Efficacy of sewage treatment plant in Moi University, Uasin Gishu County, Kenya

Abstract

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 capacity of 3,200m 3 /day, performs biological sewage treatment processes. The major environmental concern with the STP is the contamination of the effluent receiving Sambul River. In this study, efficacy of the STP was analyzed using key water quality parameters, and comparisons made with those of the National Environmental Management Authority (NEMA) and Moi University Effluent Discharge Monitoring Standards (MUEDMS). Purposive sampling design was used to select five sampling points; STP inlet where sewage is received, STP outlet where sewage has undergone bio-treatment, wetland where pollutants have been trapped from outlet sewage, downstream of Sambul River where bio-treated sewage has mixed with river Sambul waters, and upstream (control) of Sambul River where the river water does not mix with STP effluent. At each sampling point, triplicate water samples for analysis were collected bi- weekly in sterilized plastic bottles from May to August 2015. First, levels of water temperature, pH, and dissolved oxygen (DO) were determined in situ using meter probes, while biochemical oxygen demand (BOD 5 ), turbidity, total dissolved solids (TDS), total suspended solids (TSS), total phosphorus (TP) and total nitrogen (TN) were determined ex situ using standard laboratory methods. The concentration of Escherichia coli was measured using Idexx Quanti-Tray method. Finally, macroinvertebrates as bioindicators of water quality were collected using manual grab method. The impact of bio-treated effluent on the abundance of aquatic macroinvertebrates at river Sambul was evaluated using Shannon- Wiener diversity index. Results showed that levels of most physicochemical parameters were within the acceptable standards of NEMA and MUEDMS. Upstream parameters showed no significant differences with those of downstream (water temperature F 4, 115 = 8.45; P = 0.9813; pH F 4, 115 = 20.77 P = 0.9781; BOD 5 F 4, 115 = 38965.46; P = 0.9734; TDS F 4, 115 = 123.27; P = 0.9997; TSS F 4, 115 = 708.50; P= 0.9999; ammonia F 4, 115 = 50.78; P = 1.0000; nitrates F 4, 115 = 412.78; P = 0.1919; nitrites F 4, 115 = 943.53; p = 0.9986; phosphates F 4,115 = 1125.73; P = 0.9931; total phosphorus F 4,115 = 2107.17; P = 0.9972; total nitrogen F 4,115 = 81.12; P = 0.9354, indicating improved sewage quality after bio-treatment. Levels of turbidity and E. coli downstream were significantly higher (F 4, 115 = 872.0; P < 0.0001 and F 4, 115 = 935593; P < 0.0001, respectively) than those of upstream, outlet or wetland. Treated effluent had no significant effect on the aquatic macroinvertebrates’ abundance at the receiving river, as demonstrated by Shannon-Wiener diversity index (H) values at upstream (H=2.504), wetland (H=2.4096) and downstream (H=2.371). High turbidity indicates presence of colloidal matter, which affect water acceptability to consumers while high concentration of E. coli indicates possible faecal contamination after bio-treatment, hence the risk of pathogens presence. Moi University sewage treatment plant was found to be relatively efficient based on the tested parameters.