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ENVIRONMENTAL TECHNOLOGY VERIFICATION REPORT REMOVAL OF MERCURY FROM DENTAL OFFICE WASTEWATER
Citation:
ENVIRONMENTAL TECHNOLOGY VERIFICATION REPORT REMOVAL OF MERCURY FROM DENTAL OFFICE WASTEWATER. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/R-03/018, 2002.
Description:
Verification testing of the DRNA Mercury Recovery Unit (MRU) was conducted during a seven-week period, at a dental office in Michigan that had three operatory rooms and two hygiene rooms. The office operated four days per week and averaged approximately eight (8) mercury amalgam surfaces removed/placed per day. The MRU was installed in the vacuum system ahead of the air/water separator, and operated continuously over the verification test period. During an eleven-week period prior to the verification test period, a baseline characterization test was conducted with the total volume of untreated wastewater generated at the office being sampled and analyzed. The characterization data provided representative influent data for comparison with the treated water effluent data collected during the
verification test. Mercury removal was calculated by two methods. One approach used the data collected during the characterization test to represent the influent wastewater quality. The second approach used a mass balance that measured all of the mercury captured and discharged by the MRU during the verification test. The MRU achieved mercury removal, on a total mass-loading basis, of 98.3 to 99.4 percent depending on the approach used. The removal of settleable mercury, which represented 77 to 81 percent of the mercury in the wastewater, averaged 99.6 to 99.9 percent. Mercury present in the liquid fraction after settling (soluble and suspended particulate) was removed by the adsorption media in the 92.3 to 94.0 percent range. Both settleable mercury and mercury present in the liquid after settling (soluble and suspended particulate) were effectively removed from the wastewater. The system operated
throughout the verification test with no maintenance or down time. There was evidence that the activated carbon adsorption media was breaking down and exiting the unit during the verification test. DRNA indicated this was due to excess bleach being fed to the unit. The concentration of the bleach solution was subsequently decreased during the verification test, and reflects the recommended bleach concentration in the Operations and Maintenance Manual currently being supplied with their units.