PERFORMANCE EVALUATION OF A MUNICIPAL WASTEWATER STABILISATION POND SYSTEM: CASE STUDY OF LIMBE WASTEWATER TREATMENT PLANT IN BLANTYRE, SOUTHERN MALAWI
Abstract
In Malawi the need to treat wastewater is becoming more important and it has been emphasised by the existing regulatory framework institutional regulations and policy guidelines. Formalised national effluent standards also exist. Most developing countries like Malawi use waste stabilisation pond system for sewage treatment. The Limbe wastewater treatment plant was designed long time ago. The effluent from the WSPs is discharged into Limbe River. People who live near the area use the water from the river for domestic and agricultural purposes, most especially those living in the downstream. Unfortunately, there is no frequent and up to date monitoring and information providing facility on the performance of the treatment plant and the quality of the effluent being discharged into the river. The objective of this study was to evaluate the performance efficiency of Limbe WSP treatment plant. The efficiency was evaluated through periodic sampling and analysis of physicochemical and microbiological parameters of the whole system. The statistical analysis such as correlation and regression analysis were performed to assess the relationship between the parameters. The hydraulic parameters such as hydraulic loading rate (HLR) and volumetric loading rate (VLR) were also determined and it was observed that their values were below the designed values. Except for pH, temperature, dissolved oxygen (DO), Total dissolved solids (TDS), oxidation reduction potential (ORP), and nitrates (NO3-N), the rest of the parameters were above the recommended values by MBS for effluent disposal. In terms of the removal efficiency percent, only COD, BOD and TSS were above 50%. The system was overall poor in biological parameters removal but better in some physicochemical parameters comparing to the standard limits of the country. The measured values of effluent TSS, NO3-N and total coliform in the laboratory were very close to those predicted through regression-based tool. Therefore, the regression-based tool developed in this study can be used to estimate effluent parameters for performance monitoring.
Research summary
In Malawi the need to treat wastewater is becoming more important and it has been emphasised by the existing regulatory framework institutional regulations and policy guidelines. Unfortunately, there is no frequent and up to date monitoring and information providing facility on the performance of the treatment plant and the quality of the effluent being discharged into the river. The hydraulic parameters such as hydraulic loading rate (HLR) and volumetric loading rate (VLR) were also determined and it was observed that their values were below the designed values. Except for pH, temperature, dissolved oxygen (DO), Total dissolved solids (TDS), oxidation reduction potential (ORP), and nitrates (NO3-N), the rest of the parameters were above the recommended values by MBS for effluent disposal.