Speciation of heavy metals in untreated domestic wastewater sludge by time saving BCR sequential extraction method

In this work the modified three-stage sequential extraction procedure developed within the Standards, Measurement and Testing Programme (formally the Community Bureau of Reference BCR) of the European Commission, was applied for the fractionation of Cd, Cr, Cu, Ni, Pb and Zn in the untreated domestic wastewater sludge (DWS) collected from the Hyderabad city of Pakistan. The aim of our study was to evaluate the impact of different time intervals for shaking, and sample mass of sewage sludge on optimal recovery of all metals under study. Analyses of the extracts were performed by flame atomic absorption spectrometry (FAAS) and electrothermal atomic absorption spectrometry (ETAAS). The precision and accuracy of the proposed procedure was evaluated by using a certified reference material of soil amended with sewage sludge BCR 483. The maximum recoveries for Cd and Zn were observed for all three steps of BCR protocol at 26 hours (h) total shaking period, while Cr, Cu, Ni and Pb were achieved at 32 hours instead of previously reported 51 hours, with (p < 0.05). The maximum level of all heavy metals was achieved in samples mass 0.2-0.4 g, where as the extractant-sample mass ratio was kept according to the optimized BCR method. The results of the sequential extraction study of untreated DWS indicates that more easily mobilized forms (acid exchangeable) were found to be 31.0, 3.1, 2.5, 7.6, 2.6 and 8.4% of total contents of Cd, Cr, Cu, Ni, Pb and Zn, respectively. The oxidizable fraction is dominant for all the heavy metals, except Cd. The lixiviation tests (DIN 38414-S4) were used to evaluate the leaching of heavy metals from sewage sludge used for agricultural purposes.