The Biogas System


Biogas has been selected by the Government of Ghana as a priority technology to be implemented as part of the SE4ALL CAP, with the objective “To improve access to modern energy for productive uses”. The specific activity formulated within the SE4ALL CAP is “to conduct a feasibility study to establish institutional biogas systems for 200 boarding schools, hospitals and prisons”. The intended biogas systems (biogas digester) will decompose human faecal waste into biogas which will be used for cooking purposes.

In most cases the effluent needs to be pre-treated before being used for water and fertilizing purposes, to be sure the pathogens are sufficiently destroyed and the water quality meets EPA standards. The biogas needs to be dehydrated to be used in specific stoves, to prevent corrosion problems. The retention time (the time the feedstock resides in the digester) of a biogas digester treating mainly faecal waste and with a lot of water and urine does not have to be much longer than 20 days. An oxidation tank will be needed to treat the effluent from the digester to be sure it will be free of pathogens and can be used as an organic fertilizer. The retention time and the amount of input into the digester will determine the size of the dome(s). In addition to the faecal waste that can be used asa feedstock also other organic waste streams can be used. In the case of institutions, organic kitchen waste and food left-overs are the most relevant. When adding other organic waste streams, care has to be taken how and how much is added, but basically everything can goin the digester Adding additional waste streams like kitchen and food waste is very interesting as the methane potential 1 of this waste is much higher than from faecal waste as shown in Table 3. An additional advantage is that this waste does not need to be disposed of anymore, which provides additional cost reductions.