Evaluation of an Integrated System to Remove Mercury from Dental-Unit Wastewater
M. E. STONE, E. D. PEDERSON, G. K. JONES, R. S. KARAWAY, R. A. AUXER, S. L. DAVIS
[The Naval Dental Research Institute] and J. CANNON
[SolmeteX, Inc.]
Levels of mercury [Hg] released into the environment from dental treatment facilities continue to be closely monitored by local public waste treatment facilities due to stringent local, state, and federal EPA regulations. The objective of this study was to evaluate a Hg pretreatment system that used a combination of sedimentation, filtration and Hg sorbent material (Keyle:X, SolmeteX, Inc.), to remove Hg from a 35-chair dental treatment facility producing up to 16 gallons of wastewater per day. Wastewater was pumped from the air/water separating tanks of a RAMVAC dental vacuum system into a 125-gallon holding tank. The wastewater was then pumped through two amalgam separators, a 25 mm filter, Keyle:X column, a 1 mm bag filter, a second Keyle:X column, and finally through a 1 mm filter. Flow through the system was limited to 300 ml per minute. Ten baseline samples were collected prior to treatment and 10 treatment samples were collected over a 2-day period. All samples were analyzed by standard method 245.1 with a detection limit of 0.2-to-2.0 mg Hg/liter. Baseline Hg levels from the holding tank averaged 6.3 mg Hg/liter (n = 10, SD = 1.2). The Hg levels in the Keyle:X treated samples were all at non-detectable levels when analyzed at a detection limit of 2.0 mg Hg/liter (n = 10). These 10 samples were analyzed a second time (without dilution) and Hg levels were found to be non-detectable to 0.2 mg Hg/liter (n = 10). Two earlier treatment samples were found to be at non-detectable levels for Hg using standard method 1631 (with a detection limit 10 ng Hg/liter). Evaluation of this pretreatment system continues and subsequent analyses will be done using the newly approved method 1631, which has a method detection limit of 0.5 ng Hg/liter (0.5 ppt). These data indicate the SolmeteX pretreatment system is effective in reducing Hg levels to less than 0.2 mg/liter, which is the detection limit for method 245.1. Support for this study was from the Great Lakes National Program Office (GLNPO) of the United States Environmental Protection Agency (USEPA). The EPA/IGA identification number is: DW17947929-01-0. [Journal of Dental Research 79:545 #3216, 2000]
NDRI Dental Mercury Environmental Issues
