An Evaluation of Granular Activated Carbon and Ozone/Ultraviolet/Air Stripping Technologies for the Removal of Low Levels of Mercury from Water Discharges at the Y-12 National Security Complex

摘要

The Y-12 National Security Complex (Y-12 Complex) is an active manufacturing and developmental engineering facility that is located on the U.S. Department of Energy (DOE) Oak Ridge Reservation. Past operations at the Y-12 Complex led to the release of mercury to the environment. Significant environmental media at the site were contaminated by accidental releases of elemental mercury from the building process facilities piping and sumps associated with Y-12 Complex mercury handling facilities. Releases to the soil surrounding the buildings have resulted in significant levels of mercury in these areas of contamination, which is ultimately transported to Upper East Fork Poplar Creek (UEFPC), its streambed, and off-site to the Clinch River. rnThe Record of Decision (ROD) for Phase I Interim Source Control Actions in the Upper East Fork Poplar Creek Characterization Area, Oak Ridge, Tennessee, requires the construction and operation of a new 300 gpm water treatment facility to remove total mercury from groundwater discharging from Outfall 51 as well as groundwater collected in the basement sumps of Bldg. 9201-2. The water treatment system will be designed using best available technology and reduce mercury to a maximum of 200-ng/L (ppt) in the effluent. Additional methods for removal of mercury, potentially bringing levels to the ambient water quality criteria (AWQC) of 51-ng/L, or less will be evaluated as part of a pre-design characterization and testing study. (DOE 2002)rnMercury at a concentration of approximately 1400 to 5000-ng/L is found in different forms in the discharge at Outfall 51. Limited data from mass balances performed during the pilot studies at Outfall 51 indicate that approximately 28% of the mercury is present as elemental mercury [Hg (0)], 33% is present as dissolved Hg (II) and 39% is of a refractory form, which speciation is presently unknown. The term refractory is being used to designate the fraction of mercury that cannot be converted to elemental mercury in the presence of stannous chloride (SnCl2), which is added to samples before analysis. (BJC 2002) Addressing the refractory fraction of mercury is important in meeting the goal of bringing discharge levels to 200-ng/L or less as well as in the evaluation of the ability to achieve the AWQC of 51-ng/L. rnA pre-design study was performed to investigate the applicability of two treatment technologies for reducing mercury discharges at Outfall 51 in support of the design of the water treatment system. This document evaluates the results of the pre-design study for selection of the mercury removal technology for the treatment system.