title: Quantification of the interactions between Ca²⁺, Hg²⁺ and extracellular polymeric substances (EPS) of sludge.
abstract: The interactions between metals (Ca(2+) and Hg(2+)) and extracellular polymeric substances (EPS) extracted from the aerobic and anaerobic sludge in wastewater treatment reactors were investigated using a combination of zeta potential measurement and 3-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy with parallel factor (PARAFAC) analysis. Results show that Ca(2+) had no substantial effects on the EEM fluorescence spectra of the EPS, but their zeta potentials increased with the increasing Ca(2+) dosage. However, Hg(2+) had a significant effect on the EEM fluorescence spectra of the EPS, while their zeta potentials seemed not to be affected by the dose of Hg(2+). The interactions between Hg(2+) and EPS were elucidated using the fluorescence quenching with PARAFAC analysis, while the interactions between Ca(2+) and EPS were evaluated by the zeta potential technique. The binding constants for Hg(2+) and EPS were two orders of magnitude higher than those for Ca(2+) and EPS, suggesting that the binding mechanisms between Ca(2+) and EPS were different from those between Hg(2+) and EPS. The results might be useful for understanding the roles of EPS in bacterial self-protection against heavy metals and the aggregate formation mechanisms through ionic bridging interactions.
authors.affiliation: Department of Chemistry, University of Science and Technology of China, Hefei 230026, China.
authors.forename: Guo-Ping
authors.initials: GP
authors.lastname: Sheng
authors.forename: Juan
authors.initials: J
authors.lastname: Xu
authors.forename: Wei-Hua
authors.initials: WH
authors.lastname: Li
authors.forename: Han-Qing
authors.initials: HQ
authors.lastname: Yu
mesh_terms: D002118:Calcium / Q000737:chemistry*; D008628:Mercury / Q000737:chemistry*; D008956:Models, Chemical; D011135:Polysaccharides, Bacterial / Q000737:chemistry*; D012722:Sewage / Q000737:chemistry* / Q000382:microbiology
chemical_list: D011135:Polysaccharides, Bacterial; D012722:Sewage; D008628:Mercury; D002118:Calcium
keywords: Excitation–emission matrix (EEM); Extracellular polymeric substances (EPS); Metal binding; Parallel factor analysis (PARAFAC); Sludge; Zeta potential