Evaluation of Effluent Quality Trends Before and After Filtration Through the Composite Filter from Shirere Wastewater Treatment Plant to River Isiukhu in Kakamega County, Kenya

Abstract

The current stabilization ponds as wastewater treatment practices in urban areas have proven insufficient with continued discharge of untreated wastes into water bodies. Their challenge comes from inappropriate system selection and maintenance, improper design, construction mistakes, physical damage and hydraulic overload. Appropriate infrastructural technologies for waste removal that can be adopted in the drainage channels of effluents into water bodies are scarce. This study incorporates a reactor based composite filter of pumice and sand as an innovative approach for removing residual waste in effluents discharged from Shirere Wastewater Treatment Plant into River Isiukhu, Kakamega Municipality. The objective of the study was to evaluate the trend of effluent quality from Shirere wastewater treatment plant upto river Isiukhu before and after installation of composite granular filter. Effluents, drinking water from Shirere WWTP, Shikoye stream, River Isiukhu and protected spring along Shikoye stream, were collected using presterilized water sampling containers for microbial quality analysis at MMUST and KACWASCO laboratories. The measurements were carried out using UV-VIS spectrophotometer at 752 nanometer wavelengths. Research design was experimental. The average reduction of COD in the mid-season of June to August was 42.2 ±4.6%, being the highest. Concomitantly, the BOD removal by the filter in the season of June to August was19.6±7% and 15.6 ±3.5% for September to November. The average rate of TSS removal in June to August was 19.3±4.5% followed by 16.6±3.8% in September to November and 11.6±7% in March to May. The average rate of Nitrate removal in June to August was 41.8±7.6% followed by 30.0±2.2% for March to May and 25±8.6% for September to November. Phosphates had an average rate of removal in June to August at 31.9±2.7% followed by 20.6±4.8% for September to November and 20.0 ±4.3% for March to May. Specifically, for the first season of March – May 2021 at 200 mm filtration depth were carried out at effluent flow rate of 0.0032 and volume, 0.234 Concentrations of most parameters were above NEMA standards, like COD was 322mg/l yet maximum should be 100 mg/l. Therefore, it was concluded that silica pumice composite filter performance was achieved by big variations in the concentrations of COD, BOD, TSS, Phosphates and Nitrates at Shirere WWTP after filtration which was attributed to effective removing capacity. The effluent concentrations from sampling sites S1-S3 and S5-S7 were found to be above the NEEMA standards implying the high risk of using Isiukhu water and catchment area. Thus, this study recommended that, the composite filter reduced concentrations of all the parameters (COD, BOD, TSS, PO3, NO3) significantly from Shirere WWTP along Shikoye stream up to the confluence of river Isiukhu. Most of the parameters after filtration were ranging within the required standards of NEMA. The requisite measure of adopting new technology of composite filtration should be sustained.