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1、DLOGICAL DEGRADATION OF CYANIDE BYNITROGEN- FIXING CYANOBACTER AbyDr. C.J. CantzerDr. W.J. MaierUniversity of MinnesotaDepartment of Civil and Mineral EngineeringMinneapolis, MN 55455Project OfficerJames S. BridgesOffice o f Environmental Engineering and Technology DemonstrationHazardous Waste Engin
2、eering Research LaboratoryCincinnati, OH 45268This study was conducted throughMinnesota Waste Management BoardSt. Paul, MN 55108and theMinnesota Technical Assistance ProgramUniversity of MinnesotaMinneapolis, MN 55455HAZARDOUS WASTE ENGINEERING RESEARCH LABORATORYOFFICE OF RESEARCH AND DEVELOPMENTU.
3、S. ENVIRONMENTAL PROTECTION AGENCYCINCINNATI, OH 45268SECTION 1INTRODUCTIONThe basic premise of this study was that the use of nitrogen-fixing cyanobacteria (blue-green algae) in the biological treatment of small concentrations of free cyanides (HCN and CN-) can be a cost-effective alternative to ex
4、isting treatment processes.A potential application cyanobacteria-based process would be in the secondary treatment of the free cyanides that escape alkaline-chlorination. Because the extent of cyanide oxidation in alkaline-chlorination is an equilibrium-driven phenomena, use of a microbial process t
5、o detoxify the last fraction of cyanide should result in lower alkaline-chlorination operating costs. Another application of a cyanobacteria-based process could be in the treatment of the cyanide associated with metal-cyanide complexes via a two-step process. The first-step would release cyanide fro
6、m the metal-cyanide complexes by exposing the complexes to ultraviolet irradiation. In the second-step, cyanobacteria would detoxify the released cyanide. The use of nitrogen-fixing cyanobacteria in the treatment of cyanide wastes is a new concept. There are several potential advantages associated w
7、ith the use of nitrogen-fixing cyanobacteria in the treatment of small concentrations of cyanide. First, the biological treatment of cyanide with cyanobacteria should have much lower operating costs than alkaline-chlorination. The operating costs for the biological treatment of cyanide wastes with a
8、erobic heterotrophs can be less than 10% the costs for alkaline-chlorination. (Green and Smith, 1972). The costs associated with providing aeration and with providing a supplemental energy source (organic substrate) for the maintenance of large amounts of aerobic heterotroph biomass make up a consid
9、erable portion of the total operating costs for the traditional biological treatment of hazardous wastes. Because cyanobacteria are photosynthetic, they do not require aeration for oxygen and do not require the presence of organic substrates to maintain biomass (Kobayashi and Rittmann, 1982). Thus,
10、in terms of operating costs, the use of nitrogen-fixing cyanobacteria in the treatment of small amounts of cyanide should have an economic advantage over the use of heterotrophic bacteria, and, consequently, a significant economic advantage over alkaline-chlorination.Second, nitrogen-fixing cyanobac
11、teria have the ability to survive in low to moderate concentrations of hydrogen cyanide. Hydrogen cyanide is toxic because it inhibits the terminal cytochrome oxidase in respiration, which normally reduces oxygen to water. Cyanobacteria have several terminal oxidases-some of which are resistant to c
12、yanide inhibition (Fogg, et al., 1973; Degn, et al., 1978; Peschek, 1980; Henry, 1981). Cyanobacteria also have several cyanide detoxification pathways, i.e.,enzymatic pathways that transform free cyanides into a less toxic form (Castric, 1981; Higgins, et al., 1984). The most studied and perhaps th
13、e most important detoxification pathway is mediated by the enzyme rhodanese, which transfers a sulfur from a donating compound (e.g., thiosulfate) to cyanide to form thiocyanate (Westley, 1981). Other cyanide detoxification pathways result in the formation of amino acids (Solomonson, 1981). Thus, du
14、e to the presence of cyanide detoxification pathways and cyanide-resistant respiration, cyanobacteria can survive in solutions containing free cyanides. For example, Howe (1963, 1965) observed a luxuriant growth of cyanobacteria on the filter stones of a biological reactor that was treating wastes c
15、ontaining 300 ppm cyanide.Third, in addition to the above pathways, the nitrogen-fixing cyanobacteria can destroy hydrogen cyanide with the enzyme nitrogenase. While normally responsible for the reduction of molecular nitrogen (dinitrogen) to ammonia, nitrogenase can also reduce hydrogen cyanide to
16、methane and ammonia (Hardy and Knight, 1967; Hardy and Burns, 1968; Biggins and Kelley, 1970; Haystead, et al., 1970; Hwang and Burris , 1972; Hwang, et al., 1973; Zumft and Mortenson, 1975; Stewart, 1980; Li , et al., 1982). In fact, nitrogenase will preferentially reduce hydrogen cyanide instead of its normal substrate, dinitrogen (Li , et al., 1982）. Some researchers have proposed that the original role of the nitrogenase system
