Project Title:
Development of odour-free mushroom compost by modifying the
organic and inorganic nitrogen sources and process technology
Project Number:
M 3d
Project Leader:
Ralph Noble
Report:
Final Report 2001
Previous Reports:
Year 1 – Aug 1998, Year 2 - Aug 1999, Year 3 - Aug 2000
Key Workers:
Ralph Noble, Phil Hobbs, Alun Morgan,
Andreja Dobrovin-Pennington, Tom Misselbrook
Location of Project:
Horticulture Research International,
Wellesbourne, Warwick, CV35 9EF
Horticulture LINK Project 180
Institute of Grassland and Environmental Research,
North Wyke, Okehampton, Devon, EX20 2SB
Project Co-ordinator:
Mr Peter Woad
Blue Prince Mushrooms Ltd, Poling
Arundel, West Sussex, BN18 9PY
Date Project
Commenced:
1 August 1997
Date Project
Completed:
31 July 2001
Keywords:
Mushrooms, Compost, Odour, Smell, Poultry Manure,
Nitrogen Sources
Whilst reports issued under the auspices of the HDC are prepared from the best available information,
neither the authors or the HDC can accept any responsibility for inaccuracy or liability for loss, damage
or injury from the application of any concept or procedure discussed
The contents of this publication are strictly private to the Consortium of Horticulture LINK Project No.
180. No part of this publication may be copied or reproduced in any form or by any means without
prior written permission of the Consortium. © 2001 Consortium of Horticulture LINK Project No. 180.
Intellectual property rights are invested in the Consortium of Horticulture LINK Project
No. 180.
Consortium members:
Horticulture Research International
Institute of Grassland and Environmental Research
Department for the Environment, Food and Rural Affairs
Horticultural Development Council
Middlebrook Mushrooms Ltd
Blue Prince Mushrooms Ltd
Shepherds Grove Ltd
Tunnel Tech Ltd
Pond Chase Nurseries Ltd
Hensby Composts Ltd
J. Rothwell & Son Ltd
Shackleford Mushrooms Ltd
Chesswood Produce Ltd
Bulrush Peat Co Ltd
Osmetech plc
North Tamar Business Network
1
CONTENTS
Page
Consortium members
1
PRACTICAL SECTION FOR GROWERS
Project objectives and targets
Part 1: Alternative nitrogen sources
Part 2: Odour quantification techniques
Part 3: Microbial and chemical degradation of odours
Action points for growers
Project Deliverables
4
4
6
7
8
PROJECT MILESTONES
10
SCIENCE SECTION
Part 1: Alternative Nitrogen Sources
Introduction
Materials and methods
Bench-scale composting equipment
Aerated bulk composting tunnels
Windrow composting
Compost analysis
Odour analysis
Mushroom cropping procedure
Experiments
Results
Bench-scale flask composts
Aerated tunnel composts
Windrow composting
Commercial farm tests
Role of gypsum in composts
Conclusions – Part 1
Figures and Tables – Part1
12
12
12
12
13
14
14
14
14
15
17
19
20
21
22
22
23
Part 2: Odour Quantification Techniques
39
Introduction
39
Materials and methods
Odour sample collection
39
Composting yards and composts
40
Olfactometry
40
GC-MS analysis
41
Gas detector tubes
41
Electronic sulphide detectors
41
Aromascan electronic nose
42
Odour and sulphide concentrations on and around composting
sites
43
Comparison of real and synthetic mushroom composting odours 43
Results
Olfactometric analysis
43
2
GC-MS analysis
Gas detector tube analysis
Relationship between gas detector tube analysis and odour
Compost analysis and type
Performance of Aromascan electronic nose
Performance of electronic sulphide detectors
Odour concentrations on and around composting sites
Validation of the odour/sulphide relationship
Conclusions – Part 2
Figures and Tables – Part 2
43
44
44
45
45
46
46
47
47
49
Part 3: Microbial and Chemical Degradation of Sulphides in Compost
Introduction
Biodegradation of odours
Strains
Testing isolates on composting odours
Testing systems for levels of sulphides and odour
Effect of Hyphomicrobium strain and Biofilm on H2S production
Chemical degradation of odours
Conclusions - Part 3
61
61
Overall Conclusions
66
TECHNOLOGY TRANSFER
Industrial relevance and plans for future commercial exploitation
Plans for future R&D resulting from the project
Publications and Presentations resulting from the project
References
61
61
61
63
64
66
67
67
68
68
69
3
PRACTICAL SECTION FOR GROWERS
Background
Odour pollution is a major problem facing mushroom compost production in the UK
and several other countries. Conventional composting involves wetting and mixing
straw and animal manures in heaps (pre-wetting) and then in long stacks (Phase I
composting). During these stages fermentation is uncontrolled, resulting in the
evolution of gaseous pollutants, causing environmentally unacceptable odour levels.
Broiler poultry manure has largely replaced straw bedding horse manure as an integral
part of most mushroom composting due to its low cost, high N content and ease of
handling. However, supplies of poultry manure are declining and it also has a serious
odour problem both on its own and when incorporated into compost. This project will
investigate the use of alternative N sources and straw types other than wheat and their
effect on the availability of N, composting odours and subsequent mushroom yield.
Project Objectives
This project is divided into three objectives, with the overall objective of developing a
quantifiable method of producing odour-free mushroom composts.
The three objectives were to:
1. Develop alternatives to broiler poultry manure as a nitrogen source in mushroom
compost with a view to reducing the reducing the use of poultry manure by at least
50%.
2. Develop objective methods for quantifying mushroom composting odours which
relate to odour panel assessments
3. Develop microbial inocula and chemical treatments which degrade the odourants
produced during composting compared with uninoculated composts.
The project also aimed to integrate experimental odour-free composting processes and
methods of odour quantification in a commercial scale composting system (Objective
4).
Summary of results
Part 1: Alternative Nitrogen Sources
Poultry and horse manures are the main sources of sulphur in the generation of
odourous sulphides from composting. Experiments had the following objectives:
 to determine if mixtures of organic and inorganic N sources could be used to
replace or substitute poultry manure
 to determine the effect of replacing wheat straw with other straw types (rape, bean
and linseed) on composting odours and compost quality
 to examine the replacement of poultry manure with alternative N sources in
aerated and conventional windrow composting systems
 to examine the performance of the composts and composting methods on
commercial sites.
4
Initial experiments using small-scale aerated flasks for composting identified a
number of compost ingredients which could be used in large-scale experiments. These
were: spent hop waste, cocoa meal, molasses waste (AminoPro), and rape straw (in
place of wheat straw). Degradation using inorganic nitrogen sources (urea or
ammonium sulphate) was slower than with poultry manure. However, the nitrogen
from urea was readily available. Rape straw had a higher nitrogen content than wheat
straw and required a lower inclusion of poultry manure, the main cause of mushroom
composting odour. Replacing wheat straw with rape straw resulted in a significant
reduction in odour in both windrow and aerated tunnel composts without affecting
compost density, but wheat straw produced a higher yield (see Summary Table).
Mushroom yield from bean or linseed straw composts were lower than from wheat or
rape straw composts. Following farm studies, rape straw is now used at 20% inclusion
rate by one of the commercial partners (Tunnel Tech Ltd) (Summary Table).
Substituting 50% of poultry manure N with cocoa meal or urea in large-scale
experiments reduced mushroom yield, although cocoa meal was better than urea. Hop
waste as the sole N sources produced a good mushroom yield (241 kg/tonne) when
the initial compost N was less than 2% of dry matter. Using inorganic N sources (urea
or ammonium sulphate) resulted in lower compost bulk density. Substituting poultry
manure by 50% with organic (spent hop powder, cocoa meal) or inorganic
(ammonium sulphate or urea) nitrogen sources resulted in significant reductions in
odour and sulphide concentrations. In large-scale tests the release of nitrogen from
cocoa meal was more delayed than with poultry manure. This meant that the material
needed to be incorporated during the early stages of pre-wetting. Following farm
studies, this method is now used successfully at one of the commercial partners (J.
Rothwell & Son Ltd). Urea is used during pre-wetting at three commercial sites
(Tunnel Tech Ltd, Hensby Composts Ltd and Blue Prince Mushrooms Ltd) (see
Summary Table). The economics of using different N sources depend on locality and
transport costs: cocoa meal is available in the north of England and Wales, spent hop
waste is available in Kent.
Odour concentrations from windrow composts were higher than from aerated tunnel
composts using similar composting materials (see Summary Table).
The omission of gypsum (a major source of sulphur) from compost did not affect the
emission of sulphides or odour, but resulted in a large reduction in mushroom yield.
The S in gypsum is in an oxidised form (sulphate); the compost microbiota does not
appear to be able to utilise this S to produce odourous reduced (sulphide) compounds.
5
Summary Table of results with alternative nitrogen sources (Project Part 1)
Treatment
Scale
% reduction of standard
compost*
odour mushroom compost
yield
density
48 - 72
76 - 82
107 - 112
Rape straw +
poultry manure
Large
experiment
20% rape, 80% wheat straw
+ poultry manure
Farm
studies
80
100
100
Wheat straw
50% cocoa meal +
50% urea
Large
experiment
14
73
100
50% cocoa meal or urea +
50% poultry manure
Large
experiment
37 - 61
73 - 79
100
100% hop waste or
50% hop waste + 50% urea
Large
experiment
13 - 39
89
100
25% urea (pre-wet) +
75% poultry manure
Farm
studies
100
100
25% urea, 25% cocoa meal
(pre-wet) + 50% poultry m.
Farm
studies
100
100
Aeration
Large expt.
and farm st.
10
(prewet)
10
(prewet)
10
10
96
100
95
100
* Percentage compared with standard wheat straw + poultry manure or poultry
manure / horse manure composts in conventional pre-wetting and Phase I windrows.
Part 2: Odour Quantification Techniques
Odour samples obtained from eleven composting sites showed there was a close
correlation between the compost odour concentration measured by human panels
(OC) of the pre-wet and Phase I compost air samples and the combined hydrogen
sulphide and dimethyl sulphide concentrations using gas detector tubes.In order to
measure sulphide concentrations of less than 0.1 ppm (100 ppb) eight electronic
sulphide detectors were assessed. Only one instrument (a laboratory-based pulsed
fluorescence sulphide analyser, manufactured by Thermo Environmental Instruments
Ltd) responded to low sulphide concentrations in compost odour samples (see
Summary Table below).
Air samples were also obtained from five composting sites, at increasing distances
downwind from the Phase I composting stacks, to the site boundary and beyond. The
pulsed fluorescence analyser was found to be sensitive to sulphides in composting
odours at 10 ppb. There was a good correlation between the instrument readings and
6
odour concentration. The sensitivity of the analyser enabled it to detect odour plumes
at the boundary sites, about 50 m from the Phase I composting stacks.
Synthetic pre-wet and Phase I odours were prepared from sulphides, ammonia and
other odour compounds which closely simulated real composting odours when
presented to a human odour panel. These results were consistent with the hypothesis
that certain S compounds are mainly responsible for mushroom composting odour.
Odour concentrations and sulphide concentrations from aerated composting systems
were generally lower than those from non-aerated systems. There was no difference in
odour or sulphide concentrations between poultry manure composts and compost
prepared with horse and poultry manures. No relationships were found between
compost analysis and composting odours. A tenfold dilution of the air from
composting sites resulted in almost a threefold reduction in odour intensity.
Summary Table of odour quantification techniques (Project Part 2)
Method
Human odour panel
(Olfactometry)
Advantages
Relates to actual odours
High sensitivity
Disadvantages
Not on-site
High cost of measurements
Partly subjective
Gas detector tubes
(sulphides)
Cheap
Not cross sensitive to ammonia
or water vapour
Only suitable for gases in
concentrations > 0.1 ppm
Pulsed fluorescence
analyser
High sensitivity (10 ppb)
Not cross sensitive to ammonia
or water vapour
Can be used on-site
High cost (£10,000+)
Electronic nose or
electronic sulphide
detectors
Cross sensitive to ammonia
and moisture
Low sensitivity to sulphides
Part 3: Microbial and Chemical Degradation of Composting Odours
Ten bacterial isolates were obtained from mushroom compost which were able to
remove odourous sulphur containing compounds from compost air. The bacterial
isolates belong to the following species: Pseudomonas putida, Pseudomonas
fluorescens, Bacillus cereus/thurigiensis and Hyphomicrobium spp. Several compost
systems were compared for testing the use of the bacteria in removing hydrogen
sulphide and dimethyl sulphide from compost air. Ferric (iron) sulphate solution was
more effective in removing sulphides and anaerobic odours from mushroom composts
than microbial inocula (see Summary Table oppposite).
7
There was a distinct step in oxygen concentration (5%) below which anaerobic odours
and sulphides developed. Above this threshold concentration, strong odours were
prevented and no sulphides were detected (see Figure below).
Scatter plot of H2S vs O2 levels in mushroom composts contained in incubated flasks
10
02 level (%)
8
6
4
2
0
0
50
100
150
200
H2S level (ppm)
Summary Table of microbial and chemical degradation of odours (Project Part
3)
Method
Biofiltration
Hyphomicrobium spp.
Advantages
Could be used on a biofilter in
removing sulphides;
Does not require frequent
changes
Chemical scrubbing
Ferric sulphate solution
Effective at normal
composting temperatures and
pH
Not affected by compost
ammonia
Disadvantages
Cost of biofilter
Microbes sensitive to high
composting temperature,
ammonia and pH
Biofilter requires ammonia
pre-washing
Requires replacement of
ferric sulphate at intervals
Action Points for Growers
1. Sulphides appear to be the main cause of mushroom composting odours, and there
is a good correlation between odour and sulphide concentration in the air of
composting sites. Gas detection (Draeger) tubes can be used to measure the two
main sulphides (hydrogen sulphide and dimethyl sulphide) at concentrations
above 0.1 ppm. A pulsed fluorescence analyser can be used to measure sulphide
concentrations as low as 10 ppb on site boundaries.
8
2. Replacing wheat straw with rape straw reduces odour emissions without affecting
mushroom compost bulk density, but mushroom yield is lower if rape straw is
used as a 100% replacement for wheat straw. Inclusion of some rape straw (20%)
in composts reduces odours by preventing anaerobic pockets developing in the
compost, without affecting mushroom yield or compost
density or costs.
3. Replacing poultry manure with organic nitrogen sources (spent hop waste or
cocoa meal) also reduces compost odours without affecting compost density.
Mushroom yield is lower than with 100% poultry composts. Cocoa meal has been
shown to a suitable low odour additive during pre-wetting in farm studies since it
reduces odours without affecting compost quality.
4. Replacing poultry manure with inorganic nitrogen sources reduces mushroom
yield and compost bulk density although urea is better than ammonium sulphate.
Urea was successfully used in farm studies during pre-wetting in that odours were
reduced but compost quality was not affected.
5. The omission of gypsum (a major source of sulphur) from compost did not affect
the emission of sulphides or odour, but resulted in a large reduction in mushroom
yield.
6. Hyphomicrobium spp. and 10 other isolates were successfully used as biofilters in
removing sulphides in the laboratory. The filter did not require frequent changes.
However, on a commercial scale, the cost of the biofilter, its requirement for
ammonia pre-washing and sensitivity to high composting temperature, ammonia
and pH are disadvantages.
7. Ferric (iron) sulphate solution was more effective than microbial treatment in
removing sulphides and anaerobic odours from mushroom composts than
microbial inocula.
8. Aeration of pre-wet and Phase I areas, more frequent turning of windrows and
reduction in compost moisture all reduced anaerobic compost and emissions of
odours. Maintaining a minimum of oxygen concentration of 5% was found to
prevent the development of anaerobic odours.
Project Deliverables


Odours were reduced by over 90% using a combination of aeration and alternative
N sources, although completely odour-free composts were not produced
(Objective 1). New nitrogen sources which can be used as low-odour, poultry
manure alternatives in mushroom compost include: urea, cocoa meal, cotton seed
meal, spent hop waste and molasses waste. The first three have been shown to be
commercially economic, are now in commercial use, and have the potential to
meet public odour concerns. The use of rape straw in mushroom compost is
successful in reducing compost odour (less dependency on supplies of wheat straw
alone). Rape straw is now used commercially by one of the partners.
Objective 2, to develop objective methods for quantifying mushroom composting
odours which relate to odour panel assessments, was fully achieved. Identification
of a close relationship between mushroom composting odours and sulphides,
enables rapid and objective measurement of odour sources. A pulsed fluorescence
analyser method for measuring low concentrations of sulphides on site boundaries
was developed.
9


Chemical scrubbing of odours with ferric sulphate was found to be more effective
than microbial treatment (Objective 3).
Composting methods and methods for measuring sulphides were successfully
integrated on 5 commercial sites (Objective 4).
Unexpected Benefits
Rape or bean straw could be used in organic mushroom compost, particularly if there
was a shortage of organic wheat straw, or a shortage of conventional straw in some
seasons.
Cocoa meal and urea were found to be better than a proprietary compost activator,
Sporavite, with a 70% cost saving in N sources by one of the project partners (J.
Rothwell & Son Ltd). A citric acid by-product was found to be a suitable and cheaper
source of gypsum for mushroom compost than agricultural gypsum, and is now used
by three of the project partners (Hensby Composts Ltd, Blue Prince Mushrooms Ltd
and Gateforth Park - Shepherds Grove Ltd).
10
Project Milestones
Task
Target Date
Milestones
1/1
12 months
Methodology to monitor and sample odours developed:
Relationship between laboratory-based odour quantification
techniques and subjective methods established (HRI, IGER,
Aromascan plc)
1/2
1/3
12 months
Organic waste N sources analysed and processed into odourfree forms (HRI, Bulrush, Holdsworthy Bioplant)
1/4
12 months
Different N sources compared in laboratory-based composting
processes; N balance in substrate and its biomass and
mushrooms determined (HRI)
12 months
Consortium to decide whether odour quantification techniques
are sufficiently reliable to use in intermediate and large scale
composting experiments or whether further laboratory
development is needed. Decision on which N sources should
be taken into intermediate scale facilities.
2/1
18 months
If Task 1/1 completed on time, odour quantified in
intermediate-scale facilities and bulk chamber composts using
GC-MS, olfactometry and electronic nose (HRI-W, Aromascan,
IGER)
2/2
24 months
Composting temperature and aeration regimes developed for
bulk chambers (HRI)
2/3
24 months
If Tasks 1/1 and 1/2 were completed on time, quantitative
methods for measuring smell at commercial sites will have
been developed (Industrial partners a – f, HRI, IGER,
Aromascan)
2/4
24 months
If Task 2/3 was completed on time, odour of conventional
composting will have been quantified (Industrial partners a – f,
IGER, Aromascan)
2/5
24 months
Evaluation of N sources in bulk chamber experiments
completed (HRI)
24 months
Consortium to decide on which temperature/aeration regime(s)
and composting system(s) to be used for larger scale
experiments, or whether further intermediate scale experiments
are needed to develop the regimes. Decision on which N
sources are suitable for larger scale experiments.
11
24 months
Decision on whether odour quantification of conventional
composting sites is reliable or whether further assessments or
development of quantification techniques are needed.
3/1
30 months
Influence of microbial inoculation on odour emissions and
degradation and additives to enhance water retention
determined in laboratory conditions. (HRI)
3/2
30 months
Compost odours synthesised in the laboratory to test the
parameters of the electronic nose (IGER).
30 months
Consortium to assess the performance of microbial inocula in
reducing odour levels. Decision on whether larger scale
experiments with microbial inocula can commence.
3/3
36 months
If Task 2/2 was completed on time, temperature and aeration
regimes will have been evaluated at commercial sites
(Industrial Partners a – f, HRI).
3/4
36 months
Evaluation of N sources in commercial scale experiments
completed (HRI, Bulrush, Holdsworthy Bioplant, Industrial
Partners a – f).
36 months
Consortium to compare conventional and experimental
composting odour levels and to decide what levels of
improvement are necessary in the experimental and commercial
systems. Consortium to decide which further developments in
N sources are required.
4/1
42 months
If Tasks 3/1 was completed on time, the effect of microbial
additives and methods for enhancing compost water retention
in bulk chamber experiments will have been determined (HRI).
4/2
42 months
Modified N sources further examined in laboratory
experiments; methods for reducing N losses from compost
determined (HRI).
46 months
Consortium to decide on the format of the manual and
preparation of remaining publications.
4/3
47 months
Combined effect of new composting regimes, N sources,
microbial additives and methods of enhancing water retention
determined at commercial sites (Ind. Partners a-f; HRI)
4/4
48 months
Production of a manual on odour assessment, compost
preparation and N sources in compost (HRI, IGER and
Industrial Partners)
All the milestones have been achieved within the specified timescales.
12
SCIENCE SECTION
Part 1: Alternative Nitrogen Sources
Introduction
Odour pollution is a major problem facing mushroom compost production in the UK
and several other countries (Miller and Macauley, 1988; Derikx et al., 1990, Noble
and Gaze, 1994). Conventional composting involves wetting and mixing straw and
animal manures in heaps (pre-wetting) and then in long stacks (Phase I composting).
During these stages fermentation is uncontrolled, resulting in the evolution of gaseous
pollutants, causing environmentally unacceptable odour levels. The traditional
ingredient of mushroom compost, straw bedding horse manure, provided both a
source of carbon (C) and nitrogen (N). Due to difficulties in availability and
variability in the material, compost formulations with wheat straw and various N
sources were developed. These included other animal manures such as poultry, pig
and bullock (Ross, 1968; Grabbe, 1974; Dawson, 1978), other organic wastes such as
dried blood, cotton seed meal, brewery wastes, horn, whey powder, molasses and
sewage-based products (Riethus, 1962; Delmas and Laborde, 1968; Smith and
Spencer, 1997; Gerrits, 1988) and inorganic N sources such as ammonium nitrate and
sulphate, calcium nitrate, urea and urea formaldehyde (Reithus, 1962; Bech and
Rasmussen, 1968; Delmas and Laborde, 1968; MacCanna, 1968). Due to its low
cost, high N content and ease of handling, broiler poultry manure is now an integral
part of most mushroom composting in the UK and many other countries (Gerrits,
1988). However, due to subsidised use as non-fossil fuels in power stations, supplies
of broiler chicken manure and turkey manure for mushroom composting have recently
declined. In addition, poultry manure has a serious odour problem, both on its own
and when incorporated into compost. This is mainly due to the sulphur-containing
amino acids which are precursors of volatile, odourous sulphur compounds
particularly under anaerobic composting conditions (Miller and Macauley, 1988).
Wheat straw is preferred to other cereal straws such as rye, barley and oat
since it loses its structure less during composting and it is widely available (Flegg &
Loughton, 1961; Gerrits, 1988; Noble & Gaze, 1995). However, the use of other straw
types such as rape, bean and linseed, which have higher nitrogen contents, may reduce
the requirement for poultry manure, as well as increasing available straw supplies for
organic production.
In these experiments, the effects of different straw types and N sources on the
availability of N, composting odours and subsequent mushroom yield were examined.
Initial experimental work used a bench-scale flask composting system; subsequent
experiments were conducted using large-scale turned windrow and aerated bulk
tunnel composting systems.
Materials and Methods
Bench-scale composting equipment
Substrate ingredients were composted in ‘Quickfit’ multiadapter flasks immersed in
thermostatically controlled water baths, each holding two 10-litre flasks (Noble et al,
1997). The prepared ingredients (3 kg samples) were placed on a perforated stainless
steel platform within each flask and the flasks immersed in the waterbaths such that
13
the water level was above the level of the enclosed substrate. Each flask was
connected to ancillary equipment providing independent aeration of the compost. The
oxygen concentration in the substrate was controlled regularly by adjusting the
airflow through the compost in each flask within the range 0 - 16 litres kg-1 substrate
h-1 by means of flow meters. The temperature of the substrate in the flasks was
monitored with Squirrel multipoint temperature loggers (Grant Instruments Ltd,
Cambridge, UK).
For the first 48 h of the composting process, the thermostat of the waterbath
was set at 48°C to allow a natural succession and gradual build-up of microorganisms.
The substrate temperature was then increased to 72°C for 5 days, after which the
substrate was re-mixed and the temperature reduced to 47°C for the remainder of the
composting period, which was seven days, or prolonged until the air in the flask was
clear of ammonia. An oxygen concentration of 11(± 1.5)% v/v was maintained in the
substrate.
Aerated bulk composting tunnels
Bales of straw were wetted and formed into stacks using a compost turning machine.
Further water was added to the straw in a separate turn to achieve a moisture content
of 70%. After four days, 50% of the required N source was mixed into the stack; the
remaining N source and gypsum at 30 kg tonne-1 fresh compost ingredients were
mixed into the stack after a further two days. Water was added in a further three turns
after day 4, to achieve a moisture content of 78%. Stack temperatures were monitored
with platinum resistance sensors and data logger. The preparation time for the
blended compost ingredients, before filling into the tunnels was seven days.
Six aerated bulk composting tunnels at HRI Wellesbourne were used for the
experiments. Compost was filled on to a slatted base in the tunnels, mounted above
an air plenum through which a controlled flow of fresh and/or recirculated air could
be blown. Two of the tunnels consisted of modified insulated cargo containers. Both
of these tunnels had a vertical partition, which did not extend into the air plenum
below, to enable two different composts to be filled into each tunnel (Type A). The
other four tunnels consisted of insulated polythene tunnels, inside which were two
parallel walls, joined by a wall at one end (Type B). The compost was enclosed by a
removable end wall, which fitted across the sidewalls. Details of the tunnels,
temperature, oxygen and air flow measurement and control, methods for filling and
emptying the tunnel and methods for measuring ammonia concentrations are given in
Noble & Gaze (1994 & 1998).
The tunnel composting regime consisted of three stages, designated Phases 0, I
and II. The tunnels were filled with 4 t batches of blended compost ingredients to a
height of 1.5 m. The Type A tunnels were each filled with two 4 t batches of blended
compost ingredients separated by a central partition. In the Type B tunnels the
airflow was set at 9 m3h-1, unless the oxygen concentration in the compost fell below
6%, in which case the airflow was increased to 13 m3h-1 until the oxygen
concentration was above 6%. The respective airflows in the Type A tunnels were 12
and 26 m3h-1. After five days (Phase 0), the compost was emptied from the tunnels,
mixed and if necessary re-wetted to achieve a moisture content of 77%, and then refilled. The subsequent 6-day Phase I was similar to the Phase 0 regime.
For the Phase II pasteurisation regime, the tunnels were filled with 2.5 t of
material from the Phase I stage to a height of 0.9 – 1.1 depending on the ingredients.
Following a 20 h equalisation of compost temperature at 45 - 48°C, the composts
14
were pasteurised at 58 - 60°C for 6 h. Compost temperatures were then reduced to 46
- 49°C (conditioning). A minimum oxygen concentration of 13% was maintained
during Phase II. Composting was completed when the compost temperature had
fallen to within 1°C of the air temperature and ammonia could no longer be detected
in the compost. Details of temperature and airflow control during Phase II are given
in Noble & Gaze (1998).
Windrow composting
Straw bales were formed into windrows and wetted on day 0 without a pre-wetting
procedure. Nitrogen sources were added on day 2 and water applications and windrow
turns were made on alternate days during a 16 day period. Water applications after
day 10 were varied according to compost moisture content. Compost moisture content
at filling of bulk pasteurisation tunnels was 76%.
Both aerated and windrow composts were pasteurised at 58 C for 6 hours and
conditioned at 45-48 C.
Compost analysis
Analyses were conducted on freeze-dried, finely milled samples of the compost
ingredients and of the substrates before and after processing in the flask composting
equipment or Phase II tunnels. Dry matter (DM), N, ammonium (NH+4) and ash
contents and pH were determined as described previously (Noble and Gaze, 1994).
Compost sulphur content was measured according to the method in Anon (1986).
Odour analysis
Odour samples were collected in 20 L Teflon bags as follows:
(i)
from flasks by evacuating the air in the flask
(ii)
from aerated tunnel composts, 0.2 m downwind of the compost during the
emptying of the Phase 0 tunnel stage.
(iii) from windrow composts, 0.2 m downwind of the stack during turning.
The odour samples were then transported to IGER North Wyke and analysed
within 24 h. Odour concentration (OC) was determined by an odour panel using
dilution olfactometry and volatile organic compounds detected by gas
chromatography – mass spectrometry (GC – MS). A Dräger Accuro bellows pump
with appropriate detector tubes (Drägerwerk, Lübeck, Germany) was used for on-site
measurement of ammonia and specific sulphides, in the same way as sampling odours
for collection in Teflon bags. Two replicate measurements were made for each
sampling.
Mushroom cropping procedure
(i) Bench-scale flask composts
At the end of the composting period, the material in each flask was weighed. After
samples were taken for analysis, 2 kg of the residual material was inoculated with
mushroom spawn (spawned) at two percent of the fresh weight of compost with
Agaricus bisporus spawn (Hauser A15) and filled into plastic pots, 230 mm diameter
x 220 mm depth. The pots were placed in polythene bags in an incubator at 25°C and
when the substrate was fully colonised with mushroom mycelium, about 15 days after
15
spawning, the containers were cased with a moist mixture of peat and sugar beet lime
(900 g). When mushroom mycelium was visible on the surface of the casing, the
containers were transferred to a controlled environment chamber with an air
temperature of 18°C, relative humidity of 90% and a CO2 concentration of 0.1% to
induce fruiting. Mushrooms were harvested daily over a 30 day period (cap diameter
25-30 mm).
(ii) Large-scale, aerated tunnel and windrow composts
The cropping procedure is outlined in Noble & Gaze (1998). The composts were
spawned using the Hauser A15 (Sylvan Spawn Ltd, Peterborough, UK) and 2100
(Amycel-UK Ltd, Burton-on-Trent, UK) strains. Half the compost spawned with
each strain was supplemented with the soya meal-based “Betamyl 1000” (Sylvan
Spawn Ltd) at a rate of 1% of compost fresh weight. Spawned trays were stacked
four high in cropping sheds, with four replicate trays of each spawn and supplement
sub-treatment from each of eight compost treatments (128 trays per shed with 16 trays
from each of the compost treatments). A split-plot design was used with compost
treatments allocated to main plots, which were arranged in a Latin square design, and
spawn/supplement treatments allocated to sub-plots within each main plot.
Mushrooms were picked as large buttons (diameter 30-40mm) over a 24-days period
(three flushes of mushrooms). The yields of each run were analysed separately and
the means of each treatment were incorporated into the analysis structure of the tunnel
composting stage of the experiment.
Percentage dry matter content of each batch (treatment and run) of mushrooms
from the first and second flushes was calculated from the fresh weight of 20
mushrooms, and the dry weight after oven drying (Burton & Noble, 1993). The N
and ammonium (NH4+) contents of mushrooms from the first and second flush were
determined on freeze-dried samples of 20 mushrooms from each batch (Noble &
Gaze, 1994).
(iii) Commercial farm tests
Samples of compost were transported in bulk bags to tray and shelf farms. The
compost was spawned with the same strain used on the farm for standard compost,
and received the same cultural treatment. The commercial trays contained 200 kg of
compost.
Bags were also filled with samples of compost, spawned with same strains
used on the commercial farms. Batches of 20 bags, each containing 20 kg compost,
were sent to the commercial farms.
Tests with alternative nitrogen sources were conducted at one of the
commercial sites using a 100 tonne aerated composting tunnel.
Experiments
Bench-scale flask composts
Experiment 1: Effect of compost N from poultry manure on mushroom yield
Compost N content was varied by altering the ratio of broiler poultry manure to wheat
straw, taking into account the N and moisture contents of the poultry manure and
straw (Noble and Gaze, 1994). Water was first added to the straw to achieve a
moisture content of 70% before the addition of poultry manure. Gypsum was added
at 30 g kg-1 fresh compost ingredients. Further water was added over a period of 4
16
days to achieve a moisture content of 78% (±1.5%), before the substrate ingredients
were filled into the flasks.
Compost ingredients were prepared with six target N contents varying
between 1.1 and 2.6% of dry matter. Six composts were prepared with each target N
content. A total of 36 substrates were prepared. Quantities of poultry manure used
with wheat straw varied between 17 and 55% by weight.
Experiment 2: Effect of substrate N from difference N sources on mushroom yield
Compost ingredients were prepared from wheat (Triticum aestivum) straw and the
following organic, inorganic and proprietary N sources:
 Broiler poultry manure, a mixture of droppings, feathers and sawdust (control)
 Brewers' grains (Everards Brewery Ltd, Narborough, Leicester, UK)
 Hop (spent) waste powder (English Hop Products Ltd, Tonbridge, Kent, UK)
 Digester waste, animal manure-based (Holdsworthy Bioplant, Devon, UK)
 Cocoa meal, extracted from bean shells (Cadbury Ltd, Chirk, Wrexham, UK)
 Cocoa shells, pulverised (Cadbury Ltd)
 Chipboard sawdust waste, containing urea formaldehyde resin (Pelican
Fabrications Ltd, Northfleet, Kent, UK )
 Ammonium sulphate
 Urea
 Sporavite: molassed fibrous meal with added urea (a proprietary mushroom
compost activator produced by Amycel (UK) Ltd, Burton on Trent, UK)
 AminoPro: molasses waste liquid including inorganic N (marketed as a
proprietary animal feed supplement by United Molasses, Burton on Trent, UK).
 Mycelium by-product ( a waste from citric acid production)
 Amide waste (from oilseed rape processing)
Compost was also prepared from:
 Oil seed rape (Brassica napus) straw with poultry manure.
The proportions of straw and N sources in the formulations were calculated on the
basis of their N and dry matter contents using the formula in Noble & Gaze [1994] to
achieve blended ingredients with N contents of 1.6, 2.1 and 2.6 % of DM. Analyses of
the raw ingredients and the quantities used in the formulations are shown in Table 1.
Each of the 12 compost formulations x 3 N content treatments had 3 replicates.
Brewers' grains, cocoa shells and animal digester waste were not used at the highest N
rate (2.6 % of DM) because the N content was too low (Table 1). Analyses of the
composts at spawning are shown in Table 2.
Aerated tunnel composting
Experiment 3: Use of different compost nitrogen and sources and straw types
The substrates were prepared from wheat (Triticum aestivum) and oilseed rape
(Brassica napus) straws as the main carbon (C) source. Rape straw was only used
with broiler poultry manure. Wheat straw was used with poultry manure (control
treatment), cocoa meal, spent hop powder, ammonium sulphate and urea. The analysis
of the raw ingredients and the quantities used in the formulations are shown in Table
3. The proportions of C and N sources in the formulations were calculated on the
basis of their N and dry matter contents using the formula in Noble & Gaze (1994) to
achieve blended ingredients with an N content of 1.8 and 2.3% of dry matter. The
moisture content of the composts at filling of the Phase 0 tunnels was 77 - 78%.
17
Analyses of the composts at filling of the Phase II tunnels and at spawning are shown
in Table 4.
Windrow composting
Experiment 4: Composting different straw types and N sources in windrows
Substrates were prepared from wheat, oilseed rape, bean and linseed (flax) (Linum
usitatissimum) straws. All the straw types were used with broiler poultry manure.
Wheat straw was also used with three other organic N sources in combination with
urea: cocoa meal, spent hop waste, and molasses waste (AminoPro). In the latter two
formulations, the organic N sources and urea each provided 50% of the supplemented
N. Linseed straw was used only once. The combinations of straw types, organic and
inorganic N sources are shown in Table 7. Analyses of ingredients are shown in Table
1. Compost formulations were prepared with an initial N content of 2 % of DM.
Composts were analysed, gaseous emissions measured with detector tubes, and
mushroom yields and DM contents determined as previously described. The
experiment was conducted as a series of three runs, with six tunnels (two Type A and
four Type B).
Role of gypsum in compost
Since the 1930s, gypsum (calcium sulphate) has been a traditional ingredient in
mushroom compost, partly as a flocculating agent to prevent 'greasiness' and partly to
reduce the emission of ammonia from ammonium nitrogen. However, it also one of
the main sources of sulphur in mushroom compost, but there is no information
available regarding its role in the production of odourous S compounds. Experiments
were conducted to determine whether:
 gypsum contributes to the emission of sulphides from mushroom compost?
 mushroom yield is influenced by the addition or rate of gypsum in compost?
 there are differences between sources of gypsum in terms of composting and
mushroom yield?
Anaerobic, straw-poultry manure composts with gypsum added at 0%, 0.5% and 3.5%
w/w fresh weight were prepared in flasks.
Windrow (6 tonne) stacks of compost were prepared with (1) agricultural
gypsum added at 25 kg/tonne compost ingredients (2) citric acid by-product gypsum
added at 25 kg dry gypsum (33 kg fresh material) /tonne compost ingredients (3) no
gypsum. The experiment was repeated twice.
Results
Bench-scale flask composts
Experiment 1: Effect of compost N from poultry manure on mushroom yield
Increasing the N content of the compost ingredients from 1.1 to 2.6% of DM
increased the duration to clear NH3 from the compost from 71 hours to 343 hours and
increased the maximum NH3 concentration in the flasks from 200 to 840 ppm. This
resulted in an increase in compost N losses from 352 to 3142 mg/kg. Final ammonium
and dry matter content and pH of the composts were: (mean values) 0.09 (±0.03)% of
DM, 27(±2.3)% and 7.4 (± 0.31)%.
18
There was considerable variation in the mushroom yields obtained from the
small pots. The optimum compost N content at spawning in terms of mushroom yield
was 2-2.5% of DM. This was equivalent to an initial compost N content of 1.5 to
1.8% of DM.
Experiment 2: Effect of substrate N from difference N sources on mushroom yield
Analysis of materials
Analyses of the N sources used are shown in Table 1. The molasses waste
(AminoPro), Croda amide waste and mycelium by-product had N contents above 3%
of dry matter, although the molasses waste and mycelium by-product had higher
moisture contents. The cocoa shells waste and brewers grains had lower N contents
than poultry manure, cocoa meal waste or spent hop waste. The N content of hop
haulm waste on a fresh weight basis was significantly lower than that of the other
alternative N sources. Hemp straw had a similar N content to wheat straw. These
latter materials were therefore not tested in the composting experiment.
Compost DM at spawning was 27.0 ± 1.1%. Increasing the N rate in the
compost increased the maximum NH3 concentration, and NH3 and N losses from
compost (P<0.001) (Table 2). Ammonium contents of the composts at spawning
increased with initial compost N rate (P<0.001). Maximum NH3 concentration and
NH3 and N losses during composting were greater from Sporavite composts than from
other compost formulations (Table 2). With urea, Sporavite and AminoPro composts,
NH3 was an immediately evolved from the composts in the flasks, but emission
whereas with other formulations, there was delay in the main evolution of NH3 until
the compost temperature had been increased to 72°C (Figure 1). Maximum NH3
concentrations were higher from poultry manure, brewers' grains, hop waste and urea
composts than from the remaining formulations (Table 2; Figure 1). Losses of NH3
and N from digester waste, chipboard waste, and cocoa meal or shells composts were
lower than from other formulations. Composts prepared from digester waste, cocoa
meal and shells, and chipboard waste had lower ammonium contents at spawning than
poultry manure or urea composts; the highest levels were in ammonium sulphate,
Sporavite and AminoPro composts (P<0.001).
The ash contents at spawning of digester waste composts were higher than
those of other formulations, except poultry manure composts. The pH values of cocoa
meal or shells and Sporavite composts were higher than those of digester and
chipboard wastes, brewers' grains, AminoPro and ammonium sulphate composts, with
other formulations intermediate in pH (Table 2). Increasing N rate in the compost
from 1.6 to 2.1 or 2.6% of DM resulted in a higher ash content at spawning but did
not significantly affect pH (Table 2).
Mushroom cropping. There was a significant interaction between the effects of N rate
and N source on mushroom yield (P<0.001) (Table 3). Cocoa meal and Sporavite
composts produced higher yields at the 1.6% N rate than at the higher rates, whereas
hop waste and rape straw composts produced higher yields at the 2.1% rate than at the
1.6 % N rate. The 2.6% N rate produced either a lower yield than the 1.6 and 2.1% N
rates or no mushrooms (cocoa shells and Sporavite composts), with the exception of
rape straw + poultry manure compost, where there was no significant difference in
yield between the 2.1 and 2.6% N rates. Mushroom yield results for the 2.6% N rate
are therefore not shown.
At the 1.6% N rate, the highest mushroom yields were obtained from cocoa
meal and Sporavite composts (Table 3). The cocoa meal compost also produced the
19
highest yield in terms of numbers of mushrooms. At the 2.1 and 2.6% N rates, rape
straw + poultry manure compost produced the highest yield, both in terms of weight
and numbers of mushrooms. At all three N rates, yields from digester and chipboard
wastes, and ammonium sulphate composts were lower than from the wheat straw +
poultry manure composts. At the 1.6% N rate, yields from urea, hop waste and rape
straw composts were lower than from the wheat straw + poultry manure compost.
Cocoa shells compost produced only one mushroom per pot. Yields N-Rich and
amide waste composts were also low and these treatments were therefore not
repeated.
Aerated tunnel composts
Experiment 3: Use of different compost nitrogen and sources and straw types
Analysis of composts
Analyses of the materials used in the experiment are shown in Table 3. The cocoa
meal and spent hop powder had similar N contents on a fresh weight basis to the
poultry manure. Rape straw had a significantly higher N content than wheat straw.
During composting, composts with organic N sources reached higher
temperatures than those with inorganic N sources (ammonium sulphate or urea)
(Table 4). Initial S contents of poultry manure composts (1.0–1.1% of DM) were
intermediate between those of ammonium sulphate composts (1.8% of DM) and the
other formulations (0.8–0.9% of DM). Of this S, about 0.8% could be attributed to the
inclusion of gypsum. Losses of S during composting followed a similar pattern to the
initial S content of treatments (Table 4) with S losses from ammonium sulphate
composts greater than from poultry manure composts, which in turn lost more S than
the other formulations (P<0.001). There was no significant effect of compost N rate
on S losses. Maximum NH3 concentrations, NH3 and N losses were greater from the
2.3% N rate than from the 1.8% N rate composts (P<0.001). Maximum NH3
concentrations and losses were also higher from the poultry manure and urea
composts than from the cocoa meal, hop waste, and ammonium sulphate formulations
(P<0.01) (Figure 2). This corresponded to higher N contents at spawning in the latter
composts (P<0.01). Ammonium contents of all composts at spawning were in the
range 0.02–0.10% of DM.
At spawning compost DM was not significantly different between treatments
(26.9 ± 1.4%), but ash contents of poultry manure compost was higher that of urea
compost. The pH of hop waste composts were higher, and those of ammonium
sulphate composts lower than those of other composts (P<0.001). There was no
significant effect of N rate on compost ash content, pH or bulk density at spawning.
However, composts prepared with organic N sources had greater bulk densities at
spawning than those prepared with inorganic N sources (urea or ammonium sulphate)
(P<0.001).
Mushroom cropping. Mushroom yield was higher from the wheat straw + poultry
manure composts than from the rape straw + poultry manure and hop waste (1.8% N)
composts, which produced higher (P<0.01) yields than the remaining formulations
(Table 3). Hop waste compost with an initial N content of 1.8% of DM produced a
higher yield than the 2.3% N rate. There were no other significant effects of N rate on
mushroom yield. There were no significant differences in mushroom yield between
the strains A15 and 2100, or between supplemented and unsupplemented compost.
20
Mushroom DM (mean 8.2 ± 0.4%), N (mean 5.8 ± 1.0% of DM), and ammonium (0.6
± 0.2% of DM) contents were not significantly affected by the treatments (Table 7).
Odour and gaseous emissions. The bag sample OC of wheat straw + poultry manure
compost (2.3% N rate) was higher than that of the other composts (Table 5). The other
poultry manure composts and hop waste compost (2.3% N rate) had higher OCs than
the remaining formulations. With all the N sources, the 1.8% N rate produced a higher
OC than the 2.3% N rate.
Compounds found in concentrations exceeding their detection thresholds
(Devos et al, 1990) were NH3, butanol and those containing S (Table 5). Several other
compounds (mainly organic acids) were found at concentrations just above their
detection thresholds, but were not significantly different between treatments (footnote
to Table 4). The S-containing compound mainly responsible for exceeding its
detection threshold in compost air was dimethyl sulphide (DMS), followed by H2S,
except in ammonium sulphate composts where methanethiol (MeSH) predominated.
Little or no sulphides were detected in the air from cocoa meal, hop waste or urea
composts. In the other formulations, increasing the rate of the N source increased the
emission of sulphides. The concentrations of NH3 and acetone were also higher from
all the 2.3% N rate composts than from the 1.8% N rate composts, and butanol
concentration was higher from the 2.3% N rate composts prepared with poultry
manure or hop waste.
There was a close correlation between the combined on-site concentration of
H2S + DMS and the bag sample OC of compost air. There was no correlation between
OC and total losses of S during composting (Table 4).
Windrow composting
Experiment 4: Use of different compost nitrogen and sources and straw types
Composting process and compost analysis
Composting process and compost analysis. Compost prepared from linseed straw was
slow to degrade and maximum compost temperature was only 55°C. Subsequent
compost bulk density and mushroom yield were very low (Table 8) and the treatment
was therefore not repeated. Maximum temperatures during composting were not
significantly different between the other treatments (mean 73 ± 3°C). Maximum NH3
concentrations from poultry manure composts (wheat, rape or bean straws) were
higher than from the other wheat straw formulations (P<0.01)(Table 6; Fig. 3).
Maximum NH3 concentration during composting was correlated positively with NH3
and N losses (r = 0.74 and 0.71; P<0.05), and negatively with compost N content at
spawning (r = 0.68; P<0.05). Composts prepared with cocoa meal had higher N
contents at spawning than the other formulations. Calculated N losses during
composting of equivalent formulations in windrows (Table 6) and aerated tunnels
(Table 4) were similar. However, maximum NH3 concentrations and calculated losses
were higher for aerated tunnel composts with equivalent formulations. This was
probably due to the dilution of NH3 concentrations during recording of open-air
windrow composting. At spawning, all composts in Experiment 4 had ammonium
contents in the range 0.03–0.11% of DM.
Compost DM content at spawning was 27.1 ± 1.2% and was not significantly
different between treatments. The ash content and pH of the AminoPro + urea
compost was lower than that of the other composts except for the pH of rape straw
21
compost. The ash contents of windrow composts (Table 6) were higher than those of
aerated tunnel composts (Table 4) or flask composts (Table 2) where equivalent
formulations were used. This indicates that carbon losses and compost degradation
were greater in windrow composting.
Compost bulk densities of bean straw, hop waste + urea and AminoPro + urea
composts were significantly lower than those of the other treatments. Bulk densities of
windrow (Table 6) and aerated tunnel composts (Table 4) were similar.
Mushroom cropping. Mushroom yield from wheat straw + poultry manure was
significantly greater than that from other compost formulations (Table 8). AminoPro
+ urea produced a significantly lower mushroom yield than rape straw + poultry
manure or hop waste + urea. In both Experiments 2 and 3, there was a correlation
between the maximum NH3 concentration and mushroom yield obtained from
different compost formulations (r = 0.61 and 0.68; P<0.05), indicating that
availability and release of N for compost degradation is a factor in determining
subsequent mushroom growth. This is not the only factor since NH3 was released
more readily from urea-based composts than from poultry manure-based composts
although mushroom yield was poorer. However, it was observed that mushroom
mycelial growth on the casing layer over urea-based composts was more vigorous
than on the other treatments. There were no significant differences in mushroom
yield between supplemented and unsupplemented compost, but strain A15 produced a
higher yield than 2100 (mean values 227 and 213 kg t-1. Mushroom dry matter content
was not significantly different between treatments or different from that in aerated
tunnels, Experiment 3 (mean 8.3 ± 0.5%) (Table 9).
Odour and gaseous emissions. The bag sample odour concentrations (OCs) of poultry
manure composts were significantly higher than those of compost formulations which
did not include poultry manure (Table 6). The H2S and DMS concentrations of the
wheat straw + poultry manure compost were significantly higher than those of the
rape or bean straw + poultry manure composts, which in turn were higher than the
concentrations from other treatments. As in Experiment 3, there was a correlation
between the combined on-site concentration of H2S + DMS and the bag sample OC of
compost air.
Commercial farm tests
All the experimental composts produced lower yields than the commercial standard
composts. Poultry manure and poultry manure + cocoa meal performed better than
cocoa meal + urea (Table 10).
Cocoa meal, cotton seed meal and urea were used as pre-wetting materials in
place of poultry manure at J. Rothwell & Son Ltd. At Hensby Composts Ltd, Blue
Prince Mushrooms Ltd and Tunnel Tech Ltd, 50% of the poultry manure applied
during pre-wetting was replaced with urea. In all cases, there was a large (>90%)
reduction in odour during pre-wetting, with no effect on mushroom yield, quality or
compost density. At Tunnel Tech Ltd, 20% of the wheat straw was replaced with rape
straw. This reduced the formation of anaerobic pockets in the compost, and did not
affect the quality or cost of the compost.
22
Role of gypsum in compost
Since gypsum is a major source of S in mushroom compost, it may have been
expected that the presence or absence of gypsum in compost would influence the
emission of S compounds. Hydrogen sulphide and dimethyl sulphide concentrations
in the anaerobic flasks after 24 and 72h exceeded 1000 ppm and there were no
significant differences between treatments (composts with and without gypsum at 0.5
and 3.5 % w/w).
There was no significant difference in odour, air sulphide or ammonia concentrations
from the windrow composts with different gypsum treatments. There were no clear
differences in compost analysis at Phase I or Phase II between treatments, except that
the first replicate compost had higher moisture than the second Tables 11 and 12). The
absence of gypsum resulted in a large yield reduction (about 90%) in both crops
(Table 13). There were no significant differences in mushroom yield or compost
analysis between the agricultural and citric acid by-product gypsum sources. Further
windrow composting tests showed that there was no significant effect of gypsum
inclusion rate in compost (0.5 to 3.5 %) on mushroom yield (Fig.4).
The results indicate that gypsum is a necessary ingredient in mushroom
compost (particularly if wet) but it has no significant effect on sulphide or odour
emissions. The S in gypsum is in an oxidised form (sulphate); the compost microbiota
does not appear to be able to utilise this S to produce odourous, reduced (sulphide)
compounds.
Conclusions - Part 1
1.
2.
3.
4.
5.
6.
7.
8.
Replacing wheat straw with rape straw resulted in a significant reduction in
odour in both windrow and aerated tunnel composts without affecting compost
density, but mushroom yield was lower (see Summary Table below). Rape
straw has a higher nitrogen content than wheat straw and required a lower
inclusion of poultry manure, the main cause of mushroom composting odour.
Mushroom yield and compost density from bean straw and linseed straw
composts were lower than from wheat straw or rape straw composts.
Substituting poultry manure by 50% with organic (spent hop waste, cocoa
meal, or molasses waste) or inorganic (ammonium sulphate or urea) nitrogen
sources resulted in significant reductions in odour and sulphide concentrations,
but also reduced mushroom yield. However, cocoa meal and cotton seed meal
were found to be suitable as low odour N sources during pre-wetting in farm
studies (see Summary Table).
Spent hop waste as the sole N source produced a good mushroom yield (241
kg/tonne) when the initial compost N was l.8% of dry matter (summary
Table).
Using inorganic N sources (urea or ammonium sulphate) resulted in lower
compost bulk density and mushroom yield than poultry manure compost.
Release of ammonia from urea is more rapid than from poultry manure, but
from cocoa meal it is more delayed. This material was successfully used for
pre-wetting in farm studies (summary Table).
Odour concentrations from windrow composts were higher than from aerated
tunnel composts using similar composting materials (Summary Table).
The omission of gypsum from compost did not significantly affect the
emission of sulphides or odours but resulted in a significant yield reduction.
23
9.
There was no difference in mushroom yield between two types of gypsum
(agricultural or citric acid production by-product).
Summary table of results with alternative nitrogen sources (Project Part 1)
Treatment
Scale
% reduction of standard compost*
odour
mushroom compost
yield
density
48 - 72
76 - 82
107 - 112
Rape straw +
poultry manure
Large
experiment
20% rape, 80% wheat straw
+ poultry manure
Farm
studies
80
100
100
Wheat straw
50% cocoa meal +
50% urea
Large
experiment
14
73
100
50% cocoa meal or urea +
50% poultry manure
Large
experiment
37 - 61
73 - 79
100
100% hop waste or
50% hop waste + 50% urea
Large
experiment
13 - 39
89
100
25% urea (pre-wet) +
75% poultry manure
Farm
studies
10
(pre-wet)
100
100
25% urea, 25% cocoa meal
(pre-wet) + 50% poultry m.
Farm
studies
10
(pre-wet)
100
100
Aeration
Large expt.
and farm st.
10
10
96
100
95
100
* Percentage compared with standard wheat straw + poultry manure or poultry
manure / horse manure composts in conventional pre-wetting and Phase I windrows.
24
Table 1
Analysis of straw types and N sources used in the experiments and quantities used in the
compost formulations in Experiments 1 and 2. Each value is the mean of 5 determinations (± S.D.)
Straw typea or
N source
Rateb
% w/w
DM %
Wheat straw
17-97
Rape straw
Price, £c
% of DM
N
NH+4
Ash
t-1
kg-1N
88 (±1.4)
0.5 (±0.15)
0.05 (±0.007)
7 (±1.3)
36
8.18
57-73
85 (±2.6)
1.2 (±0.09)
0.04 (±0.008)
6 (±1.8)
30
2.94
Bean straw
72
88 (±2.1)
0.6 (±0.12)
0.01 (±0.006)
4 (±1.2)
35
6.63
Linseed straw
68
87 (±1.3)
0.7 (±0.08)
0.01 (±0.006)
4 (±1.1)
30
4.93
Poultry manure
23-49
69 (±6.8)
5.9 (±0.59)
0.98 (±0.361)
15 (±0.8)
3
0.07
Digester waste
40-73
27 (±1.6)
2.8 (±0.51)
1.03 (±0.110)
22 (±2.7)
0
0
Cocoa meal
29-50
93 (±2.5)
4.2 (±0.23)
0.07 (±0.004)
5 (±1.5)
50
1.28
Cocoa shells
50-75
98 (±0.7)
2.6 (±0.15)
0.12 (±0.002)
9 (±0.6)
25
0.98
Hop waste
38-60
90 (±2.0)
3.3 (±0.52)
0.05(±0.007)
8 (±0.5)
50
1.68
Brewers' grains
69-83
24 (±5.2)
2.8 (±0.30)
0.04 (±0.001)
5 (±0.9)
22
3.27
Chipboard waste
39-67
87 (±4.5)
3.1 (±0.58)
0.26 (±0.149)
1 (±0.2)
0
0
Amm. sulphate
5-12
100
21.2
27.27
-
235
1.11
Urea
3-5
100
46.7
0
-
260
0.56
AminoPro
15-26
61 (±2.2)
6.3 (±0.32)
3.37 (±0.053)
9 (±1.6)
70
1.82
Sporavite
23-44
75 (±1.9)
6.6 (±0.54)
2.30 (±0.099)
16 (±1.9)
150
3.03
a
Wheat straw was used in combination with all the N sources, inclusion rates with individual N sources
were (100 - N source) %; rape, bean and linseed straws were only used with poultry manure.
b
Original fresh weight in compost excluding added water and gypsum.
c
Average UK prices, excluding transport and tax (Farmers Weekly and companies listed in Experiment
1).
25
Table 2 Ammonia and nitrogen losses during flask composting, compost analysis at spawning, and mushroom yield in Experiment 2. Values for compost parameters are the
means of three N rates (1.6, 2.1 and 2.6% of DM) and two replicate composts.
Straw type and
N source in
compost
During composting
Compost at spawning
Max. NH3
NH3 loss
N loss
conc., μL L-1
mg kg-1
mg kg-1
% of DM
pH
N
NH4+
Ash
Mushroom
yield , g kg
a
numbers per pot
-1
1.6%N 2.1%N
1.6%N
2.1%N
Wheat straw +
Poultry manure
339
[5.83] b
689
[6.54] b
385
[5.95] b
2.28
0.15
16
8.1
126
138
15
[3.9] c
16
[4.0]
Digester waste
30
[3.42]
170
[5.14]
18
[2.93]
1.77
0.05
22
7.8
79
60
16
[4.1]
15
[4.0]
8
[2.08]
135
[4.91]
151
[5.02]
2.36
0.06
12
7.7
55
55
18
[4.2]
17
[4.2]
119
[4.78]
516
[6.25]
148
[5.00]
2.22
0.38
12
7.4
93
97
16
[4.1]
18
[4.3]
Cocoa meal
17
[2.87]
67
[4.21]
77
[4.35]
2.42
0.07
10
8.4
199
94
24
[5.0]
14
[3.9]
Cocoa shells
10
[2.33]
53
[3.97]
403
[6.00]
2.16
0.06
11
8.5
10
0
1
[1.3]
0
[0.6]
Hop waste
103
[4.63]
544
[6.30]
78
[4.36]
2.54
0.10
13
8.0
89
132
13
[3.6]
23
[4.8]
Sporavite
927
[6.83]
4538
[8.42]
2490
[7.82]
2.21
0.62
14
8.2
168
0
16
[4.0]
0
[0.6]
AminoPro
80
[4.39]
897
[6.80]
698
[6.55]
2.72
0.56
13
7.8
118
97
10
[3.3]
16
[4.0]
309
[5.73]
1740
[7.46]
1315
[7.18]
1.85
0.17
12
7.9
89
108
11
[3.3]
18
[4.2]
78
[4.36]
428
[6.06]
444
[6.10]
2.41
0.50
9
6.9
74
98
14
[3.8]
16
[4.0]
Chipboard waste
Brewers' grains
Urea
Amm. sulphate
N-Rich
Amide waste
1
5
12
2.35
0.03
11
7.2
53
42
13
7
100
412
316
2.29
0.04
11
8.4
50
65
7
12
[7.50]
2.18
0.14
15
8.0
82
177
13
[2.18]
0.26
0.06
4
0.3
46
46
Rape straw +
Poultry manure
LSD (P < 0.05)
a
651
[6.48]
[1.18]
1261
[7.14]
[1.24]
1812
[3.7]
[1.0]
27
[5.0]
[1.0]
Mushroom yield expressed as g mushrooms per kg of spawned compost, in composts with initial N content of 1.6 and 2.1% of DM.
Figures in square parentheses are loge transformations, shown next to back-transformed values. c Figures in square parentheses are square root transformations, shown next to
back-transformed values.
b
26
Table 3. Analysis of straw and N sources and quantities used in aerated tunnel composts.
Analyses are means of three replicate samples.
% w/wc
N-rate
% of DM
DM%
Ingredient
1.8
2.2
N
N
Wheat straw
100-N source
87
0.7
0
Rape straw
100-poultry manureb
84
1.2
0
0
Poultry manurea
34.5
40.4
71
4.9
Poultry manureb
31.0
39.1
-
-
Spent hop powder
36.6
52.7
89
3.8
0
Shell extracted
cocoa meal
35.9
44.1
90
4.3
0
Ammonium
sulphate
3.2
6.7
100
21.2
2
Urea
2.1
3.6
100
46.7
a
rate with wheat straw
b
rate with rape straw
c
original fresh weight in compost excluding added water and gypsum,
at compost N-rates of 1.8 and 2.1%
27
Table 4 Compost temperatures, ammonia and nitrogen losses during aerated tunnel composting, compost analysis at spawning, and mushroom yield in Experiment 3.
Values are the means of two replicate composts.
Compost formulation
Straw type
and N source
N rate
During composting
a
% of DM
Compost at spawning
Max.
Max. NH3
NH3 loss
N loss
S loss
% of DM
temp. °C
conc., μL L-1
mg kg-1
mg kg-1
mg kg-1
N
Ash
pH
Mushroom
BD
b
kg m-3
kg t-1
Wheat straw +
1.8
76.8
358
[5.88] d
721
[6.58] d
1043
[6.95] d
43
2.41
18
7.7
446
268
Poultry manure
2.3
76.8
881
[6.78]
4024
[8.30]
1525
[7.33]
145
2.66
23
7.7
458
273
Rape straw +
1.8
78.3
299
[5.70]
1772
[7.48]
1054
[6.96]
85
2.12
20
7.6
496
207
Poultry manure
2.3
78.3
876
[6.78]
4583
[8.43]
1604
[7.38]
48
2.35
19
7.6
508
206
Wheat straw +
1.8
80.9
14
[2.68]
62
[4.12]
22
[3.11]
21
3.01
16
7.6
445
108
Cocoa meal
2.3
77.9
77
[4.35]
196
[5.28]
133
[4.89]
19
3.15
12
7.6
470
107
Wheat straw +
1.8
76.9
29
[3.36]
308
[5.73]
889
[6.79]
17
2.60
17
8.0
507
241
Hop waste
2.3
81.4
104
[4.65]
578
[6.36]
1353
[7.21]
0
3.20
11
8.2
520
159
Wheat straw +
1.8
70.8
31
[3.45]
446
[6.10]
388
[5.96]
155
2.56
14
6.7
347
135
Amm. sulphate
2.3
67.8
176
[5.18]
706
[6.56]
461
[6.13]
169
2.79
15
6.4
359
85
Wheat straw +
1.8
70.3
191
[5.25]
2368
[7.77]
1686
[7.43]
49
1.61
15
7.8
397
122
Urea
2.3
74.3
322
[5.78]
4915
[8.50]
2276
[7.73]
36
2.20
11
7.6
397
120
[1.75]
38
0.66
9
0.5
81
16
LSD (P < 0.05)
8.1
[1.77]
[1.11]
a
N content of blended compost ingredients before Phase 0 tunnel composting.
b
Bulk density.
c
Mushroom yield expressed as kg mushrooms per tonne of spawned compost, mean of strains A15 and 2100, supplemented and unsupplemented compost.
d
yieldc
Figures in square parentheses are loge transformations, shown next to back-transformed values.
29
Table 5 Odour and gas (GC-MS) concentrations of bag samples from different aerated tunnel compost formulations in Experiment 3.
Values are the means of two replicate composts and two bag samples per compost.
Compost
N
Odour conc.
Concentration, mg m-3
formulation
rate a
OU m-3
H 2S
DMS
MeSH b
NH3
acetone
ethanol
butanol
propanol c
Wheat straw +
1.8
2216
[7.70] b
0.09
0.26
0.07
7
[1.97] d
0.74
[0.03] d
3.05
[1.23] d
2.58
[1.08] d
1.03
Poultry manure
2.3
6342
[8.76]
0.73
2.06
0.46
80
[4.38]
1.38
[0.07]
10.26
[2.36]
13.60
[2.64]
3.84
Rape straw +
1.8
2619
[7.87]
0.07
0.34
0.15
41
[3.73]
0.29
[-0.41]
2.92
[1.19]
1.94
[0.84]
0.28
Poultry manure
2.3
3584
[8.18]
0.49
0.52
0.33
107
[4.68]
1.25
[0.49]
12.65
[2.57]
13.52
[2.63]
0.15
Wheat straw +
1.8
488
[6.19]
0
0
0
9
[2.24]
0.21
[-0.53]
0.86
[0.21]
1.08
[0.38]
0.29
Cocoa meal
2.3
977
[6.89]
0
0
0
23
[3.16]
0.63
[0.01]
0.08
[-0.79]
0.83
[0.19]
0.10
Wheat straw +
1.8
854
[6.70]
0
0
0
2
[0.91]
1.07
[0.37]
2.07
[0.90]
0.23
[-0.51]
0.63
Hop waste
2.3
2970
[8.00]
0.05
0.13
0.09
50
[3.93]
1.60
[0.69]
1.66
[0.71]
8.16
[2.14]
0.45
Wheat straw +
1.8
699
[6.55]
0
0
0.12
12
[2.49]
0.34
[-0.34]
3.28
[1.30]
2.44
[1.04]
0
Amm. sulphate
2.3
1045
[6.95]
0.02
0.12
0.27
20
[3.00]
1.44
[0.59]
6.04
[1.86]
1.89
[0.82]
0.37
Wheat straw +
1.8
670
[6.51]
0
0
0
5
[1.71]
0.65
[0.03]
1.16
[0.43]
1.18
[0.44]
0
Urea
2.3
843
[6.74]
0
0.02
0
41
[3.71]
0.70
[0.07]
0.55
[-0.07]
0.88
[0.23]
0.15
[1.50]
0.11
1.15
0.35
[1.77]
2.47
0.03
0.006
0.002
LSD (P < 0.05)
Detection threshold [rf]
[3.11]
[0.99]
4
34.67
[2.49]
54.95
1.51
6.03
a
N content of DM of blended compost ingredients before Phase 0 tunnel composting.
b
methanethiol.
c
Other odourants identified with GC-MS which were not significantly different between treatments were (range in concentrations in mg m -3): acetic acid (0.37-1.043), butanoic
acid (0.70-2.68), propanoic acid (0.14-0.74), pentanoic acid (0.63-2.48), methyl ethyl ketone (1.76-4.68), iso-propyl-alcohol( 0.28-0.79), dimethyl disulphide (0.10-0.19), methyl
propanoic acid (0.33-1.07), phenol (0.29-0.51), 4 methyl phenol (0.14-0.33), methyl butanoic acid (0.66-4.92). Ammonia was measured with detector tubes.
d
Figures in square parentheses are loge transformations, shown next to back-transformed values.
30
Table 6 Odour concentration of bag samples, on-site sulphide and ammonia concentrations, N and ammonia losses during windrow and aerated Phase II composting, compost
analysis at spawning, and mushroom yields and dry matter content from different windrow compost formulations in Experiment 4. Values are the means of three replicate
composts, except the linseed straw compost which was not repeated.
Compost formulation
Inclusion rate (% w/w)
Straw
During composting
Odour conc.
a
H2S
OU m-3
N source
DMS
mg m-3
Compost at spawning
Max. NH3
NH3 loss
N loss
% of DM
conc., μL L-1
mg kg-1
mg kg-1
N
Ash
pH
BDb
kg m-3
Wheat (63)
Poultry manure (37)
11950
[9.39] d
2.63
4.97
141
[4.95] d
796
[6.68] d
483
[6.18] d
2.85
25
7.8
463
Rape (67)
Poultry manure (33)
5729
[8.65]
1.97
2.23
242
[5.49]
1366
[7.22]
1287
[7.16]
2.34
24
7.7
496
Bean (72)
Poultry manure (28)
4189
[8.34]
1.06
1.84
141
[4.96]
1703
[7.44]
672
[6.51]
2.77
20
8.0
452
Linseed (68)
Poultry manure (32)
-
-
-
94
[4.54]
584
[6.37]
829
[6.72]
2.49
16
7.7
400
Wheat (78)
Poultry manure (21) +
4458
[8.40]
0.43
0.07
50
[3.92]
534
[6.28]
75
[4.32]
2.73
24
7.9
488
7320
[8.90]
0.50
0.08
8
[2.16]
380
[5.94]
65
[4.17]
3.53
22
8.0
489
-
Urea (1)
Wheat (64)
Poultry manure (18) +
Cocoa meal (18)
Wheat (78)
Cocoa meal (21) + Urea (1)
1716
[7.45]
0.24
0.23
27
[3.31]
94
[4.54]
233
[5.45]
3.23
22
7.8
480
Wheat (77)
Hop waste (22) + Urea (1)
1609
[7.38]
0.18
0.18
23
[3.14]
35
[3.55]
372
[5.92]
2.67
20
8.0
444
Wheat (84)
AminoPro (15) + Urea (1)
1406
[7.25]
0
0
13
[2.62]
63
[4.15]
330
[5.80]
2.79
15
7.5
423
[0.94]
0.38
0.94
[2.62]
0.65
4
0.3
39
LSD (P < 0.05)
[1.61]
[2.95]
a
Figures in parentheses are percentage w/w inclusion rates, before the addition of water and gypsum.
b
Bulk density.
c
Mushroom yield expressed as kg mushrooms per tonne of spawned compost, mean of strains A15 and 2100 and supplemented and unsupplemented compost.
d
Figures in square parentheses are loge transformations, shown next to back-transformed values.
31
Table 7.
Mushroom dry matter and nitrogen contents from aerated tunnel composts,
strain A15, mean of flushes 1 and 2.
Treatment
N rate at
Fill, % of DM
Mushroom DM
%
Mushroom N
% of DM
Wheat straw +
poultry manure
1.8
2.2
7.82
7.89
6.08
6.25
Rape straw +
poultry manure
1.8
2.2
7.68
7.44
4.76
4.82
Ammonium sulphate
1.8
2.2
7.48
7.72
6.10
7.08
Urea
1.8
2.2
8.72
8.46
6.25
6.35
Cocoa waste
1.8
2.2
7.89
8.03
6.90
6.91
Spent hop powder
1.8
2.2
8.40
7.96
6.32
6.31
32
Table 8. Mushroom yields (kg t-1 spawned compost) from windrow composts with different straw types
and N sources. Mean of 3 replicate crops
Treatment*
Strain
Betamyl
A15
2100
-
+
-
+
Poultry manure (control)*
288
289
277
276
Rape straw + poultry manure
228
241
208
227
Bean straw + poultry manure
222
220
198
200
Linseed straw + poultry manure
83
103
71
105
Cocoa meal + urea
205
204
204
195
Spent hop powder + urea
239
217
227
254
Poultry manure + urea
239
238
211
207
Cocoa meal + poultry manure
230
203
206
182
* Wheat straw was used unless stated
33
Table 9. Mushroom dry matter contents from windrow composts, mushroom strain
A15 unsupplemented compost, mean of flushes 1 and 2 and 3 replicate runs.
Treatment*
Mushroom DM, %
Poultry manure (control)*
7.83
Rape straw + poultry manure
8.81
Bean straw + poultry manure
8.24
Linseed straw + poultry manure
7.88
Cocoa meal + urea
8.24
Spent hop powder + urea
8.27
Poultry manure + urea
8.33
Cocoa meal + poultry manure
7.96
AminoPro + urea
7.83
*wheat straw was used unless stated
34
Table 10. Mushroom yields from experimental composts on commercial farms
___________________________________________________________________
Compost
treatment
Test site
Mushroom
strain
Mushroom yield
Experimental Commercial
standard
__________________________________________________________________
Poultry manure/
wheat straw
h
512
15.4 kg/m2
17.9 kg/m2
Cocoa meal + urea
h
512
13.6 kg/m2
17.9 kg/m2
Cocoa meal + poultry
f
2100
170 kg/tonne 216 kg/tonne
__________________________________________________________________
35
Table 11. Effect of Gypsum Treatments on Phase I Compost Analysis
Treatment
Rep.
No gypsum
1
2
1
2
1
2
Agri. gypsum
Citric acid
gypsum
NH4+
Ash
% of dry matter
2.20
0.30
13
2.21
0.15
15
1.93
0.04
15
2.14
0.16
15
1.79
0.13
12
2.04
0.19
11
N
pH
moisture
%
79
78
78
76
78
78
8.2
7.9
7.8
8.7
7.9
8.2
Table 12. Effect of Gypsum Treatments on Phase II Compost Analysis
Treatment
Rep.
No gypsum
1
2
1
2
1
2
Agri. gypsum
Citric acid
gypsum
NH4+
Ash
% of dry matter
2.21
0.19
14
2.53
0.07
22
2.00
0.07
14
2.46
0.06
23
1.93
0.19
12
2.55
0.08
24
N
pH
moisture
%
75
69
75
74
75
67
8.0
7.9
8.5
8.0
8.3
7.8
Table 13. Effect of gypsum treatments on mushroom yield
Treatment
Replicate crop
1
2
No gypsum
31
177
Agricultural gypsum
210
324
Citric acid by-product gypsum
243
340
__________________________________________________________________________
36
1
0
0
0
p
o
u
lt
r
y
m
a
n
u
r
e
r
a
p
e
s
t
r
a
w
+
p
o
u
lt
r
y
m
a
n
u
r
e
d
ig
e
s
t
e
rw
a
s
t
e
c
h
ip
b
o
a
r
d
w
a
s
t
e
LL -1
8
0
0
6
0
0
Ammonia,
4
0
0
2
0
0
0
1
0
0
0
0
1
0
0
2
0
0
4
0
0
5
0
0
h
o
p
w
a
s
t
e
b
r
e
w
e
r
s
'g
r
a
in
s
c
o
c
o
a
m
e
a
l
c
o
c
o
a
s
h
e
lls
8
0
0
LL -1
3
0
0
6
0
0
Ammonia,
4
0
0
2
0
0
0
LL -1
1
0
0
0
0
1
0
0
2
0
0
3
0
0
4
0
0
5
0
0
S
p
o
r
a
v
it
e
u
r
e
a
A
m
in
o
P
r
o
a
m
m
o
n
iu
m
s
u
lfa
t
e
8
0
0
6
0
0
Ammonia,
4
0
0
2
0
0
0
0
1
0
0
2
0
0
3
0
0
4
0
0
5
0
0
c
o
m
p
o
s
tr
e
m
ix
e
d
7
0
Compostemperature,C
6
0
5
0
0
1
0
0
2
0
0 3
0
0
T
im
e
,h
4
0
0
Fig.1 Ammonia concentrations and compost temperature in flasks with different compost N
sources. All composts were based on wheat straw unless stated.
37
Fig. 2a Ammonia emissions during Phases 0 and l:
poultry manure composts, N = 2.2% of DM at filling
1400
Rape straw
Wheat straw
1200
Ammonia, ppm
1000
800
600
400
200
0
0
100
200
300
400
500
Fig. 2b Ammomia emissions during Phases 0 and l:
inorganic N composts, N = 2.2% of DM at filling
1400
1200
urea
ammonium sulphate
Ammonia, ppm
1000
800
600
400
200
0
0
100
200
300
400
500
Fig. 2c Ammonia emissions during Phases 0 and l:
organic N composts, N = 2.2% ofDM at fillin
1400
Cocoa waste
Hop waste
1200
Ammonia, ppm
1000
800
600
400
200
0
0
100
200
38
Time, hours
300
400
500
Fig. 3a Ammonia emissions during windrow composting and Phase II.
N = 2.2% of DM at filling of Phase II.
200
Poultry manure composts
Wheat straw
Rape straw
Bean straw
Ammonia, ppm
150
100
50
0
0
200
400
600
800
Time, hours
Fig. 3b Ammonia emissions during windrow composting and Phase II.
N = 2.2% of DM at filling of Phase II.
120
Alternative materials
Cocoa waste + urea
Poultry manure + urea
Hop waste + urea
100
Ammonia, ppm
80
60
40
20
0
0
200
400
Time, hours
39
600
800
Fig.4 Effect of compost gypsum rate on mushroom yield
400
A12
A15
Mushroom yield, kg/tonne
350
300
A 12
A15
250
200
150
2.4
2.6
3.0
2.8
Compost gypsum rate, % dry weight basis
40
3.2
3.4
Part 2: Odour Quantification Techniques
Introduction
In order to assess the effectiveness of new composting methods in odour reduction, such as
forced aeration and changes to the raw ingredients (Perrin and Gaze, 1987; Gerrits, 1989),
techniques are needed for quantifying odour levels. Olfactometry is used to measure the
concentration of odour in air through the use of a serial diluter, or an olfactometer, to present
odourous air with odourless air dilutions to a panel of people. However, olfactometry is
costly, time consuming, subject to error and incurs delays between sampling and
measurement (Hobbs et al., 1995).
Several studies have attempted to identify the individual compounds associated with
compost odours using gas chromatography-mass spectrometry (GC-MS) (Miller and
Macauley, 1988; Derikx et al., 1990; Duns et al., 1997). Compounds shown to be
responsible for compost odour include amines, ammonia, organic acids and most
importantly, sulphur containing compounds. However, GC-MS analysis and interpretation is
impractical on a day-to-day basis due to the large numbers of compounds involved, cost and
the delay between sampling and measurement. However, many of the important odourants
can be measured quickly and cheaply using gas detection tubes (Anon, 1997, 1998).
There has been research into the development of electronic nose systems for odour
detection and measurement. These instruments employ an array of non-specific electronic
gas sensors in an attempt to mimic the human olfactory system by utilisation of artificial
intelligence (Gardner et al., 1992). Equipment has been developed for a number of
applications, mostly in the food industry, but also for agricultural malodour applications
(Persaud et al., 1996; Misselbrook et al., 1997).
The AromaScan (AromaScan plc, Crewe, UK) instrument uses an array of
conducting polymer sensors, which display reversible changes in electrical resistance when
volatile molecules adsorb and desorb from their surface. Such instruments have been shown
to successfully distinguish between odours from pig and chicken slurry (Hobbs et al., 1995)
between odours from slurry from pigs fed with different diets (Byun et al., 1997) and
between breath odours from healthy cows and cows with ketosis (Elliott-Martin et al., 1997).
Several sulphide detector instruments are available which operate using different
principles. The suitability of these instruments for detecting sulphides from mushroom
composting or other organic wastes has not be reported.
The objective of the present work was to analyse the odours from mushroom
composting using the different methods outlined above, and to determine the relationships
between these methods.
Materials and Methods
Odour sample collection
Odour samples were collected in 20 L Teflon bags by placing the bag in a pressure vessel
with a PTFE tubing sampling line connected and then evacuating the vessel, thus drawing
sample air into the bag over a 4 min period (Hobbs et al., 1995). The open end of the
sampling line was held 0.2 m downwind from the compost heap or stack, during turning.
Replicate samples were collected simultaneously. Background samples were
collected 200 m upwind of the composting sites. Samples were transported to IGER, North
Wyke for GC-MS and olfactometry analysis. Two replicate samples were collected for each
of the analyses, which were conducted 24 h after sampling.
41
Windspeed at the point of odour sampling was measured with a vane anemometer
(Type 949079, airflow Developments Ltd, High Wycombe, UK).
Composting yards and composts
Odour samples were taken from eleven sites: Blue Prince, Chesswoods (Sussex), Gateforth
Park, Hensbys, HRI Wellesbourne, Monaghan Middlebrook (Avon and Market Harborough),
Pond Chase, Shepherds Grove, and Tunnel-Tech (North and South). Six of the sites
produced a windrow Phase I compost, turned at two-daily intervals; four sites had an aerated
tunnel Phase I and HRI Wellesbourne produced compost using both types of Phase I. With
the exception of HRI, all the sites had separate pre-wet and Phase I areas. At Blue Prince,
Chesswoods, HRI, Monaghan (Avon), Shepherds Grove and Tunnel-Tech (South), prewetting was conducted partially or completely in windrows and at Gateforth Park and Pond
Chase, pre-wetting was conducted on an aerated pad. Pre-wetting was conducted in flat
heaps on the remaining sites. All the sites used proportions of wheat straw, broiler poultry
manure and gypsum, although the proportions of these materials and addition of other
manures and additives differed between sites. The total durations of pre-wetting and Phase I
composting were 7-14 d and 6-7 d. The duration of the combined pre-wet and Phase I
windrows at HRI was 16 d. Phase I tunnel composts at HRI were pre-wetted for 7 d. The
pre-wet areas were sampled 3-6 d after setting up of the heaps and the Phase I windrows or
tunnels were samples 3-7 d after the start. The combined pre-wet and Phase I windrows at
HRI were sampled after 12 d.
All the composts were analysed for moisture, nitrogen and ammonium contents and
pH according the methods in Noble and Gaze (1994).
Olfactometry
A dynamic dilution olfactometer (type DTM, Project Research, Amsterdam) was used
according to recommendations in van den Berg (1992), ie a forced choice type presentation
where six panellists were required to choose between two sniffing ports, one containing
odourless air, and the other diluted, odourous air. Threshold values, at which 50% of the
panel could just detect an odour, were determined and odour concentration (OC) expressed
as Odour Units m-3 (OU m-3) air. A range of six dilutions was presented to the panellists in
steps of ascending concentrations, each differing from the next by a factor of two and each
range being presented twice. OC was calculated according to the Dravneiks and Prokov
(1975) method. Measurements of the sensitivity of the odour panellists for each set of OC
measurements was performed with 198.2 mg m-3 (60 ppm) butan-1-ol in nitrogen.
Samples were also tested with a newer Olfactomat "C" Project Research, Amsterdam
instrument, which operated on the same principles as the DTM instrument.
The odour panellists also made an assessment of odour intensity of the samples
according to Burton et al (1997). A range of dilutions differing by a factor of two each time
were presented to each panellist a number of times through one known port of the
olfactometer. The highest dilution was equivalent to the 75% odour threshold value. At each
dilution, the panellists were required to indicate the subjective strength of the odour,
according to the following scale:
0 No odour
1 Very faint odour
2 Faint odour
3 Distinct odour
4 Strong odour
5 Very strong odour
42
6 Extremely strong odour.
The relationship between intensity and odour concentration was calculated by linear
regression.
GC-MS analysis
Volatile compounds were preconcentrated from a 600 ml odour samples by adsorbtion onto
silica (Orbo 52, Supelco Inc., Supelco Park, Bellefonte, PA, 16823-0048 USA) and carbon
(Orbo 32) based adsorbents. The concentrated odourants were then thermally desorbed from
the adsorbents into the GC-MS system for identification and quantification.
Chromatographic retention time and mass spectral matching were used to confirm odourant
identity. Quantification was performed by desorbing 8 μl of a standard odour identified in
the preconcentrated headspace, from the adsorbent.
A Hewlett Packard (hp) (hp Ltd, Heathside Park Road, Cheadle Heath, Stockport,
Cheshire, UK) GC-MS system consisting of a 5890 II Series gas chromatograph and a
5972A mass selective detector (MSD II) was used for analysis. A 25 m fused silica (cross
linked methyl siloxane) hp-1 column with an internal diameter (id) of 0.2 mm and a 0.34 μm
film with a 1m deactivated fused silica guard column (0.25mm id) were used. The flow rate
of the helium the eluting gas was 0.75 ml min-1. The Optic temperature programmable
injector (Ai Cambridge Ltd, Pampisford, Cambridge, UK) was used to desorb headspace
samples from the adsorbents and was initially at 30˚C and heated to 16˚C s-1 for 1 min. An
electronic pressure controller was used to offset peak pressure broadening with increasing
GC column temperature. The GC oven conditions were an initial temperature of 40˚C, then
to 220˚C at 15˚C min-1 and remaining at 220˚C for 1 min. The GC-MS interface was at
280˚C. The mass spectrometer scanned from 35 to 250 mass units every 0.2 s to give
responses in the ng range.
Volatile organic compounds (VOCs) detected by the mass spectrometer were
identified using a probability based matching algorithm and a NIST mass spectral library.
Compounds were declared unknown if their matching probability was less than 80 (100
being a perfect match).
Gas detector tubes
A Dräger Accuro bellows pump (Drägerwerek, Lübeck, Germany) was used in conjunction
with appropriate detector tubes: acetic acid (6722101), amines (8101061), NH3 (CH2051 and
CH31901), carbon disulphide, CS2 (8101891), DMS (6728451), H2S (8101991 and
8101831), mercaptan (thiols) (6728981) and phenol (8101641). Detector tubes were used
on-site in the same way as sampling odours for collection in Teflon bags, 24h after on-site
sampling. In addition to the eleven sites where odour samples were collected, detector tube
measurements were also conducted on two further sites: Shackleford Mushrooms and J.
Rothwell & Son. Two replicate measurements were made for each sampling.
Electronic sulphide detectors
The following electrochemical sulphide detectors from the following companies were
examined:
 Analox Sensor Technology Ltd, Stokesley, Cleveland, UK
 Draeger Ltd, Blyth, Northumberland, UK
 Gas Measurement Instruments Ltd, Renfrew, UK
The remaining four instruments had differing modes of operation:
43

Graseby Dynamics Ltd, Watford, UK: ‘Environmental Vapour Monitor’ utilizing gas
chromatography (GC) and ion mobility spectrometry.
 'Chemcassette' hydrogen sulphide analyser. Electronic optical measurement of gas
sensitive colorimetric paper tape (Type 7100 Zellweger Analytics Ltd, Bishops Stortford,
Herts.,UK).
 PE Photovac, Norwalk, CT, USA: ‘Voyager’ portable gas chromatograph, utilizing GC
and a photoionization detector (PID)
 Pulsed fluorescence sulphur dioxide (SO2) analyser (Type 43C, Thermo Environmental
Instruments Ltd, Franklin, MA, USA) coupled to a sulphide to SO2 converter (Type 45C,
Thermo Environmental Instruments Ltd). The analyser was supplied by Unicam
Chromatography, Cambridge, UK.
All except the latter of these instruments were portable, although data from the Graseby
Dynamics and PE Photovac instruments needed to be downloaded to PC for observation and
analysis. Specifications of the instruments tested are shown in Table 20.
Odour samples were drawn into the analysers using an internal electric pump. Each
analysis took about 2 minutes to complete. The analysers were also tested with gas samples
containing known concentrations of three sulphides at concentrations from 10 to 1400 ppb:
hydrogen sulphide, dimethyl sulphide and methanethiol.
Aromascan electronic nose
A commercially available electronic nose instrument (AromaScan Sample Station, A8S,
AromaScan plc, Crewe, UK) was used. The instrument used an array of 32 conducting
polypyrrole sensors. A small pump pulled air across the sensor array at approximately 100
ml/min and the change in resistance of individual sensors was recorded as ∆R/R, where ∆R
was the change in resistance and R the base resistance of the sensor. The degree of response
of each sensor to a given volatile depends upon the type of polymer used, so a pattern of
resistance changes across the array was recorded for a particular odour. The instrument
incorporated a reference line, which consisted of filtered ambient air of the same relative
humidity as the odour sample, which was used to provide the base resistance for sensors.
The odour samples were passed across the sensor array for 8s.
An initial problem encountered was the high sensitivity of the sensors to ammonia in
the odour samples, to the exclusion of a response to other volatiles in the sample. The odour
samples were therefore first passed through a Nafion tube gas dryer (Perma Pure Inc., Toms
River, New Jersey, USA). Nafion is a copolymer of tetrafluoroethylene (Teflon) and
perflouro-3,6-dioxa-4-methyl-7-octane-sulphonic acid. It has selective retention for sulphur
compounds, simple hydrocarbons and oxides (CO2, SOX, NOX) but does not retain ammonia,
amines, polar organic compounds (alcohols and organic acids) and water vapour. The
Nafion tubing (3 mm diameter) was fitted inside a 16 mm diameter PTFE shell tubing. The
relative humidity of the air in the shell tubing was controlled to the relative humidity of the
odour sample in the Nafion tubing, to avoid changes in the relative humidity of the odour
sample. Nafion tube lengths of 0.1, 0.3 and 0.6 m were used. The odour samples were
passed over the sensors for 6 min when the Nafion tubing was used.
The electronic nose was tested with and without the Nafion tubing with known
concentrations of the following gases in air: ammonia (NH3), dimethyl sulphide (DMS) and
hydrogen sulphide (H2S). Tests were also conducted on control samples with known
concentrations of the above gases with unknown concentrations of other compost odourants,
obtained from flask composting equipment.
44
Odour and sulphide concentrations on and around composting sites
Air samples were obtained from five composting sites, (Tunnel Tech South, Shepherds
Grove, Gateforth Park, HRI Wellesbourne and Monaghan Middlebrook Avon) at increasing
distances downwind from the Phase I composting stacks, to the site boundary and beyond.
Odour samples were collected in 20 L nalophane bags. Samples were obtained downwind of
the compost stacks during turning at distances of about 0.2, 5, 15, 30, 40 and 50 m.
Replicate samples were collected simultaneously. Background samples were
collected 200 m upwind of the composting sites. Samples were transported to IGER, North
Wyke for analysis using gas chromatography - mass spectrometry (GC-MS), pulsed
fluorescence sulphide detector and olfactometry as described previously. Two replicate
samples were collected for each of the analyses, which were conducted 24 h after sampling.
Comparison of real and synthetic mushroom compost odours
In order to test the reliability of the chemical analysis of composting odours, synthetic
odours of typical pre-wet and Phase I compost odours were prepared. These were prepared
from the six compounds which exceeded their detection thresholds by the greatest order of
magnitude in real pre-wet and Phase I odour samples. These compounds were dimethyl
sulphide, H2S, butanoic acid, methanethiol, butanoic acid (in both the pre-wet and Phase I
odours), indole (pre-wet only) and trimethylamine (Phase I only). Since ammonia occurred
in all the compost odours, this was also added to both synthetic mixtures. The concentration
of each chemical was the average concentration found in real compost odours. Synthetic and
real odours were presented to an odour panel in a series of dilutions. Each mixture was
presented twice.
Synthetic odour mixtures were also prepared without the ammonia, fatty acids and
amine removed in order to test the influence of sulphides with and without other odourants in
the air sample.
Results
Olfactometric analysis
There was considerable variation in odour concentration (OC), and the relative strengths of
the OC of the pre-wet and Phase I areas differed between both sites and sampling dates on
the same site. Whilst there was no significant difference in OC between the pre-wet and
Phase I composting stages, aeration (sites D, E, G and K) significantly (P<0.001) reduced
OC (Table 14). There was no evidence of this aeration effect varying between the two
composting stages.
GC-MS analysis
Odourants detected more than once with GC-MS in the pre-wet and Phase I air bag samples
are shown in Table 15. There was considerable variation in odourant concentrations, both
between sites and within sites. Acetone, NH3, ethanol and butanol were detected in all the
samples in Table 15. Compounds for which the mean concentrations exceeded their
published olfactory detection thresholds were volatile fatty acids (VFAs), sulfur containing
compounds, NH3, amines, indole and 4-methyl phenol. In decreasing order, H2S, DMS,
butanoic acid, methanethiol and trimethylamine were found to exceed their detection
thresholds by the greatest order of magnitude (x100 or greater). Trimethylamine and VFAs
were generally at a higher concentration in the Phase I air samples than in the pre-wet air
45
samples; alcohols showed the reverse pattern although the mean concentrations were either
below, or in the case of butanol close to their detection thresholds. Odourants detected only
once in the pre-wet and Phase I air samples were: acetaldehyde, butanone, heptanol,
methanol, 2-methyl propanal, 2-methyl propanol, 2-pentanone and p-xylene.
Gas detector tubes analysis
Aeration significantly reduced both H2S (P<0.001) and DMS (P<0.001) emissions (Table 16
and 17). After adjusting for this aeration effect, Phase I composting areas had significantly
(P<0.05) higher H2S and DMS concentrations than the pre-wet areas (Table 16 and 17).
Ammonia concentrations were significantly (P<0.01) higher from the Phase I areas than
from the pre-wet areas (Table 18) but there was no significant effect of aeration on NH3
concentration. There were no significant interactions between the effects of aeration and
stage of composting for H2S, DMS or NH3 concentrations.
The concentration of H2S measured in nalophane bags after 24 h was, on average,
52% of that measured on-site. There were no significant reductions in the concentrations of
DMS or NH3 after 24 h. Gas detector tube measurements of H2S and DMS in nalophane
bags, 24 h after sampling, were closely correlated with GC-MS measurements made at the
same time (r = 0.81, P<0.001 and 0.86, P<0.001 respectively, based on 42 d.f.). The values
obtained for H2S and DMS with detector tubes were, on average, 13% and 7 % lower than
those obtained with GC-MS.
Thiols could only be detected with gas detector tubes at site I (0.2 μL L-1 and 0.5 μL
-1
L for the pre-wet and Phase I areas) and acetic acid could only be detected in the Phase I
area of site I (0.6 μL/L). CS2 and phenol could not be detected with the tubes previously
listed on any of the sites. Values obtained from the amines + NH3 test corresponded with the
NH3 concentration, ie additional amines were not detected with detector tubes.
Relationship between gas detector tube measurements and odour concentration
There was a very close correlation between the combined on-site concentrations of
H2S + DMS and the bag sample odour concentration (OC) of pre-wet or Phase I odour
samples (Fig. 8). The linear regression equation, with loge transformed data, was:
loge OC = 7.601 + 0.934 loge (H2S + DMS + 0.375), r = 0.948 P<0.001
[1]
where H2S and DMS were on-site concentrations (μL L-1) and OC was measured using bag
samples (OU m-3). The correlation was higher than the individual correlations of OC with
H2S concentration (r = 0.912; 42 d.f.) or DMS (r = 0.905; 42 d.f.). There was no effect on
the fitted relationship of either stage of composting (pre-wet or Phase I) or aeration.
Similarly, multiple regression using H2S and DMS as separate independent variables did not
improve the goodness-of-fit. Concentrations of NH3 were above the detection threshold in 42
out of 44 odour sources, but were not significantly correlated with OC. The inclusion of NH3
concentration in the multiple regression model described above did not improve the
goodness-of-fit.
The CO2 concentrations of the bag samples were 403 to 1223 μL L-1 (mean 841 μL L1
) for the pre-wet areas and 510 to 1489 μL L-1 (mean 786 μL L-1) for the Phase I areas. There
were no relationships between the CO2 concentrations and any of the other gas
concentrations or OC. Wind speed at the point of sampling ranged from 0 to 4.5 m s-1 (mean
2.4 m s-1), but there were no consistent relationships between wind speed and any of the
odour or gas concentrations.
46
During the third year of the project , a new olfactometer was installed at IGER
(Olfactomat "C"). Compost odour samples were presented to the panellists through both the
original and new olfactometers. Both machines were calibrated with a known concentration
of butanol gas. Although there was still a good correlation between sample odour and
sulphide concentrations (Fig.9), the new machine gave a significantly higher odour
concentration for samples of an equivalent sulphide concentration. This was probably due to
the reduced metal pipe work in the new olfactometer, resulting in reduced absorption of
sulphides, and hence higher odour concentrations to the panellists. This emphasises the need
to specify the type of olfactometer being used to assess odour concentration of air samples
containing sulphides.
Compost analysis and type
Both moisture and N contents of the Phase I composts were higher than those of the pre-wet
composts, but the NH4+ contents and pH of the pre-wet and Phase I composts were similar
(Table 19). Aeration slightly reduced the pH of compost (significant at P<0.05) but there
were no other effects of aeration on compost analysis (Table 19). There was a weak positive
correlation between the compost NH4+ content and the NH3 concentration (r = 0.40, 42 d.f.,
P<0.05). No other correlations between gas concentrations, the proportions of H2S and DMS,
or OC, and compost analysis factors were found.
There was no significant difference in the compost analyses between poultry manurebased composts and poultry and horse manure-based composts. These manure types had no
significant effect on OC or gas concentrations and there were no interactions between the
effects of manure type and aeration or composting stage on these concentrations.
Performance of the Aromascan (Osmetech) electronic nose
The results from the instrument are presented as the change in resistance of the 32 sensors
relative to the base resistance in air of the same rh (∆R/R). This response is affected both by
the chemical species present and their intensity. The relative response of the 32 sensors can
also be presented as a normalised response to produce a ‘fingerprint’ which is characteristic
of the chemical species adsorbed (Persaud et al., 1996). In this situation, the response of the
sensors is expressed as a proportion of the response of the entire array of 32 sensors so that
the intensity components are nearly eliminated.
The duration that the odour samples pass over the sensors could be varied. Due to
strong response of the sensors to the odour samples in the absence of the Nafion tubing, this
period was restricted to 8 s so that ∆R/R did not generally exceed 15%. The average
response of each sensor over this period was used. In the presence of the Nafion tubing, the
response of the sensors to the odour samples was delayed and much weaker, so that the
period of sensing could be extended to 6 min without ∆R/R exceeding 15%. The average
response of each sensor over the final 10 s of this period was used.
Ammonia response. All the sensors of the Aromascan responded positively to ammonia at
concentrations below 2 ppm. The normalised responses of the sensors to 2 and 50 ppm NH3
were similar with sensor numbers 19 and 31 producing the strongest response. There was a
positive relationship between the NH3 concentration in compost odour samples and the
average sensor response during the first 8 s of sampling.
Hydrogen sulphide and DMS responses. All of the Aromascan sensors responded negatively
to both hydrogen sulphide and DMS although the responses were weak and more delayed
than for NH3. The normalised responses to 50 and 180 ppm H2S or DMS were similar, as
47
were the normalised responses to 20 and 110 ppm DMS. The strongest (negative) responses
to both H2S and DMS were generally in sensors 19, 21 and 31. Lower concentrations of H2S
or DMS resulted in a loss in the normalised response pattern for the particular gas. Passing
the samples through a 0.6 m length Nafion tube did not significantly change the sensor
response to H2S or DMS but reduced the sensor response to ammonia. The detection
thresholds for H2S and DMS were about 50 ppm and 20 ppm.
Compost odour mixture responses. Without Nafion tubing, the NH3 component (50 ppm)
dominated, producing strong positive responses in all the sensors. After the gas mixtures
were first passed through a 0.6 m length of Nafion tube, the H2S and DMS components
dominated (both 60 ppm), producing negative responses in all the sensors. However, if the
H2S and DMS components were below their sensor detection thresholds, there was either no
significant sensor response or, if NH3 was present, a positive sensor response. Site I, which
had high NH3, H2S and DMS concentrations, produced negative sensor responses for both
the pre-wet and Phase I samples with the Nafion tube, but positive responses without.
Compost odour samples with OCs of 30,000 OU m-3 could not be distinguished from less
odourous samples with OCs of less than 10,000 OU m-3 from either the average sensor
response or normalised sensor response pattern.
There were negative relationships between average sensor response and the
concentrations of H2S or DMS in compost odour samples, after passing through a 0.6 m
Nafion tubing. These relationships were not present without the use of Nafion tube and all
of the odour samples in produced positive sensor responses due to the presence of NH3.
The Aromascan electronic nose was not sufficiently sensitive to odourous sulphurcontaining compounds and too sensitive to ammonia to be of use in evaluating composting
odours.
Performance of electronic sulphide detectors
The three electrochemical sensors tested were found to be cross-sensitive to ammonia and,
therefore, unsuitable for measuring sulphide levels in compost odour samples. The Draeger
instrument was sensitive to water vapour, and H2S could not be detected in compost odour
below 20 ppm. The GMI instrument did not give reliable H2S readings below 2 ppm; the
Analox analyser could detect less than 1 ppm H2S, but only in the absence of ammonia.
The Zellweger instrument was sensitive to hydrogen sulphide and methanethiol at 50
ppb but was insensitive to dimethyl sulphide at over 1000 ppb. There were no relationships
between the Zellweger readings and the sample odour concentration or the sulphide readings
from the pulsed fluorescence analyser.
The pulsed fluorescence analyser was sensitive to all three sulphides tested (hydrogen
sulphide, dimethyl sulphide and methanethiol) at a concentration of 10 ppb. There was a
good correlation between the instrument readings (up to 500 ppb) and odour concentration
(Fig.5).
Odour and sulphide concentrations on and around composting sites
The odour and sulphide concentrations decreased logarithmically with increasing distance
from the main odour source (turned Phase I stacks) (Figures 6 and 7). The pulsed
fluorescence instrument was able to detect sulphides at 10 ppb in odour samples from site
boundaries, about 50 m downwind of the Phase I stacks. Both the odour and sulphide
concentrations on the downwind site boundaries were significantly above the background
(upwind) concentrations (Figures 6 and 7).
48
Validation of the compost odour / sulphide relationship
Comparison of real and synthetic compost odours
The synthetic pre-wet and Phase I odours smelt similar to poultry manure and the real
and synthetic odours had similar detection thresholds. When presented as a series of
dilutions, odour intensity score v odour concentration was similar for all the real and
synthetic samples (Fig.10). This indicates that the six-compound mixtures were good
simulations of pre-wet and Phase I odours, and that the measurement of a large number of
compounds is unnecessary. Figure 10 shows that a tenfold dilution of the air from
composting sites or synthetic composting odours resulted in almost a threefold reduction in
odour intensity.
Removing the fatty acids and trimethylamine from the synthetic compost odour
mixtures had little effect on the odour concentration (Table 21). Most of the odour
concentration of the synthetic pre-wet mixture was due to the sulphides (H2S, DMS and
methanethiol) since removal of the ammonia also had little effect on the odour concentration.
However, removal of the ammonia from the synthetic Phase I mixtures had a significant
effect on reducing odour concentration (Table 21).
Conclusions - Part 2
1. Sulphur containing compounds in compost odour samples were found to be most
important in exceeding detection thresholds, but volatile fatty acids and trimethylamine
were also found in odour samples at concentrations exceeding their detection thresholds.
2. There was a close correlation between the compost odour concentration of the pre-wet
and Phase I composts samples and the combined hydrogen sulphide + dimethyl sulphide
concentration from gas detector tubes. Concentrations of ammonia were above the
detection threshold in most of the odour samples, but were not correlated with odour
concentration.
3. Out of eight electronic instruments examined, only one was found to be sensitive to
sulphide levels less than 60 ppb in compost air samples (see Summary Table below).
4. A pulsed fluorescence analyser was found to be sensitive to sulphides in composting
odours at 10 ppb. There was a good correlation between the instrument readings and
odour concentration.
5. The sensitivity of the analyser enabled it to detect odour plumes at the boundary sites,
about 50 m from the Phase I composting stacks.
6. The Aromascan electronic nose was not sufficiently sensitive to odourous sulphurcontaining compounds and too sensitive to ammonia to be of use in evaluating
composting odours (Summary Table).
7. Synthetic pre-wet and Phase I odours were prepared from sulphides, ammonia and other
odour compounds which closely simulated real composting odours when presented to an
odour panel. These results were consistent with the hypothesis that certain S compounds
are mainly responsible for mushroom composting odour.
8. Most of the odour concentration of synthetic pre-wet odours could be attributed to the
sulphide (hydrogen sulphide, dimethyl sulphide and methanethiol) content, although
ammonia contributed strongly to the odour concentration of synthetic Phase I mixtures.
9. The type of olfactometer used in measuring odour concentration should be specified,
since different types of machines can give different values.
10. Odour concentrations and sulphide concentrations from aerated composting systems
were generally lower than those from non-aerated systems.
49
11. There was no significant difference in odour concentration between poultry manure
based composts and those prepared with horse and poultry manures. No relationships
were found between compost analysis and odour concentration.
12. A tenfold dilution of the air from composting sites or synthetic composting odours
resulted in almost a threefold reduction in odour intensity.
Summary Table of odour quantification techniques (Project Part 2)
Method
Human odour panel
(Olfactometry)
Advantages
Relates to actual odours
High sensitivity
Gas detector tubes
(sulphides)
Cheap
Not cross sensitive to ammonia
or water vapour
High sensitivity (5 ppb)
Not cross sensitive to ammonia
or water vapour
Can be used on-site
Pulsed fluorescence
analyser
Electronic nose or
electronic sulphide
detectors
Disadvantages
Not on-site
High cost of measurements
Partly subjective
Only suitable for gases in
concentrations > 0.1 ppm
High cost (£10,000+)
Cross sensitive to ammonia
and moisture
Low sensitivity to sulphides
50
Table 14.
Compost
yard
Odour concentrations by olfactometry for compost yards in different years
Year 1
Odour concentration, OU m-3 air
Pre-wet
Phase I
Year 2
Year 3/4
Year 1
Year 2
Year 3/4
A
-
-
-
17894
71702
4465
B
11796
3849
34958
10316
395533
81379
C
26777
25177
-
3965
2043
-
D
6721
1933
-
20139
921
-
E
1209
3698
-
919
885
-
F
10467
4821
-
31823
16864
-
G
6146
538
-
666
804
-
H
10144
3430
8061
19607
20213
34459
I
245100
9553
2248
263758
72319
9518
J
-
1626
-
13015
1957
-
K
-
993
-
-
2919
-
L.S.D. (P = 0.05) = 492
Aerated composts are shown in bold.
51
Table 15.
Concentrationsa and odour detection thresholdsb for odourants identified with
GC-MS in compost yard odour samples, μg m-3 air. Compounds with mean
values exceeding the detection threshold are shown in bold.
Odourant
Acetic acid
Acetone
Ammoniac
Butanoic acid
Butanol
2-Butanone
Carbon disulphide
Dimethyl sulphide
Dimethyl disulphide
Dimethyl trisulphide
Ethanol
4-Ethyl phenol
Hexane
Hydrogen sulphide
Indole
Iso-propyl-alcohol
Methanethiol
2-Methyl butanoic acid
3-Methyl butanoic acid
Methyl ethyl ketone
Methyl phenol
Methyl propanoic acid
Methyl sulphide
Pentanoic acid
Phenol
Propanoic acid
Propanol
Toluene
Triethylamine
Trimethylamine
p-Xylene
Pre-wet
Phase I
Detection
threshold
Characteristic
odour
1588(±941)
3007(±5644)
27976(±28840)
481
3003(±6774)
697
trace
1667(±3290)
657(±1626)
83(±170)
53460(±103860)
75
150(±276)
730(±1310)
7
1837
211(±246)
238
206
660
101(±50)
26
156
216
139(±77)
2004(±2323)
5928(±13171)
30
179(±99)
trace
113
1952(±1362)
2679(±5114)
75740(±62750)
2603(±3442)
2715(±6628)
287(±457)
trace
3528(±6921)
287(±896)
130(±292)
10808(±16281)
79(±90)
86(±112)
49480(±10595)
3(±3)
195(±245)
126(±165)
165(±350)
869(±1531)
5720(±3354)
196(±101)
444(±379)
167
700(±1231)
189(±170)
351(±259)
678(±879)
18
169(±151)
trace
25
25,000
770,000
260
1 x 10-3
33,000
18,000
2.6
255
15.3
2.6 x 10-2
93,000
vinegar
ethereal
dry urine
rancid
fusel oil
foul
foul
foul
vinous
1.1
600
ethereal
rotten egg
faecal
1.1
rotten cabbage
unpleasant
5,000
80,000
220
800
12,000
3 ,000
80,000
140,000
4
96,000
acetone-like
disagreeable
unpleasant
characteristic
rancid
stupefying
ammonical
fishy
mean and ± standard deviation; compounds without standard deviations were identified in
less than five samples
a
b
after Summer (1971), van Gemert and Nettenbreijer (1977) and Overcash et al (1983)
c
measured with gas detection tubes
d
after Budavari (1989)
52
Table 16. Hydrogen sulphide concentrations determined with detector tubes on compost
yards in different years
Compost
yard
Year 1
Hydrogen sulphide concentration, ppm
Pre-wet
Phase I
Year 2
Year 3/4
Year 1
Year 2
Year 3/4
A
-
-
-
22
2
0.4
B
10
0.2
1.1
4
160
110
C
0.3
6.5
-
0.5
0.2
-
D
3
0.6
-
11
0.4
-
E
0.3
0.1
-
0.1
0.1
-
F
2
0.3
-
7
9
-
G
0.2
0
-
0
0
-
H
0.8
0.6
0.4
3
2
30
I
57
6
0.1
95
41
3
J
-
0.4
-
3
0
-
K
-
0.1
-
-
0
-
L
-
-
-
-
3
-
M
-
0.7
-
-
0
-
L.S.D. (P = 0.05) = 0.6
Aerated composts are shown in bold.
53
Table 17.
Compost
yard
Dimethyl sulphide concentrations determined with detector tubes on compost
yards in different years
Year 1
Dimethyl sulphide concentration, ppm
Pre-wet
Phase I
Year 2
Year 3/4
Year 1
Year 2
Year 3/4
A
-
-
-
6
4
1
B
2
1
7
4
52
63
C
12
10
-
1
0.6
-
D
2
1
-
1
1
-
E
0.2
0.5
-
0.2
0.3
-
F
0.1
1
-
4
7
-
G
1
0.2
-
0.6
0
-
H
2
0.8
2
7
3
0
I
24
2
0.5
97
32
5
J
-
1
-
4
0
-
K
-
0.1
-
-
0.1
-
L
-
-
-
-
2
-
M
-
2
-
-
0
-
L.S.D. (P = 0.05) = 0.5
Aerated composts are shown in bold.
54
Table 18.
Compost
yard
Ammonia concentrations determined with detector tubes on compost yards in
different years
Year 1
Ammonia concentration, ppm
Pre-wet
Phase I
Year 2
Year 3/4
Year 1
Year 2
Year 3/4
A
-
-
-
105
120
40
B
5
55
5
40
100
90
C
120
7.5
-
30
26
-
D
5
400
-
30
550
-
E
8
60
-
35
50
-
F
19
10
-
4
30
-
G
14
2
-
15
20
-
H
22
30
50
110
45
70
I
27
4
22
276
39
8
J
-
5
-
180
110
-
K
-
75
-
-
35
-
L
-
-
-
-
20
-
6
-
-
5
-
M
L.S.D. (P = 0.05) = 4
Aerated composts are shown in bold.
55
Table 19. Compost analysis, mean values from 11 sites and two visits per site.
________________________________________________________________
Moisture
%
% of dry matter
N
pH
NH4
________________________________________________________________
Stage of
composting
Pre-wet
77.0
1.76
0.49
8.20
Phase I
75.7
2.09
0.51
8.13
0.248
0.103
0.196
LSD† (42 d.f.)
1.15
Aeration
Aerated
75.9
2.01
0.49
8.01
Unaerated
76.6
1.88
0.50
8.25
0.281
0.109
0.196
LSD†† (42 d.f.)
1.27
________________________________________________________________
†
Least significant difference, calculated at P < 0.05, for comparing stages of
composting and †† for comparing aerated and unaerated composts.
56
Table 20. Electronic sulphide analysers and electronic nose
Company
Analox
Aromascan
Draeger
Analyser
Mode of
Operation
Compounds
Measured
Specified
L.D.L.*
101DZ
electrochemical
H2S
0.1 ppm
Cross
Sensitivity
ammonia
other sulphides
Portable
Cost
£K
Yes
3
No
32
A8S
conducting polypyrroles
polar compounds
-
ammonia
alcohols
PacIII
electrochemical
H2S
2 ppm
ammonia
other sulphides
Yes
2
Yes
2
Personal
surveyor
electrochemical
H2S
1 ppm
ammonia
other sulphides
EVM
GC+ion mobility
spectrometry
ionized molecules
-
-
Yes
9
PE Photovac
Voyager
GC+ photoionization
volatile organic
-
-
Yes
18
Thermo Env. Instru.
43C+45C
pulsed
fluorescence
sulphur containing
0.5 ppb
-
No
18
7100
colorometric paper
H2S
2 ppb
other sulphides
Yes
5
GMI
Graseby Dynamics
Zellweger
* lower detection limit
57
Table 21. Synthetic odour mixtures used to simulate typical pre-wet and Phase I compost
odours
Concentration in mixture, µg m-3
Compound
All compounds
Sulphides +
ammonia
Pre-wet Phase I
Pre-wet
Phase I
Dimethyl
sulphide
1667
3528
1667
Hydrogen
sulphide
730
4362
Methanethiol
211
Butanoic acid
Sulphides
Pre-wet
Phase I
3528
1667
3528
730
4362
730
4362
126
211
126
211
126
33
2129
-
-
-
-
3-methyl
butanoic-acid
-
869
-
-
-
-
Trimethylamine
-
582
-
-
-
-
Indole
7
-
-
-
-
-
Ammonia
27976
75740
27976
75740
-
-
Odour conc.
OU m-3
1359
3442
3955
11378
1829
2623
9837
14191
1851
252
1881
5778
58
Fig. 5 Relationship between pulsed fluorescence
sulphides (Unicam analyser) and odour concentration
10000
8000
OC, OU/m3
6000
4000
2000
r 2 = 0.61
0
0
100
200
300
Unicam sulphides, ppb
59
400
500
Fig.6 Odour plumes from turned composting stacks.
Distances down-wind are from the turned windrows;
background measurements are 200m up-wind of composting sites.
11
50,000
site and date
MM(Nov 2000)
TunTech(Nov 2000)
9
MM(Dec 1999)
5,000
8
7
6
500
5
background
4
50
0
10
20
30
40
50
60
Distance down wind, m
Fig.7 Plume of sulphides from turned composting stacks.
Distances down-wind are from the turned windrows;
background measurements are 200m up-wind of composting sites.
12
site and date
MM(Nov 2000)
TunTech(Nov 2000)
MM(Dec 1999)
TunTech(Dec 1999)
Sulphide conc., ppb
100,000
10
8
10,000
10006
100
4
2
10
background
0
0
0
10
20
60
30
Distance from stacks, m
40
50
60
Odour conc. (OU/m3)
loge odour conc. (OU/m3)
10
Odour Concentration, Odour Units m-3
106
12
105
10
104
8
103
6
loge OC = 7.601 + 0.934 loge (H2S + DMS + 0.375)
r = 0.948 ( P < 0.001 )
102
0
5
0.5
50
500
H2S + DMS concentration, ppm
Fig. 8 Relationship between the combined on-site hydrogen sulphide
and dimethyl sulphide concentrations and the odour concentration of
bag odour samples from mushroom composting yards. Each point is
the mean of two sample determinations. Solid circles are 1997/98
measrurements; open circles are for 1999/2000 measurements
14
loge OC = 8.774 + 0.838 loge (H2S + DMS)
r = 0.883
13
loge OC
12
11
new
old
10
9
8
7
-2
-1
0
1
2
3
4
5
6
loge H2S + DMS + 0.375
Fig.9 Relationship between the combined hydrogen sulphide and
DMS concentrations and odour concentration, new olfactometer
61
Fig. 10 Relationship between air sample concentration and intensity score (0 to 6 scale) for real compost yard odour samples
(a and b) and synthetic compost odour samples produced by mixing the most important odourant compounds in their typical
concentrations (c and d). Each value is the mean of six determinations.
(b) HRI Wellesbourne, Phase I
(a) Gateforth Park, Pre-wet
6.0
y = 1.41x + 1.87
R2 = 0.95
5.0
4.0
intensity score
intensity score
6.0
3.0
2.0
1.0
0.0
0.00
0.50
1.00
1.50
2.00
2.50
y = 1.28x + 2.06
R2 = 0.93
5.0
4.0
3.0
2.0
1.0
0.0
0.00
0.50
log 10 concentration
1.00
intensity score
intensity score
y = 1.27x + 1.89
R2 = 0.95
0.50
1.50
1.50
2.00
2.50
(d) Synthetised Phase I
( c) Synthesised Pre-wet
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0.00
1.00
log 10 concentration
2.00
2.50
3.00
6.0
5.0
4.0
3.0
2.0
1.0
0.0
0.00
y = 1.48x + 1.13
R2 = 1.00
0.50
1.00
1.50
log 10 concentration
log 10 concentration
62
2.00
2.50
Part 3: Microbial and Chemical Degradation of Odours
Introduction
The target odour compounds identified for removal from compost are H2S and dimethyl
sulphide (DMS). Bacterial strains known to remove H2S have been isolated from
environmental samples and when re-applied to a biofiltration system can remove this
compound from emissions. The isolates used in these types of study are normally present in a
separate unit where ammonia has been removed, the temperature and other conditions within
the system have been controlled. Such biofiltration systems are expensive and normally
require specialised ducting, equipment and out-buildings. This part of the project aimed to
isolate bacteria capable of removing H2S and DMS from the environment, and re-inoculating
them on to the compost to test if they could remove these compounds directly from the stack.
The isolates would have to function on the outside of the stack or on a matrix applied over its
surface. As well as isolating strains, the development of reproducible compost capable of
generating stable levels of the target compounds were needed.
Bioremediation of odours
Strains
As a positive control for testing strains isolated from compost, one strain Hyphomicrobium
species (a gift Dr H. Op den Camp, Netherlands) known to remove H2S in pure culture was
used in these studies. The strain was tested for its ability to grow on simple nutrient media at
a range of temperatures and large scale laboratory growth conditions in Luria Broth/Luria
agar. Ten isolates obtained from the outer layer (5cm) of the compost stack were tested for
their ability to remove H2S and DMS. Seven of the ten isolates performed as well as the
Hyphomicrobium strain, the remaining three isolates significantly reduced the levels of H2S
and DMS from samples, however they were approximately 3 times less active than the other
isolates. All 11 strains had the following general characters; they grew between 25 and 40 oC,
within a pH range of 6.5 and 8.5, and were aerobic. The 16S ribosomal RNA gene of each
isolate was amplified using the universal primers 8f and 1654r. A region within the gene of
approximately 500bp from each isolate was sequenced. Analysis of the sequence revealed
that the isolates fell into the following lineages:
Pseudomonas putida-lineage
Pseudomonas fluorescens-lineage
Bacillus cereus/thuringiensis/etc - lineage
Hyphommicrobium- lineage
Testing isolates on compost odours
The Hyphomicrobium isolate was introduced on an agar plate or as a broth suspension into
an air sample collected from above an 8-day-old compost sample. At time=0 the compost air
sample was found to contain 30ppm H2S and 5ppm DMS. After 8 hours at 30oC the sample
with the Hyphomicrobium strain had no detectable H2S or DMS, while in the untreated
sample 20ppm H2S and no DMS was detected. This indicated that the strain effectively
removed the H2S from the sample. Similar results were found for the 10 isolates used on 2
separate treatments, although slightly different starting conditions for both experiments were
obtained (H2S 15ppm and 25ppm, and DMS 8ppm and 0ppm at the start). The decline in H2S
and DMS detected in the control samples indicated that these molecules were unstable
during the incubation period. The results also indicate that the microorganisms removed H2S
from samples of compost air sample.
63
Testing model systems for levels of H2S and 02.
In this experiment a series of model compost systems were set up on three occasions (A, B.
C) and monitored for H2S and O2 levels. From a complete compost stack on the mushroom
unit (1 week old) 600g (wet wt) material was placed into the model system (2L volume) and
closed. Moisture levels were determined to be 75%. These systems were incubated at 55oC in
a steam room and subsequently sampled over a 5d period. A Draeger tube placed into the
compost headspace was used to measure H2S levels, and 02 levels were measured by
destructively sampling the system at the end of the experiment. The results are presented
below (Figure 11).
These results indicate that a fixed O2 concentration within this model system dictates if it
is likely to produce H2S at a level of 200+ppm. This level is around 3.8% O2. It may not be
the overall value that is the key to H2S production, but that within samples with this overall
level, regions exist where the O2 level is lower and H2S production takes place. Higher O2
levels may prevent these regions developing. The results also demonstrate that there appears
Figure 12. Scatter plot of H2S vs O2 levels in mushroom composts
contained in incubated flasks
10
02 level (%)
8
6
4
2
0
0
50
100
150
200
H2S level (ppm)
to be a cut off at which point H2S production starts, producing very high levels within the
system. It is likely that such areas developing within discrete regions within a compost stack
result in the H2S and odour. From this point a dilution effect takes place which results in
lower H2S levels at the surface or around the large stack. This is probably why we have been
unable to develop model systems where 50ppm H2S is present in the headspace, consistently
within the model system. If the O2 level is above the threshold we get no H2S production,
and below this threshold we get greater than 2000ppm H2S.
64
Effect of Hyphomicrobium strain and Biofilm on H2S production from model compost
systems
Hyphomicrobium species has been shown to remove H2S when incubated in odourous
mushroom air samples collected from above the stack. In this work, 500g of compost was
placed in 2L flasks. Model systems were inoculated with the bacterium pre-grown at 30oC
for 1 day on a nutrient agar plate, the agar was cut up and added to the top of the flask. A
total of 6 inoculated and 6 control flasks were set up and incubated at 55oC in a water bath.
Moisture content was 76%. The results can be seen in Table 22.
In this experiment the H2S levels in the inoculated samples were higher than that in
the control samples. Although the levels of H2S were lower than desired probably due to the
use of a water bath and partial immersion. In a repeat of this experiment where the systems
were placed at 55oC in a steam room, H2S levels were above 200ppm for all samples,
inoculated and controls. In an additional experiment a biofilm sample was taken from a
biofilter on a composting yard operating a treatment plant (250g of this material placed on
the surface of the model systems). Samples were incubated at 55oC in a water bath. The
results are presented in Table 23.
In these results again poor H2S levels were detected within samples and if anything higher
levels were detected within treatments compared to controls. In both these experiments the
compost model system was only partially submerged in a water bath held at 55oC so that the
surface of the compost exposed for treatment could be maintained at a lower temperature.
This was used since the bacterium can only tolerate 42oC, and the on site measurements of
the biofilter indicated it was operating at 20oC. The results indicate that these conditions are
not suitable for generating H2S in our model systems. Overall the data obtained does not give
any indication that either treatment will work.
Table 22. H2S levels detected in model systems treated with Hyphomicrobium.
Sample
H2S 24h
H2S 48h
H2S 5d
Control 1 0
0
0
Control 2 0
6
0.1
Control 3 0.1
0
0
Control 4 0.1
0.5
0
Control 5 0
0
0
Control 6 0.1
0.1
0.1
Inoc. 7
0.2
0.5
0.1
Inoc. 8
0.5
0.1
0.1
Inoc. 9
3.5
0.5
0
Inoc. 10
10
0.5
4
Inoc. 11
0.5
2.5
2
Inoc. 12
0.2
0.1
0.1
65
Table 23. H2S levels detected in model systems treated with biofilter material from two
locations within 1 treatment plant.
Control
Sample A
Sample B
H2S 24h
H2S 5d
1
0.1
0
2
10
6
3
10
0
4
0.1
0
5
20
0
6
60
2
7
180
0
8
400
5
9
120
2
10
2.0
10
11
120
2
12
180
30
Chemical degradation of odours - Ferric Sulphate treatment
The use of ferric sulphate to eliminate sulphide malodours was developed on waste-water by
Song at al (2001). To test the use of this material for mushroom composting odours, model
systems were established as before. To these systems, ferric sulphate at 200mM and 500mM
were added to chopped straw and this material placed on the surface of the compost. All
flasks were placed in a 55oC room. The results can be seen in Table 24.
The results illustrate that after 24 h 200mM ferric sulphate had removed over 88% of the
H2S, and 500mM over 95% of the H2S . After 48h, 500mM ferric sulphate had still removed
80% of the H2S. In a repeat of this experiment a good effect was seen where H2S had fallen
from 745ppm to 43ppm (+/-66.5), and DMS levels fallen from 409ppm to 58ppm (+/- 53).
Again we were detecting 95% removal of H2S, and 85% removal of DMS. These results are
very encouraging, as we have carried out no optimisation of the treatments used. Further
work to study this in greater detail is therefore needed.
66
Table 24. The effect of ferric sulphate on H2S production from mushroom compost in
incubated flasks.
H2S 24h
H2S 48h
02
1
800
800
5.2
2
2000
2000
4.5
3
2000
2000
4.9
4
2000
2000
4.2
200mM
5
400
2000
4.4
ferric
6
200
2000
5.4
sulphate
7
20
800
5.1
8
400
2000
4.6
500mM
9
60
10
5.8
ferric
10
70
10
4.8
sulphate
11
120
600
5.5
12
90
100
5.2
Control
Figure12. Structure of the model systems. A, laboratory microcosm; B, compost stack
experiment
Less than 1ppm H2S
B
A
AIR
H2S
DMS
Am
o
C
8 sq ft.
H2S-10ppm
DMS-5ppm
C
50-55oC
67
Less than 1ppm
1.5 sq ft
H2S-<1ppm
DMS-<5ppm
Conclusions - Part 3
1.
2.
3.
4.
Ten bacterial isolates were obtained from mushroom compost which were able to
remove odourous sulphur containing compounds from compost air. The bacterial
isolates belong to the following species: Pseudomonas putida, Pseudomonas
flurescens, Bacillus cereus/thurigiensis and Hyphomicrobium spp.
Ferric (iron) sulphate solution was more effective in removing sulphides and
anaerobic odours from mushroom composts than microbial inocula.
There was a distinct step in oxygen concentration (5%) below which anaerobic
odours and sulphides developed. Above this threshold concentration, strong odours
were prevented and no sulphides were detected.
Conditions in composting stacks are too unfavourable (high temperatures and pH) for
the survival of sulphide metabolising bacteria.
Summary Table of microbial and chemical degradation of odours (Project Part 3)
Method
Biofiltration
Hyphomicrobium spp.
Advantages
Could be used on a biofilter in
removing sulphides;
Does not require frequent
changes
Chemical scrubbing
Ferric sulphate solution
Effective at normal
composting temperatures and
pH
Not affected by compost
ammonia
Disadvantages
Cost of biofilter
Microbes sensitive to high
composting temperature,
ammonia and pH
Biofilter requires ammonia
pre-washing
Requires replacement of
ferric sulphate at intervals
Overall Conclusions
1. Replacing wheat straw with rape straw resulted in a significant reduction in odour in both
windrow and aerated tunnel composts without affecting compost density, but mushroom
yield was lower. Rape straw has a higher nitrogen content than wheat straw and required
a lower inclusion of poultry manure.
2. Substituting poultry manure by 50% with organic (spent hop waste, cocoa meal, or
molasses waste) or inorganic (ammonium sulphate or urea) nitrogen sources resulted in
significant reductions in odour and sulphide concentrations, but also reduced mushroom
yield. However, these materials may be suitable as low odour N sources during prewetting.
3. Release of ammonia from urea is more rapid than from poultry manure, but from cocoa
meal it is more delayed. This material should therefore be used in the early stages of prewetting.
4. The omission of gypsum from compost did not significantly affect the emission of
sulphides or odours but resulted in a significant yield reduction. There was no difference
in mushroom yield between two types of gypsum (agricultural or citric acid production
by-product).
5. Sulphur containing compounds in compost odour samples were found to be most
important in exceeding detection thresholds, but volatile fatty acids and trimethylamine
were also found in odour samples at concentrations exceeding their detection thresholds.
68
6. There was a close correlation between the compost odour concentration of the pre-wet
and Phase I composts samples and the combined hydrogen sulphide + dimethyl sulphide
concentration from gas detector tubes. Concentrations of ammonia were above the
detection threshold in most of the odour samples, but were not correlated with odour
concentration.
7. A pulsed fluorescence analyser was found to be sensitive to sulphides in composting
odours at 10 ppb. There was a good correlation between the instrument readings and
odour concentration. The sensitivity of the analyser enabled it to detect odour plumes at
the boundary sites, about 50 m from the Phase I composting stacks.
8. Odour concentrations and sulphide concentrations from aerated composting systems
were generally lower than those from non-aerated systems.
9. There was no significant difference in odour concentration between poultry manure
based composts and those prepared with horse and poultry manures. No relationships
were found between compost analysis and odour concentration.
10. A tenfold dilution of the air from composting sites or synthetic composting odours
resulted in almost a threefold reduction in odour intensity.
11. Ferric (iron) sulphate solution was more effective in removing sulphides and anaerobic
odours from mushroom composts than microbial inocula.
12. There was a distinct step in oxygen concentration (5%) below which anaerobic odours
and sulphides developed. Above this threshold concentration, strong odours were
prevented and no sulphides were detected.
TECHNOLOGY TRANSFER
Industrial relevance and plans for future commercial exploitation
Results from the research work have been transferred to commercial sites as described in
Objective 4 of the research results. This commercial exploitation on mushroom composting
sites includes the following areas:
waste, cotton seed meal and urea) at Hensby Composts Ltd, Blue Prince Mushrooms Ltd,
Tunnel Tech Ltd, Pond Chase Nurseries Ltd and J. Rothwell & Son Ltd. Sources of the first
two of these materials for mushroom composting have been agreed with Cadburys Ltd and
English Hop Products Ltd.
use of objective methods for measuring odours and sulphides using gas detector tubes and
a pulsed fluorescence analyser for site boundary measurements at all the commercial
composting sites
of 5% v/v in compost
in aerated systems at Blue Prince Mushrooms Ltd, J. Rothwell Ltd, Pond Chase Nurseries
Ltd, Shepherds Grove (Gateforth Park) and Tunnel Tech Ltd.
-product gypsum in mushroom compost mushroom
compost at Hensby Composts Ltd, Blue Prince Mushrooms Ltd and Gateforth Park
(Shepherds Grove Ltd)
cost saving in N sources for one of the project partners (J. Rothwell & Son Ltd)
The results of the project can be used in preparing new composting best practice guidelines,
which are due to be renewed by the Environment Agency during 2002. Some of the project
results have already been published in scientific journals and industry-based publications
(HDC News etc) - see section on publications. Further publicity of the project results will
continue in publications and posters, after agreement of content with the project consortium
69
(the Project Consortium will continue to meet at six-monthly intervals as part of the project
application indicated in the previous section).
The exploitation of results from this project in other related areas will be examined (odour
measurement and reduction in waste composting and sewage treatment plants). This will
form part of the new BBSRC project, which includes a component on waste composting
emissions.
Plans for future R&D resulting from the project
A research project proposal has been submitted to the Biological and Biotechnology
Research Council (BBSRC) in October 2001 entitled 'Identification of early indicators to
improve the environmental impact of composting'. The science partners are the Institute of
Grassland and Environmental Research (North Wyke), Horticulture Research International
(Wellesbourne) and the University of Manchester Institute of Science and Technology, and
the industrial partners include 7 of the existing project consortium, as well as 5 new
industrial partners. The mushroom composting part of the project will cover the following
areas:
ct of compost nitrogen on composting odours
- effects on compost odours and compost quality
populations.
The project will also cover waste composting emissions, enabling cross-fertilisation of
methods from mushroom composting. As part of this project, the partners will continue to
meet as a consortium on a regular basis.
On-site testing of compost ingredients developed in this LINK project is continuing
by individual project consortium members: Tunnel Tech Ltd, Hensby Composts Ltd (at own
sites), J. Rothwell Ltd (at Horticulture Research International)
Publications and Presentations resulting from the project
Publications
Noble R., Hobbs P. J., Dobrovin-Pennington A., Misselbrook T.H. & Mead A. (2001)
Olfactory response to mushroom composting emissions as a function of chemical
concentration. Journal of Environmental Quality 30: 760 - 767.
Noble R., Hobbs P.J., Mead A., & Dobrovin-Pennington A. (2001) Influence of straw types
and nitrogen sources on mushroom composting emissions and compost productivity.
Submitted to Journal of Industrial Microbiology and Biotechnology.
Noble R., Gaze R.H., Dobrovin-Pennington A. & Hobbs P. (1999) The development of
odour-free mushroom compost. HDC News 56: 10 – 11.
Noble R. (1999) Odour-free mushroom composting. Agriculture LINK Newsletter. Jan-Mar,
p10.
Noble R., Morgan A., Dobrovin-Pennington A. & Hobbs P. (2000) Compost without the
smell. HDC News 66: 22,23.
Odour-free mushroom composting. HortLink Leaflet.
The project featured as a photograph of odour sampling at Middlebrook Mushrooms Ltd on
the front cover of the above May issue of the Journal of Environmental Quality.
70
Presentations
Mushroom compost research. Presentation by R. Noble at HRI/HDC Mushroom Subject
Day, HRI Wellesbourne, June 2000
Measuring mushroom composting odours. Presentation by R. Noble at Pennsylvania
Workshop on Mushroom composting odours, November 1999.
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