I saw a thing that was built in India (no shortage of raw materials there either). They had a pit that they filled with manure and pond water. A large dome made of brass fit over this, and slid down into the circular sistern of scum. As the bacteria produce methane under the dome, the wieght of the dome compressed the gas, which was fed out the top of the dome with a flexible hose. They used the gas for cooking and lighting. 
Just wanted to say hi and welcome!MVchickens said:Hi there. Im new here but have some experience and knowledge with methane digesters. Turns out it is not feasible to build a small scale digester, I built and studied everything from table-top models to larger models. I am still working on some projects but that will come later on as I go onto college to study chemical engineering.
