The MBR Book: Principles and Applications of Membrane

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Fundamentals 95 2.3.9.2 Employing appropriate physical or chemical cleaning protocols Cleaning strategies have been outlined in Section 2.1.4.3, and protocols applied in practice are detailed in Chapters 4 (for comparative pilot plant studies) and 5 (fullscale reference sites). A summary of these data is presented in Section 3.3.1.2, along with the implications of the physical and chemical cleaning protocols on process design and operation. Results from selected bench-scale studies are given below. Physical cleaning Key general cleaning parameters are duration and frequency, since these determine process downtime. For backflushing, a further key parameter is the backflush flux, generally of 1–3 times the operational flux and determined by the backflush TMP. Less frequent, longer backflushing (600 s filtration/45 s backflushing) has been found to be more efficient than more frequent but shorter backflushing (200 s filtration/15 s backflush) (Jiang et al., 2005). In another study based on factorial design, backflush frequency (between 8 and 16 min) was found to have more effect on fouling removal than either aeration intensity (0.3 to 0.9 m 3 /h per m 2 membrane area) or backflush duration (25–45 s) for an HF iMBR (Schoeberl et al., 2005). Hence, although more effective cleaning would generally be expected for more frequent and longer backflushing, the possible permutations need exploring to minimise energy demand. This has been achieved through the design of a generic control system which automatically optimised backflush duration according to the monitored TMP value (Smith et al., 2005). However, increasing backflush flux leads to more loss product and reduces the net flux. Air can also be used to affect backflushing (Sun et al., 2004) or to enhance backflush with water. Up to 400% in the net flux over that attained from continuous operation has been recorded using an air backflush, although in this case 15 min of air backflush were required every 15 min of filtration (Visvanathan et al., 1997). Whilst air backflushing is undoubtedly effective, anecdotal evidence suggests that it can lead to partial drying out of some membranes, which can then produce embrittlement and so problems of membrane integrity. Membrane relaxation encourages diffusive back transport of foulants away from the membrane surface under a concentration gradient, which is further enhanced by the shear created by air scouring (Chua et al., 2002; Hong et al., 2002). Detailed study of the TMP behaviour during this type of operation revealed that, although the fouling rate is generally higher than for continuous filtration, membrane relaxation allows filtration to be maintained for longer periods of time before the need for cleaning arises (Ng et al., 2005). Although some authors have reported that this type of operation may not be economically feasible for operation of large-scale MBRs (Hong et al., 2002), relaxation is almost ubiquitous in modern full-scale iMBRs (Chapter 5). Recent studies assessing maintenance protocols have tended to combine relaxation with backflushing for optimum results (Vallero et al., 2005; Zhang et al., 2005). In practice, physical cleaning protocols tend to follow those recommended by the suppliers. Relaxation is typically applied for 1–2 min every 8–15 min of operation, both for FS and HF systems. For HF systems, backflushing, if employed, is usually applied at fluxes of around 2–3 times the operating flux and usually supplements rather than displaces relaxation. It is likely that operation without backflushing, whilst notionally increasing the risk of slow accumulation of foulants on or within
96 The MBR Book Table 2.14 Examples of intensive chemical cleaning protocols, four MBR suppliers Technology Type Chemical Concentration (%) Protocols Mitsubishi CIP NaOCl 0.3 Backflow through membrane (2 h) � soaking (2 h) Citric acid 0.2 Zenon CIA NaOCl 0.2 Backpulse and recirculate Citric acid 0.2–0.3 Memcor CIA NaOCl 0.01 Recirculate through lumens, mixed liquors and in-tank air manifolds Citric acid 0.2 Kubota CIP NaOCl 0.5 Backflow and soaking (2 h) Oxalic acid 1 Exact protocol for chemical cleaning can vary from one plant to another (Section 3.3.1.2). CIP: Cleaning in place, without membrane tank draining; chemical solutions generally backflushed under gravity in-to-out. CIA: Cleaning in air, where membrane tank is isolated and drained; module rinsed before soaking in cleaning solution and rinsed after soaking to remove excess reagent. the membrane, conversely largely preserves the biofilm on the membrane which affords a measure of protection. This fouling layer is substantially less permeable and more selective than the membrane itself, and thus can be beneficial to the process provided the total resistance it offers does not become too great. Chemical cleaning Physical cleaning is supplemented with chemical cleaning to remove “irreversible” fouling (Fig. 2.10), this type of cleaning tending to comprise some combination of: ● CEB (on a daily basis), ● Maintenance cleaning with higher chemical concentration (weekly), ● Intensive (or recovery) chemical cleaning (once or twice a year). Maintenance cleaning is conducted in situ and is used to maintain membrane permeability and helps reduce the frequency of intensive cleaning. It is performed either with the membrane in situ, a normal CIP, or with the membrane tank drained, sometimes referred to as “cleaning in air” (CIA). Intensive, or recovery, cleaning is either conducted ex situ or in the drained membrane tank to allow the membranes to be soaked in cleaning reagent. Intensive cleaning is generally carried out when further filtration is no longer sustainable because of an elevated TMP. Recovery chemical cleaning methods recommended by suppliers (Table 2.14) are all based on a combination of hypochlorite for removing organic matter, and organic acid (either citric or oxalic) for removing inorganic scalants. Whilst some scientific studies of the impacts of chemical cleaning on the MBR system, such as the microbial community (Lim et al., 2004), have been conducted, there has been no systematic study comparing the efficacy of a range of cleaning reagents or cleaning conditions on permeability recovery. Some experiments with augmented cleaning, such as sonically-enhanced processes (Fang and Shi, 2005; Lim and Bai, 2003), have been conducted, however.
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The MBR Book
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The MBR Book: Principles and Applic
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Contents Preface ix Contributors xi
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Contents vii 4.2.5 The Industrial T
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Preface What’s In and What’s No
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Term Meaning Common units MLD Megal
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Contributors A number of individual
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Contributor(s) Association/Organisa
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Introduction With acknowledgements
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such as the filtration market, tech
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D R IVE R S R EST R AI N TS Bathing
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Introduction 7 Much of the legislat
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of non-point source pollution contr
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exploitation index (WEI), the value
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1 500 000 1 250 000 1 000 000 750 0
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Alternative immersed FS and HF memb
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1.6 Conclusions Whilst the most sig
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Introduction 19 USEPA (2006b) www.e
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Fundamentals With acknowledgements
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they can be put, which then provide
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3µm (a) (b) membrane is chemically
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Table 2.2 Membrane configurations C
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2.1.4 Membrane process operation 2.
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only pseudo-steady-state (or stabil
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P max P dP/dt backwash cycle t b Ba
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Fundamentals 35 2.1.4.6 Critical fl
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neo-exponential increase at fluxes
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Screened raw sewage biologically ar
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Table 2.4 Microbial metabolism type
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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
Page 102 and 103: (Cui et al., 2003) by inducing liqu
Page 104 and 105: Fundamentals 87 air cannot be used
Page 106 and 107: Table 2.12 Dynamic effects Determin
Page 108 and 109: Fundamentals 91 Table 2.13 Sub-crit
Page 110 and 111: Fundamentals 93 sludge (Cho and Fan
Page 114 and 115: Fundamentals 97 Whilst ultrasonic c
Page 116 and 117: and immersed hybrid PAC-MBR (Kim an
Page 118 and 119: Lastly, the vast majority of all st
Page 120 and 121: Fundamentals 103 Brookes, A., Judd,
Page 122 and 123: Fundamentals 105 Côté, P., Buisso
Page 124 and 125: Fundamentals 107 Fuchs, W., Schatzm
Page 126 and 127: Fundamentals 109 Howell, J.A., Chua
Page 128 and 129: Fundamentals 111 Krauth, K. and Sta
Page 130 and 131: Fundamentals 113 Liu, R., Huang, X.
Page 132 and 133: Fundamentals 115 Nielson, P.H. and
Page 134 and 135: Fundamentals 117 Sato, T. and Ishii
Page 136 and 137: Fundamentals 119 Van Lier, J.B. (19
Page 138 and 139: Fundamentals 121 Zhang, Y., Bu, D.,
Page 140 and 141: Design With acknowledgements to: Ch
Page 142 and 143: Other contributions to pumping ener
Page 144 and 145: where J c is the cleaning flux. Fro
Page 146 and 147: Table 3.1 Main features of aeration
Page 148 and 149: Table 3.2 Biological operating para
Page 150 and 151: Table 3.3 Physical operating parame
Page 152 and 153: Table 3.4 Comparative pilot plant t
Page 154 and 155: Table 3.7 O&M data Design 137 Kubot
Page 156 and 157: Table 3.8 Feedwater quality, PLWTP
Page 158 and 159: Table 3.11 Cleaning protocols for t
Page 160 and 161: 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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The MBR Book: Principles and Applications of Membrane

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