污泥基生物炭中重金属的形态分布及潜在生态风险研究

摘要

Heavy metals are one of the limited factors to the resource utilization of municipal sludge, which can be greatly decreased and solidified by carbonation. In this study, Tessier sequential extraction was used to characterize the speciation of heavy metal in sludge and sludge-derived biochar from different pyrolyzed temperatures (300~700 ℃). Meanwhile, potential ecological risk of sludge-derived biochar was assessed using Hakanson method. The conclusion showed that the highest content of heavy metal in sludge and biochar were Zn and Cu. The order of heavy metal in sludge and sludge-derived biochar was Zn>Cu>Ni>As>Pb>Cd. With the increment of temperature, the speciation of heavy metal was mainly distributed in the residual fraction. When the temperature was 700 ℃, the residue fraction of Cu, Zn, Pb, Cd, Ni and As was 95%, 53%, 71%, 59%, 57%and 58%at 700 ℃, respectively. Heavy metals in sludge-derived biochar were distributed in residual fraction, except Ni. The results of potential ecological risk indicated that the main risk factors were As, Cd and Zn. Compared with raw sludge, the potential ecological risk of sludge-derived biochar obviously decreased. When the pyrolyzed temperature was 700 ℃, the potential ecological risk index decreased from 489.32 (raw sludge) to 73.27. Therefore, from the perspective of heavy metal environmental risk, the recommended temperature range for preparation of sludge-derived biochar was 600~700 ℃.%重金属是城市污泥资源化利用的限制因子。炭化是污泥处理处置的重要途径。本研究中采用 Tessier 序列提取方法研究城市污水处理厂污泥及不同温度制备（300~700℃）的污泥基生物炭中重金属的形态分布，并运用Hakanson方法评价污泥及污泥基生物炭的潜在生态风险。结果表明：污泥和污泥生物炭中重金属含量最高的均为Zn和Cu。污泥及污泥基生物炭中重金属含量总体的次序规律是：Zn>Cu>Ni>As>Pb>Cd。随着热解温度增加，重金属更多的转化到残渣态中。600~700℃制备的污泥基生物炭中的重金属主要分布残渣态中，除Ni之外。热解温度为700℃时，污泥基生物炭中Cu、Zn、Pb、Cd、Ni和As的残渣态分别占到95%、53%、71%、59%、57%和58%。根据单个重金属的潜在生态指数（Er）可知，污泥及污泥基生物炭中的主要风险因子是As﹑Cd和Zn。当热解温度为700℃时，污泥基生物炭的潜在风险指数（RI）从原污泥的489.32降低至73.27。可见，污泥基生物炭中重金属的潜在生态风险显著降低。因此，从重金属环境风险的角度考虑，污泥基生物炭制备的合适温度在600~700℃。