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reverse-osmosis treatment trains, containing over 40,000 membrane elements.) This process constitutes 30%–40% of the water cost. The theoretical minimum amount of energy needed for RO desalination from seawater is around a kilowatthour per cubic meter, though even the most efficient actual plants do not drop below about four times this theoretical minimum. For example, the Ashkelon plant has a contractual specific energy of 3.9 kWh (kilowatt-hour)/m3 , and actual performance is 10%–15% below this. In Ashkelon, the facility is to be powered by two redundant sources: a natural, dedicated power plant fueled by natural gas, located adjacent to the desalination plant, and high-voltage linkage to the national electricity grid. Boron Concentrations While boron is found in very low levels in drinking water (on the order of 0.03 mg/l), it is present at much higher levels (more than two orders of magnitude greater) in seawater (4–7 mg/l). Since boron at these levels can cause reproductive and developmental toxicity in animals and also effects crops, additional boron removal processes must be added to desalination plants. Israel was forced to address this issue as a result of damage to sensitive crops when the Eilat plant went on line without boron removal. It was the first country to set a boron limit of 0.04 mg/l for the first generation of desalination plants, and stringent limits (lower than WHO standards) were written into the requirements for the current generation of plants recently tendered. At the Ashkelon plant, for example, the Boron Polishing System installed demands 10% of overall plant energy. Overly Pure Produced Water Desalinated water is remarkably pure H2O. This is largely a boon, but may also be a hazard in some respects. Reverse osmosis lowers calcium and carbonate concentrations , which make the product water acidic enough to corrode the distribution system . This reduces the useful life of the system and can also introduce iron and other toxic metals (copper, lead, cadmium, zinc, nickel) into water. Post-treatment of desalinated water with lime or limestone corrects this problem. In addition, since the desalting process largely removes a range of ions normally found in drinking water, and which may have a supplementary dietary role, especially in certain high-risk populations , blending or chemical addition may be necessary (Cotruvo 2005). Additional consequences for agriculture of the altered chemical profile of desalinated water have also received wider attention for the first time due to research on Israeli experiences with water from the Ashkelon and Eilat facilities (Yermiyahu et al. 2007). Purity of the Intake Water Some toxic materials in source water, such as arsenic and small petroleum molecules , can pass through RO membranes. Others can be filtered but may compromise the efficiency of the desalination process. For example, during the first 15 months of operation of the Ashkelon plant, there was a summer deterioration in seawater quality, most likely from organic load (particularly sewage) from Gaza yaakov garb 242 entering the plant inlet, causing reduction in production. In wastewater desalination , such as that conceived for the Shafdan facility, a broader suite of contaminants may be present, including metals, other chemicals, and pharmaceuticals (as mundane as caffeine and as worrying as endocrine disruptors). Introduced Impurities and Brine Discharge The RO process can introduce a variety of substances into the discharged water (backwash liquids containing chemicals used to prevent scaling, corrosion, and fouling of the filters as well as for pretreatment processes), in addition to the intrinsic production of saline brine that is two to three times saltier than seawater. In the Ashkelon plant, for example, the most notable effect observed so far is from ferric sulfate coagulant, which, even at levels of 28 ppm, adds about 450 tons of iron a year to the sea. Even when mixed with the cooling water of the Ashkelon power station, the discharge discolors the sea with a red plume, a situation now being monitored and presumably managed. It is unclear whether this is simply an aesthetic blight or will have more significant effects on the marine environment. While there is still too little known about the marine impacts of discharges from desalination plants, precautionary suggestions to reduce these include use of more environmentally friendly anti-scalants, reduction of iron content, pretreatment of brine for nitrogen so as to avoid eutrophication, and the release of organic cleaning solutions. Microbes Many microbial organisms, including bacteria, protozoa, and viruses in seawater, may be pathogenic. Not all...

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