Relations between extraction protocols for activated sludge extracellular polymeric substances (EPS) and complexation properties of Pb and Cd with EPS: Part II. Consequences of EPS extraction methods on Pb2+ and Cd2+ complexation

To study the effect of extraction protocols on extracellular polymeric substances (EPS) metal binding ability, EPS from two activated sludges were extracted by eight extraction protocols: three chemical treatments, four physical treatments and a control. Two pKa, for each EPS, were determined: pKa1 may be specific for carboxyl and phosphoric and pKa2 may be attributed to phenolic and amino functional groups according to EPS composition and IR spectra. EPS pKa values could be affected by the presence of extraction reagents and/or the modifications of EPS by extraction reagents. Complexation study performed at pH 7 by a polarographic method has always showed a greater affinity of EPS for Pb2+ than for Cd2+. The complexation properties of EPS extracted by chemical methods were greatly modified. Concerning EPS extracted by physical methods, their complexation properties were close except for EPS obtained by heating. Standardized extraction methods must be established as a function of the aims of the EPS study.