MCH biogas plant ready for commissioning

By C. Maya

THIRUVANANTHAPURAM, NOV. 2. A nightsoil-based biogas plant, which is capable of disposing of sewage in a highly energy-efficient and environment-friendly manner, is ready for commissioning in the Medical College in the city.

Two plants, each of 35 cubic metre capacity, have been set up by the Agency for Non Conventional Energy and Rural Technology (Anert), one near the SAT and another near the Medical College canteen. The gas collecting points are connected to a 10 KW dual fuel engine, which can generate 50 units of electricity a day, enough for uninterrupted use for five or six hours.

The capacity of the plant has been fixed at 35 cubic metres on the assumption that at least 1,500 people would be using the toilets on the MCH campus, says Mr. J. M. Jayamohan, Technical Officer, who is in charge of the project.

At present, the plant near SAT connects about 60 per cent of the sewage lines on the SAT campus, while the other has been connected to all the sewage lines in MCH. A third plant would be required if all of the sewage in MCH has to be converted to biogas.

There is no need for any fears that there might be foul smell or any kind of pollution, says Mr. Jayamohan. The biogas plant at MCH is buried in the earth, with just two gas collection points (pipes) extending outside. The slurry which comes out is clean and mosquitoes cannot breed in it, he says.

The total project cost, including the 10 KW engine, was Rs. 9.75 lakhs. The project enjoys the subsidy of the Ministry of Non- conventional Energy Sources and the Anert, to the tune of Rs. 6 lakhs.

The technology could be used to improve sanitation in slum areas by connecting all sewage lines to biogas plants, say Anert officials.

Using the same technology, the Anert had set up a biogas plant of 25 cubic metre capacity on the campus of the Hindustan Latex last year.

The unit has been using kitchen and canteen wastes as raw material to produce biogas, the equivalent of two LPG cylinders a day.

While biogas plants using cow dung as the base material are quite popular, the technology of producing biogas by treating human waste is one which has been successfully modified and tested out by the Anert in the State.

In the last one year, the Anert had commissioned 25 community or institutional biogas plants, all of which use either kitchen/canteen waste or nightsoil as the raw material. The biogas thus generated is being used by institutions to produce electricity for their in-house requirement and as a substitute or supplement for fuel.

"This technology not only helps us generate energy from waste which pollutes the environment, but also improves sanitation facilities," says Mr. Subhakar, the head of the R&D division of Anert.

The technology is based on anaerobic digestion. Sewage lines are connected to an air-tight digester, where due to microbial action, bacterial growth is stimulated. As there is no oxygen inside, the biological decomposition of the biomass takes place to sustain the bacteria.

The hydraulic retention time or the total time required for the complete release of gas from slurry is 14 to 18 days.

Large amounts of methane and some carbon dioxide thus produced is collected in a gas holder, from where it is directed to burners or pipes. Biogas is a clean fuel, it does not cause pollution and is considered better than natural gas or LPG because it does not contain sulphur.

When directed to a dual fuel engine, it can generate electricity.

As methane and carbon dioxide destroy all pathogenic organisms, the treated slurry which comes out is not only clean and environmentally safe, it is also a nitrogen-enriched fertilizer for plants.

The Anert has had to modify the technology to suit Kerala conditions, where people are known to use a lot of water in their toilets. The technology had to be so modified that excess water was removed before the slurry entered the anaerobic digester.

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