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A bio-latrine is a low maintenance system comprising a combination of a toilet and a bio-digester unit. It can be constructed using local materials and requires no machinery or fuel input other than human waste.
In developing countries bio-latrines can vary dramatically in size, from household level to a system which serves a small community. The biogas generated can be used for cooking, lighting, refrigeration, heating and electricity production purposes or even as a substitute to petrol and diesel in engines.
How does the system work?
Many different types of the bio-latrines components exist but all are built to minimise the risk of gas leakage. This is most likely to occur on comers and joints; therefore a cylindrical or halfsphere shape tends to be favoured. The three most common designs of plant are fixed dome, floating drum and flexible bag digesters which are often adapted to suit local situations and requirements.
Regardless of the bio-latrine unit design, the human waste from the toilet or toilet block is fed via a pipe into the bio-digester chamber of the biogas unit which should be at least 0.3 m below the floor of the toilet to prevent flooding.
Once the waste material has entered the bio-digester chamber a number of biological processes take place, resulting in the formation of fatty acids such as acetic acid, which will be broken down further via anaerobic fermentation. This encourages the waste to decompose into a mixture of slurry and biogas, primarily comprised of methane. The fermentation process requires the presence of a dark and air-free environment with temperature of 30-40° C or 45-60°C. Therefore, this is most easily achieved in tropical or sub-tropical countries.
Biogas collects in the upper part of the bio-digester chamber and passes through an outlet pipe at the top of the dome either to a storage facility or through pipes directly to the stoves and other appliances where it is required, whilst the slurry can be accessed by an outlet either directly or via in more chambers.
Important factors
For the bio-latrine system to work, a tested and proven design must be built by professional trained and skilled individuals who must also ensure that the construction details are followed carefully. For example, the bio-digester chamber of a...