Composition and Anaerobic Digestion of Single and Combined Organic Fractions of Municipal Solid Waste of Dar es Salaam

Abstract

The composition of major categories of municipal solid waste (MSW) of Dar es salaam city was determined. Food remains and vegetable matter constituted 80-90% of the categories. Organic fractions of the individual categories contained 18-20 % total solid (TS), 30-50 % (dry weight) total fibre and 1-1.3 % nitrogen. The assorted organic fractions were tested for anaerobic conversion into biogas at 55°C in batch cultures for 14 days with a mixed population of microorganisms. At a substrate concentration of 6-8 g volatile solids per litre fermenter volume (g VS l-1 FV) individual fractions were degraded by 51-75% and gave methane yields in the range of 390-492 ml per gram VS added. Combining individual fractions with chicken manure at a ratio of 1:1 (TS) increased the N-content of the fractions by 16-133% and the VS content of the fermenting substrate doubled. Overall methane production by the combined fractions increased by 8-20% over that measured for the individual fraction incubations, but methane yields decreased by 30-50%. The mixed waste category constituting a substrate concentration of 6 g VS l-1 FV was degraded by 65% and gave a yield of 428 ml CH4 per gram VS added. This study concludes that individual fractions of MSW of Dar es salaam city are suitable as feedstocks for biogas digesters. The decreased overall conversion of the fractions when combined with chicken manure was attributed to high ash content of the manure.