The influence of macroelements on energy consumption during periodic power electrokinetic remediation of heavy metals contaminated black soil

Two periodic power (12 h ON/12 h OFF and 18 h ON/6 h OFF) electrokinetic (EK) treatments were conducted to investigate their influence on the removal of heavy metals (Cd, Cu, Ni, Pb and Zn), depletion of soil macroelements (K, Na, Ca, Mg, Fe and Mn) and electric energy consumption. The results indicated that the removal efficiencies of heavy metals were higher than 80% in all the tested EK treatments. Periodic power EK treatment reduced the depletion of Fe and the electrical energy consumption compared with the constant power EK treatment. The lowest energy consumption and depletion of Fe were obtained in the periodic power of 12 h ON/12 h OFF EK treatment. A specific energy concept was developed based on the assumption that all the metals were removed by electromigration and used to predict the energy consumption for each metal. The results showed that more than 40% of electric energy was consumed to remove Fe in all the tested EK treatments. In comparison with the constant power EK treatment, the energy consumption for Fe reduced by 1264 kWh/m3 in the periodic power (12 h ON/12 h OFF) EK treatment, which accounted for 54.74% of the total reduction energy consumption in this EK treatment. Our results demonstrated that the reduction of energy consumption for Fe was one of the main contributors to save the total energy consumption.