Improving Enhanced Biological Phosphorus Removal with Return Activated Sludge Fermentation and Carbon Addition in a Benchtop Sequencing Batch Reactor Treating Real Wastewater

Enhanced biological phosphorus (P) removal (EBPR) with return activated sludge (RAS) fermentation (S2EBPR) is a recent EBPR innovation suggested to achieve more stable and efficient P removal. However, consensus around these benefits and the mechanisms of S2EBPR is still developing. To further this understanding, three pilot sequencing batch reactors treating real domestic wastewater were operated as S2EBPR or conventional EBPR, with or without external carbon addition, and as S2EBPR with or without the anaerobic phase. Findings include the following: (1) S2EBPR showed a small P removal improvement over conventional EBPR; (2) S2EBPR performed substantially better with a small dose of external carbon added, while conventional EBPR did not, but microbial community stability was increased in both; (3) when external carbon to S2EBPR was stopped, high P removal continued for two solids retention times; (4) the measured fermentation yield suggested a larger benefit to S2EBPR P removal than was observed; (5) S2EBPR without the anaerobic phase did not achieve good P removal; and (6) although microbial community trends were similar, S2EBPR enriched more metabolically flexible polyphosphate accumulating organisms than conventional EBPR, importantly, Candidatus Phosphoribacter. Overall, RAS fermentation was beneficial to EBPR performance and stability with external carbon addition but minimally without.