Performance and Microbial Population in Side-Stream Enhanced Biological Phosphorus Removal Systems

Side-Stream Enhanced Biological Phosphorus Removal (S2EBPR) Enables Effective Phosphorus Removal in a Pilot-scale Shortcut Nitrogen Removal System

“…Known GAOs, including Competibacter and Propionivibrio, were detected in the system, and the vast majority (~97%) are Competibacter. A decrease in the relative abundance of total known GAOs was observed (from 3.13±1.20% in Phase 1 to 1.91±0.89% in Phase 2) (Figure 5B), which has also been observed in previous S2EBPR studies (Onnis-Hayden et al 2020. It suggests that the conditions in the P(D)N-S2EBPR system (e.g., the combination of side-stream RAS fermentation) could provide competitive advantages to PAOs over GAOs, as discussed in Section 3.2.1.…”

“…The anaerobic P release to VFA uptake ratio (P/VFA) in fermentate and HAc feeding batch tests is 0.16 and 0.25 P-mol/Cmol, respectively (Table 2), which are considerably lower than the values predicted in the PAO models (0.37-0.50 P-mol/C-mol) (Hesselmann et al 2000, Smolders et al 1995 and some EBPR systems (Lanham et al 2013, Onnis-Hayden et al 2020). Relatively low P/VFA ratios have also been reported previously in some EBPR systems with good P removal performance, such as in an Accumulibacter clade II culture exhibiting a mixed PAO-GAO metabolism (0.22 P-mol/C-mol) (Welles et al 2015), as well as in an S2EBPR facility run in an unmixed in-line MLSS fermentation (UMIF) configuration (0.16 P-mol/C-mol) (Onnis-Hayden et al 2020).…”

“…For the typical S2EBPR process in side-stream RAS fermentation (SSR) configurations without supplemental carbon addition, a 16-48 h HRTSS was recommended to ensure sufficient VFA production via RAS fermentation (Gu et al 2019). In the alternative SSR with supplemental carbon (SSRC) configurations, additional carbon flow (e.g., sludge fermentate) was added to the side-stream reactor to increase the C/P ratio (Wang et al 2019), with a smaller S2EBPR volume and shorter HRTSS of 1-4 h , Onnis-Hayden et al 2020). In our P(D)N-S2EBPR system, ~20-30% RAS and A-stage WAS fermentate were blended in the S2EBPR reactor, yielding a HRTSS of ~3.7 h (Table S1).…”

“…The supplemental carbon sources added to the B-stage influent for EBPR, however, would potentially compromise NOB suppression, undermining the stability of shortcut N removal performance (Jia et al 2023, Li et al 2020b. Recently, the successful implementation of side-stream EBPR (S2EBPR) processes, which involve a side-stream anaerobic reactor for simultaneous PAO enrichment and volatile fatty acid (VFA) generation via hydrolysis and fermentation of return activated sludge (RAS) and/or mixed liquor, has promised the potential to enable stable EBPR performance with more flexible configurations without direct dependence on influent carbon (Barnard et al 2017, Onnis-Hayden et al 2020. Compared to conventional EBPR, S2EBPR offers unique conditions that favor PAOs over GAOs, which holds the key to EBPR performance and stability, by introducing a more complex composition of VFAs (i.e., a mixture of acetate and propionate) that leads to higher PAO diversity (Onnis-Hayden et al 2020, Srinivasan et al 2021, and consequently, different P release/uptake kinetics.…”

“…Recently, the successful implementation of side-stream EBPR (S2EBPR) processes, which involve a side-stream anaerobic reactor for simultaneous PAO enrichment and volatile fatty acid (VFA) generation via hydrolysis and fermentation of return activated sludge (RAS) and/or mixed liquor, has promised the potential to enable stable EBPR performance with more flexible configurations without direct dependence on influent carbon (Barnard et al 2017, Onnis-Hayden et al 2020. Compared to conventional EBPR, S2EBPR offers unique conditions that favor PAOs over GAOs, which holds the key to EBPR performance and stability, by introducing a more complex composition of VFAs (i.e., a mixture of acetate and propionate) that leads to higher PAO diversity (Onnis-Hayden et al 2020, Srinivasan et al 2021, and consequently, different P release/uptake kinetics. In addition, extended anaerobic conditions in S2EBPR further give PAOs competitive advantages due to their distinct maintenance and delayed decay associated with the versatility of metabolic pathways and the possession of multiple intracellular polymers (i.e., PHA, glycogen, and polyP) (Li et al 2020a).…”