Recent Papers on Flocculation
- Application of particle-size analysis in coagulation/flocculation for reclamation of a secondary effluent
- Coagulation–flocculation studies of tannery wastewater using cationic polymers as a replacement of metal salts
- Significance of flocculation for NOM removal by coagulation–ceramic membrane microfiltration
- A new design of flocculation tank: the Turbomix® applied to weighted flocculation
- Extracellular polymers in partly ozonated return activated sludge: impact on flocculation and dewaterability
- Membrane-flocculation-adsorption hybrid system in wastewater treatment: micro and nano size organic matter removal
- Temperature effects on flocculation, using different coagulants
- Influence of flocculation conditions in the performance of an experimental domestic sewage treatment plant consisting of an anaerobic expanded bed reactor followed by dissolved air flotation
- Relationship between flocculation of activated sludge and composition of extracellular polymeric substances
- Automation in sludge dewatering by novel on-line characterisation of flocculation
Application of particle-size analysis in coagulation/flocculation for reclamation of a secondary effluent
Water Science & Technology—WST Vol 60 No 6 pp 1455–1463 © IWA Publishing 2009 doi:10.2166/wst.2009.485
Hongbo Liu, Liping Sun, Yan Wang, Siqing Xia and Linshen Le
Shanghai Municipal Water Resource Development and Utilization National Engineering Center, 200082 Shanghai, China E-mail: lhb_7906@163.com
Tianjin Key Laboratory of Water Quality Science and Technology, Department of Environmental and Municipal Engineering, Tianjin Institute of Urban Construction, 300384 Tianjin, China
State Key Lab of Pollution Control and Resource Reuse, Tongji University, 200092 Shanghai, China
Abstract
Reclaimed secondary effluent is an important alternative water resource for urban areas; the particle-size distribution approach was applied in this study for purpose of screening and evaluating treatment processes for reclamation of a secondary effluent. Two particle-size analysing technologies namely (1) the laser light scattering technology and (2) the sequential membrane filtration technology were used in this study; particulate characteristics of the secondary effluent, of the reclaimed water by coagulation and of the reclaimed water by combined coagulation/flocculation were investigated. Optimisation of coagulation and/or combined coagulation/flocculation technologies were carried out with the help of particulate analysis of priority pollutants, following which studies on turbidity removing mechanisms of both processes were discussed. Comparison studies indicated that increase of turbidity removal efficiency by flocculation happened mainly in the particulate range of 0.2–0.3 mm and 5–8 mm; flocculation did not help or even slightly deteriorated turbidity removal of particles whose sizes are smaller than 0.2 mm and/or in the range of 0.3–5 mm
Coagulation–flocculation studies of tannery wastewater using cationic polymers as a replacement of metal salts
Water Science & Technology—WST Vol 59 No 2 pp 381–390 © IWA Publishing 2009 doi:10.2166/wst.2009.864
Sajjad Haydar and Javed Anwar Aziz
Institute of Environmental Engineering and Research (IEER), University of Engineering and Technology (UET), Lahore, Pakistan E-mail: sajj@brain.net.pk; sajjad@uet.edu.pk
Abstract
Studies were conducted to evaluate the efficiency of cationic polymers as a suitable replacement of metal salts for the treatment of a local tannery wastewater. Eleven cationic polymers of varying molecular weights (MW) and charge densities (CD) were examined using jar test apparatus. Three cationic polymers: one with MW of 4 million Dalton and CD of 55%; second with MW of 6 million Dalton and CD of 40%; and the third with MW of 8 million Dalton and CD of 40% were found suitable for tannery wastewater treatment at an optimum dose of 20 mg/L for each. Percentage removals with these three cationic polymers for turbidity, total suspended solids (TSS), total chemical oxygen demand (TCOD) and chromium lied in a range of 91–95%, 69–83%, 25–29% and 96–97%, respectively with respect to plain settled wastewater. The cost of the most suitable cationic polymer C-496 at its optimum dose was $0.09 per cubic metre of wastewater and sludge production was 35 mL/L. The results demonstrated that treatment of tannery wastewater with cationic polymers is a viable and economical option when compared with metal salts.
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Significance of flocculation for NOM removal by coagulation–ceramic membrane microfiltration
Water Science & Technology: Water Supply—WSTWS Vol 8 No 6 pp 691–700 © IWA Publishing 2008 doi:10.2166/ws.2008.148
T. Meyn, A. Bahn and T. O. Leiknes
Department of Hydraulic and Environmental Engineering, NTNU-Norwegian University of Science and Technology, S. P. Andersensvei 5, 7491, Trondheim, Norway E-mail: thomas.meyn@ntnu.no
Department for chemical engineering, Technical University Berlin, Straße des 17. Juni 135, 10623, Berlin, Germany
Abstract
Potable water treatment with coupling coagulation–microfiltration processes are still rarely applied in commercial treatment plants. Raw water with a high content of organic matter, typical for Norwegian surface water sources, was treated in this study using a ceramic microfiltration membrane system. Three different pre-treatment options were investigated, a classical two-stage flocculation, a simplified one-stage fast mixing step and an inline flocculation treatment, using an iron chloride coagulant. DOC removal was similar (76–81%, 5.5 mg C/L in raw water) in all compared setups. The more compact, energy efficient inline configuration was investigated further, varying flux (140 and 220 LMH), pH (4.5, 5.5 & 6.5), G-value (60 and 300 s-1) and HRT in the pipe (7 and 30 s), while monitoring DOC removal, fouling rate and residual iron concentrations. DOC removal was strongly pH dependent; 70% at pH 4.5, and 47% at pH 6.5. At high flux of 220 LMH the membrane fouled quickly and sustainable operation was not possible. At 140 LMH fouling was much less and no severe fouling was observed during the experimental period. Residual metal concentration was found to be the limiting parameter in the design and operation of the process configuration. Metal concentrations below the regulation limits (200 mgFe/L) were only achieved at pH 6.5. Reversible fouling was only observed at higher pH values.
A new design of flocculation tank: the Turbomix® applied to weighted flocculation
Water Science & Technology Vol 56 No 11 pp 141–149 © IWA Publishing 2007 doi:10.2166/wst.2007.774
C. Levecq*, C. Breda*, V. Ursel**, P. Marteil* and P. Sauvignet**
*Veolia Environnement R&D, Chemin de la Digue, 78603, Maisons Laffitte, France (E-mail: celine.levecq@veolia.com)
Technical Division of Veolia Water, 1 Rue Giovanni Battista Pirelli, 94410, St Maurice, France (E-mail: philippe.sauvignet@veoliaeau.fr)
Abstract
As far as flocculation is concerned, the agglomeration of suspended particles into flocs is highly linked to the hydraulic behaviour of the agitation. The Turbomix® is a special design of mixing tank; its design was developed to better control the flow during the flocculation stage. It enables a significant decrease in footprint of the process. The combination of the Turbomix® and ballasted flocculation has been studied during pilot trials in terms of treatment efficiency. Its controlled hydraulic behaviour explains the efficiency of the process as proved by CFD investigation.
Extracellular polymers in partly ozonated return activated sludge: impact on flocculation and dewaterability
Water Science & Technology Vol 54 No 9 pp 155–164 © IWA Publishing 2006 doi:10.2166/wst.2006.873
M.A. Dytczak*, K. Londry**, H. Siegrist*** and J.A. Oleszkiewicz****
*Department of Civil Engineering, University of Manitoba, Winnipeg, R3T 5V6, Canada (E-mail: umdytcza@cc.umanitoba.ca)
**Department of Microbiology, University of Manitoba, Winnipeg, R3T 2N2, Canada (E-mail: londryk@cc.umanitoba.ca)
***EAWAG, CH-8600 Dübendorf, Switzerland (E-mail: hansruedi.siegrist@eawag.ch)
****Department of Civil Engineering, University of Manitoba, Winnipeg, R3T 5V6, Canada (E-mail: oleszkie@cc.umanitoba.ca)
Abstract
The purpose of this study was to evaluate the influence of partial ozonation of return activated sludge on settling properties and dewaterability of sludge. Sequencing batch reactors with two sets of aerobic and alternating anoxic/aerobic conditions were used. In each set, one reactor served as a control and the other was subject to the ozone treatment (doses in the range of 0.016–0.080 mg O3/mg TSS of initial excess sludge). The level of total suspended solids (TSS) in each reactor was controlled at 1,800 mg/l. To evaluate settleability and dewaterability, settling kinetic studies, sludge volume index (SVI) and capillary suction time test (CST) were used. For extraction and quantifying sludge biopolymers, thermal-ethanolic extraction was employed. The ratio of bound-to-total extracellular polymer substances (EPS) was higher for the strictly aerobic reactor than for the alternating anoxic/aerobic one, indicating the stronger structure of the aerobic flocs. After ozone treatment, the fraction of bound EPS was released and solubilized, increasing soluble EPS. Increased apparent food-to-microorganism (F/M) ratio favoured production of EPS in ozonated reactors, enhancing flocculation, which had potential to improve settling. Dewaterability, measured by CST test, was better in alternating anoxic/aerobic reactors than in aerobic ones, indicating that incorporation of an anoxic zone for biological nutrient removal leads to improvement in sludge dewatering. The negative impact of ozonation on dewaterability was minimal in terms of the long-term operation.
Membrane-flocculation-adsorption hybrid system in wastewater treatment: micro and nano size organic matter removal
Water Science & Technology Vol 50 No 12 pp 265–271 © IWA Publishing 2004
S. Vigneswaran*, H.K. Shon**, S. Boonthanon***, H.H. Ngo**** and R.B. Aim*****
*Faculty of Engineering, University of Technology, Sydney, P.O. Box 123, Broadway, NSW 2007, Australia (E-mail: s.vigneswaran@eng.uts.edu.au)
**Faculty of Engineering, University of Technology, Sydney, P.O. Box 123, Broadway, NSW 2007, Australia (E-mail: s.vigneswaran@eng.uts.edu.au)
***Clean Technology, Bangkok, Thailand
****Faculty of Engineering, University of Technology, Sydney, P.O. Box 123, Broadway, NSW 2007, Australia (E-mail: s.vigneswaran@eng.uts.edu.au)
*****INSA, Toulouse, France
Abstract
Cross flow microfiltration with in-line flocculation reduces the fouling of membranes thus leading to high quality product water. A detailed experimental study conducted with an artificial suspension (particle size distribution similar to that of surface water) revealed that the filtration rate can be increased by several times by adopting in-line flocculation. In-line flocculation-microfiltration is therefore an attractive technique to reduce internal clogging while improving the permeate flux significantly. A detailed ultrafiltration (UF) study was conducted with biologically treated sewage effluent with pretreatment by flocculation and powdered activated carbon adsorption. The TOC removal by the NTR 7410 UF membrane alone was 43.6%. The TOC removal increased significantly by the use of pretreatment: 69.3% by flocculation and 91% by flocculation followed by adsorption. The organic colloidal portion (between 3,500 dalton and 0.45 
m) in the biologically treated effluent was removed up to more than 65% by the pretreatment of flocculation. The molecular weight of the biologically treated effluent ranged from 250 to about 3,573 dalton with the highest fraction in the range of 250-845 dalton. By the incorporation of pretreatment, the majority of both large and small molecular weight organic matter was removed. This hybrid system led to practically no filtration flux decline in membrane filtration.
Temperature effects on flocculation, using different coagulants
Water Science & Technology Vol 50 No 12 pp 171–175 © IWA Publishing 2004
C.S.B. Fitzpatrick*, E. Fradin** and J. Gregory***
*Department of Civil and Environmental Engineering, University College London, Gower St, London WC1E 6BT, UK (E-mail: c.fitzpatrick@ucl.ac.uk; j.gregory@ucl.ac.uk)
**Ecole Nationale du Genie de L'Eau et de L'Environnement de Strasbourg, 1 Quai Koch, BP 1039 F, 67070 Strasbourg Cedex, Franc (E-mail: EFRADIN@engees-e.u-strasbg.fr)
***Department of Civil and Environmental Engineering, University College London, Gower St, London WC1E 6BT, UK (E-mail: c.fitzpatrick@ucl.ac.uk; j.gregory@ucl.ac.uk)
Abstract
Temperature is known to affect flocculation and filter performance. Jar tests have been conducted in the laboratory, using a photometric dispersion analyser (PDA) to assess the effects of temperature on floc formation, breakage and reformation. Alum, ferric sulphate and three polyaluminium chloride (PACl) coagulants have been investigated for temperatures ranging between 6 and 29°C for a suspension of kaolin clay in London tap water. Results confirm that floc formation is slower at lower temperatures for all coagulants. A commercial PACl product, PAX XL 19, produces the largest flocs for all temperatures; and alum the smallest. Increasing the shear rate results in floc breakage in all cases and the flocs never reform to their original size. This effect is most notable for temperatures around 15°C. Breakage, in terms of floc size reduction, is greater for higher temperatures, suggesting a weaker floc. Recovery after increased shear is greater at lower temperatures implying that floc break-up is more reversible for lower temperatures.
Influence of flocculation conditions in the performance of an experimental domestic sewage treatment plant consisting of an anaerobic expanded bed reactor followed by dissolved air flotation
Water Science & Technology Vol 48 No 6 pp 285–293 © IWA Publishing 2003
R.G. Penetra*, M.A.P. Reali** and J.R. Campos***
*Department of Hidraulic and Sanitary Engineering, S‹o Carlos School of Engineering, University of Sao Paulo (SHS-EESC-USP), Av. Trabalhador Sao-carlense, 400, Sao Carlos - SP - Brasil, ZIP code: 13560-250 (E-mail: penetra@otv.com.br)
**Department of Hidraulic and Sanitary Engineering, S‹o Carlos School of Engineering, University of Sao Paulo (SHS-EESC-USP), Av. Trabalhador Sao-carlense, 400, Sao Carlos - SP - Brasil, ZIP code: 13560-250 (E-mail: mapreali@sc.usp.br)
***Department of Hidraulic and Sanitary Engineering, S‹o Carlos School of Engineering, University of Sao Paulo (SHS-EESC-USP), Av. Trabalhador Sao-carlense, 400, Sao Carlos - SP - Brasil, ZIP code: 13560-250
Abstract
This paper presents the results of a study performed with an experimental domestic sewage treatment plant (240 m3.d-1 flow) consisting of expanded bed anaerobic reactor (EBAR) followed by dissolved air flotation (DAF) unit. For the flotation step, the anaerobic reactor effluent was previously coagulated with 50 mgFeCl3.l-1 and flocculated under different conditions (mean velocity gradient, Gf, and flocculation time, Tf). The Gf values were from 60 to 100 s-1 associated with 13 and 20 min Tf values. During the tests, the following operational conditions of the flotation unit were maintained: chemical addition (50 mgFeCl3.l-1), 18% recirculation rate associated with a pressure of 450 ± 10 kPa in the saturation chamber and overflow rate of 180 m3.mÐ2.d-1. Temperature ranged from 23.8¡C to 30.01/4C. Best results were achieved for Gf = 80 s-1 and Tf = 20 min. For these conditions, the DAF unit removal efficiencies were: 94.4% for chemical oxygen demand (with 53 mg.l-1 COD residual), 87% for phosphorus (with 0.80 mgP.l-1 residual), 96.7% for total suspended solids (with 9 mg.l-1 TSS residual) and 96.4% for turbidity (with 12.9 NTU residual), when the anaerobic reactor effluents have worst quality during the whole day.
Relationship between flocculation of activated sludge and composition of extracellular polymeric substances
Water Science & Technology Vol 47 No 12 pp 95–103 © IWA Publishing 2003
B.-M. Wilén*, B. Jin** and P. Lant***
*Advanced Wastewater Management Centre, The University of Queensland, St Lucia, Qld 4072, Australia Sweden (E-mail: britt-marie.wilen@wet.chalmers.se). Water Environment Transport, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
**Advanced Wastewater Management Centre, The University of Queensland, St Lucia, Qld 4072, Australia Sweden (E-mail: bojin@awmc.uq.edu.au)
***Advanced Wastewater Management Centre, The University of Queensland, St Lucia, Qld 4072, Australia Sweden (E-mail: paull@awmc.uq.edu.au)
Abstract
Activated sludge flocs are a flocculated mass of microorganisms, extracellular polymeric substances (EPS) and adsorbed organic and inorganic material. The structure of the flocs is very heterogeneous and flocs with very different properties and morphologies may occur, depending on the conditions in the activated sludge treatment plant and wastewater composition. Present thinking suggests that cations, such as calcium, create cationic bridges with EPS excreted by the bacteria and thereby hold the various floc constituents together. However, due to the complex and heterogeneous nature of activated sludge, the mechanisms have neither been thoroughly investigated nor successfully quantified. A better understanding and description of the biological flocculation process is necessary in order to establish more efficient operational strategies. The main aim of this study was to get a comprehensive and unique insight into the floc properties of activated sludge and to assess the relative impact of chemical and physical parameters. A variety of sludges from full scale treatment plants with different settling properties were characterised. The interrelationships between floc parameters such as composition of EPS, surface properties and floc structure, and their effect on the flocculation and separation properties were assessed. The results indicate that the EPS, both in terms of quantity and quality, are very important for the floc properties of the activated sludge. However, presence of filaments may alter the physical properties of the flocs considerably. The EPS showed positive correlations to sludge volume index (SVI) if only sludges with low or moderate numbers of filaments were included. The surface properties were more affected by the composition of the EPS than by the number of filaments. The EPS showed positive correlation to negative surface charge and a negative correlation to relative hydrophobicity and flocculation ability. The negative correlation between flocculation ability and amount of EPS was surprising. The shear sensitivity, measured as degree of erosion of flocs when subjected to shear, was more affected by floc size and number of filaments than amount of EPS.
Automation in sludge dewatering by novel on-line characterisation of flocculation
Water Science & Technology Vol 47 No 2 pp 157–164 © IWA Publishing 2003
M. Sievers*, C. Schroeder**, H. Bormann***, T.I. Onyeche****, O. Schlaefer***** and S. Schaefer******
*CUTEC-Institut GmbH (Clausthal Environment Technology Institute), Leibnizstr. 21+23, 38678 Clausthal-Zellerfeld, Germany (E-mail: michael.sievers@cutec.de)
**CUTEC-Institut GmbH (Clausthal Environment Technology Institute), Leibnizstr. 21+23, 38678 Clausthal-Zellerfeld, Germany (E-mail: michael.sievers@cutec.de)
***CUTEC-Institut GmbH (Clausthal Environment Technology Institute), Leibnizstr. 21+23, 38678 Clausthal-Zellerfeld, Germany (E-mail: michael.sievers@cutec.de)
****CUTEC-Institut GmbH (Clausthal Environment Technology Institute), Leibnizstr. 21+23, 38678 Clausthal-Zellerfeld, Germany (E-mail: michael.sievers@cutec.de)
*****CUTEC-Institut GmbH (Clausthal Environment Technology Institute), Leibnizstr. 21+23, 38678 Clausthal-Zellerfeld, Germany (E-mail: michael.sievers@cutec.de)
******CUTEC-Institut GmbH (Clausthal Environment Technology Institute), Leibnizstr. 21+23, 38678 Clausthal-Zellerfeld, Germany (E-mail: michael.sievers@cutec.de)
Abstract
A novel on-line method and system for characterisation of sludge flocs in view of improving sludge dewatering has been developed. The characterisation of sludge flocs was carried out after the conditioning or the flocculation process. The system uses a conventional CCD-line scan camera providing an on-line monitoring of the relative floc size distribution by image processing procedures. The image processing procedure has been re-evaluated and adapted to the practical dewatering results, obtained from a chamber filter press of 250 
250 mm size. A good correlation between the calculated sensor signal and the sludge dewaterability of digested sludge in terms of the up-concentration factor was found. Although different sludge compositions and flocculation systems have been tested within the whole experimental period of six months, a good reproducibility of this correlation was also found. A well balanced floc size distribution is necessary showing that not too many but still some fine flocs and also not too large but compact flocs lead to improved dewaterability. This has been illustrated by an extended range of floc size measurements ranging between 50 mm and 29 mm. The conditioning monitoring system would be suitable for the control of production of good size-balanced flocs to compensate fluctuations in sludge characteristics of the sludge to be conditioned.
