Sewage disposal from prisons is a major health hazard for both the prison and the surrounding area. Prisons in Rwanda, as in many other parts of Africa, also impact the surrounding area through their demand for fuelwood for cooking.
The Kigali Institute of Science, Technology and Management (KIST), has developed and installed large-scale biogas plants in prisons in Rwanda to treat toilet wastes and generate biogas for cooking. Each prison is supplied with a linked series of underground biogas digesters, in which the waste decomposes to produce biogas. After this treatment, the bio-effluent is safe to be used as fertiliser for production of crops and fuelwood.
Using biogas digesters to manage animal or human sewage is not a new idea, but in Rwanda has been applied on an enormous scale, and with great success. Managing sewage improves hygiene and sanitation and reduces smells. The biogas produced is used for cooking and halves the demand for fuelwood, cutting costs and reducing pressure on local wood resources. KIST staff manage the construction of the biogas plants, and provide on-the-job training to both civilian technicians and prisoners.
The first prison biogas plant started operation in 2001 and by 2011 plants were in operation in 10 prisons. The largest has a series of twelve individual digesters, each 100 m3 in volume.