Assessment of the potential contribution of biogas to mitigation of climate change in south africa

Includes bibliographical references.South Africa has its fair share in the global greenhouse gas (GHG) emissions, with recorded 2010 emissions per capita of 10tons/year. This is caused by the energy supply of the country which relies heavily on fossil fuels to drive its energy intensive economy. If this continues under “business as usual”, consequences like water and food shortage may be exacerbated. The waste sector has a share of 3 in national GHG emissions. These are caused by methane from biogas produced through anaerobic digestion of organic waste. The objective of this study was to assess the potential contribution that can be achieved in reducing the national GHG emissions by converting waste emissions into useful energy or capturing and destroying them. Three waste resources were investigated because of their abundance in the country: municipal solid waste, municipal wastewater and livestock manure. The national picture of municipal waste was extrapolated from the waste data available in 7 metros in the country (City of Cape Town, Johannesburg, Tshwane, Ekurhuleni, EThekwini, Nelson Mandela Bay, and Buffalo City municipalities). Projected GDP and population growths were used as indicators for extrapolating the national data. The total national organic waste derived from these waste categories was used to estimate their emission share in national GHG emissions and biogas generation in terms of methane production from each waste type. This was forecasted from 2010 to 2025. The methane gas production was optimised by assuming different waste combinations like: municipal solid waste and wastewater, wastewater and livestock manure, and remaining wastewater. In addition, the possible amount of electricity or heat produced from this biogas was estimated. This useful energy was used to evaluate the emission reduction potential (ERP) in the national GHG emissions of the country under “growth without constraints”. All these computations were performed by using MS Excel software. It was found that the total organic waste predicted during this period varied from 12 to 17Mton, with the waste emissions share being about 2 of the national GHG emission. Methane generated from this waste was about 644-1075Mm3 while the total optimal methane generated from these waste combinations was estimated to be 1770- 2650Mm3. In addition, 673-1123GWh of electricity and 1255-2150GWh of heat could be produced (without optimization) from methane over the same period of the forecast. For optimal methane production, the possible useful energy was estimated to be 1362-2037GWh of electricity and 2894- 4362GWh of heat. The ERP of methane capture and conversion to useful energy was about 2.1- 2.5. It is concluded that a) capturing and utilisation of methane gas from waste contributes to the reduction of the GHG emissions, b) optimisation of biogas production from waste increase methane yield and therefore useful energy, and c) the best contribution of biogas in climate change mitigation in South Africa would come from the optimal production of methane from waste