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| Removal of Cu and Zn from sewage sludge by saponin |
| Received:December 11, 2015 |
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| KeyWord:saponin;heavy metal;sewage sludge;washing |
| Author Name | Affiliation | E-mail | | ZHANG Bin | Agro-environment Protection Institute Ministry of Agriculture, Tianjin 300191, China
College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China | | | HUANG Li | College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China | daisyh@mail.hzau.edu.cn | | ZHANG Ke-qiang | Agro-environment Protection Institute Ministry of Agriculture, Tianjin 300191, China | | | YE Tao | College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China | | | DU Lian-zhu | Agro-environment Protection Institute Ministry of Agriculture, Tianjin 300191, China | | | QIN Fan-qi | College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China | |
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| Abstract: |
| A chemical washing experiment was conducted to investigate the performance and mechanism of Cu and Zn removal from four types of sewage sludge by saponin. The effects of various factors such as saponin concentration(0~7%), pH(2~6), contact time(0~48 h), temperature(10, 25, 40 ℃), and washing number(1~4) on Cu and Zn removal and the changes of heavy metal distribution before and after washing were examined. The pH changes of effluent during the removal of Cu and Zn from sewage sludge was also monitored. In single washing, the removal efficiency of Cu was better than that of Zn. The pH of saponin solution had no significant effect on the removal of Cu, whereas higher removal efficiency of Zn was obtained when pH was decreased to 2. The maximum Cu removal was achieved when the reaction time was 6~12 h. However, a better removal of Zn needed a longer reaction time(48 h). With increasing temperature, the removal efficiency of Cu was decreased but that of Zn was increased. The cumulative efficiencies of Cu and Zn removal were increased with increasing number of washing. The removal of Cu mainly happened at the first washing, while the Zn removal remained good during all 4 washing. Four washing with 3% saponin at natural pH removed Cu and Zn by 32.61% and 39.32%, respectively. The effluent pH decreased with increases in contact time, temperature, and number of washing but with decreases in pH values of saponin solution. After washing with 3% saponin, all fractions of Cu were reduced, with acid soluble fraction being removed more than 66%, while Zn fractions(reducible, oxidizable, and residual) except acid soluble fraction showed decreases, with the most reduction found in residual fraction. |
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