Factors affecting efficiency of industrial wastewater treatment: case study of Njoro industrial sewage works, Nakuru County, Kenya

Abstract

The efficiency of the sewage works depends on the quality and quantity of the influent and the design of the sewage works. Inefficiency of the sewage work has adverse health impact to the aquatic ecosystem. Pollutants can bio-accumulate and bio-magnify in the food chain causing health impact to both human being and wildlife. The main objective of this study was to assess the effectiveness of wastewater management system of Njoro industrial sewage works. This study used descriptive research design while purposive sampling was used to select the major industries. Data collection was done using questionnaire and laboratory experiment. Data was analysed using descriptive statistics and Analysis of Variance (ANOVA) and student t-test. Major pollutants discharged into Njoro sewage works were organic, inorganic and heavy metals. Three industries (Bidco Company, Tanners and Menengai oil refinery) pre-treated their wastewater before being discharged into the sewer line. The management systems used to pre-treat wastewater include; interceptor, stabilization ponds and wetland. There was no significant difference at the inlet and outlet for the concentration of pH (0.14), Conductivity (0.4), Total Dissolved Solids (TDS) (0.35), Lead (0.34), Copper (0.64), Zinc (0.35), Total alkalinity (0.66) and Chromium (0.11) at the influent and effluent of Njoro sewage works. There was a significant difference of the concentration of Chemical Oxygen Demand (COD) (0.05, Biological Oxygen Demand (BOD) (0.01), Dissolved Oxygen (DO) (0.000) and Total Suspended Solids (TSS) (0.01) at the influent and effluent of Njoro sewage works. Njoro sewage works was not effective in the reduction of heavy metals, TDS, conductivity and pH. It was effective in the reduction of COD, BOD, DO and TSS in the wastewater. The study therefore recommends that the pollutants be determined at the source of wastewater. The National Environment Management Authority (NEMA) and the Department of Water and Environment should intensify enforcement of wastewater standards of all industries and establish a forum with the industries