AWWA MTC61172

The growing interest in reverse osmosis includes not only coastal areas for desalination of seawater but also inland areas where reverse osmosis is proposed for desalination of brackish groundwater, particularly in arid climates where freshwater is extremely scarce. Most existing reverse osmosis facilities are in coastal areas, and the most common concentrate disposal methods are discharge to surface water, discharge to a municipal sewer system, and deep well injection. In inland areas, these disposal options may not be available, and the remaining options may be expensive and difficult to implement. Furthermore, in inland areas, the concentrate represents not only a significant management problem, but also a waste of a precious resource, the water. This paper discusses Several issues in regard to concentrate in inland areas. First, the concentrate must be isolated from the surrounding freshwater resources so that the existing resources are not contaminated. Evaporation ponds and deep wells (if suitable injection zones can be identified) can be constructed to fit these criteria. The second issue, however, is to recover as much of the freshwater from the concentrate as possible, to minimize wasting of the natural resource. Technologies to increase recovery or convert the concentrate into solid salts (zero liquid discharge) using mechanical evaporators or distillation systems are discussed. Identification of appropriate methods of concentrate management is necessary for determining the feasibility of a reverse osmosis project. An attractive solution to the concentrate disposal issue is to convert this disposal problem into a natural resource. The paper discusses possible beneficial uses of concentrate that include: land application or irrigation of salt tolerant crops; saline aquaculture, farming of brine shrimp or other saltwater species; restoration of brackish waterways or development of saltwater marshes, wetlands or habitats; energy generation using solar gradient ponds; industrial uses as feedstock or process stream; and, production of marketable salts or mineral commodities. The selection of a concentrate disposal option depends on site-specific conditions of the treatment plant. The variables that may affect the selection include economics, quality and quantity of concentrate, regulatory concerns, availability of the receiving site, public acceptance, and the climatic and geographical considerations. Includes 25 references, tables, figure.