Electrocoagulation of petrochemical wastewater by a novel alternative Al-Al electrodes: optimisation and modelling with the response surface method

Abstract

ABSTRACT New electrocoagulation (EC) method by alternative anode–cathode Al-Al (aluminium–aluminium) electrodes was used to reduce COD in petrochemical wastewater. No report of alternative electrocoagulation using switching electrocoagulation (SEC) has been published. The effect of voltage and current density (consumption energy), switching time, total time and the number of electrodes were investigated, and the removal efficiency, isotherms and kinetic data were calculated. Then, the process was optimised with the response surface methodology (RSM) and statistically significant factors, which affect the removal efficiency identified based on the Box–Behnken design (BBD). The interactions between voltage and switching time, and total time on the COD removal were statistically significant for both, two and four Al-Al electrodes. From the analysis of variance (ANOVA), quadratic models have been employed for COD removal, showing high coefficients of determination (R 2) of 0.9692 and 0.9442 for Al-Al electrodes. The optimum conditions for voltage, switching time and total time is 5 V, 15 s and 10 min, respectively, where 98.09% of COD removal by Al-Al could be obtained. Optimised COD removal per cent per energy consumption was 8.9396%/kJ. Biodegradability improvement confirmed by COD, total dissolved solids (TDS) and surface area analysis (BET) of the raw and treated wastewater showed removal and/or demand of aluminium and metal cations and other pollutions.