Electrokinetic deposition and removal of heavy metals from sewage sludge enhanced with ammonia complexation

The experiment used an in-house designed electrokinetic equipment in order to remove heavy metals from municipal wastewater sludge. Ammonia was added and mixed with four groups of sludge samples at ratios of 0, 0.08, 0.10, 0.12 (V:V, NH3·H2O/sludge sample). The samples were electrolyzed for 120 hours at a constant DC voltage. The effects of anodic acid generation coupled with ammonia complexation on the enhanced removal of heavy metals from sewage sludge was measured. The results indicated that anodic acidification had a moderate removal rate on heavy metals. Although adding ammonia had no impact on pH and electric current density in the electrokinetic process, it enhanced the trapping and removal rate of heavy metals in the sludge. Results further indicated that different amount of ammonia exerted different levels of removal rates under electrokinetic treatment. When ammonia water was added at a ratio of 0.12, removal rates of Zn and Cu were 91.62% and 71.49%, respectively. Optimal remediation was achieved ata ratio of 0.08 for Pb with a removal rate of 47.85%. The enhanced removal effect by adding ammonia was presumably the result of decreased residual fractions and organic bound fractions, as well as the increased exchangeable fractions of these metals. ©, 2014, Chinese Society for Environmental Sciences. All right reserved.