System Template 5: Biogas System

Considerations

This system is best suited to rural and peri-urban areas where there is appropriate space, a regular source of organic substrate for the Biogas Reactor and a use for the digestate and Biogas.

The reactor itself can be built underground (e.g., under agricultural land, and in some cases roads) and, therefore, does not require a lot of space. Although a reactor may be feasible in a dense urban area, proper Sludge management is crucial and needs specific attention. Because the digestate production is continuous, there must be provisions made for year-round use and/or transport away from the site.

The Biogas Reactor can function with a large range of inputs and is especially suitable where a constant source of animal manure is available, or where market and kitchen waste is abundant. On farms, for example, large quantities of Biogas can be produced if animal manure is co-digested with the Blackwater, whereas significant gas production would not be achieved from human Excreta alone. Wood material or straw are difficult to degrade and should be avoided in the substrate.

Achieving a good balance between Excreta (both human and animal), organic waste and water can take some time, though the system is generally forgiving. However, care should be taken not to overload the system with either too many solids or too much liquid (e.g., Greywater should not be added into the Biogas Reactor as it substantially reduces the hydraulic retention time).

Most types of Dry Cleansing Materials and Organics can be discharged into the Biogas Reactor, although to accelerate digestion and ensure even reactions within the tank, large items should be broken or cut into small pieces.

Guidelines for the safe use of Sludge have been published by the World Health Organization (WHO) and are referenced on the relevant technology information sheets.