Beneficial reuse of RO concentrate: Innovative approaches

Desalination of brackish waters and reclaimed waters using reverse osmosis (RO) is often limited by the options available for concentrate disposal, particularly in inland areas. Dewatering the concentrate is alternative approach to disposal but the available thermal and membrane technologies are still cost prohibitive for most applications. Beneficial reuse of the RO concentrate represents a sustainable alternative to more traditional concentrate disposal and treatment options because the concentrate becomes a resource rather than a pollutant. This paper presents results from a series of innovative tests utilizing bipolar membrane Electrodialysis (BMED) and Electrochlorination (EC) technologies to produce useful products from RO concentrate that can be utilized at the treatment facility instead of having to dispose of the waste brine into the environment. Experiments were conducted on RO concentrate obtained from a pilot-scale integrated membrane system (IMS) treating wastewater. BMED was used for generating mixed acids and bases from the RO concentrate solution after suitable softening pretreatment. Reasonably high concentrations of acids and bases (0.2-0.5 M) were produced and were shown to be dependent on the concentration and the volume of the used salt solution. Additionally, the RO concentrate was desalted as well. Electrochlorination using RO concentrate was utilized to convert this waste stream into hypochlorite disinfectant of 0.6% similar to that currently being utilized at water treatment plants.