As part of our judging process earlier this year, David Fulford had the chance to catch up with BIOTECH Ltd, in Kerala, India. Their award-winning work is building domestic, commercial and municipal biogas plants. BIOTECH has grown a lot since winning in 2007 and as a result of their ongoing research and development, they’ve now developed two innovations which takes them closer to meeting the large demand for their biogas systems.
The need for biogas is massive in urban areas; food waste from markets, for example, is a huge problem. Animals often break open refuse bags and municipal councils and households are looking for a good way to deal with a stinky and unhygienic problem.
A biogas plant works by taking food waste or even sewage and letting microbes digest it in a sealed container until a gas is produced. This gas can then be then burnt safely and used for cooking, lighting or running engines. If you’d like a more in-depth explanation of how it works, we’ve got great technical pages .
BIOTECH were doing well when they won an award, but now their trade is really soaring. They’ve sold 22,000 domestic plants 270 institutional plants and 62 waste-to-electricity plants – councils love these as they can use the electricity to light streets in the early mornings and evenings. This mobile demonstration unit is in constant demand in towns and villages:
Changing the material that domestic plants are made from has made a huge difference. David Fulford reports on why BIOTECH took the step to move from using glass reinforced plastic (grp) to High Density Polyethene (HDPE):
“The problem with the original domestic systems is that the demand is growing rapidly, but the production capacity is limited. Biotech’s grp manufacturing unit can only make one domestic plant a day for each set of moulds. In order to meet the increasing demand, they worked with Capital Polymers of Thiruvananthapuram, Kerala to design and make dies for a domestic biogas plant made from spun HDPE. One stainless steel die can be used to make 20 to 25 units a day. At present they have 3 dies in use and have installed 400 of these systems. Biotech Ltd has moved from a cottage industry to a factory production line. They are now selling between 5 and 10 units a day and demand is still increasing.”
For their larger systems BIOTECH have also developed a modular two stage digestion system made from grp which are much quicker to install and is much more efficient than their original designs. This system is still under development.
David, who had the chance to see one of these in action while he was visiting, explains how they work:
“The system is designed to work mainly with gravity, although there is one pump to recycle the effluent liquid to the feed tank. The food waste - kitchen peelings, leftovers and cooking water - is put in the feed hopper of one of several pre-digesters. Inside the vessel is a screen that prevents the solid material from continuing through the system. The liquid from the outlet of the digester is pumped into a storage tank, from which it flows slowly through the pre-digester. The microbes in the liquid dissolve out digestible matter, which is flushed into the main digester tanks.
Once a predigester is filled with solid material, which takes several weeks (up to three months) the next one is used. The full pre-digester is drained of liquid and the solid matter removed by hand. The food materials are not crushed or ground, but the microbes dissolve any digestible matter over time. The material that is left has little smell and forms good quality compost quickly. Both the solid compost and the excess liquor can be sold as biofertiliser and there is a good market in places such as Kochi for farmers and gardeners.
The main digester tanks are designed to be high-rate digesters. There are usually two or more main digester tanks connected in series. Biogas is generated in the pre and main digesters and taken from the top of the containers through pipes to a gas storage system. The gas is cleaned of hydrogen sulphide and stored in flexible synthetic bags, enclosed in a cylindrical tank. A system of counterbalances and weights controls the gas pressure in the bags. The gas is either used for cooking in kitchens or to run an engine to generate electricity for lighting.”
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