Urban waste management and the environmental impact of organic waste treatment systems in Kampala, Uganda

摘要

In Kampala, Uganda, about 28,000 tonnes of waste are collected and delivered to landfill every month. Kampala Capital City Authority records show that this represents udapproximately 40 % of the waste generated in the city. The remaining uncollected waste is normally burnt and/or dumped in unauthorised sites, causing health and udenvironmental problems. However, the organic fraction of domestic waste can provide an opportunity to improve livelihoods and incomes through fertiliser and energy udproduction. This study employed environmental systems analysis to identify the most environmentally efficient technologies for treating the organic waste generated. The work was undertaken through interrelated studies. These were a literature review of waste hierarchy practices suitable to the development of a sub-Saharan African city using Kampala as a case study; a physical and chemical characterisation of municipal waste collected and delivered to Kampala’s landfill over the span of a year to cover both dry and wet seasons; a mapping of the location of animal farms and the udestablishment of animal feeding and waste management practices on animal farms in Kampala; treatment of Kampala's organic waste by means of the vermicompost method and finally using life cycle analysis to identify the best waste treatment method for organic waste generated out of anaerobic digestion, compost, vermicompost and fly larvae waste treatment technologies. The impact categories assessed were energy use, udglobal warming and eutrophication potentials. Generally, the results showed that re-use and waste prevention waste hierarchy methods are the most feasible for the uddevelopment of waste management in Kampala: over 92 % of the waste generated is organic in nature, containing on average a moisture content of 71.1 %, 1.65 % nitrogen, ud0.28 % phosphorus, 2.38 % potassium and a gross energy content of 17 MJ/kg; most animal farms are located on the periphery of the city, and the most popular animal feeds udare peelings and pasture; 60 % of the animal manure generated is discarded and 32 % used as fertiliser; a 60.3% material degradation was achieved in the vermicompost process while the feed-to-biomass conversion rate was 3.6 % on a dry matter basis; and finally anaerobic digestion performs best in terms of energy use, global warming potential and eutrophication potential. However the study concluded that poorly managed anaerobic digestion technology with extensive methane leakages will make a considerable contribution to global warming. Further research is needed to establish the viability of fly larvae waste composting in sub-Saharan Africa and to measure direct emissions from the different organic waste treatment technologies in a sub-Sahara African city setting.