Assessing the performance of a septic tank in terms of physical and chemical pollutants removal
Ninsiima, Nyinamwiru Esther
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In Kampala, the use of septic tanks has been widely adopted mainly because it is technically and economically unfeasible to connect to the national sewer system. However, the effluent released by the septic tank has been known to contain pollutants that could have adverse impacts on public and environmental health. The main goal of this study was to assess the performance of existing septic tanks in terms of physical and chemical pollutants removal in relation to features they possess. Influent and effluent wastewater from 20 different septic tanks was sampled and taken to the laboratory for analysis. The parameters namely pH, temperature, Nitrogen, BOD, COD, FOG, TSS and E.coli were selected mainly because they are known indicators of wastewater quality. The results indicated a significant difference between the influent and effluent concentration of the pollutants specifically, BOD, COD, Nitrogen, and TSS supported by p<0.05. Septic tanks with longer retention time had better removal efficiencies as opposed to those with shorter duration and those with bigger volume performed better than the shallow ones in terms of removal of BOD, TSS, and Nitrogen. However, there was an insignificant relationship between the length to width ratio and the tank’s performance which contradicted past studies that strongly related the septic tank performance to its dimensions. Septic tanks with longer retention time days had higher concentration of E.coli which shows that E.coli had the ability to multiply in the septic tank environment which contradicts the presumption that the growth of E.coli is inhibited outside their host and proposes that its growth is intensified during its retention time in the tank. While this study mainly focused on septic tanks in the greater Kampala areas in Uganda, the findings obtained should be relevant in other developed and developing countries that have adopted septic tanks as a means of domestic wastewater disposal.