This report describes a project to develop a method of treating flue gas desulfurization (FGD) wastewater using an innovative combination of physical and chemical treatment processes. The treatment process involves removing divalent cations (calcium (Ca) and magnesium (Mg)) and anions (sulfate (SO4)) from the FGD wastewater, leaving behind sodium (Na) and chloride (Cl). The wastewater is first treated to remove dissolved CO2 by air stripping at low pH. Magnesium is removed as magnesium hydroxide (Mg(OH)2) by precipitation at high pH. Calcium is removed by ion exchange (IX), and SO4 is removed by nanofiltration (NF) using a softening membrane. The treated water would then be recovered for reuse by a desalination process such as membrane distillation (MD) or reverse osmosis (RO). Cation regenerants from the IX process containing Ca and concentrate solution from NF containing SO4 is combined to precipitate gypsum (CaSO4�2H2O). The concentrated brine from the desalination process would consist of a high strength NaCl solution that would be used to regenerate the IX resins and excess concentrate would be subject to disposal. Hazardous contaminants in the FGD wastewater would be concentrated and disposed of in the NaCl brine. The specific objectives of the process developed in this project are to: (1) Recover wastewater from the FGD process for subsequent reuse. (2) Recover marketable commodities (gypsum (CaSO4�2H2O) and magnesium hydroxide (Mg(OH2)) from FGD wastewater for commercial sale. (3) Treat FGD wastewater to remove regulated constituents including arsenic (As), nitrate (NO3), and selenium (Se). (4) Reduce the volume and mass of waste requiring disposal from FGD wastewater. The selective precipitation, IX, and NF processes were tested in laboratory experiments and produced high quality commodities (>
95% purity) and removal of As and Se. Little removal of NO3 was achieved. A chemical process model was developed that allows calculation of process performance, mass and liquid flow rates that can be used to optimize the system according to FGD wastewater quality and scrubber operation.