皂角苷和柠檬酸联合对市政污泥中重金属的去除与风险评价

污泥的重金属污染严重制约其资源化利用,为探讨皂角苷和柠檬酸联合淋洗去除污泥中重金属的效果,为污泥的资源化利用提供理论依据,以武汉市4个市政污泥样品(S₁、S₂、S₃、S₄)为研究对象,选取1%的皂角苷和0.1 mol/L的柠檬酸联合淋洗1~4次,对淋洗前后污泥中重金属Cu、Ni、Pb、Zn、Cd和Cr的含量和形态进行了分析,并运用M_F指数法和潜在生态风险指数法对淋洗后污泥中重金属的迁移性和环境效应进行了评价。结果表明:经过1次淋洗后,污泥中Zn的去除率最高,为71.04%(S₁),而Ni的去除率较低,为20%左右(S₂),污泥中Cr、Cu、Pb和Cd的最大去除率在23.16%~43.00%之间;经过4次淋洗后,污泥中Zn、Pb、Cr、Cu、Cd和Ni的去除率最高分别为84.79%、81.73%、80.77%、78.89%、56.71%和55.51%;经过淋洗后污泥中各重金属酸溶态所占的比例降至5.41%以下,污泥中Cu以残渣态和可氧化态为主,其他重金属以残渣态为主;皂角苷与柠檬酸联合淋洗后,污泥中重金属的M_F(移动性指数)和E_i(潜在生态风险指数)值下降,说明污泥中重金属的移动性、生物有效性和潜在生态风险减弱,其中污泥中Ni、Pb、Zn的潜在生态风险均由中降为低,污泥中Cu、Cr和Cd的潜在生态风险也有所降低;1.5 g/L的熟石灰对污泥淋洗废液中Cu、Ni的回收率在25%左右,对Pb、Zn、Cd、Cr的回收率在58%~80%之间。皂角苷和柠檬酸联合淋洗可以较好地去除供试污泥中的重金属,降低重金属的移动性和潜在生态风险。

Removal and Risk Assessment of Heavy Metals in Municipal Sludge by Saponin and Citric Acid

Heavy metal pollution of sludge severely restricts its resource utilization.To investigate the effect of combined leachings of saponin and citric acid to remove heavy metals in sludges,and to provide a theore-tical basis for the sludge resource utilization,taking four municipal sludge samples(S₁,S₂,S₃ and S₄)in Wuhan as the objects,this research selects 1%saponin and 0.1 mol/L citric acid to leach the tested sludges 1 to 4 times,and analyzes the contents and forms of Cu,Ni,Pb,Zn,Cd and Cr in sludges before and after combining leachings with saponin and citric acid,and also uses the MF factor and potential ecological risk index to evaluate the mobility and environmental effect of heavy metals in the sludges after leachings.The results show that after once leaching,the highest Zn removal rate is 71.04%(S₁),while the removal rates of Ni and Cr are lower,about 20%.The highest removal rates of Cu,Pb and Cd are between 23.16%-43.00%.After leaching 4 times,the highest removal rates of Zn,Pb,Cr,Cu,Cd and Ni are 84.79%,81.73%,80.77%,78.89%,56.71%and 55.51%,respectively.After leachings,the proportions of heavy metals in acid soluble fraction are below 5.41%.Cu is mainly in residual fraction and oxidation fraction,and others are mainly in residual fraction.After leachings,the M_F and E_i values of heavy metals decrease,indicating that their mobility,bioavailability and potential ecological risk are reduced.The potential ecological risks of Ni,Pb,and Zn are reduced from medium to low,and the potential ecological risks of Cu,Cr,and Cd are also reduced.When treating the leaching waste liquid,the recovery rates of Cu and Ni with 1.5 g/L slaked lime are about 25%,while the recovery rates of Pb,Zn,Cd,and Cr are 58%~80%.It is shown that the combined leachings of saponin and citric acid can better remove heavy metals in the tested sludges and reduce the mobility and potential ecological risk of heavy metals.