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Article: PIV characterisation of flocculation dynamics and floc structure in water treatment

TitlePIV characterisation of flocculation dynamics and floc structure in water treatment
Authors
KeywordsAggregation-breakage-re-flocculation
Humic acid
Hydrodynamics
Particle image velocimetry (PIV)
Chemical water treatment
Issue Date2011
PublisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/colsurfa
Citation
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011, v. 379 n. 1-3, p. 27-35 How to Cite?
AbstractParticle flocculation with chemical flocculant addition is an essential step in water treatment. The performance of flocculation and the property of the flocs formed affect the overall results of the treatment process. In addition to particulate impurities, the presence of organic matter in water, such as natural organic materials (NOM), also influence the effectiveness of chemical flocculation. In this paper, the PIV system was employed to investigate the flocculation dynamics for different flocculants in different model waters. With the PIV and image analysis, the change in particle size distribution could be well recorded. Using the sequence of flocculation, shear breakage and re-flocculation on a jar-test device together with the PIV system, the rate of floc formation, the strength of the flocs, the recovery of broken flocs, and the morphological and structural features of the flocs were characterized. The results indicated that the adsorption of HA on the particle will stabilized the particles, hence hindered the flocculation process. Sweep flocculation using a higher chemical coagulant dosage was an effective means of process enhancement for the removal of particulates and associated organic matter. The dynamics of A-B-R process was characterized by particle size distribution (PSD) measurement with PIV setup. The particle strength and reversibility capability were examined. Strength index showed the HA flocs have comparable strength, while recovery index indicated a less recovery capability with the increasing of HA concentration after exposure to a higher shear, especially for ferric HA flocs. It appears that the bonds holding HA flocs together are not purely physical bonds given the limited regrowth seen. Finally, evolution of floc structure during A-B-R process was analysed by investigated the fractal dimension Db. The results were generally consistent with previous PSD measurements. It suggested that the structure of flocs in breakage became more compact with little permeability. An increase in floc compaction provides a further explanation for the limited regrowth for most of flocs. According to the performances of alum and ferric, it can be noticed that HA flocs have different properties dependent on which chemical coagulant is used. Alum produced larger HA flocs which endured a higher recovery capability after exploring higher shear, hence, compared to ferric, it could be preferred to using in the practical enhanced coagulation unit.
Persistent Identifierhttp://hdl.handle.net/10722/137238
ISSN
2015 Impact Factor: 2.76
2015 SCImago Journal Rankings: 0.831
ISI Accession Number ID
References

 

DC FieldValueLanguage
dc.contributor.authorXiao, Fen_US
dc.contributor.authorLam, KMen_US
dc.contributor.authorLi, XYen_US
dc.contributor.authorZhong, RSen_US
dc.contributor.authorZhang, XHen_US
dc.date.accessioned2011-08-26T14:21:39Z-
dc.date.available2011-08-26T14:21:39Z-
dc.date.issued2011en_US
dc.identifier.citationColloids and Surfaces A: Physicochemical and Engineering Aspects, 2011, v. 379 n. 1-3, p. 27-35en_US
dc.identifier.issn0927-7757-
dc.identifier.urihttp://hdl.handle.net/10722/137238-
dc.description.abstractParticle flocculation with chemical flocculant addition is an essential step in water treatment. The performance of flocculation and the property of the flocs formed affect the overall results of the treatment process. In addition to particulate impurities, the presence of organic matter in water, such as natural organic materials (NOM), also influence the effectiveness of chemical flocculation. In this paper, the PIV system was employed to investigate the flocculation dynamics for different flocculants in different model waters. With the PIV and image analysis, the change in particle size distribution could be well recorded. Using the sequence of flocculation, shear breakage and re-flocculation on a jar-test device together with the PIV system, the rate of floc formation, the strength of the flocs, the recovery of broken flocs, and the morphological and structural features of the flocs were characterized. The results indicated that the adsorption of HA on the particle will stabilized the particles, hence hindered the flocculation process. Sweep flocculation using a higher chemical coagulant dosage was an effective means of process enhancement for the removal of particulates and associated organic matter. The dynamics of A-B-R process was characterized by particle size distribution (PSD) measurement with PIV setup. The particle strength and reversibility capability were examined. Strength index showed the HA flocs have comparable strength, while recovery index indicated a less recovery capability with the increasing of HA concentration after exposure to a higher shear, especially for ferric HA flocs. It appears that the bonds holding HA flocs together are not purely physical bonds given the limited regrowth seen. Finally, evolution of floc structure during A-B-R process was analysed by investigated the fractal dimension Db. The results were generally consistent with previous PSD measurements. It suggested that the structure of flocs in breakage became more compact with little permeability. An increase in floc compaction provides a further explanation for the limited regrowth for most of flocs. According to the performances of alum and ferric, it can be noticed that HA flocs have different properties dependent on which chemical coagulant is used. Alum produced larger HA flocs which endured a higher recovery capability after exploring higher shear, hence, compared to ferric, it could be preferred to using in the practical enhanced coagulation unit.-
dc.languageengen_US
dc.publisherElsevier BV. The Journal's web site is located at http://www.elsevier.com/locate/colsurfa-
dc.relation.ispartofColloids and Surfaces A: Physicochemical and Engineering Aspectsen_US
dc.rightsNOTICE: this is the author’s version of a work that was accepted for publication in Colloids and Surfaces A: Physicochemical and Engineering Aspects. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011, v. 379 n. 1-3, p. 27-35. DOI: 10.1016/j.colsurfa.2010.11.053-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.subjectAggregation-breakage-re-flocculation-
dc.subjectHumic acid-
dc.subjectHydrodynamics-
dc.subjectParticle image velocimetry (PIV)-
dc.subjectChemical water treatment-
dc.titlePIV characterisation of flocculation dynamics and floc structure in water treatmenten_US
dc.typeArticleen_US
dc.identifier.emailXiao, F: xjtuxf@hotmail.comen_US
dc.identifier.emailLam, KM: kmlam@hku.hken_US
dc.identifier.emailLi, XY: xlia@hkucc.hku.hk-
dc.identifier.authorityLam, KM=rp00134en_US
dc.identifier.authorityLi, XY=rp00222en_US
dc.description.naturepostprint-
dc.identifier.doi10.1016/j.colsurfa.2010.11.053-
dc.identifier.scopuseid_2-s2.0-79953302150-
dc.identifier.hkuros190469en_US
dc.relation.referenceshttp://www.scopus.com/mlt/select.url?eid=2-s2.0-79953302150&selection=ref&src=s&origin=recordpage-
dc.identifier.volume379en_US
dc.identifier.issue1-3en_US
dc.identifier.spage27en_US
dc.identifier.epage35en_US
dc.identifier.isiWOS:000289920200007-
dc.publisher.placeNetherlands-
dc.identifier.scopusauthoridXiao, F=24598323100-
dc.identifier.scopusauthoridLam, KM=7403656958-
dc.identifier.scopusauthoridLi, XY=26642887900-
dc.identifier.scopusauthoridZhong, RS=24170418700-
dc.identifier.scopusauthoridZhang, XH=36112277900-
dc.identifier.citeulike8381436-

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