Renewable Energy Potential of Sewage in Zambia

Abstract

This study was aimed at investigating the renewable energy potential of com- munal and municipal wastewater through methane production in biogas digesters and the use of the captured methane for energy production in biogas engines. It was conducted on biogas digesters receiving and pre-treating communal and municipal wastewater in the Zambian city of Livingstone. Wastewater inflow rates into biogas units including the wastewater turbidity, total dissolved solids (TDS), temperature, pH, conductivity and Chemical Oxygen Demand (COD) were measured during the study. And all the produced biogas was measured and combusted on-site during the course of the research. In order to know the methane content of the gas, the CO2 content in the biogas was measured with a CO2 indicator. The study showed that the predominant factor affecting the process of methane production from wastewater to the greatest extent is the COD concentration of the inflowing wastewater and not the system hydraulic retention times (HRT’s). The COD treatment levels of the tested systems ranged between 27 and 86 percent and the degree of breakdown primarily depended on the COD concentration of the influent wastewater. On renewable energy fuel production, about 3.54 kilograms of COD in each system produced a kilogram of methane. Communal wastewater was able to produce an average of 600 grams of methane per cubic meter of wastewater treated whilst municipal wastewater with less COD concentration was only able to produce about 64.5 grams of methane per cubic meter wastewater treated. With the use of a 45 kw Cummins 6 BT biogas engine, the respective wastewaters had potential to produce about 2.6 kWh and 0.1 kWh of electric energy per cubic meter of wastewater treated at a levelized cost of USD 9 cents per kilowatt-hour. Temperature also showed that it has significant effect on methane production as a degree temperature rise in the anaerobic system increased the methane production mass rate by 1.2 percent.