Heavy metal removal effectiveness, flow direction and speciation variations in the sludge during the biosurfactant-enhanced electrokinetic remediation

Heavy metal high content is strictly limited the land application of the sludge, which is considered as the best way for resource utilization. Hence, it is essential to explore a more effective way for reducing toxic metal. In this work, the combined biosurfactant and electrokinetic technique was used to promote toxic metals removal. Electroosmotic flow (EOF), sludge water content, electrolyte and sludge electrical conductivity variations, and removal efficiency, distribution, speciation and binding intensity of heavy metal variations were investigated during the electrokinetic process. The results demonstrated that the combined biosurfactant with electrokinetic technique could enhance toxic metals removal from sludge. In the enhanced electrokinetic treatment, the combined biosurfactant with electrokinetic technique can enhance cumulative electroosmotic flow, and the electrolyte electrical conductivity of anode and cathode, and the EK3 obtained a higher electrical conductivity (EC) than other EK treatments. Heavy metals obtained the highest removal efficiency during the EK3 treatment. Heavy metals distribution demonstrated that 58.63%, 71.34%, 63.04%, 52.95%, 61.74%, 56.24% of copper, zinc, chromium, lead, nickel and manganese migrated into the electrode solution, respectively, and 38.02%, 26.20%, 32.54%, 42.69%, 36.34%, 42.35% of copper, zinc, chromium, lead, nickel and manganese were still remained in the sludge. Heavy metal speciation indicated that the labile speciation percentage decreased. Whereas, the stable speciation percentage increased after the electrokinetic treatments. Heavy metal stability demonstrated that binding intensity increased, due to heavy metal have a higher stable speciation after the electrokinetic treatments.