting, experts suggest maintaining temperatures
between 110oF and 150oF.
http://extension.usu.edu/files/agpubs/agwm01.pdf
Microbial activity can raise the temperature of the pile's core to at least 140 °F. If the
temperature does not increase, anaerobic conditions (i.e., rotting) can occur.
http://www.epa.gov/epaoswer/non-hw/composting/science.htm
Temperature and Oxygen
Heat generated by microorganisms as they decompose organic material, increases
compost pile temperatures. There is a direct relation between temperature and rate of
oxygen consumption. The higher the temperature the higher the oxygen uptake and
the faster the rate of decomposition. Generally oxygen level of 5% by volume in a
composting mix is required for aerobic conditions. However, increasing the
concentrations over 15% may result in a temperature decrease because of the
increased airflow. Therefore temperature monitoring in conjunction with oxygen
monitoring is required. Moon (1997).
Oxygen
EPA (1996) states although composting can occur under both aerobic and anaerobuic
conditions it occur about 20 times faster under the aerobic conditions. As stated
previously anaerobic composting tends to generate more odours, as noxious gases
such as hydrogen sulphides and amines are produced. The microflora involved in the
composting process requires oxygen. In the absence of oxygen these will diminish
23
and anaerobic micro-organisms will replace them. This occurs when the oxygen in the
compost heap falls below 5-15%.
Therefore void spaces must be present within the composting material. So the oxygen
requirements of the compost heap depends on a number of factors:
1/the stage of the process - it is usually required at the initial stages but isn’t required
at the curing stage.
2/the type of feedstock - Dense nitrogen rich material will require more oxygen
3/the particle size of the feedstock - smaller feedstock will tend to condense reducing
the void space and therefore oxygen availability. Therefore the size of shredded
material in the feedstock needs to be monitored depending on the type of initial
feedstock being composted. Generally forced aeration systems can compost smaller
particle sizes but windrow systems would require more void space and bulking
material.
4/the moisture content of the feedstock – Materials with high moisture content will
generally require more oxygen. Increasing moisture content in a pile could force the
air out leading to anaerobic conditions.
Oxygen flow
In relation to windrow composting processes turning the pile, placing the pile on a
series of pipes, or including bulking agents such as wood chips and shredded
newspaper all help aerate the pile. Aerating the pile increases decomposition. Care
must be taken, however, not to provide too much oxygen, which can dry out the pile
and impede the composting process.
http://www.epa.gov/epaoswer/non-hw/composting/science.htm
pH and Materials
Composting may proceed over a range of pH’s without seriously limiting the process.
The optimum pH for micro-organisms involved in composting lies between 6.5 and
7.5 %. Optimum conditions for bacteria are 6.5 to 7.5 and 5.5 to 8.0 for fungi. The pH
of most animal manures is approximately 6.8 to 7.4. Composting itself leads to major
changes in materials and their pH’s, as decomposition occurs. For example release of
organic acids may temporarily lower the pH, and production of ammonia from
nitrogenous compounds may raise the pH in the early stages of composting. Whatever
the pH in the starting stages composting will eventually yield a stable pH usually near
neutral. http://www.agf.gov.bc.ca/resmgmt/publist/300series/382500-2.pdf
Rynk et al (1992). states the pH can also affect the amount of nutrients available to
micro-organisms. Also if the pH drops too low certain heavy metals within the
feedstock may become immobilized and therefore kill off the micro-flora.
If the pH drops below 6 micro-organisms especially die-off and decomposition slows.
If the pH rises above 9 nitrogen is converted to ammonia (NH3) and becomes
unavailable to organisms. This also slows the decomposition process.
Like temperature pH will follow a successional pattern through the composting
process. The diagram below indicates the progression of pH over time in a
composting pile. As illustrated most composting takes place between 5.5 and 9.
24
Figure 9 Compost temperature and pH variation with time.
Source: http://www.agf.gov.bc.ca/resmgmt/publist/300series/382500-2.pdf
As the diagram indicates during the start of the composting process organic acids are
typically formed and the composting materials become acidic with a pH of about 5.At
this point the acid tolerating fungi play a significant role in decomposition.
Acidophilic micro-organisms and fungi soon break down the acids and the pH levels
gradually rise to a more neutral range. The role of bacteria increases in predominance
again as the pH levels rise. If the pH doesn’t rise this could be an indication that the
compost is not fully matured or cured.
C/N ratios
The rate of carbon to nitrogen affects the rate of decomposition. The rate must be
established on the basis of available carbon. An initial ratio of 30:1 carbon: nitrogen is
considered ideal. To lower the carbon: nitrogen ratios, nitrogen rich materials e.g.,
animal manures may be added.
http://www.epa.gov/epaoswer/non-hw/muncpl/dmg2/chapter7.pdf
Moisture content
Water is essential for biological functions in general and composting is no exception.
Adding water (when needed) at the start of the composting process is very important
to ensure adequate moisture throughout the pile at the time of its function and
thereafter.
Composting proceeds best at a moisture content of 40-60% by weight. Moisture is
necessary to support the metabolic processes of the microbes. At lower moisture
levels, microbial activity is limited. At higher levels, the process is likely to become
anaerobic
and
foul-smelling.
http://compost.css.cornell.edu/monitor/monitormoisture.html
Water displaces much of the air space within the composting material when the
moisture content is above 65%. This limits the air content and leads to anaerobic
conditions. Moisture content generally decreases as the composting proceeds; so
moisture may need to added to the compost.
http://extension.usu.edu/files/agpubs/agwm01.pdf (Oct.1995)
25
Moisture content and air temperature
An important factor to consider when striving to maintain the correct moisture content
of the pile is to measure the air temperature. Steam rises from composting material
during turning. With a pile of compost, if the air comes up from the bottom of the
pile, the bottom of the pile usually dries out first because low temperature air (e.g. (10
o
C) enters the pile at the bottom and picks up moisture as the air warms. The warm
saturated air (60 oC) rises to the surface and equilibrates with the outside air. If the
outside air temperature is low, there is a zone of equilibration near the surface of the
compost, where the moisture in the hot rising air is condensed onto the surface of the
composting mass. If the outside air temperature is high, the air has much more
capacity for holding moisture, which means that the compost pile dries out faster.
This can be observed during the summer months, where compost piles often require
water
addition
because
they
dry
out
very
quickly.
http://www.wormswrangler.com/article6.html
Other factors influencing composting
Chemical composition
Dramatic changes in chemical composition occur during the composting process.
Most starting materials for composting are plant-derived residues and contain carbon
in the form of polysaccharides (cellulose and hemicellulose), lignin, and tannin. The
end-product has a low polysaccharide content, most of which is microbial cell wall
and extracellular gums, with about 25 % of the initial carbon content present in the
form of highly stabilized humic substances. Organic matter content ranges from 30 to
50 % of dry weight, with the remainder being minerals. The combination of high
organic content and a variety of minerals makes compost an excellent adsorbent for
both organic and inorganic chemicals.
http://www.epa.gov/epaoswer/non-hw/compost/analysis.txt
Toxic Substances
The high temperature achieved during the composting process also accelerates the
relative slow chemical reactions that occur in soils, where temperatures are 15-30oC
in most temperate climates. By comparison, typical temperatures during composting
are 50oC or higher. Humic materials can catalysis degradation of such compounds as
atrizane and other compounds. Also since the humic content of mature compost can
be as high as 30% by weight, whereas typical soils contain less then 5%, compost
contains a much higher concentration of reactive chemical then is found in soils
http://www.epa.gov/epaoswer/non-hw/compost/analpt2.pdf
26
Micro-organisms and the composting processes
Table 4 Micro-organisms in composting
Microflora
Bacteria
(very small plants)
Very thin, enormous numbers. Many varieties spheres, rods, filaments, Some form spores, Size
range 1-8um
Actinomycetes
They have slender branched filaments. Flourish
under hot, fairly dry conditions. Filaments 0.52um
Fungi,
moulds, Larger organisms. Usually form filaments and
yeast’s
spores (pseudohyphal yeasts). Several varities.
The thermophilic ones are very important. Size
range 3-50um.
Algae
Prefer wet conditions. Size range 10-100um
Viruses
Extremely small. Need a host organism.
Bacterium or actinomycetes, to live on. Size: head
0.1um diameter. Tail 0.2 um long
Microfauna
Protozoa
Move around with whips or hairs. Some prey on
Very small animals
the bacteria. Size range 5-80 um.
Macroflora
Macro-fungi
Or higher fungi. Grow up through the compost
(larger plants)
heap with fruiting body in the air above. Size of
the head about 25mm diameter
Macrofauna
Millipedes,
Millipedes mainly vegetarian. Centipedes
centipedes
carnivorous.
Sizes:
millipedes
20-40mm
long,centipedes 30mmlong
Mites, springtails
Wide range of sizes. Some are vegetarian, others
carnivorous. Size range 0.1-1-2 mm
Worms
Eisenia foetida, or manure worm, very important
Also
in the manure heap. Size ranges 30 –100mm.
ants,termites,spiders,
beetles
Source :Forester and Wase (1987)
The table above gives an indication of the micro-organisms present in a healthy
composting pile. Although optimum composting conditions kill pathogenic organisms
it also produces some microflora in the 1um -10um size range that may result in
respiratory problems. An important factor to be considered when composting.
Summary
To sum up, composting is a biological process influenced by a variety of
environmental factors, including the number and species of micro-organisms present,
oxygen levels, and particle size of the composting material, also nutrient level,
moisture content, temperature and pH. All of these factors are interrelated and must
be monitored and controlled throughout the composting process to ensure a quality
product.
27
The composted end product will be a stable product this means it will not undergo
rapid decomposition or produce nuisance odours when applied by users. If the
composting has undergone the adequate composting and curing procedures there
should be no problem in achieving a stable product.
In the composting process Mesophilic bacteria and fungi are dominant in the initial
warming period, thermophilic bacteria (especially actinomycetes) during the
high temperature phase, and mesophilic bacteria and fungi during the curing phase.
The resulting compost has a high microbial diversity, with microbial populations
much higher than fertile, productive soils and many times higher than in highly
disturbed or contaminated soils.
2.4
The Biochemistry of Composting
Aerobic composting is the decomposition of organic waste in the presence of oxygen,
which produces carbon dioxide, ammonia, water and heat energy.
teria

 CO2 + NH3+ other end products + heat energy.
ORGANIC MATTER aerobicbac
In the absence of oxygen the end products are methane. Carbon dioxide, ammonia,
other gases and low molecular weight organic acids.
acteria


 CO2 + H2S + NH3 +CH4 + other end products
ORGANIC MATTER anaerobicb
+ heat energy
The biochemical breakdown of organic waste is complex and depends on the nature
of the waste. Its stages correspond with the microbial growth patterns observed in
composting. (Polprasert, 1996) The biochemical processes described above take place
during the thermophillic stage. During the mesophillic stage, secondary fermentation
occurs, a slow process which ultimately leads to the formation of humus. It is also
during this stage that Nitrification occurs whereby ammonia is oxidised to Nitrite by
Nitrosomonas, then to Nitrate by Nitrobacter bacteria.
NH4+ +
3
as
O2 Nitrosomon


 NO2- + 2H+ + H2O
2
NO2- +
1
 r  NO3O2 Nitrobacte
2
During aerobic composting, oxygen has two main functions:
 A terminal electron acceptor in aerobic respiration.
 A substrate for the enzyme oxygenase.
Oxygenases are capable of incorporating oxygen into molecules from alkanes,
aromatic hydrocarbons and halogenated hydrocarbons.
Haug (1980) described the various biochemical stages of composting.
28









Release of extracellular hydrolytic enzymes by the cell and transport of
enzymes to the surface of the substrate;
Hydrolysis of substrate molecules into lower molecular weight , soluble
fractions;
Diffusion transport of solubilised substrate molecules to the cell;
Diffusion transport of substrate into the microbial cell, floc, or mycelia;
Bulk transport of oxygen (usually in air) through the voids between particles;
Transport of oxygen across the gas-liquid interface and the unmixed regions
which lie on either side of such an interface;
Diffusion transport of oxygen through the liquid region;
Diffusion transport of oxygen into the microbial cell, floc, or mycelia; and
Aerobic oxidation of the substrate by biochemical reaction with the organism.
3.0
Composting in the Agri-Business Sector
3.1
Organic waste stream from the Irish Agri-business
Waste Generated in Ireland
Waste is generated in all areas of Irish society. Information published by the
Environmental Protection Agency (EPA) in the three National Database Reports
(1995, 1998 and 2001) demonstrates a general trend towards increased waste
generation. Household waste, commercial waste and construction and demolition
waste all show clear upward trends. In line with international experience, there
appears to be a correlation between waste data and economic indicators showing
increased household waste generation with economic growth. Coupled with
decreasing available waste disposal capacity, this presents the driving force to
prevent, reuse, and recycle all waste.
http://www.ambdublin.um.dk/da/menu/Eksportraadgivning/Markedsmuligheder/Sekt
oranalyser/MiljoeOgEnergi/
The EPA National Waste Prevention Programme 2004 – 2008 states some of the more
significant waste generating sectors include agriculture, industry, and commerce.
Other areas include; the construction industry, mining, quarrying and households.
29
Figure 10 -Irish Waste Breakdown
Source:http://www.joanneum.ac.at/iea-bioenergytask38/workshops/dublin05/11_green.pdf
Agricultural wastes generated in Ireland
The EPA National Waste Prevention Programme 2004 -2008 states that the
agricultural sector is the single greatest generator of waste accounting for an estimated
56.7 million tones in 2001 or 76.5 % of all waste generated.
Agricultural waste can include such wastes as dairy wash waters to mushroom
composting. The EPA’s National Database report (2001) states the majority of the
waste arising from agriculture are all types of animal excreta (i.e., urine and faeces
from cattle, sheep pigs and poultry in the form of slurry) or where it is mixed with
straw farmyard manure. Typically this waste is applied to agricultural land to
attenuate soil and therefore doesn’t create same waste stream as municipal waste.
Principle Farm Wastes
The principle organic wastes concerning farmers are as follows:
 Animal slurries and manures
 Spent mushroom compost
Other Wastes Include
 Farm Plastics – farm films fertilizer bags, plastic drums.
As well as all of the above, there are hazardous wastes such as sheep dip and vetenary
medicines which arise on farms – these are under consideration by the EPA National
Hazardous Waste Strategy.
http://www.mayococo.ie/ConnaughtWastePlan/Part3WasteGeneration.pdf
Animal Slurries and Manures
Figures from the Environmental RTDI programme 2000-2006 show the annual
organic amendment of organic manures is 40,000,0000 tonnes which requires
management each year . Most of which is carried out at the farm stage through the
spreading of the organic waste onto soils. However limits are placed on farmers by
EU and National regulations including the revised P nutrient advice for grassland, the
EPA BATNEEC Guidelines, the national Code of Good Agricultural Practice to
Protect Groundwater from Pollution by Nitrates, and the National Rural Environment
Protection Scheme.
30
Spent Mushroom Compost (SMC)
In the National Waste Database Report 2001 the EPA states it was processing nine
waste licensing applications for composting waste facilities. The majority of these
were for the production of mushroom compost the raw materials of which consist of
straw poultry, horse manure, gypsum, and water.
Other Farm Wastes: Farm Plastics
The National Waste Management Plan (2002) recognised other on-farm waste streams
including farm yard plastics. Since 1997 Irish farm plastics group (IFFPG) have
operated a successful scheme to recover farm plastics i.e., bale wrap etc. As with the
general packaging waste scheme operated by repak, this voluntary compliance
scheme is backed by regulations made under the waste management act 1993(I.S. No
315 1997) under the regulations importers, manufacturers and suppliers are required
to participate in a waste collection and recovery scheme
Other categories of wastes generated on farms include some of the unreported
hazardous wastes for example: waste packaging (e.g., fertilizer bags, chemical;
containers, etc.) waste oils and oily sludge from machinery, unused or used crop
protection products, sheep dips, vetenary medicines etc. These waste streams are
considered product wastes are would be dealt with separately.
Hazardous waste, generated on farms include: waste packaging (E.G. fertiliser bags,
chemical containers, etc), waste oils and oily sludge’s from machinery maintenance,
unused or waste crop protection products, sheep dip, veterinary medicines, etc. These
non organic waste streams are principally ‘product waste’.
Sources of Organic Agricultural Wastes
The source of agricultural organic wastes is represented in the following pie-chart.
The 61.3% indicating cattle slurry should be animal manure.
Figure 11 – Irish Agri-Waste Breakdown
Source: EPA National Database 2001
31
Agricultural Organic Waste Production and trends
(See Appendix XIII)
Animal wastes
The graph below indicates a substantial increase in livestock numbers between 1985
and the late 1990’s. As the generation of animal waste is based on livestock numbers,
CSO (2002), this would seem to indicate a rise in the agricultural waste production
over this time period. The trend indicates a levelling off or reduction of livestock
numbers in the late 1990’s.
Figure 12 Livestock Numbers
Source:
http://www.cso.ie/releasespublications/documents/agriculture/2001/cropls_juneprovis
ional2001.pdf
Mushroom production
Mushroom production has expanded significantly over the last 20 years initially due
to increased British consumption. However in the past few years consumer
consumption has peaked and the demand has levelled off
According to the Teagasc, mushroom production continues to increase; the number of
units has declined from 576 in 1997 to 465 in 2001. The amount of compost waste
generated from mushroom production is determined by compost use. So the demand
will determine the production of waste.
Future Trends in Agricultural Organic Waste Production
As stated, the estimation of agricultural waste generation from Animals is based
primarily on animal numbers and the average waste per animal. Therefore it may be
possible to predict the future trends in the likely production of organic wastes
production. CSO publication Crops and Livestock Survey indicates the general
reduction of farm animal numbers in the period 1998-2005. The results indicate from
a total approximate number of cattle 7,571,000 in 1998 to 6,888,000 in 2004.Total
sheep numbers of 7,998,000 in 1998 to 6,204,000.2 in 2005. A pig reduction from
1,741,000 in 2001 to 1,645,000 in 2004. The results also indicate a reduction in
32
poultry numbers between 1999 and 2002. The results correspond with the results from
the EPA’s National Waste Database Report 1998-2001 that indicated a significant
change in waste generation between 1998 and 2001. In relation to agricultural waste
production the report states -agricultural waste and sludge generation have decreased.
Trends in Farm Animal and Poultry Numbers on Irish Farms
Figure 13 – Farm Animal Numbers
Cattle
Sheep
Pigs
Farm Animal Numbers
1998
1999
2000
2001
2002
2003
2004
2005
2006
9,000.00
Numbers (000')
8,000.00
7,000.00
6,000.00
5,000.00
4,000.00
3,000.00
2,000.00
1,000.00
Figure 14 – Farm poultry Numbers
Farm Poultry Numbers
Poultry
13,700.00
13,600.00
(000')
13,500.00
13,400.00
13,300.00
13,200.00
13,100.00
1998
1999
2000
2001
2002
2003
Years
Data
Source:
http://www.cso.ie/releasespublications/documents/agriculture/2001/cropls_juneprovis
ional2001.pdf
33
Data for organic agricultural waste generation 1998 - 2001
As the chart above and the graph below indicate the actual production of organic
waste on Irish farms has decreased inline with the reduction of livestock numbers.
The chart indicates a total of 10.23 % total organic agricultural waste over the time
period 1998-2001.
Table 5 -Animal Organic Waste
Source: National Waste Database 2001
Trends in Compost Production and Use in Ireland
Taegasc states it is reasonable to assume that the weight of spent mushroom compost
(SMC) is similar to weight of compost used. A census of mushroom production was
carried out by Teagasc in 1997 which estimates that 272,554 tonnes of compost was
used for mushroom production in 1997
Figure 15 –Compost Production
Compost Production and Use Ireland
1992-2002
Produced
Used
300,000
290,000
280,000
Tonnes
270,000
260,000
250,000
240,000
230,000
220,000
210,000
200,000
1992
1994
1996
1998
2000
2002
2004
Years
Year
Tonnes
1994
229,596
250,369
1996
259,257
259,512
1998
265,047
280,046
Data Source: Bord Glas/Daf/DARD/Teagasc
34
2000
259,290
270,177
2002
270,462
294,742
Management of Agricultural Wastes and Good Farm Practice
The EPA National Waste Prevention Programme (2004-2008) outlines how
agricultural wastes are typically applied to agricultural land. In the correct proportions
and when applied to suitable land its management in this way provides agronomic
benefits and may be a considered activity.
Nutrient management planning is required in many agricultural sectors (REPS, IPPClicensed) and its extension to all farms would ensure the improved management of
agricultural organic wastes. Advice on the management of agricultural organic wastes
comes with the remit of other organisations (e.g., Taegasc and the Dept. of
Agriculture and Food) and programmes (e.g., IPPC licensing). Opportunities for
reducing the volume of organic waste by good farmyard management practices and
division of clean run-off will be explored with these advisors.
http://www.ambdublin.um.dk/da/menu/Eksportraadgivning/Markedsmuligheder/Sekt
oranalyser/MiljoeOgEnergi/ (Jan.2005)
As stated The REPS scheme has specific guidelines developed on the appropriate
procedures for using other farmyard organic wastes in the attenuation of soils. These
include: Farm Yard Manure, Spent Mushroom Compost and Poultry Manure must not
be spread during the winter from November 1st.
Other guidelines include spreading of silage effluent to be completed by September
30th each year. Soiled Water and Dairy Washings can be land spread all the year
round where conditions are suitable and pollution risks minimal. Land spreading must
be
deferred
where
soils
are
saturated.
http://www.client.teagasc.ie/mayo/teagascnotes/slurry_spreading_in_reps.htm
Under Good Farming Practice, farmers outside REPS are encouraged through various
schemes (i.e., Disadvantaged Area Compensatory Allowance, Installation Aid, OnFarm Investment) not spread slurry, dungstead manure or chemical nitrogen the
winter months
Management of Agricultural Waste: Regional Approach
As prescribed in the Waste Management Act, 1996 (No. 10 of 1996) Local authorities
are encouraged to adopt a regional approach to the development of their waste
management plans, with a view to more effective provision of service and
infrastructure. In total there are 6 regional management plans incorporating 25 local
authorities. These include Dublin, the midlands, the north east, the north west,
Connacht and Cork City and County. In addition 6 counties in the south east have
waste management plans.
The Connacht has 6 local authorities- Galway Corporation and Galway City Council,
Leitrim, Mayo, Roscommon and Sligo.
http://www.forfas.ie/publications/waste_management_01/waste.pdf (Dec.2001)
The Connacht Waste Management Plan states the management of agricultural wastes
is not undertaken directly by the local authorities, but they do have the responsibility
for agricultural waste planning (under the waste management act 1996) to insure that
35
these wastes are disposed of in an environmentally friendly manner. which as stated
generally involves attenuation to lands to improve soils.
Of course if not managed correctly agricultural wastes can have adverse effects on
groundwater, surface waters and general environmental degradation of an area.
As stated under such schemes as REPS, farmers are advised as to the most appropriate
attenuation procedures for spreading slurry onto fields.
Composting of Farm Organic Waste
The EPA states a number of local authorities operate composting facilities including
Dublin City Council and Kerry County Council but these generally have emphasis on
composting of municipal waste although by 2001 the EPA were processing nine
waste licences for composting facilities engaged in the production of mushroom
compost.
Agricultural Waste Stream Disposal and Recovery
End of Use Animal Manures
The attributes of animal manure include; high organic content, high nutrient content
containing high P, K and N. Contains plant available S and Mg and has ideal water
holding capacity. Therefore, the primary management for manures is land spreading
and this likely to remain the same in the future. At present there is limited composting
of animal manures. Poultry manure is used to make compost for the mushroom
industry.
http://www.epa.ie/EnvironmentalResearch/ReportsOutputs/FileUpload,1961,en.pdf
(2002)
Poultry Manure
The use of poultry manure on REPS farms is not a viable proposition because of their
high N content. Fortunately for poultry producers, significant quantities of poultry
litter are used in making mushroom compost, and are not applied directly to land.
However, the resulting SMC is typically managed by land spreading following the
production of the mushrooms.
http://www.teagasc.ie/research/reports/environment/4026/eopr-4026.htm
The majority is managed by spreading on land as soil fertilisers. This has some
adverse effects if excessive chemicals are being used. It is considered recovery if
carried out in accordance with the farm nutrient management plan.
Spent Mushroom Compost
Approximately 280,000 tonnes of compost were used in 1998. Loss of dry matter as a
result of cropping s roughly 50kg/tonne of fresh compost with a dry matter content of
30%. However this loss is countered by the addition of a caustic layer. So the weight
of spent mushroom compost SMC is similar to the weight of the incoming layer.
http://www.epa.ie/EnvironmentalResearch/ReportsOutputs/FileUpload,1961,en.pdf
(2002)
36
Land application of SMC is attractive as an end use for SMC because it has been
practised successfully for a number of years. However, as concern over eutrophication
of Irish waters has increased, the use of phosphorus in agricultural systems has come
under closer scrutiny. Phosphorus is, therefore, the land limiting constituent in SMC.
Most crops on soils of moderate to good P status require very little P from external
sources.
Thus, in areas where mushroom growers are concentrated, such as Co. Monaghan,
need outstrips the supply of suitable land on which to apply the quantities of SMC
generated. Weather and cropping considerations further restrict the availability of land
that can receive SMC. In addition, there is competition for suitable spreading areas
posed by other organic sources of nutrients, most notably manure from livestock.
http://www.teagasc.ie/research/reports/horticulture/4444/eopr4444.htm (July 2000)
SMC as Organic Manure for Potatoes
Potatoes with their high nutrient demand and an area of 26,000 ha in 1999 are a
potential target crop for utilising SMC. This experiment was set up to assess the
suitability of SMC for use as a soil amendment and nutrient source for potato
production and studied its effects on the yield, quality and nutrient uptake of the crop.
Conclusion
The research indicates the organic waste stream from the Irish Agri-business mainly
includes animal excreta and mushroom compost. Generally in Ireland, the animal
manure produced only is only a fraction of the total waste that has to be managed.
This is usually the organic waste generated during the housing period of the animals.
This in some cases is as little as 6 weeks over the winter period. Although the EPA
National Waste Prevention Programme (2004 -2008) states that the agricultural sector
is the single greatest generator of waste. There isn’t any report as to an alternative
approach to organic on-farm waste management.
As prescribed in the Waste Management Act, 1996 (No. 10 of 1996) Local authorities
are encouraged to adopt a regional approach to the development of their waste
management plans, with a view to more effective provision of service and
infrastructure. Yet the management of waste outlined in the connacht regional waste
management plan for example is related to municipal waste streams and not farm
wastes. The traditional methods of on-farm nutrient management of spreading solid
and liquid manures seems to be the only approach with the relevant EU Directive as
guidelines and various incentive programmes as to the correct method of nutrient
management.
The research indicated the national herd has also reduced over the last 5 years so the
amount on the practice of organic waste has also decreased. Therefore, this is likely to
reduce the pressure on the practice of land spreading of manures.
As stated, land application of SMC is attractive as an end use for SMC although
concern over eutrophication of Irish waters has increase as the use of phosphorus in
agricultural systems has come under closer scrutiny. So as of yet there is little
information to the likely future use of SMC in Ireland.
37
3.2
Animal Manure as a Composting Material (selected example)
It has been estimated that 153 million tonnes (M t) of manure are produced annually
in Ireland by farmed livestock. In terms of perspective, this aggregate quantity of
manure would require 53% of the utilisable agricultural area (UAA, 4.43 M ha) if
applied at a rate of 20 t per hectare (t/ha).However, of this amount of manure, only
that produced when the animals are kept indoors requires management. Almost 43 M t
produced by cattle and sheep requires storage and spreading annually. Pig and poultry
enterprises produce an estimated 2.8 and 0.6 M t of manure, respectively, every year.
http://www.teagasc.ie/
Traditional uses of animal manure
As stated in Ireland the typical methods of disposing of animal manures is to spread it
on the land. For liquid manure techniques this involves either splash plate technique
or the band spread technique. For solid manure the rear discharge spreader or the
"sideflinger" spreader are the two most common types of spreading equipment.
Manure and odour emissions
Manure and odour emissions are almost synonymous. This is particularly true for pig
and poultry operations. Data from England indicates that there are about 4000
complaints annually about odours from farming (Pain, 1994). Pig and poultry farmers
were reported as being responsible for over 57% and 22%, respectively, of the
complaints. Land spreading causes more public odour complaints than any other
component of manure management. A recent Irish survey found 81% of odour
complaints recorded by Local Authorities derived from land spreading
Manure nutrients
The types and amounts of nutrients in manure and their eventual uptake by plants will
vary considerably from farm to farm and are determined by many factors. The major
determinants of manure nutrient content and availability are: (a) composition of the
rations fed to livestock; (b) method of waste collection and storage; (c) amount of
feed, bedding and/or water added; (d) method and time of land application, including
use of additives which preserve nutrient value; (e) characteristics of the soils; and (f)
type
of
crop
to
which
the
manure
is
applied.
http://www.ces.purdue.edu/extmedia/ID/ID-101.html
Differences in animal type, age, diet, will affect the characteristics of the manure also.
An appropriate C:N ratio and moisture content are essential for successful
composting. Poultry manure for example has a high nitrogen content then other
animal manures and is moist. Low C:N ratios is an issue and therefore nitrogen loss
and the associated odour can be a problem due to the high nitrogen content and high
pH. On the other hand the poultry manure decomposes quickly and makes excellent
compost with a high nutrient value. Horse manure is also a good composting material
and tends to be relatively dry with a high C:N ratio due to the amount of bedding. It
will compost well and can be added to wetter manure like cattle manure.
http://www.agr.gov.sk.ca/docs/crops/integrated_pest_management/Soil_fertility_fertil
izers/CompostManure02.pdf
38
Nutrient composition influenced by feedstock
The levels of nutrients and the presence or absence of certain feed additives in
livestock rations will be reflected in the nutrient composition of manure. For example,
changing the levels of inorganic salts (sodium, calcium, potassium, magnesium,
phosphate, and chloride) and feed additives (copper, arsenic compounds, sulpher,
antibiotics, or enzymes) in rations will change the concentrations of these elements
and possibly the rate of decomposition of organic matter in the manure.
http://www.ces.purdue.edu/extmedia/ID/ID-101.html
For instance, the use of a phytase enzyme in poultry and swine rations can reduce the
phosphorus content of manure by 25 to 40%. Reducing crude protein levels and
supplementing with specific synthetic amino acids to balance the ration can reduce the
N
content
of
manure
by
22
to
41%.
http://srwqis.tamu.edu/proceedings/downloads/watkins.pdf
Copper sulfphate in rations fed to pigs will decrease dry matter degradation resulting
in sludge build-up in storage, but arsenic compounds in feed will increase
liquidification of manure. Changing the kinds and amounts of roughages or
concentrates in rations will also alter the composition of manure. Increasing the
fineness
of
grind
and
pelleting
improves
feed
utilization.
http://manure.coafes.umn.edu/research/sulfide_emmisions.html
Composting Manures – An alternative
Benefits of composting manure
As outlined in section 1.1 of the project. Composting of manure has the following
benefits:







It reduces substrate mass
Improves friability and handling characteristics
Destroys weed seeds and pathogens by generating high(60-700C) temperatures
during the process
Provides phyto-sanitory effects on incorporation into soil.
Incorporates inorganic N into the organic fraction, thus protecting from
immediate loss after application
Reduces odour and ammonia emissions during land spreading
Concentrates plant nutrients enabling application rates to be lowerand the risk
of crop smothering to be reduced.
http://www.defra.gov.uk/environ/pollute/livemanure4.pdf
39
Comparison of nutrient losses during the composting process and traditional
spreading methods
Composting
The potential benefits of composting may be lost and harmful environmental impacts
caused by poor practice. Increased rates of ammonia volatilization have been
measured and ammonia emissions are dependent on temperature, total ammonia-N
content, turning frequencies, moisture content, and the composition of the manure.
Nitrogen losses can range from less than 10% with manure composted with straw to
over 75% with poultry manure composted without any straw or wood waste. An
understanding of how ammonia is lost and how composting works is required to
minimize nitrogen losses. None of the other nutrients are lost during the composting
process, as long as the compost process is done in a manner than minimizes leaching
losses. For example, other nutrients will definitely be washed out of the composting
material
if
the
material
is
exposed
to
excess
rainfall.
http://www.wormswrangler.com/article6.html
Ammonia emissions can be reduced by composting manure with an initial C:N ratio
of >35:1 and by carefully balancing the frequency of turning to meet the conflicting
requirements sufficient aeration and minimum disturbance.
Traditional methods
During traditional manure management, nitrogen losses can range from 10% during
liquid storage to over 25% with solid storage. If the manure is not incorporated within
24 hours of application to the field, a further 30-40% of the nitrogen could be lost
with liquid manure, and 10-30% with solid manure. This means that a nitrogen loss of
over 50% with traditional manure management is not uncommon. These nitrogen
losses are easier to control during the composting process than during traditional
manure management. http://www.wormswrangler.com/article6.html
Composting of manure has been proposed to play a role in manure management
programs designed to protect water quality., Composting reduces the hazards from
transporting weeds and diseases because of the high temperatures involved in the
composting process. Odors as discussed earlier are usually reduced by composting.
There is much greater public acceptance of compost than raw manure, regardless of
the properties of either material. In fact, composted manure is a marketable product in
some cases that can result in significant farm income. Thus, composting manure could
play a role in dealing with the potential environmental problems related to manure
nutrients. http://www.wcds.afns.ualberta.ca/Proceedings/1997/ch05a-97.htm
Liquid manure composting
Composting is rarely considered as an option for liquid manure because of the amount
of bulking agent required to create a solid material having a moisture content of 5060%, which is the moisture content at which composting works best. For example, the
volume of bulking agent required to bring a 75% moisture content waste to 60% is
40
similar to the volume of waste to begin with, which means that you now have double
the volume of composting waste to process. As the moisture content of the initial
waste increases, so does the bulking agent requirement
Comparison of manure and compost disposal methods
Whether manure is stored or composted, there has to be a strategy for disposing it.
Manure and compost are valuable on-farm and off-farm resources. The following
chart indicated the advantage and disadvantages of disposing of manure in the
unprocessed state and as a composted finished product.
Table 6 On Farm management options for manure and used bedding
Unprocessed
Composted
Advantages Low cost
Easier to spread on land
Low labour input
Poses lower water quality risk
Nutrient content usually Less likely to contain weed seed and/or
higher
pathogens
Improves soil structure
Less odour
Slow release form of nutrients
Compost is a superior soil amender
Can reduce volume to spread by about 50%
Disadvantag Can be difficult to spread Compost contains more labour, time and money
es
Poses
higher
water then storing and applying raw slurry
quality risks
More likely to contain
weed
seed
and/or
pathogens
Odour can be a problem
May need to add N
source to pile
Considerati Must have adequate land on which to spread manure (raw manure volume is
ons
and approximately twice that of compost)
additional
Pathogens are a human health concern if not handled improperly
information Serious water quality hazards and regulatory violations can result if
composting or raw manure is piled or stored on site indefinitely
The herbicide clopyralid (among others) will not breakdown during animal
digestion, storage of manure or composting.
Source:http://www.metrokc.gov/dnrp/swd/compostingsoils/manure/documents/final_manure.pdf
41
Table 7 Off-site management options for manure and used bedding
Give away or sell raw Give away or sell used
manure
compost
Advantages
Avoid time, labour and Finished compost
is
cost of composting easier to give away or sell
while getting rid of then raw manure
manure
Possible to make a profit
on an initial system
investment.
Disadvantages System may necessitate Compost requires more
meeting and helping labour, time and money
people interested in
acquiring manure
Source::http://www.metrokc.gov/dnrp/swd/compostingsoils/manure/documents/final_manure.pdf
3.3
Haul manure from
premises
Easiest
and
quickest
management
option
Higher expenses
pickup
and
disposal fees.
Mushroom Composting/Spent Mushroom Composting
The mushroom industry in Ireland is estimated to be worth in excess of €100 million
to the economy. Production occurs widely throughout the country with the highest
concentration of farms being concentrated in the Cavan/Monaghan region.
An operation exists whereby mushroom compost is manufactured by a central body
and then distributed to a number of satellite growers, who harvest the crop and then
supply the mushrooms back to the central body for sale and supply.
Mushroom compost is a mixture of wheaten straw and poultry manure with the
addition of gypsum and water.. (APPENDIX 2).
This mixture is composted for 6-8 days followed by pasteuration for another 7-7 days
at which point the compost is spawned with mushroom mycelium, bagged and sent
out to the mushroom producers. Upon colonisation of the compost by the mycelium,
a layer of peat/limestone mixture is added to the subsurface which induces sporophore
formation.
Once production has ceased, all that remains is a material known as Spent Mushroom
Compost (SMC). Accounting for losses of dry matter during crop production, and
allowing for the addition of a surface layer of peat/limestone mixture, the volume of
spent mushroom compost that remains is approximately equal to the volume of
original mushroom compost supplied. As much as 300,000 tonnes of this agricultural
by-product is generated in Ireland each year. (Maher et al., 2000)
Spent mushroom compost cannot be used again in the mushroom industry for reasons
of hygiene. At present, it’s mainly used for land application; however it must
compete with more traditional materials such as livestock manure for the limited
amount of land available. For this reason, bags of spent mushroom compost are often
an unsightly presence in quarries and by roadsides wherever mushrooms are
produced.
42
Spent mushroom compost is naturally high in electrical conductivity indicating a high
content of water soluble salts. Average nutrient levels are 8.0 kg N, 3.9 kg P and 7.9
kg per tonne. It has dry matter content of approximately 35% of which 65% is
organic, a low bulk density of approximately 319 g/l and an unbalanced distribution
of major plant nutrients. (Appendix III)
In 2001, the Northern Ireland Centre for Energy Research and Technology (NICERT)
published a report which aimed to assess spent mushroom compost as a potential
energy feed stock. It found that on a dry, ash free basis, spent mushroom compost
had a calorific value ranging from 12.1 – 13.7 MJ/kg, a range similar to that of
sewage sludge.
It considered two combustion plant designs, a stoker fired chain grate boiler and a
bubbling fluidised bed combustor. It noted that high moisture content of spent
mushroom compost was a potential drawback as if an auxiliary fuel needed to be used
during start up, little energy would remain for recovery. An investigation into
possible emissions from the combustion process found that NOx emissions would be
high due to high levels of nitrogen (1.8%-2.9%), however SOx emissions would
remain low as although the sulphur content of spent mushroom compost is high
(1.25% - 2.99%), approximately 70% of this was in the inorganic form.
Phosphorus (0.55%-1.37%) and Chlorine (0.43%-0.55%) levels were also estimated
to be high; however the majority of both of these substances were likely to remain in
the ash as phosphates and chlorides.
It was estimated that for a combustion facility to function efficiently, approximately
100,000 tonnes of spent mushroom compost would be required each year. It proposed
situating the combustion facility in the north Monaghan region, citing both logistical
and economic reasons. (Williams et al., 2001)
At present no such combustion plant exists in Ireland.
A Teagasc study into how to manage spent mushroom compost concluded that, in
their opinion, land application and landscaping were “the most immediately available
and environmentally sustainable end use for large quantities of spent mushroom
compost” (Appendix IV)
In their report they envisioned centralised depots which would provide for the
following:
 Receive and mechanically de-bag spent mushroom compost
 Store spent mushroom compost between the months of November and
February
 Perform further composting and processing
 Organise the distribution of spent mushroom compost for re-use.
Using county Monaghan as an example, the study examined the possibility of
introducing one or more processing facilities which would be capable of handling 650
tonnes of spent mushroom compost per week.
Teagasc estimate that such depots “would achieve economies of scale in the
management of spent mushroom compost not possible with management approaches
undertaken by individual growers”.
43
Each depot would operate using either a high capacity bunker with biofilter to
alleviate odour or an aerated pile system with odour control accomplished by frequent
turning using a front end loading machine. The following table (Table 2) represents
the estimated costs involved in running such a facility.
Table 8 Estimated Running Costs
Estimated costs for a 650 t/wk centralised SMC depot using two composting
techniques.
Cost Category
Bunker System
Aerated Pile
Depot
structure
&
€1,370,000
€793,750
machinery
Compactor truck (30 m3)
€165,000
€165,000
Running costs
€28,000
€28,000
Contract haulage, 20 loads
€257,500
€257,500
per week, 24 t truck
The above figures do not include start up costs, labour costs or any eventual profits
arising from the sale of the end product.
Assuming the involvement of 100 mushroom growers, the running costs of such a
facility would be approximately €3175, a figure similar to disposal costs currently
associated with disposal of spent mushroom compost for a grower that operates four
mushroom tunnels. (Maher et al., 2000)
Both of the above mentioned studies relate to alternative end use for large quantities
of spent mushroom compost produced in Ireland and have discussed potentially viable
alternative options to the grossly unregulated spent mushroom compost management
that exists at present. They also highlight the financial difficulties associated with
various strategies, particularly for the majority of small time mushroom growers in
Ireland.
It may be that the lack of any direct legislation in the area of composting could be
responsible for the apparent lack of progress in the area. The employment of any
management strategy would require cooperation and involvement of all mushroom
farmers in the country and it is likely that any initial costs may have to be subsidised
by the relevant local authority in a public-private partnership.
Spent mushroom compost has recently been cited as being of considerable use in the
bioremediation of soils contaminated with polycyclic aromatic hydrocarbons
(PAH’s). A study carried out by the Chinese University of Hon Kong found spent
mushroom compost of the mushroom species pleurotus pulmonarius (oyster
mushroom) immobilised the fungal liginolytic enzymes Lactase at 45°C and
Manganese Peroxidase at 75°C.
In a laboratory controlled experiment, complete degradative removal of naphthalene,
phenanthrene, benzo[a]pyrene and benzo[g,h,i]perylene (200mg PAH/kg sandy-loam
soil) by 5% spent mushroom compost was observed in just two days under continuous
agitation at 80°C. The results suggest the possible use of spent mushroom compost in
‘ex-situ’ soil bioremediation. (Lau. 2003)
44
3.4
Pesticides In composting
Persistence and Degradation of Pesticides in composting.
The composting process, as detailed in previous sections, provides for the microbial
degradation of organics which are contained within the system. There are many
factors however which may impinge on biological action within the system, and
therefore have a negative impact on the process (toxins). Apart from this there are
many organics which may resist degradation due to their chemical structure, size etc.
and cause negative effects on the receiving soils.
Within composting in the agri-business sector, pesticides and herbicides are ideal
examples of substances which may have this effect. They are residual in almost all
tillage and fodder production, and also may be persistent through the digestive
systems of livestock. (See section on Ivermectin)
In general, composting provides the optimal conditions for pesticide degradation and
volatilisation, but due to their poisonous nature and possible high concentrations we
will look at their interactions within the composting process. Examples of specific
pesticides activities in composting have been drawn from a number of sources, but for
a more complete picture of their degradation see (pesticide microbiology – book).
It is important to remember that pesticides will behave quite differently in a compost
system, as they would in a soil system due to the increased temperatures, organic
matter and microbial activity.
Exit routes for pesticides within a compost system.
Composting is well suited for pesticide removal due to reactions which may take
place within a properly managed in-vessel or windrow system.
Pesticides may be broken down through metabolism by microbial species within the
degrading material. Due to the quantity and diversity of micro-organisms which make
up the biomass of a compost heap, there is a good chance that the pesticide will
encounter a microbe that can degrade it.
Alternatively pesticides may be co-metabolised by micro-organisms. This is a process
whereby the compound is adjacent to matter which is being used as an energy source,
and is consequently degraded. The microbe gains no energy from the co-metabolite.
The great diversity of bacteria and organic matter helps to promote the chances of this
happening.
During the active phase of composting, the elevated temperatures have a direct effect
on the rate of biochemical reactions. Since many systems reach temperatures in
excess of 65°C, and the rate of reaction doubles for every 10°C rise in temperature, it
is not unreasonable to presume some reactions may take place at four times that of a
room temperature of 20°C.
45
Degradation is not the only rout of pesticide removal from compost systems as
thermophillic temperatures achieved during the active phase of composting will often
be high enough to volatilise many pesticides, or products of their degradation. In the
tests carried out by Petroska, 1985, which are detailed within this report, diazinon (an
organophosphate pesticide) and chlordane (a chlorinated hydrocarbon pesticide) both
showed high levels of volatilisation, the latter releasing over 50% of it’s carbon
content in this manner. (See appendiced report on pesticide disposal))
Alternatively pesticides may be leached from the compost heap or adsorbed into the
humic material. (http://www.ciwmb.ca.gov/publications/organics/44200015.doc ).
Figure 16 (Details the possible exit routes of organic pollutants from soil or
compost systems)
The nature of the pesticide.
The recalcitrance of a pesticide is directly related to its chemical structure (See
section 2.11. The principals or biodegradation/Recalcitrance), and as we can see from
the bench top system for evaluation of pesticide disposal by composting (appendiced)
organophosphates and less-chlorinated hydrocarbons may be degraded to some extent
through this process. Picolinic acids which include clopyralid or picloram, both used
in herbicide production, are however very persistent. Some chemical and physical
features of picolinic acids are listed in Table 1 ().
46
Table 9 Some chemical and physical features of clopyralid and picloram
(picolinic acids).
Property
clopyralid
picloram
Formula (acid)
C6H3Cl3N2O2
C6H3Cl2NO2
Solubility (water) mgL-1
1000
430
Stability
Unstable in acid
Decomposed by UV light
pKa*
2.3
2.3
Persistence (field half life,
40 (12-70)
90 (20-300)
days)
Clopyralid and picloram are growth-regulator type herbicides. Like 2,4-D and
dicamba, they work by mimicking plant growth hormones called auxins.
Hydrolytic enzymes, mono-oxygenases and di-oxygenases.
There are a great number of pesticidal compounds which are in continuous use
throughout the farming industry. Many of these are synthetic compounds which
contain functional groups within the molecule which prevent their natural
degradation.
The chemical structure also dictates some very important characteristics of the
compound, namely its water solubility. The greater the solubility of a compound in
water, the greater the bioavailability of that compound since microbes more readily
assimilate water soluble compounds. (Refer to section 2.1.2 Principles of
biodegradation/recalcitrance.)
If the functional groups of the pesticide weakly bound to the molecule, this will
increase the chances of its degradation. These weak or ‘labile’ bonds may be broken
by hydrolysis, and subsequently degraded by hydrolytic enzymes.
Pesticides capable of hydrolytic degradation include carbamate pesticides, urea
derivatives, pyrethroids, diazinon, dicamba, dichloropicolinic acid, dimethoate,
phenylalkanoic ester, dimethoate, phenylalkanoic pyrazon, atrazine, linuron, propanil,
chlorpyrifos,
and
2,4-D.
(http://www.ciwmb.ca.gov/Publications/Organics/44200015.doc)
Mono- and di-oxygenases introduce one and two atoms of oxygen into the molecule
respectively, which may increase its bioavailability. This process of oxidation may
take place at the extra-cellular level, allowing the molecule to be ingested and
degraded internally. Alternatively the now oxygenated compound may encounter an
enzyme capable of degrading it externally.
The Lists below from Mitchell (Environmental Microbiology Ralph Mitchell 1993)
shows the most favourable site conditions for the implementation of in-situ
bioremediation. These factors are relevant, though perhaps more difficult to generate
in a composting system.
47
Chemical conditions:
o Small number of organic contaminants
o Non toxic concentrations
o Diverse microbial concentrations
o Suitable electron acceptor conditions
o pH 6-8
On observation of this list and comparison to the conditions present within a compost
system it is fair to say that composting provides a good media for bioremediation of
trace contaminants within the system. There will invariably be a low concentration of
the contaminant within the system and there is a hugely diverse microbial population
at play. Also due to the incorporation of oxygen into the system and pH regulation,
these should not be limiting factors when disposing of pesticides through composting.
Hydrogeological conditions:
o Granular porous media
o High permeability
o Uniform mineralogy
o Homogenous media
o Saturated media
The above list refers to the hydro-geological conditions for bioremediation to work
most efficiently within the subsurface. All of these factors are however, at play within
a properly maintained compost heap. During the feedstock preparation and through
the additions of feedstock and bulking materials themselves, the compost which enters
a facility should be a porous and homogenous media. The material may not be fully
saturated, or of uniform mineralogy but as the material is turned and maintained there
is every chance given to populations which may degrade the contaminants within the
system.
Summary of ‘a benchtop system for the evaluation of pesticide disposal by
composting. (Appendix IX)
This is a method developed by J. A. Petruska et al., 1985, of evaluating the potential
of disposing of pesticides by composting. The article which was retrieved from
(‘Nuclear and Chemical waste management’, Vol. 5, pp. 177-182, 1985,) through the
electronic journal web of science, gives an interesting observation of the bulk disposal
of pesticides, an agricultural waste, and in doing so details the problems which may
arrive from their presence in other agricultural wastes.
48
Methods:
The compost media was contained in a glass vial with temperature control,
and aeration. All CO2 and Volatile Organic Compounds (VOC’s) which were released
from the system were captured via a system of scrubbers.
The moisture-laden air was then continuously fed to the composting system to
prevent desiccation of the compost.
Equal proportions by volume of dairy cow manure and sawdust comprised of
the compost media, the moisture content of which varied from 60-65%.
10g of this material was then aerated and heated to a temperature of 35°C for
24 h. The temperature was then raised by 5°C for every 24 h elapsed until reaching
65°C (six days incubation).
This temperature was then maintained throughout the experiment, and aeration
was provided for 1 out of 10 min, at the rate of 25 or 50 ml/min.
Diazinon
(0-0-diethyl
0-(2-isopropyl-6-methyl-4-pyrimidinyl
phosphorothiate), and Chlordane (1,2,4,5,6,7,8,8-octachloro-3a,4,7,7,a-tetrahydro-4,7methanoindane) were selected as representative organophosphate and chlorinated
hydrocarbon pesticides respectively.
Preliminary doses of pesticide were at a rate of 100µg/g (wet wt) of Diazinon
and Chlordane, and carbon dioxide evolution was used as a measure of microbial
activity. Volatiles were captured in the scrubbing apparatus and were analysed by
thin-layer chromatography (TLC).
Remaining pesticide was analyzed in the compost by solvent extraction,
evaporation and TLC.
Remaining organic carbon was combusted to CO2 and collected.
Results:
C recovery after composting:
There was very little CO2 production through the composting of either of the
pesticides. (0.2 and 0.5%).
Diazinon, the organophosphate released 16.6% total carbon as VOC’s, while
Chlordane released over 50% in this manner.
Carbon bound organics accounted for 69% of the Diazinon and just under 48%
of the Chlordane.
TLC Results:
These indicate that there was little or no transformation of Chloridane within the
system. However ‘IMHP (2-isopropyl-4-methyl-6-hydroxypyrimidine), a product of
degradation of Diazinon, ‘was present at a trace level in the standard but in significant
quantity in the solvent extracts’
49
Discussion:
This type of experiment proves that use of a benchtop study can trace all major
routes of transportation within a system.
The results indicate that the major routes of removal of these pesticides are
volatilization and hydrolysis.
Bases on TLC analysis Diazinon was almost completely transformed to
IMHP.
A Flavobacterium sp. Has been isolated that uses Diazinon as its sole carbon
source.
Chlorodane’s persistence in soil has been measured as being in excess of 12
years, and its metabolism in this experiment was negligible.
Volatilization may be the major route of removal from composting systems for
some pesticides. When monitoring on site, temperature studies throughout the system
should be preformed as volatiles may recondence on the outer edges of a composting
system (e.g. windrow systems).
Ivermectin:
Ivermectin is a pesticide which was introduced in the early 1980’s. It belongs to a
chemical group called avermectins and has the formula 22,23-dihydroavermectin B. It
is a broad spectrum anti-paracitic drug which was introduced for the treatment of
worms in sheep and cattle.
Avermectins are macrocyclic lactones with a very high degree of potency against
nematode and anthropod parasites. They are produced by the actinomycete
Streptomyces avermytilis, and are active at a fraction of a milligram per kilogram
against immature and mature nematode and anthropod paracites of sheep, cattle,
horses, dogs and swine. They are neuro-inhibitors.
(http://www.ingentaconnect.com/content/nzva/nzvj/1981/00000029/00000010/art000
03 )
The acute oral toxicity (LD50-mouse) is 29.5 mg/kg, and the aquatic toxicity is 29µg/l
in a 24 h test using daphnia magna. The products of its degradation are less toxic than
the substance itself.
In the late eighties and early nineties there was great concern about the persistence of
ivermectin in the faeces of dosed animals. Studies showed between 39 and 69 percent
of initial doses were recoverable in the faeces, which caused concern due to the
toxicity of the avermectin to all forms of degraders including earthworms. Cow-pats
and manure from treated animals was found to resist the usual processes of
degradation. This occurred for a number of reasons.
Ivermectin has a very low volatility (15x109 mg Hg) and is therefore unlikely to
disperse to the atmosphere. It has an octanol-water partition coefficient (Kow) of 1651,
and is therefore more readily adsorbed onto soil/humus particles than leached out
through the flushing action of water. This means that the main method of removal
from
soil/compost
systems
will
be
microbial/chemical
degradation.(http://www.doc.govt.nz/Publications/004~Science-and-Research/DOCScience-Internal-Series/PDF/DSIS67.pdf )
50
Conclusion.
Pesticides are a great concern within the agri-composting industry. There are however
many factors in place which facilitate their removal without any specific methods
being employed. The major factor at play when considering their potential adverse
affects is the type of pesticide that is present.
As a whole many of the more nuisance pesticides will be present at lower levels, due
to the relationship between pesticidal character and persistence in the environment.
Many may be degraded (organophosphates) or volatilised (chlorinated hydrocarbons),
through natural processes, but the more persistent and recalcitrant forms may
significantly impair composting systems if present in sufficient concentrations.
3.5
Composting Manure – A Marketable Product in Ireland?
There are over 140,000 farm holdings in Ireland, with an average size of almost 30
hectares, or 74 acres. Around 270,000 people work either on a full time or part time
capacity in farming.
Teagasc
reports
available
at
http://www.teagasc.ie/http://www.epa.ie/NewsCentre/ReportsPublications/Waste/File
Upload,5983,en.pdf outline the farm types in Ireland.
Teagasc states farms in Ireland can be divided into three categories based on nutrient
balances:
The first is the tillage farms with no livestock, grassland farms or intensive
agricultural enterprises. On tillage farms the crops (e.g. wheat, barley, and sugar beet)
are exported off the farm. The resulting removal of the nutrients in the crop creates a
farm nutrient deficit. Just 6 %, or approximately 280,000 hectares is used for tillage.
The second farm type is the grassland farms. Grass grown on the farm is used to feed
the animals. But only about 20% of the nutrients ingested by the animals produces
animal product and the remainder is excreted as waste. These farms are likely to
produce an excess of nutrients.
The third category of farm is known as an IAE or Intensive Agricultural
Enterprises.Most nutrients are imported in the form of cereal-based animal feeds or in
the form of imported substrates such as composts (poultry litter and straw are the
primary ingredients) on mushroom farms. Therefore there is also an annual nutrient
surplus is generated on an IAE. Teagasc restates the excess nutrients are contained in
the manure or compost, and exported to farms with nutrient deficits, e.g. grassland or
tillage farms.
Teagasc also states properly managing manure (liquid and solid) and other organic
wastes on farms is essential to achieving sustainability, both in environmental and
economic terms and the recycling of animal manures back to the land is the most
viable approach.
So in order for nutrient s to be sustainably managed in Irish farming it is necessary to
transfer animal wastes between different farm types depending on their nutrient
requirements. But on the other hand the vast majority of Irish farms are grass farms
and IAE’s with only 6% tillage of land used for tillage farming. As tillage farms are
51
the most likely to be nutrient deficient and the other two most likely to produce excess
waste, there will be an excess supply of nutrients.
As stated earlier there are many environmental concerns to using manure (both solid
and liquid) as a nutrient to be spread on land. This has lead to increasingly strong
legislative controls on the spreading of nutrients onto land in the form of EU
Directives and farm management initiatives. By 2006 it is expected 70,000 + farmers
will be participating in the REPS scheme.
Typical problems associated with animal waste nutrients include phosphates in water
courses which can lead to alga blooms while Nitrates in water can have even more
serious human health effects as methemoglobinemia or blue baby syndrome. The
knock on effect is that farmers are finding it increasingly difficult to dispose of animal
wastes.
Spreading manure on nutrient deficient tillage farm land is an option as outlined by
Teagasc, but transport costs have to be considered here as animal manures can be
difficult to move especially liquid manures with high water contents and could prove
costly for farmers. Also farmers in areas of Greater IAE’s concentration like Caven,
for example will have to travel greater distances to dispose of their wastes onto tillage
farms which tend to be concentrated in the southern counties.
An alternative to land spreading of manure is to compost it. The composted product
has a reduced C content of between 30-50%, so is easier to handle, a moisture content
that is greatly reduced and odourless stable end product humus. This would make it
more economical to transport between farms. The stability of compost gives it greater
utility over manure. It can be stored for greater periods, and spread onto land during
different seasons and climatic conditions with little or no legislative restrictions and
none of the environmental problems associated with manure (i.e., odour, volatilization
nutrient loss, leaching and pathogens). Although there are some problems of
pathogenic colonisation of bioaerosols to be considered. The partial sterilization of
pathogenic organisms during the thermophilic composting stage means it can also be
spread under fruit trees and vegetables without risk of soil bourne plant diseases. A
Composted product can fill a greater scope of niche markets, including large scale
operations including ; use on golf courses, horticulture, soil attenuation on farms,
large scale landscaping and to reduce soil erosion. Also other markets include;
gardening, potting plants, soil attenuation on lawns and root cover during the winter.
Also the need to maintain a buffer zone or the proximity to humans during application
would not be an issue with compost as it would with manure.
The disadvantage of compost over manure is the cost of setting up a composting
system. Of course this is relative to the type and scale of composting being carried
out. The average farm size in Ireland is 30 ha. And whether composting of on-farm
organic waste is likely to be cost effective is difficult to determine. Also the amount
of bulking material required for high liquid content manures like slurry is very high.
As stated, the volume of bulking agent required to bring 75% moisture content waste
to 60% is similar to the volume of waste to begin with, which means that you now
have double the volume of composting waste to process.
At present there is basically no research into the composting of agricultural manure
wastes in Ireland. In relation to agri-waste composting, Teagasc reports deal only with
the composting of spent mushroom compost (SMC). Teagasc reports tend to focus on
the correct procedures for the spreading of agri-wastes and new and advanced
52
technologies to do so. The EPA National Waste Database only deal with the
composting of municipal organic waste and mentions the legislative guidelines
farmers must comply with when disposing of organic agri-waste. Similarly the
Connacht Regional Waste Management Plan (1999-2005) refers only to the
importance of Complying with the Code of Good Agricultural and Nutrient
Management Plans when dealing with farm organic waste. There doesn’t seem to be
any change for the revised plan (2005-1010)
Whether composting of agricultural organic waste becomes a part of waste disposal
and nutrient management on Irish farms in the future is difficult to say. As the
traditional method for nutrient waste management like manure has been to spread it
on land, the idea of composting it would be a break from tradition. But as nutrient
management legislation becomes increasingly more stringent and new EU Directives
as the WFD Directive are being transposed into Irish legislation, the composting of
organic farm wastes may become more viable. An option may be to form a
composting co-op between a number of farms where equiptment is shared. But
whatever the approach it needs to be spearheaded by the Teagasc, the Irish
Agricultural and Food Authority as well as other Farming organizations.
4.0
Case Studies
4.1` Cork green waste shredder scheme
The green waste shredder scheme which was established by cork county council in
1998 is located at landfill and civic amenity sites within County Cork.
In the past these sites saw the transit of green waste mixed with other household
waste, all of which was destined for landfill. Since 1995 however, and the
establishment of the Cork waste management strategy the steadily rising volumes of
waste destined for landfill have been significantly reduced.
The Cork waste management strategy is a joint initiative between Cork County
Council and Cork City Council. It’s most notable initiative is the 20/20 vision public
awareness campaign, which is based on the three R’s of reduce, reuse and recycle,
focusing on the 280,000 residents of the County.
The strategy’s level of public awareness and involvement has been essential in its
success, as the management strategy includes a high degree of advertising, as well as
school visits, newsletters, broadcasts on local television, public education campaigns
and
green
awards.
http://www.corkcorp.ie/ourservices/environment/waste_management_strategy.shtml
53
An essential element of the present process is the application of the green waste
shredder scheme to local drop off points for waste. There is also a mobile shredder
unit which operates after the Christmas season. The volume of green waste which is
disposed of in this manner amounts to approximately 1000 tonnes per year.(
www.europa.eu.int/comm/environment/waste/publications/pdf/compost_en.pdf)
The aim of the green waste shredder scheme is to influence the reduction of municipal
solid waste going to landfill from 225,000 tonnes to 200,000 tonnes by the year 2020.
This may not appear extremely optimistic, but as the quantity has been forecast to rise
to as much as 450,000 tonnes per year, it will take a great number of changes to fulfil.
The Government target figures of 50% reduction in biodegradable waste destined for
landfill by 2013 are certainly not being met, and schemes of this nature are becoming
more and more popular as an effort to meet these targets.
The composting method is the windrow system and this takes place at Ballincollig
nurseries, which is owned by cork county council. The finished compost is applied to
nursery plants and used in public landscaping projects such as parks, roundabouts and
road margins.
At present there is no commercial exploitation of the product but with ever increasing
volumes and an increased general awareness (relative reduction in advertising costs)
this is becoming more of a possibility. Future plans for the scheme involve the
purchase of additional shredders and the sale of the compost mulch. New civic
amenity sites in the County and a greater presence of the shredders will further
increase the volumes of material being composted.
4.2
International Case Study
A new approach to on-farm nutrient management.
One of the principle advantages of composting on farms is the reduction of organic
waste that is generated during farm production processes. Today, environmental
concerns and tight profit margins have forced livestock producers to re-evaluate their
manure handling programs. Manure is considered less as a liability to be disposed of
and more as an asset to be stored and applied in a way that maximizes its nutrient
value http://www.ces.purdue.edu/extmedia/ID/ID-101.html
The following International composting case study process using integrated biosystems. This system incorporates composting as an integrated nutrient management
plan for a farm. The process outlines the waste streams that flow through a farm and
the processes that are used to manage them, including composting. The waste on the
farm is fully management without having to invest in disposing the waste off-site e.g.,
composting leachate off site, therefore incurring additional costs. Also the waste is
managed as a resource rather then a waste and is utilised completely to reduce the
overall farm running costs. Although it is an international example- with the stricter
legislative disposal requirements for spreading of nutrients in Ireland it may be a valid
alternative.
54
Background to Integrated Bio-systems
Integrated bio-systems connect different food production activities with other
operations such as waste treatment and fuel generation. Integrated bio-systems treat
production and consumption as a continuous closed loop system where outputs of one
operation become inputs into another, thus reusing resources and minimising
environmental impacts.
http://www.rirdc.gov.au/reports/Ras/01-174.pdf
The Integrated Bio-Systems (IBS) approach follows three basic principles. The first
principle is to use all biological organic materials and wastes instead of throwing it
away. The second principle is to obtain at least two products from a waste. The third
principle is to close the loop for the material and nutrient flows to achieve total use of
a resource and zero waste disposal. The IBS approach has many benefits
and potentials but it also has limitations.
http://www.ias.unu.edu/proceedings/icibs/mansson
Traditional integrated bio-systems often use labour-intensive bio-systems or
technologies in low-input, organic farming that can provide a variety of products at a
micro-level. They recycle nutrients in solids and liquids into bio-fertilisers, feeds,
aquatic plants, fish and food. In the past century, access to chemical fertilisers,
pesticides, herbicides and mechanization led to monoculture crop production. This
replaced the practice of the traditional integrated farming systems in many countries.
H:\Integrated Bio-Systems AGlobal Perspective.htm
Factors to be considered:
Simple connections are made to the flow of materials through a system these include
the following:
Simple connections – e.g., livestock manure is used as a fertiliser or a plant crop.
Intermediate connections- e.g., organic wastes- compost or vermiculture – Plant crops
Fuel generation – e.g., organic wastes – biodigester and biogas
Remediation and nutrient recovery – e.g., effluent from sewage treatment plant is
pumped into storage lagoons and used to grow aquatic plants (e.g., duckweed)
Duckweed growth reduces the originally high nutrient load to a level where the water
is suitable for irrigation (e.g., for fibre crops) The duckweed is harvested for food for
ducks and fish.
http://www.rirdc.gov.au/reports/Ras/01-174.pdf
The Case Study
Integrated Biosystems used in Practice
Pozo Verde Natural Reserve is an integrated farm located in the Cauca Valley
Province in South western Colombia at 950 metres above sea level. This is an
example of a large IBS farm. Pozo Verde Farm is a livestock farm of 50 ha in size, of
which 2 ha is used for building space and the rest for forage (42 ha of sugar cane, taro,
grass, forage trees, aquatic plants) with an additional 5 ha of wetlands. It buys
ingredients and formulated feed for the sows, growing and fattening pigs, and
broilers. All manure (920 tons/yr) is used in the farm to produce energy (19,200 m3
biogas), vermi-compost (160 tons), feed additives (52.6 tons as chicken manure), and
forage (6,323 tons) for cattle and pigs.
55
Organic Matter Recycling
There are several methods in the farm to recycle the organic residues produced in the
different subsystems. The purpose of these systems is to use efficiently all the byproducts of the farm, to replace inorganic fertilisers and to reduce the impact caused
by water and air pollution.
Composting using earth worm culture (Eisenia foetida)
The solid fraction of cattle and buffalo dung collected every day, as well as other
organic residues from households and garden maintenance are processed in a 300 m2
area of worm culture. (See Appendix VIII)
In total 230 tons of cattle dung and 37 tons of buffalo dung are used per year, to
produce 160 tons of worm-compost that is used mainly to fertilise grasslands and
crops, although an important fraction is sold to the market.
Productive water decontamination system 1
This system was installed to treat the wastewater from the pregnant sows building,
equivalent to 912 m3 per year. It consists of two plastic tube biodigesters of 14 m3
each and a channel of 64.5 m2 of water hyacinth (Eichhornia crassipes),
complemented with plantain, banana, giant taro and nacedero tree (Trichanthera
gigantea) planted along the channel.
Wastewater passes through the two bio-digesters and them to the aquatic plants. Table
below shows the efficiency of the system to remove Biochemical Oxygen Demand
(BOD) and Total Suspended Solids (TSS) in kg per year.
Table 10 Average BOD and TSS removal in the productive water
decontamination system 1 (kg/year).
Wastewater
Biochemical
1722
Oxygen Demand
(Kg/year)
Total
Suspended 2663
Solids (Kg/year)
Biodigesters outlet
111
Aquatic
plants
channel outlet
27.9
426
10
Aquatic plants and sludge produced in the channel are used as fertiliser for the
associated crops and the water is pumped to irrigate adjacent grass lands. A total of
4.6 tons of water hyacinth (Eichhornia crassipes) were harvested per year in this
system.
Biogas obtained in this system is stored in a 49 m3 and used for electric power
generation in a diesel engine.
56
Decontamination System 2
This system receives the wastewater from the dairy stable and from lactating sows,
growing and fattening pigs.
It consists of two 75 m3 plastic tube biodigesters and a storage tank (See Figure 16)
that process in total 12,448 m3 of wastewater per year.
Biodigesters effluent is stored in the tank and them pumped to fertilise 30.8 ha of
pastures and crops in the farm. In total it is estimated that 15,000 m3 are pumped
every
year.
Biogas produced in this system is estimated in 19,200 m3 per year used in 51 burners
for heating piglets from birth up to 60 days. Burners used for this purpose are shown
in Photo 7. The remaining biogas is piped to the same storage bag of system 1 to be
used
for
electric
power
generation.
Figure 16 Materials flow diagram on the farm
http://www.ias.unu.edu/proceedings/icibs/ic-mfa/chara/paper.htm
This case study shows how the composting process- in this case vermiculture can be
applied to compost solid waste manure while liquid manure is used to fertilise crop
fields (before planting) and washing from dairy stable and from lactating sows is
diverted to a nutrient pond via a biodigester growing aquatic plants – these plants are
grown and harvested to feed ducks. The process fully utilises the waste on the farm
itself to the benefit of production on the farm. Any waste from the composting
process –i.e., leachate is also fully utilised therefore reducing the cost of disposal..
57
Conclusion
Negative environmental impact is reduced due to the recycling of organic "wastes" in
the farm, which avoids water, soil, and air pollution. The use of organic fertilisers also
benefits biota in the soil and improves its physical properties. Mixed crops with trees,
grass and other fodder plants, as well as the wetland in the farm are providing nest
and food for wildlife, particularly for birds. The composting products and by-products
are utilised on the farm as part of the overall nutrient management. Some compost is
also marketed and sold. No waste leaves the farm and therefore the disposal costs of
wastes are eliminated as are the cost of buying fertilisers and other external inputs
such as foodstuff, fossil fuels and electricity.
Although this isn’t an exclusive system of composting of farm waste it is an
indication of how composting can become an integral part of the on farm nutrient
management plan. In most instances composting per se may not be the answer to a
financial viable method for on-Farm nutrient management but it is probably part of
the solution.
5.0
Health Hazards and Mitigation Measures
5.1
Bioaerosols in Composting
Overview
The microbial nature of the composting process together with frequent agitation of the
compost pile in the form of turning, permit for the presence of high numbers of microorganisms in the air surrounding a compost facility.
Where composting is concerned, the bioaerosol present may include a range of
bacteria, fungi, actinomycetes as well as material of plant origin.
They are of considerable concern due to their potential to cause adverse health effects
in those who work in the composting industry, those who use the end product and also
the general public, particularly those who reside close to a compost facility.
The Environmental Protection Agency in Ireland regards bioaerosol emissions as
being a potential drawback to the developing compost industry in the country.
Pathogens present in compost bioaerosol tend to secondary in nature that is they grow
during the composting process rather than being present rather than being present in
the raw material. (Prasad et al., 2004)
Health Effects
Bioaerosols are known to have the potential to cause infection, allergy or poisonings
among susceptible populations. Allergy and hypersensitivity are the main effects
where composting bioaerosols are concerned.
In immuno-compromised individuals, responses to bioaerosol contact range from
inflammation and allergy to tissue or systemic infection caused by bacterial
58
endotoxin. (Millner., 1995) Much work to date has focused on Aspergillus fumigatus
and the condition it causes in humans and animals, Aspergillosis.
An epidemiological study conducted by Clarke et al, 1984, on compost workers at
nine sludge composting plants in the USA, on behalf of the water pollution control
federation, found that there was a higher health risk for those working in the compost
industry than for control groups. The main findings of the study were:
 Excess nasal, ear and skin infections in compost and intermediate exposed
workers,
 Symptoms of burning eyes and skin irritation were higher in compost workers
and intermediate exposed workers,
 Evidence of higher white blood cell counts and haemolytic complement in
compost workers,
 Higher antibody levels to compost endotoxin in compost workers.
Aspergillus fumigatus and Aspergillosis
The genuses Aspergillus are ubiquitous fungi that include 132 species and 18 variants.
Several species are pathogenic to humans and other animals and include Aspergillus
niger, Aspergillus terreus, Aspergillus flavus, Aspergillus clavatus, Aspergillus
nidulans and Aspergillus fumigatus. Of these species, Aspergillus fumigatus is
responsible for up to 80% of Aspergillosis related illnesses in humans.
Aspergillus fumigatus functions between the temperatures of 15°C and 53°C. It is
commonly associated with compost piles, mulches and sewage treatment facilities.
(Appendix V) Conidia spores produced by this species range in diameter from 1.5µm
to6.0 µm, and when inhaled by humans are capable of reaching the lower respiratory
tract.
Aspergillus is the general term to describe the spectrum of diseases caused by the
Aspergillus genus. Clinical manifestations may range from Aspergilloma, a
saprophytic colonisation of pre-formed cavities or dilapidated tissue to Allergic
bronchopulmonary Aspergillosis (ABPA), a type of hypersensitivity pneumonitis
which
can
cause
life
threatening
complications.
(http://www.medscape.com/viewarticle/408747)
Migratory potential
After odour, bioaerosol concentration is the issue most likely by the public concerning
composting facilities. For those living adjacent to a composting operation, the
bioaerosol to which they may be exposed is much dependent on a number of factors;
wind speed and direction, weather, nature of the composting activity and
concentration of the bioaerosol at source. (Reinthaler et al., 1998/99)
Several studies have been undertaken to try establish a safe distance from a compost
facility at which bioaerosol concentrations are reduced to background concentrations.
Results from some of these studies are displayed in Appendix VI and can be seen to
range from 61-2614 metres. With such high variance amongst results, it’s not
surprising that no European country has yet decided on such a safe distance.
59
In Austria and Germany, regulations exist concerning buffer zone distances between
compost facilities and residential areas; however these regulations are in relation to
odour only.
In the United Kingdom, The UK Environmental Agency recommends a buffer
distance of 250 metres, after a study found that spore concentrations decreased by
80%-90% at a distance of 20-40 metres from source. (Casella Science and
Environment Ltd., 2001)
Dust
Dust occurring at compost facilities is technically not bioaerosol, but may contain
microbial constituents which have adhered to the particle surfaces. (Prasad et al.,
2004)
As with bioaerosol, the concentration of dust in the air at a composting facility is a
function of the weather, wind speed, wind direction and the nature of the composting
operation.
The single most important factor concerning dust at a composting site is moisture
content. Epstein (2001) has reported how dust concentrations decrease dramatically
as moisture content increases. Dust concentrations have also been found to diminish
significantly as one moves away from the composting site. Van der Werf et al, 1996
report how dust concentrations decrease considerably 10 metres upwind and
downwind of the facility. Dust from a compost facility is therefore likely to be an
issue for the compost worker rather than the general public.
5.2
Odour
One of the major problems encountered at composting sites is odour. Cheremisinoff
(2003) describes the development of odour problems in four stages:




Odorous compounds must be present initially or be produced during the
processing.
These odours must be released from the pile
The odours must travel off-site.
They must be detected by sensitive individuals.
Prevention of odour at a composting site can be achieved at any of these stages. But in
most cases prevention of odour problems can be best achieved by preventing odour
formation in the first place.
In theory aerobic composting does not generate odorous compounds, as anaerobic
processes do. However, objectionable odours can come from certain raw materials or
the process itself if conditions are not right. There are three primary sources of odours
at the composting facility: odorous materials, ammonia lost from high nitrogen
materials, and anaerobic conditions within windrows and piles.
60
Aerobic verses anaerobic composting
Aerobic micro-organisms thrive at oxygen levels greater then 5 % (fresh air is
approximately 20% oxygen). They are the preferred micro-organisms as they provide
the most rapid and effective composting. Anaerobic micro-organisms thrive when the
compost pile is oxygen deficient. The decomposition by anaerobic micro-organisms is
known as fermentation. Anaerobic composting is undesirable in a composting pile as
some of the products of anaerobic composting produce offensive odours. Some of
these include the following: Hydrogen sulphide, Cadaverine and putrescine. In
addition anaerobic processes can cause the production of acids and alcohols which
are damaging to plants.
http://www.agf.gov.bc.ca/resmgmt/publist/300series/382500-2.pdf
Cheremisinoff (2003) also describes the by products of anaerobic conditions include;
volatile organic acids (which have a vinegar, cheesy, goaty and sour odours),
alcohols, and esters (fruity, floral alcohol like), and amines and sulphur compounds
(barnyard, fishy, rotten) can be produced. In contrast in aerobic conditions only a mild
earthly odour is expected.
The process of reducing the odour from composting material is outlined by
Cheremisinoff (2003) who states since many of the odorous compounds in
composting material are acidic in nature , raising the pH (neutralizing the acids) will
convert them to an ionized (negatively charged, disassociated) form. In this form they
cannot be released to the air and will remain in the pile.
This method of odour reduction may be ineffective with odours generated from grass
clippings or other high nitrogen wastes. Ammonia and amines are weak bases rather
then acids and raising the pH may therefore actually increase odour release.
NH4+ = NH3 + H+
Odour may require odour control technologies these include masking agents, wet
scrubbers, activated carbon filters, thermal oxidation and biofilters. It is the biofilters
that are becoming the most popular. Biofiltration is a relatively simple process and is
effectively a high C:N ratio compost pile and is capable of removing a large range of
odorous compounds. The efficiency of the biofilters is dependent on the sorption
capabilities particles and the regeneration of the absorbed chemicals. As air is pumped
through the biofilter, odorous compounds are absorbed on to the media surface or
dissolved on the any moisture present. The process efficiency is therefore proportional
to the surface area of the media particles.
Regeneration of sorbed compounds involves microbial degradation, thermal processes
and the chemical reactions. It is the microbial processes which are dominant in
biofilters as they require less energy, however do require an adequate amount of
moisture.
An example of microbial regeneration is the oxidation of hydrogen sulphate by
thiobacillus bacteria to H+ ions in the sulphate ions which are both odorous. It may
take some time for a biofilteration operations to equilibrate on site, as it relies on a
balance of sorption and regeneration processes i.e., the regeneration ratio must at least
equal the absorption ratio. This can be achieved by monitoring flow ratio and assess
its correlation with the elimination of odours.
61
Positioning of Composting Material on-site
Odour and leachate
One way in which leachate may form a problem is by forming small pools or ‘ponds’
in windrow composting process. Cheremisinoff (2003) states ponding is of concern
because it can create odour problems; since anaerobic conditions are likely to occur
both in the pool and in the base of the saturated piles. Prevention by properly grading
the site, is the best remedy. Also windrows should run down slope instead of across.,
making it easier for the water to run off rather then accumulate between the
windrows. Other problems from composting leachate may include fish kills if the high
BOD leachate gets into surface waters.
5.3
Pathogens In composting
When composting on a large scale, and especially when using wastes of an
agricultural nature, the issue of pathogen survival within the compost is of paramount
importance. Although the potential for human pathogens presence in manure is
dependant on the type of waste, type of manure and the source of the manure,
livestock manures naturally contain a wide range of bacteria, viruses and protozoa.
Harmful bacteria within animal manure may include E.Coli (including 0157:H7),
Salmonella spp., Listeria, Streptococcus spp., Campylobacter, Clostridium spp., and
protozoa including Giardia and Cryptosporidium. In the past, applications of raw
manure onto food crops have caused infections by Cytosporidium parvum and
Giardia duodenalis, not to mention Campylobacter, Salmonella, E.Coli and Yersinia.
Yard trimmings, which are a common component of most composting systems also
contain E. coli, Giardia and helminths.
(www.ciwmb.ca.gov/publications/organics/44200014.doc).
Plate 1 (Bacteria (rods) one source of pathogens in composting)
62
Plate 2 (Fungal spores which cause a great number of respiratory diseases in
humans)
There are many methods of disinfection which will ensure that compost is pathogen
free, however these methods add an extra stage to an already laborious process, and
live cultures within the compost are hugely beneficial, especially if the amterial is to
be used as a soil additive. There is also the latent effect of the disinfectant method,
which could so damage to receiving media further down the line. Destruction of the
soil biota is not a viable option when removing pathogens from compost.
It is therefore very convenient that pathogen destruction is yet another function of the
compost biota themselves. The compost bacteria themselves and the composting
process, under the right conditions, create an environment which is detrimental to the
survival of human pathogens.
There are two factors to consider when assessing pathogen destruction within a
compost system. First is the amount of time a pathogen can survive without a host
(composting is a process of many weeks/months), and second is the creation of
adverse conditions, within the compost heap, by the compost bacteria themselves.
The survival of these pathogens in manure will largely depend on the temperature and
moisture content of the materials. Other factors are oxygen level, pH, ammonium
content, microbial competition, etc. It is safe to say, however that longer storage times
and higher temperatures, are direct factors in the destruction of pathogens within soil
or compost systems.
See table of pathogen survival times in soil, below.
Table 11 : Typical survival times of pathogens in soils: (from Broaders, 2004)
Pathogen
Maximum survival time
Common maximum survival
time
1 year
2 months
Bacteria
6 Months
3 Months
Viruses
10 Days
2 days
Protozoa
7
Years
2 Years
Helminths
63
We can see that the above table (from Broaders, 2004 (notes)) shows a large
proportion of pathogens cannot survive without a host for any great length of time.
We must also bear in mind that these are maximum survival times for some of the
most host-independent micro-organisms.
Composting duration varies considerably depending on the organic materials being
composted as well as other conditions. An ideal composting system may take twelve
to fifteen weeks to complete. This progresses to a curing period which lasts for
another four to six weeks. During this time, a considerable proportion of the microorganisms in the above table will be destroyed.
The remaining proportion are not a threat either as they will most likely have been
already destroyed by this stage due to the production of adverse conditions such as
increased temperature within the compost pile.
As pathogen destruction in compost is achieved by the process itself, we must look at
the parameters which have been identified as useful in pathogen destruction.
Pathogens are generally accepted to be killed off when temperatures are maintained
above 55°C for at least three days within an in-vessel or aerated composting system.
The core of a windrow system may reach these temperatures, and indeed points other
than the core may, but the outermost layers of a windrow system will have lower
temperatures.
(http://www.environmentalxpert.com/magazine/biocycle/march2000/article1.htm ). Repeated turnings are
therefore necessary to ensure that all areas of the windrow will reach these
temperatures. This is however already carried out in order to introduce oxygen into
the core.
It is generally recommended that windrows maintain a core temperature of 55ºC for
15 days with at least 5 turnings. Due to the need for proper mixing and consistent high
temperatures, pathogen reduction in windrow composting has sometimes been found
to be less consistent than when using well-managed, aerated static pile or in-vessel
systems.
(http://www.environmentalxpert.com/magazine/biocycle/march2000/article1.htm)
64
The following plates show the active heat generation of windrow compost systems.
Plate 3 (windrow system showing heat production in the form of steam)
Plate 4 ( a windrow system releasing steam while being mechanically turned)
65
6.0
Discussion and Conclusion of the Research
The overall research into the report indicated there to be a wide variety of
technologies available for composting. The chosen technology depends on the type
and scale of composting to be carried out. At present there is no standard legislative
framework in relation to composting throughout Europe. Also in the Irish Context
there is no standard regulation within Ireland either.
In the European context Ireland is rated a category IV in relation to its level of organic
waste recycling facilities. This is the lowest score in a1-4 rating where countries like
Sweden, Germany, and Italy scored a 1 rating due to their established separate
collection and composting facilities.
The research indicated the greatest amount of waste generated in Ireland is in the
Agricultural sector. Some of the main agri-waste products in Ireland include Spent
Mushroom Compost and Animal manure. At present the main waste disposal methods
of these agri-waste products are to spread them on land as outlined in Taegasc reports.
Ultimately both products compete against each other for land spreading space. The
time and place of spreading is also being reduced due to stricter EU environmental
legislation. However, the research has indicated, in relation to waste from the agribusiness, the national herd has actually decreased in the last four years and this has
lead to a slight decrease in manure output. Mushroom compost production on the
other hand has increased significantly in output in the late 1990’s but has also
stabilised. Still the need to find alternative methods for disposal of this waste is
necessary.
The lack of real progress in the composting of agri-waste as an alternative to land
spreading may be due to the legislative grey area of the composting process as stated
above. The research indicated the composting process can ultimately take a waste
product like manure or spent mushroom compost and through the composting process
produce an end product with a greater utility and market potential. Yet, although the
composting process kills pathogens and the end product is stable humus, the research
indicated composting does have its problems especially in the way of bioaerosols and
in certain situations odour. Alas, the use of pesticides in the agri-business and its
effects on the composting process needs to be researched and determined with
legislation developed in relation to this also. On another level there are no standards
set in relation to the quality of the compost. Therefore it is difficult to market a
product with no quality standards as guide lines to determine what is being sold. At
the time of the research ‘Cre’ The composting Association of Ireland were in the
process of developing standards.
In the future if composting is to be developed as a viable option for agri-waste
disposal many of the above factors need to be considered.
Conclusion
 There are no EU legislation standards for composting
 There are no EU legislation for compost quality
 At present composting agri-waste isn’t being considered as an
alternative to traditional methods of organic agri-waste
disposal in Ireland.
66
7.0 Calculations of the Adjustments Required to Find the
Optimum C:N Ratios for both Cattle Manure and Spent Mushroom
Compost
The following calculation determines the amount of manure and spent mushroom
compost that are required to create the correct C:N ratio for a successful composting
process to be developed.
Due to the low C:N ratio of both cattle manure and spent mushroom, it was decided
that the theoretical sawdust requirements of each should be calculated in order to
further investigate their viability as compost feed stocks.
This was achieved by the following mathematical analysis:
Feed Stock
Material
Moisture Content
(%)
Nitrogen (% D.W.)
C:N Ratio
Cattle Manure
Spent Mushroom
Compost
Sawdust
81
69
35
2.4
19:1
2.1
18:1
0.11
500:1
Every kg of feedstock contains:
Cattle Manure
Water (kg)
Dry Matter (kg)
Nitrogen (kg)
Organic Carbon
(kg)
0.81
0.19
0.00456
Spent Mushroom
Compost
0.69
0.31
0.00651
0.35
0.65
0.000715
0.08664
0.11718
0.3575
Sawdust
When equal parts of both cattle manure and sawdust are mixed, the C:N ratio is as
follows:
C:N Ratio = C (Cattle Manure + Sawdust)
N (Cattle Manure + Sawdust)
C:N Ratio = 84.197:1
When equal parts of both SMC and sawdust are mixed, the C:N ratio is as follows:
C:N Ratio = C (SMC + Sawdust)
N (SMC + Sawdust)
C:N Ratio = 65.699:1
67
To calculate the weight/kg of sawdust required to achieve a C:N ratio of 30:1, the
following formula is applied:
X(Kg of Sawdust needed for C:N ratio of 30:1)=
% Nb ( R  Rb (1  Mb)
x
x
% Na ( Ra  R ) (1  Ma )
Where,
a = Sawdust
b = Cattle Manure/ Spent Mushroom Compost
Na = % Nitrogen in Sawdust
Nb = % Nitrogen in Cattle Manure/ Spent Mushroom Compost
R = Desired C:N Ratio
Ra = C:N Ratio of Sawdust
Rb = C:N Ratio of Cattle Manure/ Spent Mushroom Compost
Ma = Moisture content of Sawdust
Mb = Moisture content of Cattle Manure/ Spent Mushroom Compost
Cattle Manure
X(Kg of Sawdust needed for C:N ratio of 30:1)=
2.4 (30  19) (1  0.81)
x
x
0.11 (500  30) (1  0.35)
X = 0.1492,
Therefore, in order to achieve a C:N ratio of 30:1, 0.1492 kg of sawdust must be
added to each kg of cattle manure.
Spent Mushroom Compost
X(Kg of Sawdust needed for C:N ratio of 30:1)=
2.1 (30  18) (1  0.69)
x
x
0.11 (500  30) (1  0.35)
X = 0.23215,
Therefore, in order to achieve a C:N ratio of 30:1, 0.23215 kg of sawdust must be
added to each kg of Spent Mushroom Compost.
68
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http://www.compostnetwork.info/biowaste/biowaste.htm
http://www.medscape.com/viewarticle/408747
http://www.ciwmb.ca.gov/publications/organics/44200013.doc).
http://compost.css.cornell.edu/microorg.html
www.ciwmb.ca.gov/publications/organics/44200014.doc
http://www.environmentalxpert.com/magazine/biocycle/march2000/article1.htm
http://www.ciwmb.ca.gov/publications/organics/44200015.doc
http://www.ingentaconnect.com/content/nzva/nzvj/1981/00000029/00000010/
art00003
http://www.corkcorp.ie/ourservices/environment/waste_management_strategy
.shtml
www.europa.eu.int/comm/environment/waste/publications/pdf/compost_en.pdf
http://www.doc.govt.nz/Publications/004~Science-and-Research/DOCScience-Internal-Series/PDF/DSIS67.pdf
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9.0
Appendices
Appendix I
Table 12
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Appendix II
Table 13- Composting Flow Chart
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Appendix III
Table 14 Composition of Irish Spent Mushroom Compost
Composition of Irish Spent Mushroom Compost
Constituent
Available
Mean
Minimum
Nutrients*
pH
6.6
5.9
EC (mS/m)
750
580
NO3
62
21
NH4
49
2
P
31
11
K
2130
1450
Na
253
160
Cl
118
40
Total
Nutrient
Content
N (g/kg DM)
25.5
23.1
P
12.5
10.3
K
25
17
Ca
72.5
42
Mg
6.7
5.2
S
15.9
9.6
Na
2.67
1.7
Fe (mg/kg DM)
2153
1300
Mn
376
320
B
37
32
Cu
46
36
Zn
273
220
Bulk Density (g/l)
%Dry Matter (DM)
% Ash
319
31.5
35
257
24.1
30.4
Maximum
7.4
903
87
133
73
2650
350
157
28.2
15.3
32
99
8.7
22
3.2
3200
460
43
65
390
395
35.1
41.5
* mg/l in a 1.5 distilled water to 1 spent mushroom compost volume extract.
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Appendix IV
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Appendix V
Table15
15
Appendix VI
Table 16
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Appendix VII
A BENCHTOP SYSTEM FOR EVALUATION OF PESTICIDE DISPOSAL BY
COMPOSTING.
J. A. Petruska et al., 1985.
This is a method of disposing of pesticides by composting. The article which was
retrieved from ‘Nuclear and Chemical waste management’, Vol. 5, pp. 177-182, 1985,
through the electronic journal web of science, gives an interesting observation of the
bulk disposal of pesticides, an agricultural waste, and in doing so details the problems
which may arrive from their presence in other agricultural wastes.
Methods:
The compost media was contained in a glass vial with temperature control,
and aeration. All CO2 and Volatile Organic Compounds (VOC’s) which were released
from the system were captured via a system of scrubbers.
The moisture-laden air was then continuously fed to the composting system to
prevent desiccation of the compost.
Equal proportions by volume of dairy cow manure and sawdust comprised of
the compost media, the moisture content of which varied from 60-65%.
10g of this material was then aerated and heated to a temperature of 35°C for
24 h. The temperature was then raised by 5°C for every 24 h elapsed until reaching
65°C (six days incubation).
This temperature was then maintained throughout the experiment, and aeration
was provided for 1 out of 10 min, at the rate of 25 or 50 ml/min.
Diazinon
(0-0-diethyl
0-(2-isopropyl-6-methyl-4-pyrimidinyl
phosphorothiate), and Chlordane (1,2,4,5,6,7,8,8-octachloro-3a,4,7,7,a-tetrahydro-4,7methanoindane) were selected as representative organophosphate and chlorinated
hydrocarbon pesticides respectively.
Preliminary doses of pesticide were at a rate of 100µg/g (wet wt) of Diazinon
and Chlordane, and carbon dioxide evolution was used as a measure of microbial
activity. Volatiles were captured in the scrubbing apparatus and were analysed by
thin-layer chromatography (TLC).
Remaining pesticide was analyzed in the compost by solvent extraction,
evaporation and TLC.
Remaining organic carbon was combusted to CO2 and collected.
Results:
C recovery after composting:
There was very little CO2 production through the composting of either of the
pesticides. (0.2 and 0.5%).
Diazinon, the organophosphate released 16.6% total carbon as VOC’s, while
Chlordane released over 50% in this manner.
Carbon bound organics accounted for 69% of the Diazinon and just under 48%
of the Chlordane.
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TLC Results:
These indicate that there was little or no transformation of Chloridane within the
system. However ‘IMHP (2-isopropyl-4-methyl-6-hydroxypyrimidine), a product of
degradation of Diazinon, ‘was present at a trace level in the standard but in significant
quantity in the solvent extracts’
Discussion:
This type of experiment proves that use of a benchtop study can trace all major
routes of transportation within a system.
The results indicate that the major routes of removal of these pesticides are
volatilization and hydrolysis.
Bases on TLC analysis Diazinon was almost completely transformed to
IMHP.
A Flavobacterium sp. Has been isolated that uses Diazinon as its sole carbon
source.
Chlorodane’s persistence in soil has been measured as being in excess of 12
years, and its metabolism in this experiment was negligible.
Volatilization may be the major route of removal from composting systems for
some pesticides. When monitoring on site, temperature studies throughout the system
should be preformed as volatiles may recondence on the outer edges of a composting
system.
VIII Appendix
Methodology to estimate quantities of neat excretia (urine and faeces) Produced
by different classes of livestock (source: EPA National Waste Database 2001)
The factors used to derive the total factors of organic waste arising from the various
agricultural sectors. These factors are applied to the livestock population in 2001.
The proportion of managed (i.e., collected and stored and applied to the land at a later
date) organic slurries and manures is estimated by applying the following average
winter housing periods – cattle 20 weeks and sheep 6 weeks (lowland ewes only).It is
assumed that the total amount of slurry and manure arising from the pig and poultry
sector is collected, stored and subsequently applied to land.
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Appendix VIII
Table 17 - Central Statistics Office-Agricultural Data
Source:
http://www.cso.ie/releasespublications/documents/agriculture/2001/cropls_juneprovisional2001.pdf
Source:
http://www.cso.ie/releasespublications/documents/agriculture/2001/cropls_juneprovisional2001.pdf
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Figure 16 Animal Waste Irish Agri-business
Source:
National Waste Database 2001
Appendix IX
Vermicomposting
Vermicomposting is the process whereby earthworms are used as a biological
degrader of organic wastes in a controlled environment, and the earthworms
themselves are the main product of degradation.
Earthworms have long been credited with increasing the porosity, friability, and
general health of soils. Charles Darwin stated that ‘It may be doubted whether there
are many other animals which have played so important a part in the history of the
world, as have these lowly organized creatures’.
Earthworms used in vermicomposting eat approximately their own body weight each
day, and reproduction is rapid where conditions are favourable. Vermicomposting is
becoming increasingly popular in both domestic and agricultural applications as the
product of the application is an increase in the fertility of any soils.
As sub surface feeders earthworms used in this practice will only colonise 8-12 inches
of material so deeper bins are lined with porous bedding material, and organic matter
is layered on top. Additions of new material are made by rotating the top couple of
inches in order to bury the new material. This keeps the organic material away from
flies and birds, as well as denying it access to regions lacking in oxygen.
Optimum conditions:
Like any form of composting, one of the most important factors is aeration, so it goes
without saying that this factor is crucial too for the survival of oxygen dependant
earthworms. In larger scale applications the consistency of the material is crucial as
the harder wastes from crop production alone are too tough, where as this material is
necessary to provide aeration. Also the pore space of the bedding material is crucial to
provide both aeration and moisture removal.
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Extensive studies in vermiculture have revealed that earthworms eat all kinds of
organic wastes, from the many grades of sewage sludge to pulverised eggshells.
However limited amounts of citrus, or other acidic plant wastes may be added as the
pH of the system must be kept above pH 6.0. The optimum pH is 6.5 and the upper
limit is pH7.0.
Earthworms also dislike strong light or heat so the temperature of the system should
be kept in check. The optimum temperatures for degradation are 12 - 25°C but the red
worms used in the process can survive temperature of just above freezing to 30°C.
The moisture content of the material should be high enough to allow the softening of
the harder components of the compost, but not high enough so as to retard aeration.
Piles must be covered from rainfall. (Edwards, 1998)
System management:
The process is generally a resilient one whereby if too much organic matter is added
to the systems gas production will be noticed through the presence of odours. When
this happens the solution is simply to stop adding organic matter until the worms have
a chance to catch up. On the other hand if too little new matter is added natural
competition will simply reduce the number of competitors and the system will
stabilise again.
Worms are very sensitive to some forms of pesticides (See section on Ivermectin) so
it is therefore unlikely that vermicomposting could be applied to conventional areas of
crop producing agriculture where the use of these chemicals is greater than any other
area. The process may be more applicable to areas where very little or no pesticides
are used such as tuber production or the various practices in organic farming.
Harvesting the system.
There are three basic methods involved in harvesting the worms from the system
(usually carries out every 2 – 3 months. The first involves simply moving the old
material and worms over to one side of the digester and beginning the process again
on the cleared space. Worms contained within the composted material should colonise
the new material. This method will eventually require the removal of worms however,
unless the mass of composted material is continuously increased.
To completely separate the composted material from the worms the material may be
sifted with a suitably sized mesh, or alternatively piles of material may be left in
strong sunlight. The worms dislike of strong light and heat will cause them to
concentrate in the centre of the pile. Repeating this process should produce a
concentration of worms ready to be used in soil applications.
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