Comparison of Cr(VI) removal by direct and pulse current electrocoagulation: Implications for energy consumption optimization, sludge reduction and floc magnetism

Abstract Conventional direct current electrocoagulation (DC-EC) suffers from issues of plate passivation, large energy consumption and sludge weight, which greatly restrict its application to wastewater treatment with Cr(VI). In this study, positive single pulse current electrocoagulation (PSPC-EC) and alternating pulse current electrocoagulation (APC-EC) were used to solve the above problems. The optimum removal efficiencies of Cr(VI) obtained by DC-EC, PSPC-EC and APC-EC were all over 99 %. The energy consumptions of DC-EC, PSPC-EC and APC-EC were 3.8 × 10−3, 4.0 × 10−4 and 7.6 × 10−4 kWh/mgCr(VI) and the amounts of dry sludge produced were 1.8612, 1.3024 and 1.1246 g/L, respectively. Among the three types of EC, PSPC-EC consumed the least electrical energy and APC-EC produced the least amount of sludge, indicating their advantages over DC-EC. The flocs produced by PSPC-EC had a better spread performance than those of DC-EC and APC-EC, which contributed to a larger surface area for adsorbing Cr(VI). It should be noted that EC may generate magnetic flocs with easily available iron electrode. Our findings indicate it is possible to adjust the magnetic strength of the flocs simply by adjusting the pulse current on electrode, which has not been reported in previous studies. This exhibits the potential to avoid adding complicated synthetic magnetic coagulants in the water treatment construction and cut down chemical operation cost. Also, it enlightens those dedicated to electrochemistry to develop magnetic-floc-generating electrodes for enhancing contaminant separation and water purification.