Extraction of extracellular polymeric substances of activated sludge and their application for wastewater treatment

Abstract

Extracellular polymeric substances (EPS) are efficient and environmentally friendly bioflocculants in wastewater pollution that are free from the shortcomings typical of traditional coagulants and flocculants which can pose direct threat to human health and life as well as to the environment. In this paper, the authors have investigated the possibilities of extracting EPS from excess activated sludge and subsequent use of the obtained fractions as reagents for wastewater treatment. The study analyzes the existing methods for extracting EPS, with further selection and implementation of four biopolymer extraction methods. As part of the work, soluble, loosely bound and tightly bound activated sludge EPS fractions were generated using each method. The study of EPS chemical composition demonstrated a significant difference in the obtained fractions from each other; moreover, all the fractions showed the prevailing content of EPS protein components over polysaccharides and humic acids. The most efficient method for extracting proteins from the excess activated sludge biomass is the NH4OH/EDTA method; the one for extracting polysaccharides – the HCHO/NaOH method, and the one for extraction of humic acids – the CH3NO/EDTA method. The study of efficiency of wastewater treatment with the use of obtained fractions has shown that EPS extraction method has an impact not only on the extraction performance, but also on the feasibility of using extracted biopolymers for wastewater treatment. The efficiency of wastewater treatment ranged from 0.2 to 62.6%, depending on the EPS fraction used as a reagent.