Biopolymer Production in a Full-Scale Activated Sludge Wastewater Treatment Plant: Seasonal Changes and Promising Bacterial Producers

Wastewater treatment plants (WWTPs) offer the possibility of recovering valuable substances produced by microorganisms, such as extracellular polymeric substances (EPSs). This study aimed to investigate the generation and properties of biopolymers and microbial communities of activated sludge from a large, full-scale WWTP. EPS composition in the activated sludge changed mostly during the transition period from winter to spring. Higher temperatures favored higher protein (PN) concentrations and a higher PN/PSs (polysaccharides) ratio in tightly-bound EPS, stimulating bacterial aggregation. In the sludge, filamentous Microthrix sp. were abundant (~6%) but the settling properties of the sludge improved with increasing PN content in the bound EPS fraction. The content of alginate (ALE)-like polymers averaged 55–60 mg/g Mixed Liquor Suspended Solids, and ALE content in sludge and characteristics were stable during the year. The abundance of Nitrospira sp. and the marine group NS9 in activated sludge correlated with the ALE content in the biomass, pointing to the importance of biopolymer production for nitrogen-transforming microorganisms. The most common EPS-producer was, Candidatus Competibacter (3–4%). The abundance of the Roseiflexaceae family significantly increased in summer, as did the abundance of Trichoccus sp. and Flavobacterium sp. in winter. The study shows that seasonal temperature fluctuations do not significantly affect the production of polymers, especially alginate, which favors commercial ALE recovery. The non-uniform composition of ALE-like polymers shows the possibility of their use in areas that do not require a specific polymer composition, e.g., as environmentally friendly coating materials or sorbents. The study contributes to biopolymer recovery and valorization of activated sludge.