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The Worm Research Centre was set up to provide objective information about the use of worms to the benefit of the environment ...
   

 

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Steve Ross-Smith is the founder of the Worm Research Centre. He has a wealth of environmental and farming experience having run an organic farm since 1986. His many practical skills bring originality and efficiency to all the projects undertaken here at the Centre. He is an innovative thinker and, recognising the enormous gaps in information regarding small scale composting and vermiculture, has been tackling the problem head on. Using his skills in engineering, design and technology (HND Distinctions) many new ideas are now being researched and developed to create workable solutions to the enormous organic waste stream problems faced by small commercial businesses. Please contact us if you think there is something we can help you with. The Centre are the North of England key Compost Doctors working with CRN UK (Community Recycling Network UK) and the CCN (Community Composting Network), to support businesses in improving their environmental resource efficiency. See the relevant tab for more information on how we can support you.

The WRC in Action :

Seagull Recycling Project

Growing Heap

VERMICOMPOSTING
THE VERMICOMPOSTING INDUSTRY

VERMICOMPOSTING AT THE WORM RESEARCH CENTRE

The composting sector of the UK waste industry is rapidly developing due to the need to restrict the landfilling of biodegradable wastes in favour of promoting more sustainable waste management practices. Composting is now seen as a vital element in the Government's waste strategy and a number of key targets have been set, which are designed to increase the capacity of the large-scale and domestic composting sectors. Government predictions that a three or four fold increase in the size of the composting industry will be needed to cope with the implementation of the European Landfill Directive is likely to promote the development of a wide range of composting processes and technologies. The key to achieving the European targets will be increased diversity. Vermicomposting operations, which employ many millions of earthworms as the main waste-processing agent, can have advantages over traditional composting methods. Vermicomposting has been adopted worldwide, often with great success where conditions are suitable and could undoubtedly play a significant role in the developing composting industry. As with traditional composting, vermicomposting can be used for home composting and also applied on a large-scale at centralised sites. However, little published information is available on the technical and commercial viability of large-scale vermicomposting systems, particularly when operating under UK conditions.



While it is clear that vermicomposting is being very widely practiced in the UK, there is very little data available on the nature of the vermicomposting industry or on the extent of domestic and large-scale adoption of the technique. Recent research into the large-scale vermicomposting industry carried out by the Open University and the Worm Research Centre, suggests that there are at least several hundred large-scale vermicomposting operations in the UK. There are at least six companies engaged in selling and setting up large-scale outdoor worm composting (or worm farming) systems in the UK. The typical size of modular units sold is 1,000 m2 and each costs around 15,000 to buy and install. Larger units have also been commissioned (10,000 m2) and these would be comparable in waste processing capacity to many medium sized municipal composting facilities. The Composting Association's survey of the composting sector carried out in 2000, suggested that around 58% of centralised composting facilities were medium sized, processing around 5,000 tonnes of waste or less per year. In comparison with municipal composting facilities, vermicomposting tends to be carried out in rural locations mainly by farmers needing to diversify. Informal feedback from purchasers of outdoor vermicomposting systems suggests that there is a very high degree of dissatisfaction with the performance of these systems. Compared with other branches of composting, there has been little reliable and objective information available to prospective or actual purchasers of large-scale vermicomposting systems. Consequently, up until now it has been almost impossible to evaluate the technical and commercial performance of vermicomposting systems, which are designed to operate outdoors in variable climatic conditions.



At a time when the market for all composting systems is rapidly increasing, there is increasing scepticism that these outdoor systems perform as well as devotees would claim and one key reason for this is the low ambient temperatures under which they operate for most of the year. The Worm Research Centre (WRC) in collaboration with the Open University has been undertaking a programme of trials over the last 10 years aimed at evaluating large-scale vermicomposting and, more importantly, to improve the performance and cost-effectiveness of the process. The trials have also addressed the uncertainty about the environmental impact of vermicomposting systems, in particular leachate control, which has serious waste licensing implications. In addition to determining essential waste processing rates and evaluating outputs, independent research by WRC has also investigated cost-effective methods of mechanising these systems in order to reduce labour charges and to improve their economic performance through improved bed design. In particular, many existing operators have identified the need to introduce mechanised waste loading measures and earthworm harvesting/sorting devices. Some operators have already developed rudimentary machines and improvements and refinements arising from these prototypes need to be evaluated on a continuing basis. Current work at WRC involves combining vermicomposting with in-vessel composting systems to accelerate waste processing rates and to extend the types of wastes that can be processed.

VERMICOMPOSTING

Vermicomposting, is considered to be a branch of composting but one which relies on the use of selected species of earthworms, working with microorganisms, to achieve accelerated decomposition. The main advantages of vermicomposting compared to composting is the potential for producing a comparatively nutrient-rich compost. What makes this system really work is the use of a specially selected species of earthworms that maximise the level of discomposure and transform organic wastes into high-grade compost. Traditional composting is both labour and machinery intensive whereas with vermicomposting it is the earthworms that fragment, mix and help aerate the waste. 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 25C), compared with composting, where pile temperatures can exceed 70C. 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 35C, 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 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 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 depend on many factors such as the system being used, the nature of the wastes and the ratio of earthworms to waste. 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 high densities of earthworms. New layers of waste are applied to beds on a regular basis and the earthworms move upwards 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. A number of factors can affect the life cycle of earthworms and hence determine vermicompost output and the number of earthworms that are produced. In particular, temperature, moisture, waste characteristics and earthworm density are all important. Research carried out at the Worm Research Centre has proved that maintaining vermicomposting systems at a constant temperature of around 20C provide maximum vermicompost output and ensure maximum earthworm growth and reproduction. The new bed system (WormPod) has incorporated all the advantages discovered in the most recent research. In UK conditions, if vermicomposting is carried out in unheated beds significantly lower outputs can be expected. Earthworms prefer material that is fairly damp, in the range 70 - 90% moisture. So depending on the waste stream type there is sometimes a need to add more moisture to the waste material before and during vermicomposting than with composting. 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, brewery waste, mixed household waste, garden and vegetable wastes and many other biodegradable materials can be 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 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. Outputs from vermicomposting

VERMICOMPOST

Vermicompost is the processed material that is egested from earthworms as casts. As earthworms feed on the rich diet of organic matter and microorganisms in waste, this ingested material is finely ground by the earthworms gut. This helps microorganisms decompose the organic matter and stimulates mineralization of complex compounds into simple nutrients, easily utilized by plants. At the same time the organic matter and microbial cells are glued together by the secretions from the earthworms gut forming casts with excellent physical characteristics. The amount of time that the waste spends in the earthworm gut is only a few hours and therefore the egested material is very microbially active and continues to decompose and mature in the form of vermicompost. The characteristics of the feed material or waste will often determine the characteristics of the final vermicompost. However, compared with windrow composts, vermicomposts are likely to contain higher levels of plant available nitrogen because vermicomposting temperatures and nitrogen losses are typically much lower. Although it is known that some species can selectively accumulate and concentrate particular heavy metals from waste 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 plant growth mixes (10 - 20%) give excellent results.