BIOLOGICAL TREATMENT OF MERCURY WASTE

Conly L Hansen and Gour S. Choudhury Department of Nutrition and Food Sciences and Department of Civil and Environmental Engineering, Utah State University 

Mercury is one of the most significant examples of toxic heavy metal pollution. Anthropogenic sources of mercury include those associated with its use in chlor-alkali, paint, agriculture, pharmaceutical, and paper and pulp industries. 

A widely used method for removing mercury from polluted water is addition of sodium sulfide. Insoluble mercuric sulfide (HgS), which forms is removed as a sludge (Price et al. 1972) that is then landfilled. It has been assumed that HgS remains permanently insoluble, thus preventing movement of mercury into the surrounding environment. Mercury waste has been treated and buried in this manner for many years. 

However chemical methods of mercury detoxification are far from adequate. It has become evident that mercury can be solubilized from HgS under conditions that could be present in a landfill. We have demonstrated chemical solubilization followed by volatilization with Fe2(S04)3, a product of oxidation of FeS04 (pyrite) by Thiobacillus ferrooxidans (data not shown). Other researchers have indicated that T. ferrooxidans can facilitate solubilization and volatilization of Hg° from HgS. Growth of T. ferrooxidans in the presence of cinnabar (mercury ore-contains HgS and some impurities) by Silver and Torma (1984) resulted in dissolved mercury concentration in the bioreactor of 64 mg/L (the form of Hg was not given). In similar experiments with T. ferrooxidans and cinnabar, Baldi and Olson (1987) did not 

---