Effectiveness of a Wastewater Treatment Plant located at EPZ in reducing Pollutants Discharged into River Athi, Kenya

Information about effectiveness of a wastewater treatment plant is vital in ensuring the quality of water discharged into water bodies and the environment in general meet set standards. In this study, the performance of a wastewater treatment plant located at the Export Processing Zone (EPZ) along River Athi in Machakos County, Kenya was assessed because the final effluent from the treatment plant is released into the river where water is used downstream. Effectiveness of the plant was assessed through the reduction percentage of pollutants between influent and effluent during the dry and wet seasons. Samples of water were collected from the following points i.e. inlet, outflow pool, outlet and along the river. The samples were analyzed for heavy metals, Total Dissolved Solids (TDS), Total Suspended Solids (TSS), Chemical Oxygen Demand (COD), Biological Oxygen Demand (BOD), organic nitrogen, phosphate, color, temperature, pH, and total coliforms. The resulting data was compared with the established standards. Standard methodologies of laboratory analysis were employed as per Kenyan regulations of 2006 on waste water treatment and discharge.  From the results, the waste water treatment plant was not effective in reducing nitrates, phosphates, TDS, TSS, color, and heavy metals i.e. mercury, lead, selenium, copper and cadmium. The inefficiency was more pronounced in rain season. Nitrates (-2.04%), phosphates (-66%), mercury (-48%), lead (-48%), selenium (-2.29%) and copper (-9.75%) were high in the effluent after treatment process during the rains than in the influent. However, the treatment plant was effective in reducing Chemical Oxygen Demand (COD) and Biological Oxygen Demand (BOD). Some parameters like pH, conductivity, temperature, color and TSS were within allowable values described by Kenyan and International standards for effluent discharge into public waters. The study recommends expansion or re-designing of the treatment plant and better monitoring of the sources or types of wastewaters received at the plant for efficient and proper treatment process. Further research required on the seasonal fluctuation of pollutants along River Athi to reduce pollution of the waters. This should be coupled with studying the role of river gradient in self-cleansing of the pollutants.