Global Insights into Extracellular Polymeric Substances from Activated Sludge Yield, Composition, and Microbial Communities

Activated sludge (AS) wastewater treatment generates substantial excess sludge which needs to be discarded and thereby increasing operational costs. Extracellular polymeric substances (EPS) within activated sludge (AS) present a potential resource for recovery, reducing sludge volume and mass while adding value. To achieve this, EPS must be better characterized, and the link between EPS composition and its producers, namely the microbial community, remains poorly understood. Here, we analysed extracted EPS from 16 wastewater treatment plants across 13 countries and 5 continents and found alkaline extractable EPS yields varied widely. The microbial community composition of abundant species varied across plants and particularly across continents but did not correlate to the EPS yield. Only sludge retention time had a significant correlation (p = 0.027). Traditional colorimetric assays failed to detect compositional trends of the EPS, but Fourier Transform Infrared (FTIR) analysis indicated that extracted EPS from biological phosphorus removal systems had higher lipid and polysaccharide content, while chemical phosphorus removal systems had higher relative protein content. Thus, FTIR proved effective for distinguishing extracted EPS composition, demonstrating its potential as a high-throughput characterization tool. These findings highlight that the wastewater treatment design and operation may shape the functional groups in EPS when using the alkaline method. More investigations are needed to find possible correlations between the composition of extracted EPS and the microbial community structure. Overall, the study presents a baseline for the amount and overall composition of biopolymers that can be extracted from global AS plants for recovery.