Is it just me, or is there nothing quite like a casual sight-seeing venture yielding a lesson in biogas and anaerobic digestion? I mean, don’t get me wrong; there’s plenty of value in a pretty vista– what was in today’s case a view of Tamil Nadu’s agricultural smorgasbord and a breathtaking, silky and sleek waterfall. But despite the landscape, I was left most impressed by an ingenious contraption we happened upon while passing through the family-owned spice plantation between our parking space and the scenic spot.
This is a gobar gas plant. It converts the dung of the four cows owned by this family (who graciously let guests tromp through their yard to get to the view point) into methane, which they then use for cooking fuel and to light lamps.
The diagram above roughly illustrates this structure’s layout, and I can do no better than this description of its function:
First a pit is dug, perhaps ten feet deep. Then a water-tight cement cylinder (with brick or gravel) is constructed. Next, a wall is built across the middle, extending up from the bottom, not quite to the top. Intake and outgo pipes are installed. The whole unit is water-tight.
The manure is mixed with water in the intake basin to make a slurry, which then goes down the pipe to the bottom of the left side. This side of the cylinder gradually fills and overflows to the right side. Meanwhile, the whole mass bubbles methane up to the top. It collects under the large metal bell-like cover. The gas builds pressure, and can be taken off through a rubber tube to a gas stove in a kitchen.
When both sides of the cylinder are full, the effluent flows out from the bottom of the right side each time more raw manure is added to the left. What comes out on the right is of more value as fertilizer than the raw manure. So the methane is an added byproduct literally “something for nothing”, once the capital expense of the construction is paid.
India is a leader in gobar gas technology, and there are hundreds of thousands of gobar gas plants in India.
Maybe I’m the last person who didn’t know that cow dung could be altered in such a way, and on such a small scale, to create enough cooking fuel for an entire household. But if I am, consider me also among the most amazed. You can call me a tenderfoot or an insulated suburbanite, but I’ve seen some technology in my time as a 21st century young adult and no laser light show or SteveJobsPresents! toy has impressed me as much as this piece of proven mechanics.
I mean… cow dung! into gas!