TP11 Metals in the Environment: Aquatic Biological Perspectives
Tuesday, 15 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(EGG-1117-824358) Assessment of specially designed constructed wetland treatment systems for flue gas desulfurization wastewaters.

Eggert, D¹, Iannacone, M², Castle, J², Murray-Gulde, C³, Mooney, D³, Huddleston, G³, Rodgers, Jr., J¹, ¹ Clemson Universtiy, Department of Forestry and Natural Resources, Environmental Toxicology, Clemson, SC, USA² Clemson Universtiy, Department of Geology, Clemson, SC, USA³ ENTRIX Inc., Pendleton, SC, USA

ABSTRACT- Federal laws regarding ambient air quality are currently requiring industries to reduce emissions of sulfur and nitrous oxides. Coal-fired power plants have therefore begun implementing flue gas desulfurization (FGD) scrubbers that utilize calcium carbonate saturated water to precipitate some of these gases. The resulting wastewater produced from this process (FGD wastewater) must be treated before discharge due to high concentrations of elements that elicit toxicity. The chemical compositions of FGD wastewaters are dependent on the combustion processes and coal types used and include such elements as arsenic, mercury, selenium, chloride, and sulfur. Our research objectives were: (1) to evaluate treatment efficiency of specially designed pilot-scale constructed wetland treatment systems (CWTS) for multiple FGD wastewaters, (2) to determine removal rates and extents for arsenic, mercury, and selenium within these systems, and (3) to assess toxicity of pre- and post-treatment wastewater using Ceriodaphnia dubia. Four different FGD wastewaters were received from Duke Energy (Marshall, NC) and were separately loaded into CWTS after chloride dilution to 4000 mg/L. Removal rates ranged from 64 to 99% for mercury and 30 to 90% for selenium. Removal of these elements was, however, dependent on inflow concentrations for all wastewaters with the exception of a single wastewater sample, in which selenium removal decreased in comparison to a similar wastewater (Week 2). Effluent criteria for selenium were achieved for three of the four wastewater samples. Toxicity evaluations using C. dubia indicated that CWTS significantly decreased the toxic effects, in comparison to control organisms (all treatment weeks after chloride dilutions to approximately 500 mg/L). CWTS are viable treatment systems for many FGD wastewaters and can be utilized by industry to met NPDES limits and toxicity tests with co-management strategies for chloride dilution.

Key words: constructed wetlands, mercury, selenium, ceriodaphnia dubia