The Effects and the Mechanism of Pretreatments on Electrokinetic Technology of Sewage Sludge
|School||East China Normal University|
|Keywords||Sewage sludge Heavy metals Electrokinetic removal Freezing-thawing Saponin Composting|
The huge amount of heavy metals in sewage sludge limits its reuse as a resource, and the removal efficiency was not ideal if only electrokinetics was applied. Hence, it is necessary to investigate the sludge pretreatments. In this thesis, different pretreatments on electrokinetic removal of heavy metals in sewage sludge was investigated. The following results were obtained:The effects of freezing-thawing on electrokinetic removal of heavy metals in sewage sludge were investigated. After freezing and thawing, the instable forms of Cu、Zn、Cd and Ni were increased by5.84%.4.49%.15.09%and.4.23%,respectively;the potential availability of Cu. Zn. Cd and Ni were raised by57.14%.22.16%.127.67%and19.08%.The current of freezing-thawing sludge rised33mA in the12hours. Through freezing and thawing,the strengthen times of Cu. Zn. Cd and Ni in2009sludge were188.8.131.52.1.85and0.72, respectively. For2011sludge, the strengthen times of Cu. Zn. Cd and Ni were184.108.40.206.1.44and1.39, respectively. All of these indicated that freezing-thawing was an effective pretreatment on electrokinetic removal of heavy metals.The effects of the biosurfactant saponin on electrokinetic removal of heavy metals in sewage sludge were investigated.The desorption efficiencies of heavy metals were the best with3%of saponin applied to sludge. The current of the sludge with saponin was increasing, but that of the control sludge (without saponin) was reducing. The average pH of the sludge with saponin was lower0.16than the original sludge. The strengthen times of Cu. Zn. Cd and Ni in sludge with saponin were220.127.116.11.2.34and2.13, respectively. It showed that the changeable of Cu fractionation in sludge with saponin is the smallest, but the removal efficiencies of exchangeable metals were significant.The effects of the composting on electrokinetic removal of heavy metals in sewage sludge were investigated. The changeable trends of heavy metals removal differed with the composting time. The best removal efficiencies of Cu was14.51%when the sludge composted for90days; the removal efficiency of Zn was the best when the sludge composted for30days. The removal efficiencies of Cd and Ni were reducing with the time, becoming lower than the original sludge.The current of composting sludge was reducing, but the original current of composted90days was higher than the original sludge. The average pH of the composted sludge was higher0.03than the original sludge. After electrokinetic treatment, the oxidizable metals in composted sludge increased, which connected with the organic matter in the sludge.