This textbook covers theory and practice and is intended for designers, operators, consultants, suppliers and students. Principles of ultra- and nanofiltration and reverse osmosis (RO) are discussed, enabling the reader to understand the link between design, operation and fouling and scaling. Fouling (particulate, organic -including algal bloom events, inorganic, and biofouling) and scaling are treated in detail, including parameters to determine fouling and scaling potential of feed waters. Principles of conventional and advanced pre-treatment processes are highlighted and their effect on preventing fouling and scaling. In addition, the process design of RO systems and the recent advances in seawater RO and emerging membrane-based processes for seawater desalination are presented.
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This process is inverted in reverse osmosis. We take in seawater, a highly concentrated solution, and force it through the membrane by adding pressure. On the other side, we obtain salt-free water, while back on the first side the remaining water still holds the salt the membrane prevented from passing through.
In reverse osmosis desalination, water is taken from the sea and receives a first treatment to eliminate impurities, oil, seaweed, rubbish, and so on. Once free of organic substances, the saltwater can be subjected to reverse osmosis. After the filtering, we have two streams: one brine and the other freshwater. The brine solution is diluted before being returned to the sea, avoiding high concentrations of salt which could harm the ecosystem. The freshwater passes through a remineralization and chlorination process, after which it is stored in tanks and then sent to the distribution network for consumption.
Reverse osmosis membrane technology has developed over the past 40 years to a 44% share in world desalting production capacity, and an 80% share in the total number of desalination plants installed worldwide. The use of membrane desalination has increased as materials have improved and costs have decreased. Today, reverse osmosis membranes are the leading technology for new desalination installations, and they are applied to a variety of salt water resources using tailored pretreatment and membrane system design. Two distinct branches of reverse osmosis desalination have emerged: seawater reverse osmosis and brackish water reverse osmosis. Differences between the two water sources, including foulants, salinity, waste brine (concentrate) disposal options, and plant location, have created significant differences in process development, implementation, and key technical problems. Pretreatment options are similar for both types of reverse osmosis and depend on the specific components of the water source. Both brackish water and seawater reverse osmosis (RO) will continue to be used worldwide; new technology in energy recovery and renewable energy, as well as innovative plant design, will allow greater use of desalination for inland and rural communities, while providing more affordable water for large coastal cities. A wide variety of research and general information on RO desalination is available; however, a direct comparison of seawater and brackish water RO systems is necessary to highlight similarities and differences in process development. This article brings to light key parameters of an RO process and process modifications due to feed water characteristics.
Regarding RO membrane development, more than 60 years have passed since UCLA first announced the development of an innovative asymmetric cellulose acetate RO membrane in 1960. Furthermore, new generation polyamide hollow fiber RO and thin-film composite (TFC) aromatic polyamide RO membranes were developed one after another in the early 1970s and 1977. As a result of continuous improvements, the TFC RO membrane performance has been greatly improved, and it is now widely used for a variety of applications. As for the future membrane desalination technology, three technologies were raised in National Geographic, April 2010 . These three technologies promised to reduce the energy requirement of desalination up to 30% are forward osmosis, carbon nanotubes, and biomimetics. Among those, nanoporous membranes, including porous graphene, carbon nanotubes, and graphene oxide, etc., attracted much attention from academic researchers . However, it does not seem easy to produce commercial-based defect-free RO membranes with nanoporous materials. A way of overcoming material limitations for RO applications is to utilize composite materials comprising nanoporous materials within a polymer matrix. The use of thin-film nanocomposite (TFN) membranes for water purification was first described for BWRO membranes by Jeong et al. . After that, many research works on the TFN membranes have been conducted [7,8].
The following example is the seawater desalination plant with an 18,000 m3/d capacity in Santa Barbara, Curacao . Chlorine is dosed in the beach clear well. SBS is injected after a CF when shock pre-chlorine is performed. After an initial lag period, the differential pressure (DP) increase becomes more rapid. During the first 15 months, the plant had to conduct CIP five times. The autopsy data demonstrates that this DP increase is due to biological growth on the membrane. To reduce the rate of biofilm growth, a program of weekly, overnight biocide soaks with a commercial non-oxidative biocide was implemented. The result was a significant reduction in the rate of DP increase. A subsequent attempt was to control SBS dosing. In the original design for the Santa Barbara plant, SBS dosing was based on the free chlorine level anticipated during the regular shock chlorination. This practice ensures that no chlorine reaches the membrane; however, it also results in an excessive SBS residual in the feed. Then, the SBS addition program was modified to reduce the SBS excess. After the cleaning was performed, the rate of DP increase was immediately and positively affected by the change in SBS addition.
Later, to minimize SBS consumption for deoxygenation, a vacuum degasifier was installed. Along with this modification, the SBS dosing point was moved after the CF. However, a 500 ppm SBS shock treatment method was continued for these changes. As a result, it was reported that the problem of microbial regrowth was resolved, and the DP increase of the reverse osmosis module was suppressed . As for the PEC-1000 RO, Heyden  reported that 500 ppm of SBS shock treatment (twice daily) was applied to a 600,000 gallon per day (gpd) SWRO plant at Tanajib, Arabian Gulf Coast.
Yes, semipermeable membranes enable the feed water to pass through it at a much higher volume than dissolved salts. Reverse osmosis systems work by applying pressure as freshwater streams through its membranes to filter out the concentrated saline in the feed water, as well as minerals and pollutants. These unwanted impurities are either flushed away, recycled, or processed. Seawater reverse osmosis systems utilize more than one membrane to boost the load of purified water turned out each day.
With an ever-increasing human population, access to clean water for human use is a growing concern across the world. Seawater desalination to produce usable water is essential to meet future clean water demand. Desalination processes, such as reverse osmosis and multi-stage flash have been implemented worldwide. Reverse osmosis is the most effective technology, which uses a semipermeable membrane to produce clean water under an applied pressure. However, membrane biofouling is the main issue faced by such plants, which requires continuous cleaning or regular replacement of the membranes. Chlorination is the most commonly used disinfection process to pretreat the water to reduce biofouling. Although chlorination is widely used, it has several disadvantages, such as formation of disinfection by-products and being ineffective against some types of microbes. This review aims to discuss the adverse effect of chlorination on reverse osmosis membranes and to identify other possible alternatives of chlorination to reduce biofouling of the membranes. Reverse osmosis membrane degradation and mitigation of chlorines effects, along with newly emerging disinfection technologies, are discussed, providing insight to both academic institutions and industries for the design of improved reverse osmosis systems.
Typical seawater desalination processes for high production of treated water are reverse osmosis (RO), multi-stage flash (MSF), and multiple effect distillation (MED). The most common desalination technology is RO accounting for over 60% of the total worldwide installed capacity.3 Seawater contains suspended particles, natural organic matter, mono- and multivalent ions, microorganisms, and organic and inorganic colloids. Some of these constituents block the pores of the RO membranes, also known as fouling, rendering them inefficient after short operation times. Colloidal, particulate, organic or biological fouling (biofouling) as well as scaling occurs very easily during desalination using RO membranes. It is essential to remove the foulants to prevent the failure of the RO processes.4
An interesting work have been done103 to study a new way of pre-treatment disinfection step prior to RO desalination by utilizing medium pressure ultraviolet (MP-UV) treatment. The study was conducted for four months at a brackish water reverse osmosis (BWRO) desalination plant. It was reported that MP-UV prolonged the performance between cleaning in the desalination plant also affecting the characteristics of the microorganisms and creatures on RO membranes asextracellular polymeric substances (EPS) were found to be significantly reduced. In another work,104 H2O2 with MP-UV was found to reduce the amount of heterotrophic counts biofilm cells and EPS on the RO mem