The Real Know How

Biogas System

This is the best small farm biogas system video I’ve seen so far.

As with many other useful technologies, we don’t hear much about biogas in this part of the world while it’s being rolled out extensively in the developing world and is a technology that could be universally useful.

Here a small farmer, Edward, in Uganda shows us his underground biogas system. It’s actually pretty elaborate and if maintained properly, he says should last about 70 years.

Edward keeps cows and sheep but seems to just use the cow’s dung and urine for the biogas system. He says that he mixes one part dung and one part water or urine and lets this mixture drop into a digester.

From the digester the digested solids and gas are separated in an underground dome (7 feet deep and 14 feet across).

From there the gas is piped into the farm house to the stove (which looked pretty much like a normal propane stove to me) and to fuel one gas lamp (which I found produced very dim light, but before they probably had no light at night or used kerosene lamps, so for them it’s a huge improvement).

The digested solids, now good for use as fertilizer/compost, drain out into a kind of pond area.

Edward notes that the covers to all of the biogas system access points are very heavy concrete to prevent children or vandals from fiddling around with them and either falling into the dome to their deaths or letting the precious biogas escape.

As he shows us his biogas system, Edward also points out his 10,000 liter rain water collection cistern.

Note that this system only uses waste from livestock but that other systems would also use humanure.

John Njendahayo, a Ugandan engineer, explains more about this kind of domed biogas system. Cue the following video to 4:25 where he starts to talk about the system itself. He covers the sizing of the systems, the relationship of input to output and what you can run on the biogas (including a modified paraffin fridge).

The system uses dome shapes so that none of the gas gets trapped in corners as it would in a rectangular digester. He notes that the reason for burying the digesters is to keep the temperature constant for the bacteria.

Here he talks about being able to sell the compost the digester produces as fertilizer and about needing to clear the pipes of condensation and how the gas is piped into the house.