Metal binding properties of extracellular polymeric substances extracted from anaerobic granular sludges

Abstract

Extracellular polymeric substances (EPS) were extracted from four anaerobic granular sludges with different procedures to study their involvement in biosorption of metallic elements. EPS extracts are composed of closely associated organic and mineral fractions. The EPS macromolecules (proteins, polysaccharides, humic-like substances, nucleic, and uronic acids) have functional groups potentially available for the binding of metallic elements. The acidic constants of these ionizable groups are: pKa1 (4-5) corresponding to the carboxyl groups; pKa2 (6-7) corresponding to the phosphoric groups; pKa3 (8-10) and pKa4 (≈10) corresponding to the phenolic, hydroxyl, and amino groups. The polarographic study confirms the higher affinity of the EPS to bind to lead than to cadmium. Moreover, the binding of these metallic compounds with the EPS is a mix of several sorption mechanisms including surface complexation, ion exchange, and flocculation. Inorganic elements were found as ions linked to organic molecules or as solid particles. The mineral fraction affects the binding properties of the EPS, as the presence of salts decreases the EPS binding ability. Calcite and apatite particles observed on SEM images of EPS extracts can also sorb metallic elements through ion exchange or surface complexation.

Component analysis and heavy metal adsorption ability of extracellular polymeric substances (EPS) from sulfate reducing bacteria

“…The second zone was located at pH 6.4, which was attributed to thiol or phosphate groups. The third buffering zone was located at pH 9.6, which was attributed to amino or hydroxyl groups (D'Abzac et al, 2013). The peaks indicated a maximum variation in pH corresponding to the equivalence points, and the local minima indicated a minimum variation in pH, which is indicative of buffering (Braissant et al, 2007).…”

“…It was concluded that Cu 2+ and Zn 2+ had greater binding affinity for the functional groups of polysaccharides in the EPS. For example, Cu 2+ binds the carboxyl groups of EPS, while carboxyl and phosphoric functional groups are involved in the binding between Pb 2+ and EPS (Li and Yu, 2014;D'Abzac et al, 2013).…”

“…The potentiometric titration using Protofit Software v. 2.1 allows the determination of the acidic constants (pK a ) of the functional groups involved in proton binding (D'Abzac et al, 2013). The potentiometric titration of EPS showed three buffering zones.…”

Evidence of glycoproteins and sulphated proteoglycan-like presence in extracellular polymeric substance from anaerobic granular sludge

“…-------------------- Table 1 2.1.2 EPS extraction and characterization EPS extraction procedures were carried out according to the methods developed by [18].…”

“…For protein content, the protocol established by [20] was used. For analysis of the mineral composition, protocol from [18] is followed: 3 mL of EPS sample was submitted acid digestion; then digestion was performed with a microwave 3000 (Anton Paar) The metal concentrations in the acid-digested samples were quantified using an atomic absorption spectrometer (Varian Zeeman ASS 800) and inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS) (by ACME Analytical Laboratory Itd. (Vancouver, Canada)) for EPS from GS Sm and GS Ee respectively.…”