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 mgNO_x -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 mgNO_x -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.

Keywords: EBPR; Parcubacteria; post-anoxic denitrification; specific denitrification rate.