Hydrolysis of particulate settleable solids (PSS) in activated sludge is determined by the bacteria initially adsorbed in the sewage

Benneouala, Mourad; Bareha, Y.; Mengelle, E.; Bounouba, Mansour; Sperandio, Mathieu; Bessière, Yolaine; Paul, Etienne

doi:10.1016/j.watres.2017.08.058

Cited by 24 publications

(9 citation statements)

References 21 publications

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“…The remaining particulate carbohydrates might keep hydrolyzing during feeding to the reactor; during a 1-h feeding period, a maximum of 10% of the total carbohydrates could be degraded by the enzymes in the influent. A previous study suggested that the hydrolysis of influent suspended solids would be mainly performed by microorganisms in the influent (Benneouala et al 2017 ). Besides, a recent study on the microbial composition of the wastewater treatment plant of Garmerwolde identified several hydrolyzing microorganisms in the influent (Ali et al 2019 ).…”

Section: Discussionmentioning

confidence: 99%

Anaerobic hydrolysis of complex substrates in full-scale aerobic granular sludge: enzymatic activity determined in different sludge fractions

Ortega

Pronk

Kreuk

2021

Appl Microbiol Biotechnol

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Complex substrates, like proteins, carbohydrates, and lipids, are major components of domestic wastewater, and yet their degradation in biofilm-based wastewater treatment technologies, such as aerobic granular sludge (AGS), is not well understood. Hydrolysis is considered the rate-limiting step in the bioconversion of complex substrates, and as such, it will impact the utilization of a large wastewater COD (chemical oxygen demand) fraction by the biofilms or granules. To study the hydrolysis of complex substrates within these types of biomass, this paper investigates the anaerobic activity of major hydrolytic enzymes in the different sludge fractions of a full-scale AGS reactor. Chromogenic substrates were used under fully mixed anaerobic conditions to determine lipase, protease, α-glucosidase, and β-glucosidase activities in large granules (>1 mm in diameter), small granules (0.2–1 mm), flocculent sludge (0.045–0.2 mm), and bulk liquid. Furthermore, composition and hydrolytic activity of influent wastewater samples were determined. Our results showed an overcapacity of the sludge to hydrolyze wastewater soluble and colloidal polymeric substrates. The highest specific hydrolytic activity was associated with the flocculent sludge fraction (1.5–7.5 times that of large and smaller granules), in agreement with its large available surface area. However, the biomass in the full-scale reactor consisted of 84% large granules, making the large granules account for 55–68% of the total hydrolytic activity potential in the reactor. These observations shine a new light on the contribution of large granules to the conversion of polymeric COD and suggest that large granules can hydrolyze a significant amount of this influent fraction. The anaerobic removal of polymeric soluble and colloidal substrates could clarify the stable granule formation that is observed in full-scale installations, even when those are fed with complex wastewaters. Key points • Large and small granules contain >70% of the hydrolysis potential in an AGS reactor. • Flocculent sludge has high hydrolytic activity but constitutes <10% VS in AGS. • AGS has an overcapacity to hydrolyze complex substrates in domestic wastewater. Graphical abstract

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Section: Discussionmentioning

confidence: 99%

Anaerobic hydrolysis of complex substrates in full-scale aerobic granular sludge: enzymatic activity determined in different sludge fractions

Ortega

Pronk

Kreuk

2021

Appl Microbiol Biotechnol

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“…On the contrary, the high proportions of non-diffusible X B in the influent of R3 and R4 hampered the granulation process. Several phenomena lead to the conclusion that hydrolysis is only partial during anaerobic plug-flow feeding: (1) WW particles are often large, from several μm up to 1–2 mm (Levine et al., 1985; Dimock and Morgenroth, 2006), (2) hydrolysis is a very slow process (Benneouala et al., 2017; Morgenroth et al., 2002; Jabari et al., 2016), and (3) the anaerobic feeding duration of 1–2 h typically applied in AGS systems is insufficient to provide full hydrolysis of X B (Wagner et al., 2015; Jabari et al., 2016). Therefore partial anaerobic conversion of X B is unavoidable and results in a high availability of substrate during the subsequent aerobic phase, which in turn supports the growth of OHO (Wagner et al., 2015).…”

Section: Discussionmentioning

confidence: 99%

Organic substrate diffusibility governs microbial community composition, nutrient removal performance and kinetics of granulation of aerobic granular sludge

et al. 2019

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Basic understanding of formation of aerobic granular sludge (AGS) has mainly been derived from lab-scale systems with simple influents containing only highly diffusible volatile fatty acids (VFA) as organic substrate. This study compares start-up of AGS systems fed by different synthetic and municipal wastewaters (WW), characterised by increasing complexity in terms of non-diffusible organic substrate. Four AGS reactors were started with the same inoculum activated sludge and operated for one year. The development of AGS, settling characteristics, nutrient and substrate removal performance as well as microbial community composition were monitored. Our results indicate that the higher the content of diffusible organic substrate in the WW, the faster the formation of AGS. The presence of non-diffusible organic substrate in the influent WW led to the formation of small granules and to the presence of 20–40% (% of total suspended solids) of flocs in the AGS. When AGS was fed with complex influent WW, the classical phosphorus and glycogen accumulating organisms (PAO, GAO) were outcompeted by their fermentative equivalents. Substrate and nutrient removal was observed in all reactors, despite the difference in physical and settling properties of the AGS, but the levels of P and N removal depended on the influent carbon composition. Mechanistically, our results indicate that increased levels of non-diffusible organic substrate in the influent lower the potential for microbial growth deep inside the granules. Additionally, non-diffusible organic substrates give a competitive advantage to the main opponents of AGS formation – ordinary heterotrophic organisms (OHO). Both of these mechanisms are suspected to limit AGS formation. The presented study has relevant implications for both practice and research. Start-up duration of AGS systems treating high complexity WW were one order of magnitude higher than a typical lab-scale system treating VFA-rich synthetic WW, and biomass as flocs persisted as a significant fraction. Finally, the complex synthetic influent WW – composed of VFA, soluble fermentable and particulate substrate - tested here seems to be a more adequate surrogate of real municipal WW for laboratory studies than 100%-VFA WW.

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“…Importantly, particulate, colloidal COD and soluble macromolecules constitute a large proportion of the organics pool in biological wastewater treatment (Figure S19), hydrolysis, and acidogenic fermentation of such organics can increase the availability of rbCOD or VFAs for PAOs but they are usually the overall rate-limiting steps. 53 Given the slow growth of HFB in non-EBPR plants, their immigration from the influent microflora is the major determinant for improved phosphorus removal by intensifying their cooperation with PAOs. It should be noted that the much higher sludge concentrations of MBRs over conventional activated sludge processes would also play a role in generating anaerobic pockets within the sludge, promoting the activity of these HFB.…”

Section: ■ Discussionmentioning

confidence: 99%

“…In addition, the long SRT of sewer biofilm communities could lead to the improvement of hydrolysis/fermentation . Moreover, Benneouala et al found that hydrolysis/fermentation process appeared to be more governed by the bacteria initially adsorbed in the influent wastewater than by the activated sludge community . Overall, the influent microflora played a key role in the hydrolysis/fermentation process in the downstream sludge community.…”

Section: Discussionmentioning

confidence: 99%

Overlooked Ecological Roles of Influent Wastewater Microflora in Improving Biological Phosphorus Removal in an Anoxic/Aerobic MBR Process

Fan

Lin

et al. 2021

Environ. Sci. Technol.

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The ecological roles of influent microflora in activated sludge communities have not been well investigated. Herein, parallel lab-scale anoxic/aerobic (A/O) membrane bioreactors (MBRs), which were fed with raw (MBR-C) and sterilized (MBR-T) municipal wastewater, were operated. The MBRs showed comparable nitrogen removal but superior phosphorus removal in MBR-C than MBR-T over the long-term operation. The MBR-C sludge community had higher diversity and deterministic assembly than the MBR-T sludge community as revealed by 16S rRNA gene sequencing and null model analysis. Moreover, the MBR-C sludge community had higher abundance of polyphosphate accumulating organisms (PAOs) and hydrolytic/fermentative bacteria (HFB) but lower abundance of glycogen-accumulating organisms (GAOs), in comparison with MBR-T sludge. Intriguingly, the results of both the net growth rate and Sloan’s neutral model demonstrated that HFB in the sludge community were generally slow-growing or nongrowing and their consistent presence in activated sludge was primarily attributed to the HFB immigration from influent microflora. Positive correlations between PAOs and HFB and potential competitions between HFB and GAOs were observed, as revealed by the putative species–species associations in the ecological networks. Taken together, this work deciphers the positive ecological roles of influent microflora, particularly HFB, in system functioning and highlights the necessity of incorporating influent microbiota for the design and modeling of A/O MBR plants.

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Hydrolysis of particulate settleable solids (PSS) in activated sludge is determined by the bacteria initially adsorbed in the sewage

Cited by 24 publications

References 21 publications

Anaerobic hydrolysis of complex substrates in full-scale aerobic granular sludge: enzymatic activity determined in different sludge fractions

Anaerobic hydrolysis of complex substrates in full-scale aerobic granular sludge: enzymatic activity determined in different sludge fractions

Organic substrate diffusibility governs microbial community composition, nutrient removal performance and kinetics of granulation of aerobic granular sludge

Overlooked Ecological Roles of Influent Wastewater Microflora in Improving Biological Phosphorus Removal in an Anoxic/Aerobic MBR Process

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