Sulfate reducing bacteria , reaction

The manner in which many of these bacteria cany on their chemical processes is qmte comphcated and in some cases not fuUy understood. The role of sulfate-reducing bacteria (anaerobic) in promoting corrosion has been extensively investigated. The sulfates in shghtly acid to alkaline (pH 6 to 9) soils are reduced by these bacteria to form calcium sulfide and hydrogen sulfide. When these compounds come in contact with underground iron pipes, conversion of the iron to iron sulfide occurs. As these bacieria thrive under these conditions, they will continue to promote this reaction until failure of the pipe occurs. 

The pathways for the degradation of toluene and xylene under denitrifying and sulfate-reducing conditions have been studied most extensively, and they take place by reactions quite different from those used by aerobic bacteria. As an example, two anaerobes affiliated with known sulfate-reducing bacteria isolated from enrichments with crude oil were able to grow at the expense of a number of alkylated benzenes—strain oXySl with toluene, o-xylene, and o-ethyltoluene and strain mXySl with toluene, m-xylene, and m-ethyltoluene (Harms et al. 1999). 

Rabus R, J Heider (1998) Initial reactions of anaerobic metabolism of alkylbenzenes in denitrifying and sulfate-reducing bacteria. Arch Microbiol 170 377-384. 

At many sites, the subsurface environment will be anoxic or even anaerobic due to the activity of aerobic and facultatively anaerobic bacteria in the surface layers of the soil. It is therefore essential to take into consideration the extent to which anaerobic degradation may be expected to be significant. Reactions may take place under sulfidogenic or methanogenic conditions, and the occurrence of sulfate at sites containing building material waste and the metabolic versatility of sulfate-reducing bacteria makes them particularly attractive. 

Metal contaminants can in some cases be immobilized in situ by oxidation or reduction, or precipitated by reaction with sulfide. Sulfate reducing bacteria are sometimes stimulated to produce sulfide, or a sulfur-bearing compound such as calcium polysulfide can be injected into the subsurface as a reductant and sulfide source. In certain cases where the contamination poses little immediate threat, it can safely be left to attenuate naturally (e.g., Brady et al., 1998), a procedure known as monitored natural attenuation. 

To establish the stoichiometry of the sulfide formation, Equation (6.3) must be combined with the oxidation process for the organic matter that is the actual electron donor for the heterotrophic sulfate-reducing bacteria. The procedure for the combination of the oxidation and the reduction process steps is the same as outlined in Section 2.1.3. If organic matter is considered simply as CH20, the combination of the oxidation process as depicted in Example 2.2 and the reduction reaction for sulfate shown in Equation (6.3) result in the following redox process ... 

Some sulfate-reducing bacteria have been shown to contain SODs and catalases, but other species do not demonstrate the expected activities for these enzymes (Hatchikian et al. 1977 van Niel and Gottschal 1998 Dos Santos et al. 2000). The apparent absence of these enzymes can be rationalized on the basis that their catalytic dismutation reactions (Eqs. 10.1 and 10.2) generate dioxygen, which may be disadvantageous for strict anaerobes but raises the question of how these organisms protect themselves against transient air exposure. 

These processes are catalyzed by bacteria and probably involve both inorganic and organic iron and manganese species (22). They may also be strongly controlled by microbial competition between Fe(III) and sulfate-reducing bacteria (27). Associated with these reduction reactions is the reduction of residual sulfate (produced in the oxic zone by bacterially catalyzed reactions) similar to eq 7 (21). 

Microbiological action in starch dispersions results in a drop in pH, loss of viscosity and the development of odor. Retrogradation may be accelerated by the drop in pH or especially if butanol, which complexes with amylose, is generated via starch fermentation. Sulfate-reducing bacteria will cause black deposits due to reaction with iron in the process water. For quality control, preservatives are added to starch slurry, cooked starch, surface size and coating color. 

Wetlands, at times, may be a poor environment for the formation of metal oxides and/or oxyhydroxides because of the typically low redox potential (Eh). Optimizing the activity of sulfate-reducing bacteria (e.g., desulfovibrio) in the anaerobic zone would be a more effective way of removing metals and sulfates from AD (Kleinmann, 1989). These sulfate-reducing bacteria consume acidity and most of the hydrogen sulfide they produce reacts with heavy metals to create insoluble precipitates. The reactions are shown below ... 

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