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

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 S1,S3,S5 and S6 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.