Mercury Removal From Dental Operatory Wastewater Using Polymers.

E. D. PEDERSON, M. E. STONE, S. A. RALLS, W. C. RODDY
Naval Dental Research Institute, Building 1-H, Great Lakes, IL, 60088
and P. L. CHOO, Nalco Chemical Co, Naperville, IL 60563,USA. 

Changing state and federal regulations regarding the levels of mercury [Hg] and other heavy metals that can be released into the environment are becoming increasingly stringent. Therefore, the removal of mercury from dental wastewater is becoming increasingly important. Existing commercial methods for Hg removal have met with various levels of success. Mechanical separators can make Hg removal more difficult. The aim of this study was to test the efficacy of polymers for the removal of Hg from the dental-unit wastewater stream. Commercially available polymers N8186 and 93NP058 [NALCO] were combined with aliquots of dental operatory waste to the following final concentrations: 0.0%[control], 0.00067%, 0.0067%, 0.013%, 0.033%, and 0.33%. Each polymer was added separately at each concentration and combinations of the two polymers at each concentration were also tested. Each test sample was mixed by swirling for two minutes and the precipitates which formed were allowed to settle by gravity overnight. The following morning, samples of the supernatants were carefully removed and sent to a testing facility using EPA test method 245.1. N8186 lowered the Hg levels from 597 ppb to 163 ppb while 93NP058 by itself reached 69 ppb. The 0.013, 0.033 and 0.33 percent combinations of the polymers reached 31, 18.5 and 14.5 ppb Hg respectively, demonstrating a removal of 94.8-97.6% of the total [soluble and insoluble] Hg. Our preliminary results indicate that the treatment of dental operatory wastes with a combination of the two polymers tested reduce mercury levels to those acceptable for release into many public sewer systems. The precipitates can be disposed of as hazardous waste or the precious metals reclaimed. 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 #160, 1996]