The MBR Book: Principles and Applications of Membrane

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Fundamentals 35 2.1.4.6 Critical flux The critical flux concept was originally presented by Field et al. (1995). These authors stated that: “The critical flux hypothesis for microfiltration/ultrafiltration processes is that on start-up there exists a flux below which a decline of flux with time does not occur; above it, fouling is observed”. Two distinct forms of the concept have been defined. In the strong form, the flux obtained during sub-critical flux is equated to the clean water flux measured under the same conditions. However, clean water fluxes are rarely attained for most real feedwaters due to irreversible adsorption of some solutes. In the alternative weak form, the sub-critical flux is the flux rapidly established and maintained during start-up of filtration, but does not necessarily equate to the clean water flux. Alternatively, stable filtration operation, that is, constant permeability for an extended time period, has been defined as sub-critical operation even when preceded by an initial decline in flux (Howell, 1995). Such conditions would be expected to lead to lower critical flux values than those obtained for constant permeability operation, however, since an initial permeability decline implies foulant deposition. A number of slightly different definitions of sub-critical flux operation have been proposed, largely depending on the method employed. The most microscopically precise definition equates the critical flux to that flux below which no deposition of colloidal matter takes place. Kwon and Vigneswaran (1998) equated critical flux to the lift velocity as defined by the lateral migration theory of Green and Belfort (1980). This rigorous definition is difficult to apply because of the relative complexity of the determination of the lift velocity, particularly for heterogeneous matrices. On the other hand, experimental determination of critical flux by direct observation of material deposition onto the membrane has been conducted using model homodispersed suspensions of polystyrene latex particles (Kwon and Vigneswaran, 1998), and some authors have also used mass balance determinations (Kwon et al., 2000). Given the limitations of applying particle hydrodynamics to the identification of the critical flux in real systems, recourse generally has to be made to experimental determination. By plotting flux against the TMP it is possible to observe the transition between the linearly pressure-dependent flux and the onset of fouling, where deviation from linearity commences. The flux at this transition has been termed “secondary critical flux” (Bouhabila et al., 1998) and, more recently, the concept of “sustainable flux” has been introduced, defined as the flux for which the TMP increases gradually at an acceptable rate, such that chemical cleaning is not necessary (Ng et al., 2005). Whilst potentially useful in providing a guide value for the appropriate operating flux, the absolute value of the critical flux obtained is dependent on the exact method employed for its determination and, specifically, the rate at which the flux is varied with time. A common practice is to incrementally increase the flux for a fixed duration for each increment, giving a stable TMP at low flux but an ever-increasing rate of TMP increase at higher fluxes (Fig. 2.13). This flux-step method defines the highest flux for which TMP remains stable as the critical flux. This method is preferred over the corresponding TMP-step method since the former provides a better control of the flow of material deposition on the membrane surface, as the convective flow of solute towards the membrane is constant during the run (Defrance and Jaffrin, 1999). No single protocol has been agreed for critical flux measurement, making
36 The MBR Book TMP (mbar) 300 200 100 0 0 1 2 3 4 5 Time (h) Figure 2.13 Flux and pressure relationship for 15-min flux steps, MBR biomass (Le-Clech et al., 2003b) TMP (mbar) 150 100 50 10 LMH 8 LMH 0 0 2 4 6 8 10 Time (d) 6 LMH comparison of reported data difficult, though a practical method based on a threshold permeability change has been proposed by Le-Clech et al. (2003b). Within the last few years, it has become apparent from bench- and pilot-scale studies that irreversible fouling of MBR membranes can take place at operation well below the critical flux. Pertinent studies have been summarised by Pollice et al. (2005). Sub-critical flux fouling appears to be characterised by a sudden discontinuity of the TMP (Fig. 2.14, 4 LMH line) at very low flux operation after some extended time period (Brookes et al., 2004; Ognier et al., 2001; Wen et al., 2004) and a steady 25 20 15 10 5 0 J (LMH) 4 LMH Figure 2.14 TMP transients for sub-critical flux operation (Brookes et al., 2004) 2 LMH
Page 2 and 3: The MBR Book
Page 4 and 5: The MBR Book: Principles and Applic
Page 6 and 7: Contents Preface ix Contributors xi
Page 8 and 9: Contents vii 4.2.5 The Industrial T
Page 10 and 11: Preface What’s In and What’s No
Page 12 and 13: Term Meaning Common units MLD Megal
Page 14 and 15: Contributors A number of individual
Page 16 and 17: Contributor(s) Association/Organisa
Page 18 and 19: Introduction With acknowledgements
Page 20 and 21: such as the filtration market, tech
Page 22 and 23: D R IVE R S R EST R AI N TS Bathing
Page 24 and 25: Introduction 7 Much of the legislat
Page 26 and 27: of non-point source pollution contr
Page 28 and 29: exploitation index (WEI), the value
Page 30 and 31: 1 500 000 1 250 000 1 000 000 750 0
Page 32 and 33: Alternative immersed FS and HF memb
Page 34 and 35: 1.6 Conclusions Whilst the most sig
Page 36 and 37: Introduction 19 USEPA (2006b) www.e
Page 38 and 39: Fundamentals With acknowledgements
Page 40 and 41: they can be put, which then provide
Page 42 and 43: 3µm (a) (b) membrane is chemically
Page 44 and 45: Table 2.2 Membrane configurations C
Page 46 and 47: 2.1.4 Membrane process operation 2.
Page 48 and 49: only pseudo-steady-state (or stabil
Page 50 and 51: P max P dP/dt backwash cycle t b Ba
Page 54 and 55: neo-exponential increase at fluxes
Page 56 and 57: Screened raw sewage biologically ar
Page 58 and 59: Table 2.4 Microbial metabolism type
Page 60 and 61: which affords the operator complete
Page 62 and 63: Cumulative %ile undersize 1 0.8 0.6
Page 64 and 65: occurs from the surrounding air to
Page 66 and 67: (Madoni et al., 1993). The inter-re
Page 68 and 69: Viscosity (mPa s) 100 10 1 Viscosit
Page 70 and 71: on discharged P levels have been im
Page 72 and 73: Membrane process mode Diffusion Ext
Page 74 and 75: energy demand in kWh/m 3 permeate p
Page 76 and 77: Table 2.5 System facets of denitrif
Page 78 and 79: Fundamentals 61 Moreover, the poten
Page 80 and 81: iomass. There are also issues with
Page 82 and 83: Table 2.6 Effect of pore size on MB
Page 84 and 85: Fundamentals 67 fouling to be influ
Page 86 and 87: Fundamentals 69 fouling (i.e. membr
Page 88 and 89: 2.3.6 Feed and biomass characterist
Page 90 and 91: Fouling relative distribution (%) 1
Page 92 and 93: has been proposed by Cho and co-wor
Page 94 and 95: Fundamentals 77 in the influent. Ab
Page 96 and 97: MLSS sample Centrifugation 5 min 50
Page 98 and 99: Table 2.11 Concentration of SMP com
Page 100 and 101: Fundamentals 83 correlation of MBR
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(Cui et al., 2003) by inducing liqu
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Fundamentals 87 air cannot be used
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Table 2.12 Dynamic effects Determin
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Fundamentals 91 Table 2.13 Sub-crit
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Fundamentals 93 sludge (Cho and Fan
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Fundamentals 95 2.3.9.2 Employing a
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Fundamentals 97 Whilst ultrasonic c
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and immersed hybrid PAC-MBR (Kim an
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Lastly, the vast majority of all st
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Fundamentals 103 Brookes, A., Judd,
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Fundamentals 105 Côté, P., Buisso
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Fundamentals 107 Fuchs, W., Schatzm
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Fundamentals 109 Howell, J.A., Chua
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Fundamentals 111 Krauth, K. and Sta
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Fundamentals 113 Liu, R., Huang, X.
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Fundamentals 115 Nielson, P.H. and
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Fundamentals 117 Sato, T. and Ishii
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Fundamentals 119 Van Lier, J.B. (19
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Fundamentals 121 Zhang, Y., Bu, D.,
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Design With acknowledgements to: Ch
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Other contributions to pumping ener
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where J c is the cleaning flux. Fro
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Table 3.1 Main features of aeration
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Table 3.2 Biological operating para
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Table 3.3 Physical operating parame
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Table 3.4 Comparative pilot plant t
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Table 3.7 O&M data Design 137 Kubot
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Table 3.8 Feedwater quality, PLWTP
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Table 3.11 Cleaning protocols for t
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Figure 3.1 The planned location of
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Table 3.14 O&M data, Pietramurata W
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Design 147 Table 3.17 Design inform
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Maintenance CIP was conducted throu
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Permeability, LMH/bar 800 700 600 5
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Table 3.22 Summary of pilot plant p
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Table 3.25 Feedwater specification
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Table 3.34 Aeration design Paramete
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In short, the design calculation de
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complications arise when estimating
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Chapter 4 Commercial Technologies W
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4.1 Introduction Available and deve
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Commercial technologies 167 suction
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synonymous with R V Equation (3.13)
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(a) (b) Figure 4.8 The Huber VRM ®
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and is very robust. However, the la
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Commercial technologies 175 (a) (b)
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(a) (b) (c) Commercial technologies
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Other equipment 1.11% Process air b
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Thus far, almost all of the install
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Figure 4.22 A rack of Memcor B10R m
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Tensile elongation retention (%) 10
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Figure 4.28 Pilot plant at Mooka Co
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at 10 000-12 000 mg/L. The membrane
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4m 4m 1m Commercial technologies 19
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Figure 4.36 Ejector aerator Commerc
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Denitrification Nitrification Waste
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modules, with pore sizes ranging fr
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(a) (b) Figure 4.46 (a) Han-S Envir
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aerobic counterpart. This may be pa
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of the particularly large-diameter
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(c) air channelling, the risk of wh
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Case Studies With acknowledgements
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5.1 Introduction Membrane Bioreacto
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Case studies 211 Table 5.1 Comparis
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Case studies 213 0.6 m 3 per unit.
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Case studies 215 area of 15 840 m 2
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Aeration tank 1 FBDA FBDA 32 x J200
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Case studies 219 In this UNR config
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Table 5.6 Design criteria, Running
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Works inlet Inlet works Storm tank
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Case studies 225 to be treated to a
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Case studies 227 membranes, assembl
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Figure 5.16 A Naston package plant
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Air Influent DN N M Figure 5.18 The
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Table 5.9 Toray membrane-based MBR
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Figure 5.23 Aeration tank and cover
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Figure 5.24 The original plant at B
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Main permeate header Permeate pump
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Case studies 241 flow. Sludge waste
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Table 5.15 Water quality data, Unif
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TMP (Kpa) 80 70 60 50 40 30 20 10 0
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10 LMH; the plant operated at fluxe
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Table 5.17 Feed and treated water q
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Table 5.18 Water quality, Sobelgra
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Figure 5.37 Airlift municipal WWTP,
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Case studies 255 has been 20 g/L, b
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Case studies 257 The company had in
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Filtrate (ml) 25 20 15 10 5 IIndust
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Inflow Buffer tank Filtration Denit
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Figure 5.45 The VHP MBR (a) (b) Cas
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Figure 5.47 The Eden Project MBR Ba
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Table 5.25 Basis for process design
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5.4.7 Other Orelis plant Case studi
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two membrane module configurations.
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Appendix A Blower Power Consumption
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or or (A.4) where � is the ratio
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Appendix B MBR Biotreatment Base Pa
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Y 0.61 g VSS/g COD Fan et al. (1996
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Appendix C Hollow Fibre Module Para
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L being the internal module length
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Appendix D Membrane Products
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Table D.3 Membrane module details o
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Table D.4 (continued) Supplier Asah
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Table D.5 Membrane module details o
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Appendix E Major Recent MBR and Was
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Conference title meet Dates Locatio
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Event Last held Location Website Fo
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Appendix F Selected Professional an
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Japan Water Works Association (JWWA
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Nomenclature � Separation (m) �
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Nomenclature 305 Rsup Hydraulic res
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Abbreviations The following lists k
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PES Polyethylsulphone PP Polypropyl
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Glossary of Terms A number of key t
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Floc Aggregated solid (biomass) par
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Glossary of terms 315 Relaxation Ce
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Index A � factor 47, 49-50 and vi
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investment 9 for membrane replaceme
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I Iberia 2 immersed biomass-rejecti
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Nordkanal wastewater treatment work
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SUR unit 180 surface porosity 30 Su
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