Caitriona Gaffney
Deirdre Mulchrone
Teresa Conway

INTRODUCTION - CAITRIONA GAFFNEY
Definition, Sources, Characterisation, End Products
INTERMEDIATE - TERESA CONWAY
Waste Hierarchy, Legislation, Microbiology, Site Selection,
Types of Systems
CONCLUSIONS - DEIRDRE MULCHRONE
Environmental Factors, Problems, Economics

Definition of MSW & Irish Facts
Sources
Composting & Classification
Compost Grades
End Uses
Who Benefits

Mixed waste from Residential, Commercial & Industrial sources
Compostable potential of 60-90%
Composition includes: paper, glass, wood, plastics, soils, chemicals, food waste, plant debris, metals, textiles, street cleaning & OM
Organic material makes up 50-70% of MSW
The fewer the non-compostable materials in feedstock the better the finished compost material.

Recycling
Composting
Combustion
Landfilling

1998 The national recovery rate of MSW was 9% with
91% going to landfill
“Waste Management: Changing our Ways” published targets to be achieved over 15 year period;
 a diversion of 50% of household waste from landfill,


 recycling of 35% of MW rationalisation of municipal waste landfills – 20 state of the art facilities incorporating energy recovery & enviro protection reduce methane emission from landfill by 80%.

Changes in waste composition between the years 1995, 1998 & 2001

2001 - 2,704,035 tonnes MW produced, 4% of the total waste generated
- 86.7% landfilled & 13.3% recycled
2002 - 2,723,739 tonnes MW produced
- Landfill of MW decreased by 5%
2003 - 3,001,016 tonnes MW produced
- EPA carried out survey on waste generation & management.
- Recycling increased by 46%
- 69% of the recyclable waste was recycled abroad
- Export of hazardous waste increased by 56%
2004 - 72% of municipal waste was consigned to landfill
- Landfill capacity will still be used up within the next 10 years

Provisional data from 6 surveys carried out in Waterford
Coco & Galway City in November 2004 and March 2005

Definition:- “Composting is the biological decomposition of the organic constituents of wastes under controlled conditions to a state sufficiently stable for nuisance-free storage and utilization.”
Performed either by households or in large centralised units
Compost systems can be classified on three general bases:
1. Oxygen usage (aerobic & anaerobic)
2. Temperature (Mesophilic 15-40 O C & Thermophilic 45-65 O C)
3. Technological approach (static pile or windrow, and mechanical or "enclosed" composting)

Premium Grade
- agricultural and horticultural use
- home use, turf, pot plants
- can be freely traded
- regulations may control the application of nitrogen to land
Regulated Grade
- remediation, restoration, agriculture, forestry and non food crops
- specialist expertise necessary in trading and its use
- regulation of the application
- biological, chemical or physical hazards remain a concern
Engineering Grade
- access to composts is strictly limited
- other risk management measures in place for e.g. uses such as daily cover, or as engineering fill material - in bunds and sound barriers, or as pollution control measures such as biofilters.

Soil Improvement
- soil structure, condition and fertility
Growing media
- component of mixes used to grow crops in containers
Mulches
- suppress weed growth, conserves water and also to maintain soil temperatures. Mulching also protects plants from frost.
Restoration
- used for soil “forming” and soil improvement
Landfill Applications
- improvement of landfill covers – soil formation

Waste Hierarchy
Process Options for Organic Waste
Why Biologically Treat Waste
Legislation & Targets
Physical Processing of MSW
Biological Process of Composting



Biology
Site Selection
Types of Systems

Composting can be considered a component of
Integrated Waste Management (IWM)
Options near top are more desirable than those at the bottom

Process Options
Landfill Incineration Biological Processing Direct Land Disposal
Anaerobic Digestion Composting Specialised Methods
Marketable Products

Reduces waste going to landfill
Estimated to be 10 years’ remaining landfill capacity available for municipal waste
(Nationally in 2004)
Could be the first step in Ireland meeting its waste challenge

80%
70%
60%
50%
40%
30%
20%
10%
0%
25%
35%
60%
Paper &
Cardboard
Food & Garden
Waste
Total
Biodegradable
MSW
(EEA,2003 )

140
120
100
80
60
40
20
0
126
92
34
1998 2001
No. of Landfills
2002

Taking the Landfill Directive as a framework the following National Landfill Diversion targets were outlined in 1998 in the Policy statement
“Changing Our Ways”.
-The statement includes a number of targets to be achieved over a 15 year time period. Some of these include:

a diversion of 50% of household waste from landfill by 2013
a minimum 65% reduction in biodegradable waste consigned to landfill the development of waste recovery facilities, including the development of composting and other feasible biological treatment facilities capable of treating up to 300,000 tonnes/year

The primary statute law on waste management is contained in –
Waste Management Act, 1996 & 2001 and
Regulations made under the Act
EPA Act 1992 and Regulations under the Act
Regulations made under the European Communities
Act, 1972 in relation to waste management
Landfill Directive 99/31/EC

Microorganisms + OM -------> H
2
O + CO
2
+ Heat + Humus
3 phases under optimal conditions
(1) Mesophilic - lasts couple of days (~40 o C)
(2) Thermophilic can last a few dys to several mts ( 55 o C–65 o C)
(3) Several-month cooling and maturation phase

Abundance and variety of microbes indigenous to wastes are sufficient to compost the wastes
Microbes active in the compost process are:
Bacteria (mesophyllic and thermophyllic)
Actinomycetes
Fungi
Protoza
Rotifers

Tertiary Consumers centipedes, mites, beetles
Secondary Consumers nematodes, protozoa, rotifera ,
Primary Consumers bacteria, fungi, actinomycetes
Organic Residue

Large enough to receive projected waste volumes
& for technology used
Adequate buffer zone from neighbours with a prevailing wind that blows away from neighbours
A nearly level surface, 2-3% grade
A high soil percolation rate to avoid standing water but an impermeable surface as a base

A low water table to prevent site flooding
A central accessible location with good traffic flow
A water source for wetting compost piles & fire protection
Arrangements for leachate to be collected and treated
Windrows need shelter in regions of moderate to heavy rainfall

Quantity and characteristics of the feedstock is collected and determined – MSW differs from other feedstocks
Nonbiodegradable and biodegradable separated through:
Separation (Recovery)

Manual Separation

Mechanical Separation
• Size Reduction
• Air Classification
• Screening
• Trommel
• Magnetic Separation
Drying and Densification

-Horizontal Units
-Vertical Units
-Rotating Drums
NOTE:
Design and management of technical options must be based on the needs of microorganisms

Turned Windrows

Windrows
Composting
Sites
Natural Air Circulation in a Compost Windrow

Most preferred method used in Ireland
Commonly used for rapid composting of yard wastes
Windrows are aerated regularly by turning
Constructed to be 6 to 10 ft high, 10 to 20 ft wide
The center of the pile insulated so that composting can continue when outdoor temperatures are below freezing
Finished compost can be made between 3 mts - 2 yrs
Rate of composting is generally directly proportional to frequency of turning

Typical 18 month schedule using Turned Windrow system
Autumn
Windrows formed
Using a front end loader
Summer
Windrows turned monthly
Winter
Windrows turned monthly
Spring
Windrows turned monthly
Autumn
Windrows dismantled
Room made for new incoming material
Next 6 Months
Compost screened
Moved to curing pile
Stabilised & yields N
March/April
Finished Compost
Peak Demand

Does not employ turning – ‘static’
Air is drawn or blown through a network of perforated plastic pipes under the windrows
Faster than windrow systems
Used where aeration and temperature control are crucial, (i.e. sludge or food processing wastes)
Works best with a material that is relatively uniform in particle size ( not > 1.5 to 2 in. in any dimension)

This blower forces air into a static compost pile.

Forced aeration in a bin type system
Passively Aerated Windrow
System (PAWS)

Permanent air outlets in the pad for an aerated static pile at a site in
Washington

Also referred to as
-Contained systems
-Reactor
-Bioreactor
Computer provides greater control of composting process
Raw waste is placed in a large container, with builtin aeration and mechanical mixing equipment

Protected from severe weather and odour containment
Low retention time (RT) (often <14 days)
Requires further compost processing - low RT is insufficient for thermophilic composting stage
Expensive to build and operate

Horizontal Units
Vertical Units
Rotating Drums

Material contained and aerated in a long, horizontal reactor, usually build of concrete
Material may be moved in and out by:
A front end loader or conveyor system
Plug flow system – hydraulic ram
Moving floor system

Horizontal Bed Reactor

Small land area
Enclosed and aerated in a vertical reactor known as “silos” or “towers”.
Compaction of material at the base reactor impedes aeration - anaerobic regions developing
Good for Sludge composting industry but not MSW

A vertical in-reactor composting system

Most common in-vessel composting approach
Combined with aeration in static piles or turned windrow
Feedstock introduced into one end of slowly rotating drum, inclined at about 5 degrees from horizontal
RT varies from 4-6 hours to 2-3 days
Drum allows homogenisation and screening of materials

A large-scale, Rotating Drum Composting Vessel

Some Biological Treatment Locations in Ireland
Facility Capacity Feedstock
Tralee Composting site 3,000 Household Organics
Limerick Composting Site
Galway Corporation Depot
Lucan Green Waste Composting
Aran Island Recycling Scheme
2,000
5,000
5,000
500
Household Organics
Household Organics
Green Waste
Household Organics
Ballinasloe Composting Site
Silliot Hill, Kildare
Kildare Sludge Plant
CTO Middleton
Kinsale Road Facility
Keady Composting Facility (Armagh)
McGill Facility (Cork)
Enviro Grind Ltd.
4,000
5,200
5,200
3,000
2,000
65,000
10,000
3,000
1,000
10,000
Household Organics
Commercial and Green Waste
Municipal Sludge
Commercial Organics
Green Waste
Organic and Green Waste
Commercial Sludges
Green Waste
Household Organics/ Municipal
Sludge
Green Waste
Shannon Vermicomposting
Robert Delaney
Down District Council Composting
Site
SimproIreland Ltd.
Organic Gold
1,800
4,000
3,000
Household Organics
Green Waste
Municipal Sludge, Cattle Manure
Technology
Windrow
In-Vessel and Windrow
Aerated Pile (VAR System)
Windrow
In-Vessel (Biosal Unit)
In-Vessel and Aerated Pile (Celtic
Composting)
VCU In-Vessel
TEG In-Vessel
Windrow
Windrow
Enclosed Aerated and Windrows
Enclosed Aerated
Windrow
Windrow
Windrow
Windrow
Windrow
Windrow

Problems associated with Composting of
Municipal Waste
1.
Odours
Vector for organisms supports the proliferation of insects
Feedstock
Enhanced under anaerobic conditions
Agitation of composting materials
Bioaerosols

Problems associated with Composting of
Municipal Waste
Nuisance Problems
-Pathogens in Final Product
.
Hazard – pathogenic organisms in feedstock.
Pathway – ingestion of materials (for example from unwashed hands).
Receptor – compost site workers .
-Stored in bulk

Environmental Factors Affecting
Composting
1. Temperature
Thermophilic (45 –65 0 C) and Mesophillic (15-40 0 C).
Above this temperature spores produced (Resting Stage).
Microorganisms inactivated or die off.
Affected by its climatic surroundings and method of aeration.
In a windrow highest temperature reached in centre, lower at edges.

Environmental Factors Affecting
Composting
2. pH
Anaerobic digestion the pH level covers a narrow range (pH 6.5 to 7.5)
Aerobic- pH so broad difficulties rarely encountered with too high or too low pH in composting.
During the early stages the pH usually drops (down to about pH 5.0) because of organic acid formation.
An exception which can reduce the pH is fruit wastes which can reduce the pH to 4.5.
calcium hydroxide (lime) can be used as a buffer but it also lead to a loss in ammonium nitrogen.

Environmental Factors Affecting
Composting
3. Aeration (Anaerobic & Aerobic)
Anaerobic:
Advantages a) minimisation of the loss of nitrogen b) less costly
Disadvantages include: a) Slowness of decomposition b) Absence of high temperatures c) The presence of un-decomposed intermediates d) The un-pre-processed appearance of the product

Environmental Factors Affecting
Composting
Aerobic
Aerobic composting benefits from: a) A rapid rate of degradation b) Elevated temperature levels c) Absence of putrefactive
Oxygen uptake reflects intensity of microbial activity. Theoretically the amount of oxygen required is determined by the amount of carbon to be oxidised (Chrometzka, 1968).

Environmental Factors Affecting
Composting
4. Moisture Content
Moisture content and oxygen availability are closely related
If the moisture content of the mass is so high as to displace the air from the interstices (voids between particles) anaerobic conditions will develop within the mass .
The maximum permissible moisture content is a function of the structural strength of the particles of the material to be composted i.e. the degree of resistance of individual particles to compression.
Woodchips, straw and hay can be as high as 75 to 80% whereas paper (upon becoming wet, collapses and forms mats) has a permissible moisture content of 55 to 60%.

Factors affecting Composting
5. Substrate
The waste (referred to as the substrate) should contain all necessary nutrients.
Macronutrients
Carbon (C)
Micronutrients
Cobalt (Co)
Nitrogen (N)
Phosphorous (P)
Potassium (K)
Manganese (Mn)
Manganese (Mg)
Copper (Cu)

Factors affecting Composting
Substrate (cont.) only available if they are in a form that can be assimilated by the microbes.
Certain groups of microbes have an enzymatic complex that permits them to attack, degrade and utilise the organic matter found in freshly generated waste.
Others can only utilize decomposition products (intermediates) as a source of nutrients.

Factors affecting Composting
Carbon: Nitrogen Ratio (C: N)
The C: N ratio of the waste to be composted is the most important factor that requires attention.
A large percentage of the carbon is oxidised to carbon dioxide by the microbes in their metabolic activities .
The major consumption of nitrogen is in the synthesis of protoplasm consequently much more carbon is required.
The C: N of the substrate should fall within the range of 20-25:1.
Mmicroorganisms such as bacteria and fungi grow best with the proper level of Carbon and Nitrogen.

C: N (continued) (CAST STUDIES)
Galway City Council
At the Galway City Council composting site
-no clear cut method of establishing a
C: N ratio for the material.
-done by visual assessment and the experience of the operative
-Food waste is estimated at a C: N ratio of
15:1.
-Woodchip is added at the assessment of the operative
- Less woodchip is required if there is adequate shrub prunings in the incoming waste.
-More woodchip is added if there is a lot of grass in the incoming material as there is in summer
Celtic Composting
-The C: N of source separated biowaste is typically measured using the total nitrogen and volatile solids content of a sample screened to <10mm.
-Inclusion of large amounts of unavailable carbon from woody bulking materials will give a false high carbon reading.
- Normally bio-waste with high green waste content is fine.
-However, winter deliveries with little green waste needs nitrogen supplementation.
-In the UK, it is typical to include a lot of paper and cardboard in the bio-bins and this needs nitrogen additions also.
Similarly mixed waste composting often suffers from low nitrogen”

The costs of a composting facility include land, labour and equipment.
It will divert waste that would otherwise need costly disposal. If the compost site is closer than the other disposal site, there will be savings in transport costs.
The finished compost can be used as a substitute for purchased mulch or topsoil in municipal landscaping.
If sold commercially, compost can generate revenues, which help defray processing costs.

From an environmental perspective, composting not only reduces the problems associated with landfills and incinerators, but the finished compost adds beneficial humus and nutrients to soil. Composting is a waste management solution, which can benefit municipalities and benefit the environment at the same time.