Silver Generation Rates from Dental Wastewater. 

V. OVSEY, M. CAILAS, J. DRUMMOND, M. BABKA, R. PERRY, and T. TOEPKE [University of Illinois Chicago, Chicago, IL] W. RODDY, M. COHEN, M. STONE, and S. RALLS [Naval Dental Research Institute, Great Lakes, IL, USA] 

Dental wastewater (DWW) contains a sizeable quantity of silver from amalgam. The economic value of silver provides the impetus to recover, treat, and recycle such waste at the source. In order to quantify the silver content of the DWW, more than 70 DW samples were collected from the Great Lakes Naval Dental Center and private offices. Following nitric acid digestion, silver was analyzed by the direct flame air-acetylene method for atomic absorption spectrometry. The two fractions examined were: 1) solid fraction – particles (=>700 mm) retained on the in-line vacuum trap; 2) settled fraction – particulate settled for 24 hours. Analysis of the data identified highly skewed distributions in both fractions. The solid fraction data had a median of 414 mg Ag per day per chair and a maximum of 1946 mg Ag per day per chair. The settled fraction had a median of 202 mg Ag per day per chair and a maximum of 1490 mg Ag per day per chair. This implies that the DWW can generate approximately 616 mg Ag per day per chair (sum of solid and settled fractions’ medians). Predictive models were developed to describe the generation rates of silver per day from the DWW. These models included as explanatory variables the number of capsules used and the dry weight of each fraction, and explained more than 78% of the variance. This initial study indicates that the amount of silver from dental wastewater is not only significant but has great potential for recycling. [Journal of Dental Research, 75:37 #161, 1996]