Flue-gas desulfurization (FGD) wastewater reclamation by integrated membrane process

Flue gas desulfurization (FGD) is a process implemented at coal-fired power plants to remove sulfur dioxide from exhausted flue gas. This process is accomplished through wet scrubber technologies generating a polluted wastewater with an extremely complex composition depending on coal source, type of scrubber, makeup water quality, gypsum-dewatering system used and operational conditions. Typically, FGD wastewaters contain significantly high concentration of chloride, sulfate, nitrate, calcium and magnesium and trace-levels of heavy metals, such as Hg(II), Pb(II), Cd(II), Mn(II) and Ni(II). Total dissolved solids (TDS) are in the range 4000–50,000 mg/L, while suspended solids range from 1.4% to 17% [1]. Conventional physical, chemical and biological treatments are able to reduce the content of heavy metal ions, nitrate and soluble organic compounds of FGD wastewaters but are still limited by the high salinity of these effluents and they still produce a wastewater stream that needs to be discharged. Membrane separation technologies have been proposed as efficient alternatives to achieve zero discharge of FGD wastewater [2]. This work aims at evaluating the potential of an integrated membrane system based on the use of pre-treatment, reverse osmosis (RO) and membrane distillation (MD) to achieve water reclamation of FGD wastewaters and their reuse in FGD systems.