EPS from Activated Sludge: Prospection of Bioflocculation and Catalytic Properties

The recovery of extracellular polymeric substances (EPS) from activated sludge (AS) represents a promising strategy to transform wastewater treatment plants (WWTPs) into resource recovery facilities within a circular economy framework. In this study, EPS was extracted from an AS process in a full-scale WWTP, highlighting its catalytic and bioflocculant properties, which represent an innovation in the valorization of this biopolymer. The EPS was subsequently characterized in terms of polysaccharides, proteins, and enzymatic activities (amylase and lipase). The bioflocculation performance of the EPS was evaluated using activated sludge mixed liquor. Results showed that EPS recovery yields using 50 °C and 80 °C were 196.3 ± 38.2 mg EPS/g sludge and 283.5 ± 85.4 mg EPS/g sludge, respectively. Enzymatic assays confirmed amylase activity ranging from 100 to 350 U/g sludge according to the extraction temperature. Lipolytic activity (20 U/g sludge) was comparable to values reported in the literature for EPS from biological sludge. The addition of EPS significantly improved the sludge settling velocity (from 0.86 to 4.48 m/h) and the sludge volume index (from 118.6 to 35.5). However, EPS application also increased the resistance to filtration by 50% and reduced cellular respiration by approximately 40%. Overall, the findings demonstrate that EPS from activated sludge acts as an effective bioflocculant with relevant catalytic properties, highlighting its potential as a high-value biotechnological product while also pointing to operational challenges that require further optimization.