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Mercury Levels and Particle Size Distribution in the Dental Unit Wastewater Stream
M. STONE, W. DEUTSCH, W. C. RODDY, S. RALLS, and D. MEYER [Naval Dental Research Institute, Great Lakes, Illinois], M. CAILAS [University of Illinois at Chicago, School of Public Health], H. BATCHU, C. NALEWAY, H. CHOU, and C. MIHAILOVA [The American Dental Association], and R. KJOME and G. FRAZIER [Naval Dental Center, Norfolk, VA]
Naval Dental Center Norfolk (NDC) is a large dental-treatment facility with over 100 active dental operatories. The dental center was discharging between 20 and 10,000 mg/liter of total mercury into the Hampton Roads Sanitary District sewer system, while maximum daily limits for mercury release from a facility discharging <10,000 gallons per day is 0.1 mg/liter with a monthly average limit of 0.05 mg/liter. As a result of the discharge violations, NDC disconnected the dental-unit-wastewater lines from the sanitary-sewer system and began collecting 8-to-10 gallons of dental wastewater daily in 55-gallon drums. The average disposal cost for each partially filled drum is $900.00, resulting in an estimated annual cost to NDC of $150,000.00. Three central centrifuge based amalgam separators were added to the suction system at the clinic. Preliminary analysis for total mercury and particle size of wastewater samples before treatment, from the commercial amalgam separators, and from an experimental filtration/ion exchange system have been completed. These data suggest that there is a significant level of mercury in the soluble fraction (< 0.45 mm) of the centrifuge treated wastewater. Further characterization of the wastewater stream is needed to determine if mechanical separation alone is sufficient to enable ND Norfolk to meet the discharge limits for mercury and reconnect to the sanitary-sewer lines. [Conference on Pharmaceutical Science and Technology: International Symposium on Separation Technologies for Dental and Health Care Facilities. Chicago, IL. 22-25 August 1995]
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