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]. "

    Full-text · Dataset · Nov 2015
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    • "Also, biodegradability of EPS may depend on composition of polysaccharide and protein (More et al. 2014). The production and composition of EPS depend on the composition of wastewater and operational conditions (Knocke et al. 1993;Wilén et al. 2003Wilén et al. , 2008). In biological treatment systems like activated sludge, the type of organic substrate has a substantial effect on microbial community and metabolism; thereby, it might indirectly influence also the production of EPS. "
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    ABSTRACT: The study aims to clarify how the type of organic substrate in a wastewater affects the production and composition of extracellular polymeric substances (EPS) and hydrophobicity and surface charge of activated sludges. For this purpose, three activated sludge reactors were operated in parallel with feeds composed of the organics (i) peptone, glucose, and acetate and (ii) peptone and (iii) glucose. EPS extracted from sludges were fractionated into very loosely bound, loosely bound, and tightly bound fractions and analyzed for protein and polysaccharide. Also, molecular weight distribution of proteinswas determined by using high-pressure size exclusion chromatography (HPSEC). Regardless of the type of organic substrate, in each sludge, tightly bound EPS (TB-EPS) prevailed. The type of organic substrate affected the relative proportion of protein and polysaccharide and had an impact on hydrophobicity and surface charge. The sludge fed with peptone was distinctly more hydrophobic and had a lower negative surface charge than others. HPSEC fingerprints revealed that the variety and size of proteins were dependent on the type of feed. HPSEC also pointed to a shift of high molecular weight (MW) proteins from TB-EPS to others. In addition, results of a parallel study examining the inhibitory effect of Ag+ on three sludges were interpreted along with feed composition, EPS, and surface measurements. The response of each sludge to toxic Ag+ ion seemed to change with the type of feed.
    Full-text · Article · Sep 2015 · Environmental Science and Pollution Research
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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.
    Full-text · Article · Apr 2015 · Journal of Water Process Engineering
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