Environmental factors contributing to the “G bacteria” population in full-scale EBPR plants

Griffiths, P.C.; Stratton, Helen; Seviour, Robert J.

doi:10.2166/wst.2002.0583

Cited by 27 publications

(18 citation statements)

References 14 publications

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“…Normalized P concentration, mg/L Some GAOs have been previously observed in this plant by microscopic inspection (Griffiths et al, 2002), and certain features of the plant comply with conditions under which GAOs may dominate, namely low pH in the aeration basin and long unaerated retention times. However, with GAO dominance, there would be little P release in the anaerobic zone.…”

Section: Zonessupporting

confidence: 65%

GAOs OR SECONDARY RELEASE? Causes & Prevention of EBPR Failure

Scruggs¹,

Barnard²,

Saayman³

2003

proc water environ fed

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Despite favorable conditions for enhanced biological phosphorus removal (EBPR), there are instances where good phosphorus (P) removal is elusive. Lack of performance may be due to either excess secondary P release or dominance of Glycogen Accumulating Organisms (GAOs) over Phosphate Accumulating Organisms (PAOs).Several wastewater treatment plants were identified to illustrate what is currently known about PAOs, GAOs, secondary release of P, and conditions favoring GAO growth over that of PAOs. It will be demonstrated how one can study nutrient profiles through a plant, manipulate data, and perform experiments to determine the cause of EBPR failure. In the plants studied, it was shown that successful BPR requires sufficient influent VFA, high primary P release in the anaerobic zone, no release but rather some uptake of P in the anoxic zone, and good P uptake in the aerobic zone. In an example where secondary release was found to be responsible for poor BPR performance, good primary release in the anaerobic zone was offset by substantial secondary release in the anoxic zone, likely caused by inadequate mixed liquor recycle with rapid depletion of nitrates in the anoxic zone. This combined with a high RAS recycle rate, which returned excessive nitrates and reduced the anaerobic retention time, could account for the high effluent P. GAO dominance could not be definitively proven in any of the cases studied; in cases where GAOs were named as a possible cause for unsuccessful BPR, influent VFA concentrations were also unknown and there is the possibility that low influent VFA could be to blame.Profiles of nutrient concentrations through BNR plants can be difficult to interpret due to the influence of recycle streams, but a mass balance through the plant will reveal the true state of P release and uptake. Either secondary release or GAO dominance could be the cause of inadequate P removal in the presence of sufficient influent VFA. If secondary release is not evident from the data and the release of P in the anaerobic zone appears inadequate, a test can be performed to indicate GAO dominance. Recorded instances of BPR failure at a full-scale plant due to GAO dominance are rare. While PAO/GAO population dynamics remain an important and ongoing area of study, it is critical that the presence of GAOs in activated sludge is not used as the only possible explanation for non-performance without first examining all possibilities for secondary release.Knowing how to identify cases of GAO dominance and secondary release of P by studying P profiles through the plant will allow operators to focus their energies on process adjustments or changes that will improve EBPR operation and performance. A full understanding of the phenomena that lead to EBPR failure, coupled with good design WEFTEC ® 2003 and operational practices, will allow for optimization of the EBPR system and consistent compliance with stringent effluent P permit requirements.

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Section: Zonessupporting

confidence: 65%

GAOs OR SECONDARY RELEASE? Causes & Prevention of EBPR Failure

Scruggs¹,

Barnard²,

Saayman³

2003

proc water environ fed

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“…Griffiths et al (2002) performed morphological observations of WWTP sludges and hypothesised that the DO concentration could affect the quantity of tetrad forming organisms thought to be GAOs. Numerous studies (Li and Chen, 2011;Li et al, 2008;Zheng et al, 2009), have operated EBPR systems at very low DO concentrations (0.15e0.45 mg/L), with variable P removal efficiency achieved (61e99%).…”

Section: Introductionmentioning

confidence: 99%

The impact of aeration on the competition between polyphosphate accumulating organisms and glycogen accumulating organisms

et al. 2014

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In wastewater treatment plants (WWTPs), aeration is the major energetic cost, thus its minimisation will improve the cost-effectiveness of the process. This study shows that both the dissolved oxygen (DO) concentration and aerobic hydraulic retention time (HRT) affect the competition between polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). At low DO levels, Accumulibacter PAOs were shown to have an advantage over Competibacter GAOs, as PAOs had a higher oxygen affinity and thus largely maintained their aerobic activity at low DO levels, while GAO activity decreased. Bioreactor operation at low DO levels was found to increase the PAO fraction of the sludge. Furthermore, an increase in aerobic HRT (at a DO level of 2 mg O2/L), promoted the proliferation of GAOs over PAOs, decreasing the EBPR efficiency. Overall, this study shows that low aeration can be beneficial for EBPR performance through selecting for PAOs over GAOs, which should be incorporated into WWTP models in order to minimise energetic costs and improve WWTP sustainability.

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“…It is understood that GAOs and PAOs can co-exist within the BNR activated sludge population and are a known competitors for the limited supply of VFA typically present in the influent to BNR plants Crocetti et al 2002;Griffiths et al 2002;Saunders et al 2003;Meyer et al 2006;Burow et al 2007). It is also likely that variability in bio-P performance is potentially caused by variations in the relative population sizes of PAOs and GAOs, rather than variations in the biochemistry of a fixed population of PAOs.…”

Section: Resultsmentioning

confidence: 99%

The secret to achieving reliable biological phosphorus removal

Thomas

2008

Water Science and Technology

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The enhanced biological phosphorus removal (bio-P) activated sludge process has a reputation for variable performance. A significant factor contributing to variability in bio-P was found to be related to microbial population dynamics involving the competitive growth of polyphosphate accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs). It was found that the key factor in their competitive growth was the specific type of VFA in the influent to the bioreactor. The PAOs seem to have a competitive advantage to use propionate, whereas the GAOs have a competitive advantage to use acetate. Therefore, the secret to achieving reliable biological phosphorus removal was to ensure an adequate supply of propionate, or an alternative substrate such as molasses that can be readily fermented to propionate.When Noosa WWTP was commissioned in Nov 1997, and for several years afterwards, the bio-P performance was found to be variable. This paper outlines the findings of the research and optimisation program that was carried out, which identified the cause of the variability in bio-P and subsequently lead to implementation of an improved operating strategy. The recent long-term results demonstrate that reliable bio-P can be achieved in full-scale wastewater treatment plants without dosing metal salts. The effluent total phosphorus has been maintained below 0.5 mg/L since Jul 2001 and the 50 percentile result for the last 12 months was 0.2 mg/L.

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Environmental factors contributing to the “G bacteria” population in full-scale EBPR plants

Cited by 27 publications

References 14 publications

GAOs OR SECONDARY RELEASE? Causes & Prevention of EBPR Failure

GAOs OR SECONDARY RELEASE? Causes & Prevention of EBPR Failure

The impact of aeration on the competition between polyphosphate accumulating organisms and glycogen accumulating organisms

The secret to achieving reliable biological phosphorus removal

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