Characterization of Extracellular Polymeric Substances in Biological Wastewater Treatment Systems

Extracellular polymeric substances (EPS), as a mixture of polymers secreted from microorganisms, and produced from cellular lysis and hydrolysis of macromolecules, are the fundamental materials for the formation and stabilization of the structures of microbial aggregates. Thus, EPS play a very important role in the determination of physiochemical properties of microbial aggregates, such as conformation, adsorption, flocculation, settling, dewatering, and degradation properties, in various biological wastewater treatment processes. Many studies have been conducted for the characterization of EPS by using various techniques, such as confocal laser scanning microscopy, high-performance size exclusion chromatography (HPSEC), gas chromatography, and Fourier transforms infrared spectroscopy (FT-IR). However, the chemical and molecular properties of EPS in biological wastewater treatment processes have not been sufficiently identified and characterized. This thesis focused on the characterization of the chemical and molecular properties of soluble and bound EPS in various biological wastewater treatment systems using a variety of chemical and instrument analysis methods. The methodology of EPS characterization presented in this thesis involved using the combination of membrane filtration, chemical analysis, linear programming analysis (LPA) of titration data, advanced tetra-detector HPSEC, high-performance anion-exchange chromatography (HPAEC), and FT-IR analysis. Soluble and bound EPS obtained from an expanded granular sludge bed process, anaerobic membrane bioreactor, biological nutrient removal process, and anaerobic sludge digestion process have been analyzed and characterized in this Ph.D. project. The results showed that the combination of the analytical methods studied is effective for the determination of the composition and characteristics of EPS, including the monosaccharides composition, molecular weight distribution, viscosity, osmotic pressure, functional group, and proton binding property of EPS. The information regarding EPS obtained in this study is important to improve the understanding of the role of EPS in metal complexion, sludge bio-flocculation, sludge hydrolysis and membrane fouling. The knowledge generated from this Ph.D. program can further promote the optimization of the design and operation of biological wastewater treatment systems.