Impact of solid residence time (SRT) on functionally relevant microbial populations and performance in full‐scale enhanced biological phosphorus removal (EBPR) systems

Abstract

Investigations of the impact of solid residence time (SRT) on microbial ecology and performance of enhanced biological phosphorus removal (EBPR) process in full‐scale systems have been scarce due to the challenges in isolating and examining the SRT from other complex plant‐specific factors. This study performed a comprehensive evaluation of the influence of SRT on polyphosphate‐accumulating organisms (PAOs) and glycogen‐accumulating organisms (GAOs) dynamics and on P removal performance at Clark County Water Reclamation District Facility in Las Vegas, USA. Five parallel treatment trains with separated clarifiers were operated with five different SRTs ranging from 6 to 40 days. Microbial community analysis using multiple molecular and Raman techniques suggested that the relative abundances and diversity of PAOs and GAOs in EBPR systems are highly affected by the SRT. The resultant EBPR system stability and performance can be potentially controlled and optimized by manipulating the system SRT, and shorter SRT (<10 days) seems to be preferred. Practitioner points Phosphorus removal performance and kinetics are highly affected by the operational solid residence time (SRT), with lower and more stable effluent P level achieved at SRT < 10 days. Excessive long SRTs above that needed for nitrification may harm EBPR performance; additionally, excessive long SRT may favor GAOs to dominate over PAOs and thus further reducing efficient use of rbCOD for EBPR. Microbial population abundance and diversity, especially those functionally relevant PAOs and GAOs, can impact the P removal performances, and they are highly dependent on the operational solid residence time. EBPR performance can be potentially controlled and optimized by manipulating the system SRT, and shorter SRT (≤10 days) seems to be preferred at the influent rbCOD/P ratio and environmental conditions as in the plant studied.

Combined Enhanced Biological Phosphorus Removal (EBPR) and Nitrite Accumulation for Treating High-strength Wastewater

“…Enhanced biological phosphorus removal (EBPR) has been widely applied in treating domestic wastewater, however, the application of EBPR for high-strength waste streams has hardly been explored. EBPR has been deemed as unsuitable due to the presumptions that the high-strength wastewater characteristics may not be suitable for polyphosphate accumulating organisms (PAOs), as well as concerns regarding the performance stability that are susceptible to microbial community competitions and other factors such as pH, temperature, solids retention time, influent carbon to phosphorus ratio and system configurations (Neethling et al, 2006, Onnis-Hayden et al, 2020. A limited number of studies using lab-scale EBPR reactors to treat synthetic high-strength wastewater showed promising overall P removal efficiency (~70%), but no process optimization and comprehensive evaluations of kinetics and mechanisms of the EBPR were performed in these studies (Bickers et al, 2003).…”

“…Recent research advances in fundamental understanding and successful full-scale implementation of influent carbon-independent, return activated sludge (RAS)-fermentation S2EBPR (side-stream enhanced biological phosphorus removal) process achieved concurrence of PAOs selection in presence of sludge digested centrate and promises new opportunities for its application for P-rich wastes (Onnis-Hayden et al, 2020, Wang et al, 2019). Herein, we hypothesize that the S2EBPR concept, where extended anaerobic phases to encourage hydrolysis and fermentation of sludge incorporated in the system, can be combined with short-cut N removal process to achieve simultaneous nitrogen and phosphorus removal for high strength wastewater.…”

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

“…Factors that have been shown to influence the competition between PAOs and GAOs include influent C/P ratio, solid retention time (SRT), substrate type, hydraulic retention time (HRT), temperature, pH, dissolved oxygen, feeding strategy, etc. (Carvalheira, Oehmen, Carvalho, & Reis, ; Filipe, Daigger, & Grady, ; Oehmen, Vives, Lu, Yuan, & Keller, ; Oehmen, Yuan, Blackall, & Keller, ; Onnis‐Hayden et al, ; Rodrigo, Seco, PenyaRoja, & Ferrer, ; Tu & Schuler, ; Wang et al, ; Whang & Park, ).…”

“…Factors that have been shown to influence the competition between PAOs and GAOs include influent C/P ratio, solid retention time (SRT), substrate type, hydraulic retention time (HRT), temperature, pH, dissolved oxygen, feeding strategy, etc. (Carvalheira, Oehmen, Carvalho, & Reis, 2014;Filipe, Daigger, & Grady, 2001;Oehmen, Vives, Lu, Yuan, & Keller, 2005a;Oehmen, Yuan, Blackall, & Keller, 2005b;Onnis-Hayden et al, 2019;Rodrigo, Seco, PenyaRoja, & Ferrer, 1996;Tu & Schuler, 2013;Wang et al, 2006;Whang & Park, 2006). Evaluation of full-scale EBPR performance data reported by Gu et al (2008) indicated that process stability was positively correlated with the influent C/P ratio (as bCOD or BOD/P) and they hypothesized that although excessive available carbon can promote the proliferation of GAOs, stable process performance can be maintained as long as the operational conditions are controlled to kinetically favor the growth of PAOs over GAOs.…”

Machine Learning-Based Determination of Sampling Depth for Complex Environmental Systems: Case Study with Single-Cell Raman Spectroscopy Data in EBPR Systems

“…Briefly, each sludge sample was independently performed a phosphorus release and uptake kinetics batch test as described by Gu et al (2008) . Raman-based phenotypic survey was performed on the sludge extracted throughout the batch test following the preparing and acquisition protocol described by Majed et al (2008) and Onnis-Hayden et al (2019). − All spectra were acquired with a 400–1800 cm –1 range, which is often referred as the “fingerprint range” for various cellular or biomass substances. ,, All acquired spectra were then preprocessed with LabSpec 6 (HORIBA, 2 Miyanohigashi, Kisshoin, Minamiku Kyoto 601-8510 Japan), for cosmic spike removal, smoothing, background subtraction, baseline correction and -normalization. The survey resulted in a total of 922 spectra from eight WRRF-specific data sets labeled from A to H, with F and H had larger sample size (>200) in comparison to the rest six (80–89).…”