Thermophilic anaerobic digestion of the organic fraction of Dar es Salaam municipal solid waste.
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Date
1996
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University of Dar es Salaam
Abstract
The physical and chemical compositions of market, hotel kitchen and domestic wastes, brewery spent grains and chicken manure from the city of Dar es Salaam were determined. On the dry weight basis, the wastes contained 59.5 to 91,5 volatile solids, 34.3 to 47.9% neutral detergent fibre, 11.4 to 18.8 acid detergent fibre, 6.4 to 11.8% cellulose, 6.1 to 10.0% lignin and 0.73 to 3.1% kjeldahl nitrogen. The organic fractions of the various waste materials were examined for digestibility under thermophilic (55°C) anaerobic conditions with selected inocula including rumen fluid, hot spring water, sewage stabilisation ponds and Kisutu under refuse inocula. Of all the inocula tested, the Kisutu under refuse inoculum was found to be the most active. Methane production, volatile solids removal efficiency and specific methane production obtained with the Kisutu under refuse inoculum ranged between 2.6 and 3.6 L/L.fv, 17.7 and 75.0 and 461 and 767 ml/gvs, respectively for all the materials. The extent of degradation was hotel kitchen waste> domestic waste> market waste> brewery spent grains> chicken manure. In a comparative study of methane production for thermophilic and mesophilic incubations, hotel kitchen and market waste materials were tested with University of Dar es Salaam sewage stabilisation pond and Kisutu under refuse inocula. There was no significant difference in methane production between mesophilic and thermophilic incubation with University of Dar es Salaam sewage stabilisation inoculum. Kisutu under refuse inoculum, on the other hand, showed a significant difference. The conclusion drawn based on this observation is that the difference in methane production between mesophilic and thermophilic incubations depends on the inocula used. Digestibility of the waste materials was improved by digestion of individual materials plus chicken manure and entirely mixed waste. The percentage increase in CH, production among the various co-digestions ranged between 7.6 and 19.4%. Specific methane productions for the codigestion treatments ranged between 290 and 588 ml/gVS and that for the mixed waste digestion was 646.7 ml/gVS. The values for VS removal efficiency for co-digestion treatment were lower than their respective single waste digestion. In order to establish the effect of oil, oil with calcium chloride and bentonite-bound oil on methane production with the Kisutu under refuse inoculum, market waste was used as a substrate. Addition of 2.Og of oil per litre to the digestion of market waste increased the methane production by 9.3% and the same were obtained for the addition of oil with CaC12. However, addition of bentonite to the digestion mixture increased methane production by 18.2%. Oil concentration inhibition level for the digestion was between 2.0 and 4.0 g/1. At the concentration of 8.0g oil/1 a 59.4% reduction in methane production was observed. Specific methanogenic activities of the used and similar inocula were composition of biomass from the source ecosystems. Methanogenic activities of University of Dar es Salaam sewage stabilisation pond (USP), sisal wastewater stabilisation pond (SSP) and under acetate. The inoculum showed the highest values of activity and it was recommended to be a suitable inoculum for the start up of large scale biogas reactors. The order of activity of the tested inocula was UR> SSP> USP.
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Keywords
Anaerobic digestion, Solid waste, Dar es Salaam, Tanzania
Citation
Kitamirike, M. J. (1996). Thermophilic anaerobic digestion of the organic fraction of Dar es Salaam municipal solid waste. Master dissertation, University of Dar es Salaam. Available at (http://41.86.178.3/internetserver3.1.2/search.aspx?formtype=advanced)