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Mercury Management of Dental-Wastewater Streams Using Secondary Treatments.
E. D. PEDERSON and M. E. STONE A previous study (Pederson, et al. 1996) demonstrated that commercially available polymers N8186 and N8702 (NALCO) were capable of removing between 94.8 and 97.6 percent of the mercury from a dental-operatory waste stream. This study investigated the efficacy of the following secondary treatment agents (polishing agents) to remove additional mercury: A peat based product [HW-FIX] (Lenco Chemical, Inc.), Activated Carbon [AC] (99260-08, Cole-Parmer), 3.3 grams of three ion exchange agents [IEX] (Cole-Parmer), and silver conjugated carbon [CE-33-B5] (ADA Technologies, Inc.). Ten grams each of the four secondary treatment agents were placed into four columns. The settled supernatants from untreated wastewater (pH 5.3), pH-adjusted wastewater (pH 7.0), and pH-adjusted/polymer treated wastewater (2.5 ml of NALCO polymers N8186 and N8702 per liter) were passed through separate columns at flow rates of approximately 4 ml/minute. The mercury content of the settled supernatants were determined for all control and treatment samples using EPA method 245.1. The untreated wastewater supernatant (control) contained 3200 parts per billion (ppb) mercury. The pH adjusted wastewater supernatant contained 1300-ppb mercury, a 59.4% mercury reduction. The supernatant of the pH adjusted and polymer treated (polymers N8186 and N8702) sample contained 20-ppb mercury, a 99.4% reduction. The silver conjugated carbon product, CE-33-B5, removed the most mercury for all three wastewater fractions. The best results were obtained when the wastewater was pH adjusted and pretreated with the two Nalco polymers N8186 and N8702. Supported by NMRDC, Project Number 0603706N M0095.006-0515. Journal of Dental Research 77:191 #687, 1998] |