皂角苷和柠檬酸联合对污泥中Cu、Pb和Zn的去除及其稳定性特征

以武汉某污水处理厂的污泥为研究对象(S1和S2),通过皂角苷和柠檬酸联合振荡淋洗试验,研究不同体积比(20∶1~1∶20)、固液比(1∶20~1∶80)、淋洗时间(0~2 880 min)、淋洗次数(1~4)对污泥中重金属Cu、Pb和Zn去除的影响.分析淋洗前后各形态重金属的去除特点,并通过计算稳定性指数(I_R值)和移动性指数(MF值)探究重金属稳定性和移动性的变化.结果表明,在体积比(皂角苷∶柠檬酸)为5∶1,固液比为1∶60,淋洗时间1 440 min时,污泥中Cu、Pb和Zn的最高去除率分别可达43.16%(S1)、32.45%(S2)和38.69%(S1).增加淋洗次数对Cu和Pb的去除率有较大幅度提高,而对Zn的影响较小,尤其在2~3次淋洗后差异显著.4次淋洗后Cu、Pb和Zn的最高去除率分别为78.89%(S1)、77.08%(S2)和49.39%(S1).单次淋洗后,除酸溶态和可还原态外,污泥中其余形态的去除率均较低.增加淋洗次数,重金属的各形态去除率逐渐升高,尤其是Pb中的残渣态去除率增长明显.淋洗改变了重金属的稳定性和移动性,4次淋洗后Cu、Pb和Zn的IR值最大增长率分别为43.63%(S1)、39.44%(S2)和32.00%(S1),MF值减少30.19%~79.45%.

Evaluation of the Combined Removal of Heavy Metals by Saponin and Citric Acid from Municipal Sewage Sludges and Metal Stability Features

Sewage sludge contains a high level of nutrients, such as nitrogen, phosphorus, potassium and organic matter, with a high recovery value. The presence of heavy metals in sludges has become a major limiting factor in the utilization of these sludges. Therefore, the removal of heavy metals before land application of sewage sludge has become very necessary. Two municipal sewage sludges (S1 and S2) were collected from municipal wastewater plants in Wuhan city and were studied by oscillation leaching experiments with combination of saponin and citric acid to evaluate their removal efficiencies for Cu, Pb and Zn at different volume ratios (20:1-1:20), ratios of solid to liquid (1:20-1:80), reaction times (0-2880 min), and leaching times (1-4). The heavy metal fractions in the sewage sludges were analyzed before and after leaching to study changes in the stability and mobility of heavy metals by calculating a stability factorrelative bonding strength of heavy metals (I_R)] and a mobility factor (MF). The results show that the highest removal efficiency of Cu, Pb, and Zn was 43.16% (S1), 32.45% (S2) and 38.69% (S1), respectively under the removal conditions of a volume ratio (saponin:citric acid) of 5:1, solid-liquid ratio of 1:60, and leaching time of 1440 min. The removal efficiencies of Cu and Pb were significantly enhanced and Zn had a small increase with longer leaching times, which was significantly different after two to three washing times. The highest removal rate of Cu, Pb, and Zn was 78.89% (S1), 77.08% (S2) and 49.39% (S1) after four washing times, respectively. Beyond acid soluble and reducible fractions, other forms of heavy metals have very low removal rates after a single leaching. The removal rates of heavy metal fractions increased by increasing the leaching time, particularly for Pb, which in the residual fraction was significantly increased. The stability and mobility of heavy metals changes after each leaching. For example, the I_R of Cu, Pb, and Zn increased to 43.63% (S1), 39.44% (S2) and 32.00% (S1), respectively, and the MF of these heavy metals decreased from 30.19% to 79.45% in the sewage sludges after four washing events.