Bioprocessing for Renewable Energy Production from Municipal Wastewater in Zambia

Disposal of organic wastes in wastewater in most developing countries remains a source of environmental concern. The driving forces in keeping the environment clean are the inherent health and environmental hazards posed by wastewater. Financial constraints experienced by wastewater treatment utilities have slowed infrastructure expansion. There is therefore need to select wastewater management techniques that meet disposal challenges encountered by local municipalities. Biomethanation is one such technology that is viable and useful in dealing with organic wastes, where a consortium of bacteria breakdown the wastes in stages from complex to a simpler hydro carbon-methane in the similar way that humans exhale carbon dioxide. Sewage sludge collected from the largest wastewater plant in Lusaka, Manchinchi, was placed in 5-litre mild steel laboratory scale bioreactors. Biogas was collected through a tube by water displacement using 1 litre beakers partially filled with water and 500ml-inverted measuring cylinders, like in a mercury barometer. By scaling up, biogas capacity and energy were 1.5million m3 and 14.8 million kWh per annum respectively. Economic assessment indicated Net Present Value, (NPV), at US$ 480,000 and IRR at 23 %. Methane quality was 62 %. Greenhouse gases, (GHG), emission reduction incentive with Clean Development Mechanism, (CDM) was valued at 30,000 tons of carbon dioxide equivalents. A micro turbine with modularity for 1.7 MW was favourable in Combined Heat and Power applications, (CHP). Benefits of the application of biomethanation included sale of electricity to the grid, making energy savings and improving the operational costs at the site.