INTRODUCTION > Reverse Osmosis

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2 By applying pressure to a fluid on one side of a semi-permeable membrane, it is possible to reverse the natural flow of pure water from an area of high salt concentration to one of low concentration. This process is called Reverse Osmosis. MEMBRANE OSMOSIS Water flows through a membrane from the side of low salt concentration to the side of high salt concentration. EQUILIBRIUM Osmotic Pressure is the pressure required to stop the water flow and reach equilibrium. Osmosis In the process of Osmosis, water naturally moves from an area of low salt concentration through a semipermeable membrane to an area of high salt concentration. The movement of a pure water to equalise salt concentrations on each side of the membrane generates a pressure called Osmotic Pressure. OSMOTIC PRESSURE APPLIED PRESSURE REVERSE OSMOSIS By applying an external pressure greater than Osmotic Pressure, the flow of water is reversed. Water now flows from high to low salt concentration. Reverse Osmosis Reverse Osmosis (RO) is a filtration method that removes many types of large molecules and ions from solutions by applying pressure to the solution when it is on one side of a selective, or semi-permeable, membrane. The result is that salts are retained on the pressurised side of the membrane, and the pure water is allowed to pass to the other side. To be selective, the membrane should not allow large molecules or ions through the pores (holes), but should allow smaller components of the solution (i.e. the water itself) to pass freely. RO is most commonly known for its use in drinking water purification from seawater and brackish or waste water, removing salts and other unwanted substances from the water. It also provides the highest levels of all available filtration methods, and is often used in combination with other methods in order to optimise the overall performance and operating parameters of the system, based on the feed water quality. 01

3 Sustainable Flux In fluid dynamics, flux is the rate of volume flow across a unit area. Typical units of measurement are: gallons per square foot per day (gfd), or litres per square metre per hour (lmh). All RO systems look to maximise flux (i.e. the volume of feed water passing through a unit area of the membrane) while minimising scaling and fouling of the membrane. Scaling and fouling lead to greater energy consumption, poorer quality water being produced, and higher maintenance costs. Every membrane filtration system has a critical flux, determined by the nature of the feed water and the set of system operating parameters. Critical flux is defined as the point where the combination of the nature of the feed water and the set of system operating parameters results in a loss of flux due to fouling, scaling or particle deposits on the surface of the membrane. Sustainable flux is therefore the flux that can be maintained over an extended period for the given feed water and system operating parameters, with minimal scaling and fouling of the membrane surface. Membrane manufacturers supply membrane elements with a set of wet test parameters obtained via tests on fouling and scaling free water. In order to ensure stable operation which in most cases is well below the wet test parameters the recommended system operating parameters that will create a sustainable flux are chosen to fall below the critical flux. For instance, a low pressure RO element (8 or 16 diameter) may show 30 gfd (~51 lmh) flux in the manufacturer s wet test for a given membrane type. In the case of 8 diameter elements, however, the critical flux may be just 12 gfd (~20 lmh) under a normal set of operating parameters for secondary waste water well below the wet test flux. If the membrane were to be incorporated in a conventionallydesigned 16 diameter element, the results would be identical, or even a little lower. The operating parameters would therefore typically be chosen at 10 gfd (~17 lmh) with the purpose of operating within a safety margin. Simply put, increasing the sustainable flux rate of a RO system reduces the membrane surface area required and, therefore, the number of membrane elements and pressure vessels needed. This reduction in membrane elements translates to a smaller plant size, and lower capital and operating costs as membrane replacement and general maintenance costs are reduced. A more efficient plant means lower water-cleaning costs. 02

4 FILTRATION MICRO-FILTRATION ULTRA-FILTRATION NANO-FILTRATION REVERSE OSMOSIS SAND BACTERIA VIRUSES PROTEINS IONS 10+ MICRONS THE FILTRATION SPECTRUM A comparison of the rejection capabilities of reverse osmosis with other membrane technologies. NuWater RO Treatment Plants NuWater RO treatment plants utilise large diameter 16 pressure vessels and membrane elements, incorporating our proprietary Integrated Flow Distributor (IFD) and Electromagnetic Field (EMF) device, as well as an innovative membrane element configuration. This combination of technologies radically improves hydraulic conditions within the pressure vessels and membrane elements, resulting in a substantial increase in critical flux, and therefore sustainable flux. NuWater 16" plants are simply more efficient than conventional 8" plants. In the case of secondary waste water, the critical flux in a NuWater RO module is around 28 gfd (~48 lmh) and the sustainable flux can therefore be comfortably chosen at 24 gfd (41 lmh). This is significantly better than conventional 8 systems where the corresponding sustainable flux is in the region of 10 gfd (17 lmh). Similar improvements in hydraulic conditions are achieved for NuWater s seawater desalination plants. The wet test data for a seawater element typically indicates flux in the region of 20 gfd (34 lmh). Most conventional SWRO plants using conventional 8 elements operate at a sustainable flux of 6 to 10 gfd (~10 to 17 lmh). NuWater SWRO large diameter 16 plants consistently operate at a significantly higher sustainable flux of 13 to 16 gfd (~22 to 27 lmh). The improved hydraulic conditions in NuWater plant RO modules is achieved by far greater control over fouling, scaling and particle deposits on the elements, with the IFD greatly reducing or completely eliminating microbial fouling in the front end of the plant. This type of fouling is generally the limiting parameter for sustainable flux in conventional plants using 8 diameter elements. The IFD ensures an even distribution of the feed flow and creates higher cross-flow velocity, allowing flux to be increased without the normally-associated fouling of the membrane surface. Our EMF device further reduces fouling potential by causing microbes (particles) to aggregate, thereby preventing them from depositing on the membrane surface. The EMF device also changes the morphology of potential scaling substances that can form in the last few elements of the vessel where solubility of the substances may be exceeded. In a NuWater plant, for instance, calcium sulfate will precipitate as a fluffy, instead of a crystalline substance, which can form a boundary (or cake) layer on the membrane. The fluffy substance is easily swept away by the concentrate flow without depositing on the membrane surface, avoiding harmful build-up of scale. NuWater s innovative 16 plants also use a maximum of four elements per pressure vessel, ensuring optimum concentrate flow and facilitating a simple clean-in-place (CIP) process that runs without interrupting production. Membrane and plant performance levels are therefore maintained. Conversely, it is generally accepted that conventional 8 RO plants require a thorough off-line cleaning procedure when the plant has lost 10% to 15% flux due to fouling, which results in a reduction in plant capacity. NuWater plants therefore achieve something new and unique; a high sustainable flux over long periods of time without performing tedious, expensive and time-consuming cleaning procedures. 03

5 NuWater RO Benefits The 16 RO technology incorporated in NuWater s water treatment plants has confounded academics and competitors alike, as it defies long-held views on achievable sustainable flux. NuWater s plants consist of coupled trailer-mounted modules, making them scalable, more cost-effective and smaller than conventional 8 RO plants. These higher sustainable flux rates, and the use of large diameter 16 pressure vessels and membrane elements, mean that NuWater plants have footprints significantly smaller than conventional 8 plants. This allows NuWater large capacity plants to be modular and mobile, providing customers with the most flexible options to address their water-cleaning requirements. Smaller and more efficient plants allow NuWater to offer competitively priced fully managed watercleaning services with the highest levels of customer service that are difficult for competitors to match. Challenge us to clean your water. Tap Tomorrow 04

6 Tap Tomorrow SOUTH AFRICA NuWater Campus, 87 Capricorn Drive, Capricorn Park, Muizenberg, 7945, Cape Town, South Africa TEL / info@nuwater.co.za Almost 70% of Earth s fresh water is frozen in ice sheets, glaciers, snow and permafrost, with Antarctica holding about 90% of this water. The only rivers in Antarctica are meltwater streams. SINGAPORE Innovation Centre, Block 2 Unit 245, 18 Nanyang Drive, NTU, Singapore TEL / info@nuwater.com.sg UNITED KINGDOM 39 Elmfield Avenue, Teddington, Middlesex, TW11 8BU, United Kingdom TEL / info@nuwaterglobal.com WEBSITE