Journal of Biology and Nature

Sewage comprises of about 99% water, with the remainder being ions, suspended solids and harmful bacteria that must be removed before the water is released into the ecosystem. Moi University sewage treatment plant (STP), with a series of six stabilization ponds, performs biological sewage treatment. In this study, efficacy of the STP was analysed using key water quality parameters. Two sampling points were selected; inlet where sewage is received and outlet where sewage has undergone bio-treatment. At each sampling point, triplicate water samples for analysis were collected bi-weekly in sterilized bottles from May to August 2015. First, levels of dissolved oxygen (DO) were determined in situ using meter probes, while biochemical oxygen demand (BOD), total nitrogen (TN) total phosphorus (TP) and total dissolved solids (TDS), were determined ex situ using standard laboratory methods. The concentration of Escherichia coli (E.coli) was measured using Idexx Quanti-Tray method. Results showed an average of 90% removal of physicochemical parameters from inlet to outlet points. Inlet parameters showed significant differences with those of outlet (BOD F_{4, 115} = 38965.46; p < 0.0001; DO F_{4, 115} = 5156.61; p < 0.0001; TDS F_{4, 115} = 123.27; p < 0.0001; TN F_{4, 115} = 81.12; p = 0.0753; TP F_{4, 115} = 2107.17; p < 0.0001 and E. coli F_{4, 115} = 935593.30; p < 0.0001) indicating improved sewage quality after bio-treatment. The Moi University STP is efficient and guarantees the protection of the effluent receiving river Sambul based on the tested parameters.