Assessment of the performance of a pilot scale decentralized faecal sludge treatment and re-use based system in peri-urban Kampala

Abstract

A pilot decentralized faecal sludge treatment system (DEFASTS) for the treatment of faecal sludge was constructed for the purpose of assessing the performance and evaluating the potential benefits of the treatment system. The system consisted of a sedimentation tank of capacity 2 m3, in which the liquid overflow passed sequentially through a two-chambered anaerobic baffled reactor (ABR) and two-chambered anaerobic filter (AF). Effluent polishing was achieved through a Cyperus papyrus planted gravel filter. The system mimicked DEWATS, which were designed, piloted and are being scaled up in different parts of the world by the Bremen Overseas Research and Development Association (BORDA). During the study period of 10 months (June 2014 to July 2015), the system was loaded daily with 0.5m3/day of mixed raw faecal sludge from both septic tanks and pit latrines (lined and not lined) and operated with a total retention time of 12.5 days. The following parameters (of influent and effluent) were measured: Chemical Oxygen Demand (COD), five-day Biochemical Oxygen Demand (BOD5), total suspended solids (TSS), pH, temperature, total phosphorus (TP), total nitrogen (TN), faecal coliforms (FC), total volatile solids (TVS), ash content, calorific value and biogas yield was estimated. The average percentage removals with standard deviations of COD, BOD5, TSS, TN, TP, and FC by DEFASTS were 88.3±24 %, 88.1±1.9%, 97.7±1.8%, 98± 24.2%, 74±29.8% and 99 ±1.6% respectively. With the exception of FC, the mean values of the rest of the effluent concentrations exceeded the Ugandan effluent discharge standards. The biogas yield ranged between 0.1 and 11.5 (M3/day). The average calorific value of FS was 8.9±1.9 MJ/KgTS. The study demonstrated enough evidence to show satisfactory performance of DEFASTS for the removal of organic, nutrients and pathogens from FS in peri-urban areas. The methane from biogas can be used as fuel and the remaining biosolids are potential raw materials for organic fertilizer. Furthermore, the reclaimed waste water can be further investigated for irrigation use. Finally, pellets made from the dewatered and stabilized FS can be used as soil conditioner/organic fertilizer. These results can support the development and scaling up of DEFASTS for institutions, small towns and peri-urban areas of big towns for sustainable faecal sludge management.