In an attempt to divert waste from landfill, the government has increased landfill gate fees with plans to ban all organic waste to landfill within the next few years. Anaerobic digestion (AD) is a potentially effective organic waste treatment method and landfill alternative which several waste producers have begun to utilise or consider.
Treatment of waste in an anaerobic digester both accelerates the decomposition process and produces useful by-products in the form of biogas and digestate. Biogas consists of approximately 50% methane and 50% carbon dioxide and can be upgraded to compressed natural gas, which is used as an LPG replacement or combusted directly in a generator to produce electricity and heat. The digestate produced is nutrient rich and can be used as a liquid fertiliser which returns nutrients to the soil and thereby closes the loop.
Less than 20 large scale AD installations exist in South Africa, of which, far fewer are currently operating as intended. This can be attributed to several factors. AD is a biologically mediated process generally occurring at low temperature and pressure. There are several operational challenges associated with biological systems which require a constant and regulated environment specific to the needs of the microbial community in order to operate optimally. Small deviations can result in huge process upsets and can take much longer to rectify.
As result of the small biogas industry in South Africa, very few companies and people have the experience necessary to operate anaerobic digesters. Additionally, many anaerobic digesters have been installed by international companies with very poor transfer of knowledge and training taking place before project handover. As a result, many companies with new biogas installations find themselves in the position where they are unequipped to operate their new digester and are unable to call on the expertise of others in South Africa. In many cases existing designs have been installed without a full investigation into the appropriateness for the specific waste stream, resulting, in a sub-optimal process.