Characterization of Proton Binding Properties of Extracellular Polymeric Substances in an Expanded Granular Sludge Bed Using Linear Programming Analysis

Aims: Extracellular polymeric substances (EPS) produced in biological wastewater treatment processes are from substrate metabolisms and biomass decay and mainly consist of proteins, polysaccharides, and nucleic acids. The chemical functional groups associated with these polymeric substances determine the charge, hydrophobicity, and chelating capacity of EPS. In spite of the fundamental importance of the proton binding properties of EPS, very limited studies have, to date, been conducted to explore the proton binding properties of colloidal and soluble EPS in biological wastewater treatment systems. The aims of this paper are to demonstrate the application of linear programming analysis of titration data in characterization of the pKa, intensity, and chemical functional properties of proton binding sites of EPS in biological wastewater treatment systems.

Methodology: In this study, EPS has been sampled from a full-scale expanded granular sludge bed (EGSB) and a combined chemical composition analysis, linear programming analysis of titration data, and FT-IR analysis method was used to characterize the proton binding properties of the EGSB EPS.

Results: The linear programing analysis determined that the EGSB EPS has 4 proton binding sites with pKa values of 6.4, 7.3, 7.6, and 9.7 at intensities of 1.26, 0.14, 0.25, and 3.12 mmol/g-EPS, respectively. The chemical composition analysis showed that the main acid/base reaction species in the titration sample are proteins, polysaccharides, and phosphates. The FT-IR analysis confirmed that the identified sites could be associated with carboxyl, phosphate, and amine chemical functional groups.

Conclusions: This study illustrated that the combination of chemical composition analysis, the linear programming analysis of titration data, and FT-IR analysis is an effective approach to determine the pKa, intensity, and chemical functional properties of proton binding sites of EPS. Determining the chemical functional properties of EPS is of great importance for studying the fate of heavy metals in biological wastewater treatment processes, sludge bio-flocculation principles, and EPS membrane fouling in wastewater treatment membrane bioreactors (MBRs).