Electrochemical treatment of high strength chrome bathwater: A comparative study for best-operating conditions

Abstract

In this study, high strength chromium (1500 ​ppm) wastewater was treated by electrochemical and chemical precipitation. Preliminary experiments using synthetic wastewater were carried out to optimize the process parameters viz. pH, current density and treatment time by systematically varying these variables as per response surface methodology (RSM) approach. The results showed that 97.5% chromium removal efficiency was achieved under optimized process conditions, i.e. pH 5, current density 68 A/m2 and treatment time 17 ​min. The electrolyte concentration beyond 4 ​g/L does not significantly improve chromium removal efficiency. The optimized process conditions from simulated solution were used to treat real chrome bathwater, but due to the highly acidic nature of the chrome bath, negligible chromium removal was obtained. Thus, two industrial wastewater management approaches were used to improve the chromium removal efficiency (i) dilution of the chrome bathwater (ii) chemical precipitation before electrocoagulation. Electrocoagulation treatment of five-fold diluted chrome bathwater has 99.9% chromium removal efficiency in 55 ​min of treatment time consuming specific energy consumption (SEC) of 10.3 ​KWh/kg of chromium. By integration of chemical precipitation and electrochemical treatment, the chromium removal efficiency of 97.3% was observed in 240 ​min of treatment time with SEC of 27.3 ​kWh/kg of chromium. Integration of reduction-precipitation before electrochemical treatment is another choice, in contrast, to sample dilution with an option for retrofitting of existing treatment schemes.