Electrokinetic Gathering and Removal of Heavy Metals from Sewage Sludge by Ethylenediamine Chelation

Wastewater sludge in Hangzhou Qige Municipal Sewage Plant was used to study the removal rate of heavy metals in sludge using a novel equipment designed in our laboratory. Five groups of sludge samples, mixed with ethylenediamine at the V/V ratio of 0, 0.04, 0.05, 0.06 and 0.07 (C2H8N2 /Sludge sample) were electrified for 120 hours at a constant direct voltage of 18 V. The effects of heavy metals removal on acidification of sludge generated by anode together with ethylenediamine chelation were studied. The results show that acidification generated by anode has played an important role in removing heavy metals from sludge. The addition of ethylenediamine has no significant effect on pH decrease and electric current density in the electric repair process; however, it effectively improved the removal of heavy metals in sludge. Moreover, it was found that various ethylenediamine dosage leads to different reaction efficiencies during the electrokinetic remediation. When ethylenediamine was added at a ratio of 0.06, the removal rates of Zn, Cu and Pb were 87.51%, 67.64% and 57.79% respectively, the overall removal rate is the best. The addition of ethylenediamine has a significant effect on the change of the migration process of heavy metals present in the experimental sludge. We observed the decreased amount of heavy metals in their stable species such as residual state and organic state as well as the increase in transferable form such as exchangeable state.