Abstract：
The heavy metals (HMs) contained in sewage sludge are some of the largest obstacles that hamper the usage of sewage sludge in land application (e.g. fertilizer, soil improver). The conventional chelators, e.g., ethylenediaminetetraacetic acid (EDTA), were effective in the remediation of HMs polluted sewage sludge, but suffered from an evident drawback of low biodegradability. Therefore, the applicability of a new biodegradable chelator, methyl glycine diacetic acid (MGDA), to extract HMs from sewage sludge was carried out and compared with EDTA. The experimental parameters affecting the performance of MGDA were optimized. Leaching results showed that in general, MGDA exhibited higher Zn leaching efficiency and similar Cu, Ni and Cr leaching efficiencies with EDTA at same pH and dosage conditions. The maximum Zn, Cu, Ni and Cr leaching efficiencies of MGDA were 94.1% ± 4.5%, 58.2% ± 3.1%, 78.2% ± 2.3% and 54.6% ± 2.5%, respectively. The leaching efficiency plateaued within a reaction time of 4 h, but that of Cu and Ni showed a slightly decreasing trend during hours 4 to 10. In raw sewage sludge, the Zn and Cu were mainly presented in the organically bound fraction, i.e., 45.3 ± 3.2% of total Zn and 48.3 ± 1.4% of total Cu. The addition of MGDA and EDTA caused obvious distribution transformations in Zn and Cu from the organically bound fraction to soluble fraction. According to the reduced partition index calculation, the mobility of Zn, Cu, Ni, and Cr was not significantly lowered after the MGDA treatment. However, the HMs secondary pollution risk of the sludge was reduced due to the drop of the total HMs content after chelator leaching. Findings from this study suggest that MGDA could be a potential environment-friendly alternative for refractory chelators (e.g. EDTA) in the decontamination of HMs from sludge.
摘要：
污水污泥中含有的重金属（HMs）是阻碍污水污泥在土地应用中使用的一些最大障碍（例如肥料，土壤改良剂)。传统的螯合剂，例如，乙二胺四乙酸(EDTA),有效地修复了HMs污染的污水污泥，但具有明显的生物降解性低的缺点。因此,一种新的可生物降解的螯合剂的适用性，甲基甘氨酸二乙酸（MGDA），从污水污泥中提取HMs，并与EDTA进行比较。优化了影响MGDA性能的实验参数。浸出结果表明，总的来说，MGDA表现出更高的Zn浸出效率和相似的Cu，在相同的pH和用量条件下，EDTA的Ni和Cr浸出效率。最大Zn,Cu,MGDA的Ni和Cr浸出效率为94.1%±4.5%，58.2%±3.1%,78.2%±2.3%和54.6%±2.5%，分别。浸出效率在4h的反应时间内达到稳定，但是Cu和Ni在4至10小时期间显示出略微下降的趋势。在原污水污泥中，Zn和Cu主要存在于有机结合部分，即，总Zn的45.3±3.2%和总Cu的48.3±1.4%。MGDA和EDTA的添加导致Zn和Cu从有机结合部分到可溶性部分的明显分布转变。根据简化的分区指数计算，锌的迁移率，Cu,Ni,MGDA处理后Cr没有显著降低。然而,由于螯合剂浸出后总HMs含量的下降，降低了污泥HMs的二次污染风险。这项研究的结果表明，MGDA可能是一种潜在的环境友好的替代品，用于从污泥中清除HMs的难降解螯合剂（例如EDTA）。
