Reverse osmosis municipal water treatment

Municipal water treatment(s), 26 123-125 activated carbon application, 4 752-753 bioremediation and, 3 755 goal of filtration in, 26 105 reverse osmosis in, 27 647-648... 

Finally, other dissolved, nonnutrient salts may have to be removed for water reuse in some water conservation programs. This may best be accomplished using reverse osmosis, or electrodialysis [53], or ion exchange [54]. The operating details of these processes are discussed with municipal water treatment. 

Makeup. Makeup treatment depends extensively on the source water. Some steam systems use municipal water as a source. These systems may require dechlorination followed by reverse osmosis (qv) and ion exchange. Other systems use weUwater. In hard water areas, these systems include softening before further purification. Surface waters may require removal of suspended soHds by sedimentation (qv), coagulation, flocculation, and filtration. Calcium may be reduced by precipitation softening or lime softening. Organic contaminants can be removed by absorption on activated carbon. Details of makeup water treatment may be found in many handbooks (22—24) as well as in technical Hterature from water treatment chemical suppHers. 

Water quality is usually defined in terms of chemical and bacteriological purity, particulate matter content, and endotoxin levels. Potable water is normally from the municipal water system, which may have been treated with chlorine to control microbiological growth. Soft water and deionized water have undergone ion exchange or similar treatment to eliminate unwanted ionic species, such as Mg2+ and/or Ca2+. Purified water, water for injection, and other types of water meeting compendial specifications are produced by ion exchange, reverse osmosis, distillation, or a combination of such treatments. 

A unique set of circumstances was responsible for symptoms resembling hard water syndrome [64] followed by an epidemic of acute Al encephalopathy in a dialysis unit (Diatel) on the island of Curasao. A tragic coincidence is that the intoxication happened about two months before the planned installation of a water treatment system with deionization and reverse osmosis (RO). Traditionally, municipal water had been used for more than two decades without extended purification for the production of dialysate. The pure... 

The equilibrium of sulfide in water, the percentages of H2S, HS, and species, is dependent on the pH. Figure 1 shows the distribution of each species at various pH. At a pH of approx 5.7, the sulfide species in water would be near 100% H2S and at approx pH 7, 50% of the sulfide species in water would be H2S and the other 50% would be HS species. The H2S species are volatile as a result, the aeration process effectively removes it from the water. Therefore, the removal efficiency of sulfide depends on pH. As the pH increases, aeration becomes less effective because there are fewer sulfides in the form of H2S, which is readily removed by aeration. This process is utilized by both municipalities and chemical industries. In water treatment, the process is called degasification, and is effectively used to remove both H2S and carbon dioxide from well water and product water from the reverse osmosis process. 

Reverse osmosis membrane is widely used in seawater and brackish water desalination processes. Compared to traditional distillation, there is no energy-intensive phase change involved in membrane processes. Therefore, desalination with RO membrane is more energy efficient. In addition to the traditional desalination processes, RO membranes have also found wide application in industrial and municipal wastewater treatment, in pure water production for the electronic and pharmaceutical industries, and in the food industries. 

Water reclamation, the treatment of wastewater to meet the water quality standards of various applications economically, is becoming increasingly important in view of the increasing world population and scarcity of fresh water sources. The major technology used for water reclamation is membrane technology. This entry gives an overview of the major membrane types used for water reclamation reverse osmosis, nanofiltration, ultrafiltration, microfiltration, and liquid membranes. Applications of these membranes in municipal and industrial wastewater reclamation have been described. 

One of the most innovative industrial uses of reverse osmosis is at the Petromin Refinery in Riyadh, Saudi Arabia. The refinery takes an unusable municipal wastewater, secondary effluent from the Riyadh sewage treatment plant, and by using lime clarification, filtration, reverse osmosis and ion exchange demineralization, it converts that useless waste into the entire process water requirements for the refinery. Figure 4.16 is the process flow schematic for the refinery water treatment plant. 

Finally, as the world becomes more aware of the environmental damage caused by indiscriminate waste disposal it is apparent the RO process will play a key role in mitigating that problem. It appears that the next market for the RO process will be in industrial waste treatment in the United States to be followed by application in other countries. Eventually, the world will be forced to use reverse osmosis to reclaim municipal wastewater on a large scale and to put the reclaimed water to a number of already demonstrated beneficial uses. 

Hemodialysis/hemofiltration alone had sales of over US 2200 million in 1998. Reverse osmosis (RO), ultrafiltration (UF) and microfiltration (MF) together accounted for 1.8 billion dollars in sales in 1998. At that time about US 400 million worth of membranes and modules were sold each year worldwide for use in reverse osmosis. About 50% of the RO market was controlled by Dow/FihnTec and Hydranautics/Nitto. They were followed by DuPont and Osmonics. Membranes are apphed during sea-water desahnation, municipal/ brackish water treatment and in the industrial sectors. The market for RO and nanofiltration is growing at a rate higher than 10%/year. The market for desali-... 

The FDA regulates the quality of bottled water. The water passes through one or more purification steps (Figure 11.12). The three purification methods (which can also be done in home treatment systems)—distillation, carbon filtration, and reverse osmosis— have already been discussed as methods used for treating municipal water. The maximum levels of contaminants allowed by the EPA after these treatments are listed in Table 11.10. Each of these methods is expensive and results in a high cost per gallon of treated water. In the case of bottled water or home water treatment, the cost of treatment is not the major factor, because only the small amount of water needed for human consumption needs to be specially purified. Figure 11.12 shows... 

Dialynas E et al (2008) Advanced treatment of the reverse osmosis concentrate produced during reclamation of municipal wastewater. Water Res 42(18) 4603 608... 

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