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Which chemical is used as a pretreatment step for feed water to a cellulose acetate (RO) membrane?
Sodium hydroxide
Acid
Chlorine
Alum
The correct answer is: Acid
In the context of pretreatment for feed water to a cellulose acetate reverse osmosis (RO) membrane, the use of acid plays a vital role in adjusting the pH of the water. Cellulose acetate membranes are sensitive to high pH levels, which can lead to hydrolysis and degradation of the membrane material. By adding an acid during the pretreatment step, the pH of the feed water can be lowered to a more suitable level that minimizes the risk of membrane damage. The acid helps to dissolve scale-forming minerals and also assists in controlling fouling by modifying the surface properties of the feed water. This lowers the potential for precipitation of calcium carbonate and other salts that could clog the membrane, ensuring better efficiency and longevity of the RO process. Proper pH adjustment is crucial in ensuring that the RO membranes function optimally, thus maintaining high water quality and extending the lifespan of the membranes.