Sdudy On The Removal Of Heavy Metals In Excess Sludge By Biosurfactant

The generation of large quantities of sludge was settled down in municipal sewage treatment plant, which had the very big development space for the higher nutrition value of sludge for agricultural. However, the heavy metals in sewage sludge were one of the important factors of its agricultural limitation. Therefore, it was necessary to remove heavy metals from sludge. Biosurfactant, which not only contained the advantages of synthetic surfactants but also showed an environmentally-friendly extraction, was suitable to be applied for remediation of heavy metal pollution in sludge.The washing process in a batch experiment was conducted to investigate the performance of rhamnolipid, saponin on removal of copper(Cu), zinc(Zn), nickel(Ni) from excess sludge. Various factors such as concentration, pH, contact time, washing times and distributions of heavy metals were studied. The results showed that:(1) The removal efficiency of copper, zinc and nickel increased with the increase of rhamnolipid concentration. Rhamnolipid showed a better removal efficiency of copper, zinc and nickel in alkaline condition, getting the highest removal efficiency of80.77%,10.86%,46.74%, respectively. For saponin, the higher saponin concentration and lower pH contributed to a better removal efficiency of heavy metals. The maximum removal efficiency of copper, zinc and nickel reached37.83%、44.21%、24.31%, respectively, by a7%saponin solution at pH value of2with24h of shaking.(2) With the increase of contact time and washing times, higher removal efficiency was obtained and rhamnolipid/saponin performed significantly better than deionized water. The removal efficiency was relevant to the combination between heavy metals with biosurfactant molecules and the speciations of heavy metals in sludge. However, too much wsshing times and contact time would not only showed an inefficiency removal but also increased the energy consumption.(3) The fractionations of heavy metals were identified using the sequential extraction. It indicated that rhamnolipid and saponin were effective in removing the exchangeable and carbonated fractions of heavy metals from sludge, getting little removal of residual fractions.Such a remediation procedure indicates that rhamnolipid and saponin were a promising agent for remediation of the municipal sludge containing heavy metals. This study will provide a reference solutions and theoretical foundation to the problems of security risks of heavy metals in recycling excess sludge.