Operation parameters and temperature affected sludge microbial metabolisms: An integrated perspective considering extracellular polymeric substances, soluble microbial products, biomass quantities, and community shifts

Abstract

Effluent soluble microbial products (SMP) and extracellular polymeric substances (EPS) are significant organics that pose challenges to advanced treatment processes. However, their production, transformation, and decomposition remain unclear due to their heterogeneity and the combined effects of environmental and operational factors. In this work, we investigated the impact of solids retention time (SRT), hydraulic retention time (HRT), and temperature on the changes in effluent SMP, with the consideration of the co-variation of EPS, sludge biomass, and community structures. Results show that longer SRT increased the biomass and relative abundance of functional microorganisms such as Myxococcota, Actinobacteria, and Terrimonas, which hindered EPS-to-SMP turnover and/or facilitated SMP consumption. This resulted in the accumulation of EPS and lower SMP concentrations at the beginning of the SRT adjustment. Both longer and shorter HRT (12 h and 8 h) led to increased SMP concentration, with the shorter HRT nearly doubling it (from approximately 6 to 12 mg/L), especially in terms of its protein and polysaccharide contents. Lower temperatures increased the SMP concentration and the relative abundance of Proteobacteria (including Zoogloea, the most dominant phylum and genus, relative abundance from 15.7 % to 61.1 %) while decreasing fluorescent EPS components, indicating the key role of Proteobacteria in SMP production and fluorescent EPS-to-SMP transformation. The results provided key insights into how changes in operational/environmental parameters impact sludge-EPS-SMP interactions, which could benefit the model development and operational optimization of activated sludge systems. This study also highlighted the important role of the sludge community in the EPS/SMP dynamics.