Page last updated 30/08/2018
The future of anaerobic digestion (AD) technology in LDCs lies in converting food wastes and food
processing residues into energy and compost. In South Asia, the use of AD fed with cattle dung is less
appealing. The number of cattle in countries such as India and Nepal is reducing. Farmers prefer using
tractors to bullocks for transport and farm work. In urban areas, the numbers of wandering cattle on roads
is reduced because the traffic is growing rapidly. The land value in urban areas means that the gardens in
which animals can stay are disappearing for building sites. A further factor is the migration of young
people, who usually look after animals, to work and earn money in other places.
In Nepal, reports suggest that many plants built to use cattle dung as a feed material are not now being
used, as a result of these changes. Some people have realised that they can feed their plant with the food
wastes they used to give to the animals and still obtain gas for cooking. In the developed world many
anaerobic digestion systems have been built to use the organic fraction of municipal solid wastes (OFMSW),
but these systems are too large, complicated and expensive to use widely in LDCs.
Research and Development is required to find low cost approaches to making biogas plants that can use
OFMSW and also local food wastes and food processing residues to generate energy and compost. There
are two challenges:
making digesters that are big enough to process larger quantities of material
finding low cost ways to pre-process raw organic matter.
There are many groups in India offering AD systems to process OFMSW and food processing residues, but
these systems are not considered economic. The Nisargruna system was developed by BARC (Bhabha
Atomic Research Centre) in Mumbai. It uses a pulveriser to break up the organic material. The main
digester is a large KVIC drum plant. A report that included an economic analysis suggests that the system
is cost-effective, although companies that have licensed this system are struggling to make it successful.
Biotech Ltd, based in Trivandrum in South India, use predigesters made from glass-fibre reinforced plastic
(grp). Their older systems used KVIC drum digesters, but later systems use main digesters also made from
grp. The economics of these systems is marginal.
The success of the domestic systems made from masonry suggests that larger systems made in the same
way would be cheaper to build. Large Deenbandhu plants have been made by KIST in Rwanda and also
BTAL Ltd in Ghana. Kingdom Bioenergy Ltd designed a large dome plant, which was constructed by SKG
Sangha for CMC (Christian Medical College) in Vellore, South India to use in their Recycling Centre. The
capital cost was estimated to be 1/3 less than for a similar KVIC plant. New research is needed to find a
way to make large concrete dome plants. It is hoped to test the use of inflatable moulds over which
concrete domes can be cast.
The use of pulverisers to preprocess organic materials works well, but these machines are expensive to
install and operate. They also use energy to run. A predigester uses microbial action (hydrolysis) to remove
digestible matter, which dissolves in the liquor (the contents of a digester), from indigestible matter, such
as lignin. If the liquor is recycled, by passing it from the main digester to the predigester and back again,
the indigestible matter is left in the predigester and can be removed from there. It can then be turned into
compost. Since the dissolved matter contains obnoxious smelling VFAs which are converted into biogas, the
remaining compost is almost odour free.
If liquor flows through solid matter, is is called a “leach bed”. Research has shown that leach beds work
better when the liquor flows from the bottom (upward flow or counter flow). Research is being done on
CFLB (counter-flow leach bed) digesters.
More information on biogas technology in developing countries can be found in “Small-scale, Rural Biogas
Programmes” and “Running a Biogas Programme”.
Future of Biogas Technology
Biotech Ltd digester
Newer Biotech Ltd
KIST dome digester
Large dome built for
Mailhem group in Pune