There are a very wide range of uses for biogas. It can be used both as a fuel and as a raw material for the production of a wide range of most if not all organic compounds, depending on the sequence of reactions and degree of polymerization carried out.
Here is a list of the main uses for biogas:
1. For direct combustion at its point of production for heat
2. For direct combustion at its point of production in an (reciprocating) engine for the production of electrical power
3. For both 1. and 2. above, simultaneously which means that far more of the power is usefully used, because an engine will never be 100% efficient and always produce heat as hot water as a by-product. Biogas use projects, which provide both power and heat, are generally called CHP schemes (Combined Heat and Power).
4. As in 2. or 3. above but using a turbine or microturbine, instead of an "engine"
5. For use as a substitute for CNG (Compressed Natural Gas) for use at the point of production, potentially to run vehicles after use of readily available conversion kits on standard petrol driven vehicles. The biogas will require scrubbing or other cleaning before this can be done but such equipment is readily available.
6. Once CNG is produced, this can also be on a technical basis pumped into a regional natural gas mains distribution system. However, at the time of writing the operator of the natural gas mains may not permit this as a matter of policy. In many nations moves will be made over the next few years to (at government level) allow distributed biogas sources to replace natural gas, subject to stringent quality control on the biogas introduced into the public gas mains
7. Biogas can be used to produce bio-diesel after first processing as in 5., and then carrying out a sequence of reactions. A very many biocrop based Anaerobic Digestion Plants have been built with this being their primary purpose and this was of all the uses of biogas, the first to be used in large numbers in the western nations.
8. In the Eastern nations biogas is also used as a direct fuel for domestic cooking, and is generated from small buried digestors which use domestic sewage and also at times night soil.
The world is only just beginning to wake up to the huge importance of renewable sustainable biogas in the post fossil-fuel world. To be one of the people who gets in on this early, go to the biogas digester web site. Biogas is produced by the anaerobic digestion process - which you will also need to know about.