Relationship Between Floc Composition and Flocculation and Settling Properties Studied at a Full Scale Activated Sludge Plant

Department of Civil and Environmental Engineering, Water Environment Technology, Chalmers University of Technology, Sven Hultins gata 8, SE-412 96 Göteborg, Sweden.
Water Research (Impact Factor: 5.53). 09/2008; 42(16):4404-18. DOI: 10.1016/j.watres.2008.07.033
Source: PubMed


The variation in activated sludge floc composition, flocculation and settling properties was studied at a full scale plant over a 2-year period. A comprehensive set of process parameters was analysed and related to the floc properties to increase the understanding of the factors affecting floc formation. The composition of the activated sludge showed a seasonal change with higher concentrations of extractable extracellular polymeric substances (EPS) during the winter months. The protein content of the total sludge and EPS increased significantly during the winter. This coincided with higher effluent suspended solids concentrations and increased shear sensitivity of the sludge flocs. Only poor correlations between EPS contents and stirred sludge volume index (SSVI) could be observed. High iron concentrations in the sludge due to dosage of iron salt to precipitate phosphorus were found to have a negative impact on the settling and compaction properties of the sludge, whereas it had a positive impact on floc stability. Higher organic loading due to by-passed primary settlers leads to improved settling and compaction properties.

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    • "Among organisms listed, the highest level of abundances is achieved by protozoa, at the same time; they remain the required component of the activated sludge biocoenosis [5] [6] [7] [8]. Protozoa is of a primary importance through the all stages of sewage treatment, starting from process of activated sludge flocks forming [8] [9] [10] [11] [12]. As bacteria consumer, protozoa participates in processes of organic matters destruction and at the same time stimulates the growth of bacterial populations, supporting their biochemical activity [13] [14] [15] [16]. "
    K JarominrGle'n · R Babko · G Bagód · H Sobczuk ·

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    • "Previous studies also revealed that digital image analysis could determine a good linear relationship between floc morphology and SS precipitation efficiency [23], and that automatic image analysis could identify filamentous bulking, pinpoint flocs formation and viscous bulking [10]. Nevertheless, although fullscale studies of ASP are valuable, most flocculation studies have been conducted in laboratory conditions or at the pilot scale [15]. None have performed the on-line monitoring of activated sludge floc morphology. "
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    ABSTRACT: An on-line device for the optical monitoring of activated sludge flocs was set up and tested in situ at a municipal wastewater treatment plant over eight months. A charge-coupled device camera was used to image the flocs and filaments, and an automated image analysis programme was used to analyse the morphological parameters of the flocs. Results were compared to those obtained from offline laboratory analysis for water quality indicators, such as suspended solids. The results showed that the activated sludge process has produced different levels of settling quality. Large and round flocs enabled good settling, whereas small and irregularly shaped flocs, as well as the large amount of filaments, led to poor settling. The image analysis results obtained from the on-line device indicated that the poor settling was most likely caused by filamentous bulking. Such bulking was most likely due to the compositional variations in incoming wastewater; the poorly settled sludge was characterised by much lower solids content, which could have been responsible for the growth of filamentous bacteria. The image analysis results also revealed that the changes in floc morphology occurred slowly, indicating the potential for optical monitoring to control and optimise the activated sludge process.
    Journal of Water Process Engineering 04/2015; 5. DOI:10.1016/j.jwpe.2014.12.009
    • "Addition of polyvalent cationic polymers enhances flocculation by charge neutralization and polymer bridging (Bolton and Gregory, 2007). Data show that addition of flocculant with efficient mixing increases floc size, increases SFF, and lowers cake compressibility (Chu et al., 2003; Chen et al., 2005; Wil en et al., 2008). Low dosages do not provide sufficient charge neutralization/polymer bridging for flocculation to be efficient, whereas very high concentrations lead to deflocculation due to charge inversion and/or steric hindrance , which demonstrates that an optimum dosage of flocculants exists (Abo-Orf and Dentel, 1997; Poon and Chu, 1999; Lee and Liu, 2000; Yen et al., 2002; Chu et al., 2003; Chen et al., 2005). "
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    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.
    Water Research 04/2015; 82. DOI:10.1016/j.watres.2015.04.019 · 5.53 Impact Factor
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