Secondary transport mechanisms in amino acid fed enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) water resource recovery facilities (WRRFs) often fail to meet phosphorus discharge permit limits, indicating a need to improve EBPR to reduce environmental phosphorus discharges. EBPR designs are largely based on the Accumulibacter polyphosphate accumulating organism (PAO) metabolism, while understudied Tetrasphaera PAOs are equally important to EBPR in many facilities worldwide. Anaerobic organic carbon competition is believed to be a key driver of EBPR reliability. However, the relationship between Tetrasphaera PAOs' organic carbon uptake mechanisms and their energy metabolism must be fully understood to help reduce EBPR WRRF process upsets, achieve consistently low effluent P concentrations, and inform optimization strategies. We evaluated amino acid uptake mechanisms by monitoring inorganic phosphate, pH, and Na ⁺ changes in anaerobic batch tests of a Tetrasphaera PAO-enriched culture over an initial pH range from 4.5 to 8.8 using anionic aspartate and neutral glycine as sole organic carbon sources. Using amino acids with different charges allowed us to determine that H⁺-driven rather than Na⁺-driven secondary transport was the most likely mechanism used by our Tetrasphaera-enriched culture. Meanwhile, phosphate releases increased alkalinity by the same amount as reducing 4.9 to 7.7 mg-/L of nitrate nitrogen over the initial pH range from 6.0 to 8.0, suggesting that the H⁺ loop created by the secondary transport of amino acids and phosphate plays an important role in anaerobic pH equilibrium and could help provide a stabilizing effect in full-scale EBPR WRRFs where amino acid-utilizing PAOs are the main contributors to EBPR.