Variations in microcolony strength of probe-defined bacteria in activated sludge flocs

Section of Environmental Engineering, Department of Life Sciences, Aalborg University, DK-9000 Aalborg, Denmark.
FEMS Microbiology Ecology (Impact Factor: 3.57). 12/2004; 50(2):123-32. DOI: 10.1016/j.femsec.2004.06.005
Source: PubMed


The strength of activated sludge flocs is important for the flocculation, settling and dewatering properties of activated sludge and thus the performance of wastewater treatment plants. Little is known about how different bacteria affect the floc properties, so in this study it was investigated whether the strength and other characteristics of large microcolonies within activated sludge flocs from a full-scale nutrient removal plant varied significantly between different phylogenetic groups of bacteria. The investigation was carried out by using a shear method for deflocculation of activated sludge flocs, combined with different chemical manipulations under defined conditions. The identification and quantification of the microcolony-forming bacteria were conducted with group-specific gene probes and fluorescence in situ hybridization. The focus was on the microcolonies and not on the entire sludge flocs. In general, the results showed large difference in the strength and colloid-chemical properties of the different probe-defined microcolonies. By applying extensive shear to the system, less than 12% of the microcolony biovolume of the Beta-, Gamma- and Deltaproteobacteria and Actinobacteria could be disrupted, thus forming strong microcolonies. Alphaproteobacteria and Firmicutes formed weaker microcolonies (42-61% could be disrupted by shear). For most groups, several intermolecular forces determined the strength of the microcolonies: hydrophobic interactions, cross-linking by multivalent cations and perhaps entanglements of extracellular polymeric substances. However, the dominant force varied between the various phylogenetic groups. The large difference between the different phylogenetic groups indicated that only a few species were present within each group, rather than many different bacterial species within each phylogenetic group had similar floc properties.


Available from: Per Halkjær Nielsen, Sep 08, 2014
    • "The species composition of the activated sludge influences the floc properties to a certain extent and thus the solideliquid separation processes (Nielsen et al., 2002, 2004; Klausen et al., 2004; Larsen et al., 2006, 2008; Bugge et al., 2013). Some species form filaments, some strong microcolonies , and some weak flocs. "
    [Show abstract] [Hide abstract] ABSTRACT: Biological wastewater treatment removes organic materials, nitrogen, and phosphorus from wastewater using microbial biomass (activated sludge, biofilm, granules) which is separated from the liquid in a clarifier or by a membrane. Part of this biomass (excess sludge) is transported to digesters for bioenergy production and then dewatered, it is dewatered directly, often by using belt filters or decanter centrifuges before further handling, or it is dewatered by sludge mineralization beds. Sludge is generally difficult to dewater, but great variations in dewaterability are observed for sludges from different wastewater treatment plants as a consequence of differences in plant design and physical-chemical factors. This review gives an overview of key parameters affecting sludge dewatering, i.e. filtration and consolidation. The best dewaterability is observed for activated sludge that contains strong, compact flocs without single cells and dissolved extracellular polymeric substances. Polyvalent ions such as calcium ions improve floc strength and dewaterability, whereas sodium ions (e.g. from road salt, sea water intrusion, and industry) reduce dewaterability because flocs disintegrate at high conductivity. Dewaterability dramatically decreases at high pH due to floc disintegration. Storage under anaerobic conditions lowers dewaterability. High shear levels destroy the flocs and reduce dewaterability. Thus, pumping and mixing should be gentle and in pipes without sharp bends. Copyright © 2015 Elsevier Ltd. All rights reserved.
    No preview · Article · Apr 2015 · Water Research
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    • "The ASP is based on the growth of microbial populations in a flocculated form (Zartarian et al. 1997). The efficiency of the ASP has a strong influence on solid–liquid separation which is affected by the structure and the strength of the flocs (Klausen et al. 2004). The floc strength is critical because the flocs can break up into smaller particles due to shear forces, for example, during aeration, dewatering, and transfer through pumps (Wilén et al. 2003; Jarvis et al. 2005; Liu et al. 2005). "
    [Show abstract] [Hide abstract] ABSTRACT: Optical monitoring with a charge-couple device camera was used to assess the breakage of activated sludge flocs obtained from three different activated sludge plants: two municipal and one industrial. In this method, the samples were processed through the imaging unit and recycled back to a beaker using a centrifugal pump which causes the breakage of flocs together with hydrodynamics forces. Based on the image analysis results, the breakage models of the activated sludge flocs vary between the plants. The major breakage model in the two municipal plants was surface erosion whereas it was large-scale fragmentation in the industrial plant. A larger amount of filaments in the industrial plant most likely caused the large-scale fragmentation. Furthermore, the effect of the addition of a cationic polymer on the strength of activated sludge floc was studied in one sample. When the cationic polymer was used, the flocs started to grow at the start of the breakage process. However, they broke up at the end of the process and remained small, as found in flocs not exposed to any chemical treatment. Based on the results, the optical monitoring seems to be suitable for analysing the breakage of flocs.
    Full-text · Article · Mar 2015 · Particulate Science And Technology
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    • "The scanning electron microscope analysis of Sears et al. (2005) revealed that there are many circular microcolonies throughout the floc, which ranged in size from approximately 5 to 10 mm in diameter. Klausen et al. (2004) investigated the microcolony strength of bacteria in activated sludge and concluded that different phylogenetic groups of microcolonies have their own strength and colloid-chemical properties. Larsen et al. (2006, 2008) reported that microcolonies of phosphorous accumulating organisms and nitrifying bacteria are more resistant to imposed shear force. "
    [Show abstract] [Hide abstract] ABSTRACT: Extracellular polymeric substances (EPS) play a crucial role in the formation of activated sludge flocs. However, until now, the EPS are rather classified by the method used for extraction than by a theoretical consideration of their function and composition. In this paper, a new classification paradigm of EPS was proposed, which offered a novel approach to identify the role of EPS in the formation of activated sludge flocs. The current study gave an exploration to distinguish the EPS in the floc level (extra-microcolony polymers, EMPS) and in the microcolony level (extra-cellular polymers, ECPS). It was found that cation exchange resin treatment is efficient to disintegrate the flocs for EMPS extraction, however, inefficient to disaggregate the microcolonies for ECPS harvesting. A two-steps extraction strategy (cation exchange resin treatment followed by ultrasonication-high speed centrifugation treatment) was suggested to separate these two types of EPS in activated sludge flocs and the physicochemical characteristics of EMPS and ECPS were compared. The protein/polysaccharide ratio of ECPS was higher than that of EMPS and the molecular weight of proteins in EMPS and ECPS were found to be different. The ECPS contained higher molecular weight proteins and more hydrophobic substances than the EMPS contained. The result of excitation-emission matrix fluorescence spectroscopy analysis also showed that the EMPS and the ECPS have different fluorescent expressions and the components of EMPS were more diverse than that of ECPS. All results reported herein demonstrated that two different types of exopolymers exist in the activated sludge flocs and the inter-particle forces for aggregation of activated sludge flocs are not identical between the floc level and the microcolony level. It suggested that cation bridging interactions are more crucial in floc level flocculation, while the entanglement and hydrophobic interactions are more important in microcolony level cohesion.
    Full-text · Article · Nov 2014 · Water Research
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