Evaluation and Characterization of Wastewater from Tannery industries and their Impact on Water Quality of the Receiving River, Ethiopia

Tannery industries are heavy source of pollution of water body. The objective of this research is to evaluate the current status of physico-chemical properties of tannery wastewater from tannery industries concentrated in Mojo town and their impact on water quality of Mojo River. Accordingly, from seven tanneries, effluents at outlet channel, river water and sediments were collected. Physico- chemical parameters and chromium in samples were analyzed. The results revealed in the ranges of PH (5.85 – 12.04) , TDS (3412 - 4660 mg/L), TSS (158.5 -2162.5.5 mg/L), PO4-3 (0.1 – 0.9 mg/L), SO4-2 (456 – 912 mg/L),  NH3-N (31.5 – 358.2 mg/L), NO3− (97.4 – 121.3 mg/L), COD (718 -2380.5 mg/L), BOD5 (706 -2276 mg/L), Cl- (560.9 - 4779 mg/L), S-2(6.4 – 136.1 mg/L) and Phenol (4.3 – 11.7 mg/L). The study also revealed that the concentrations of chromium ranged from ND - 23.43 mg/L, 0.12- 1.6 mg/L and 60.1- 264 mg/Kg in effluents, river water and sediments respectively. The mean value of TDS, TSS, SO42−, NO3− Cl−, ammonia, sulfide, BOD5, COD in wastewater and river water were above the standard of Ethiopian tannery effluent disposal limits and WHO respectively and Cr in friendship tannery effluents and river water at site MS02 and LS01, were also above the standard of Ethiopian tannery effluent disposal limits and WHO standard permissible limits. Similarly, the level of Cr at downstream of river sediment was higher as compared to the standard of USEPA sediment quality guidelines. Generally, this study indicated that the river was polluted by the direct discharge of tannery wastewater. Therefore, discharging of tannery effluents without treatment is worse for the aquatic environment. The researchers had the inference that the tannery industries can adopt the best available technology and management practice before they discharge their effluents into the receiving water body