title: Understanding the properties of aerobic sludge granules as hydrogels.
abstract: Aerobic sludge granules are larger, denser microbial aggregates than activated sludge flocs with a smoother and more regular surface, which facilitates greater wastewater treatment intensity. Factors important in their growth are still poorly understood, which is an impediment to the construction and operation of full-scale aerobic sludge granule processes. Data in this article obtained with granules treating an abattoir wastewater provide evidence that aerobic sludge granules are hydrogels. The results also demonstrate a method for characterizing macromolecular associations. The rheological profile of these granules was found to be analogous with that of typical polymer gels. Water uptake or swelling reflects an equilibrium between granule elastic modulus and osmotic pressure, whereby uptake is increased by reducing solute concentration or the elastic modulus. A weakening of the extracellular polymeric substance (EPS) matrix as demonstrated with mechanical spectroscopy was induced by several environmental factors including temperature, pH and ionic strength. Uniform and elastic deformation was observed at low strain. Enzymatic degradation studies indicate that proteins and alpha-polysaccharides were the major granule structural materials. The aerobic sludge granules in the current study were therefore protein-polysaccharide composite physical hydrogels. While aerobic sludge granules treating an abattoir wastewater are used as a case study, many of the fundamental principles detailed here are relevant to other granulation processes. The paradigm established in this study can potentially be applied to better understand the formation of aerobic sludge granules and thus overcome a hurdle in the acceptance of aerobic sludge granulation as an alternative to more traditional wastewater treatment processes.
authors.affiliation: Advanced Water Management Centre (AWMC), The University of Queensland, St. Lucia, QLD 4072, Australia.
authors.forename: Thomas
authors.initials: T
authors.lastname: Seviour
authors.forename: Maite
authors.initials: M
authors.lastname: Pijuan
authors.forename: Timothy
authors.initials: T
authors.lastname: Nicholson
authors.forename: Jürg
authors.initials: J
authors.lastname: Keller
authors.forename: Zhiguo
authors.initials: Z
authors.lastname: Yuan
mesh_terms: D000332:Aerobiosis; D001419:Bacteria / Q000254:growth & development*; D001422:Bacterial Adhesion; D018407:Bacterial Physiological Phenomena; D001426:Bacterial Proteins / Q000378:metabolism; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D012722:Sewage / Q000737:chemistry* / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins; D011135:Polysaccharides, Bacterial; D012722:Sewage; D020136:Hydrogel, Polyethylene Glycol Dimethacrylate