Comparative toxicological studies of distillery effluent treatments such as UASB reactor followed by an oxidizer unit using Cyprinus carpio fish

The aim of the present study was to evaluate the acute toxicity of anaerobically treated distillery effluent and oxidized effluent on freshwater fish, Cyprinus carpio. The untreated distillery effluent (Sample A) was treated with up-flow anaerobic sludge blanket (UASB) reactor (Sample B) and followed by an oxidizer system (Sample C and D) under optimized conditions. The comparative acute toxicity of Sample A and treated effluents (Sample B, C and D) was studied using Cyprinus carpio (common carp) as a model fish for various exposure times (24 to 96 h) after suitable dilutions. The parameters for toxicity determination included assessment of behavioural response of the fish under study and their mortality study, and histopathological analysis. The behavioural response parameters showed prominent changes as erratic swimming activity, increase in opercular movement, jerk and violent reaction, loss of equilibrium, and aggressiveness in fish when exposed to varying concentrations of distillery effluent. The prominent features of death were respiratory distress, paralysis and loss of equilibrium. The mortality study involved calculation of median lethal toxicity (LC50) using static bioassay method. The histopathological analysis of tissues like gills, intestine and kidney of exposed fish showed varied degrees of damage, which increased with increasing the strength of the distillery effluent. Thus, the present study underscores the effectiveness of the two-step process (anaerobic treatment followed by oxidation) for the treatment of distillery effluent in terms of significantly lesser dilution requirements (about 5-fold lesser as compared to the untreated effluent) before discharging the distillery effluent safely to the ecosystem.