For some years now we have been looking at minimising our energy consumption, and at alternative forms of energy creation in order to produce the energy we need. As we have animal systems in place here at PRI Sunshine Coast, we have a fair bit of manure on the property. As well as animal manure, we also have waterless (composting) toilets, so humanure is another resource on our property waiting to be used more efficiently than we currently are.  After a lot of research over the past few years, Tom decided that a Biogas system would be the best way to go for us.

Biogas is extracted from many raw (organic) materials in nature besides human and animal manure: leaves, twigs, grasses, garbage and agricultural and industrial wastes with an organic content greater than 2%.  Biogas can be used for cooking, lighting (gas lamps), to generate electricity, as fuel to operate cars and other machinery and other energy needs. Biogas is a form of energy produced by anaerobic digestion (the decomposition of constituents of biodegradable matter in an oxygen-free environment). It is a mixture of gases, mainly carbon dioxide and methane. It consist of around 55-65% Methane, 30-35% carbon dioxide, 1-5% water vapour, 0-3% hydrogen sulphide and 0-1% hydrogen. In order to produce Biogas, we need a bio-digester.

A bio-digester is a structure that facilitates the decomposition of organic materials such as manure, to produce methane gas . Bio-digesters can be made of concrete, brick, metal or polyethylene plastic. To keep the footprint as low as possible, but still ensuring we have a unit which is as corrosion resistant as possible, we have elected to build the bio-digester from fired bricks (making a double wall) and concrete.

The bio-digester will have an input area for manure and other organic materials, a sealed chamber which facilitates the anaerobic process, and an output area for effluent that has passed through the bio-digester. From the sealed chamber Biogas will be pressure fed into holding tanks for use. The effluent can be further composted and used on the gardens.

Advantages of bio-digesters:

• Reduces organic content of waste materials by 30-50% and produces a stabilised liquid effluent.
• Provides a sanitary way for disposal and/or processing of human and animal wastes.
• Produces a large amount of methane gas which can be stored at ambient temperature.
• Produces free flowing, almost clear liquid odourless effluent, which can be added to compost or used as fertiliser.
• Weed seeds are destroyed and pathogens are either destroyed or greatly reduced in number.
• Rodents and flies are not attracted to the end product of the process. Access of pests and vermin to wastes is limited.
• Closed cycle process which eliminates the need for external energy sources.

It is important that proper operating conditions are maintained in the digester for optimum gas production and that the effluent is handled correctly to eliminate potential water pollution problems.

A great number of developing countries are now taking initiatives to install bio-digesters, since they eliminate a number of escalating problems these countries are experiencing. Firewood and other energy sources such as kerosene are becoming rare and expensive in these countries. There are also problems with sanitising toilet areas and indoor air pollution through kerosene lamps and wood fired stoves. Biogas solves all these problems, plus they get fertiliser for their crops as well, thus reducing or even stopping the need for them to buy it in.

Even though developing countries are increasingly supporting the building of bio-digesters, they remain rare in developed countries. There are some smaller ones available for sale, or you can find plans to build a small one yourself, for urban situations. The principles remain the same as for larger ones. If you are someone who would like to learn by actually making one, PRI Sunshine Coast is building a bio-digester this year, spread over 3 courses:

Week 1 - Mon 18 - Fri 22 March 2013: Planning and design of the bio-digester, putting in footings

Week 2 - Mon 27 - Fri 31 May 2013: Pouring the cement floor and building the double brick walls, building the inlet and outlet

Week 3 - Mon 26 - Fri 30 August 2013: Finishing the building and connecting the outlets, testing connections

You can do one of the courses or do them all, investment is $795 for a one week course, which includes camping accommodation (byo tent) and all meals. Come and join us for this exciting project and learn to make Biogas! Courses are capped at 15 students. Click here for links to online booking pages.

Resources: Guyana Energy Agency: Bio-Digester information and construction manual for small farmers; The National Bio-Digester programme in Cambodia