Impact of operational strategies on a sidestream enhanced biological phosphorus removal (S2EBPR) reactor in a carbon limited wastewater plant.

Water resource recovery facilities are faced with stringent effluent phosphorus limits to reduce nutrient pollution. Enhanced biological phosphorus removal (EBPR) is the most common biological route to remove phosphorus; however, many facilities struggle to achieve consistent performance due to limited carbon availability in the influent wastewater. A promising process to improve carbon availability is through return activated sludge (RAS) fermentation via sidestream EBPR (S2EBPR). In this study, a full-scale S2EBPR pilot was operated with a sidestream plus carbon configuration (SSRC) at a carbon-limited facility. A model based on the pilot test was developed and calibrated in the SUMO platform and used to explore routes for improving orthophosphate (OP) effluent compliance. Modeling results showed that RAS diversion by itself was not sufficient to drive OP removal to permit limits of 1 mg L-1, therefore, other strategies were evaluated. Supplemental carbon addition of MicroC® at 1.90 L min-1 and controlling the phosphorus concentration below 3.5 mgP L-1 in the primary effluent (PE) proved to be valid supplemental strategies to achieve OP removal below 1 mg L-1 most of the time. In particular, the proposed supplemental carbon flow rate would result in an improvement of the rbCOD:P ratio from 17:1 to 26:1. The synergistic approach of RAS diversion and supplemental carbon addition increased the polyphosphate accumulating organisms (PAO) population while minimizing the supplemental carbon needed to achieve consistent phosphorus removal. Overall, this pilot and modeling study shows that joint strategies, including RAS diversion, carbon addition and PE control, can be effective to achieve optimal control of OP effluent.

Enhancing resource recovery via cranberry syrup waste at the Wisconsin Rapids WRRF: An experimental and modeling study.

The Wisconsin Rapids Wastewater Treatment Plant (WRWWTP) is faced with a more stringent effluent phosphorus requirement that will drive capital investment between 2020 and 2025. The facility will need to achieve a monthly average value of 0.36 mg L-1 of total phosphorus (TP). While the facility has sufficient influent carbon to drive a conventional enhanced biological phosphorus removal (EBPR) configuration, the existing infrastructure makes the addition of influent selector zones cost prohibitive. Underutilized aeration basin capacity was repurposed for testing return activated sludge (RAS) fermentation. The WRWWTP began pilot testing of RAS fermentation in April 2021. The facility moved through a series of operational setpoints to optimize phosphorus removal in a sidestream RAS (SSR) configuration, including RAS diversion, decrease of DO in aeration basins and chemical dosing shutoff. One of the key implementations was the addition of cranberry syrup waste to provide additional carbon for RAS fermentation, converting the process to a SSR plus carbon (SSRC) configuration. By the end of the testing period, effluent total phosphorus was averaging less than 0.4 mg L-1 with no chemical addition. A model was developed in the SUMO platform and was used to capture orthophosphate trends during the testing period. The model investigated microbial population dynamics and found that the operational changes including RAS diversion, chemical dosing shutoff and cranberry syrup waste addition impacted the enrichment of phosphorus accumulating organisms (PAO). After performing a sensitivity analysis on hydrolysis parameters, the predicted hydrolysis rate around 1.8-1.9 mg COD g VSS-1 hr-1 was found to match the batch rate testing data. This is the first study where cranberry syrup waste was used to successfully enhance EBPR performance, resulting in 90% TP removal. While further research is needed regarding the composition of the waste matrix and the microbial community composition, this expands the routes for resource recovery in the field of wastewater treatment.

Survey of full-scale sidestream enhanced biological phosphorus removal (S2EBPR) systems and comparison with conventional EBPRs in North America: Process stability, kinetics, and microbial populations.

Sidestream EBPR (S2EBPR) is an emerging alternative process to address common challenges in EBPR related to weak wastewater influent and may improve EBPR process stability. A systematic evaluation and comparison of the process performance and microbial community structure was conducted between conventional and S2EBPR facilities in North America. The statistical analysis suggested higher performance stability in S2EBPR than conventional EBPR, although possible bias associated with other plant-specific factors might have affected the comparison. Variations in stoichiometric values related to EBPR activity and discrepancies between the observed values and current model predictions suggested a varying degree of metabolic versatility of PAOs in S2EBPR systems that warrant further investigation. Microbial community analysis using various techniques suggested comparable known candidate PAO relative abundances in S2EBPR and conventional EBPR systems, whereas the relative abundance of known candidate GAOs seemed to be consistently lower in S2EBPR facilities than conventional EBPR facilities. 16S rRNA gene sequencing analysis revealed differences in the community phylogenetic fingerprints between S2EBPR and conventional facilities and indicated statistically higher microbial diversity index values in S2EBPR facilities than those in conventional EBPRs. PRACTITIONER POINTS: Sidestream EBPR (S2EBPR) can be implemented with varying and flexible configurations, and they offer advantages over conventional configurations for addressing the common challenges in EBPR related to weak wastewater influent and may improve EBPR process stability. Survey of S2EBPR plants in North America suggested statistically more stable phosphorus removal performance in S2EBPR plants than conventional EBPRs, although possible bias might affect the comparison due to other plant-specific factors. The EBPR kinetics and stoichiometry of the S2EBPR facilities seemed to vary and are associated with metabolic versatility of PAOs in S2EBPR systems that warrant further investigation. The abundance of known candidate PAOs in S2EBPR plants was similar to those in conventional EBPRs, and the abundance of known candidate GAOs was generally lower in S2EBPR than conventional EBPR facilities. Further finer-resolution analysis of PAOs and GAOs, as well as identification of other unknown PAOs and GAOs, is needed. Microbial diversity is higher in S2EBPR facilities compared with conventional ones, implying that S2EBPR microbial communities could show better resilience to perturbations due to potential functional redundancy.

Recent advances in bio-P modelling - a new approach verified by full-scale observations.

This paper summarizes recent developments in biological phosphorus removal modelling, with special attention to side-stream enhanced biological phosphorus removal (S2EBPR) systems on which previous models proved to be ineffective without case-by-case parameter adjustments. Through the research and experience of experts and practitioners, a new bio-kinetic model was developed including an additional group of biomass (glycogen accumulating organisms - GAOs) and new processes (such as aerobic and anoxic maintenance for PAO and GAO; enhanced denitrification processes; fermentation by PAOs which - along with PAO selection - is driven by oxidation-reduction potential (ORP)). This model successfully described various conditions in laboratory measurements and full plant data. The calibration data set is provided by Clean Water Services from Rock Creek Facility (Hillsboro, OR) including two parallel trains: conventional A2O and Westbank configurations, allowing the model to be verified on conventional and side-stream EBPR systems as well.

Rethinking the Mechanisms of Biological Phosphorus Removal.

Enhanced biological phosphorus removal (EBPR) was observed in high-rate, non-nitrifying plants in the United States that were operated in a plug-flow mode. In facilities designed for nitrification and denitrification, a first-stage anaerobic zone, free of nitrate and nitrite was needed to accomplish EBPR, and this is referred to as the Phoredox (a.k.a. the AO and A2O) process. When a biological mechanism responsible for EBPR was proposed, these treatment configurations were accepted as normal practice, but many later observations showed that more reliable phosphorus removal could be achieved with alternative configurations. This paper discusses the development of alternative configurations for EBPR and the likelihood that a host of phosphate accumulating organisms (PAOs) that react to different environmental conditions might play a much bigger role in reliable and sustainable biological phosphorus removal. The conclusion is that conventional designs might have inadvertently selected for less efficient PAOs, while alternative configurations allowed for the growth of multiple PAO species such as Tetrasphaera, which can ferment higher carbon forms and take up phosphorus under anoxic conditions.