[Comparison of Extraction Methods of Extracellular Polymeric Substances from Activated Sludge]

Extracellular polymeric substances (EPSs) are biosynthetic polymers of microbial origin in the sludge activation process and crucially affect the properties of sludge in biological wastewater treatment reactors, such as the formation of sludge flocs, stabilization of sludge structure, and protection of microbes against noxious environmental conditions. However, the EPS extraction efficiency differs significantly according to the extraction method used. In this study, soluble EPSs and loosely bound EPSs can be extracted by centrifugation first and tightly bound EPSs in activated sludge require additional eight treatments for extraction, respectively. Three physical methods (centrifugation, sonication, and heating) and five chemical methods (cation exchange resin, NaOH, formaldehyde+NaOH, EDTA, and formaldehyde+EDTA) were tested, and the content and composition of TB-EPS were analyzed. Meanwhile, the functional groups and elements in TB-EPS were investigated. Results showed that the heating method did not introduce exogenous substances during the EPS extraction process and that the destruction of cells from this method was relatively slight. Heating was shown to be a gentle and efficient method in this study. The three-dimensional excitation and emission matrix (EEM) fluorescence spectroscopy showed that the cation exchange resin method had good extraction effect on humic-like and protein-like substances. As to fulvic-acid-like substances, NaOH was better than the other seven methods. Infrared spectroscopy showed that no notable difference appeared in the functional groups of the TB-EPS extracted by physical methods, whereas chemical methods induced big differences and showed particular bands that did not appear in the TB-EPS extracted by physical methods. Overall, the amounts of TB-EPS elements extracted using chemical methods were greater than those extracted using physical methods. In conclusion, a method must be selected and established for each case, taking into consideration the experimental purpose, and the most appropriate method should be chosen carefully.