In this study, the effect of three Mg/Ca molar ratios (5.0, 3.8 and 1.7) on denitrifying phosphate removal performance, biomass morphology, and Extracellular Polymeric Substances (EPS) were examined. Results showed that when the influent Mg/Ca molar ratio was 3.8, the anaerobic-anoxic EBPR performed complete phosphate removal. The microbial bacterial population was a mixed culture comprised of 81 ± 3% DPAO and 13 ± 2% denitrifying glycogen accumulating organisms (DGAO). A higher influent Mg/Ca molar ratio (5.0) had a distinct impact on phosphate removal, biomass morphology, and EPS. This probably induced the deterioration of the anaerobic-anoxic Enhanced Biological Phosphorus Removal (EBPR). The results of this study may inform the proper operation of an anaerobic-anoxic EBPR, and contribute to its application in the real world.

Enhanced Biological phosphorous removal (EBPR) processes, often operated at low temperatures, are utilised world-wide, but currently little is known regarding enrichment cultures and the characteristics of active organisms (“Candidatus Accumulibacter phosphatis” (Accumulibacter)) under psychrophilic conditions. This study assesses the long-term performance, metabolic activity, microbial community characteristics and sludge morphology in an EBPR community enriched from activated sludge at 10 °C. Long solid retention times (SRT) and low temperatures resulted in the dominance of Accumulibacter type II over type I. Despite changes in the microbial community, P-removal efficiencies did not show obvious differences and although no specific measures were implemented, the enriched Accumulibacter-PAO culture formed stable dense granules. A high level of Alginate-like exopolysaccharides (ALE) were observed, with a large number of Guluronic acid-Guluronic acid (GG) blocks derived from the biomass at 10 °C. This characteristic favors sludge granulation, increasing the mechanical strength of granules formed, which encourages solid-liquid separation and consequently, contributes to the stable operation of EBPR systems.