3. System Design3.1 IntroductionAn entire reverse osmosis (RO)/nanofiltration (NF) water treatment system consists of the pretreatment section, themembrane element section, and the post-treatment section. Pretreatment techniques are discussed in Section 2, WaterChemistry and Pretreatment. Post-treatment is employed to achieve the required product quality. In seawater desalination,this is usually pH adjustment, rehardening and disinfection. In ultrapure water (UPW) production, the permeate is usuallypost-treated by polishing ion exchange demineralization.In this section, the membrane system is addressed. The system includes a set of membrane elements, housed in pressurevessels that are arranged in a certain manner. A high-pressure pump is used to feed the pressure vessels. Instrumentation,spare parts and tools for services are added as required. A clean-in-place (CIP) system facilitates cleaning of themembranes. This is described in Section 6, Cleaning and Sanitization.The membrane system is a complete plant with an inlet for feed water and outlets for permeate and concentrate. RO/NFsystem performance is typically characterized by two parameters, permeate (or product) flow and permeate quality. Theseparameters should always be referenced to a given feed water analysis, feed pressure and recovery. The goal of thedesigner of an RO/NF system for a certain required permeate flow is to minimize feed pressure and membrane costs whilemaximizing permeate quality and recovery.The optimum design depends on the relative importance of these aspects. The recovery of brackish water systems is limitedby the solubility of sparingly soluble salts (see Section 2.4, Scaling Calculations)—90% is about the maximum. In seawaterdesalination, the limit of about 50% recovery is dictated by the osmotic pressure of the concentrate stream, whichapproaches the physical pressure limit of the FILMTEC seawater element.Obtaining the requested salt rejection is mainly a matter of membrane selection. The NF (NF270 > NF200 > NF90), brackishwater (BW) (extra low energy (XLE) > BW30LE > BW30), SW (seawater), and SWHR (seawater high rejection) versions ofthe FILMTEC NF and RO membrane have higher salt rejections in this order, but they also need higher feed pressuresunder the same conditions. Therefore, the NF to BW30LE membrane is typically applied to feed waters up to 2,000 mg/Ltotal dissolved solids (TDS), BW30 up to 10,000 mg/l, and SW and SWHR to high salinity feed waters up to 50,000 mg/L.For given operating conditions, the permeate quality can be calculated.The feed pressure needed to produce the required permeate flow for a given membrane depends on the designed permeateflux (permeate flow rate per unit membrane area). The higher the permeate flow per unit of active membrane area, thehigher the feed pressure. In seawater systems the permeate flux is relatively low even at maximum allowed pressure.However, the permeate flux could be very high in brackish water systems without reaching the limit of 600 psi (41 bar) forbrackish water elements. Although it is tempting to increase the permeate flux to minimize the costs for membrane elements,the flux has to be limited to minimize fouling.From experience, the flux limit to be used in system design depends on the fouling tendency of the feed water. A systemdesigned with high permeate flux rates is likely to experience higher fouling rates and more frequent chemical cleaning. Onlyexperience can set the limits on permeate flux for different types of waters. When designing a membrane system for aspecific feed water, it is advantageous to know the performance of other membrane systems operating on the same water.However, quite often there are no other membrane systems for comparison. Then the system design suggestions in DesignGuidelines for 8-inch (Section 3.9.1) and Midsize FILMTEC elements (Section 3.9.2) could be followed.Further information required to design a system is best collected by using the forms of Table 3.1 and Table 3.2. The morecomplete this information, the better the system design can be optimized towards the customer’s needs.Page 70 of 180 ® Trademark of The Dow Chemical <strong>Company</strong> ("Dow") or an affiliated company of Dow Form No. 609-00071
Table 3.1 System design informationQuotation Number:.............. Date Requested:........................Date Submitted: .................. Requested By: ...........................Customer/OEM: .................................................................................................................................................Address:.............................................................................................................................................................Proposed Location: ............................................................................................................................................Brief Description:......................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................Required Product Flow Rate (gpd or m 3 /h): .......................................................................................................Expected Recovery:...........................................................................................................................................Annual Water Temperature Range High °C: ...............................................................................................Low °C:................................................................................................Design °C: ...........................................................................................NF/RO Plant: Indoors OutdoorsDesigned for Continuous Use: Yes NoIf not, state needed peak hourly capacity:......................Plant Will Be Operated By: Enduser Yes NoTrained Personnel Yes NoEquipment Manufacturer Yes NoOthers Yes NoWater Source: Well Water Softened water Surface Water Filtered Effluent Water Sea Water OtherExisting Pretreatment Yes No SDI...................................................................List of Pretreatment Steps:............................................................................................................................................................................................................................................................................................................Planned Pretreatment: .......................................................................................................................................Bacterial Control: Yes No Dechlorination: Ac-FilterChlorine Used Yes No Na-BisulfiteChloramines Used: Yes No OtherAntiscalant Used: Yes No Which One?................................................Desired Acidification: HCl H 2 SO 4 NoneBrief Description of Other Pretreatment Steps:..................................................................................................(e.g., clarification, flocculation, multimedia/sand filtration, etc.......................................................................................................................................................................................................................................................Application: Potable Water Industrial Supply for: Boiler Feed Pharma Electronics OtherSpecify Water Quality Needed after RO Treatment: .....................................................................................................................................................................................................................................................................State Other Desired Design Criteria:........................................................................................................................................................................................................................................................................................................................................................................................................................................................................Page 71 of 180 ® Trademark of The Dow Chemical <strong>Company</strong> ("Dow") or an affiliated company of Dow Form No. 609-00071
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DowWater SolutionsFILMTEC Reverse O
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2.6 Biological Fouling Prevention .
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1. Basics of Reverse Osmosis and Na
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Nanofiltration (NF)Nanofiltration r
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How to Use Reverse Osmosis and Nano
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1.4 Membrane DescriptionThe FILMTEC
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Membrane systems are typically desi
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1.8 Element CharacteristicsFILMTEC
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- Page 21 and 22: SeawaterSeawater with TDS of 35,000
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4. During recirculation of cleaning
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2. The cleaning pump should be size
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6.7 Effect of pH on Foulant Removal
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Cleaning ProcedureThere are seven s
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If the organic fouling is the resul
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There are two factors that greatly
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7. Handling, Preservation and Stora
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7.4 Preservation of RO and NF Syste
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If the normalized actual performanc
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8.3.3 Localization of High Solute P
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Figure 8.2 Permeate probing apparat
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8.4.5 Performance TestThe standard
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8.5.1.1 Low Flow and Normal Solute
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. Metal Oxide FoulingMetal oxide fo
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. Organic FoulingThe adsorption of
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8.5.3 High Pressure DropHigh differ
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In case of fullfit or heat sanitiza
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Breakpoint chlorinationBreak tankBr
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FeedThe input solution to a treatme
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Milligram per litre (mg/L)Mixed-bed
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SBS Sodium bisulfite, NaHSO 3.Scale
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9.2 Specific Conductance of Sodium
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Figure 9.1 Conductivity of ionic so
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9.6 Temperature Correction FactorTa
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9.9 Osmotic Pressure of Sodium Chlo
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Details - TestEquipment andSpecific
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satisfactory for such a determinati
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case for almost all tested biocides
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9.12 Key Word IndexAbrasion - 150 B
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Positive displacement pump - 95 Shu