EVALUATION OF THE EFFECTIVENESS OF A WASTEWATER TREATMENT PLANT AT THE EXPORT PROCESSING ZONE IN REDUCING CONCENTRATIONS OF POLLUTANTS DISCHARGED INTO RIVER ATHI, KENYA

Abstract

Information about the effectiveness of a wastewater treatment plant is vital in ensuring that the water quality discharged into water bodies and the environment in general meets set standards. In this study, the performance of the wastewater treatment plant located at the Export Processing Zone (EPZ) along River Athi in Machakos County was assessed. The final effluent from the treatment plant is released into the river and the water is used downstream. The effectiveness of the plant was determined through the percentage reduction of pollutants between influent and effluent during the dry (April) and rainy (July) seasons. Samples of water were collected from five sampling points i.e. inlet works, the outflow pool, outlet and points along the river at 500m from the overflow points either sides of upstream and downstream. The samples were analyzed for E. coli, total coliforms, TSS, TDS, BOD, COD, temperature, pH, phosphorus, nitrates, conductivity, color, odour, organic nitrogen and heavy metals. The resulting data was compared with the established standards. Standard methodologies of laboratory analysis were employed as per the Kenyan regulations of 2006 on waste water treatment and discharge. The waste water treatment plant was not effective in reducing pollutants for nitrates, phosphates, Total dissolved solids (TDS), Total suspended solids (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 higher in the effluent after treatment process during the rains than at the influent. However, the treatment plant was effective in reducing chemical oxygen demand (COD) and biological oxygen demand (BOD). Some physical parameters like pH, conductivity, temperature, color, TSS were within allowable values described by Kenyan and International standards for effluent discharge into public waters. Seasonal weather changes significantly affected the vi concentration of pollutants in the waste waters for phosphates, mercury, COD, BOD and coliform bacteria, which were high during the dry season, while nitrates, lead, selenium, Total dissolved solids (TDS) and Total suspended solids (TSS) increased during rains. Generally, there was high pollution at discharge point of the effluent from the treatment plant compared to low levels upstream and downstream. In conclusion, the study recommends expansion or re-designing the treatment plant for increased efficiency to meet discharge standards. Further research is required on the seasonal fluctuation of pollutants along River Athi to reduce pollution of the waters. Key Words: Wastewater, Effectiveness, Treatment Plant, Pollution