Declaration of Rachel J. Watters on Authentication of Publication
`
`1, Rachel J. Watters, am a librarian, and the Head of Resource Sharing for the
`
`General Library System, Memorial Library, located at 728 State Street, Madison,
`
`Wisconsin, 53706. Part of my job responsibilities include oversight of Wisconsin
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`TechSearch (“WTS”), an interlibrary loan department at the University of Wisconsin—
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`Madison.
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`I have worked as a librarian at the University of Wisconsin library system
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`since 1998, starting as a graduate student employee in the Kurt F. Wendt Engineering
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`Library and WTS, then as a librarian in Interlibrary Loan at Memorial Library.
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`I began
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`professional employment at WTS in 2002 and became WTS Director in 2011. In 2019,
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`I became of Head of Resource Sharing for UW-Madison’s General Library System.
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`I
`
`have a master’s degree in Library and Information Studies from the University of
`
`Wisconsin—Madison. Through the course of my studies and employment, I have
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`become well informed about the operations of the University of Wisconsin library
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`system, which follows standard library practices.
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`This Declaration relates to the dates of receipt and availability of the following:
`
`Han, M.Y., Park, Y.H., and Yu, T.J. (2002). Development of a
`new method of measuring bubble size. Water Science and
`Technology: Water Supply, 2(2), 77-83.
`
`Standard 0 eratz'n
`
`racedures or materials at the Universz'
`
`0 Wisconsin-
`
`Madison Libraries. When an issue was received by the Library, it would be checked in,
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`stamped with the date of receipt, added to library holdings records, and made available
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`Tennant Company
`Exhibit 1138
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`Tennant Company
`Exhibit 1138
`
`

`

`Declaration of Rachel J. Watters on Authentication of Publication
`
`to readers as soon after its arrival as possible. The procedure normally took a few days
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`or at most 2 to 3 weeks.
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`Exhibit A to this Declaration is a true and accurate copy of the title page with
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`library date stamp of Water Science and Technology: Water Supply (2002), from the
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`University of Wisconsin-Madison Library collection. Exhibit A also includes an
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`excerpt of pages 77 to 83 of that issue, showing the article entitled Development ofa
`
`new method ofmeasuring bubble size (2002). Based on this information, the date stamp
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`on the journal title page indicates Development ofa new method ofmeasuring bubble
`
`size (2002) was received by the Kurt F. Wendt Library, University of Wisconsin—
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`Madison on May 20, 2002.
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`Based on the information in Exhibit A, it is clear that the issue was received by
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`the library on or before May 20, 2002, catalogued and available to library patrons within
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`a few days or at most 2 to 3 weeks after May 20, 2002.
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`Members of the interested public could locate the Water Science and Technology:
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`Water Supply (2002) publication after it was cataloged by searching the public library
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`catalog or requesting a search through WTS. The search could be done by title and/or
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`subject key words. Members of the interested public could access the publication by
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`I declare that all statements made herein of my own knowledge are true and that
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`all statements made on information and belief are believed to be true; and further that
`
`2
`
`

`

`Declaration of Rachel J. Watters on Authentication of Publication
`
`these statements were made with the knowledge that willful false statements and the like
`
`so made are punishable by fine or imprisonment, or both, under Section 1001 of Title 18
`
`of the United States Code.
`
`Date: December 17, 2020
`
`Memorial Library
`728 State Street
`
`Madison, Wisconsin 53706
`
`1 % :
`
`J. Watters
`
`Rac
`
`Head of Resource Sharing
`
`

`

`Water Science & Technology:
`
`; Water Supply
`
`issue Editors
`
`IWA Programme Committee
`
`.
`
`Volume 02
`Number 02 2002
`
`.3\
`
`ISSN 1606—9749
`
`2nd World Water Congress: Drinking Water
`
`Treatment
`
`
`‘L
`
`

`

`Editor-in-Chief
`
`Peter Wilderer Technical University of Munich, Germany
`
`Editors
`
`Erik Arvin Technical University of Denmark
`Linda Blackall University of Queensland, Australia
`Mohamed F Hamoda University of Kuwait
`Peter Steen Mikkelsen Technical University of Denmark
`Eberhard Morgenroth University of Illinois at Urbana-Champaign
`Ralf Otterpohl Technical University of Hamburg-Harburg, Germany
`Marie-Noelle Pons Institute National Polytechnique de Lorraine. University of Nancy, France
`Wolfgang Rauch University of Innsbruck, Austria
`Tom Stephenson Cranfield University, UK
`Zaini Ujang Universiti Teknologi Malaysia
`Zhu .Iianrong Tsinghua University. China
`
`Journals Manager
`Paul Nagle
`
`Editorial Office
`
`Paul Nagle, IWA Publishing, Alliance House, 12 Caxton Street, London SW1 H 008, UK
`Telephone: +44 (0)20 7654 5500
`Fax: +44 (0)20 7654 5555
`E-mail: pnagle@iwap.co.uk
`www.iwapub|ishing.com
`
`Aims and Scope
`Water Science and Technology: Water Supply publishes the selected proceedings of IWA
`conferences, symposia and workshops. All papers have been selected for publication after ref-
`ereeing under the auspices of the conference editor(s) and the Programme Committee for each
`IWA event, and after review by a member of the board of editors.
`
`Water Science and Technology: Water Supply incorporates the journal Water Supply (ISSN
`0735-1917) formerly published by the International Water Services Association.
`
`Copyright © 2002 IWA Publishing
`Except as otherwise permitted under the Copyright, Designs and Patents Act, 1988, this
`publication may only be reproduced, stored or transmitted, in any form or by any other means,
`with the prior permission in writing of the publisher, or in the case of xerographic reproduction,
`in accordance with the terms of a licence issued by the Copyright Licence Agency. In particu~
`lar, lWA Publishing permits the making of a single photocopy of an article from this issue (under
`sections 29 and 38 of this Act) for an individual for the purposes of research or private study.
`
`This paper meets the requirements of ISO 9706:1994. Information and documentation - Paper to!
`documents - Requirements for permanence.
`Cover and text design by Smith & Gilmour, London, UK, Typeset and printed byJ W Arrowsmith Ltd, Bristol, UK.
`
`

`

`Water Science & Technology: Water Supply
`
`2nd World Water Congress: Drinking
`
`Water Treatment
`
`

`

`Contents
`
`Micropollutants and drinking water perspective
`New approaches for structural characterization of organic matter in drinking water
`and wastewater effluents
`J.E. Drewes and .l.-P. Croue
`
`A systems analysis comparing drinking water systems - central physical-chemical
`treatment and local membrane filtration
`T. Wesirell, O. Bergstedt. G. Heinicke and
`E. Karrman
`
`Pharmaceuticals degradation by UV and UV/H202 treatments A. Bozzi, A. Lopez,
`G. Mascolo and G. Tiravanti
`
`The removal of Cu (ll), Cd (II), Ni (II) and Pb (II) from dilute aqueous solution by a
`poly(acrylic acid) flocculant and its cross-linked analogue C, Morlay, Y. Mougino’t,
`M. Cromer and O. Vittori
`
`A hybrid biofilm reactor for nitrate and pesticide removal
`T. Katahira
`
`Y. Sakakibara, Z. Feleke and
`
`Drinking water quality assessment practices: an international perspective
`M.C. Steynberg
`'
`Sequential anaerobic/aerobic biodegradation of chlorinated hydrocarbons in
`activated carbon barriers A. Tiehm, M. Gozan, A. M‘uller, H. Schell, H. Lorbeer and
`P. Werner
`
`In the (adsorption) competition between NOM and Mia, who is the winner, and why?
`G. Newcombe, J. Morrison, C. Hepplewhite and D.R.U. Knappe
`
`Particle separation
`Flow structures in a dissolved air flotation pilot tank and the influence on the
`separation of MBBR floc M. Lundh, L. Jonsson and J. Dahlquist
`Development of a new method of measuring bubble size M.Y. Han, Y.H. Park and
`T.J. Yu
`
`Fate and removal of Cryptosporidium in a dissolved air flotation water plant with and
`without recycle of waste filter backwash water
`J.K. Edzwald and J.E. Tobiason
`
`Investigations on the filtration of natural aquatic suspensions supported by dosing
`small amounts of Fe(III)-salts (BFe s 0.1 mg L"): mode of action and basic design
`criteria
`R. Winzenbacher, R. Schick, H.—H. Stabel and M. Jekel
`
`Structure of AI-humic flocs and their removal at slightly acidic and neutral pH
`X.C. Wang, P.K. Jin and J. Gregory
`
`J. Wang, P. Deevanhxay.
`A pilot plant study of polysilicato-iron coagulant
`T. Hasegawa, Y. Ehara, M. Kurokawa, K. Hashimoto, W. Nishijima and M. Okada
`Characterization and destabilization of spent filter backwash water particles
`A. Adin. L. Dean. F. Bonner, A. Nasser and Z. Huberman
`
`Full-scale studies
`
`System development and testing of wind-powered reverse osmosis desalination for
`remote Pacific islands C.C.K. Liu. R. Migita and J.-W. Park
`Optimisation of coagulation and chlorination in drinking water treatment: laboratory
`and full-scale studies N.D. Basson and GE Schutte
`
`Addressing the sustainability of small-user rural water treatment systems in South
`Africa G.S. Mackintosh. P.F. de Souza and E. Delport
`
`11
`
`19
`
`27
`
`35
`
`48
`
`51
`
`59
`
`69
`
`77
`
`85
`
`91
`
`99
`
`107
`
`115
`
`123
`
`131
`
`139
`
`

`

`145
`
`151
`
`161
`
`169
`
`177
`
`185
`
`193
`
`201
`
`207
`
`213
`
`223
`
`229
`
`237
`
`247
`
`259
`
`267
`
`275
`
`281
`
`289
`
`297
`
`305
`
`Using percentile analysis for determination of alarm values R.C. Lake. P.A. Agutter
`and T. Burke
`
`Pilot and bench-scale studies
`
`Determination of mass transport characteristics for natural organic matter (NOM) in
`ultrafiltration (UF) and nanofiltration (NF) membranes
`S. Lee, Y. Shim, LS. Kim,
`J. Sohn, S.K. Yim and .1. Che
`
`Removal of nitrate from water in a novel ion exchange membrane bioreactor
`S. Velizarov. J.G. Crespo and MA. Reis
`
`Ammonia oxidation at low temperature in a high concentration powdered activated
`carbon membrane bioreactor G. Sec, 8. Takizawa and S. Ohgaki
`Performance and membrane foulant in the pilot operation of a novel biofilm-
`membrane reactor
`K. Kimura and Y. Watanabe
`
`Pilot plant study on the performance and optimization of submerged membranes for
`taste and odor removal
`L. Schideman, V.L. Snoeyink, BJ. Marinas and M. Kosterman
`
`Blofilter pretreatment for the control of microfiltration membrane fouling
`S. Takizawa, H. Katayama and S. Ohgaki
`The effect of various operating conditions and water quality parameters on the
`removal of perchlorate in a biologically active carbon filter
`J.C. Brown,
`V.L. Snoeyink, L.M. Raskin. J.C. Ghee-Sanford and R. Lin
`
`J. Park,
`
`Denaturing gradient gel electrophoresis analysis of a methyl fert-butyl ether
`degrading culture applied in a membrane bioreactor A. Pruden, M. Suidan. J. Morrison
`and A. Venosa
`
`Treatment of groundwater
`Improved ultraviolet spectrophotometric method for determination of nitrate in
`natural waters
`N. Kishimoto. l. Somiya and R. Taniyama
`Influence of gasoline hydrocarbons on methyl tert-butyl ether biotreatment in
`fluidized bed bioreactors W.T. Stringfellow and K.-C. Oh
`
`Fenton process for the combined removal of iron and organic micropollutants in
`groundwater treatment G.F. ijeiaar. M. Groenendijk, J.G. Kruithof and J.C. Schippers
`Arsenic removal by iron hydroxides, produced by enhanced corrosion of iron
`K. Karschunke and M. Jekel
`
`Characterisation of coated sand from Iron removal plants
`B. Petrusevski and J.C. Schippers
`
`S.K. Sharma,
`
`Perchlorate as a secondary substrate in a denitrifying, hollow-fiber membrane
`biofiim reactor
`R. Nerenberg and BE. Rittmann
`
`Arsenic removal
`
`Concept for an integrated evaluation of arsenic removal technologies: demonstrated
`in a case study A. Ruhland and M. Jekel
`
`Arsenic removal - experience with the GEH® process in Germany W. Driehaus
`
`A low cost technique of arsenic removal from drinking water by coagulation using
`ferric chloride salt and alum M.M.T. Khan. K. Yamamoto and M.F_. Ahmed
`
`Innovative membrane processes
`Large scale pilot plant for treating flocculated reservoir water and membrane
`integrity monitoring G. Hagmeyer. R. Gimbel and W. Dautzenberg
`
`an
`
`Hydraulic distribution of water and air over a membrane module using AlrFluSh
`J.G.J.C.Verberk, P.E. Hoogeveen. H. Futselaar and J.G. van Dijk
`
`Effects of particle size distribution on the cake formation in crossflow mlcrofiltra
`S. Kim. S.-H. Cho and H. Park
`
`tlofl
`
`
`
`vi
`
`

`

`My. Han', Y.H. Park* and TJ. Yu**
`* School of Civil, Urban & Geosystem Engineering, Seoul National University, San 56-1, Shilim-dong,
`Kwanak-gu, Seoul,'Korea. (E-mail: myhan@gong.snu.ac.kr; yhpark@waterfirst.snu.ac.kr)
`v Department of Civil and Environmental Engineering, Kwangju University, 592-1,Jinwo|—dong, Nam-gu,
`Kwangju, Korea. (E-mail: t/'yu@hosim.kwangju.ac.kr)
`
`Abstract The use of bubbles in water and wastewater treatment, including dissolved air flotation (DAF) and
`electro-flotation (EF), is attracting much interest recently. These flotation processes are governed by
`characteristics of the bubbles as well as the particles, and therefore it is necessary to investigate the size
`distribution of the bubbles that are generated. In this research, a new method has been developed to
`measure the bubble size, using commercially available batch-type and on-Iine particle counters. The results
`are compared with the traditional image analysis method. Although there are some discrepancies, the results
`show that an on-Iine particle counter can produce reasonably accurate size distributions conveniently and
`efficiently. The bubble size measurement technique developed in this study will assist understanding and
`improvement of the DAF and EF processes, from both theoretical and practical points of view.
`Keywords Bubble size; dissolved air flotation (DAF); electro-flotation (EF); image analysis;
`particle counter
`
` Development of a new method of measuring bubble size
`
`In DAF, bubbles are generated when air—saturated water is released into atmospheric
`pressure. The size of bubbles is mostly affected by pressure difference across the injection
`system and type of nozzle (AWWA, 1999). The size range is generally reported to be
`10—100 pm, with the average being approximately 40 pm, under a pressure of 4—6 atmos—
`pheres (Edzwald, 1995). In EF, hydrogen and oxygen bubbles are generated when current
`is applied to the solution through metal electrodes. The average size range is reported to be
`around 20—40 pm, which is a smaller range than that of DAF (Burns et al., 1997).
`Several methods have been developed to measure the size of bubbles. The most straight-
`forward method is image analysis. Because this method requires a complicated experi—
`mental setup and is time-consuming, it is not easy to produce enough data to generate size
`distributions under different conditions. Another method is to measure the rising velocity
`0f the bubbles and to calculate the sizes by Stokes’ Law. However, because the sizes of
`bubbles are not uniform, and because the rising velocity of many bubbles is different from
`that of a single bubble, no general equations are available to predict the size distribution of
`bubbles from the rising velocities.
`In this study, a new method to measure the size of bubbles, using particle counters, was
`developed. The bubble counting results obtained from both image analysis and particle
`
`Introduction
`
`The use of bubbles in water and wastewater treatment, including dissolved air flotation
`(DAF) and electro-flotation (EF), has attracted much interest recently. Although the funda-
`mental characteristics of the micro-bubble/partic1e/solution system should affect the
`removal efficiency of the process, the effect of each governing physical—chemical parame-
`ter has not been investigated fully, either experimentally or theoretically. According to
`recent modeling of the DAF process, the most important parameters that affect the removal
`efficiency are the size and zeta potential of both bubbles and particles (Han et (11., 2001;
`Han, 2002).
`
`
`
`
`
`
`
`3.10qu199'41pureSuiqsuqndVMI3005©93—“dd30Nz|oAMddns1919M:Kfiolouuoelpueaoueios1919M'
`
`
`
`
`
`
`
`77
`
`

`

`counters are compared by measuring the bubbles that are generated under the same
`conditions in DAF and EF.
`
`Methods
`Bubble generation conditions
`
`79119ueH'A'W
`
`Dissolved-air-flotation. Air was pressurized and dissolved into water under 6 atm. To
`reduce interference from particles of solids, distilled and deionized water was used
`Although particles smaller than 10 um can be detected by the particle counter, only those
`larger than 10 mm were regarded as bubbles To avoid over-counting the larger bubbles
`formed by bubble coalescence inside the tubing, the observations were made directly after
`the valve. Only a small volume of bubbles was generated to avoid the possibility that a high
`concentration might decrease the accuracy of the particle counters and increase bubble
`coalescence.
`
`Electra-flotation. To generate bubbles by EF, distilled and deionized water (as above) was
`mixed with the same volume of tap water. Aluminium electrodes 5 cm square and of thick-
`ness 0.5 mm were used, and a DC voltage of 12 V was applied. The method relies on gener-
`ation of hydrogen bubbles from the cathode. When aluminium electrodes are used, A13+
`
`ions and oxygen bubbles are generated from the anode. The aluminium ions hydrolyze in
`water, producing floc particles that interfere with the measurements of bubble size. To
`
`avoid this, the anode was wrapped with GF/C filters (pore size: 0.45 pm) to prevent floc
`particles and oxygen bubbles being introduced into the sampling tube.
`
`Bubble size measurement
`
`Image analysis. The image analysis system, which is illustrated in Figure 1, includes a
`measuring cell, a microscope, a CCD camera, and a computer for image processing.
`Bubbles were generated inside the measuring cell to prevent the change of bubble size
`when bubbles are introduced into the cell through a tube in both DAF and EF. Images of
`bubbles were taken using the CCD camera. Their sizes were measured using a micrometer.
`The upper part of the cell was kept open because the pressure difference inside the cell can
`affect the bubble size. The microscope was focused at the point directly after the valve in
`DAF and directly above the cathode in EF.
`
`Batch-type particle counters. A batch-type particle counter (Multisizer II, Coulter) was
`used to measure the sizes of bubbles. Figure 2 shows the configuration of the measuring 0611
`
`Microscope
`
` DAF or EF
`
`78
`
`Figure 1
`
`Image analysis system
`
`
`
`

`

`External Electrode
`
`Internal Electrode
`
`
`
` Sensing Zone
`0 0 0 o
`
`
`
`00 g 0 Aperture Tube
`0
`
`
`00
`O
`
`
`
`Figure 2 Schematic of batch-type particle counter
`
`of the Multisizer II. Bubbles generated inside the cell were introduced through the opening
`in the aperture. An aperture size of 200 pm was used in the experiment. In this method, a
`constant electric current passes between the two electrodes through the electrolyte. When
`particles (bubbles in this research) pass through the sensing zone, the electrolyte volume
`decreases, which increases the resistance to the electric current. The amount of resistance is
`
`exactly proportional to the volume of particles, and this volume is converted to the size of
`equivalent spherical particles or bubbles. Although the result might be considered accurate
`because of the narrowly divided channel (256 channels), the application is limited to
`laboratory experiments because sampling and measuring is quite difficult. Furthermore,
`bubbles generated by EF cannot be measured, because of the electrical disturbance to the
`measuring system.
`
`On-line particle counters. An on-line particle counter (Chemtrac Model PC2400 D, USA)
`was used to measure the sizes of bubbles. In this method, a laser light shines through the
`sensor onto the detector. When the sample passes through the sensor, the light is scattered
`and obscured by the particles. This scattering and obscuring of the light causes a decrease in
`the intensity of the light reaching the detector that is proportional to the particle size.
`According to the decrease, a voltage pulse is generated. Here, the number of pulses repre-
`sents the number of particles, and the height of the pulse the size of the particles. This
`instrument can measure over the size range of 2—400 pm in seven user-definable size
`ranges. In this research, two identical particle counters were used to record data for 14
`Channels. To minimize possible bubble coalescence inside the tube, a straight tube, which
`Was kept as short as possible, was used, and the sampling flow rate was kept at 100 ml/min
`Which is recommended by the manufacturer.
`
`
`
`7219ueHMN
`
`79
`
`

`

`Sample out T
`
` Sample Outlet
`
`Laser
`
`i
`
`i
`
`Particle
`
`Sample Inlet
`
`Cell Windows
`
`Detector
`antale Output
`
`FocusingLens |\ [- (mV)
`
`
`
`Figure 3 Schematic of on-Iine particle counter and details of the sensor
`
`Results and discussions
`Comparison of each method
`
`Three different methods of measuring bubble sizes (image analysis, a batch-type particle 3
`counter, and an on-line particle counter) were tested, and the characteristics of each method
`are compared in Table 1. The batch-type particle counter is not suitable for bubbles gener—
`ated by EF. Continuous size measurement is not possible using the image analysis method
`and the batch-type particle counter.
`However, the results are much more accurate than those from the on-line particle count-
`er. The most useful feature of the on-line particle counters is the very rapid rate at which
`data can be acquired. The time needed to measure 2,000 bubbles by each method was 3,000,
`30, and 10 minutes, respectively.
`
`Bubble size in DAF
`
`The size and size distribution of bubbles generated from DAF were measured by image
`analysis, batch and online particle counters, respectively. It is important to keep the pres-
`sure constant (6 atm.) throughout the DAF experiments, because the size of the bubbles is
`dependent on the pressure. The results from each method are comparable, as illustrated in
`Figure 4 and listed in Table 2.
`The average bubble size and modal bubble size recorded by each method was similar.
`but the size range was not. The size range of bubbles from particle counting methods is
`wider than from image analysis, which means that a small number of larger bubbles W511s
`detected in the particle counting methods. One possible reason for this might be the coales-
`cence of bubbles during transport to the sensor. Another reason, applicable to the on—line
`particle counter, is possible overlapping of bubbles inside the sensor, which would result in
`counting fewer but larger bubbles. This is an inherent shortcoming of the instrument
`
`.
`
`Table 1 Comparison of characteristics of bubble size measurement methods
`_—__—___—_//
`Application
`.
`On-Ilne
`Size
`Measurlng tlme
`DAF
`EF
`measurement
`accuracy
`(mln)'
`_—_—_—_//
`
`3000
`Excellent
`X
`O
`0
`Image analysis
`30
`Excellent
`X
`X
`Batch-type particle counter O
`10
`Good
`0
`O
`On-Iine particle counter
`O
`*‘—//
`* For measurement of approximately 2,000 bubbles
`
`7219ueH7m
`
`80
`
`

`

`1 7
`
`219ueH"AW
`
`50%
`
`40%
`
`a
`5
`
`g 20%
`
`10%
`
`Cumulative Size Distribution of DAF Bubbles
`
`Size Distributlon of DAF Bubbles
`
`
`100%
`—O—-On-line Counter
`
`u
`80%
`5"I:
`94
`0
`
`
`
`
`
`+Bateh-typeCounter
`+ImageAnalysls
`
`
`
`
`
`
`
`
`7
`
`515 25
`
`35
`
`55
`45
`SizeQim)
`
`65
`
`75
`
`$5
`
`95
`
`5
`5
`
`'°
`
`20%
`
`0%
`
`
`+0n-line Counter
`I Multisizerll
`.
`+Image Analysis
`
`-
`515 25
`35
`45
`55
`65
`75
`85
`95
`Sizeulm)
`
`
`
`Figure 4 Comparison of bubble size distribution of DAF
`
`Table 2 Size characteristics of bubbles measured by each method
`/—*———
`Slze range
`Average slze
`Modal slze
`d5;
`(um)
`(uM)
`(um)
`
`
`99.0%_
`25
`32
`14—56
`Image analysis
`99.0%
`25
`31
`13—96
`Batch-type particle counter
`
`
`
`
`On-Iine particle counter 97.6% 15—85 28 25
`
`* Fraction of bubbles smaller than 55 um
`
`Nevertheless, the fraction of bubbles smaller than 55 pm ((155) in all measurements is more
`than 97%, so that the difference in size range is of little importance.
`From this comparison, the accuracy of measuring bubbles generated from DAF by a par-
`ticle counter is considered good enough to be used for process monitoring. The fast
`response of the on-line particle counter is an especially good feature.
`
`Bubble size in EF
`
`Both the image analysis method and the on-line particle counting method were used to
`measure the size of hydrogen bubbles generated from EF. The batch—type particle counting
`method cannot be used for EF, as described previously. The size distribution and cumula-
`tive distribution of bubbles are compared in Figure 5. The average size, modal size, and size
`range of bubbles are compared in Table 3.
`As the result of DAF experiments, a wider bubble size range was observed for the on-
`line particle counter compared with image analysis. The reason for this is expected to be the
`
`same as with DAF. The difference between the two methods for average bubble size and (135
`is slightly larger than observed for DAF. This is because of disturbance by the floc particles
`produced during electrolysis. Another error in the application of the new method in EF is
`
`80%
`
`60%
`
`G
`E"
`g 40%
`3
`
`20‘"
`’9
`
`0%
`
`
`Size Distribution of EF Bubbles
`Cumulative Size Dlstrlbutian of EF Bubbles
`1W6
`+0n-line
`
`
`
`« ———V7~_ fl- V w
`
`__ 7k
`
`
`
`‘
`+ImageAnalys|s
`
`m6 »
`
`g,l
`,
`"
`E 60% >
`2
`1'; 40%
`E
`0 N96 W.
`
`
`
`
`.
`
`.
`
`25
`
`35
`
`.
`
`5
`
`15
`
`.
`
`55
`45
`Sizefltm)
`
`.
`
`r
`
`75
`
`65
`
`85
`
`95
`
`0%
`
`i
`
`5
`
`15
`
`25
`
`35
`
`#
`55
`45
`SizeLum)
`
`..___..___..............................
`
`,_
`
`. On-llne
`
`
`+IrnageAnalysis
`l
`65
`75
`85
`95
`
`Figure 5 Comparison of bubble size distribution of EF
`
`81
`
`
`
`

`

`7919L19H'A'W
`
`Table 3 Size characteristics of bubbles measured by each method
`
`Size range
`Average slze
`Modal slze
`(135 '
`
` (um) (um) (um)
`
`
`
`Image analysis
`
`
`99.6%
`15
`18
`5—40
`On-Iine particle counter 94.2% 15—65 22 15
`
`
`
`
`* Fraction of bubbles smaller than 35 pm
`
`that bubbles smaller than 10 um cannot be counted even though those bubbles are actually
`generated in EF. However, because the fraction of those bubbles is very small, 4% in this
`study, the new method is considered to be quite acceptable also in EF in spite of these
`problems.
`
`Bubble size comparison between DAF and EF
`
`Since it is found from above experiments that the on-line particle counting method can pro-
`duce data of reasonable accuracy, the sizes of bubbles generated from DAF and EF are
`compared as in Figure 6 and Table 4.
`The size of bubbles produced in DAF is in the range of 15—85 pm and the average size is
`around 28 pm, whereas the size produced by EF is in the range of 15—65 pm and the average
`is 22 pm. This result supports the generally known fact that DAF generates larger bubbles
`than EF does.
`
`The average size of the bubbles produced by DAF in this work is smaller than those sizes
`reported in the literature. The reason is that in this study the bubbles are measured immedi-
`ately after release from a 6 atm pressure vessel. Literature values are measured from a con—
`tact zone in an operating DAF plant in which the pressures are reduced by passage through
`piping, valve, and orifice. Lower pressures tend to increase the size of the bubbles. In addi—
`tion, because the chance of bubble coalescence increases with the time between generation
`and measurement, the size of bubbles will increase.
`
`In practice, it has been a generally accepted concept that smaller bubbles are preferred in
`order to achieve a larger bubble surface area and so to maximize mass transfer. However, if
`the collision and attachment mechanisms are considered in DAF and EF processes, the
`Cumulative Size Distribution ofDAF and EF Bubbles
`Comparison of DAF and EF Bubble Size
`
`..._L.,u.
`
`mg.4..2has
`
`_ +DAF _
`
`
`
`Percentage
`
` Sizemm) -
`
`
`
`
`
`
`CumulativePercentage
`
`Figure 6 Comparison of DAF and EF bubble size distribution
`
`Table 4 Size characteristics of bubbles generated by DAF and EF
`h—J
`Slze range
`Average slze
`Modal slze
`das'
`(um)
`(um)
`(um)
`\_——_—__—_—//
`
`DAF
`EIectro-flotation
`
`15—85
`15—65
`
`28
`22
`
`87.6%
`25
`
`15 94.2%
`
`82
`
`* Fraction of bubbles smalier than 35 pm
`
`

`

`optimum size of bubbles should be dependent on the size of particles to be removed. The
`effect of bubble size and particle size on the collision efficiency in DAF has been modeled
`by Han (2001).
`
`conclusion
`In this research, a new method to measure bubble size distribution was developed by using
`commercially available batch-type and on-line particle counters. The results compare well
`with the traditional but laborious image analysis method. The batch—type counter is not
`suitable for measurement of the size of bubbles generated from EF because of disturbance
`by the EF electric current. Although there are some discrepancies, the on—line particle
`counter can produce reasonably accurate results in a very short time.
`The bubble counting method described in this paper will be helpful for research in DAF
`, and EF processes, either theoretically or practically. The mechanism of bubble and particle
`collision and its effect on the removal efficiency can be described. An optimum operating
`condition of the bubble generation system and/or pretreatment system can be diagnosed by
`measuring the size of bubble at several places in the reactor and processes.
`
`Acknowledgement
`The authors wish to acknowledge J. Lee (Seoul National University) for the contribution
`and assistance during the experiment. This work is funded by MOCT under the project,
`2001-JAYU A09.
`
`References
`Water Quality and Treatment 5!]: Ed. (1999). American Water Works Association, McGraw Hill, USA.
`Burns, S.E., Yiacoumi, S. and Tsouris, C. (1997). Microbubble Generation for Environmental and
`Industrial Separations, Separation and Purification Technology 11, 221—232.
`Edzwald, J. (1995). Principles and Applications of Dissolved Air Flotation. Wat. Sci. & Tech, 31(3—4),
`1—23.
`
`Han, M.Y. (2002). Modeling of DAF: the effect of particle and bubble characteristics, Journal of Water
`Supply: Research and Technology —AQUA 51 27—34.
`Han, M.Y., Kim, W.T. and Dockko, S. (2001). Collision Efficiency Factor of Bubble and Particle (abp) in
`DAF: Theory and Experimental Verification, Wat. Sci. & Tee/1., 43(8), 139—144.
`
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`