Assessment of the physico-chemical characteristics of a tannery wastewater and its pollution impact on the water quality of Little Akaki River

Abstract

Tannery wastewater is one of the most hazardous industrial pollutants containing organic and inorganic substances. For this reason, tanneries are required to treat their wastewater before discharging into the environment. The objective of this study was to evaluate efficiency of Batu tannery wastewater treatment plant and the impact of the tannery affluent on the quality of the Little Akaki River. The physico-chemical characteristics of tannery wastewater before and after treatment were determined based on triplicate measurements for each sample. The data showed that raw tannery wastewater has high loads of pollutants. The highest COD, TDS, ammoniaN, sulfate, total nitrogen, sulfide and total chromium observed in the raw tannery wastewater was 7213 mg/l, 6236 mg/l, 228 mg/l, 352 mg/l, 310 mg/l, 294 mg/l and 26 mg/l, respectively. Average removal efficiency of the treatment system for the COD, sulfide, ammonia-N, TDS, total nitrogen was 51%, 62.6%, 48%, 47%, 59.5% and 52.7%, respectively. The pH, temperature and electrical conductivity was reduced by less than 10% in treated tannery effluent, but COD, TN, sulfide, total chromium, sulfate and TDS exceeded the national discharge limit for the tannery effluent. Analysis of similar parameters in the Little Akaki River showed that insufficiently treated tannery effluent caused an increase in the river water physicochemical characteristics except for temperature and pH. However, one-way analysis of variance showed that only the COD, total chromium and sulfate of downstream LAR water were significantly (p<0.05) different from upstream similar parameters. This showed that impact of the tannery effluent on the river water quality is insignificant for most of the studied parameters. Nevertheless, the physico-chemical data of upstream LAR water showed that the river is severely polluted by other upstream sources and the river water is beyond the recommended water quality values for human, animal and agricultural uses.

Keywords/phrases: Leather, Little Akaki River, Physico-chemical characteristics, Tannery, Wastewater