Electrocoagulation induced treatment of indigo carmine textile dye in an aqueous medium: the effect of process variables on efficiency evaluated using biochemical response of Gammarus pulex

Indigo carmine removal from aqueous solutions was investigated by the electrocoagulation process and biochemical responses of Gammarus pulex to solutions before and after treatment were studied. Electrocoagulation experiments in the first stage were carried out with central composite design (CCD) using response surface methodology (RSM). Optimization of process variables that maximize indigo carmine removal by electrocoagulation process was carried out by using a second-order model within the studied test range of various process variables. According to the optimization results, optimum conditions for obtaining 82.55% maximum indigo carmine removal were pH 5.86, a current density of 13.31 mA/cm2, an indigo carmine concentration of 20.01 mg/L, and a time period of 115.80 min. Under optimum conditions for indigo carmine removal, the amount of sludge formed was 0.928 kg/m3, electrode consumption was 0.0305 kg/m3, and energy consumption was 7.461 kWh/m3. The operating cost was calculated as 0.79 US$/m3 under treatment conditions where optimum indigo carmine removal was achieved. In the second stage, G. pulex was exposed to treated and untreated synthetic indigo carmine solutions obtained from experiments according to optimum conditions in order to investigate the biochemical response for 24 and 96 h. Treatment efficiency was evaluated with superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and cytochrome P450 1A1 (CYP1A1) biomarkers. Results clearly showed that the electrocoagulation process was a simple and effective treatment method for the decolorization of wastewaters containing indigo carmine dye. The bioassays used in the present study provided good credibility for checking the detoxification of treated and untreated indigo carmine solutions.