WERF Phase 2: The Impact of Digestion and Dewatering on Reactivation and Regrowth of Viable but Non-Culturable Indicator Bacteria

Higgins, Matthew J.; Chen, Yen-Chih; Murthy, Sudhir; Hendrickson, Donald; Schafer, Perry; Farrell, Jay A.

doi:10.2175/193864706783751825

Cited by 4 publications

(6 citation statements)

References 8 publications

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“…Research on E. coli dynamics in sewage sludge suggests that the E. coli indicator bacteria may enter a VBNC state during digestion that is reversed after centrifuge dewatering under favourable biosolids storage conditions (Higgins et al, 2006;Higgins et al, 2007b;Fane et al, 2019a). Evidence for this was shown by a comparison of standard culturing methods and quantitative polymerase chain reaction (qPCR) which showed a three order of magnitude increase in E. coli per g DS from qPCR measurements after thermophilic digestion (Higgins et al, 2007b).…”

Section: E Coli Dynamics During Storagementioning

confidence: 99%

Characterisation and control of the biosolids storage environment: Implications for E. coli dynamics

Fane

Nocker

Vale

et al. 2021

Science of The Total Environment

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E. coli survival in biosolids storage may present a risk of non-compliance with guidelines designed to ensure a quality product safe for agricultural use. The storage environment may affect E. coli survival but presently, storage characteristics are not well profiled. Typically biosolids storage environments are not actively controlled or monitored to support increased product quality or improved microbial compliance. This two-phased study aimed to identify the environmental factors that control bacterial concentrations through a long term, controlled monitoring study (phase 1) and a field-scale demonstration trial modifying precursors to bacterial growth (phase 2). Digested and dewatered biosolids were stored in operational-scale stockpiles to elucidate factors controlling E. coli dynamics. E. coli concentrations, stockpile dry solids, temperature, redox and ambient weather data were monitored. Results from ANCOVA analysis showed statistically significant (p <0.05) E. coli reductions across storage periods with greater die-off in summer months. Stockpile temperature had a statistically significant effect on E. coli survival. A 4.5 Log reduction was measured in summer (maximum temperature 31°C). In the phase 2 modification trials, covered stockpiles were able to maintain a temperature >25°C for a 28 day period and achieved a 3.7 Log E. coli reduction. In winter months E. coli suppression was limited with concentrations >6 Log10 CFU g -1 DS maintained. The ANCOVA analysis has identified the significant role that physical environmental factors, such as stockpile temperature, has on E. coli dynamics and the opportunities for control.

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Section: E Coli Dynamics During Storagementioning

confidence: 99%

Characterisation and control of the biosolids storage environment: Implications for E. coli dynamics

Fane

Nocker

Vale

et al. 2021

Science of The Total Environment

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“…Mechanical dewatering relies upon polymers to condition the sludge, forming flocs and inevitably aggregating bacteria and sludge organic matter. Research has shown that large amounts of bioavailable protein and polysaccharide exist in centrifuge dewatered cakes [4]. These elements will be incorporated within floc matrices and could provide a substrate source promoting bacterial growth.…”

Section: Dewatering Shear Effects and Chemical Modificationmentioning

confidence: 99%

“…Challenges in meeting these required standards surface post mechanical dewatering, which aims to increase the economical transport value of the product by limiting the volume of water associated with the solid material. Studies on dewatering operations have highlighted a significant increase in pathogenic indicator bacteria [2][3][4][5][6][7][8]. Examples of indicator increases range from − 0.4 log to + 6.4 log units after centrifuge dewatering [9] emphasising the highly variable effects amongst treatment plants.…”

Section: Introductionmentioning

confidence: 99%

Influence of Innate Sludge Factors and Ambient Environmental Parameters in Biosolids Storage on Indicator Bacteria Survival: A Review

Fane

Vale

Fernández

et al. 2019

Waste Biomass Valor

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The potential health risks associated with sludge cake application to agricultural land are managed by controlling the levels of Escherichia coli (E. coli) bacteria which indicate the risk of pathogen transfer. Analyses undertaken following postdigestion sludge dewatering have shown unpredictable levels of E. coli increase in stored sludge cake. Presently there is limited understanding on environmental parameters controlling the indicator bacteria density in storage and the contributory effects dewatering may have. This review aims to establish the state of current knowledge on innate and environmental factors influencing E. coli dynamics and survival in biosolids. A key factor identified is the effect of mechanical dewatering processes, which transform the sludge matrix environmental conditions through the increased availability of growth factors (e.g. nutrient and oxygen). Examples of storage practices from the agricultural and food industries are also discussed as successful methods to inhibit bacterial growth and survival, which could be extrapolated to the biosolids sector to regulate E. coli concentrations.

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“…The reasons for indicator increase in stored biosolids post-dewatering have not yet been clearly identified (Dentel et al 2008). One possible explanation is that following suppression during thermal anaerobic digestion (AD) treatment, the release of readily bioavailable nutrients during mechanical dewatering processes may provide substrates for bacterial growth during subsequent storage periods (Higgins et al 2006(Higgins et al , 2007aChen et al 2011;Sun et al 2015). The pre-conditioning of the digested sludge with polyelectrolyte to form flocs aggregates the sludge organic matter, which could favour the growth of bacterial cells held within the floc matrix.…”

Section: Introductionmentioning

confidence: 99%

Disruption of cells in biosolids affects E. coli dynamics in storage

et al. 2019

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Achieving microbial compliance during biosolids storage can be complicated by the unpredictable increase of Escherichia coli. Thermal treatment during anaerobic digestion (AD) and the effects of dewatering may be a significant factor contributing to indicator survival. Shear forces present during dewatering may promote cell damage, releasing nutrient for E. coli growth. The effect of cell damage on E. coli survival was assessed in laboratory-scale thermal and physical disruption experiments. E. coli growth curves for disrupted treatments were compared with control conditions and quantified using flow cytometry and membrane filtration techniques. A significant difference (p < 0.05) in the level of damaged cells between control and disrupted conditions was observed. For thermal and physical disruption treatments, the peak of E. coli concentration increased significantly by 1.8 Log and 2.4 Log (CFU (colony forming units) g−1 DS), respectively, compared with control treatments. Research findings contribute to the understanding of bacterial growth and death dynamics in biosolids.

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WERF Phase 2: The Impact of Digestion and Dewatering on Reactivation and Regrowth of Viable but Non-Culturable Indicator Bacteria

Cited by 4 publications

References 8 publications

Characterisation and control of the biosolids storage environment: Implications for E. coli dynamics

Characterisation and control of the biosolids storage environment: Implications for E. coli dynamics

Influence of Innate Sludge Factors and Ambient Environmental Parameters in Biosolids Storage on Indicator Bacteria Survival: A Review

Disruption of cells in biosolids affects E. coli dynamics in storage

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