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Conversion of Household Wastes from Gaborone Municipality into Useful Biogas through Anaerobic Co-Digestion with Cow Dung

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2018 ASABE Annual International Meeting  1800176.(doi:10.13031/aim.201800176)
Authors:   Kevin N. Nwaigwe, Abhishek Agarwal, Oagana M. Modirelabangwe, Robert R. Mbene, Sabbas N. Asoegwu
Keywords:   Biogas, bioreactor, cow dung, household waste.

Abstract. A work on the production of biogas using co-digested household wastes and cow dung sourced from Gaborone municipality in Botswana is presented. Management of household wastes has remained an enormous environmental management issue in the urban centre of Gaborone, Botswana due to the fast growing population within the city when compared to other city centres within the country. Given that Gaborone has only one landfill which is already overflowing, the need to find alternative use for wastes is very urgent. Collected wastes were categorized and a locally developed mechanical digester was used in co-digestion of household wastes organic fraction and cow dung in different ratios. By-products of an operational biogas digester in Kanye, a suburb of Botswana, was used as inoculum to improve digestion of the substrates. Results of yield indicated that household wastes co-digested with cow dung in the ratio of 3:1 showed significant biogas yield with volumetric production at a rate of 1.6litres/day. Gas production was highest on the 19th day with a volume of 3.34 litres/day and corresponding digestion temperature of 31.5 oC. Total volume of gas generated was 54.8 litres per 30kg slurry with lag-time of 10 days. Biogas yield was compared with an equivalent 30kg of cow dung and total volume of generated biogas was 70.4 litres. Given that the Gaborone landfill has an estimated waste disposal rate of 151,383 tonnes/annum amounting to about 3.1 kg of waste per person per day, a 54.8 litres of biogas per 30kg of household waste provides enormous source of energy from generated household wastes and is an excellent waste management strategy towards freeing the only already overflowing landfill in Gaborone.

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