Treatment of Simulated Membrane Concentrate for Specific Pollutant Removal

Demands for potable water change as populations grow and shift, in some cases necessitating the use of lower quality water supplies that may require advanced treatment processes using nanofiltration (NF) or reverse osmosis (RO) membranes. In turn, protection of existing source waters becomes increasingly important as they become limited. Implementation of membrane processes that produce significant waste streams (residuals or concentrate) will result in increased concern and restriction over disposal of process residuals. Currently, guidance pertaining to treatment and disposal or reuse of the waste streams from membrane treatment processes is limited due to the emerging nature of this problem. The overall goal of this research project is to increase fundamental and practical knowledge regarding the treatment of residual streams produced by NF or RO membranes used for drinking water production. The hypothesis of this research is that trace pollutants can be removed from membrane concentrate by chemical treatment (coagulation with metal salts and/or precipitative softening through addition of base) to levels that will allow for reuse or increased options for disposal of the concentrate. Specific issues to be addressed include the extent of pollutant removal, optimal treatment conditions, competition between ions, and effects of antiscalant chemicals. This investigation also seeks to compare concentrate treatment with chemical treatment prior to membrane filtration for removal of specific pollutants. This paper presents the background and approach to this research as well as some of the initial results of computer simulations and bench-scale tests of the chemical treatment of simple solutions that serve as approximations of membrane concentrates.