BIOGAS DIGESTER

Biogas Digester
Name Biogas digester (various other names for this: biogas toilets, bio-digesters, 3 + 1 systems)

Type of technology Treatment technology or Collection and Treatment technology (dry or low water use sanitation system for human excrements and animal waste; decentralised systems at household level; blackwater treatment)Click Here!

Description The biogas digester is an onsite facility, in which organic material is broken down under anaerobic conditions (without oxygen). This process produces biogas (consisting about two thirds (by volume) of methane), which can be used for cooking and lighting. In some countries, the biogas digester is commonly introduced for households with husbandry activities, to generate energy (biogas), to cover a daily need (the households often need additional energy sources, especially in colder seasons). But it is also possible to use this technology for domestic wastewater only, especially when the user prefers a low flush toilet, and has other competitive energy sources.
Biogas digesters operate best in warm climates, as high temperatures assure a sufficient production of biogas and destruction of pathogens.
The effluent from the reactor, a dark slurry, is a nutrient-rich fertilizer for agriculture and aquaculture, due to conservation of nitrogen during the anaerobic process. To assure hygienic quality, especially when mixing human wastes, a long retention time (>60 days) should be used, and/or a post treatment step (e.g. wetlands, drain fields). This technology can be used to replace existing septic tanks, by integrating the septic tanks as an inlet chamber.Click Here!

There are different designs available, especially in the leading countries for household biogas technology, namely China, India and Nepal. The size ranges commonly from 6 to 10 m3. Larger biogas digesters serving several households or a whole community are also feasible (up to 50 m3). Biogas digesters are usually built underground to protect them from temperature variations and also to prevent accidental damage. Hence, they use very little space.Picture
Operation and Maintenance Operational requirements are low, due to automatic influent feeding and mixing of animal and toilets wastes
Limited operator skill required (but household members need training to understand the system)
Needs checking for gas leaks, especially distribution pipes
Desludging occasionally necessary
Advantages Provides source of biogas, this results in less dependence on fossil fuels, which may not be readily available to households
Improves the household overall sanitation by treating blackwater, organic wastes, and manure
Effluent is a nutrient rich fertilizer, and more hygienic than untreated human waste
Less frequent/ almost no desludging required compared to septic tanks
Can be built locally
Through airtight design, no leakages will occur Disadvantages Requires good design Click Here!
Skilled, trained labour is required for the construction of the biogas digester
Requires availability of animal excrements for optimal biogas production
There are sometimes cultural prejudices against using gas from human waste
Relative costs (to similar techniques) Medium capital costs
High revenue by saving of energy costs and higher agricultural yields

Suitable for SIDS and low income coastal countries? Suitable for rural areas, especially when families also have animal waste, and where there is a need for gas for cooking
High ambient temperatures increase biogas production.
More about this technology The Bio Digester and the Bio Digester Septic Tank Click Here!