Organic acids oxidizing iron reducers

Dissimilatory sulfate reducers such as Desul-fovibrio derive their energy from the anaerobic oxidation of organic compounds such as lactic acid and acetic acid. Sulfate is reduced and large amounts of hydrogen sulfide are generated in this process. The black sediments of aquatic habitats that smell of sulfide are due to the activities of these bacteria. The black coloration is caused by the formation of metal sulfides, primarily iron sulfide. These bacteria are especially important in marine habitats because of the high concentrations of sulfate that exists there. 

The necessary conditions are sources of iron oxide, dissolved 804 and organic matter, and sufficiently reducing conditions for reduction of 804 coupled to intermittent or localized oxidizing conditions to produce elemental 8 or polysulfide. Potential acidity develops by the removal of alkalinity (represented by HC03 in Equation 7.2) from the sediment by diffusion and tidal action. What... 

Environmental applications require detoxification of hazardous substances to a level of parts per million (ppm) and even parts per billion (ppb). These purity levels, which were rarely considered in product synthesis, are now possible for wastewater due to Fenton s reagent. Fenton s oxidant is cost effective and relatively fast in destroying many toxics (Bigda, 1996). It attacks all reactive substrate concentrations under acidic conditions. Hydrogen peroxide is used to remove such contaminants as cyanide, sulfides, sulfites, chrome, and heavy metals by varying batch conditions. With an iron catalyst, the process often oxidizes organics, as well as reducing hexavalent chrome to trivalent precipitable form. 

Free oxygen is important in the decomposition of reduced materials (Box 4.3), typically iron, sulphur and organic matter. For example, the oxidation of reduced iron (Fe2+) and sulphur (S) in the common sulphide, pyrite (FeS2), results in the formation of sulphuric acid (H2S04), a strong acid ... 

It has been shown that iron-reducing bacteria are able to reduce humic acids using acetate, lactate, or H2 as reductants (Lovley et al. 1996,1998) thereby mediating the oxidation of organic substrates such as acetate with the reduction of Fe(III). 

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