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Water pollution is a major global concern which calls for regular evaluation of levels of contamination of water bodies. It has been suggested that water borne infections account for over 14,000 people daily in the world. Point source pollution can be defined as contaminants from a single identifiable source. The major environmental concern by the residents around Sambul River is pollution of waters of Sambul River by effluent from Moi University sewage treatment plant (STP). Sambul River is the main source of water for both domestic and agricultural use among residents of Sambul area. This study focused on analysis of efficacy of the (sewage treatment plant) using macro-invertebrates as bio-indicators of contamination of waters of Sambul River. Purposive sampling design was used to select three sampling points; downstream of Sambul River where bio-treated sewage has mixed with waters of Sambul River, at point of effluent discharge to the river and upstream (control) of Sambul River where the river water does not mix with STP effluent. Triplicate water samples were collected at each sampling point bi-weekly and transported to the Laboratory for analysis. Sampling was done from May to August 2015. The impact of bio-treated effluent on the abundance of aquatic macro invertebrates at Sambul River was evaluated using Shannon- Wiener diversity index. The findings revealed that treated effluent had no significant effect on the aquatic macro invertebrate abundance at the receiving river, as demonstrated by Shannon-Wiener diversity index (H) and ANOVA. H-values were; upstream (H=2.504), wetland (H=2.4096) and downstream (H=2.371). High H-value indicates less number of species diversity while a lower value of H indicates a higher diversity of macro-invertebrates. Higher biodiversity is an indicator that the effluent from the STP is treated to recommended standard as required by National Environmental Management Authority (NEMA). Phosphate values for the different sampled points ranged from 0.05 ± 0.01 to 5.50 ± 0.15 mg/L. Mean phosphate level for upstream (control) was significantly lower than that of outlet (F4, 115 = 1125.73; p < 0.0001) and inlet (F4, 115 = 1125.73; p < 0.0001), but showed no significant differences from that of downstream (F4, 115 = 1125.73; p = 0.9931) and wetland (F4, 115 = 1125.73; p = 1.0000). The findings of this research are important to demonstrate to concerned parties, including the public and the government; NEMA that the effluent from Moi University STP is treated to expectation. This will return confidence to the public on consumption of water from Sambul River.
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