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. |
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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.
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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 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 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 20°C 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.
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