东北地区城市污水处理厂污泥中重金属的形态分布及其潜在生态风险评价

Fractional distribution and assessment of potential ecological risk of heavy metals in municipal sludges from wastewater treatment plants in Northeast China

分析了东北地区7个城市污水处理厂脱水污泥中Cu、Zn、Cr、Ni、Mn的含量,利用修正的BCR法研究了污泥中重金属的形态分布特征,并使用地累积指数(Igeo)法和内梅罗指数法(PI)评估了污泥在土地利用过程中重金属的潜在生态风险.结果表明,污水厂污泥中Zn含量超过了国家标准(GB4284—1984)限值,且污泥中Cu、Zn和Mn的含量远远超过东北耕地黑土中的背景含量.污泥中Cu和Cr的有机物结合态(即可氧化态)所占比例较大,可迁移形态含量最高的重金属是Zn,Ni广泛分布于可交换态、酸溶态、可还原态、可氧化态和残渣态中,Mn的残渣态在5种形态中所占比例最高.5种金属中迁移性最强的是Zn,其次为Mn,Cr的迁移性最差.内梅罗单项污染指数法和地累积指数法的评价结果表明,Cu、Zn和Mn是污泥土地利用过程中潜在的污染元素.内梅罗综合指数法的评价结果显示,种脱水污泥均对耕地黑土环境存在严重的潜7在生态风险.

The total concentrations of heavy metals in municipal sludges from seven individual Wastewater Treatment Plants （WWTPs） were determined by microwave digestion process; the fractional distribution of heavy metals was obtained by modified BCR sequential extraction procedure; the potential ecological risk of heavy metals for sludge land application was evaluated by nemerow and geo-accumulation pollution index. The results indicated that Zn in SI, $3, $5 and $6 was higher than the threshold values for agriculture application （GB 4284--1984） , and contents of Cu, Zn and Mn were much higher than background values in black soils. Predominant Cu and Cr were existent in organic combined fraction; Zn mainly existed in transferrable fraction; Ni was widely distributed in five chemical fractions; the residue fraction of Mn is higher than other fractions in sludge. The metal with the strongest mobility is Zn, followed by Mn, and Cr the weakest. Results of nemerow and geo-accumulation pollution index revealed that Cu, Zn, Mn had potential ecological risk for sludge land applications. This observation suggests heavy metals will cause serious ecological risk when sludge was directly utilized as fertilizer.