Innovative Approaches to RO Concentrate Management: Beneficial Reuse and Concentrate Minimization

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 ion exchange (IX), bipolar membrane Electrodialysis (BMED) and Electrochlorination (EC) technologies to recover useful products from RO concentrate that can be utilized at the treatment facility. Two of these technologies including the BMED and the EC are currently in the patent process for this and other applications. Experiments were conducted on RO concentrate obtained from a pilot-scale integrated membrane system (IMS) treating wastewater. The IX experiments focussed on recovering phosphate from RO concentrate using a chelating ion exchange resin and converting the phosphate rich regenerant into struvite, a commercially viable fertilizer. Reasonably long run lengths of up to 700 BVs were obtained with actual RO concentrate using one of the tested resins. BMED was used for generating mixed acids and bases from the RO concentrate solution after suitable 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. It is expected that upto 1 M acid and base concentrations can be produced from this process. 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.The above processes present the potentially viable alternative of utilizing the RO concentrate for the production of useful products instead of having to dispose of the waste brine into the environment. Costs are currently being developed for implementation of these three strategies and will be presented at the conference.