Electrochemical treatment of carwash wastewater using Fe and Al electrode: Techno-economic analysis and sludge characterization

The present study was conducted to investigate the electrochemical treatment of carwash wastewater using electrocoagulation (EC) process with Fe and Al electrodes. The effects of operating conditions such as initial pH (2-10), current density (0.1-5 mA/cm2) and operating time (5-50 min) on chemical oxygen demand (COD), oil-grease, chloride removal efficiencies as well as total operating costs were studied. The optimum conditions that achieve higher removal efficiencies were found as pH: 8, current density: 3 mA/cm2, operating time: 30 min for Fe electrode and pH: 6, current density: 1 mA/cm2, operating time: 30 min for Al electrode. The removal efficiencies for COD, oil-grease and chloride were obtained as 88%, 90% and 50% for Fe and 88%, 68% and 33% for Al electrodes under the optimum conditions. The total operating costs at the optimum conditions were calculated as 0.6 $/m3 and 0.3 $/m3 for Fe and Al electrodes, respectively. The sludge samples generated after EC process were characterized with Fourier transform infrared (FTIR) spectroscopy and zeta potential measurements for both electrodes. The analyses showed the presence of hydroxides and oxyhydroxides in the sludge samples and the surface of the sludge samples was negatively charged in the wide range of pH. As a conclusion, this study revealed that EC process using Fe electrode should be a feasible technology for higher COD and oil-grease removals from carwash wastewaters.