USING CONSTRUCTED WETLAND TREATMENT SYSTEMS TO DETERMINE REMOVAL RATES OF TARGETED CONSTITUENTS AND TOXICITY OF FLUE GAS DESULFURIZATION WASTEWATER, SEDIMENTS, AND PARTICULATES

Federal laws regarding ambient air quality are requiring industries to reduce emissions of sulfur and nitrous oxides. Coal-fired power plants have begun implementing flue gas desulfurization (FGD) scrubbers that utilize calcium carbonate saturated water to precipitate gaseous sulfur compounds (i.e. calcium sulfate). The resulting wastewater produced from this process (FGD wastewater) must be treated before discharge due to high concentrations of elements that elicit toxic effects in receiving systems. Constituents of concern in the wastewater include arsenic (As), mercury (Hg), selenium (Se), chlorides, and sulfates. The purpose of our research is to investigate the use of constructed wetland treatment systems (CWTS) for the treatment of this wastewater. A pilot-scale CWTS used in this investigation includes a simulated equalization basin and a series of wetland microcosms. Our specific research objectives are: (1) to determine settling rates of particles in the simulated equalization basin and if As, Hg, and Se are removed; (2) to evaluate the treatment efficiency of specifically designed pilot-scale CWTS for multiple FGD wastewaters (i.e. removal rates and extents for As, Hg, and Se); and (3) to assess toxicity for settled particulates in the simulated equalization basin, pre- and post-treatment wastewater, and exposed sediment within the CWTS using aqueous sentinel toxicity species. Wastewater particulate settling occurred within the first 12 hours of suspension, and the removal of the targeted constituents depended on the concentration of the elements within each wastewater. Removal rates using the CWTS ranged from 64 to 99% for mercury and 30 to 90% for selenium. These removal rates were dependent on inflow concentrations for most of the wastewaters. Toxicity evaluations using Ceriodaphnia dubia, a microcrustacean, indicated that these CWTS significantly decreased the toxicity effects (mortality and reproductive impairment) in comparison to control organisms. Specifically designed constructed wetland systems can provide effective treatment of many FGD wastewaters and can be utilized by industry to meet water quality discharge limits.