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A study was conducted on the effects of pH of the medium, composition of Fenton's reagent, and the effect of soil's preequilibration with the chemical, on the degradation of 14C‐labeled free and complex cyanide in aqueous and soil‐containing systems The application of Fenton's reagent (1% H2O2, 10 mM FeSO4) resulted in degradation of 80% and 67% of potassium cyanide in aqueous systems at pH 7 2 and 10 0, respectively No appreciable amount of K4[Fe(CN)6] was degraded at either pH tested Under the alkaline condition, negligible amounts of cyanide were converted to HCN and were removed from liquid phase due to precipitation In the soil systems containing uncontaminated topsoil or manufactured gas plant (MGP) soil, both freshly amended with free cyanide, 80% of the compound was degraded by the Fenton's reagent of the same composition Similar to the aqueous systems, no complex cyanide was degraded in soil slurries In both soils, previously equilibrated with free and complex cyanides, the extent of degradation caused by Fenton's reagent was not more than 6% at either pH However, at alkaline pH, up to 21% of previously added complex cyanide was leached out into a liquid phase where it could be further degraded The optimum composition of Fenton's reagent under alkaline pH was found to be 1% of H2O2 and 1 mM FeSO4 We suggest that the application of Fenton's reagent under alkaline conditions may be useful in a combined physicochemical treatment for the remediation of sites contaminated with cyanides

A metered blend of anaerobic-grade N2, CO2, and H2S gases was introduced into an illuminated, 800-ml liquid volume, continuously stirred tank reactor. The system, described as an anaerobic gas-to-liquid phase fed-batch reactor, was used to investigate the effects of H2S flow rate and light energy on the accumulation of oxidized sulfur compounds formed by the photoautotroph Chlorobium limicola forma thiosulfatophilum during growth. Elemental sulfur was formed and accumulated in stoichiometric quantities when light energy and H2S molar flow rate levels were optimally adjusted in the presence of nonlimiting CO2. Deviation from the optimal H2S and light energy levels resulted in either oxidation of sulfur or complete inhibition of sulfide oxidation. Based on these observations, a model of sulfide and sulfur oxidases electrochemically coupled to the photosynthetic reaction center of Chlorobium spp. is presented. The dynamic deregulation of oxidative pathways may be a mechanism for supplying the photosynthetic reaction center with a continuous source of electrons during periods of varying light and substrate availability, as in pond ecosystems where Chlorobium spp. are found. Possible applications for a sulfide gas removal process are discussed.