The effect of pH on the competition between polyphosphate-accumulating organisms and glycogen-accumulating organisms

Recycled Phosphorus Bioamendments from Wastewater Impact Rhizomicrobiome and Benefit Crop Growth: Sustainability Implications at Water-Food Nexus

Phosphorus recovery through enhanced biological phosphorus removal (EBPR) processes from agricultural wastes holds promise in mitigating the impending global P shortage. However, the complex nutrient forms and the microbial augments, expected to exert a profound impact on crop rhizomicrobiome and thus crop health, remained unexplored. In this study, we investigated the impacts of EBPR biosolids on crops growth and rhizomicrobiome in comparison to chemical fertilizer and Vermont manure compost. Our findings revealed that EBPR biosolid augmentation promoted the best maize shoot growth traits with the least nutrient deficiency, evidencing its agricultural benefits. Biosolid augmentation significantly impacted the rhizomicrobiome with decreased biodiversity but higher activities with enriched taxa capable of utilizing various carbon sources. The novel single-cell Raman spectroscopy phenotyping technique uncovered the surprisingly high abundance (up to 30%) of polyphosphate-accumulating organisms (PAOs) in the rhizosphere and their distinctive variations in different biosolid amendments. Furthermore, the interactions between EBPR-derived PAOs such as Candidatus Accumulibacter phosphatis and soil native plant growth promoting rhizobacteria highlighted the previously overlooked status and yet-to-be-characterized functions of PAOs in P cycling. This study provides a novel perspective leveraging EBPR biosolids to facilitate plant growth with agronomic benefits, thereby contributing to more sustainable and ecologically responsible agricultural practices.

Secondary transport mechanisms in amino acid fed enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) water resource recovery facilities (WRRFs) often fail to meet phosphorus discharge permit limits, indicating a need to improve EBPR to reduce environmental phosphorus discharges. EBPR designs are largely based on the Accumulibacter polyphosphate accumulating organism (PAO) metabolism, while understudied Tetrasphaera PAOs are equally important to EBPR in many facilities worldwide. Anaerobic organic carbon competition is believed to be a key driver of EBPR reliability. However, the relationship between Tetrasphaera PAOs' organic carbon uptake mechanisms and their energy metabolism must be fully understood to help reduce EBPR WRRF process upsets, achieve consistently low effluent P concentrations, and inform optimization strategies. We evaluated amino acid uptake mechanisms by monitoring inorganic phosphate, pH, and Na + changes in anaerobic batch tests of a Tetrasphaera PAO-enriched culture over an initial pH range from 4.5 to 8.8 using anionic aspartate and neutral glycine as sole organic carbon sources. Using amino acids with different charges allowed us to determine that H+-driven rather than Na+-driven secondary transport was the most likely mechanism used by our Tetrasphaera-enriched culture. Meanwhile, phosphate releases increased alkalinity by the same amount as reducing 4.9 to 7.7 mg-/L of nitrate nitrogen over the initial pH range from 6.0 to 8.0, suggesting that the H+ loop created by the secondary transport of amino acids and phosphate plays an important role in anaerobic pH equilibrium and could help provide a stabilizing effect in full-scale EBPR WRRFs where amino acid-utilizing PAOs are the main contributors to EBPR.

Carbon, nitrogen, and phosphorus metabolic relationships and reaction mechanisms in SBBR processes in the plateau habitat

In this study, two laboratory-scale SBBR reactors were established in a plateau habitat. Using high flux sequencing, the SBBR process was compared by natural sediment and autotrophic sludge to characterize the functional modules and functional genes of carbon, nitrogen, and phosphorus metabolism under different working conditions and to analyze the reaction mechanism. The results showed that all the functional modules of carbon metabolism and nitrogen metabolism were found in the SBBR process, except for methane metabolism, which occurred at 25 °C in tank 2, the functional modules related to methane metabolism are enhanced at all working conditions. Except for methane metabolism, all functional genes in tank 2 are inhibited by different working conditions, whereas tank 1 shows a slight enhancement. The different working conditions in nitrogen metabolism demonstrate inhibition of functional modules and functional genes in both tanks. Oxidative phosphorylation was missing five functional modules, except for M00153, where only two genes, K00424 and K22501, are missing, all of the required genes are missing in the other four functional modules. Overall the different conditions demonstrated some inhibition in both reaction tanks of the SBBR process. It is preferable to use self-cultivated sludge for membrane acclimation when operating the SBBR process in a plateau habitat. The findings of this study can be used to further research microbial carbon, nitrogen, and phosphorus metabolism mechanisms in SBBR processes in plateau habitats.

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.

Toward Integrating EBPR and the Short-Cut Nitrogen Removal Process in a One-Stage System for Treating High-Strength Wastewater

Enhanced biological phosphorus removal (EBPR) is an economical and sustainable process for phosphorus removal from wastewater. Despite the widespread application of EBPR for low-strength domestic wastewater treatment, limited investigations have been conducted to apply EBPR to the high-strength wastewaters, particularly, the integration of EBPR and the short-cut nitrogen removal process in the one-stage system remains challenging. Herein, we reported a novel proof-of-concept demonstration of integrating EBPR and nitritation (oxidation of ammonium to nitrite) in a one-stage sequencing batch reactor to achieve simultaneous high-strength phosphorus and short-cut nitrogen removal. Excellent EBPR performance of effluent 0.8 ± 1.0 mg P/L and >99% removal efficiency was achieved fed with synthetic high-strength phosphorus wastewater. Long-term sludge acclimation proved that the dominant polyphosphate accumulating organisms (PAOs), Candidatus Accumulibacter, could evolve to a specific subtype that can tolerate the nitrite inhibition as revealed by operational taxonomic unit (OTU)-based oligotyping analysis. The EBPR kinetic and stoichiometric evaluations combined with the amplicon sequencing proved that the Candidatus Competibacter, as the dominant glycogen accumulating organisms (GAOs), could well coexist with PAOs (15.3-24.9% and 14.2-33.1%, respectively) and did not deteriorate the EBPR performance. The nitrification activity assessment, amplicon sequencing, and functional-based gene marker quantification verified that the unexpected nitrite accumulation (10.7-21.0 mg N/L) in the high-strength EBPR system was likely caused by the nitritation process, in which the nitrite-oxidizing bacteria (NOB) were successfully out-selected (<0.1% relative abundance). We hypothesized that the introduction of the anaerobic phase with high VFA concentrations could be the potential selection force for achieving nitritation based on the literature review and our preliminary batch tests. This study sheds light on developing a new feasible technical route for integrating EBPR with short-cut nitrogen removal for efficient high-strength wastewater treatment.

The impact of pH on the anaerobic and aerobic metabolism of Tetrasphaera-enriched polyphosphate accumulating organisms

Members of the genus Tetrasphaera are putative polyphosphate accumulating organisms (PAOs) that have been found in greater abundance than Accumulibacter in many full-scale enhanced biological phosphorus removal (EBPR) wastewater treatment plants worldwide. Nevertheless, previous studies on the effect of environmental conditions, such as pH, on the performance of EBPR have focused mainly on the response of Accumulibacter to pH changes. This study examines the impact of pH on a Tetrasphaera PAO enriched culture, over a pH range from 6.0 to 8.0 under both anaerobic and aerobic conditions, to assess its impact on the stoichiometry and kinetics of Tetrasphaera metabolism. It was discovered that the rates of phosphorus (P) uptake and P release increased with an increase of pH within the tested range, while PHA production, glycogen consumption and substrate uptake rate were less sensitive to pH changes. The results suggest that Tetrasphaera PAOs display kinetic advantages at high pH levels, which is consistent with what has been observed previously for Accumulibacter PAOs. The results of this study show that pH has a substantial impact on the P release and uptake kinetics of PAOs, where the P release rate was >3 times higher and the P uptake rate was >2 times higher at pH 8.0 vs pH 6.0, respectively. Process operational strategies promoting both Tetrasphaera and Accumulibacter activity at high pH do not conflict with each other, but lead to a potentially synergistic impact that can benefit EBPR performance.

Enhanced Bio-P removal: Past, present, and future - A comprehensive review

Excess amounts of phosphorus (P) and nitrogen (N) from anthropogenic activities such as population growth, municipal and industrial wastewater discharges, agriculture fertilization and storm water runoffs, have affected surface water chemistry, resulting in episodes of eutrophication. Enhanced biological phosphorus removal (EBPR) based treatment processes are an economical and environmentally friendly solution to address the present environmental impacts caused by excess P present in municipal discharges. EBPR practices have been researched and operated for more than five decades worldwide, with promising results in decreasing orthophosphate to acceptable levels. The advent of molecular tools targeting bacterial genomic deoxyribonucleic acid (DNA) has also helped us reveal the identity of potential polyphosphate-accumulating organisms (PAO) and denitrifying PAO (DPAO) responsible for the success of EBPR. Integration of process engineering and environmental microbiology has provided much-needed confidence to the wastewater community for the successful implementation of EBPR practices around the globe. Despite these successes, the process of EBPR continues to evolve in terms of its microbiology and application in light of other biological processes such as anaerobic ammonia oxidation and on-site carbon capture. This review provides an overview of the history of EBPR, discusses different operational parameters critical for the successful operation of EBPR systems, reviews current knowledge of EBPR microbiology, the influence of PAO/DPAO on the disintegration of microbial communities, stoichiometry, EBPR clades, current practices, and upcoming potential innovations.

Research advances of the phosphorus-accumulating organisms of Candidatus Accumulibacter, Dechloromonas and Tetrasphaera: Metabolic mechanisms, applications and influencing factors

Phosphorus-accumulating organisms (PAOs), which harbor metabolic mechanisms for phosphorus removal, are widely applied in wastewater treatment. Recently, novel PAOs and phosphorus removal metabolic pathways have been identified and studied. Specifically, Dechloromonas and Tetrasphaera can remove phosphorus via the denitrifying phosphorus removal and fermentation phosphorus removal pathways, respectively. As the main PAOs in biological phosphorus removal systems, the conventional PAO Candidatus Accumulibacter and the novel PAOs Dechloromonas and Tetrasphaera are thoroughly discussed in this paper, with a specific focus on their phosphorus removal metabolic mechanisms, process applications, community abundance and influencing factors. Dechloromonas can achieve simultaneous nitrogen and phosphorus removal in an anoxic environment through the denitrifying phosphorus removal metabolic pathway, which can further reduce carbon source requirements and aeration energy consumption. The metabolic pathways of Tetrasphaera are diverse, with phosphorus removal occurring in conjunction with macromolecular organics degradation through anaerobic fermentation. A collaborative oxic phosphorus removal pathway between Tetrasphaera and Ca. Accumulibacter, or a collaborative anoxic denitrifying phosphorus removal pathway between Tetrasphaera and Dechloromonas are future development directions for biological phosphorus removal technologies, which can further reduce carbon source and energy consumption while achieving enhanced phosphorus removal.

The phylogeny, ecology and ecophysiology of the glycogen accumulating organism (GAO) Defluviicoccus in wastewater treatment plants

This comprehensive review looks critically what is known about members of the genus Defluviicoccus, an example of a glycogen accumulating organism (GAO), in wastewater treatment plants, but found also in other habitats. It considers the operating conditions thought to affect its performance in activated sludge plants designed to remove phosphorus microbiologically, including the still controversial view that it competes with the polyphosphate accumulating bacterium Ca. Accumulibacter for readily biodegradable substrates in the anaerobic zone receiving the influent raw sewage. It looks at its present phylogeny and what is known about it's physiology and biochemistry under the highly selective conditions of these plants, where the biomass is recycled continuously through alternative anaerobic (feed); aerobic (famine) conditions encountered there. The impact of whole genome sequence data, which have revealed considerable intra- and interclade genotypic diversity, on our understanding of its in situ behaviour is also addressed. Particular attention is paid to the problems in much of the literature data based on clone library and next generation DNA sequencing data, where Defluviicoccus identification is restricted to genus level only. Equally problematic, in many publications no attempt has been made to distinguish between Defluviicoccus and the other known GAO, especially Ca. Competibacter, which, as shown here, has a very different ecophysiology. The impact this has had and continues to have on our understanding of members of this genus is discussed, as is the present controversy over its taxonomy. It also suggests where research should be directed to answer some of the important research questions raised in this review.

Insight into aerobic phosphorus removal from wastewater in algal-bacterial aerobic granular sludge system

This study aimed to figure out the main contributors to aerobic phosphorus (P) removal in the algal-bacterial aerobic granular sludge (AGS)-based wastewater treatment system. Kinetics study showed that aerobic P removal was controlled by macropore (contributing to 64-75% P removal) and micropore diffusion, and the different light intensity (0, 4.0, 12.3, and 24.4 klux) didn't exert significant (p > 0.05) influence on P removal. On the other hand, the increasing light intensity did promote microalgae metabolism, leading to the elevated wastewater pH (8.0-9.8). The resultant pH increase had a strongly negative relationship (R² = 0.9723) with P uptake by polyphosphate-accumulating organisms, while promoted chemical Ca-P precipitation at a molar Ca/P ratio of 1.05. Results from this work could provide an in-depth understanding of microalgae-bacteria symbiotic interaction, which is helpful to better design and operate the algal-bacterial AGS systems.

Long-term exposure to zinc oxide nanoparticles improves PAOs function in enhanced biological phosphorus removal

As the most widely applied process for biological phosphorus removal, enhanced biological phosphorus removal (EBPR) relies on phosphorus accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), whose function is crucial for the removal of phosphorus. In this study, the effect of zinc oxide nanoparticles (ZnO NPs, 0-50 mg/L) on EBPR performance was investigated in both long-term reactors and batch experiments. It was found that the performance of biological phosphorus removal was recovered from 0% (day 0) to >99% (day 70) after long-term exposure of ZnO NPs (50 mg/L). Further studies revealed that ZnO NPs treatment caused no significant effects on the morphology and settleability of activated sludge, but enhanced the release and uptake of phosphorus as well as the transformations of polyhydroxyalkanoates and glycogen in activated sludge, which suggested that PAOs were re-activated during long-term exposure to ZnO NPs. Fluorescence in-situ hybridization (FISH) analysis showed that the relative abundance of PAOs was increased after long-term exposure. Meanwhile, the enzymatic activities of PPX and PPK were also enhanced. These results indicated that compared with short-term exposure, long-term exposure to ZnO NPs favours PAOs function and thus led to the recovery of biological phosphorus removal.

Toxicity and combined effects of antibiotics and nano ZnO on a phosphorus-removing Shewanella strain in wastewater treatment

Antibiotics and nanoparticles, which are emerging contaminants, can occur simultaneously in biological wastewater treatment systems, potentially resulting in complex interactive effects. This study investigated the effects of individual and complex zinc oxide nanoparticles (nZnO) and antibiotics (quinolone and sulfonamide), on the Shewanella strain used to remove phosphorus (PO₄^3-), metabolic processes, as well as its complexing and toxicity mechanisms. The inhibition of PO₄^3- removal increased from 30.7% to 100.0% with increased nZnO concentrations (half maximal effective concentration (EC50) = 1.1 mg Zn/L) by affecting poly-p and glycogen metabolites. The combined exposure to nZnO and ciprofloxacin/norfloxacin (CIP/NOR) had a significant antagonistic effect on the removal of PO₄^3- and on the metabolism of poly-p and glycogen in phosphate-accumulating organisms (PAOs), whereas the complexing of sulfonamide and nZnO had no significant additional effect. Thus, the complexing of nanoparticles and antibiotics exhibited different toxicity effects from the antibiotic structure-based complex reactions. These results can be used to improve wastewater treatment processes and reduce risks associated with wastewater discharge.

Simultaneous nitrogen and phosphorus removal from simulated digested piggery wastewater in a single-stage biofilm process coupling anammox and intracellular carbon metabolism

A Single-stage biofilm process coupling Anammox and Intracellular Carbon metabolism (SAIC) was constructed for treating simulated digested piggery wastewater with low carbon/nitrogen ratio (C/N) in this study. TN removal in SAIC system increased by more than 12.77% compared to the reference, and the maximum total phosphorus (TP) removal efficiency reached to 83.70% (C/N = 1.5). Denitrification driven by intracellular carbon, mainly poly-β-hydroxybutyrate (PHB, 78.57%), contributed 32.60% of TN elimination at most, and at least 67.40% should be attributed to anammox. Phosphorus was thought to be mainly removed through biological route, while chemical precipitation also explained around 10% of removed TP. Furthermore, commensalism of glycogen accumulating organisms (GAOs), phosphate accumulating organisms (PAOs), nitrifiers and anammox bacteria was revealed by combining 16S rRNA amplicon sequencing and metagenomics. As a result, multiple metabolic pathways including anammox, (partial) nitrification, endogenous (partial) denitrification and biological P-removal played synergistic effect in SAIC system.

Effects of the carbon/nitrogen (C/N) ratio on a system coupling simultaneous nitrification and denitrification (SND) and denitrifying phosphorus removal (DPR)

Simultaneous nitrification and denitrification (SND) were coupled with a denitrifying phosphorus removal (DPR) to achieve simultaneous nutrient and carbon removal. With influent chemical oxygen demand (COD), ammonia-N (NH₄⁺-N), and total phosphorus (TP) concentrations of 250, 50, and 8 mg/L, the SND-DPR coupled system achieved stable nutrient removal efficiency of COD, NH₄⁺-N, TN and TP were 91.8 ± 1.7%, 88.4 ± 1.8%, 64 ± 3.3% and 99.2 ± 0.6%, respectively. Enhancing the C/N ratio strengthened the storage of intracellular polymers and provided sufficient intracellular carbon sources for phosphorus uptake. The nutrient removal efficiency reached the highest level at a C/N ratio of 5, and no advantage was observed after increasing the C/N ratio to 7. Nutrients were mainly removed during the aerobic stage at a low DO concentration as well during the anoxic stage, which helped achieve concurrent nitrification and denitrification by ordinary heterotrophic organisms (OHOs), promote denitrifying and aerobic phosphorus removal, and conserve organic carbon demand and energy consumption for aeration. The system was limited for DO in the aerobic stage at a low DO concentration, resulting in a deficiency in electron acceptors (O₂ and NO₃^-N) and limiting the subsequent promotion of phosphorus uptake and TN removal. The limited DO content in the low DO stage was the key factor involved in enhancing the nutrient removal efficiency along with the increasing influent C/N ratio.

Resource recovery in aerobic granular sludge systems: is it feasible or still a long way to go?

Lately, wastewater treatment plants are much often being designed as wastewater-resource factories inserted in circular cities. Among biological treatment technologies, aerobic granular sludge (AGS), considered an evolution of activated sludge (AS), has received great attention regarding its resource recovery potential. This review presents the state-of-the-art concerning the influence of operational parameters on the recovery of alginate-like exopolysaccharides (ALE), tryptophan, phosphorus, and polyhydroxyalkanoates (PHA) from AGS systems. The carbon to nitrogen ratio was identified as a parameter that plays an important role for the optimal production of ALE, tryptophan, and PHA. The sludge retention time effect is more pronounced for the production of ALE and tryptophan. Additionally, salinity levels in the bioreactors can potentially be manipulated to increase ALE and phosphorus yields simultaneously. Some existing knowledge gaps in the scientific literature concerning the recovery of these resources from AGS were also identified. Regarding industrial applications, tryptophan has the longest way to go. On the other hand, ALE production/recovery could be considered the most mature process if we take into account that existing alternatives for phosphorus and PHA production/recovery are optimized for activated sludge rather than granular sludge. Consequently, to maintain the same effectiveness, these processes likely could not be applied to AGS without undergoing some modification. Therefore, investigating to what extent these adaptations are necessary and designing alternatives is essential.

The impact of temperature on the metabolism of volatile fatty acids by polyphosphate accumulating organisms (PAOs)

This study investigated the effects of different carbon sources on enriched Accumulibacter PAO cultures at high temperature (30 °C) and compared the carbon transformation with low temperature (20 °C) cases reported in literature, revealing several key metabolic differences. While PAOs seemed to prefer propionate anaerobically as compared to other VFAs at high temperature, high aerobic glycogen replenishment was realized with propionate as the anaerobic carbon source, a trait not previously observed at low temperatures. Therefore, it was found that propionate is not correlated with high P removal by Accumulibacter PAO at high temperatures. A combined substrate of acetate, propionate and perhaps butyrate seemed to be a better carbon source combination, since the total VFA uptake rate increased by up to 46%, and this increased the aerobic P-removal efficiency by up to 38.4% and reduced the glycogen recovery by more than 63% compared to the use of only propionate as substrate. This study improves our understanding of how to stimulate successful EBPR operation in warm climates by augmenting the P removal performance of PAOs.

Toxicity of tetracycline and its transformation products to a phosphorus removing Shewanella strain

Tetracycline (TC) as an emerging contaminant has raised serious concerns about its toxicity and removal in wastewater treatment processes. The more toxic transformation products of TC, 4-epitetracycline (ETC), anhydrotetracycline (ATC) and 4-epianhydrotetracycline (EATC) are also widely detected. This study investigated the antibacterial and bactericidal activity of TC, ETC, ATC, EATC against Shewanella sp, using Escherichia coli and Pseudomonas aeruginosa strains as quality controls. Further, batch assays were conducted to investigate the inhibition of these antibiotics on the phosphorus removal of the Shewanella strain, and removal mechanisms of TC and its transformation products (TCs). The inhibition on phosphorus removal by the Shewanella strain at 20 mg L^-1 was in the order of ATC > EATC > TC > ETC. COD removal, poly-P accumulation and glycogen synthesis by the Shewanella strain were also inhibited. Biodegradation was the main removal mechanism of TC and ETC, while adsorption was the main one of ATC and EATC. This study helps to further understand the structure-activity relationship of TC.

A novel metabolic-ASM model for full-scale biological nutrient removal systems

This study demonstrates that META-ASM, a new integrated metabolic activated sludge model, provides an overall platform to describe the activity of the key organisms and processes relevant to biological nutrient removal (BNR) systems with a robust single-set of default parameters. This model overcomes various shortcomings of existing enhanced biological phosphorous removal (EBPR) models studied over the last twenty years. The model has been tested against 34 data sets from enriched lab polyphosphate accumulating organism (PAO)-glycogen accumulating organism (GAO) cultures and experiments with full-scale sludge from five water resource recovery facilities (WRRFs) with two different process configurations: three stage Phoredox (A2/O) and adapted Biodenitro™ combined with a return sludge sidestream hydrolysis tank (RSS). Special attention is given to the operational conditions affecting the competition between PAOs and GAOs, capability of PAOs and GAOs to denitrify, metabolic shifts as a function of storage polymer concentrations, as well as the role of these polymers in endogenous processes and fermentation. The overall good correlations obtained between the predicted versus measured EBPR profiles from different data sets support that this new model, which is based on in-depth understanding of EBPR, reduces calibration efforts. On the other hand, the performance comparison between META-ASM and literature models demonstrates that existing literature models require extensive parameter changes and have limited predictive power, especially in the prediction of long-term EBPR performance. The development of such a model able to describe in detail the microbial and chemical transformations of BNR systems with minimal adjustment to parameters suggests that the META-ASM model is a powerful tool to predict and mitigate EBPR upsets, optimise EBPR performance and to evaluate new process designs.

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.

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

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.

Nutrient removal and microbial community structure variation in the two-sludge system treating low carbon/nitrogen domestic wastewater

A two-sludge system with separated phosphorus removal unit and nitrification unit was used to treat the actual municipal sewage deficient in organic carbon sources, with the carbon/nitrogen (C/N) ratio of 4.39. The system was first operated as anaerobic/oxic-nitrification (A/O-N) mode for 60 days (phase I), and then transformed into anaerobic/anoxic/oxic-nitrification (A/A/O-N) mode for the next following 80 days (phase II). Noteworthy, oxygen and nitrate acted as electronic acceptors for phosphorus removal in chronological order. Results indicated that deep phosphorus removal and complete nitrification were achieved at both phase I and phase II, and the system exhibited a higher microbial diversity. Microbial community abundance on genus level analysis indicated that Dechloromonas and Accumulibacter were respectively accumulated with 11.6 and 2.42% abundance (A/A/O sludge); and 9.31 and 1.29% Nitrospira and Nitrosomonas occupied the biofilm, and they performed denitrifying phosphorus removal (DNPR) and nitrification, respectively.

Global Sensitivity Analysis of Metabolic Models for Phosphorus Accumulating Organisms in Enhanced Biological Phosphorus Removal

The aim of this study was to identify, quantify and prioritize for the first time the sources of uncertainty in a mechanistic model describing the anaerobic-aerobic metabolism of phosphorus accumulating organisms (PAO) in enhanced biological phosphorus removal (EBPR) systems. These wastewater treatment systems play an important role in preventing eutrophication and metabolic models provide an advanced tool for improving their stability via system design, monitoring and prediction. To this end, a global sensitivity analysis was conducted using standard regression coefficients and Sobol sensitivity indices, taking into account the effect of 39 input parameters on 10 output variables. Input uncertainty was characterized with data in the literature and propagated to the output using the Monte Carlo method. The low degree of linearity between input parameters and model outputs showed that model simplification by linearization can be pursued only in very well defined circumstances. Differences between first and total-order sensitivity indices showed that variance in model predictions was due to interactions between combinations of inputs, as opposed to the direct effect of individual inputs. The major sources of uncertainty affecting the prediction of liquid phase concentrations, as well as intra-cellular glycogen and poly-phosphate was due to 64% of the input parameters. In contrast, the contribution to variance in intra-cellular PHA constituents was uniformly distributed among all inputs. In addition to the intra-cellular biomass constituents, notably PHB, PH₂MV and glycogen, uncertainty with respect to input parameters directly related to anaerobic propionate uptake, aerobic poly-phosphate formation, glycogen formation and temperature contributed most to the variance of all model outputs. Based on the distribution of total-order sensitivities, characterization of the influent stream and intra-cellular fractions of PHA can be expected to significantly improve model reliability. The variance of EBPR metabolic model predictions was quantified. The means to account for this variance, with respect to each quantity of interest, given knowledge of the corresponding input uncertainties, was prescribed. On this basis, possible avenues and pre-requisite requirements to simplify EBPR metabolic models for PAO, both structurally via linearization, as well as by reduction of the number of non-influential variables were outlined.

Enhancement of anaerobic digestion effluent treatment by microalgae immobilization: Characterized by fluorescence excitation-emission matrix coupled with parallel factor analysis in the photobioreactor

The bacterial-microalgal consortium has been investigated to anaerobic digestion effluent (ADE) treatment in the photobioreactor (PBR). However, the high concentrations of nutrients reduced the ADE treatment efficiency and the transformation of organic pollutants in PBR was still unclear. In this study, two-sequencing batch PBRs were operated with suspended Microcystis aeruginosa (M. aeruginosa, SMA) and immobilized M. aeruginosa (IMA) to compare the ADE treatment performance. Fluorescence excitation-emission matrix coupled with parallel factor analysis (EEM-PARAFAC) was conducted to identify organics degradations. The results showed that the proportion of living M. aeruginosa cell (86.4%) in PBR (IMA) was highly significant (p < 0.05) higher than that in PBR (SMA) (75.2%). This indicated immobilized microalgae beads enhanced the resistance to the high concentration of nutrients in PBR (IMA). EEM-PARAFAC analysis displayed the biodegradation order in the bacterial-microalgal consortium system was humic-like substances > tyrosine-like substances > tryptophan-like substances. The removals of humic-like matters (94.05 ± 0.92%) and tyrosine-like matters (91.13 ± 2.49%) in PBR (IMA) were significantly (p < 0.01) higher than those in PBR (SMA). Notably, the average removals of nutrients in PBR (IMA) were significantly (p < 0.05) higher than those in PBR (SMA). This result verified that microalgae immobilization benefitted nutrients removals with 93.05 ± 1.45% of NH₄⁺-N and complete PO₄^3--P removal in PBR (IMA). Moreover, the enrichment of functional genera Flavobacterium and Opitutus contributed to decreasing the organics loadings and strengthening the ADE treatment performance. Therefore, this study verified microalgae immobilization enhanced the actual ADE treatment. Additionally, fluorescent organic pollutants degradations were further evaluated by EEM-PARAFAC analysis in the bacterial-microalgal consortium.

Free nitrous acid-based nitrifying sludge treatment in a two-sludge system obtains high polyhydroxyalkanoates accumulation and satisfied biological nutrients removal

A novel strategy to achieve substantial polyhydroxyalkanoates (PHA) accumulation in waste activated sludge (WAS) was developed, which was conducted in a two-sludge system consisted of an anaerobic/anoxic/oxic reactor (AAO-SBR) and a nitrifying reactor (N-SBR), where the nitrifying-sludge was treated by free nitrous acid (FNA). Initially, 0.98 ± 0.09 and 1.46 ± 0.10 mmol-c/g VSS of PHA were respectively determined in the control-SBR and AAO-SBR. When 1/16 of nitrifying sludge was daily treated with 1.49 mg N/L FNA for 24 h, ∼46.5% of nitrite was accumulated in the N-SBR, ∼2.43 ± 0.12 mmol-c/g VSS of PHA was accumulated in WAS in AAO-SBR without deteriorating nutrient removal. However, nutrient removal of control-SBR was completely collapsed after implementing the same FNA treatment. Further investigations revealed that the activity and abundance of nitrite oxidizing bacteria (NOB) was decreased significantly after FNA treatment. Finally, sludge with high PHA level to generate more methane was confirmed.

Achieving mainstream nitrogen and phosphorus removal through Simultaneous partial Nitrification, Anammox, Denitrification, and Denitrifying Phosphorus Removal (SNADPR) process in a single-tank integrative reactor

Simultaneous partial Nitrification, Anammox, and Denitrification (SNAD) is a promising and energy-efficient nitrogen removal process, which is powerless to eliminate phosphorus and confronted the problem of excessive effluent nitrate once applied in municipal sewage treatment characterized with high C/N ratio (≥2). Herein, by coupling SNAD with denitrifying phosphorus removal (DPR) process in a single-tank reactor, a novel integrative process (termed as SNADPR) was designed to treat municipal sewage. The removal efficiencies of TN, PO₄^3--P, and COD under the optimized conditions (T = 30 °C, HRT = 24 h, DO = 0.45 mg/L) were 89.15 ± 2.19%, 92.93 ± 0.60%, and 99.17 ± 1.58%, respectively. Distinctive microbial community distribution was harvested, where anammox bacteria (AnAOB, Candidatus_Kuenenia and Candidatus_Brocadia) were mainly located in biofilm, whereas denitrifying polyphosphate-accumulating organisms (DPAOs, Dechloromonas and Pseudomonas) and ammonium oxidizing bacteria (AOB, Nitrosomonas) basically lived in suspended floc. The SRT separation between biofilm and floc was reached by conserving AnAOB-rich biofilm and termly discharging phosphorus-rich floc.

Granulation of activated sludge using butyrate and valerate as additional carbon source and granular phosphorus removal capacity during wastewater treatment

As an efficient and low-cost phosphorus (P) removal method from wastewater, enhanced biological phosphorus removal process always faces the insufficient carbon source issue. In this study, two identical sequencing batch reactors were used to cultivate aerobic granular sludge, in which butyrate (Rb) and valerate (Rv), two major volatile fatty acids that can be produced from anaerobic fermentation of waste biomass, were respectively applied as additional carbon source. Both reactors exhibited almost same excellent organics and total nitrogen removals during 120 days' operation, about 95.2-95.7% and 67.9-68.0% respectively with noticeable difference in P removal. Compared to the granules in Rv (24.3 mg P/g-total solids), bigger and more stable ones with higher P removal capacity (11.5 mg P/g-volatile solids∙d) were finally achieved in Rb, containing higher P content (36.0 mg P/g-total solids) with more orthophosphate and polyphosphate accumulated. Microbial community analysis reflected more polyphosphate-accumulating organisms (Rhodocyclus-related bacteria and Actinobacteria) in the granules from Rb.

A critical review of volatile fatty acids produced from waste activated sludge: enhanced strategies and its applications

This paper reviews the recent achievements in the enhanced production of volatile fatty acids (VFAs) from waste activated sludge (WAS). The enhanced strategies are divided into two approaches. The first strategy focuses on the regulation of carbon-to-nitrogen (C/N) ratio by co-digestion of WAS with carbon-rich substrates, including municipal solid wastes (MSW), marine algae, agricultural residues, and animal manures. The other strategy is to enhance the solubilization and hydrolysis of WAS or inhibit the methanogenesis by applying various pretreatments, such as mechanical, chemical, enzymatic, and thermal pretreatment. Finally, the applications of WAS-derived VFAs are discussed. The future researches in enhancing VFAs production and wide application of the VFAs from both technical and economic perspectives are proposed.

Modelling phosphorus uptake in microalgae

Phosphorus (P) is an essential non-renewable nutrient that frequently limits plant growth. It is the foundation of modern agriculture and, to a large extent, demand for P is met from phosphate rock deposits which are limited and becoming increasingly scarce. Adding an extra stroke to this already desolate picture is the fact that a high percentage of P, through agricultural runoff and waste, makes its way into rivers and oceans leading to eutrophication and collapse of ecosystems. Therefore, there is a critical need to practise P recovery from waste and establish a circular economy applicable to P resources. The potential of microalgae to uptake large quantities of P and use of this P enriched algal biomass as biofertiliser has been regarded as a promising way to redirect P from wastewater to the field. This also makes the study of molecular mechanisms underlying P uptake and storage in microalgae of great interest. In the present paper, we review phosphate models, which express the growth rate as a function of intra- and extracellular phosphorus content for better understanding of phosphate uptake and dynamics of phosphate pools.

Denitrifying capabilities of Tetrasphaera and their contribution towards nitrous oxide production in enhanced biological phosphorus removal processes

Denitrifying enhanced biological phosphorus removal (EBPR) systems can be an efficient means of removing phosphate (P) and nitrate (NO₃^-) with low carbon source and oxygen requirements. Tetrasphaera is one of the most abundant polyphosphate accumulating organisms present in EBPR systems, but their capacity to achieve denitrifying EBPR has not previously been determined. An enriched Tetrasphaera culture, comprising over 80% of the bacterial biovolume was obtained in this work. Despite the denitrification capacity of Tetrasphaera, this culture achieved only low levels of anoxic P-uptake. Batch tests with different combinations of NO₃^-, nitrite (NO₂^-) and nitrous oxide (N₂O) revealed lower N₂O accumulation by Tetrasphaera as compared to Accumulibacter and Competibacter when multiple electron acceptors were added. Electron competition was observed during the addition of multiple nitrogen electron acceptors species, where P uptake appeared to be slightly favoured over glycogen production in these situations. This study increases our understanding of the role of Tetrasphaera-related organisms in denitrifying EBPR systems.

Phosphorus removal by in situ generated Fe(II): Efficacy, kinetics and mechanism

The application of in situ electrochemical generation of ferrous (Fe(II)) ions for phosphorus (P) removal in wastewater treatment was investigated with attention to the efficacy, kinetics and mechanism. At concentrations typical of municipal wastewater, P could be removed by in situ Fe(II) with removal efficiency higher than achieved on addition of FeSO₄ and close to that of FeCl₃ under both anoxic and oxic conditions. The generation of alkalinity due to water electrolysis at the cathode created much higher pH conditions compared to FeSO₄ dosing thereby resulting in very different pathways of Fe solid phase formation and associated P removal mechanisms. The remarkably similar dependence of P removal on accumulated Fe for all investigated currents, initial P concentrations and DO conditions indicated that kinetic aspects did not play a role in P removal during in situ Fe(II) dosing. Thermodynamic modelling was undertaken to investigate possible solid phase formation pathways under anoxic conditions and these insights were extended to oxic conditions. The exclusive formation of ferrous hydroxide during anoxic in situ Fe(II) dosing implied that P removal occurred via coprecipitation and adsorption. Under oxic conditions, the high pH conditions would have resulted in rapid Fe(II) oxidation and formation of ferric oxyhydroxides with associated coprecipitation and adsorption effecting P removal in a similar pattern to that observed under anoxic conditions. In situ Fe(II) dosing represents a versatile option for chemical P removal with the precise control of Fe dosage to optimize FeP forms for possible P recovery.

The feasibility of enhanced biological phosphorus removal in the novel oxic/extended idle process using fermentation liquid from sludge fermentation

Carbon sources are essential for biological phosphorus removal (BPR); the carbon sources, however, are often inadequate in municipal wastewater treatment plants. This study demonstrated the feasibility of sludge fermentation liquid enhanced by biosurfactant alkylpolyglycosides (APG) as carbon sources to improve the performance of BPR in the novel oxic/extended idle (O/EI) reactor and the underlying mechanism was also investigated. The results showed that APG induced fermentation liquid could enhance the BPR performance in the O/EI reactor, and the BPR efficiency was 95.2%, which was significantly higher than that in the conventional anaerobic/oxic (A/O) reactor. Mechanism investigation showed that compared with the A/O reactor, the O/EI reactor enriched more polyphosphate accumulating organisms (PAOs) (38.2%), but less glycogen accumulating organisms (GAOs) when the APG-induced fermentation liquid was used as carbon source. The transformations of the polyhydroxyalkanoates (PHA) and glycogen in the O/EI reactor were lower than those in the A/O reactor. Further study found that the activities of polyphosphate kinase (PPK) and acetyl-CoA synthases (ACS) in the O/EI reactor were significantly higher than those of the A/O reactor, which was consistent with the higher BPR efficiency in the O/EI reactor.

Long-term effect of fermented liquid as carbon source on effluent COD and SOP in O/EI reactor.

Trends in the recovery of phosphorus in bioavailable forms from wastewater

Addressing food security issues arising from phosphorus (P) scarcity is described as one of the greatest global challenges of the 21st Century. Dependence on inorganic phosphate fertilisers derived from limited geological sources of P creates an urgent need to recover P from wastes and treated waters, in safe forms that are also effective agriculturally - the established process of P removal by chemical precipitation using Fe or Al salts, is effective for P removal but leads to residues with limited bioavailability and contamination concerns. One of the greatest opportunities for P recovery is at wastewater treatment plants (WWTPs) where the crystallisation of struvite and Ca-P from enhanced biological P removal (EBPR) sludge is well developed and already shown to be economically and operationally feasible in some WWTPs. However, recovery through this approach can be limited to <25% efficiency unless chemical extraction is applied. Thermochemical treatment of sludge ash produces detoxified residues that are currently utilised by the fertiliser industry; wet chemical extraction can be economically feasible in recovering P and other by-products. The bioavailability of recovered P depends on soil pH as well as the P-rich material in question. Struvite is a superior recovered P product in terms of plant availability, while use of Ca-P and thermochemically treated sewage sludge ash is limited to acidic soils. These technologies, in addition to others less developed, will be commercially pushed forward by revised fertiliser legislation and foreseeable legislative limits for WWTPs to achieve discharges of <1 mg P/L.

Enrichment culture of denitrifying phosphorus removal sludge and its microbial community analysis

An efficient one-step domestication method with mixed electron acceptors and short-time post-aeration was developed for the enrichment culture of denitrifying phosphorus removal sludge. The acclimation time, performance of nitrogen and phosphorus simultaneous removal and microbial community structure were investigated to reveal the difference among the obtained phosphorus removal sludge using different acclimation ways. Results showed that the proposed method with optimal proportion of nitrite and nitrate could significantly shorten domestication time (28 days) compared with the traditional two-step method (60 days), but exerted nearly no influence on the removal efficiency of nitrogen and phosphorus. High-throughput sequencing revealed that similar microbial community structure of DPAOs sludge was obtained with different acclimation methods. Compared with seed sludge, microbial community shifted obviously, and the dominant microbial population of Dechloromonas-related phosphorus removal bacteria increased significantly. It could be inferred that the appropriate concentration of nitrite was conducive to the rapid enrichment of DPAOs under alternative anaerobic/anoxic operation. Meanwhile, anaerobic/oxic condition was favorable for the enrichment of Candidatus Accumulibacter-related phosphorus removal organisms, and short-time post-aeration in the proposed method could reduce the potential public health hazard.

Denitrifying sulfur conversion-associated EBPR: The effect of pH on anaerobic metabolism and performance

The performance of the denitrifying sulfur conversion-associated enhanced biological phosphorus removal (DS-EBPR) process tends to be unstable and requires further study and development. This in turn requires extensive study of the anaerobic metabolism in terms of its stoichiometry and kinetics. This study evaluates the corresponding responses of DS-EBPR to pH, as it significantly influences both stoichiometry and biochemical kinetics. The impacts of five representative pH values ranging between 6.5 and 8.5 on the anaerobic metabolism were investigated, followed by identification of the optimal pH for performance optimization. A mature DS-EBPR sludge was used in the study, enriched with approximately 30% sulfate-reducing bacteria (SRB) and 33% sulfide-oxidizing bacteria (SOB). Through a series of batch tests, the optimal pH range was determined as 7.0-7.5. In this pH range, the anaerobic stoichiometry of phosphorus released/volatile fatty acid (VFA) uptake ratio, sulfate reduction, and internal polymer production (including poly-β-hydroxyalkanoates and polysulfide and/or elemental sulfur) all increased along with the anaerobic kinetics of the VFA uptake ratio. Consequently, phosphorus removal was maximized at this pH range (≥95% vs. 84-93% at other pH values), as was sulfur conversion (16 mg S/L vs. 10-13 mg S/L). This pH range therefore favors the activity and synergy of the key functional bacteria (i.e. SRB and SOB). Anaerobic maintenance tests showed these bacteria required 38-61% less energy for maintenance than that reported for GAOs regardless of pH changes, improving their ability to cope with anaerobic starvation. Adversely, both bacteria showed much lower VFA uptake rates than that of GAOs at all tested pH values (0.03-0.06 vs. 0.2-0.24 mol-C/C-mol biomass/h), possibly revealing the primary cause of frequent instability in the DS-EBPR process.

Metabolism and ecological niche of Tetrasphaera and Ca. Accumulibacter in enhanced biological phosphorus removal

Tetrasphaera and Candidatus Accumulibacter are two abundant polyphosphate accumulating organisms in full-scale enhanced biological phosphorus removal (EBPR) systems. However, little is known about the metabolic behaviour and ecological niche that each organism exhibits in mixed communities. In this study, an enriched culture of Tetrasphaera and Ca. Accumulibacter was obtained using casein hydrolysate as sole carbon source. This culture was able to achieve a high phosphorus removal efficiency (>99%), storing polyphosphate while consuming amino acids anaerobically. Microautoradiography and fluorescence in situ hybridisation confirmed that more than 90% Tetrasphaera cells were responsible for amino acid consumption while Ca. Accumulibacter likely survived on fermentation products. Tetrasphaera performed the majority of the P removal (approximately 80%) in this culture, and batch tests showed that the metabolism of some carbon sources could actually lead to anaerobic orthophosphate (Pi) uptake (9.0 ± 2.1 mg-P/L) through energy generated by fermentation of glucose and amino acids. This anaerobic Pi uptake may lead to lower net Pi release to C uptake ratios and reduce the Pi needed to be removed aerobically in WWTPs. Intracellular metabolites such as amino acids, sugars, volatile fatty acids and small amines were observed as potential storage products, which may serve as energy sources in the aerobic phase. Evidence of the urea cycle was found, which could be involved in reducing the intracellular nitrogen content. This study improves our understanding of how phosphorus is removed in EBPR systems and can enable novel process optimisation strategies.

Dominant Candidatus Accumulibacter phosphatis Enriched in Response to Phosphate Concentrations in EBPR Process

Candidatus Accumulibacter phosphatis (Accumulibacter), which plays an important role in enhanced biological phosphorus removal in wastewater treatment plants, is phylogenetically classified into two major types (Types I and II). Phosphate concentrations affect the Accumulibacter community of the biomass enriched in treatment plants. Therefore, in the present study, Accumulibacter enrichments were conducted using a down-flow hanging sponge reactor under five conditions and a wide range of controlled phosphate concentrations in order to investigate how phosphate governs the community. We found that excessive phosphate levels inhibited Accumulibacter activity, that this inhibitory effect was greater for Type II. In addition, the affinity of Type II for phosphate was higher than that of Type I. Type IIA-B dominated at a phosphate concentration less than 5 mg P L^-1, while Type IA was dominant at 50 and 500 mg P L^-1. These patterns of enrichment may be explained by an inhibition kinetics model.

Cooperation between Candidatus Competibacter and Candidatus Accumulibacter clade I, in denitrification and phosphate removal processes

Although simultaneous P-removal and nitrate reduction has been observed in laboratory studies as well as full-scale plants, there are contradictory reports on the ability of PAO I to efficiently use nitrate as electron acceptor. Such discrepancy could be due to other microbial groups performing partial denitrification from nitrate to nitrite. The denitrification capacities of two different cultures, a highly enriched PAO I and a PAO I-GAO cultures were assessed through batch activity tests conducted before and after acclimatization to nitrate. Negligible anoxic phosphate uptake coupled with a reduction of nitrate was observed in the highly enriched PAO I culture. On the opposite, the PAO I-GAO culture showed a higher anoxic phosphate uptake activity. Both cultures exhibited good anoxic phosphate uptake activity with nitrite (8.7 ± 0.3 and 9.6 ± 1.8 mgPO₄-P/gVSS.h in the PAO I and PAO I-GAO cultures, respectively). These findings suggest that other microbial populations, such as GAOs, were responsible to reduce nitrate to nitrite in this EBPR system, and that PAO I used the nitrite generated for anoxic phosphate uptake. Moreover, the simultaneous denitrification and phosphate removal process using nitrite as electron acceptor may be a more sustainable process as can: i) reduce the carbon consumption, ii) reduce oxygen demand of WWTP, and iii) due to a lower growth yield contribute to a lower sludge production.

Formation of aerobic granular sludge during the treatment of petrochemical wastewater

In this study, petrochemical wastewater from the port of Antwerp was used for the development of aerobic granular sludge. Two different reactor setups were used, (1) a completely aerated sequencing batch reactor (SBR_ae) with a feast/famine regime and (2) a sequencing batch reactor operated with an anaerobic feast/aerobic famine strategy (SBR_an). The seed sludge showed poor settling characteristics with a sludge volume index (SVI) of 285mL.gMLSS^-1 and a median particle size by volume of 86.0µm±1.9µm. In both reactors, granulation was reached after 30days with a SVI of 71mL.gMLSS^-1 and median granule size of 264.7µm in SBR_an and a SVI of 56mL.gMLSS^-1 and median granule size of 307.4µm in SBR_ae. The chemical oxygen demand (COD) and dissolved organic carbon (DOC) removal was similar in both reactors and above 95%. The anaerobic DOC uptake increased from 0.13% to 43.2% in 60days in SBR_an.

Multi-cycle operation of enhanced biological phosphorus removal (EBPR) with different carbon sources under high temperature

Many studies reported that it is challenging to apply enhanced biological phosphorus removal (EBPR) process at high temperature. Glycogen accumulating organisms (GAOs) could easily gain their dominance over poly-phosphate accumulating organisms (PAOs) when the operating temperature was in the range of 25 °C-30 °C. However, a few successful EBPR processes operated at high temperature have been reported recently. This study aimed to have an in-depth understanding on the impact of feeding strategy and carbon source types on EBPR performance in tropical climate. P-removal performance of two EBPR systems was monitored through tracking effluent quality and cyclic studies. The results confirmed that EBPR was successfully obtained and maintained at high temperature with a multi-cycle strategy. More stable performance was observed with acetate as the sole carbon source compared to propionate. Stoichiometric ratios of phosphorus and carbon transformation during both anaerobic and aerobic phases were higher at high temperature than low temperature (20±1 °C) except anaerobic PHA/C ratios within most of the sub-cycles. Furthermore, the fractions of PHA and glycogen in biomass were lower compared with one-cycle pulse feed operation. The microbial community structure was more stable in acetate-fed sequencing batch reactor (C2-SBR) than that in propionate-fed reactor (C3-SBR). Accumulibacter Clade IIC was found to be highly abundant in both reactors.

A review: Driving factors and regulation strategies of microbial community structure and dynamics in wastewater treatment systems

The performance and stabilization of biological wastewater treatment systems ¹are closely related to the microbial community structure and dynamics. In this paper, the effects and mechanisms of influent composition, process configuration, operating parameters (dissolved oxygen [DO], pH, hydraulic retention time [HRT] and sludge retention time [SRT]) and environmental condition (temperature) to the change of microbial community structure and process performance (nitrification, denitrification, biological phosphorus removal, organics mineralization and utilization, etc.) are critically reviewed. Furthermore, some strategies for microbial community structure regulation, mainly bioaugmentation, process adjustment and operating parameters optimization, applied in the current wastewater treatment systems are also discussed. Although the recent studies have strengthened our understanding on the relationship between microbial community structure and wastewater treatment process performance, how to fully tap the microbial information, optimize the microbial community structure and maintain the process performance in wastewater treatment systems are still full of challenges.

Exploring the Shift in Structure and Function of Microbial Communities Performing Biological Phosphorus Removal

A sequencing batch reactor fed mainly by acetate was operated to perform enhanced biological phosphorus removal (EBPR). A short-term pH shock from 7.0 to 6.0 led to a complete loss of phosphate-removing capability and a drastic change of microbial communities. 16S rRNA gene pyrosequencing showed that large proportions of glycogen accumulating organisms (GAOs) (accounted for 16% of bacteria) bloomed, including Candidatus Competibacter phosphatis and Defluviicoccus-related tetrad-forming organism, causing deteriorated EBPR performance. The EBPR performance recovered with time and the dominant Candidatus Accumulibacter (Accumulibacter) clades shifted from Clade IIC to IIA while GAOs populations shrank significantly. The Accumulibacter population variation provided a good opportunity for genome binning using a bi-dimensional coverage method, and a genome of Accumulibacter Clade IIC was well retrieved with over 90% completeness. Comparative genomic analysis demonstrated that Accumulibacter clades had different abilities in nitrogen metabolism and carbon fixation, which shed light on enriching different Accumulibacter populations selectively.

Acetate favors more phosphorus accumulation into aerobic granular sludge than propionate during the treatment of synthetic fermentation liquor

Anaerobic digestion (AD) is an efficient biotechnology widely applied for energy and resource recovery from organic waste and wastewater treatment. The effluent from AD or fermentation liquor containing organic substances like volatile fatty acids (VFAs) and mineral nutrients (such as N and P), however, will trigger serious environmental issues if not properly dealt with. In this study two identical sequencing batch reactors (SBRs), namely Ra and Rp were used to cultivate aerobic granules for P recovery from synthetic fermentation liquor, respectively using acetate and propionate as additional carbon source. Larger and more stable granules were achieved in Ra with higher P removal capability (9.4mgP/g-VSS·d) and higher anaerobic P release (6.9mgP/g-VSS·h). In addition to much higher P content (78mgP/g-SS), bioavailable P in Ra-granules increased to 45mgP/g-SS, approximately 2-times those of seed sludge and Rp-granules. Microbial community analysis indicated that more GAOs were accumulated in Rp-granules.

Improved biological phosphorus removal induced by an oxic/extended-idle process using glycerol and acetate at equal fractions

Variations of effluent SOP concentration and SOP removal efficiency in O/EI reactor during long-term operation.

Calcium effect on the metabolic pathway of phosphorus accumulating organisms in enhanced biological phosphorus removal systems

Phosphorus accumulating organisms (PAOs) have been found to act as glycogen-accumulating organisms (GAOs) under certain conditions, thus, the deterioration in the performance of enhanced biological phosphorus removal systems is not always attributed to the proliferation of GAOs. In this work, the effects of calcium on the metabolic pathway of PAOs were explored. It was found that when the influent Ca(2+) concentration was elevated, the tendency and extent of extracellular calcium phosphate precipitation increased, and the intracellular inert Ca-bound polyphosphate was synthesized, while the microbial population remained almost unchanged. The changes in the ratios of phosphorus released/acetate uptaken, the glycogen degraded/acetate uptaken and the poly-β-hydroxyalkanoates synthesized/acetate uptaken during the anaerobic period confirm that, as the influent Ca(2+) concentration was increased, the polyphosphate-accumulating metabolism was partially shifted to the glycogen-accumulating metabolism. At an influent Ca(2+) around 50 mg/L, in addition to the extracellular calcium phosphate precipitation, the intracellular inert Ca-bound polyphosphate synthesis might also be involved in the metabolic change of PAOs. The results of the present work would be beneficial to better understand the biochemical metabolism of PAOs in enhanced biological phosphorus removal systems.

Microbiological study of bacteriophage induction in the presence of chemical stress factors in enhanced biological phosphorus removal (EBPR)

Polyphosphate accumulating organisms (PAOs) are responsible for carrying the enhanced biological phosphorus removal (EBPR). Although the EBPR process is well studied, the failure of EBPR performance at both laboratory and full-scale plants has revealed a lack of knowledge about the ecological and microbiological aspects of EBPR processes. Bacteriophages are viruses that infect bacteria as their sole host. Bacteriophage infection of polyphosphate accumulating organisms (PAOs) has not been considered as a main contributor to biological phosphorus removal upsets. This study examined the effects of different stress factors on the dynamics of bacteriophages and the corresponding effects on the phosphorus removal performance in a lab-scale EBPR system. The results showed that copper (heavy metal), cyanide (toxic chemical), and ciprofloxacin (antibiotic), as three different anthropogenic stress factors, can induce phages integrated onto bacterial genomes (i.e. prophages) in an enriched EBPR sequencing batch reactor, resulting in a decrease in the polyphosphate kinase gene ppk1 clades copy number, phosphorus accumulation capacity, and phosphorus removal performance. This study opens opportunities for further research on the effects of bacteriophages in nutrient cycles both in controlled systems such as wastewater treatment plants and natural ecosystems.

Aerobic granulation utilizing fermented municipal wastewater under low pH and alkalinity conditions in a sequencing batch reactor

The aim of this study was to achieve aerobic granulation utilizing fermented municipal wastewater under low pH, and alkalinity conditions. Stable granulation was achieved after a 166-day start-up period. Due to low influent strength, supplemental carbon addition, in the form of sucrose, was added to the feed storage tank on the 82nd day of start-up to facilitate granulation. This increased the system's organic loading rate from 1.43 ± 0.14 to 2.53 ± 0.18 kg COD/m(3)/d, and reduced the influent pH due to fermentation of the added sucrose. Although granulation was successful, the nutrient removal was limited. Removal rates at an influent pH of 6.23 ± 0.06 were 54.4% ± 8.3% for phosphorus, 21.9% ± 4.1% for ammonium, and 84.0% ± 3.0% for total chemical oxygen demand (COD). During the second phase of experimentation, increased amounts of sucrose were added to the feed, which resulted in increased volatile fatty acid concentrations and pH reduction to 5.62 ± 0.12 due to fermentation. Under further reduced pH conditions, phosphorus, ammonium, and total COD removal were found to be 58.9% ± 4.7%, 37.9% ± 4.7%, and 87.1% ± 0.9%, respectively. Settling volume indexes, SVI10 and SVI30, were found to be 148.8 ± 28.9 mL/g, for the influent pH of 6.23 ± 0.06, and 157.5 ± 40.6 mL/g, for the influent pH of 5.62 ± 0.12. This high SVI is indicative of the formation of lower-density granules in comparison to high-ash-content granules. The absence of denitrification-induced chemical phosphorus precipitation within the granule was likely a contributing factor to the low granule density observed in the system.

Enhancement of post-anoxic denitrification for biological nutrient removal: effect of different carbon sources

Previous research has demonstrated that post-anoxic denitrification and biological nutrient removal could be achieved in the oxic/anoxic/extended-idle wastewater treatment regime. This study further investigated the effect of different carbon sources on post-anoxic denitrification and biological nutrient removal. Acetate, propionate (volatile fatty acids (VFAs)), glucose (carbohydrate), methanol, and ethanol (alcohol) were used as the sole carbon source, respectively. The experimental results showed that VFA substrates led to an improvement in nitrogen and phosphorus removal. The total nitrogen and phosphorus removal efficiency values driven by acetate achieved 93 and 99%, respectively. In contrast, glucose present in mixed liquor deteriorated total nitrogen and phosphorus removal efficiency values to 72 and 54%. In the reactors cultured with methanol and ethanol, 66 and 63% of the total nitrogen were removed, and phosphorus removal efficiency values were 78 and 71%, respectively. The mechanism studies revealed that different carbon sources affected the transformations of intracellular polyhydroxyalkanoates (PHAs) and glycogen. PHAs are the dominant storages for microorganisms cultured with VFA substrates. Though glycogen is not the favorable energy and carbon source for polyphosphate-accumulating organisms, it can be consumed by microorganisms related to biological nitrogen removal and is able to serve as the electron donor for post-anoxic denitrification.

Coupling the treatment of low strength anaerobic effluent with fermented biowaste for nutrient removal via nitrite

Nutrient removal via nitrite was investigated in a sequencing batch reactor (SBR) treating low strength effluent produced from an upflow anaerobic sludge blanket (UASB). Domestic organic waste (DOW) and vegetable and fruit waste (VFW) were fermented and applied as external carbon source to the SBR. Nutrient removal via nitrite was much higher when DOW fermentation liquid (FL) was applied rather than VFW FL and acetic acid. The DOW FL contained propionic acid and butyric acid in significant proportions, favouring the nutrient removal via nitrite, while the VFW FL contained mainly acetic acid, which was associated with lower nutrient via nitrite activity. The application of high volumetric nitrogen loading rate (vNLR = 0.19-0.21 kgN m(-3) d(-1)) in combination with low dissolved oxygen (DO) concentration during the aerobic phase, resulted in high and stable nitrite accumulation (NO2-N/NOx-N >97%). These conditions favoured the phosphorus uptake via nitrite, which reached high rates (5.95 ± 2.21 mgP (gVSS h)(-1)), while the aerobic phosphorus removal was much lower. Through mass balances, it was demonstrated that the application of the UASB-SBR process with nutrient removal via nitrite at a decentralized level is a sustainable solution for effective co-treatment of domestic sewage and biowaste.