Every village in China has one, but Biodigesters are an unfashionable energy source — now they may be due for a comeback.
As a system for getting energy from organic waste Biodigesters have two main components that people prefer not to discuss: human waste and methane. But they can be a great source of alternative energy, particularly in densely populated areas like high rise apartments but also in rural environments, or anywhere livestock is housed.
As long as you have a good supply of water, the other main ingredient, you should be able to harvest stored energy as solids that are removed after the digestion make great fertilizer.
The cost of a large biodigester serving say an apartment block can be $250,000 or more depending on the size. But you can repay that within 5-10 years in energy savings. And having all your energy needs produced from waste is a big plus since it can cost up to $200 per person per year to deal with household organic waste and $200 per cow per year on a farm.
For those of us who are looking into a digester instead of composting there is a great article on Biodigester Design and Construction from Rural Costa Rica.com shows how to build a personal digester as well as pointers on what is required daily. It is a viable option for personal or city community as well as a farm/ranch energy source.
Another plus is that even the solids have uses. From fertilizer for your crops, bedding for livestock, to plant pots, and now even flooring. Researchers at Michigan State University and the U.S.Department of Agriculture think that floors made from manure are the next big step. According to a story on Discovery Channel flooring made from these solids match or beat the quality of those made from sawdust.