A new interpretation of ASM2d for modeling of SBR performance for enhanced biological phosphorus removal under different P/HAc ratios

This study evaluated the prediction capability of Activated Sludge Model No. 2d (ASM2d), for the enhanced biological phosphorus removal (EBPR) performance of a sequencing batch reactor (SBR) receiving variable influent phosphate load. For this purpose, a laboratory-scale SBR was operated with a synthetic feed containing acetate as the sole carbon source. The experiments were conducted in four different Runs to ensure a range of different phosphate/acetate ratios in the influent. Model evaluations were carried out using concentration profiles measured throughout a representative cycle at steady state. An iterative calibration methodology was developed based on sensitivity analysis and applied to four different sets of experimental data on relevant model parameters reflecting SBR performance. ASM2d was able to predict the steady state behavior of the SBR system receiving variable influent phosphate loads only with the recalibrated parameter set. The regular changing pattern of the coefficients could be interpreted with the ability of the SBR system to sustain glycogen accumulating microorganisms, GAOs, which can store substrate under anaerobic conditions without polyphosphate energy, but deriving energy from the degradation of glycogen. Thus they are capable of prevailing at lower P/Ac ratios. The results indicate the need to include glycogen and GAOs as model components for processes involving both phosphate accumulating organisms, (PAOs) and GAOs, in order to obtain a better prediction of X(PHA) and oxygen uptake rate (OUR) profiles in the system.     

A metabolic model for acetate uptake under anaerobic conditions by glycogen accumulating organisms: Stoichiometry, kinetics, and the effect of pH

A metabolic model for the stoichiometry of acetate uptake under anaerobic conditions by an enriched culture of glycogen accumulating organisms (GAOs) was developed and tested by experimental studies. Glycogen served as the source of both reducing power and energy to drive the process of acetate uptake. The amount of glycogen consumed and poly-beta-hydroxyvalerate (PHV) accumulated in the cells increased with increasing pH, indicating that the energy requirements for acetate uptake increased with pH. The composition of the accumulated poly-beta-hydroxyalkanoates (PHAs) was adequately predicted using the assumption that acetyl-CoA and propionyl-CoA condense randomly to produce PHA. In addition, the rate of acetate uptake was strongly affected by the pH. The rate decreased with increasing pH and this dependence could be described with a saturation type of expression. A comparison of the rate of acetate uptake at low pH with the rates observed in enriched cultures of phosphorus accumulating organisms (PAOs) indicated that GAOs are able to compete effectively with PAOs in nutrient removal systems under certain conditions.     

Model-based analysis of anaerobic acetate uptake by a mixed culture of polyphosphate-accumulating and glycogen-accumulating organisms

An increasing number of studies shows that the glycogen-accumulating organisms (GAOs) can survive and may indeed proliferate under the alternating anaerobic/aerobic conditions found in EBPR systems, thus forming a strong competitor of the polyphosphate-accumulating organisms (PAOs). Understanding their behaviors in a mixed PAO and GAO culture under various operational conditions is essential for developing operating strategies that disadvantage the growth of this group of unwanted organisms. A model-based data analysis method is developed in this paper for the study of the anaerobic PAO and GAO activities in a mixed PAO and GAO culture. The method primarily makes use of the hydrogen ion production rate and the carbon dioxide transfer rate resulting from the acetate uptake processes by PAOs and GAOs, measured with a recently developed titration and off-gas analysis (TOGA) sensor. The method is demonstrated using the data from a laboratory-scale sequencing batch reactor (SBR) operated under alternating anaerobic and aerobic conditions. The data analysis using the proposed method strongly indicates a coexistence of PAOs and GAOs in the system, which was independently confirmed by fluorescent in situ hybridization (FISH) measurement. The model-based analysis also allowed the identification of the respective acetate uptake rates by PAOs and GAOs, along with a number of kinetic and stoichiometric parameters involved in the PAO and GAO models. The excellent fit between the model predictions and the experimental data not involved in parameter identification shows that the parameter values found are reliable and accurate. It also demonstrates that the current anaerobic PAO and GAO models are able to accurately characterize the PAO/GAO mixed culture obtained in this study. This is of major importance as no pure culture of either PAOs or GAOs has been reported to date, and hence the current PAO and GAO models were developed for the interpretation of experimental results of mixed cultures. The proposed method is readily applicable for detailed investigations of the competition between PAOs and GAOs in enriched cultures. However, the fermentation of organic substrates carried out by ordinary heterotrophs needs to be accounted for when the method is applied to the study of PAO and GAO competition in full-scale sludges.     

Comparison of acetate and propionate uptake by polyphosphate accumulating organisms and glycogen accumulating organisms

Enhanced biological phosphorus removal (EBPR) performance is directly affected by the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). This study investigates the effects of carbon source on PAO and GAO metabolism. Enriched PAO and GAO cultures were tested with the two most commonly found volatile fatty acids (VFAs) in wastewater systems, acetate and propionate. Four sequencing batch reactors (SBRs) were operated under similar conditions and influent compositions with either acetate or propionate as the sole carbon source. The stimulus for selection of the PAO and GAO phenotypes was provided only through variation of the phosphorus concentration in the feed. The abundance of PAOs and GAOs was quantified using fluorescence in situ hybridisation (FISH). In the acetate fed PAO and GAO reactors, "Candidatus Accumulibacter phosphatis" (a known PAO) and "Candidatus Competibacter phosphatis" (a known GAO) were present in abundance. A novel GAO, likely belonging to the group of Alphaproteobacteria, was found to dominate the propionate fed GAO reactor. The results clearly show that there are some very distinctive differences between PAOs and GAOs in their ability to take up acetate and propionate. PAOs enriched with acetate as the sole carbon source were immediately able to take up propionate, likely at a similar rate as acetate. However, an enrichment of GAOs with acetate as the sole carbon source took up propionate at a much slower rate (only about 5% of the rate of acetate uptake on a COD basis) during a short-term switch in carbon source. A GAO enrichment with propionate as the sole carbon source took up acetate at a rate that was less than half of the propionate uptake rate on a COD basis. These results, along with literature reports showing that PAOs fed with propionate (also dominated by Accumulibacter) can immediately switch to acetate, suggesting that PAOs are more adaptable to changes in carbon source as compared to GAOs. This study suggests that the PAO and GAO competition could be influenced in favour of PAOs through the provision of propionate in the feed or even by regularly switching the dominant VFA species in the wastewater. Further study is necessary in order to provide greater support for these hypotheses.     

Anaerobic metabolism of propionate by polyphosphate-accumulating organisms in enhanced biological phosphorus removal systems

Propionate, a carbon substrate abundant in many prefermenters, has been shown in several previous studies to be a more favorable substrate than acetate for enhanced biological phosphorus removal (EBPR). The anaerobic metabolism of propionate by polyphosphate accumulating organisms (PAOs) is studied in this paper. A metabolic model is proposed to characterize the anaerobic biochemical transformations of propionate uptake by PAOs. The model is demonstrated to predict very well the experimental data from a PAO culture enriched in a laboratory-scale reactor with propionate as the sole carbon source. Quantitative fluorescence in-situ hybridization (FISH) analysis shows that Candidatus Accumulibacter phosphatis, the only identified PAO to date, constitute 63% of the bacterial population in this culture. Unlike the anaerobic metabolism of acetate by PAOs, which induces mainly poly-beta-hydroxybutyrate (PHB) production, the major fractions of poly-beta-hydroxyalkanoate (PHA) produced with propionate as the carbon source are poly-beta-hydroxyvalerate (PHV) and poly-beta-hydroxy-2-methylvalerate (PH2MV). PHA formation correlates very well with a selective (or nonrandom) condensation of acetyl-CoA and propionyl-CoA molecules. The maximum specific propionate uptake rate by PAOs found in this study is 0.18 C-mol/C-mol-biomass . h, which is very similar to the maximum specific acetate uptake rate reported in literature. The energy required for transporting 1 carbon-mole of propionate across the PAO cell membrane is also determined to be similar to the transportation of 1 carbon-mole of acetate. Furthermore, the experimental results suggest that PAOs possess a similar preference toward acetate and propionate uptake on a carbon-mole basis.     

Ecophysiology of a group of uncultured Gammaproteobacterial glycogen-accumulating organisms in full-scale enhanced biological phosphorus removal wastewater treatment plants

The presence of glycogen-accumulating organisms (GAOs) in enhanced biological phosphorus removal (EBPR) plants can seriously deteriorate the biological P-removal by out-competing the polyphosphate-accumulating organisms (PAOs). In this study, uncultured putative GAOs (the GB group, belonging to the Gammaproteobacteria) were investigated in detail in 12 full-scale EBPR plants. Fluorescence in situ hybridization (FISH) revealed that the biovolume of the GB bacteria constituted 2-6% of total bacterial biovolume. At least six different subgroups of the GB bacteria were found, and the number of dominant subgroups present in each plant varied between one and five. Ecophysiological investigations using microautoradiography in combination with FISH showed that, under aerobic or anaerobic conditions, all subgroups of the GB bacteria could take up acetate, pyruvate, propionate and some amino acids, while some subgroups in addition could take up formate and thymidine. Glucose, ethanol, butyrate and several other organic substrates were not taken up. Glycolysis was essential for the anaerobic uptake of organic substrates. Polyhydroxyalkanoates (PHA) but not polyphosphate (polyP) granules were detected in all GB bacterial cells. Polyhydroxyalkanoate formation after anaerobic uptake of acetate was confirmed by measuring the increase in fluorescence intensity of PHA granules inside GB bacterial cells after Nile blue staining. One GB subgroup was possibly able to denitrify, and several others were able to reduce nitrate to nitrite. PAOs were also enumerated by FISH in the same treatment plants. Rhodocyclus-related PAOs and Actinobacteria-related PAOs constituted up to 7% and 29% of total bacterial biovolume respectively. Rhodocyclus-related PAOs always coexisted with the GB bacteria and showed many physiological similarities. Factors of importance for the competition between the three groups of important bacteria in EBPR plants are discussed.     

Deciphering the Genome of Polyphosphate Accumulating Actinobacterium Microlunatus phosphovorus

Polyphosphate accumulating organisms (PAOs) belong mostly to Proteobacteria and Actinobacteria and are quite divergent. Under aerobic conditions, they accumulate intracellular polyphosphate (polyP), while they typically synthesize polyhydroxyalkanoates (PHAs) under anaerobic conditions. Many ecological, physiological, and genomic analyses have been performed with proteobacterial PAOs, but few with actinobacterial PAOs. In this study, the whole genome sequence of an actinobacterial PAO, Microlunatus phosphovorus NM-1^T (NBRC 101784^T), was determined. The number of genes for polyP metabolism was greater in M. phosphovorus than in other actinobacteria; it possesses genes for four polyP kinases (ppks), two polyP-dependent glucokinases (ppgks), and three phosphate transporters (pits). In contrast, it harbours only a single ppx gene for exopolyphosphatase, although two copies of ppx are generally present in other actinobacteria. Furthermore, M. phosphovorus lacks the phaABC genes for PHA synthesis and the actP gene encoding an acetate/H⁺ symporter, both of which play crucial roles in anaerobic PHA accumulation in proteobacterial PAOs. Thus, while the general features of M. phosphovorus regarding aerobic polyP accumulation are similar to those of proteobacterial PAOs, its anaerobic polyP use and PHA synthesis appear to be different.     

The utilization of glycogen accumulating organisms for mixed culture production of polyhydroxyalkanoates

Production of polyhydroxyalkanoates (PHAs) by an open mixed culture enriched in glycogen accumulating organisms (GAOs) under alternating anaerobic–aerobic conditions with acetate as carbon source was investigated. The culture exhibited a stable enrichment performance over the 450‐day operating period with regards to phenotypic behavior and microbial community structure. Candidatus Competibacter phosphatis dominated the culture at between 54% and 70% of the bacterial biomass throughout the study, as determined by fluorescence in situ hybridization. In batch experiments under anaerobic conditions, PHA containing 3‐hydroxybutyrate (3HB) and 27 mol‐% 3‐hydroxyvalerate (3HV) was accumulated up to 49% of cell dry weight utilizing the glycogen pool stored in the SBR cycle. Under aerobic and ammonia limited conditions, PHA comprising only 3HB was accumulated to 60% of cell dry weight. Glycogen was consumed during aerobic PHA accumulation as well as under anaerobic conditions, but with different stoichiometry. Under aerobic conditions 0.31 C‐mol glycogen was consumed per consumed C‐mol acetate compared to 0.99 under anaerobic conditions. Both the PHA biomass content and the specific PHA production rate obtained were similar to what is typically obtained using the more commonly applied aerobic dynamic feeding strategy. Biotechnol. Bioeng. 2009; 104: 698–708 © 2009 Wiley Periodicals, Inc.     

Metabolic model for glycogen-accumulating organisms in anaerobic/aerobic activated sludge systems

Glycogen-accumulating organisms (GAO) have the potential to directly compete with polyphosphate-accumulating organisms (PAO) in EBPR systems as both are able to take up VFA anaerobically and grow on the intracellular storage products aerobically. Under anaerobic conditions GAO hydrolyse glycogen to gain energy and reducing equivalents to take up VFA and to synthesise polyhydroxyalkanoate (PHA). In the subsequent aerobic stage, PHA is being oxidised to gain energy for glycogen replenishment (from PHA) and for cell growth. This article describes a complete anaerobic and aerobic model for GAO based on the understanding of their metabolic pathways. The anaerobic model has been developed and reported previously, while the aerobic metabolic model was developed in this study. It is based on the assumption that acetyl-CoA and propionyl-CoA go through the catabolic and anabolic processes independently. Experimental validation shows that the integrated model can predict the anaerobic and aerobic results very well. It was found in this study that at pH 7 the maximum acetate uptake rate of GAO was slower than that reported for PAO in the anaerobic stage. On the other hand, the net biomass production per C-mol acetate added is about 9% higher for GAO than for PAO. This would indicate that PAO and GAO each have certain competitive advantages during different parts of the anaerobic/aerobic process cycle.     

Metabolic Characteristics of a Glycogen-Accumulating Organism in Defluviicoccus Cluster II Revealed by Comparative Genomics

Glycogen-accumulating organisms (GAOs) may compete with phosphate-accumulating organisms (PAOs) for short-chain fatty acids (VFAs) in anaerobic polyhydroxyalkanoates (PHA) synthesis, but no consequently aerobic polyphosphate accumulation in enhanced biological phosphorus removal (EBPR) process, thus deteriorating the EBPR process. They are detected frequently in the deteriorated EBPR process, but their metabolisms are still far from our comprehensions for there is seldom pure culture. In this study, a nearly complete draft genome of a GAOs in Defluviicoccus cluster II, GAO-HK, is recruited from the metagenome of activated sludge in a full-scale industrial anoxic/aerobic wastewater plant. Comparative genomics reveal similar metabolisms of PHA and glycogen in GAOs of GAO-HK, Defluviicoccus tetraformis TFO71 (TFO71) and Competibacter phosphatis clade IIA (CPIIA), and PAOs of Accumulibacter clade IIA UW-1 (UW-1) and Tetrasphaera elongata Lp2 (Lp2). Although there are similar gene cassettes related with polyphosphate metabolism in these GAOs and PAOs, especially for Defluviicoccus-relative bacteria and UW-1, ppk1 in GAOs are diverse from those in the identified PAOs, implying the difference of polyphosphate metabolism in GAOs and PAOs. Additionally, genes related to the dissimilatory denitrification are absent in TFO71 and GAO-HK, implying that additional nitrate or nitrite may favor PAOs over Defluviicoccus-relative GAOs. Therefore, PAOs suffering from competition of Defluviicoccus-relative GAOs might be rescued with the additional nitrate/nitrite, which is important to improve the stability of EBPR processes.     

Production of targeted poly(3-hydroxyalkanoates) copolymers by glycogen accumulating organisms using acetate as sole carbon source

One of the main limitations in bacterial polyhydroxyalkanoate (PHA) production with mixed cultures is the fact that primarily polyhydroxybutyrate (PHB) homopolymers are generated from acetate as the main carbon source, which is brittle and quite fragile. The incorporation of different 3-hydroxyalkanoate (HA) components into the polymers requires the addition of additional carbon sources, leading to extra costs and complexity. In this study, the production of poly(3-hydroxybutyrate (3HB)-co-3-hydroxyvalerate (3HV)-co-3-hydroxy-2-methylvalerate (3HMV)), with 7-35C-mol% of 3HV fractions from acetate as the only carbon source was achieved with the use of glycogen accumulating organisms (GAOs). An enriched GAO culture was obtained in a lab-scale reactor operated under alternating anaerobic and aerobic conditions with acetate fed at the beginning of the anaerobic period. The production of PHAs utilizing the enriched GAO culture was investigated under both aerobic and anaerobic conditions. A polymer content of 14-41% of dry cell weight was obtained. The PHA product accumulated by GAOs under anaerobic conditions contained a relatively constant proportion of non-3HB monomers (30+/-5C-mol%), irrespective of the amount of acetate assimilated. In contrast, under aerobic conditions, GAOs only produced 3HB monomers from acetate causing a gradually decreasing 3HV fraction during this aerobic feeding period. The PHAs were characterized by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The data demonstrated that the copolymers possessed similar characteristics to those of commercially available poly(3HB-co-3HV) (PHBV) products. The PHAs produced under solely anaerobic conditions possessed lower melting points and crystallinity, higher molecular weights, and narrower molecular-weight distributions, compared to the aerobically produced polymers. This paper hence demonstrates the significant potential of GAOs to produce high quality polymers from a simple and cheap carbon source, contributing considerably to the growing research body on bacterial PHA production by mixed cultures.     

Competition between polyphosphate and glycogen accumulating organisms in enhanced biological phosphorus removal systems with acetate and propionate as carbon sources

Enhanced biological phosphorus removal (EBPR) is a widely used process for achieving phosphorus removal from wastewater. A potential reason for EBPR failure is the undesirable growth of glycogen accumulating organisms (GAOs), which can compete for carbon sources with the bacterial group responsible for phosphorus removal from wastewater: the polyphosphate accumulating organisms (PAOs). This study investigates the impact of carbon source on EBPR performance and the competition between PAOs and GAOs. Two sequencing batch reactors (SBRs) were operated during a 4-6 month period and fed with a media containing acetate or propionate, respectively, as the sole carbon source. It was found that the acetate fed SBR rarely achieved a high level of phosphorus removal, and that a large portion of the microbial community was comprised of "Candidatus Competibacter phosphatis", a known GAO. The propionate fed SBR, however, achieved stable phosphorus removal throughout the study, apart from one brief disturbance. The bacterial community of the propionate fed SBR was dominated by "Candidatus Accumulibacter phosphatis", a known PAO, and did not contain Competibacter. In a separate experiment, another SBR was seeded with a mixture of PAOs and a group of alphaproteobacterial GAOs, both enriched with propionate as the sole carbon source. Stable EBPR was achieved and the PAO population increased while the GAOs appeared to be out-competed. The results of this paper suggest that propionate may provide PAOs with a selective advantage over GAOs in the PAO-GAO competition, particularly through the minimisation of Competibacter. Propionate may be a more suitable substrate than acetate for enhancing phosphorus removal in EBPR systems.     

Experimental evaluation of decrease in the activities of polyphosphate/glycogen‐accumulating organisms due to cell death and activity decay in activated sludge

Decrease in bacterial activity (biomass decay) in activated sludge can result from cell death (reduction in the amount of active bacteria) and activity decay (reduction in the specific activity of active bacteria). The goal of this study was to experimentally differentiate between cell death and activity decay as the cause of decrease in bacterial activity. By means of measuring maximal anaerobic phosphate release rates, verifying membrane integrity by live/dead staining and verifying presence of 16S rRNA with fluorescence in situ hybridization (FISH), the decay rates and death rates of polyphosphate‐accumulating organisms (PAOs) in a biological nutrient removal (BNR) system and a laboratory phosphate removing sequencing batch reactor (SBR) system were determined, respectively, under famine conditions. In addition, the decay rate and death rate of glycogen‐accumulating organisms (GAOs) in a SBR system with an enrichment culture of GAOs were also measured under famine conditions. Hereto the maximal anaerobic volatile fatty acid uptake rates, live/dead staining, and FISH were used. The experiments revealed that in the BNR and enriched PAO‐SBR systems, activity decay contributed 58% and 80% to the decreased activities of PAOs, and that cell death was responsible for 42% and 20% of decreases in their respective activities. In the enriched GAOs system, activity decay constituted a proportion of 74% of the decreased activity of GAOs, and cell death only accounted for 26% of the decrease of their activity. Biotechnol. Bioeng. 2010; 106: 399–407. © 2010 Wiley Periodicals, Inc.     

Stoichiometry and kinetics of acetate uptake under anaerobic conditions by an enriched culture of phosphorus-accumulating organisms at different pHs

The effect of pH on the stoichiometry and kinetics of acetate uptake by phosphorus-accumulating organisms (PAOs) was studied. The stoichiometry of glycogen consumption and poly-beta-hydroxy-alkanoates (PHA) accumulation was independent of the pH over the range 6.5 to 8.0. It was again demonstrated that the amount of phosphorus released per acetate taken up (P/Hac ratio) was linearly dependent on pH, because of additional energy requirements for acetate transport at higher pH. The slope of this relationship was similar to that in previously published work, but the absolute values were different, indicating that the P/Hac ratio is the most variable stoichiometric parameter associated with the anaerobic metabolism of PAOs. A kinetic expression for acetate-uptake rate was developed and tested. It assumes a zero-order form when the polyphosphate content of the biomass is not limiting. When the polyphosphate content becomes low, the rate is significantly decreased. The expression was tested in situations in which polyphosphate was a limiting factor in the rate of acetate uptake, in which the glycogen content of the biomass became very low, and in which both glycogen and polyphosphate were present in excess. The model was able to simulate the three situations adequately. Additionally, the rate of acetate uptake was independent of the pH for the range studied (6.5 to 8.0).     

Effect of different carbon sources on the enhanced biological phosphorus removal in a sequencing batch reactor

The effect of the different carbon sources acetate, acetate/glucose or glucose on the enhanced biological phosphorus removal (EBPR) process was studied by experiments under alternating anaerobic–aerobic conditions in one sequencing batch reactor for each carbon source. The glucose was consumed completely within the first 30 min of the anaerobic phase whereas acetate degradation was slow and incomplete. Phosphate was released independently of the carbon source during the whole anaerobic phase. The highest phosphate release (27 mg P l⁻¹) and polyhydroxyalkanoate (PHA) storage (20 mg C g⁻¹ dry matter (DM)) during the anaerobic phase as well as the highest polyphosphate (poly-P) (8 mg P g⁻¹ DM) and glycogen storage (17 mg C g⁻¹ DM) during the aerobic phase were observed with acetate. In contrast to other investigations, glycogen storage did not increase with glucose as substrate but was significantly smaller than with acetate. The PHA composition was also influenced strongly by the carbon source. The polyhydroxyvalerate (PHV) portion of the PHA was maximal 17% for acetate and 82% for glucose. Due to the strong influence of the carbon source on the PHA concentration and composition, PHA storage seems to regulate mainly the phosphate release and uptake. This revised version was published online in July 2006 with corrections to the Cover Date.     

Decolorization of azo-reactive dye by polyphosphate- and glycogen-accumulating organisms in an anaerobic-aerobic sequencing batch reactor

An anaerobic-aerobic sequencing batch reactor with a sludge age of 8 days and anaerobic + aerobic + settling times of 18 + 5 + 1 h, was used to decolorize an azo-reactive dye wastewater. The nutrient broth (NB) and sodium acetate (SA) solution at 500 + 0, 350 + 150, 250 + 250 and 0 + 500 mg/l as COD was fed to the system to promote the polyphosphate-accumulating organisms (PAOs), while only glucose (500 mg/l COD) was used as a glycogen-accumulating organisms (GAOs) promoting substrate. The decolorization capability of the process was about 73-77 and 59-64% in terms of ADMI for the systems which the PAOs and GAOs proliferated, respectively. The color reduction was mainly achieved within the first 2 h of the anaerobic stage.     

Influence of sludge retention time on tolerance of copper toxicity for polyphosphate accumulating organisms linked to polyhydroxyalkanoates metabolism and phosphate removal

This study explored the influence of sludge retention time (SRT) on tolerance of copper invasion for polyphosphate accumulating organisms (PAOs) in an enhanced biological phosphorus removal (EBPR). The experimental data showed the anaerobic polyhydroxyalkanoates (PHA) storage for the sludge at 10d SRT was less influenced by copper invasion than those at 5d and 15d SRTs. The reaction of PAOs aerobically taking up phosphate for the sludge at 5d or 15d SRT almost ceased at 2 mg Cu L⁻¹, whereas PAOs in the sludge at 10d SRT retained half of the ability to take up phosphate. Both the PHAs degradation and synthesis rates decreased with increasing copper concentration, regardless of the SRTs. However, the copper inhibition of the former was greater than that of the later.     

Characterizing the biochemical activity of full-scale enhanced biological phosphorus removal systems: A comparison with metabolic models

The metabolism of polyphosphate accumulating organisms (PAOs) has been widely studied through the use of lab-scale enrichments. Various metabolic models have been formulated, based on the results from lab-scale experiments using enriched PAO cultures. A comparison between the anaerobic stoichiometry predicted by metabolic models with that exhibited by full-scale sludge in enhanced biological phosphorus removal (EBPR) wastewater treatment plants (WWTPs) was performed in this study. Batch experiments were carried out with either acetate or propionate as the sole carbon source, using sludges from two different EBPR-WWTPs in Australia that achieved different phosphorus removal performances. The results support the hypothesis that the anaerobic degradation of glycogen is the primary source of reducing equivalents generated by PAOs, however, they also suggested a partial contribution of the tricarboxylic acid (TCA) cycle in some cases. The experimental results obtained when acetate was the carbon source suggest the involvement of the modified succinate-propionate pathway for the generation of poly-beta-hydroxyvalerate (PHV). Overall, the batch test results obtained from full-scale EBPR sludge with both substrates were generally well described by metabolic model predictions for PAOs.     

增强型生物除磷过程中聚磷酸盐积累微生物的研究进展

从磷污染控制、污水脱磷和磷资源角度论述了生物除磷的作用,并着重论述了增强型生物除磷过程中聚磷酸盐微生物(PAO)的研究历史、代谢特征及研究方法．聚磷酸盐广泛存在于自然界,但只有少数PAO微生物被分离、培养、鉴定出来．培养基能否分离出PAO和PAO能否在实验室条件下表现出polyP积累特征,均至关重要．糖原积累微生物(GAO)与PAO对碳源存在竞争关系,影响EBPR的效率．原位荧光分子杂交、激光共聚焦扫描电镜、微量放射自显影术、活体核磁共振光谱等现代科学技术的发展。使我们能够观察原位微生物群落组成、空间结构和功能变化．对PAO的深入研究,可改进污水脱磷的效率,提高对磷在环境中迁移转化的认识     

Inducing mechanism of biological phosphorus removal driven by the aerobic/extended-idle regime

Recently, it was found that excess phosphorus (Pi) removal could be achieved in activated sludge with an aerobic/extended‐idle (AEI) process. In this study, batch tests were performed to further reveal the inducing mechanism of Pi removal involved in the AEI process. Unlike the classical anaerobic/aerobic process where an anaerobic Pi release along with a significant polyhydroxyalkanoate (PHA) accumulation drives polyphosphate (poly‐P) accumulating organisms (PAOs) to over‐store Pi as poly‐P, an idle Pi release accompanied by a low‐idle PHA production, which is usually considered to be detrimental for biological Pi removal, was observed to induce some cells to effectively uptake Pi in excess of metabolic requirement in the AEI process. With the increase of idle Pi release, Pi removal efficiency linearly increased. The results also showed that a long idle period with a low level of intracellular glycogen could significantly increase Pi release contents, thus remarkably enhancing Pi removal performances. Fluorescence in situ hybridization analysis further revealed that activated sludge in the AEI process contained 37.6% of Accumulibacter (PAOs) and 28.2% of Competibacter and Defluviicoccus‐related organisms (glycogen accumulating organisms). This study revealed an actually existent, yet previously unrecognized, inducing mechanism of poly‐P accumulation, and this mechanism behind the AEI regime may provide a scientific basis for the development of an alternative strategy for Pi removal from wastewaters. Biotechnol. Bioeng. 2012; 109: 2798–2807. © 2012 Wiley Periodicals, Inc.