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Mercury Removal Method and Device for Dental Operatory Wastewater.
S. A. RALLS, W. C. RODDY and E. D. PEDERSON
The removal of mercury [Hg] from waste products released into the environment is becoming increasingly important in light of state and federal regulations. Existing methods for Hg removal from dental wastewater achieve various levels of success. The aim of this study was to develop methodology to enhance the reduction of Hg in the effluent to less than 0.05 ppm total Hg. Subsequent to treatment, 10,000 gal/month of this effluent from the test dental facility could then be directed to the local public waste treatment facility. A commercially available 60 gal air/water holding tank was modified to allow for internal cleansing/mixing by fresh water and the settling of particulates through a drain at the conical bottom added to the tank. The particulates were allowed to settle overnight and directed by gravity into a separate container to allow for ease of removal and replacement. The clarified effluent was then directed to a series of filters [50.0-0.5 micron] and a final ion-exchange treatment. The dental wastes from 35 dental operatories, which averaged 671.6 ppm prior to treatment, yielded an effluent averaging 0.46 ppm, which contained only 0.12 ppm following filtration and 0.034 ppm after ion-exchange treatment. Our results indicate that treatment with the modified settling tank together with filtration and ion-exchange treatments reduced Hg to acceptable levels for release into many public sewer systems. Also, the precipitates collected in a separate container were easily handled and prepared for either hazardous waste disposal or recovery procedures. Supported by the Office of Naval Research, Naval Medical Research and Development Command, Bethesda, Maryland, project number 063706N M0095.006-0509.[Journal of Dental Research, 75:37 #1212, 1996] |