Waste disposal typically involves contaminating fresh water and sea water ecosystems, but in many areas of the world sanitation is not implemented. Both of these scenarios lend themselves to the contamination of the environment due to untreated pathogens mixing with nature, on a large and local scale respectively. Instead of damaging our planet the surplus of untreated human waste can be utilised by either reducing the matter to compost that will go into fertilising the land, or by being processed into as to create Biogas. Composting toilets are dry wastage systems that process waste aerobically (in open air, not sealed off) either on or off site, usually using sawdust, coconut coir or peat moss to facilitate the aerobic process, liquid absorption and odour mitigation. Biogas is created from the anaerobic (sealed off, no air) digestion of organic material by micro-organisms. The result is a methane rich gas that can be used as fuel, digestate and a source of nutrients to be used as fertiliser. It makes the most out of feedstock such as food and drink waste, processing residues, agricultural residues, crops and sewage sludge by using it as a renewable energy source. Biogas is a mixture of 60% methane and 40% carbon dioxide, which can be used to create heat or electricity separately or combined and a Biomethane injection which can be put into a gas grid and used for transport.
http://www.biogas-info.co.uk/about/feedstocks/