EVALUATION OF SALINITY GRADIENT SOLAR PONDS FOR INTEGRATED BRINE DISPOSAL

The feasibility of using RO (reverse osmosis) brines for salinity gradient solar ponds was investigated. Two major obstacles were identified: algae growth and density requirement. Five chemicals were tested and hydrochloric acid was found most effective in controlling the green algae in the RO brine taken from the Scottsdale Water Campus. The algae problem could be overcome by acidification, though the density requirement is more difficult to handle. The stability criteria for a solar pond requires that the brine at the bottom layer has to have a salinity of over 200,000 ppm of TDS. This means the RO brine has to be concentrated for more than 30 times. Evaporation test was conducted on the RO brine at 65---70°C. Sequential precipitation occurred with calcium carbonate being the first followed by other salts at lower concentrations than calcium carbonate. The evaporation test also revealed a possible additional problem for the implementation of a solar pond: The UV absorption was increased from 0.6 to 14 when the brine was evaporated from 6,000 ppm to 120,000 ppm TDS. The color could be a serious problem as it affects the light transmission and hence the efficiency of the pond. The possibility of combining an RO brine solar pond with a Dewvaporation unit, a patented desalination system, was also explored and the statistics from the preliminary analysis was presented in the end.