Interrogating the performance and microbial ecology of an enhanced biological phosphorus removal/post‐anoxic denitrification process at bench and pilot scales

Abstract

Research focused on interrogating post‐anoxic enhanced biological phosphorus removal (EBPR) at bench and pilot scales. Average bench‐scale effluent ranged from 0.33 to 1.4 mgP/L, 0.35 to 3.7 mgNH3‐N/L, and 1.1 to 3.9 mgNOx‐N/L. Comparatively, the pilot achieved effluent (50th percentile/average) of 0.13/0.2 mgP/L, 9.7/8.2 mgNH3‐N/L, and 0.38/3.3 mgNOx‐N/L under dynamic influent and environmental conditions. For EBPR process monitoring, P:C ratio data indicated that 0.2–0.4 molP/molC will result in stable EBPR; relatedly, a target design influent volatile fatty acid (VFA):P ratio would exceed 15 mgCOD/mgP. Post‐anoxic EBPR was enriched for Nitrobacter spp. at 1.70%–20.27%, with Parcubacteria also dominating; the former is putatively associated with nitritation and the latter is a putative fermenting heterotrophic organism. Post‐anoxic specific denitrification rates (SDNRs) (20°C) ranged from 0.70 to 3.10 mgN/gVSS/h; there was a strong correlation (R2 = 0.94) between the SDNR and %Parcubacteria for systems operated at a 20‐day solids residence time (SRT). These results suggest that carbon substrate potentially generated by this putative fermenter may enhance post‐anoxic EBPR. Practitioner Points Post‐anoxic EBPR can achieve effluent of <0.2 mgP/L and <12 mgN/L. The P:C and VFA:P ratios can be predictive for EBPR process monitoring. Post‐anoxic EBPR was enriched for Nitrobacter spp. over Nitrospira spp. and also for Parcubacteria, which is a putative fermenting heterotrophic organism. Post‐anoxic specific denitrification rates (20°C) ranged from 0.70 to 3.10 mgN/gVSS/h. BLASTn analysis of 16S rDNA PAO primer set was shown to be improved to 93.8% for Ca. Accumulibacter phosphatis and 73.2%–94.0% for all potential PAOs.