Impact of Solids Loading on the Performance of Settling Thickening Tanks at Lubigi Faecal Sludge Treatment Plant

Abstract

Faecal sludge management is becoming increasingly important due to the increasing world population served by on-site sanitation technologies. However, there isn’t adequate operational experience in managing faecal sludge due to the highly varying characteristics and high strength. This study was aimed at studying the impact of the solids loading on the performance of sedimentation tanks that are used for solids-liquid separation at Lubigi faecal sludge treatment plant. A total of 5 composite samples were obtained from the influent and effluent on a weekly basis. These samples were analysed for Total Solids and Total Suspended Solids which are the key parameters evaluated for tank performance. The volume of faecal sludge delivered to the plant on the day of sampling was also determined. The average daily flow of 856.7m3 was considerably higher than the 400m3 design flow for the tanks. The suspended solids removal percentage was 42%, which is lower than the 60-80% achieved by similar tanks. The results obtained suggest that the greatest factor contributing to the underperformance of the tanks is the reduced liquid retention time caused by solids build up in the tank and high flows.