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

Metabolic modelling of anaerobic amino acid uptake and storage by fermentative polyphosphate accumulating organisms

Existing enhanced biological phosphorus removal (EBPR) models do not fully describe the metabolism of fermentative polyphosphate accumulating organisms (fPAOs), particularly under mixed substrate conditions representative of fermentation-enhanced EBPR (F-EBPR) processes. This study presents a steady-state metabolic model integrating anaerobic amino acid (AA) fermentation and storage processes in fPAOs. The model identifies key metabolic interactions underlying fPAO metabolism, prioritising substrate accumulation over fermentation. This results in significant changes to ATP and reduction-oxidation (redox) flows as compared to when relying on previous AA fermentation models typically used to describe fPAO metabolism, with medium-chain-length (MCL) polyhydroxyalkanoate (PHA) formation and polyphosphate (polyP) consumption acting as important electron and energy management mechanisms, respectively. Succinate, rather than volatile fatty acids (VFAs), was identified as the more likely synergetic substrate between fermentative and conventional PAOs (cPAOs) under these conditions. Moreover, conditions favourable of VFA efflux by fPAOs may also favour a shift away from a polyP accumulation to a fermentation dominant metabolism. Further work is required to verify the role of MCL-PHA fractions, alongside the contribution of free intracellular AA accumulation as compared to polymers such as cyanophycin or polyglutamate on fPAO metabolism. This metabolic model provides a framework for better understanding the role of fPAOs and their interactions with cPAOs within EBPR processes, informing future modelling and optimisation of F-EBPR systems.

Unlocking the potential of sidestream EBPR: exploring the coexistence of PAO, GAO and DGAO for effective phosphorus and nitrogen removal

Wastewater treatment facilities use enhanced biological phosphorus removal (EBPR) to meet discharge quality limits. However, the EBPR process can experience upsets due to a lack of influent carbon or inadequate anaerobic zones. By using a sidestream EBPR (S2EBPR) process, carbon can be generated internally through fermentation processes and a higher anaerobic mass fraction can be attained in smaller volumes. This study investigates nutrient removal and microbial community trends in a full-scale S2EBPR demonstration at the Calumet Water Reclamation Plant. The study aims to improve a process model of the system by better representing the activity of glycogen-accumulating organisms (GAO) and potential competitors of phosphorus-accumulating organisms (PAO), which were found in high abundance in this study. Modifying anaerobic hydrolysis, GAO glycogen storage and ORP activity parameters resulted in model prediction improvements of approximately 5% for nitrate and nitrite and 10-60% for phosphorus. The study also uses shotgun metagenomic sequencing to profile denitrification pathways of PAO and GAO. It shows that denitrifying GAO may contribute to nitric oxide reduction to a greater degree than denitrifying PAO. This study improves process modeling predictions for S2EBPR and highlights the potential role of denitrifying PAO and GAO in combined phosphorus and nitrogen removal in S2EBPR.

Modeling versatile and dynamic anaerobic metabolism for PAOs/GAOs competition using agent-based model and verification via single cell Raman Micro-spectroscopy

Side-stream enhanced biological phosphorus removal process (S2EBPR) has been demonstrated to improve performance stability and offers a suite of advantages compared to conventional EBPR design. Design and optimization of S2EBPR require modification of the current EBPR models that were not able to fully reflect the metabolic functions of and competition between the polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) under extended anaerobic conditions as in the S2EBPR conditions. In this study, we proposed and validated an improved model (iEBPR) for simulating PAO and GAO competition that incorporated heterogeneity and versatility in PAO sequential polymer usage, staged maintenance-decay, and glycolysis-TCA pathway shifts. The iEBPR model was first calibrated against bulk batch testing experiment data and proved to perform better than the previous EBPR model for predicting the soluble orthoP, ammonia, biomass glycogen, and PHA temporal profiles in a starvation batch testing under prolonged anaerobic conditions. We further validated the model with another independent set of anaerobic testing data that included high-resolution single-cell and specific population level intracellular polymer measurements acquired with single-cell Raman micro-spectroscopy technique. The model accurately predicted the temporal changes in the intracellular polymers at cellular and population levels within PAOs and GAOs, and further confirmed the proposed mechanism of sequential polymer utilization, and polymer availability-dependent and staged maintenance-decay in PAOs. These results indicate that under extended anaerobic phases as in S2EBPR, the PAOs may gain competitive advantages over GAOs due to the possession of multiple intracellular polymers and the adaptive switching of the anaerobic metabolic pathways that consequently lead to the later and slower decay in PAOs than GAOs. The iEBPR model can be applied to facilitate and optimize the design and operations of S2EBPR for more reliable nutrient removal and recovery from wastewater.

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.