Sulfur, inorganic, microbial oxidation

Kelly DP, Wood AP. 1994. Whole organism methods for inorganic sulfur oxidation by chemolithotrophs and photolithotrophs. In Peck HD, LeGall J, editors. Inorganic microbial sulfur metabolism. Volume 243, Methods in enzymology. p 510-20. 

Also, as precombustion sulfur removal becomes an attractive alternative to flue gas scrubbers, scientists have explored several methods of removing inorganic sulfur from coal and coal chars. Oxidation, microbial oxidation/desulfurization, and halogenation are avenues that are now, and have been, under investigation for some time (Thomas, 1995). 

Beyer et al. (49) found that, during microbial desulfurization, pyritic sulfur decreases and elemental sulfur increases with time, whereas the organic sulfur remains unchanged. They suggested that microbial oxidation of pyrite produces ferric sulfate [Fe2(S04)3] and that the simultaneous inorganic reaction of ferric iron with pyrite produces elemental sulfur and ferrous iron, as follows ... 

Figure 1 Schematic of the multi-step process of organic degradation in anaerobic systems, indicating the influence of H2. Boxes indieate major chemical pools, arrows with text indicate microbially-mediated process. Superscripts on arrow text indicate the mode of control by H2 (F)—facultative interspecies H2 transfer (O)—obligate interspecies H2 transfer (B)—H2 can be a by-product, shifting the product yield (U)— the reaction becomes thermodynamically unfavorable when H2 concentrations are too low (R)—the process is demonstrated or hypothesized to be reversible, based on H2 concentrations. Note ( ) important inorganic oxidants may include NO, Mn , Fe , and various oxidized sulfur speeies (e.g., S04 ) Xred corresponds to the redueed form (e.g., H2S). Adpated from Ref. [19].

The distinction between oxidative and reductive systems is a useful way to divide the world of microbial desulfurization, as it refiects a basic difference in the underlying biochemistry. In this article, the major areas of research in biological desulfurization of inorganic and organic sulfur compounds in waste streams and petroleum-derived fuels are addressed. Both reductive and oxidative approaches are covered. 

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