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PubMedDate not supplied

Comparison of fatty acid composition and kinetics of phosphorus-accumulating organisms and glycogen-accumulating organisms.

It was demonstrated that glycogen-accumulating organisms (GAOs) were able to compete with phosphorus-accumulating organisms (PAOs) for acetate in a biological phosphorus removal (BPR) process, leading to a loss of BPR capability. Cellular fatty acid composition, which serves as a fingerprint for microbial identification, was used to determine microbial population change and to investigate the competition mechanisms of PAOs and GAOs. Analysis of cellular fatty acid composition indicated that PAOs grown with acetate and glucose were different species and that GAOs and PAOs grown with the same substrate were also different species. Glycogen-accumulating organisms seemed to coexist with PAOs even in a well-developed BPR process. The GAOs were able to accumulate more poly-beta-hydroxybutyrate (PHB) and glycogen than PAOs during the anaerobic stage of the BPR process. The GAOs synthesized more in-cell glycogen than PAOs. The growth rate for PAOs was always greater than that for GAOs at various acetate or glucose concentrations, while GAOs had higher acetate uptake and PHB synthesis rates than PAOs. Therefore, GAOs are thought to compete with PAOs only at long solids retention times (> or = 20 days).

Bacteria↗

PubMed2001

A modification to the Activated Sludge Model No. 2 based on the competition between phosphorus-accumulating organisms and glycogen-accumulating organisms.

A modification to the ASM2 is proposed which permits representation of the competition between phosphorus accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs) in a nutrient removal activated sludge system. Some important aspects, which are not considered in ASM2, are discussed. The proposed modification includes denitrification by PAOs, PAO glycogen storage capability and GAO metabolism model. It is shown that the proposed modification is capable of describing pilot plant data using a single set of stoichiometric and kinetic parameters over three different sludge ages (16, 14 and 12 days). The modified ASM2 may be applicable to a wide range of situations where PAOs and GAOs can compete. This modification may well provide a better understanding about GAO behaviour.

Aerobiosis↗

PubMedDate not supplied

Effects of pH on the rates of aerobic metabolism of phosphate-accumulating and glycogen-accumulating organisms.

The effect of pH on the aerobic metabolism of phosphorus-accumulating organisms (PAOs) and glycogen-accumulating organisms (GAOs) was studied using aerobic batch experiments performed at pH 6.5, 7.0, and 7.5. For PAOs, the rates of phosphate uptake, polyhydroxy-alkanoates consumption, and biomass growth observed at pH 6.5 were 42, 70, and 53%, respectively, of the rates observed at pH 7.0. In contrast, the rates for GAOs were relatively independent of pH for the range tested. The results suggest that the stability of biological excess phosphorus removal (BEPR) is strongly dependent on the pH in the aerobic zone. If the pH is low, growth of PAOs will be inhibited whereas the growth of GAOs will be only mildly affected. This may lead to the proliferation of GAOs in BEPR systems, resulting in reduced phosphorus removal.

Bacteria↗

PubMed2003

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.

Acyl Coenzyme A↗

PubMed2003

Enrichment of denitrifying glycogen-accumulating organisms in anaerobic/anoxic activated sludge system.

Denitrifying glycogen-accumulating organisms (DGAO) were successfully enriched in a lab-scale sequencing batch reactor (SBR) running with anaerobic/anoxic cycles and acetate feeding during the anaerobic period. Acetate was completely taken up anaerobically, which was accompanied by the consumption of glycogen and the production of poly-beta-hydroxy-alkanoates (PHA). In the subsequent anoxic stage, nitrate or nitrite was utilized as electron acceptor for the oxidation of PHA, resulting in glycogen replenishment and cell growth. The above phenotype showed by the enrichment culture demonstrates the existence of DGAO. Further, it was found that the anaerobic behavior of DGAO could be predicted well by the anaerobic GAO model of Filipe et al. (2001) and Zeng et al. (2002a). The final product of denitrification during anoxic stage was mainly nitrous oxide (N(2)O) rather than N(2). The data strongly suggests that N(2)O production may be caused by the inhibition of nitrous oxide reductase by an elevated level of nitrite accumulated during denitrification. The existence of these organisms is a concern in biological nutrient removal systems that typically have an anaerobic/anoxic/aerobic reactor sequence since they are potential competitors to the polyphosphate-accumulating organisms.

Acetates↗

PubMed2002

Competition between polyphosphate- and glycogen-accumulating organisms in biological phosphorus removal systems--effect of temperature.

This study demonstrated that temperature is an important factor in determining the outcome of competition between polyphosphate-accumulating organisms (PAOs) and glycogen-accumulating non-poly-P organisms (GAOs) and the resultant stability of enhanced biological phosphorus removal (EBPR) systems. At 20 degrees C and a 10-day sludge age, PAOs were dominant in the anaerobic/aerobic (A/O) SBR, however, at 30 degrees C and a 10-day sludge age, GAOs were dominant in the A/O SBR. For kinetic batch studies, the anaerobic specific acetate uptake rate of GAO-dominated sludge (1.34 x 10(-3) mg C/mg VSS x minute) was higher than the rate of PAO-dominated sludge (0.89 x 10(-3) mg C/mg VSS x minute) at 30 degrees C, leading to the eventual failure of EBPR processes at high temperatures.

Bioreactors↗

PubMed2003

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.

Acetates↗

PubMedDate not supplied

pH as a key factor in the competition between glycogen-accumulating organisms and phosphorus-accumulating organisms.

The effects of pH on the anaerobic metabolism of glycogen-accumulating organisms (GAOs) and phosphorus-accumulating organisms (PAOs) were compared using models for the kinetics of acetate uptake. The comparison revealed that GAOs take up acetate faster than PAOs when the pH of the anaerobic zone is less than 7.25, but that PAOs remove acetate faster than GAOs at pHs greater than 7.5. It was also found that the growth efficiencies of the two organisms are similar. Furthermore, the amount of polyhydroxy-alkanoates available after replenishment of the polymers used during acetate uptake under anaerobic conditions is similar for the two organisms, making GAOs highly competitive in nutrient removal systems. The effects of pH on the competition between the two organisms were demonstrated during the operation of a laboratory-scale sequencing batch reactor. When the overall pH of the system was low, poor phosphate removal was observed. When the pH of the system was allowed to increase to a maximum of 7.5, phosphate removal improved, but was still incomplete. Total removal was only achieved when the pH of the system was never allowed to drop lower than 7.25. After the minimum pH in the system was increased, total removal of phosphate was achieved in 14 days. The results showed that pH control is a promising strategy for minimizing the accumulation of GAOs and increasing the reliability of biological excess phosphorus removal systems.

Bacteria↗

PubMed2002

Proposed modifications to metabolic model for glycogen-accumulating organisms under anaerobic conditions.

Filipe et al. (2001) proposed an anaerobic metabolic model for glycogen-accumulating organisms (GAO) in which the succinate-propionate pathway was used to describe the production of propionyl-CoA. However, propionyl-CoA is only an intermediate product in the above pathway. Stopping at propionyl-CoA instead of propionate (the end product of the pathway) results in the consumption of one ATP from succinate to succinyl-CoA, which was not accounted for in the model of Filipe et al. (2001). This resulted in significant errors in the stoichiometric coefficients in the final metabolic model. A modified model is presented in this communication and is shown to fit the experimental data significantly better than the original model.

Acetyl Coenzyme A↗

PubMed2001

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.

Aerobiosis↗

PubMed2002

Glycogen-accumulating organisms in laboratory-scale and full-scale wastewater treatment processes.

Laboratory-scale sequencing batch reactors (SBRs) as models for wastewater treatment processes were used to identify glycogen-accumulating organisms (GAOs), which are thought to be responsible for the deterioration of enhanced biological phosphorus removal (EBPR). The SBRs (called Q and T), operated under alternating anaerobic-aerobic conditions typical for EBPR, generated mixed microbial communities (sludges) demonstrating the GAO phenotype. Intracellular glycogen and poly-beta-hydroxyalkanoate (PHA) transformations typical of efficient EBPR occurred but polyphosphate was not bioaccumulated and the sludges contained 1.8% P (sludge Q) and 1.5% P (sludge T). 16S rDNA clone libraries were prepared from DNA extracted from the Q and T sludges. Clone inserts were grouped into operational taxonomic units (OTUs) by restriction fragment length polymorphism banding profiles. OTU representatives were sequenced and phylogenetically analysed. The Q sludge library comprised four OTUs and all six determined sequences were 99.7% identical, forming a cluster in the gamma-Proteobacteria radiation. The T sludge library comprised eight OTUs and the majority of clones were Acidobacteria subphylum 4 (49% of the library) and candidate phylum OP10 (39% of the library). One OTU (two clones, of which one was sequenced) was in the gamma-Proteobacteria radiation with 95% sequence identity to the Q sludge clones. Oligonucleotide probes (called GAOQ431 and GAOQ989) were designed from the gamma-Proteobacteria clone sequences for use in fluorescence in situ hybridization (FISH); 92% of the Q sludge bacteria and 28% of the T sludge bacteria bound these probes in FISH. FISH and post-FISH chemical staining for PHA were used to determine that bacteria from a novel gamma-Proteobacteria cluster were phenotypically GAOs in one laboratory-scale SBR and two full-scale wastewater treatment plants. It is suggested that the GAOs from the novel cluster in the gamma-Proteobacteria radiation be named 'Candidatus Competibacter phosphatis'.

Bacteria↗

PubMed2002

Characterization of an acetate-degrading sludge without intracellular accumulation of polyphosphate and glycogen.

A sequencing batch reactor (SBR) was operated in the conventional anaerobic-aerobic mode for enhanced biological phosphate removal (EBPR) using acetate as the sole substrate. Results showed that, however, the reactor was unable to remove phosphate from wastewater. The sludge containing 1.65% of phosphate did not exhibit the typical characteristics of polyphosphate-accumulating organisms (PAO) or glycogen-accumulating organisms (GAO). Phylogenetic analysis, based on 16S rDNA sequences of individual microorganisms, showed that the microbial community of this acetate-degrading sludge was closely related to Comamonas testosteroni (43.8% of total population) of beta-1-proteobacteria, Zoogloea resiniphila (25.0%) of beta-2-proteobacteria, and Xanthomonas maltophilia (19.8%) of gamma-proteobacteria. Results of this study imply that GAO might not be the sole group of bacteria responsible to the deterioration of phosphate removal efficiency in an EBPR reactor.

Acetates↗

PubMed2003

Temperature effect on microbial community of enhanced biological phosphorus removal system.

Microbial population dynamics to gradual temperature change in an enhanced biological phosphorus removal system was kinetically investigated. As the temperature rose from 20.0 degrees C to 30.0 degrees C, and to 35.5 degrees C, the predominant microbial group changed from the phosphorus-accumulating organisms, PAOs (47-70% of total VSS) to the glycogen-accumulating organisms (64-75% of total VSS), and to the ordinary heterotrophs (90% of total VSS), respectively. Despite the species alteration, the phosphorus contents of the PAOs appeared to be steady within 0.182-0.308 mg/mg VSS(PAO) regardless of the temperature level. The initial specific phosphorus release rates, which are solely due to the PAOs activities, increased with the temperature from 37.5-55.9 to 51.8-61.3, 52.0-76.9, 147.2-210.3, and 374.2-756.3 mgP/gmVSS(PAO) h, at 20.0 degrees C, 25.0 degrees C, 30.0 degrees C, 32.5 degrees C, and 35.0 degrees C, respectively. On the other hand, mean initial specific phosphorus uptake rates of the biomass decreased as the temperature increased; however, the data implied that the rate of the PAOs was higher than the other two microbial groups. These results indicate that the PAOs are lower-range mesophiles or possibly psychrophiles. As the temperature rises, the portion of energy required for maintenance increases substantially which reduces the energy availability for cell reproduction; hence, the PAOs are washed out from the system.

Bacteria↗

PubMed2002

Analysis of the microbial community structure and function of a laboratory scale enhanced biological phosphorus removal reactor.

A laboratory scale sequencing batch reactor (SBR) operating for enhanced biological phosphorus removal (EBPR) and fed with a mixture of volatile fatty acids (VFAs) showed stable and efficient EBPR capacity over a four-year-period. Phosphorus (P), poly-beta-hydroxyalkanoate (PHA) and glycogen cycling consistent with classical anaerobic/aerobic EBPR were demonstrated with the order of anaerobic VFA uptake being propionate, acetate then butyrate. The SBR was operated without pH control and 63.67 +/- 13.86 mg P l-1 was released anaerobically. The P% of the sludge fluctuated between 6% and 10% over the operating period (average of 8.04 +/- 1.31%). Four main morphological types of floc-forming bacteria were observed in the sludge during one year of in-tensive microscopic observation. Two of them were mainly responsible for anaerobic/aerobic P and PHA transformations. Fluorescence in situ hybridization (FISH) and post-FISH chemical staining for intracellular polyphosphate and PHA were used to determine that 'Candidatus Accumulibacter phosphatis' was the most abundant polyphosphate accumulating organism (PAO), forming large clusters of coccobacilli (1.0-1.5 micro m) and comprising 53% of the sludge bacteria. Also by these methods, large coccobacillus-shaped gammaproteobacteria (2.5-3.5 micro m) from a recently described novel cluster were glycogen-accumulating organisms (GAOs) comprising 13% of the bacteria. Tetrad-forming organisms (TFOs) consistent with the 'G bacterium' morphotype were alphaproteobacteria, but not Amaricoccus spp., and comprised 25% of all bacteria. According to chemical staining, TFOs were occasionally able to store PHA anaerobically and utilize it aerobically.

Bacteria, Anaerobic↗

PubMed2001

Effect of operating parameters on anoxic biological phosphorus removal in anaerobic anoxic sequencing batch reactor.

Optimizing anoxic biological phosphorus removal in the anaerobic-anoxic sequencing batch reactor (A2 SBR) was observed to depend greatly on three parameters: the amount of added nitrate, the sludge retention time (SRT) and the phosphorus/carbon feeding ratio (P/C, wt/wt). The concentration of 120 mg N-NO3 l-1 in the anoxic medium corresponding to 800 mg COD l-1 acetic acid and 60 mg P-PO4 l-1 in the synthetic wastewater, the SRT of 15 days and the P/C feeding ratio of 20/100 were determined as optimal for complete phosphorus removal in the A2 SBR. The acetate uptake, the phosphorus release and the phosphorus removal increased with the P/C feeding ratio and the phosphorus sludge content (Ps). The polyphosphate-accumulating organisms (PAO) were dominant under operation at all P/C feeding ratios tested except 2/100. At a P/C feeding ratio of 20/100, PAO could accumulate a high content of polyphosphate compared with other P/C ratios. In contrast, the P/C ratio of 2/100 caused a decrease in the polyphosphate content in PAO, the deterioration of enhanced biological phosphorus removal (EBPR) activity, and the dominance of glycogen-accumulating organisms (GAO). This study was completed by microscopic observations which revealed three morphological types of PAO. This is the first time that an oval form of PAO could be observed in the A2 SBR.

Bacteria, Anaerobic↗

PubMed2003

Denitrifying characteristics of the multiple stages enhanced biological nutrient removal process with external carbon sources.

This research investigated denitrifying activity of activated sludge with three external carbon sources (sodium acetate, methanol and glucose) via a series of batch experiments. Activated sludge used was cultivated in a multiple stages enhanced biological nutrient removal (EBNR) process that exhibited high removal efficiency of effective carbon, nitrogen, and phosphorus. Results showed type of external carbon source had a significant influence on specific nitrate utilization rate, nitrite accumulation, adaptive time of microorganisms, and nitrate removal efficiency. Sodium acetate addition resulted in high phosphate concentration in effluent; meanwhile methanol caused increasing turbidity and carbon breakthrough problem. When glucose was fed to be the external carbon source, accumulative nitrite concentration was higher than that with sodium acetate or methanol addition. When sodium acetate, methanol and glucose were used to be the electron donor, average dosages for nitrate elimination were 6.97, 5.85, and 5.65 mg-COD/mg-N, respectively. Because the final polyhydroxyalkanoates (PHAs) concentrations contained within the biomass were more than the original level and no phosphate re-release was observed, glycogen-accumulating organisms (GAOs) might exist in the multiple stages EBNR process and increased carbon dosage for further nitrate removal.

Biodegradation, Environmental↗

PubMedDate not supplied

Enhanced biological phosphorus removal in an anaerobic-aerobic sequencing batch reactor: effect of pH.

Enhanced biological phosphorus removal (EBPR) is not always successfully achieved in activated-sludge processes by anaerobic-aerobic operation. It has been reported that the deterioration of EBPR has been caused by domination of glycogen-accumulating organisms (GAOs) in microbial sludge. After repeated operation of a sequencing batch reactor (SBR) supplied with acetate as a sole carbon source, it was found that an operational variable, pH, could be a tool to control the competition between GAOs and polyphosphate-accumulating organisms PAOs, which could mediate the success of EBPR. When anaerobic phase pH in the SBR was controlled at 7.0, GAOs dominated the culture, resulting in failure of EBPR. Without pH control, the pH during the anaerobic phase increased to 8.4 as a result of denitrification and acetate uptake. In this relatively high pH condition, almost complete EBPR was achieved. In this report, the mechanism of pH effect on the competition between GAOs and PAOs was elucidated through a characterization of activated sludge using previously proposed biochemical models.

Acetates↗

PubMed2026

Genome-Resolved Metagenomics Revealed the Functional Potential of Core Novel and Known Genera Key to Processes in Full-Scale Aerobic Granular Sludge Plants.

Microbial communities are critical for nutrient removal in aerobic granular sludge (AGS) wastewater treatment plants (WWTPs). Despite the stable long-term operation of full-scale AGS WWTPs, the microbial populations and functional traits sustaining stable long-term performance remain poorly resolved. To address this gap, the recovered MAG catalog from nine full-scale AGS WWTPs across five countries was analyzed. From this catalog, 74 high-quality core MAGs were identified and used for downstream taxonomic characterization and functional analyses. These high-quality core MAGs spanned 48 established and 7 novel genera, representing 31 known and 43 novel species. Functional analysis linked core MAGs to key WWTP processes: polyphosphate accumulation (9), glycogen accumulation (12), denitrification (62), and nitrification (1). These included four novel MAGs with glycogen-accumulating (3) and polyphosphate-accumulating (1) potential and 11 capable of nitrous oxide reduction, critical for mitigating greenhouse gas emissions. Ca. Phosphoribacter was the most abundant genus, highlighting its underestimated role caused by misclassification as Tetrasphaera in 16S rRNA surveys. Specifically, Ca. P. hodrii was the dominant species, exhibiting enhanced sugar uptake and amino acid synthesis as likely drivers of its enrichment in the AGS WWTPs. Overall, this study resolves for the first time the taxa and functional traits consistently enriched in full-scale AGS systems, enabling a shift from an empirical performance assessment toward biologically informed process interpretation.

Sewage↗