The role of cellular polysaccharides in the formation and stability of aerobic granules

Tay, Joo‐Hwa; Liu, Q.-S.; Liu, Yan

doi:10.1046/j.1472-765x.2001.00986.x

Cited by 253 publications

(164 citation statements)

References 17 publications

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“…As in other microbial aggregates, such as biofi lms and biofl ocs, the EPS produced in biogranules are also composed of variable amounts of proteins, polysaccharides, nucleic acids, humic-like substances, lipids and glycoproteins, but the content of EPS in biogranules have been found to be much higher than that of biofl ocs and biofi lms [3]. Moreover, extracellular polymers likely play an important role in maintaining the structural and functional integrity of the granule.…”

Section: Biogranules and Metal Removalmentioning

confidence: 99%

“…Although, these biogenic polymers mediate contact and exchange processes with biotic and abiotic environments, they may not be essential for growth and viability in free-living bacterial cultures. But during growth under natural environment, bacterial EPS play important role in cell adhesion, formation of microbial aggregates such as biofi lms, fl ocs, sludges and biogranules [2][3][4] and protect cells from hostile environments. They are also involved in the degradation of particulate substances, sorption of dissolved materials including heavy metals, [5] leaching of minerals from sulphidic ores as well as biocorrosion [6].…”

Section: Introductionmentioning

confidence: 99%

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Microbial extracellular polymeric substances: central elements in heavy metal bioremediation

2008

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Extracellular polymeric substances (EPS) of microbial origin are a complex mixture of biopolymers comprising polysaccharides, proteins, nucleic acids, uronic acids, humic substances, lipids, etc. Bacterial secretions, shedding of cell surface materials, cell lysates and adsorption of organic constituents from the environment result in EPS formation in a wide variety of free-living bacteria as well as microbial aggregates like biofi lms, biofl ocs and biogranules. Irrespective of origin, EPS may be loosely attached to the cell surface or bacteria may be embedded in EPS. Compositional variation exists amongst EPS extracted from pure bacterial cultures and heterogeneous microbial communities which are regulated by the organic and inorganic constituents of the microenvironment. Functionally, EPS aid in cell-to-cell aggregation, adhesion to substratum, formation of fl ocs, protection from dessication and resistance to harmful exogenous materials. In addition, exopolymers serve as biosorbing agents by accumulating nutrients from the surrounding environment and also play a crucial role in biosorption of heavy metals. Being polyanionic in nature, EPS forms complexes with metal cations resulting in metal immobilization within the exopolymeric matrix. These complexes generally result from electrostatic interactions between the metal ligands and negatively charged components of biopolymers. Moreover, enzymatic activities in EPS also assist detoxifi cation of heavy metals by transformation and subsequent precipitation in the polymeric mass. Although the core mechanism for metal binding and / or transformation using microbial exopolymer remains identical, the existence and complexity of EPS from pure bacterial cultures, biofi lms, biogranules and activated sludge systems differ signifi cantly, which in turn affects the EPS -metal interactions. This paper presents the features of EPS from various sources with a view to establish their role as central elements in bioremediation of heavy metals.

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Section: Biogranules and Metal Removalmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Microbial extracellular polymeric substances: central elements in heavy metal bioremediation

2008

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“…It is not fully understood what factors increase EPS formation, although several researchers hypothesize that hydraulic shear may contribute (21). Tay et al (21) reported that increased aeration rates in a granular SBR resulted in an increased polysaccharide content and that granular sludge disintegrated when polysaccharides were lost from the system. Aerobic granules have also failed to form in systems with reduced aeration rates (6,22).…”

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confidence: 99%

Composition and Distribution of Extracellular Polymeric Substances in Aerobic Flocs and Granular Sludge

McSwain

Irvine

Hausner

et al. 2005

Appl Environ Microbiol

642

282

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Extracellular polymeric substances (EPS) were quantified in flocculent and aerobic granular sludge developed in two sequencing batch reactors with the same shear force but different settling times. Several EPS extraction methods were compared to investigate how different methods affect EPS chemical characterization, and fluorescent stains were used to visualize EPS in intact samples and 20-m cryosections. Reactor 1 (operated with a 10-min settle) enriched predominantly flocculent sludge with a sludge volume index (SVI) of 120 ؎ 12 ml g ؊1 , and reactor 2 (2-min settle time) formed compact aerobic granules with an SVI of 50 ؎ 2 ml g ؊1 . EPS extraction by using a cation-exchange resin showed that proteins were more dominant than polysaccharides in all samples, and the protein content was 50% more in granular EPS than flocculent EPS. NaOH and heat extraction produced a higher protein and polysaccharide content from cell lysis. In situ EPS staining of granules showed that cells and polysaccharides were localized to the outer edge of granules, whereas the center was comprised mostly of proteins. These observations confirm the chemical extraction data and indicate that granule formation and stability are dependent on a noncellular, protein core. The comparison of EPS methods explains how significant cell lysis and contamination by dead biomass leads to different and opposing conclusions.The efficiency of biological wastewater treatment depends, first, upon the selection and growth of metabolically capable microorganisms and, second, upon the efficient separation of those organisms from the treated effluent. Bacteria usually aggregate to form suspended flocs, which can cause bulking and foaming problems if filamentous bacteria are present. Activated sludge flocs also settle relatively slowly, requiring large primary and secondary settling tanks before clear effluent can be released. Alternatively, aerobic granular sludge aggregates have been formed in sequencing batch reactors (SBRs) with short fill periods and various substrates (1a, 13, 15). As opposed to flocs, granules are dense and have high settling velocities. They can be described as a collection of self-immobilized cells into a somewhat spherical form and are considered to be a special case of biofilm growth (10).Microbial aggregates form biofilms by creating a network of cells and extracellular polymeric substances (EPS), which include any substances of biological origin (9). The abbreviation "EPS" has often been expanded to extracellular polysaccharides or exopolysaccharides. However, EPS have been shown to be a rich matrix of polymers, including polysaccharides, proteins, glycoproteins, nucleic acids, phospholipids, and humic acids. EPS are typically reported to aid in the formation of a gel-like network that keeps bacteria together in biofilms, cause the adherence of biofilms to surfaces, and protect bacteria against noxious environmental conditions (24).Because EPS are a major component of cell flocs and biofilms, they are hypothesized to play a central ...

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“…PS has been reported as a polymeric viscous material that can stick to microbes and enhance the aggregation of microbes. In addition, the filamentous PS among the microbes can connect the dispersive microbes and the communities [30]. Therefore, the fewer PS of R3, relative to R1 and R2, partially resulted in the poor stability of granular sludge.…”

Section: The Stability Of Aerobic Granular Sludgementioning

confidence: 99%

Effects of the Food-to-Microorganism (F/M) Ratio on N2O Emissions in Aerobic Granular Sludge Sequencing Batch Airlift Reactors

Guo

Zhang

Xie

et al. 2017

Water

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The present study investigated the effect of the food-to-microorganism (F/M) ratio on nitrous oxide (N 2 O) emissions in aerobic granular sludge sequencing batch airlift reactors. Three identical sequencing batch airlift reactors were fed with sodium acetate-based wastewater at different chemical oxygen demand (COD) concentrations, resulting in F/M ratios from 0.2 to 0.67 g COD/g SS. The results indicated that N 2 O emissions increased with an increase of the F/M ratio. N 2 O emissions at the high F/M ratio of 0.67 g COD/g SS were the highest (4.4 ± 0.94 mg/d). The main source of the high N 2 O emissions at the F/M ratio of 0.67 g COD/g SS was nitrifier denitrification, rather than heterotrophic denitrification, confirmed by the qPCR (quantitative real-time PCR) results. The heterotrophic denitrification was destroyed by the DO (dissolved oxygen) diffusing into the sludge particles with porous structures. This study offers theoretical support to study the N 2 O emissions in aerobic granular sludge, and can provide guidance for conducting risk assessment and enhancing our ability to predict N 2 O production in aerobic granular sludge at different F/M ratios.

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The role of cellular polysaccharides in the formation and stability of aerobic granules

Cited by 253 publications

References 17 publications

Microbial extracellular polymeric substances: central elements in heavy metal bioremediation

Microbial extracellular polymeric substances: central elements in heavy metal bioremediation

Composition and Distribution of Extracellular Polymeric Substances in Aerobic Flocs and Granular Sludge

Effects of the Food-to-Microorganism (F/M) Ratio on N2O Emissions in Aerobic Granular Sludge Sequencing Batch Airlift Reactors

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