Project Number:M 3Dhorticulture LINK Project 180

Project Title:Development of odour-free mushroom compost by modifying the organic andinorganic nitrogen sources and process technology

Project Number:M 3dHorticulture LINK Project 180

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

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.

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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

CONTENTSPage

Consortium members1

PRACTICAL SECTION FOR GROWERS4

Project objectives and targets

Part 1: Alternative nitrogen sources4

Part 2: Odour quantification techniques6

Part 3: Microbial and chemical degradation of odours7

Action points for growers8

Project Deliverables

PROJECT MILESTONES10

SCIENCE SECTION12

Part 1: Alternative Nitrogen Sources12

Introduction12

Materials and methods

Bench-scale composting equipment12

Aerated bulk composting tunnels13

Windrow composting14

Compost analysis14

Odour analysis14

Mushroom cropping procedure14

Experiments15

Results

Bench-scale flask composts17

Aerated tunnel composts19

Windrow composting20

Commercial farm tests21

Role of gypsum in composts22

Conclusions – Part 122

Figures and Tables – Part123

Part 2: Odour Quantification Techniques39

Introduction39

Materials and methods

Odour sample collection39

Composting yards and composts40

Olfactometry40

GC-MS analysis41

Gas detector tubes41

Electronic sulphide detectors41

Aromascan electronic nose42

Odour and sulphide concentrations on and around composting

sites43

Comparison of real and synthetic mushroom composting odours43

Results

Olfactometric analysis43

GC-MS analysis43

Gas detector tube analysis44

Relationship between gas detector tube analysis and odour44

Compost analysis and type45

Performance of Aromascan electronic nose45

Performance of electronic sulphide detectors46 Odour concentrations on and around composting sites 46

Validation of the odour/sulphide relationship47

Conclusions – Part 247

Figures and Tables – Part 249

Part 3: Microbial and Chemical Degradation of Sulphides in Compost61

Introduction61

Biodegradation of odours

Strains61

Testing isolates on composting odours 61

Testing systems for levels of sulphides and odour61

Effect of Hyphomicrobium strain and Biofilm on H2S production 63

Chemical degradation of odours64

Conclusions - Part 366

Overall Conclusions66

TECHNOLOGY TRANSFER67

Industrial relevance and plans for future commercial exploitation67

Plans for future R&D resulting from the project68

Publications and Presentations resulting from the project68

References69

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.

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.

Summary Table of results with alternative nitrogen sources (Project Part 1)

Treatment / Scale / % reduction of standard compost*
odour / mushroom
yield / compost
density
Rape straw +
poultry manure / Large
experiment / 48 - 72 / 76 - 82 / 107 - 112
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.

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 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 / Advantages / Disadvantages
Human odour panel
(Olfactometry) / Relates to actual odours
High sensitivity / 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).

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).

Summary Table of microbial and chemical degradation of odours (Project Part 3)

Method / Advantages / Disadvantages
Biofiltration
Hyphomicrobium spp. / Could be used on a biofilter in removing sulphides;
Does not require frequent changes / Cost of biofilter
Microbes sensitive to high composting temperature, ammonia and pH
Biofilter requires ammonia pre-washing
Chemical scrubbing
Ferric sulphate solution / Effective at normal composting temperatures and pH
Not affected by compost ammonia / 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.
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.

1. 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.
2. 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.
3. 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.
4. 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.
5. Ferric (iron) sulphate solution was more effective than microbial treatment in removing sulphides and anaerobic odours from mushroom composts than microbial inocula.
6. 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.
• 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).

Project Milestones

TaskTarget DateMilestones

1/112 monthsMethodology to monitor and sample odours developed:

Relationship between laboratory-based odour quantification techniques and subjective methods established (HRI, IGER, Aromascan plc)

1/212 monthsOrganic waste N sources analysed and processed into odour-

1/3free forms (HRI, Bulrush, Holdsworthy Bioplant)

1/412 monthsDifferent N sources compared in laboratory-based composting processes; N balance in substrate and its biomass and mushrooms determined (HRI)