Beneficial use of waste by-products requires innovative consideration of brine as a product as opposed to waste. Such beneficial use may hold potential to generate income from products that could offset some portion of the treatment cost. Such a treatment process might involve alternating applications of RO with previously discussed precipitation processes designed to remove the least soluble salts under conditions of controlled mixing, salt seeding, chemical addition, residence time, temperature, and pH. After removal of the salts that limited recovery in the primary RO, the brine could be treated again in a secondary RO for further product water recovery and brine volume reduction. Factors that must be considered in evaluating beneficial use of desalination by-products include the following:
• technical feasibility of isolating salts of the requisite morphology and purity,
• additional cost required to produce salt products,
• size and location of the market for specific salt products, and
• transportation costs to deliver salt products to market.
The salts that could potentially be produced from desalinated brine depend on the relative ion concentrations and the treatment processes used. For example, potential products from a shallow groundwater might include calcium carbonate, gypsum, magnesium hydroxide, calcium chloride, and sodium chloride. These salt products could potentially be generated for use in the manufacture of paper, ink, plastics, and paint products, as fertilizers and soil conditioners, as fillers for lightweight and fireproof building products, as chemical agents in water and wastewater treatment, and as dust suppressants. In order for a salt product recapture system to work, a demonstrated market for the sale of the salts must be available and proximal to the desalination site. Presently, the technical and economic feasibility of generating salt products from drinking water desalination still needs to be demonstrated, so enhanced evaporation systems remain a potentially viable disposal option.
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