Physicochemical characteristics of septic tank sludge treated with calcium oxide in Kinshasa, Democratic Republic of Congo

Abstract

Various chemicals are used to disinfect septic tank sludge. Their influence on sludge quality is the main focus of this study. This research focuses on manual septic tank cleaners who typically use a hole dug in the ground as a disposal site for sludge. The study is conducted on a laboratory scale on the characteristics of this sewage sludge when treated with calcium oxide (quicklime). Sewage sludge from on-site sanitation systems is contaminated with pathogenic microorganisms; it is possible to modify their biotic characteristics to an acceptable level by treating them with calcium oxide.  Several parameters considered to be indicators of pollution are targeted and analyzed in samples of fresh sewage sludge or sludge treated at three levels: 10%, 15%, and 20% CaO; These include total bacteria, fecal coliforms, total streptococci, fecal streptococci, staphylococci, and helminth eggs. The reduction rate for each parameter was used to evaluate the effectiveness of the treatment. The 20% treatment produced interesting results, with a reduction rate ranging from 98.00% to 100% for the bacteriological parameters. The quantities of sewage sludge and lime, their physical state, temperature, pH, contact time, and inhibitors are parameters that influence the speed of this reaction. The results show that chemical treatment with calcium oxide reduces the risk of biological contamination. Sewage sludge from septic tanks treated in this way can be used to improve agricultural soils.