References Appendices Page No

75 - 93

Part One

Technical report prepared by Jim Frederickson

Integrated Waste Systems The Open University

1. Foreword

The Vermicomposting Project has been a collaborative effort between Urban Mines Ltd, the Worm Research Centre (WRC) and Jim Frederickson of the Open University, with financial support being provided by shanks first

Urban Mines is a not-for-profit environmental organisation concerned with the development and application of soundly based and practical approaches to the better management of the waste stream. The organisation works in partnership with a wide range of public, private and voluntary bodies in order to promote materials recovery, economic regeneration, job creation and environmental improvement. Most of their projects demonstrate a concern with the direct application of proven techniques and methods of management whilst others are more theoretical and conceptual.

Established in July 2000, the Worm Research Centre was developed from an existing worm farm in East Yorkshire that was struggling to find answers to the operational problems posed by outdoor worm farming. The aims of the Centre have evolved during the course of the project and it is now dedicated to providing objective information about large-scale vermicomposting systems operating under UK conditions.

Jim Frederickson is one of the UK’s leading environmental scientists in the area of waste research, with over 20 years experience in managing, utilising and recycling biodegradable wastes. He was a founder member of the Composting Association in the UK and is now a Director. His research embraces many aspects of composting and organic waste utilisation including the environmental impact of organic waste processing systems. He is also a world authority on the use of earthworms in waste and environmental management and currently holds a UK patent relating to sustainable land restoration. He has been commissioned to undertake composting and environmental research for the UK Environment Agency and many leading companies and local authorities.

Having introduced the established practice of composting and vermicomposting in particular, this report presents the objectives of the present study. The findings of the study, both scientific and operational are then discussed in detail. Finally, after outlining the commercial possibilities of this research, recommendations are made for further work.

The research effort has involved contributions from many people within the three main organisations as well as a number of others in partner organisations. However, particular thanks is given to the following people: Steve Ross-Smith of the Worm Research Centre; Jim Frederickson of the Open University; Alan Phillips of Urban Mines; Paul Ellwood; Mike Waldron (M&M Worms); Graham Howell; Andrew Hobson; Professor Bill Radley (shanks first).

2. Executive Summary

The vermicomposting evaluation project described in this report was managed by Urban Mines Ltd, with funding from shanks first. The project was carried out at the Worm Research Centre (WRC), which is managed by Steve Ross-Smith. The WRC provided support for the experimental research and also conducted the mechanisation trials. The scientific and experimental research was directed by Jim Frederickson with support from Graham Howell (Open University). The final report was written by Jim Frederickson with contributions from Steve Ross-Smith and Urban Mines Ltd (Financial Evaluation and Market Potential).

2.1 The project aims were:

i) The project sought to investigate the technical performance of outdoor vermicomposting, using a specifically designed bed system, which facilitated the research methods employed.

ii) The project identified low processing temperature as a limiting factor and investigated bed heating as a method of enhancing performance. iii) The environmental impact of the outdoor vermicomposting system was evaluated in terms of leachate production and greenhouse gas emissions. iv) Ways of mechanising the process were explored with particular emphasis on waste application to the processing beds.

v) The cost-effectiveness and market potential of outdoor vermicomposting systems was assessed, with particular regard to basing the study on new technical knowledge gained during the course of the project and practical techniques developed.

1. An outdoor, experimental vermicomposting system was designed andinstalled comprising 400 m² of waste processing beds. Each block contained a leachate drainage and collection system. The environmental impact of leachate and greenhouse gas emissions was undertaken. Beds were unheated apart from one complete block, which was heated during periods of cold weather. Air and bed temperatures were continuously monitored. Beds were inoculated with known densities of earthworms and populations were rigorously determined every eight weeks.
2. Following construction of the vermicomposting beds, the monitoring andexperimental phase of the project commenced on 1st January 2001. The experimental phase duration was 56 weeks. The earthworm species used during the research was Dendrobaena veneta.
3. Air and bed temperatures were monitored continuously throughout the year.For the unheated blocks the average temperature of the beds over the coldest months was 7.2 �C. (around 60% of the year). The average temperature for the heated beds, during this same 30 week period, was controlled at 13.8 �C. For the

hottest summer months, the average temperatures in the centre of the beds were around 20 –25 �C, but the maximum temperature recorded in the core of the beds was 32 �C. Optimum temperature for growth and reproduction of Dendrobaena veneta.is considered to be 20 –25 �C, whilst temperatures above 35 �C are thought to be lethal.

1. The performance of the unheated beds in terms of producing earthworms andoffspring was relatively poor. For most of the beds, the weight of earthworms after six months had declined to around half of the initial weight. This was maintained for the duration of the project. The first significant numbers of cocoons and hatchling earthworms were recorded after 16 weeks and 32 weeks respectively. The adult population of earthworms began to increase after week 32 due to the presence of the newly produced hatchlings but then declined rapidly by the end of the project. It is estimated that the sustainable population of earthworms that this unheated system would support would be around 2 kg earthworms per m³ of bed. This is similar to other commercial systems that were investigated and this would be adequate for processing a limited amount of waste and could produce some earthworms for harvesting in the longer term. Migration of earthworms out of the beds was observed and this would appear to significantly reduce earthworm numbers.
2. Heating the beds greatly increased earthworm populations compared with notheating. For example, after the first 24 weeks in operation, the number of hatchling earthworms in the heated beds was approximately 40 times greater than in the unheated beds. The heated beds show the potential to support a working earthworm density of at least 4 kg per m³ of bed and this could be achieved after one year. It has been estimated that a possible 3 kg of mature earthworms per m² of bed could be harvested per year from such a system. However, this will only be achieved if earthworms are contained within the beds and migration prevented. Periodic mass migration of earthworms out of the beds was observed on one occasion resulting in the loss of an estimated one third of the population of adult earthworms.
3. The waste applied to the processing beds was potato slurry. When theheated beds had become established the beds processed approximately 1.2 kg potato slurry per m² of bed per day. This is equivalent to 0.6 kg of waste being processed by 1 kg of earthworms per day. It is estimated that at least 0.8 kg of waste per kg of earthworms should be achievable. For a heated bed with a working population of around 4 kg earthworms per m² of bed, a processing rate of approximately 3.2 kg waste per m² of bed per day should be possible.
4. The earthworm populations in the bedding material processed the wastepotato slurry applied to the beds. The resulting mix of earthworm casts and bedding is termed vermicompost. When compared with typical green waste compost, the vermicompost was found to be richer in nitrogen and other valuable plant nutrients. If vermicomposts were eligible for the Composting Association

National Compost Standards scheme, the vermicompost produced during the project would have met the requirements for the parameters tested.

2.9 The environmental impact of vermicomposting was investigated. Thevermicomposting system produced a significant volume of leachate during the project and the amount would have been broadly related to rainfall. While the leachate appeared to have the potential to pollute, it was found to be less polluting compared with typical leachate from composting sites. Vermicomposting leachate was found have a consistently low BOD, although COD was moderately high. It contained useful concentrations of plant nutrients making it potentially useful as a liquid fertilizing medium, if used with care.

Greenhouse gas emissions were monitored. Methane emissions were only detected during severe waterlogging of beds. However, research carried out during this project has identified vermicomposting as one of the most significant point sources of nitrous oxide emissions yet discovered. Nitrous oxide is a powerful greenhouse gas. There is a pressing need to investigate the extent of the problem as soon as possible and to identify mitigation options, if appropriate.

1. Research into mechanised methods of applying waste slurries to processingbeds was undertaken and a successful system was developed.
2. A preliminary financial evaluation of the experimental vermicomposting system at WRC was undertaken. This suggests that the direct cost of operating the system is estimated to be within the range £8 to £30 per tonne of waste, depending on the income received for sales of worms and compost. At this time it is not possible to determine the overhead charges relating to the operation (business costs such as management, marketing and administration overheads). Figures for overheads quoted in this report are estimates only. The overhead charge is estimated to be approximately £15 per tonne. Hence, waste providers would need to pay a gate fee of between £23 and £45 per tonne in order to process suitable waste using the technology and systems described in this report.

Recommendations

It is recommended that vermicomposting systems should be operated as waste processing facilities that also have the potential to produce a limited amount of marketable earthworms.

It is recommended that research is undertaken into devising effective methods of containing earthworms in the processing beds. Despite installing a typical containment device for this project, a protruding lip on top of the beds, it was estimated that on one particular occasion, over one third of the adult earthworms migrated from an experimental block. Other separate mass migration events also

occurred and this would appear to be expected for open-air systems, which flood periodically causing hostile bed conditions.

It is recommended that consideration is given to stabilizing conditions in processing beds so that the earthworm populations are given every chance to develop. In particular, periodic waterlogging of processing beds regularly took place during the project and prevention of rainfall entering beds should be a priority. If conditions in the beds are hostile for earthworms, it is likely that more effective containment methods will only lead to increased mortality.

It is recommended that processing beds be heated to at least 15 �C during the coldest months of the year. Methods of heating will vary depending on local conditions but insulating beds as a minimum first step should be a priority.

It is recommended that research is continued into identifying better methods of preparing and applying waste to the processing beds.

It is recommended that the emission and mitigation of greenhouse gases (nitrous oxide) from vermicomposting be investigated as a matter of priority.

It is recommended that increased research into large-scale vermicomposting is undertaken and that the findings be made readily available to the rapidly developing vermicomposting sector.

3. Introduction

Large-scale composting has been shown to be an important element in sustainable waste management for the UK and could have a vital role to play in meeting the obligations of the Landfill Directive. While it is clear that the composting sector is currently dominated by municipal windrow composting, there is enormous potential for the development of alternative composting systems such as vermicomposting.

There has been sustained growth in the composting sector for some time and over the last five years the number of operational centralised sites has grown on average by around 25% per annum. Moreover, the expansion has relied predominantly on the processing of relatively benign garden waste. This reliance on garden waste has led to the adoption of the low cost, very unsophisticated practice of open-air windrow composting at small-scale centralised sites and this approach currently dominates the UK industry. In 1999, 88% of waste composted was processed in open-air mechanically turned windrows. Despite an increase in the size of some sites, centralised composting sites still tend to be relatively small. In 1999, 56% of composting sites were each processing a maximum of only 7,000 tonnes of waste per year.

However, there is now evidence of the introduction of a wide range of novel and more advanced composting technologies, such as in-vessel and vermicomposting systems. While these systems currently form only a small part of the industry, evolving landfill and biodegradable waste legislation, and accompanying statutory targets, are likely to have a profound effect on the collection and processing of biodegradable waste, creating opportunities for the development of the composting sector. In particular, there is a pressing need for increased diversity in the composting sector and, as shown above, relatively small-scale and unsophisticated composting operations already play a very important role. This trend is likely to continue and is especially relevant for decentralised composting of putrescible and more difficult wastes such as food processing residues. Decentralised processing of industrial and commercial wastes is likely to be the focus of much attention in the next phase of composting developments in the UK.

Using earthworms to help process industrial and commercial wastes could have a very important role to play in the future. Many people are now familiar with the idea of using earthworms to compost domestic waste and many tens of thousands of small “worm compost bins” are owned by households up and down the country (See Figure 1).

Figure 1 Examples of home composting units

A list of suppliers of home wormeries and other worm composting units can be found in Appendix 10.

However, very few people know much about the widespread science and practice of using earthworms to compost waste on a large-scale. Vermicomposting is the name that is often applied to the process of composting organic waste using selected species of earthworms. Some of the existing commercial vermicomposting units in the UK are now capable of composting thousands of tonnes of waste per year and yet there is very little objective information about either the technical performance or the commercial viability of large-scale systems. The numbers and size of large-scale vermicomposting units appear to be increasing rapidly in line with increased composting and collectively, they should make a significant contribution towards sustainable organic waste management. However, the extent of this contribution is currently unknown and therefore the potential of vermicomposting cannot easily be assessed.

To a large extent, the interest in large-scale vermicomposting has arisen from the established but fragmented, worm-farming sector whose main aim was to produce earthworms for the fish bait market. However, recently the emphasis has changed and there is increasing interest in securing a gate fee for processing organic waste and in the marketing of the high quality compost that often results. Vermicomposting is the use of selected species of earthworms to help decompose and transform organic wastes into useful compost. However, as with all composting processes, it is the aerobic microorganisms, such as fungi and bacteria, which mainly decompose the waste; the action of the earthworms merely accelerates this process and also physically improves the characteristics of the final compost. Compared with municipal composting where waste is composted in batches, vermicomposting is a continuous process and is particularly suited to processing highly putrescible wastes. Very wet food-processing waste and paper sludges are particularly suited to vermicomposting and it is normal to apply these wastes on a frequent basis to earthworm processing beds in shallow layers. In general, vermicomposting operations tend to be located in rural areas, by farmers needing to diversify, and often they are close to small food processing plants and similar industries where low-cost, decentralised waste processing makes real sense.

Large scale vermicomposting and worm farming in the UK tends to be undertaken in very unsophisticated, relatively small, outdoor worm beds and the performance of these systems is therefore temperature and weather dependent. There has been a significant amount of scientific research undertaken into the process of using earthworms to decompose organic materials but most of this has been based on laboratory studies carried out under optimum conditions. Little research has focused on practical applications of vermicomposting but it is clear from existing research that most outdoor vermicomposting systems in the UK are operating under sub-optimal conditions. There would appear to be considerable opportunities to enhance the vermicomposting process, both scientifically in terms of improving the efficiency of the process and technologically so that the system can be operated more cost-effectively. In particular, vermicomposting could offer considerable benefits when operated in conjunction with other processing technologies such as in-vessel composting systems.

The trend towards more and larger vermicomposting units, allied to the changing emphasis from earthworm production to waste management, highlights the pressing need to understand more about these types of facilities. Although many existing vermicomposting units attempt to combine earthworm production with waste processing, these two requirements are conflicting. This is because earthworm production is best achieved using low earthworm densities during vermicomposting with frequent earthworm harvesting while maximising waste processing rates depend on maintaining high earthworm densities. Hence, there is a clear need to identify the main aim of the process and this should have a profound effect on how the vermicomposting system is operated and how it is subsequently evaluated.

In general very little is known about the size and characteristics of the sector, the commercial viability of vermicomposting and the technical performance of the production processes employed. In addition, very little research has been undertaken into the environmental impact of large-scale vermicomposting and as a result, there is considerable uncertainty surrounding many aspects of planning and licensing.

One organisation that aims to address these issues is the Worm Research Centre. The Centre is based around an existing worm farm in Yorkshire and is dedicated to providing objective data on large-scale vermicomposting systems, operating under UK conditions. A key aim of the Centre is to contribute to greater public understanding of vermicomposting systems; their performance and their use. In the longer term, it is envisaged that the facilities and expertise at the Worm Research Centre will be made available to the waste management industry to investigate sustainable vermicomposting of a wide range of organic wastes.

This report is an account of an eighteen month project conducted by the Worm Research Centre. The project sought to investigate the technical performance and enhancement of outdoor vermicomposting and explore ways of improving its commercial viability, through such means as increased levels of mechanisation. The environmental impact of vermicomposting was also rigorously monitored and it is envisaged that the findings from the project will significantly contribute to the planning and licensing debate. The project and the subsequent report represent the first attempt, in the UK, to rigorously evaluate the performance of large-scale outdoor vermicomposting, with the aim of making the information available to the industry. Hence, this report is not written with the intention of being a definitive guide to “worm farming” or waste processing. It is hoped that the report will be helpful to existing and prospective operators of vermicomposting systems and that it will enable everyone in the sector to ask more informed questions about how vermicomposting is carried out. Equally, this applies to those involved with regulating and licensing such operations and it is hoped that they will benefit from the research into environmental impact.

The project was managed by Urban Mines Ltd., with funding from shanks first. The Worm Research Centre is managed by Steve Ross-Smith, who also provided support for the experimental research and conducted the mechanisation trials. The scientific and experimental research was directed by Jim Frederickson with support from Graham Howell (Open University). The report was written by Jim Frederickson , Integrated Waste Systems research group, The Open University, Walton Hall, Milton Keynes, MK7 7DL. Tel: (01908) 653387, e-mail: j.frederickson@open.ac.uk, with input from WRC and Urban Mines Limited.

4. Background to Vermicomposting

Using selected species of earthworms to help compost organic waste, known as vermicomposting, is a process that has been widely adopted throughout the world. Indeed, many countries such as Australia, the USA and several European countries have developed thriving vermicomposting industries. The roots of vermicomposting are thought to stem from the established business of vermiculture, which is the breeding of earthworms mainly for the fishing bait market. In recent years, growing awareness of the ability of earthworms to decompose and stabilize a wide variety of wastes has changed the focus of the industry from producing earthworms to producing compost. However, in practice it is almost impossible to separate the production of earthworms from the processing of waste and many vermicomposting businesses focus on both aspects. However, maximum earthworm production is best achieved using low earthworm densities during vermicomposting coupled with frequent earthworm harvesting. Maximising the waste processing rate depends on maintaining high earthworm densities throughout the vermicomposting process and this is clearly in conflict with producing maximum earthworm biomass from the system. Many years of experience of vermicomposting has shown that it can be a useful method of composting and one that is suited to a wide variety of wastes but while it has some advantages compared with traditional composting, it also has many disadvantages.

Unlike windrow composting, vermicomposting has the potential to produce an additional product in the form of earthworms and many vermicomposting systems have been started or sold on the basis of the profits to be earned from selling these. However, in an attempt to sell commercial vermicomposting systems, exaggerated claims have often been made about the ability of the vermicomposting process to produce large numbers of marketable earthworms and to transform a wide variety of wastes into premium quality vermicompost. While some of these claims are justified, many have not been adequately researched, especially on a large-scale and under sub-optimal processing conditions.

Vermicomposting and traditional composting

Vermicomposting is the use of selected species of earthworms to help decompose and transform organic wastes into useful compost. With traditional composting, the compost piles are mixed and aerated mechanically but with vermicomposting it is the earthworms that fragment, mix and help aerate the waste. There are many different methods of vermicomposting, making it impossible to present a definitive guide to best practice. Systems will vary depending on whether the aim is to produce vermicompost or earthworms, or both.

While vermicomposting and composting both involve the aerobic decomposition of organic matter by microorganisms, there are important differences in the way the two processes are carried out. The most notable being that vermicomposting is carried out at relatively low temperatures (under 25�C), compared with composting, where pile temperatures can exceed 70�C. The intention with traditional composting is to stack waste material in sufficiently large piles so that the heat produced in the intense breakdown of organic matter is retained in the compost pile. This temperature increase stimulates the proliferation of heat loving (thermophilic) microorganisms and it is mainly these that are responsible for the decomposition. With vermicomposting it is vitally important to keep the temperature below 35�C, otherwise the earthworms will be killed. It is the joint action between earthworms and the aerobic microorganisms that thrive in these lower temperatures (mesophilic) that breaks down the waste. Hence it is common with vermicomposting systems to apply waste frequently in thin layers, a few centimetres thick, to beds or boxes containing earthworms in order to prevent overheating and to help keep the waste aerobic.

It is difficult to directly compare composting with vermicomposting in terms of the time taken to produce stable and mature compost products. With vermicomposting, particles of waste spend only a few hours inside the earthworm’s gut and most of the decomposition is actually carried out by microorganisms either before or after passing through the earthworm. Hence, earthworms accelerate waste decomposition rather than being the direct agent. With in-vessel and windrow composting it usually takes at least six to twelve weeks to produce a stable compost and research suggests that vermicomposting takes around the same time. However, processing rates will crucially depend on many factors such as the system being used, the processing temperature and other factors, the nature of the wastes and the ratio of earthworms to waste.

One advantage that vermicomposting has over composting is that a net excess of earthworms can be produced and these may be harvested for a variety of purposes. It should be noted that it can take many months or even years to build up a large working population of earthworms capable of vermicomposting significant quantities of waste. Vermicomposting does have one serious disadvantage and this relates to the destruction of human and plant pathogens that can be present in some wastes. Destruction of most pathogens is more easily achieved in windrow composting due to the high operating temperatures and the intense microbial reactions taking place. Although the destruction of human pathogens has also been shown to be very effective with vermicomposting, elimination of pathogens requires very effective management of the vermicomposting process. It is often recommended that wastes, such as sewage sludge, which are known to contain human pathogens, are either pre-composted before vermicomposting or else the resulting casts should be sterilized before use.

Large-scale vermicomposting systems

The most widely used vermicomposting system worldwide is the bed method, which involves applying thin layers of waste material to the surface of beds containing relatively high densities of earthworms. New layers of waste are applied to beds on a regular basis and the earthworms move upward into the fresh waste to feed and to process the material. Earthworm numbers increase as more waste is applied until a limiting density is reached and harvesting of earthworms or dividing of beds to form new beds is usually undertaken. See Gaddie and Douglas (1978) for typical bed designs. The main disadvantage with this bed system is that low-level beds take up a considerable area of ground in relation to the relatively small amount of waste processed. It has been estimated that a bed vermicomposting system could take up to six times more land area to process the same amount of material compared with windrow composting. Because of this, more sophisticated stacking systems have been proposed since they take up less ground area.

Worldwide, a wide variety of vermicomposting systems have been invented and installed. Figure 2 shows a large-scale operation in Korea based on a series of conveyer belts containing sewage sludge and earthworms.

Figure 2 Conveyor system in Korea

Automated reactor systems have been installed which allow waste to be fed from a gantry above the reactors while finished vermicompost is collected from the base using breaker bars. Such a vermicomposting system was installed in 1991 at Montelemar, France to process organic matter from the town’s household waste stream. Mixed waste is sorted and then pre-composted for 30 days before being vermicomposted for 60 days by an estimated 1,000 million earthworms.

Around 27% of the total waste stream is converted in a number of reactors to good quality vermicompost which is then bagged and sold.

Separating the processed waste (vermicompost) from the earthworms at the cessation of processing is often performed manually but for many years earthworm harvesting machines have been commonly available in the USA and other countries. Typical trommel and vibrating screen harvesters are shown in Figure 3.

Figure 3 Typical worm/compost harvesters

In many countries, decentralised waste processing may be undertaken using small-scale reactor systems as shown in Figure 4 (see for example http://www.vermitechsystems.com/). Some versions tend to be fully automated but often they can be no more than simple containers, similar to compost bins, but supplied with earthworms. A feature of reactor systems is that they are designed to be used continuously rather than on a batch operation.

Figure 4 Small-scale reactor system

Typical vermicomposting systems in the UK

The trend towards more and larger vermicomposting units, allied to the changing emphasis from worm production to waste management, highlights the pressing need to understand more about these types of facilities. In general very little is known about the size and characteristics of the sector, the commercial viability of vermicomposting or the technical performance of the production processes employed. In addition, there is considerable uncertainty surrounding many aspects of planning and licensing.

In the UK, although the number of indoor or enclosed systems appear to be increasing, most vermicomposting systems would appear to be based on either outdoor windrows or covered shallow beds. There is very little evidence of mechanisation and the use of labour saving equipment, such as earthworm harvesters, is rare. Figure 5 shows the layout of a typical, very unsophisticated, outdoor vermicomposting bed in the UK. Strips of waste material on the surface of the bedding material can be seen. The bed shown is approximately 5 metres wide, 50 metres long and 0.5 metres deep. The beds typically comprise wooden sides covered in a woven semi-permeable fabric containing coir or shredded wood chip bedding placed directly on the soil surface.

When installed, the bed would have been inoculated with starting culture of adult earthworms at a density of approximately 0.5kg earthworms per m³ of bed. The suppliers of similar systems typically claim that the rate of increase of the starter earthworm inoculum is such that adult earthworms (weighing in excess of 1g each) may be harvested after six months of installation and that regular harvesting is possible. A commonly reported problem with such systems is that growing adult earthworms of the correct size is difficult. Some operators have

Figure 5 Typical bed system

installed separate “fattening” houses where harvested immature earthworms are allowed to grow larger under lower density conditions and with the application of some background heating.

Up until recently, most vermicomposting facilities were modest in size with bed areas around 1,000 m² but there is now a trend towards much larger units, as much as ten times this size. Very large units can process large amounts of waste, of the order of thousands of tonnes per year, making them comparable to many of the smaller municipal composting operations.

There is very little information available on the nature of the vermicomposting industry in the UK and what little exists is considered to be commercially sensitive. There are at least four major suppliers of large-scale vermicomposting systems currently operating. In year 2000, a series of interviews were conducted on behalf of WRC to ascertain the approximate number of vermicomposting systems supplied by one company. At that time, there were around 90 individual operators with 81,000 m² of beds. The total investment would have exceeded £1.25 million.

Scientific and technical aspects of vermicomposting

A number of factors affect the life cycle of earthworms and hence determine the rate of waste processing, vermicompost output and the number of earthworms

that are produced. In particular, temperature, moisture, waste characteristics and earthworm density are all important.

There is little doubt that maintaining vermicomposting systems at a constant

temperature of around 20�C would give maximum vermicompost output and ensure maximum earthworm growth and reproduction. In UK conditions, if vermicomposting is carried out in unheated beds they are likely to produce significantly lower outputs than for beds operating under optimum conditions.

Earthworms prefer material that is fairly damp, in the range 70 - 90% moisture. Hence there is usually more of a need to add more moisture to the waste material before and during vermicomposting compared with traditional composting. Since moisture is not driven off by high temperatures, as with composting, the finished vermicompost can be quite moist, and often the conversion of waste to vermicompost results in only a small weight loss, typically around 10%.

Earthworms will process more waste and will grow and reproduce more quickly when fed some wastes compared with others. Sewage sludge, animal manures, paper pulps, processed food slurries, brewery waste, mixed household waste, garden and vegetable wastes and many other biodegradable materials have been used on a large scale to produce vermicompost and to breed earthworms. Vermicomposting is similar to traditional composting in the sense that materials with carbon to nitrogen (C:N) ratios in the range 15 – 35:1 are considered to be suitable. In general, fresh, finely shredded organic materials which, decompose easily will sustain the greatest numbers and diversity of microorganisms and this in turn will result in rapid decomposition and produce the highest earthworm growth and reproduction.

The density of earthworms in any vermicomposting system is related to the rate of waste processing and if vermicompost production is the main aim then it is advisable to maintain a high density of mature earthworms. However, high earthworm densities will eventually reduce the number of earthworms produced, by regulating growth and reproduction. Hence, if the main aim is to produce a net surplus of earthworms, comparatively low densities of immature earthworms should be used. Equally, regular harvesting of earthworms and cocoons should be carried out to maintain this low density at all times.

Earthworm species

Over 3,000 individual species of earthworms have been recorded throughout the world but in the UK only around 28 species have been found or imported. It is useful to divide these various species into three broad categories depending on habitat and ‘lifestyle’. It is only the litter dwelling species that are used for vermicomposting.

Litter dwelling earthworms (Epigeic species)

There are several deeply pigmented or red species that normally live in the rotting litter or organic matter on the surface of soils. They grow and reproduce very prolifically compared with true soil dwelling earthworms. The three species most commonly used in vermicomposting in the UK are Dendrobaena veneta (blue nosed worm), Eisenia fetida (tiger or brandling worm), Eisenia andrei (red tiger worm). In warmer countries other tropical species such as Eudrilus eugeniae have been farmed.

Topsoil dwelling earthworms (Endogeic species)

Just below the surface live another group of small earthworms, in the first few centimetres of topsoil. They improve soil structure in the root zone of plants and recycle dead organic matter. One notable species is the ‘green worm’, Allolobophora chlorotica.

Deep burrowing earthworms (Anecic species)

Some of the most important species live deeper down in the soil profile in permanent vertical burrows that can be up to two metres long. They help create topsoil by dragging dead organic material from the soil surface down into their burrows, ingesting it along with soil and then egesting the mixture back on the surface as nutrient-rich earthworm casts. Species in this category are highly valued and have been successfully bred for land restoration projects. Two of the more beneficial species are Lumbricus terrestris (the lob worm or ‘common earthworm’) and Aporrectodea longa (black headed worm).

Earthworm life cycle

Vermicomposting species such as D. veneta and E. fetida can grow to weights of around 4g and 2g respectively and can live for up to three years under ideal conditions. When sexually mature they will develop a noticeable swollen band on their body, called the clitellum (‘saddle’) and after mating they roll a band of mucus from this organ, off their bodies, forming a roughly spherical cocoon, from which offspring will hatch. Earthworms are hermaphrodites, having both male and female sex organs but in general they need to mate with other earthworms of the same species to produce offspring. After mating, each earthworm will produce cocoons. Some species produce only one or two hatchlings per cocoon (D. veneta), while others can produce several such as E. fetida. Earthworms can breed all year under ideal conditions but cocoon output is known to decrease rapidly (reproductive fatigue) after a period of prolific production. For example, in sewage sludge E. fetida reproduced for around one year but maximum cocoon production occurred when the earthworms were aged between 9 - 11 weeks and declined significantly thereafter. Table 1 shows the life cycles and the maximum reproductive output for two species fed on animal and vegetable waste.

Table 1 Life cycle and maximum cocoon production under ideal conditions (Edwards, 1998)

Best conditions for vermicomposting

Temperature

The optimum range for culturing D. veneta and E. fetida is considered to be around 15 - 25�C. Temperature during vermicomposting has both positive and negative effects on growth and reproduction at different stages of the life cycle. Below 15�C, earthworms grow relatively slowly and produce few cocoons but as the temperature is increased so does growth and reproduction. For example E. fetida is known to produce up to four times more cocoons at 25�C than at 15�C. At 25�C, earthworm mortality also rises and the viability of cocoons and the number hatchlings per cocoon decrease significantly. The time taken to complete the life-cycle of Dendrobaena veneta has been studied in the laboratory and was found to be temperature dependent. It took 150 days to complete at a constant 15 �C but only 100 days at 25 �C. This confirms the positive effects that

increased temperature has on most aspects of the life cycle. Temperatures in excess of 30 - 35�C are lethal to earthworms.

Moisture content

The moisture content of organic material fed to earthworms can greatly affect growth and reproduction but it is impossible to be precise about the optimum level. In general, earthworms prefer material that is fairly damp, in the range 70 90% moisture.

Earthworm density

Higher densities will increase the rate of vermicompost production but there are maximum densities that can be achieved in processing beds or boxes. This is known as the carrying capacity of the system and is related to a host of factors such as the nutritional value of the waste being processed and the processing temperature. For E. andrei this is 2 kg per m² of bed when fed horse manure, which is low in nutritional value and 7 - 11 kg per m² of bed when fed pig manure. Lower densities are needed for best earthworm production; for example decreasing the number of E. andrei from 40 to 10 per kg of fresh waste increased their growth rate by 50% and led to a fivefold increase in the number of cocoons. Typical working densities for particular vermicomposting systems have been reported to be between 1 and 4 kg earthworms per m² of bed.

Suitable wastes

In order to produce finely-divided vermicompost, earthworms must ingest the waste. For this to happen successfully, more resistant organic materials need to be shredded or pre-composted first. Most species used for vermicomposting can convert between one quarter and twice their own weight of waste per day into vermicompost depending on waste characteristics and processing conditions. These factors determine the rate of earthworms produced as well as affecting the amount of waste produced. Using sewage sludge instead of horse manure increased earthworm biomass by 250%. Feed that has aged or been pre-composted has been shown to be much less nutritious than fresh material. For example, feeding green waste to E. andrei that had been composted for two weeks resulted in only half the number of cocoons being produced compared with feeding fresh waste. Frequent feeding is an important factor for good growth and reproduction and replacing worm worked food with fresh food every two weeks has been found to double cocoon production compared with replacing every four weeks. The acidity or alkalinity of wastes used in vermicomposting, providing the waste pH is in the range 5 – 9, appears not to significantly affect growth and reproduction. However, wastes heavily contaminated with heavy metals could be toxic to earthworms and comparatively low concentrations of some metals have been shown to adversely affect growth and reproduction.

Environmental impact of vermicomposting

As with all waste processing activities, vermicomposting has the potential to have a high environmental impact. Compared with other waste related sectors such as municipal composting or recycling, the environmental impact of large-scale vermicomposting has not been thoroughly researched. In particular, the processing of many controlled wastes is known to produce odour problems and some processes are associated with bio-aerosol emissions and leachate production. The equipment processing wastes has also been found to produce noise and dust problems as well as the emission of Volatile Organic Compounds (VOCs). A review of environmental impact related to waste processing is beyond the scope of this report but two aspects of environmental impact will be briefly highlighted because they closely relate to vermicomposting. Leachate production and the potential to emit greenhouse gases are important considerations.

Leachate from vermicomposting operations is often regarded as beneficial in the sense that when collected it can be used a liquid fertiliser, often called “worm tea”. While this is true, the leachate also has the potential to pollute when not collected and used positively. Previous studies using earthworm reactors to help treat dilute sewage found that while such reactors achieved good results, the resulting leachate was still polluting in terms of Biological Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and nitrate concentration.

The emission of greenhouse gases from waste processing plants is now receiving considerable attention. A prime factor in the move away from landfilling waste to more sustainable methods of treating biodegradable waste, is the minimisation of greenhouse gas emissions, in particular methane. However, greenhouse gas emissions have been monitored at large-scale composting sites and methane and nitrous oxide, which is a more powerful greenhouse gas compared with methane, have been detected. Methods for reducing the emission of these gases from composting plants, is being investigated. No research has been published into the potential for vermicomposting systems to emit greenhouse gases. However, earthworms are associated with high levels of nitrous oxide release from forest soils. Equally, vermicomposting systems, because they are designed to be continuous processes and operate at high moisture levels, could provide ideal conditions for methane production.

Outputs from Vermicomposting

Vermicompost

Vermicompost is the matured, processed material that is egested from earthworms as casts. As earthworms feed on the rich diet of organic matter and micro-organisms in waste, this ingested material is finely ground by the earthworms gut. This helps micro-organisms decompose the organic matter and stimulates mineralisation of complex compounds into simple nutrients, easily utilised by plants. At the same time the organic matter and microbial cells are glued together by the secretions from the earthworms gut forming casts. The amount of time that the waste spends in the earthworm gut is only a few hours and therefore the egested cast material is very microbially active and continues to decompose for some time. Once matured, the casts are known as vermicompost, which can have excellent physical and chemical characteristics. Compared with windrow composts, vermicomposts are likely to contain higher levels of nitrogen because vermicomposting temperatures and nitrogen losses are typically much lower.

The nature of the feed material or waste will often determine the characteristics of the final vermicompost with high nitrogen material, such as food processing waste, giving vermicompost rich in plant available nutrients. Equally, although it is known that some earthworm species can selectively accumulate and concentrate particular heavy metals from industrial sludges, it is not possible to use earthworms to “clean up” contaminated wastes.

As with most waste-derived composts, vermicompost when used as a plant growth medium is likely to produce better results when amended with other materials. This is because the vermicomposts made from many wastes can be very rich in nutrients and too alkaline for optimum plant growth. Vermicompost mixes have sometimes performed better than commercial and compost-based products. Mixing vermicompost with equal volumes of coir, for example, is usually sufficient to produce good plant growth media but a feature of vermicomposts is that often only small amounts in blended plant growth mixes (10 - 20%) give excellent results.

Many factors will determine how much earthworms will ingest per day and how much vermicompost can be produced per m² of bed in a certain time. For example, earthworms have been reported to eat twice their weight of sewage sludge per day and in another study a feeding rate of 0.8 kg biosolids (sewage sludge) per kg of earthworms was found. In a further experiment with biosolids, it was reported that the best vermicompost was obtained with a feeding rate of 0.75 kg biosolids per kg of earthworms per day from a bed stocked with 1.6 kg earthworms per m². In an experiment using precomposted vegetable waste, only

1.5 kg per m² of bed per day was converted to vermicompost by a bed stocked with 4 kg of earthworms per m².

Earthworms

It is an important feature of sustainable vermicomposting systems that the earthworm population should at least remain stable or preferably increase to allow for expansion of the operation. Moreover, if the emphasis is placed on producing a large number of earthworms for selling in starter kits or for use in smaller domestic worm composters, it is particularly important to provide the earthworms with the best conditions for growth and reproduction. World-wide, exaggerated claims are often made for very high rates of earthworm reproduction as a means of marketing vermicomposting systems. Population increases in excess of 1,000 fold in one year have been promised - under ideal conditions. Unfortunately, ideal conditions are seldom achieved in commercial vermicomposting operations and it is more likely that only modest increases in population can be achieved in practice.

Reported increases in earthworm biomass and population from vermicomposting systems are very variable and probably reflect different systems, temperature and breeding conditions and wastes. For vermicomposting beds fully stocked with a high density of earthworms (E. andrei), the amount of earthworm biomass harvested per year was found to be 6 kg per m² of bed when fed horse manure and 18 kg per m² of bed when fed pig manure. For beds stocked with an initial, low density starter culture of earthworms, a 10 fold increase in population in 16 months was found for E. fetida when fed sewage sludge. It must be remembered that most of the increase in population would have been in the form of very small, juvenile and hatchling earthworms and these can take many months to grow into mature adults, depending on conditions. Vermicomposting household waste for six months using E. fetida resulted in a 3 - 4 fold increase in earthworm biomass and an 80 fold increase in earthworm population. Again, it is important to note that vermicomposting can result in very impressive increases in earthworm numbers, due to large numbers of juvenile and hatchling earthworms being produced. However, increases in the total weight (biomass) of earthworms often takes significantly longer because of the time it takes for very young earthworms to grow to maturity. Unfortunately, high earthworm density, poor nutrition and other factors may prevent significant weight gain from happening and total biomass may stabilize, not increasing to any marked extent.

5. Approach to the research programme

The overall project was carried out in a number of phases and comprised several technical and non-technical components. The initial phase of the project comprised a scientific literature review focusing on vermicomposting research and practice. At the same time a number of interviews were conducted with existing operators and key stakeholders in the waste management and vermicomposting industries in order to generate background information on the commercial and practical operation of the vermicomposting sector. Lastly, two vermicomposting operations, which had been in existence for two years were selected for technical evaluation and the operators were interviewed. The processing beds and associated facilities at these establishments were extensively sampled and monitored to assess typical processing capacities and characteristics. Arising out of this background research a number of important issues were identified and these are listed below.

5.1 Identification of research issues

i) Most objective scientific literature and data relating to vermicomposting systems was derived from laboratory-based research projects, which were carried out under optimum operating conditions. The quoted performance of commercial vermicomposting systems is typically based on optimised research data. Little research had focused on large-scale systems operating under adverse weather conditions and it is highly likely that most outdoor UK vermicomposting systems are operating under sub-optimum conditions and hence, performing very poorly compared with expectations.

ii) Two major practical problems with existing vermicomposting systems were frequently cited by operators. Firstly, the poor construction and design of typical beds often led to problems with inadequate drainage and difficulty in applying waste to the beds. Secondly, many of the activities associated with operating current vermicomposting systems were perceived to be labour intensive and costly. These are activities such as applying waste to the beds and periodic harvesting of earthworms by hand. Better bed design to minimise operational problems and to enhance waste processing rates and earthworm output was considered by many to be very important. As was investigation of new methods mechanising the various processes involved with vermicomposting.

iii) No objectively verified published information relating to the performance of large-scale vermicomposting systems operating under UK conditions was available to prospective purchasers of such systems. This lack of information appeared to extend to basic operating characteristics (e.g. bed temperature, moisture and feed specifications) and performance levels such as rates of earthworm production and waste processing rates.

iv) Many existing commercial operators of worm composting systems expressed disappointment with the poor outputs from the business and the fact that higher levels of labour, time and funding were required than had been forecast. Considerable claims about the profitability of worm farming enterprises are often made by suppliers of systems but poor performance in practice appears to cast considerable doubts on the cost-effectiveness of commercial operations. No objectively verified published information relating to the financial viability of large-scale vermicomposting systems operating under UK conditions was available to prospective purchasers of such systems.

v) Large-scale vermicomposting systems operating under UK conditions tended to be almost exclusively based on the unsophisticated model of open-air, bed systems containing a bedding material and an inoculum of earthworms. Biodegradable waste is then applied to the surface of the beds and this is subsequently digested by the earthworms, decomposed and treated. Since beds are designed to be placed directly on the soil surface any bed leachate from excessive rainfall runs directly to ground. As a result of the application of biodegradable waste as a feed material for the earthworms, a key feature of these vermicomposting systems is that the earthworm population should increase over time and may be harvested and sold. However, a number of operators of such systems when interviewed expressed concern that they failed to perform as well as promised, especially in terms of earthworm production. Systems were also reported to take considerably longer than expected to become fully operational. Preliminary examination of two existing, commercial vermicomposting systems after two years of operation showed that earthworm density had increased only fourfold and this very poor level of earthworm production had serious implications for future commercial success.

vi) Until recently, large-scale vermicomposting systems operating in the UK tended to be relatively small. Typical size of bed area was 1,000 to 2,000 ² processing hundreds of tonnes of waste per year. With the development of much larger systems of the order of 10,000 m² of bed area, the waste processing capacity becomes thousands of tonnes and this compares with some smaller municipal composting facilities which need to conform to Environment Agency regulations. In particular, vermicomposting systems do not have leachate collection facilities, whereas most centralised composting operations are required to install these. No research of note has been conducted into the environmental impact of large-scale vermicomposting systems. As a result, the Environment Agency whose role is to monitor and license waste processing facilities has no technical basis on which to evaluate vermicomposting operations and very little understanding of their operation.

vii) There is no trade association or network that represents the vermicomposting or worm farming industry and which can assist in the provision of objective commercial information and research support. The vermicomposting industry is very fragmented with no means of promoting the development of the sector as a whole, in the way that the Composting Association represents the interests of large-scale composters and the Community Composting Network represents community interests.

5. 2 Aims of the project

Given the findings above there was clearly a need to generate objective information relating to both the technical and financial operation of large-scale vermicomposting systems. Two research programmes were initiated:

• An extensive technical programme of monitoring the performance, enhancement and environmental impact of experimental vermicomposting beds
• A research project which examined the financial and commercial aspects of large-scale vermicomposting.

Research Aims

• To design and install an experimental outdoor vermicomposting system, which facilitated the research programme and which incorporated design improvements compared with typical commercial systems.
• To monitor and evaluate the technical performance of the outdoor vermicomposting system.
• To investigate one simple method of enhancing the performance of an outdoor vermicomposting system, such as installing bed heating.
• To monitor and evaluate the technical performance of the outdoor vermicomposting system with bed heating.
• To monitor and evaluate the environmental impact of outdoor vermicomposting systems.
• To investigate realistic methods of mechanising aspects of the vermicomposting process, with particular regard to applying waste to the vermicomposting beds.
• To evaluate the cost-effectiveness and market potential of outdoor vermicomposting systems, with particular regard to basing the study on new technical knowledge gained and practical techniques developed during the course of the project.

1. Technical research
1. Technical research objectives
• To determine the rate of waste processing (kg/m² of bed/day) and vermicompost production over a period of 12 months for a processing system operating under normal weather and temperature conditions.
• To monitor the changes in earthworm population over a period of 12 months in order to determine potential rates of earthworm production for a processing system operating under normal weather and temperature conditions .
• To determine the time taken to full operation by monitoring the development of earthworm populations from a starter culture of 1 kg earthworms /m² of bed to establishment of working populations.
• To determine the effect of different starter culture densities (0.5 and 2.0 kg earthworms /m² of bed) on the time taken to full operation.
• To evaluate the quality of any vermicompost produced and to compare the characteristics of vermicompost to the Composting Association’s National Compost Standard.
• To monitor continuously normal bed and air temperatures over a period of 12 months.
• To install a controllable method of bed heating and investigate the extent to which bed temperature can be regulated.
• To investigate the effect of minimal bed heating on earthworm populations and waste processing rate and compare this with the unheated beds operating under normal weather and temperature conditions.
• To investigate the environmental impact of the vermicomposting operation in particular in relation to the quantity and quality of leachate produced and the emission of greenhouse gases.
• To investigate mechanical methods of applying waste to the earthworm processing beds.

6.2 Experimental vermicomposting operation and researchmethodology

The technical research carried out as part of the vermicomposting project began with a 6 month setting up and bed construction period followed by a 12 month monitoring and experimental period. Details of the experimental trials that were undertaken can be found in the next section.

The setting up period was used to construct and commission eight individual experimental blocks of beds. The eight blocks of beds were each sub-divided into 5 individual beds. The blocks of beds were constructed out of breeze blocks with a damp-proof course membrane protruding (5 cm) out from the breeze block at the top of the beds to help prevent earthworm migration. Each individual bed was

1.5 metres wide by 6.6 metres long and beds were around 1 metre deep asshown in Figure 6. The dimensions of each Block were 1.5m wide by 25m long. Total bed area available for research was 400 m². Each bed was filled with composted horse manure/wood shavings bedding material (approximately 0.5 m deep) to contain the earthworm populations.

Figure 6 Bed design

Each block contained a leachate drainage and collection system, which allowed the environmental impact of leachate from the operation to be assessed. Leachate from each bed was allowed to collect in a separate holding (200 litres) for sampling (see Figure 7), before being pumped into a central collection tank (1500 litres).

Beds were unheated apart from one complete block of five beds which was heated (Block 5). Accurately controlled temperatures for each bed were achieved using individual electric heating cables and thermostats located in the bedding material. Thermocouples and data loggers continuously recorded bed and air temperatures to ensure that composting rates and earthworm populations were linked to prevailing environmental conditions. The location of each probe in the selected beds are shown in Appendix 1 and illustrated in Figure 8. No rainfall measurements were taken at the experimental site because of the close location of the Environment Agency rainfall monitoring site at Hook, which was 2 miles away.

Figure 7 Installation of a leachate holding tank