Abstract

A study was conducted to characterize Modjo tannery effluent (wastewater) and determine its impact on the Modjo River using some physicochemical parameters. Accordingly, three tannery wastewater samples along wastewater channel at different distances have been taken and three river water samples (one upstream and two downstream) were collected along the river to determine its impact on the river. The samples have been analyzed for temperature, pH, electrical conductivity (EC), total dissolved solids (TDS), total suspended solid (TSS), chloride(Cl-), biological oxygen demand (BOD5), chemical oxygen demand (COD), total ammonia (as N), total nitrogen, total phosphorus and sulphide. The result of tannery wastewater showed that the values of temperature, pH, EC, TDS, TSS, Cl-, BOD5, COD, total ammonia, total nitrogen, total phosphorus and sulphide along the wastewater channel ranged from 26.97 to 24.93°C, 9.33 to 8.33, 15670.00 to 14496.67 mgL-1, 9370.00 to 8723.33 mgL-1, 4979.33 to 2647.67 mgL-1, 6111.67 to 5555.78 mgL-1  960.34 to 842.00 mgL-1, 2011.00 to 1950.75 mgL-1, 520.44 to 401.23 mgL-1, 720.46 to 665.43 mgL-1, 30.12 to 19.55 mgL-1 and 35.56 to 21.05 mgL-1 respectively. And most of the effluent characteristics except pH and temperature were beyond the provisional discharge limit of tannery effluent to water body set by the Ethiopian Environmental Protection Authority (EEPA) and Federal Environmental Protection Agency (FEPA). Analysis of variance (ANOVA) also showed that variation among sampling points were statistically significant (p<0.5). Similarly, the levels of all these physicochemical parameters in the downstream site of the river were higher as compared to the values obtained from the upstream site (control). This indicated that the downstream site of the river is polluted as a result of the direct discharge of the tannery effluent to it.

Key words: Modjo tannery, Modjo River, wastewater, physicochemical parameters, water pollution.