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.