Fraction of heavy metals in sludges from typical coking wastewater treatment plants by modified BCR sequential extraction procedure

Fractions of 8 heavy metals (Cd, Cr, Hg, Cu, Zn, Pb, Ni and As) in sludges from two typical coking wastewater treatment plants were determined by atomic absorption spectroscopy (AAS) using the modified the European Community Bureau of Reference sequential extraction procedure as the pretreatment technology. The sludges from biological, coagulation deposition units and the discharged sludges of two plants were sampled and the exchangeable, reducible, oxidable, residual fraction and the total content were determined. The oxidable or residual fraction was the predominant fraction in various sludges and on the contrary that the values of the exchangeable and reducible fractions were much lower. Poor biological availability and low potential environment risk of heavy metals was found in sludges from typical coking wastewater treatment plants. Further results of cluster analysis conducted by SPSS that the units with similar conditions could be classed together identified that the unit condition was one key factor affecting on the fraction of heavy metals in sludges.