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

Ammonia-dependent reducing power redistribution for purple phototrophic bacteria culture-based biohydrogen production

The global energy crisis has intensified the search for sustainable and clean alternatives, with biohydrogen emerging as a promising solution to address environmental challenges. Leveraging photo fermentation (PF) process, purple phototrophic bacteria (PPB) can harness reducing power derived from organic substrates to facilitate hydrogen production. However, existing studies report much lower H2 yields than theoretical value when using acetate as carbon source and ammonia as nitrogen source, primarily attributed to the widely employed pulse-feeding mode which suffers from ammonia inhibition effect on nitrogenase. To address this issue, a continuous feeding mode was applied to avoid ammonia accumulation in this study. On the other hand, other pathways like carbon fixation and polyhydroxyalkanoate (PHA) formation could compete reducing power with H2 production. However, the reducing power allocation under continuous feeding mode is not yet clear. In this study, the reducing power allocation and hydrogen production performance were evaluated under various ammonia loading, using acetate as carbon source and infrared LED at around 50 W·m-2 as light source. The results show that (a) The absence of ammonia resulted in the best performance for hydrogen production, with 44 % of the reducing power distributed to H2 and the highest H2 volumetric productivity, while the allocation of reducing power to hydrogen production stopped when ammonia loading was above 7.6 mg NH4-N·L-1·d-1; (b) when PPB required to eliminate reducing power under ammonia limited conditions, PHA production was the preferred pathway followed by the hydrogen production pathway, but once PHA accumulation reached saturation, hydrogen generation pathway dominated; (c) under ammonia limited conditions, the TCA cycle was more activated rendering higher NADH (i.e. reducing power) production compared with that under ammonia sufficient conditions which was verified by metagenomics analysis, and all the hydrogen production, PHA accumulation and carbon fixation pathways were highly active to dissipate reducing power. This work provides the insight of reducing power distribution and PPB biohydrogen production variated by ammonia loading under continuous feeding mode.

Oxygen affinity and light intensity induced robust phosphorus removal and fragile ammonia removal in a non-aerated bacteria-algae system

Non-aerated bacteria-algae system gaining O2 through photosynthesis presents an alternative for costly mechanical aeration. This study investigated oxygen supply and performance of nutrients removal at low and high light intensity (LL and HL). The results showed that P removal was high and robust (LL 97 ± 1.8 %, HL 95 % ± 2.9 %), while NH4+-N removal fluctuated dramatically (LL 66 ± 14.7 %, HL 84 ± 8.6 %). Oxygen generated at illumination of 200 μmol m-2 s-1, 6 h was sufficient to sustain aerobic phase for 2.25 g/L MLSS. However, O2 produced by algae was preferentially captured in the order of heterotrophic bacteria (HB), ammonia oxidizing bacteria (AOB), nitrite oxidizing bacteria (NOB). Oxygen affinity coupled with light intensity led to NOB suppression with stable nitrite accumulation ratio of 57 %. Free nitrous acid (FNA) and light stimulated the abundance of denitrifying polyphosphate accumulating organism (DPAO) of Flavobacterium, but with declined P-accumulating metabolism (PAM) of P release, P/C, K/P and Mg/P ratios. Flavobacterium and cyanobacteria Leptolyngbya, along with biologically induced CaP in extracellular polymeric substances was the key to robust P removal. AOB of Ellin6067 and DPAO of Flavobacteria offer a promising scenario for partial nitrification-denitrifying phosphorus removal.

Exploring organic matter conversion pathway and its effect on nitrogen removal in tidal flow constructed wetlands

Achieving effective nitrogen removal remains a significant challenge faced by constructed wetlands. Although organic matter is a crucial factor influencing nitrogen removal, little attention has been paid to the impact of organic matter conversion pathways on nitrogen removal in constructed wetlands. Here, we showed that endogenous microorganisms performing carbon internalization could be easily enriched in tidal flow constructed wetlands (TFCWs) under its special rhythmic cycle of anaerobic/aerobic operational mode. Endogenous microorganisms could translate influent carbon sources into intracellular carbons during the anaerobic stage and supply the carbon source for endogenous denitrification after the aerobic stage (rest period). Based on these findings, an innovative combined TFCW and Nitrifying-CW system was developed, and robust total nitrogen (TN) removal (82% on average) was achieved even under carbon source limiting conditions. This performance was a substantial improvement compared to the conventional single bed TFCW with multiple "tides" (corresponding to the multiple contact/rest periods) with TN removal of only 54% on average. Simultaneous nitrification-endogenous denitrification (SNED) was found to be the major nitrogen removal pathway in the proposed system. Compared with classical nitrification-denitrification, simultaneous nitrification-endogenous denitrification brings high nitrogen conversion rates and significantly reduces the demand for oxygen and organic carbon. Furthermore, microbial community analysis indicated that endogenous microorganisms such as Candidatus_Competibacter and Defluviicoccus were successfully enriched, accounting for 50.73% and 3.46% in CW1, and 25.25% and 1.76% in CW2, respectively. Together, these mechanisms allow the proposed system to achieve efficient TN removal.

Two new clades recovered at high temperatures provide novel phylogenetic and genomic insights into Candidatus Accumulibacter

Candidatus Accumulibacter, a key genus of polyphosphate-accumulating organisms, plays key roles in lab- and full-scale enhanced biological phosphorus removal (EBPR) systems. A total of 10 high-quality Ca. Accumulibacter genomes were recovered from EBPR systems operated at high temperatures, providing significantly updated phylogenetic and genomic insights into the Ca. Accumulibacter lineage. Among these genomes, clade IIF members SCELSE-3, SCELSE-4, and SCELSE-6 represent the to-date known genomes encoding a complete denitrification pathway, suggesting that Ca. Accumulibacter alone could achieve complete denitrification. Clade IIC members SSA1, SCUT-1, SCELCE-2, and SCELSE-8 lack the entire set of denitrifying genes, representing to-date known non-denitrifying Ca. Accumulibacter. A pan-genomic analysis with other Ca. Accumulibacter members suggested that all Ca. Accumulibacter likely has the potential to use dicarboxylic amino acids. Ca. Accumulibacter aalborgensis AALB and Ca. Accumulibacter affinis BAT3C720 seemed to be the only two members capable of using glucose for EBPR. A heat shock protein Hsp20 encoding gene was found exclusively in genomes recovered at high temperatures, which was absent in clades IA, IC, IG, IIA, IIB, IID, IIG, and II-I members. High transcription of this gene in clade IIC members SCUT-2 and SCUT-3 suggested its role in surviving high temperatures for Ca. Accumulibacter. Ambiguous clade identity was observed for newly recovered genomes (SCELSE-9 and SCELSE-10). Five machine learning models were developed using orthogroups as input features. Prediction results suggested that they belong to a new clade (IIK). The phylogeny of Ca. Accumulibacter was re-evaluated based on the laterally derived polyphosphokinase 2 gene, showing improved resolution in differentiating different clades.

Optimization of Simultaneous Nutrients and Chemical Oxygen Demand Removal from Anaerobically Digested Liquid Dairy Manure in a Two-Step Fed Sequencing Batch Reactor System Using Taguchi Method and Grey Relational Analysis

The technological development for efficient nutrient removal from liquid dairy manure is critical to a sustainable dairy industry. A nutrient removal process using a two-step fed sequencing batch reactor (SBR) system was developed in this study to achieve the applicability of simultaneous removal of phosphorus, nitrogen, and chemical oxygen demand from anaerobically digested liquid dairy manure (ADLDM). Three operating parameters, namely anaerobic time:aerobic time (min), anaerobic DO:aerobic DO (mg L-1), and hydraulic retention time (days), were systematically investigated and optimized using the Taguchi method and grey relational analysis for maximum removal efficiencies of total phosphorus (TP), ortho-phosphate (OP), ammonia-nitrogen (NH3-N), total nitrogen (TN), and chemical oxygen demand (COD) simultaneously. The results demonstrated that the optimal mean removal efficiencies of 91.21%, 92.63%, 91.82%, 88.61%, and 90.21% were achieved for TP, OP, NH3-N, TN, and COD at operating conditions, i.e., anaerobic:aerobic time of 90:90 min, anaerobic DO:aerobic DO of 0.4:2.4 mg L-1, and HRT of 3 days. Based on analysis of variance, the percentage contributions of these operating parameters towards the mean removal efficiencies of TP and COD were ranked in the order of anaerobic DO:aerobic DO > HRT > anaerobic time:aerobic time, while HRT was the most influential parameter for the mean removal efficiencies of OP, NH3-N, and TN followed by anaerobic time:aerobic time and anaerobic DO:aerobic DO. The optimal conditions obtained in this study are beneficial to the development of pilot and full-scale systems for simultaneous biological removal of phosphorus, nitrogen, and COD from ADLDM.

Assessing the performance of polyphosphate accumulating organisms in a full-scale side-stream enhanced biological phosphorous removal

Phosphorous (P) removal in wastewater treatment is essential to prevent eutrophication in water bodies. Side-stream enhanced biological phosphorous removal (S2EBPR) is utilized to improve biological P removal by recirculating internal streams within a side-stream reactor to generate biodegradable carbon (C) for polyphosphate accumulating organisms (PAOs). In this study, a full-scale S2EBPR system in a water resource recovery facility (WRRF) was evaluated for 5 months. Batch experiments revealed a strong positive correlation (r = 0.91) between temperature and C consumption rate (3.56-8.18 mg-COD/g-VSS/h) in the system, with temperature ranging from 14°C to 18°C. The anaerobic P-release to COD-uptake ratio decreased from 0.93 to 0.25 mg-P/mg-COD as the temperature increased, suggesting competition between PAOs and other C-consumers, such as heterotrophic microorganisms, to uptake bioavailable C. Microbial community analysis did not show a strong relationship between abundance and activity of PAO in the tested WRRF. An assessment of the economic feasibility was performed to compare the costs and benefits of a full scale WRRF with and without implementation of the S2EBPR technology. The results showed the higher capital costs required for S2EBPR were estimated to be compensated after 5 and 11 years of operation, respectively, compared to chemical precipitation and conventional EBPR. The results from this study can assist in the decision-making process for upgrading a conventional EBPR or chemical P removal process to S2EBPR. PRACTITIONER POINTS: Implementation of S2EBPR presents adaptable configurations, exhibiting advantages over conventional setups in addressing prevalent challenges associated with phosphorous removal. A full-scale S2EBPR WRRF was monitored over 5 months, and activity tests were used to measure the kinetic parameters. The seasonal changes impact the kinetic parameters of PAOs in the S2EBPR process, with elevated temperatures raising the carbon demand. PAOs abundance showed no strong correlation with their activity in the full-scale S2EBPR process in the tested WRRF. Feasibility assessment shows that the benefits from S2EBPR operation can offset upgrading costs from conventional BPR or chemical precipitation.

Advanced nitrogen and phosphorus removal by the symbiosis of PAOs, DPAOs and DGAOs in a pilot-scale A2O/A+MBR process with a low C/N ratio of influent

Cooperating in harmony to avoid competition with dominant functional microbial symbiosis is an efficient way in advanced nitrogen and phosphorus removal in wastewater treatment processes. In this study, a niche-based coordinating strategy was implemented to cooperate in harmony with phosphorus-accumulating organisms (PAOs), denitrifying phosphorus-accumulating organisms (DPAOs) and denitrifying glycogen-accumulating organisms (DGAOs) to advance nitrogen and phosphorus removal based on an anaerobic-anoxic-oxic-anoxic-membrane bioreactor (A²O/A+MBR) under low C/N in municipal wastewater influent. The niche-based strategy was conducted based on the ORP change during the process as an indicator combined with the adjustment of recirculation and anoxic zone shifting. The results indicated that the strategy of the post-anoxic unit could enable significant enhancement of biological nitrogen and phosphorus removal (BNPR) by 9.9% and 16.3%, respectively, with low effluent concentrations of 7.0 ± 2.2 mg N/L and 0.36±0.32 mg P/L. The satisfactory performance was dominated along with the shift in the microbial community: the relative abundance of Tetrasphaera (PAO genus) increased from 0.14±0.08% to 0.32±0.12%, while the relative abundance of Decchloromonas (DGAO genus) and Candidatus Competibacter (DGAO genus) also increased. The advanced combination of anaerobic phosphorus release, anoxic denitrification, denitrifying phosphorus removal and endogenous denitrification was qualified by the modeling simulation of the biochemical kinetics mechanism of activated sludge in the A²O+MBR and A²O/A+MBR processes, which means that cooperation in the harmony of PAOs, DPAOs and DGAOs could be efficiently realized by a promising control strategy to enhance BNPR in an A²O+MBR with a post-anoxic unit. This study provides an efficient and simple novel control strategy to overcome the limitation of traditional nitrogen and phosphorus removal under an insufficient carbon source.

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.

A potential phosphorus fertilizer to alleviate the coming "phosphorus crisis"-biochar derived from enhanced biological phosphorus removal sludge

The coming crisis of phosphate rock depletion initiates the development of various solid waste derived P fertilizer. Enhanced biological phosphorus removal (EBPR) sludge is ideal waste biomass to produce biochar-P-fertilizer. Here, the form and transformation pattern of released phosphorus (P) of EBPR sludge biochar pyrolyzed at different temperatures were comprehensively investigated. As pyrolysis temperature increased, the proportion of released polyphosphates (Poly-P) increased. The main Poly-P released from low-temperature biochar was tripolyphosphates (Tri-P), while those released from high-temperature were Tri-P and cyclic Poly-P. The presence of Ca²⁺ could strongly inhibit P-release of low-temperature biochar (e.g., pyrolyzed at 400 °C, E400) but had little effect on that of high-temperature biochar (e.g., 700 °C, E700). All the P species released from E400 and E700 could be efficiently utilized by Pseudomonas putida. Except for the cyclic Poly-P released from E700, the other P species could also be efficiently utilized by Escherichia coli. In short, Poly-P in biochar could hardly precipitate with Ca²⁺ and can be utilized by certain soil microorganisms. Therefore, high-temperature EBPR sludge biochar (>600 °C) containing a high proportion of Poly-P could be ideal P fertilizer. This study provides a new insight on pyrolysis way to recover P from the sludge.

Metagenomics reveals the metabolism of polyphosphate-accumulating organisms in biofilm sequencing batch reactor: A new model

This study assessed the impact of the operating conditions of the biofilm sequencing batch reactor (BSBR) on the community structure and the growth/metabolic pathways of its polyphosphate-accumulating organisms (PAOs). There are significant difference with reference to the enhanced biological phosphorus removal (EBPR) process. The leading PAOs in BSBR generally are capable of high affinity acetate metabolism, gluconeogenesis, and low affinity phosphate transport, and have various carbon source supplementation pathways to ensure the efficient circulation of energy and reducing power. A new model of the metabolic mechanism of PAOs in the BSBR was formulated, which features low glycogen metabolism with simultaneous gluconeogenesis and glycogenolysis and differs significantly from the classic mechanism based on Candidatus_Accumulibacter and Tetrasphaera. The findings will assist the efficient recovery of low concentration phosphate in municipal wastewater.

Global warming readiness: Feasibility of enhanced biological phosphorus removal at 35 °C

Recent research has shown enhanced biological phosphorus removal (EBPR) from municipal wastewater at warmer temperatures around 30 °C to be achievable in both laboratory-scale reactors and full-scale treatment plants. In the context of a changing climate, the feasibility of EBPR at even higher temperatures is of interest. We operated two lab-scale EBPR sequencing batch reactors for > 300 days at 30 °C and 35 °C, respectively, and followed the dynamics of the communities of polyphosphate accumulating organisms (PAOs) and competing glycogen accumulating organisms (GAOs) using a combination of 16S rRNA gene metabarcoding, quantitative PCR and fluorescence in situ hybridization analyses. Stable and nearly complete phosphorus (P) removal was achieved at 30 °C; similarly, long term P removal was stable at 35 °C with effluent PO₄^3-_P concentrations < 0.5 mg/L on half of all monitored days. Diverse and abundant Candidatus Accumulibacter amplicon sequence variants were closely related to those found in temperate environments, suggesting that EBPR at this temperature does not require a highly specialized PAO community. A slow-feeding strategy effectively limited the carbon uptake rates of GAOs, allowing PAOs to outcompete GAOs at both temperatures. Candidatus Competibacter was the main GAO, along with cluster III Defluviicoccus members. These organisms withstood the slow-feeding regime, suggesting that their bioenergetic characteristics of carbon uptake differ from those of their tetrad-forming relatives. Comparative cycle studies revealed higher carbon and P cycling activity of Ca. Accumulibacter when the temperature was increased from 30 °C to 35 °C, implying that the lowered P removal performance at 35 °C was not a direct effect of temperature, but a result of higher metabolic rates of carbon (and/or P) utilization of PAOs and GAOs, the resultant carbon deficiency, and escalated community competition. An increase in the TOC-to-PO₄^3--P ratio (from 25:1 to 40:1) effectively eased the carbon deficiency and benefited PAOs. In general, a slow-feeding strategy and sufficiently high carbon input benefited a high and stable EBPR at 35 °C, representing basic conditions suitable for full-scale treatment plants experiencing higher water temperatures.

Study on community structure and metabolic mechanism of dominant polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) in suspended biofilm based on phosphate recovery

Biofilm sequencing batch reactor (BSBR) can achieve efficient phosphate (P) removal and enrichment, but its process performance and metabolic mechanisms for P removal and enrichment of municipal wastewater remain largely unclear. In the present study, we assessed the P removal and enrichment of municipal wastewater at influent P concentrations of 2.5 mg/L and 10 mg/L. The efficiency of P removal and enzyme activity in polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) were compared, and the growth and metabolic characteristics of dominant PAOs and GAOs at different influent P concentrations were studied with the macro-sequencing technology. The results showed that the P recovery efficiencies were 70.03% and 76.19% when the influent P concentration was 2.5 mg/L and 10 mg/L in BSBR, respectively, and the maximum P concentration of recovery liquid was 81.29 mg/L and 173.12 mg/L, respectively. There were no phosphate kinase (PPK) and phosphate hydrolase (PPX) in extracellular polymeric substances (EPS). The dominant PAOs were Candidatus_Contendobacter, Dechloromonas, and Flavobacterium, and the dominant GAO was Candidatus_Competibacter. The abundance of Candidatus_Contendobacter was the highest with the most potential contribution to P removal. PAOs had competitive advantages in carbon (C) source uptake, glycogen metabolism, P metabolism, and adenosine triphosphate (ATP) metabolism. HMP was unique to PAOs, EMP had the highest abundance in glycogen metabolism, and ED was contained in PAOs of BSBR. These results indicated that BSBR provided sufficient reducing power and ATP for PAOs through different glycogen decomposition pathways to promote P uptake and obtained competitive advantages in P metabolism, C source uptake, and ATP utilization to achieve efficient P removal and enrichment. Collectively, our current findings provided valuable insights into the P removal and enrichment mechanism of BSBR in municipal sewage.

Sustained and enhanced anaerobic removal of COD and nitrogen in a zeolite amended glycogen accumulating organism dominated biofilm process

Activated sludge, the most widely used biological wastewater treatment process is known to be expensive to operate, largely due to energy expense for oxygen transfer into the bulk wastewater solution. The alternative of using passive aeration facilitates oxygen supply directly from the air resulting in aeration energy savings. The current study demonstrated sustained and improved removal of chemical oxygen demand (COD) and nitrogen in a zeolite modified glycogen accumulating organisms (GAOs) dominated biofilm reactor, which achieved anaerobic removal of COD and ammonium by the activity of GAOs and zeolite, respectively. Draining of the batch-operated reactor enabled the biofilm to directly uptake oxygen from air (passive aeration) to carry out simultaneous nitrification and denitrification due to the activity of GAO (Candidatus competibacter) and nitrifying bacteria (Nitrosomonas and Nitrospira). Under stable long-term (4-months) operation, the process achieved COD and nitrogen removal at rates of 1354 and 79.1 g m^-3 d^-1, respectively. The biofilm process demonstrated >90% nitrogen removal efficiency in multi-cycle (4/8 cycles) strategy with a short treatment time of 8 h. Due to the passive aeration scheme, the energy consumption of the proposed wastewater treatment process is calculated to be about 13-times less than that of traditional activated sludge process. Therefore, the Passive Aeration Simultaneous Nitrification and Denitrification (PASND) biofilm process is a promising low-energy treatment step for efficient removal of COD and nitrogen from wastewater.

Tropical-based EBPR process: The long-term stability, microbial community and its response towards temperature stress

Temperature is known to influence the operational efficiency of enhanced biological phosphorus removal (EBPR) systems. This study investigated the impact of thermal stress above 30°C on the properties of an EBPR community established with tropical inoculum. The results confirmed the stability of the 30°C EBPR system with high P-removal efficiency over 210 days. Accumulibacter was abundant in the community. When the EBPR sludge was subjected to a sudden temperature increase to 35°C under multiple cycles of anaerobic-aerobic phases, each lasting 4 h, high P-removal was maintained over 2 days, before gradually failing when the Competibacter appeared to outcompete Accumulibacter. These data suggested that the EBPR capacity is robust when subjected to occasional thermal stress. However, it could not be maintained even for a short time under temperature stress at 40°C. Thus, the threshold temperature for tropical EBPR failure is between 35°C and 40°C. PRACTITIONER POINTS: EBPR was stably maintained at 30°C with Accumulibacter being dominant. Good EBPR activities persisted for a short period at 35°C. EBPR was deteriorated at 40°C. The threshold temperature for tropical EBPR failure is between 35°C and 40°C.

Pilot-scale two-stage constructed wetlands based on novel solid carbon for rural wastewater treatment in southern China: Enhanced nitrogen removal and mechanism

Constructed wetlands (CWs) have been proved to be an alternative to the treatment of various wastewater. However, there are few studies focused on the removal performance and mechanisms of pollutants in pilot-scale CWs packed with novel solid carbon. In this study, we investigated the effect of poly-3-hydroxybutyrate-co-3-hydroxyvalerate/polyacetic acid (PHBV/PLA) blends as carbon source on pollutant's transformation, microbial communities and functional genes in pilot-scale aeration-anoxic two-stage CWs for polishing rural runoff in southern China. Results showed a striking improvement of TN removal in CWs with PHBV/PLA blends (64.5%) compared to that in CWs with ceramsite (52.9%). NH₄⁺-N (61.3-64.6%), COD (40.4-53.8%) and TP (43.6-47.1%) were also removed effectively in both two CWs. In addition, the strains of Rhodocyclaceae and Bacteroidetes were the primary denitrifiers on the surface of PHBV/PLA blends. Further, the aerobic stage induced gathering of 16 S and amoA genes and the anoxic zone with PHBV/PLA blends increased the nirS genes, which fundamentally explained the better denitrification performance in CW based on PHBV/PLA blends. Consequently, this study will provide straightforward guidance for the operation of engineering CWs packed with polymers to govern the low-C/N rural wastewater.

Short reaction times coupled with alkalization improves the release of phosphorus from Al-waste activated sludge

In this study, the performance and mechanism of P release from Al-waste activated sludge (WAS) via wet-chemical treatment at different reaction times were investigated. The maximum P release (46% of TP) was achieved at 20 min when the pH was maintained at 2 during acidic treatment. During alkali treatment, the maximum P concentration (363.96 mg/L, 46.07%) was achieved at 10 min when pH was initially adjusted to 12. Acidic treatment took twice as long to achieve the same efficiency of released P as the alkali treatment. Furthermore, P release mainly originated from Al-P and Ca-P during acidic treatment and Al-P dissolution during alkali treatment. The cost of chemical consumption was 483.96 USD/ton TS sludge with acidic treatment, which was 8.49 times higher than that of alkali treatment without pH control. Thus, short reaction times (ca. 10 min) coupled with alkalization provide an effective approach for improving P release from Al-WAS.

An efficient hydrodynamic-biokinetic model for the optimization of operational strategy applied in a full-scale oxidation ditch by CFD integrated with ASM2

Oxidation ditches (ODs) are often used for wastewater treatment. However, limitations of ODs like high energy expenditure and increased sludge sedimentation hinder its wide application. In this study, the computational fluid dynamics (CFD) model integrated with Activated Sludge Model No. 2 (ASM2) was proposed and applied in a full-scale OD. The integrated model provided heterogeneous information on the characteristics of hydrodynamics and biokinetics of OD, especially with respect to the simulation of total phosphorus removal by CFD-ASM2 integration model for the first time. The simulated values of flow velocities, suspended solids (SS), dissolved oxygen, chemical oxygen demand, total nitrogen, ammonium nitrogen, and total phosphorus concentrations were well validated with the measured results, with the standard deviation errors of less than 5.56%, 0.28%, 0.74%, 7.39%, 3.17%, 5.27%, and 7.40%, respectively. Based on the integrated model, four different operational strategies were simulated. The proposed operational strategy of operating 7 surface aerators and 10 submerged impellers not only met the standard discharge requirements (GB 18918-2002) but also consumed less energy by 22.3%, compared with the original strategy of operating 9 surface aerators and 13 submerged impellers. Meanwhile, this proposed operational strategy also reduced the SS concentrations in the second and fourth channels, which was beneficial to elimination of sludge sedimentation. Moreover, the proposed operational strategy was successfully applied and validated in full-scale OD. The foregoing results collectively suggest that the CFD-AMS2 integration model is numerically capable to optimize the operational strategy of ODs.

Butyrate can support PAOs but not GAOs in tropical climates

Glycogen accumulating organisms (GAOs) are thought to compete with polyphosphate accumulating organisms (PAOs) for the often-limiting carbon sources available in wastewater, deteriorating enhanced biological phosphorus removal (EBPR) performance at high temperatures. Fermentation liquids are often used to provide an additional carbon source supply in EBPR processes, where butyrate is known to be an important volatile fatty acid (VFA) produced in sludge fermentation. Nevertheless, the impact of butyrate on the PAO-GAO competition is not well understood especially at high temperature. The results of this study demonstrate that butyrate, as a supplemental or sole carbon source, could be promising for EBPR in tropical climates. When the carbon source was gradually changed from acetate to butyrate, a substantial PAO population was found under both conditions, despite a substantial shift in the abundance of Candidatus Accumulibacter phosphatis (decreased from 37.4% to 13.9%) to Rhodocyclaceae (increased from 2.0% to 14.5%), where both organisms likely played an important role in P-removal. Thus, a relatively stable P removal performance was realized throughout the whole operation period. Nevertheless, butyrate had a negative impact on GAOs. The biomass concentration and microbial diversity continually decreased in the GAO reactor, and Candidatus Competibacter phosphatis reduced from 27.3% to 6.2%, where the dominant population was replaced by Zoogloea. With the addition of butyrate as carbon source, the total amount of synthesized PHAs reduced in both PAO and GAO cultures and the composition of PHA was greatly changed. The presence of a novel PHA fraction (PHH) may disturb the microbial activity in the aerobic phase, where the GAO culture was more severely affected. Glycogen cycling also seemed to be limited in both reactors. This could reduce the GAO metabolism in both cultures and favor PAOs and P removal. Furthermore, the biomass growth rate of the PAO culture was higher than that of GAO when fed with butyrate, which also provides PAO a competitive advantage. All the above results indicate that butyrate could not be well metabolized by GAOs, but could provide PAOs a competitive advantage. Thus, mixed VFAs (i.e. acetate, propionate and butyrate) are likely to favor PAOs over GAOs in EBPR processes operated in warm climates, where the impact of substantial butyrate fractions represents an advantage towards successful process operation.

Recent advances in understanding the ecophysiology of enhanced biological phosphorus removal

Enhanced biological phosphorus removal (EBPR) is an efficient, cost-effective, and sustainable method for removing excess phosphorus from wastewater. Polyphosphate accumulating organisms (PAOs) exhibit a unique physiology alternating between anaerobic conditions for uptake of carbon substrates and aerobic or anoxic conditions for phosphorus uptake. The implementation of high-throughput sequencing technologies and advanced molecular tools along with biochemical characterization has provided many new perspectives on the EBPR process. These approaches have helped identify a wide range of carbon substrates and electron acceptors utilized by PAOs that in turn influence interactions with microbial community members and determine overall phosphorus removal efficiency. In this review, we systematically discuss the microbial diversity and metabolic response to a range of environmental conditions and process control strategies in EBPR.

Interaction of perfluorooctanoic acid with extracellular polymeric substances - Role of protein

Perfluorooctanoic acid (PFOA) is nonbiodegradable, and adsorption is the main pathway for its removal in wastewater treatment plants (WWTPs). This study compared the capability of three types of sludge on adsorbing PFOA and investigated the role of extracellular polymeric substances (EPS) in the adsorption process. Results show that enhanced biological phosphorus removal (EBPR) sludge had the highest adsorption capacity for PFOA. Studies on the interaction between EPS and PFOA reveal that proteins play a crucial role in binding PFOA to EPS/sludge. Specifically, the aromatic and amide groups on the structure of protein can attract the C-F chains and carboxylic head of PFOA via hydrophobic interaction and electrostatic attraction, respectively. EPS of EBPR sludge has the highest amount of protein and binding sites, thus exhibits the highest adsorption capability for PFOA. This study reveals the interaction mechanism between PFOA and sludge EPS and provides new insight into the function of EPS in perfluoroalkyl substances removal in WWTPs.

Comparison of nitrite accumulation performance and microbial community structure in endogenous partial denitrification process with acetate and glucose served as carbon source

Although the combination of endogenous partial denitrification (EPD) and Anammox (EPD-AMX) were developed for deep-level nitrogen removal, the effects of different carbon source were not clear. In this study, the EPD performance was investigated comparatively with acetate (EPD_A) and glucose (EPD_G). Results revealed that through regulating chemical oxygen demand to phosphate ratio, Candidatus_Competibacter was highly enriched in EPD_A (54.2%) and EPD_G (51.3%), resulting high intracellular carbon storage efficiencies (90.2% and 85.3%, respectively). More stable nitrite accumulation was observed in EPD_G than EPD_A. But, higher specific nitrite generated rate (r_NO2, 8.25 > 7.04 mgN·gVSS^-1·h^-1) and nitrate-to-nitrite transformation rate (NTR, 87.9% > 85.2%) were achieved in EPD_A than those in EPD_G. The functional bacterium was also shifted to Defluviicoccus in both EPD_A (30.6%) and EPD_G (25.8%). Moreover, with whether acetate or glucose, the EPD-AMX processes could achieve the same level of total nitrogen removal efficiencies (88.7% and 91.3%, respectively) via anammox mainly (87.8% and 89.4%, respectively).

Mechanism of nutrient removal enhancement in low carbon/nitrogen wastewater by a novel high-frequency micro-aeration/anoxic (HMOA) mode

In this study, a novel high-frequency micro-aeration/anoxic (HMOA) mode with a high aeration frequency (15 times/h) and short aeration duration (T_aer = 1 h/cycle) was proposed. Compared with continuous aeration modes, the highest nitrogen and phosphorus removal efficiencies were achieved in the sequencing batch reactor (SBR) under HMOA mode when treating wastewater with carbon/nitrogen (C/N) ratios of 4.5 (85% and 97%, respectively) and 3 (77% and 75%, respectively). Metagenomic analysis was utilized to analyse the microbial metabolic mechanism under the HMOA mode. The results showed that under the HMOA mode, the enhanced transduction and metabolism pathways of nitrate, nitrite, oxygen, phosphorus and acetate provided favourable nutritional conditions for the proliferation of denitrifiers and phosphorus accumulating organisms (PAOs), and simultaneously strengthened the survival capacity of nitrifiers under low dissolved oxygen (DO) conditions. In addition, genes involved in carbon metabolism were upregulated by the HMOA mode, which further increased the utility of carbon sources for denitrifier and PAO metabolism. Consequently, the limited carbon source could be fully utilized in nitrogen and phosphorus removal, which improved the efficiency of treating low C/N wastewater. This study proposed a potential aeration mode for microbial metabolism regulation to enhance nutrient removal in biological wastewater treatment processes.

Long-term simulation of a full-scale EBPR plant with a novel metabolic-ASM model and its use as a diagnostic tool

This study evaluates the predictive capacity of the META-ASM model, a new integrated metabolic activated sludge model, in describing the long-term performance of a full-scale enhanced biological phosphorus removal (EBPR) system that suffers from inconsistent performance. In order to elucidate the causes of EBPR upsets and troubleshoot the process accordingly, the META-ASM model was tested as an operational diagnostic tool in a 1336-day long-term dynamic simulation, while its performance was compared with the ASM-inCTRL model, a version based on the Barker & Dold model. Overall, the predictions obtained with the META-ASM without changing default parameters were more reliable and effective at describing the active biomass of polyphosphate accumulating organisms (PAOs) and the dynamics of their storage polymers. The primary causes of the EBPR upsets were the high aerobic hydraulic retention times (HRTs) and low organic loading rates (OLRs) of the plant, which led to periods of starvation. The impact of these factors on EBPR performance were only identified with the META-ASM model. Furthermore, the first signs of process upsets were predicted by variations in the aerobic PAO maintenance rates, suggesting that the META-ASM model has potential to provide an early warning of process upset. The simulation of a new viable operational strategy indicated that troubleshooting the process could be achieved by reducing the aerated volume by switching off air in the first half of the aeration tank. In this new strategy, the META-ASM model predicted a simultaneous improvement in the biological phosphorus (P) and nitrogen (N) removal due to the enhancement of the hydrolysis and fermentation of the mixed liquor sludge in the new unaerated zone, which increased the availability of volatile fatty acids (VFAs) for PAOs. This study demonstrates that the META-ASM model is a powerful operational diagnostic tool for EBPR systems, capable of predicting and mitigating upsets, optimising performance and evaluating new process designs.

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.

Effects of polyaluminium chloride addition on community structures of polyphosphate and glycogen accumulating organisms in biological phosphorus removal (BPR) systems

Polyaluminium chloride (PAC) was added into the biological phosphorus removal (BPR) systems to investigate the populations of polyphosphate and glycogen accumulating organisms (PAOs and GAOs). Typical BPR performed under Al:P of 1:1, while BPR almost disappeared at Al:P of 4:1. Even with high PAC addition, PAOs still existed in systems. Compared to the BPR with no PAC addition, the relative abundance of Accumulibacter, Tetrasphaera and Commnadaceae slightly increased with PAC addition. The relative abundance of Dechloromonas was improved from 0.87% to 3.82%, becoming the most dominant PAOs. The specific structures of Accumulibacter and Tetrasphaera changed little, but that of Dechloromonas and Comamonadaceae significantly altered. Regarding the GAOs, the relative abundance of Competibacter and Defluviicoccus significantly declined. Additionally, PAC addition effectively inhibited the proliferation of filamentous bacteria, indicating its potential in inhibiting the sludge filamentous bulking. This study provided guidance for the selection of the phosphorus removal process and operational conditions.

Biotransformation of phosphorus in enhanced biological phosphorus removal sludge biochar

Biochar derived from enhanced biological phosphorus removal (EBPR) sludge could be a potential phosphorus (P) fertilizer. Soil microorganisms play a regulating role on the turnover of P in soil. When the EBPR sludge biochar is added to soil, it would inevitably interact with soil microorganisms. Thus, for the wise use of the EBPR sludge biochar, it is imperative to understand the interaction between the biochar and soil microorganisms. In this study, Pseudomonas putida (P. putida), a common soil microorganism, was applied to investigate the biotransformation of P in two EBPR sludge biochars. The results reveal that P released from biochar produced at 700 °C (E700) was more easily absorbed by P. putida than that released from biochar produced at 400 °C (E400). This is attributed to the higher polyphosphates (poly-P) content in E700 and poly-P has higher affinity to P. putida surface compared to orthophosphates. Furthermore, E400 has a negative effect on intracellular poly-P formation in P. putida, which is probably caused by the oxidative stress induced by the free radicals from E400. As intracellular poly-P plays a critical role on bacteria survival and their interaction with surrounding environment, high-temperature biochar (E700) in this case would be more suitable for soil remediation.

Alkaline fermentation promotes organics and phosphorus recovery from polyaluminum chloride-enhanced primary sedimentation sludge

In this study, alkaline fermentation was applied to promote organics and P recovery from polyaluminum chloride (PACl)-enhanced primary sedimentation sludge. Coagulant results demonstrated that the optimum PACl dosage of 100 mg/L resulted in the effective concentration of 73% of organic matter and 90% of P from wastewater into sludge. Batch fermentation results highlighted the ability of alkaline fermentation in improving the biodegradability of PACl sludge. More specifically, at pH 11, 43.3% of soluble organics and 36.49% of P were released to the fermentation supernatant. Furthermore, P fractionation fermented sludge results revealed that partial Al-P dissolution and organic phosphorus hydrolysis were the main drivers of the released P. Finally, at pH 11, 85% of P was recovered as magnesium ammonium phosphate from the fermentation supernatant at the 2:1 Mg/P molar ratio. In conclusion, 24.9% of organics and 27.9% of P from raw wastewater were converted to valuable products via alkaline fermentation.

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.

Multiple-cycle operation of sulphur-cycle-enhanced biological phosphorus removal to maintain stable performance at high temperatures

This study investigated a new method of multiple-cycle operation of a sulphur-cycle-enhanced biological phosphorus (P) removal system to maintain good phosphorus removal performance at a high temperature (30 °C). The findings demonstrate that P removal was low and unstable under a normal cycle (77 ± 18%), but multiple cycles resulted in a high and quite stable level of P removal (88 ± 9%). Moreover, in the normal mode, the polyhydroxyalkanoate levels increased significantly from 2 to 15 mg C/g of VSS, the glycogen level doubled from 5 to 10 mg C/g of VSS and the polyhydroxyalkanoate and glycogen levels were maintained at considerably low levels after multiple cycles (only 5 C/g of VSS). The 16S rRNA high-throughput sequencing analysis revealed that the genera Thioalbus and Psychrobacter in the gamma-Proteobacteria class were the key functional communities. These findings suggest a high level of P removal with multiple cycles of sulphur-cycle enhanced biological phosphorus removal.

Layered Extraction and Adsorption Performance of Extracellular Polymeric Substances from Activated Sludge in the Enhanced Biological Phosphorus Removal Process

A large amount of phosphorus was found in the extracellular polymeric substances (EPS) of activated sludge used in enhanced biological phosphorus removal (EBPR), so the role of EPS and extracellular phosphorus in EBPR should not be neglected. The composition and properties of tightly bound EPS (TB-EPS) and loosely bound EPS (LB-EPS) were significantly different, and it was necessary to study the adsorption performance of EPS through the fractionating of activated sludge into LB-EPS, TB-EPS and microbial cells. In this study, the adsorption performance of LB-EPS and TB-EPS for phosphate was explored by extracting LB-EPS and TB-EPS via sonication and cation exchange resin (CER), respectively. The results indicated that the sonication-CER method was an efficient and reliable extraction method for EPS with a synergistic effect. The performance of EPS in the adsorption/complexing of phosphate was excellent because of its abundant functional groups. Specifically, the type and content of metal elements and functional groups in TB-EPS were much greater than those in LB-EPS, which led to the key role of TB-EPS in the adsorption/complexing of phosphate. Finally, a metabolic model for EBPR with consideration of the adsorption performance of LB-EPS and TB-EPS was proposed.

Low-temperature-steam activation of phosphorus in biochar derived from enhanced biological phosphorus removal (EBPR) sludge

The property and release behavior of phosphorus in biochar derived from enhanced biological phosphorus removal sludge (EBPR sludge) were investigated. A low-temperature-steam (LTS) activation method was developed to increase the P availability in the biochar. The results demonstrate that the P content in the biochar is comparable to that in typical P fertilizers. The biochar contained a considerable portion of fast-release P. Polyphosphates (poly-P) were the predominant P species in the biochar. LTS greatly improved P availability in biochar produced at 700 °C by hydrolyzing insoluble poly-P to soluble pyro-P and ortho-P. In addition, the presence of Ca²⁺ could greatly reduce the P-release from biochar produced at lower temperature, e.g. 400 °C, due to that Ca²⁺ could facilitate the precipitation/adsorption of orthophosohates/pyrophosphates released from the low temperature biochars. Such phenomena was not observed with high temperature biochar, as the soluble poly-P released from 700 °C biochar could complex with Ca²⁺ rather than precipitated with it. Other environmental conditions, i.e., environmental pH, ionic strength of the soil porewater, and presence of low-molecular-weight acid, only had minor or negligible effects on the P-release of most studied biochars. This study concludes that LTS-activated-700 °C biochar could be a promising P fertilizer given its high, rapid, and unaffected P-release under various environmentally relevant conditions.

Re-evaluating the microbiology of the enhanced biological phosphorus removal process

We have critically assessed some of the dogmas in the microbiology of enhanced biological phosphorus removal (EBPR) and argue that the genus Tetrasphaera can be as important as Ca. Accumulibacter for phosphorus removal; and that proliferation of their competitors, the glycogen accumulating organisms, does not appear to be a practical problem for EBPR efficiency even under tropical conditions. An increasing number of EBPR-related genomes are changing our understanding of their physiology, for example, their potential to participate in denitrification. Rather than trying to identify organisms that adhere to strict phenotype metabolic models, we advocate for broader analyses of the whole microbial communities in EBPR plants by iterative studies with isolates, lab enrichments, and full-scale systems.

Operation mode of a step-feed anoxic/oxic process with distribution of carbon source from anaerobic zone on nutrient removal and microbial properties

This study investigated the operation mode of a step-feed anoxic/oxic (A/O) process with distribution of the carbon source from the anaerobic zone in terms of the treatment effects on sewage with low carbon and high nitrogen and phosphorus. After seven phases of operation, an optimal flow distribution ratio of 75%:25% was obtained from the anaerobic zone, and the concentrations of chemical oxygen demand, ammonia nitrogen, total nitrogen, and total phosphorous in the effluent were 20.8, 0.64, 14.2, and 0.89 mg/L, respectively. The presence of an internal reflux system in the deaeration zone improved the treatment. 16S rRNA high-throughput sequencing revealed that the microbial communities in aerobic zone I(O1) of the first-step A/O sludge were different from those in aerobic zone I (O2) of the second-step A/O sludge, whereas microbial communities of the seed sludge were similar to those in O2 of the second-step A/O sludge. The richness and diversity of microbial communities in O1 of the first-step A/O sludge samples were higher than those in O2 of the second-step A/O and seed sludge. At the optimal flow distribution ratio, the microbial abundance and treatment removal efficiency were the highest.

Polyphosphate-accumulating organisms in full-scale tropical wastewater treatment plants use diverse carbon sources

Enhanced biological phosphorus removal (EBPR) is considered challenging in the tropics, based on a great number of laboratory-based studies showing that the polyphosphate-accumulating organism (PAO) Candidatus Accumulibacter does not compete well with glycogen accumulating organisms (GAOs) at temperatures above 25 °C. Yet limited information is available on the PAO community and the metabolic capabilities in full-scale EBPR systems operating at high temperature. We studied the composition of the key functional PAO communities in three full-scale wastewater treatment plants (WWTPs) with high in-situ EBPR activity in Singapore, their EBPR-associated carbon usage characteristics, and the relationship between carbon usage and community composition. Each plant had a signature community composed of diverse putative PAOs with multiple operational taxonomic units (OTUs) affiliated to Ca. Accumulibacter, Tetrasphaera spp., Dechloromonas and Ca. Obscuribacter. Despite the differences in community composition, ex-situ anaerobic phosphorus (P)-release tests with 24 organic compounds from five categories (including four sugars, three alcohols, three volatile fatty acids (VFAs), eight amino acids and six other carboxylic acids) showed that a wide range of organic compounds could potentially contribute to EBPR. VFAs induced the highest P release (12.0-18.2 mg P/g MLSS for acetate with a P release-to-carbon uptake (P:C) ratio of 0.35-0.66 mol P/mol C, 9.4-18.5 mg P/g MLSS for propionate with a P:C ratio of 0.38-0.60, and 9.5-17.3 mg P/g MLSS for n-butyrate), followed by some carboxylic acids (10.1-18.1 mg P/g MLSS for pyruvate, 4.5-11.7 mg P/g MLSS for lactate and 3.7-12.4 mg P/g MLSS for fumarate) and amino acids (3.66-7.33 mg P/g MLSS for glutamate with a P:C ratio of 0.16-0.43 mol P/mol C, and 4.01-7.37 mg P/g MLSS for aspartate with a P:C ratio of 0.17-0.48 mol P/mol C). P-release profiles (induced by different carbon sources) correlated closely with PAO community composition. High micro-diversity was observed within the Ca. Accumulibacter lineage, which represented the most abundant PAOs. The total population of Ca. Accumulibacter taxa was highly correlated with P-release induced by VFAs, highlighting the latter's importance in tropical EBPR systems. There was a strong link between the relative abundance of individual Ca. Accumulibacter OTUs and the extent of P release induced by distinct carbon sources (e.g., OTU 81 and amino acids, and OTU 246 and ethanol), suggesting niche differentiation among Ca. Accumulibacter taxa. A diverse PAO community and the ability to use numerous organic compounds are considered key factors for stable EBPR in full-scale plants at elevated temperatures.