Geo-Microbial Technologies, Inc., has developed an anaerobic biotreatment technology to release metals from liquefaction catalyst wastes derived from spent coal that are also contaminated with complex organic compounds. This anaerobic metals release (AMR) technology may be adapted to treat other wastes with metals contamination.
Current biohydrometallurgy systems use aerobic acidophilic bacteria, which oxidize mineral sulfides while solubilizing metals and forming large amounts of acid. This aerobic process can result in acidic drainage from natural sources of metal sulfides. For example, acidophilic bacteria convert the pyrite and iron-containing minerals in coal into oxidized iron and sulfuric acid. The acid then further solubilizes the pyrite and other sulfide minerals. The result is contamination of streams and lakes due to acidification and an increase in soluble heavy metals.
The AMR technology operates anaerobically and at a near-neutral pH, employing anaerobic Thiobacillus cultures in consortium with heterotrophic denitrifying cultures. The diversity of the inhabiting denitrifers allows multiple carbon sources, including some organic pollutants, to be used and treated.
The anaerobic environment is adjusted by introducing low levels of nitrate salts that function as an alternate electron acceptor source, selectively enhancing the inherent denitrifying microflora.
This process increases the denitrifying population that releases the metals. The soils containing the metals are then flooded with the dilute nitrate solutions. These improved anaerobic leaching solutions permeate the soils, allowing the metals to be solubilized into the leachate by the microbial consortium. The nitrate concentration is adjusted so that the effluent is free of nitrate; the nitrate concentration is monitored so that the process operation can be closely controlled. The solubilized metals in the leachate are recaptured by established processes, and the metal-free effluent is recycled within the process. The nitrate-based ecology has the added advantage of decreasing levels of sulfate-reducing bacteria and sulfide generation.
The versatility and low operating constraints of the AMR technology offer multiple process options. The technology can be adapted for in situ flooding or modified to flood a waste pile in a heap-leaching operation. The elimination of any aeration requirement allows the process to be easily designed and considered for bioslurry applications. Thus, the technology offers a greater range of treatment applications for environmental waste situations that were considered difficult to treat.
The AMR technology targets toxic metal- contaminated soils, sludges, and sediments, which can also be contaminated with other wastes, including hydrocarbons and organic pollutants. While metals are the primary pollutant treated, the biological system is also designed to degrade and remove associated organic contaminants.
This technology was accepted into the SITE Emerging Technology Program in July 1994. Studies under the Emerging Technology Program will evaluate how effectively the AMR technology removes metals from soil.
EPA PROJECT MANAGER:
Jack Hubbard
U.S. EPA
National Risk Management Research Laboratory
26 West Martin Luther King Drive
Cincinnati, OH 45268
513-569-7507
Fax: 513-569-7620
TECHNOLOGY DEVELOPER CONTACT:
Donald Hitzman
Geo-Microbial Technologies, Inc.
East Main Street
P.O. Box 132
Ochelata, OK 74051
918-535-2281
Fax: 918-535-2564