Bacteria, sulfate-reducing

Although most of the sulfate-reducing bacteria are heterotrophic, some lithotrophic sulfate-reducing bacteria are known these bacteria grow by oxidizing hydrogen gas (H2) with sulfate (S042 ) (Fig. 1.11). 

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Arsenic is another element with different bioavailabiUty in its different redox states. Arsenic is not known to be an essential nutrient for eukaryotes, but arsenate (As(V)) and arsenite (As(III)) are toxic, with the latter being rather more so, at least to mammals. Nevertheless, some microorganisms grow at the expense of reducing arsenate to arsenite (81), while others are able to reduce these species to more reduced forms. In this case it is known that the element can be immobilized as an insoluble polymetallic sulfide by sulfate reducing bacteria, presumably adventitiously due to the production of hydrogen sulfide (82). Indeed many contaminant metal and metalloid ions can be immobilized as metal sulfides by sulfate reducing bacteria. 

Although the process requires the addition of a phosphate donor, such as glycerol-2-phosphate, it may be a valuable tool for cleaning water contaminated with radionuchdes. An alternative mode of uranium precipitation is driven by sulfate-reducing bacteria such as Desulfovibrio desulfuricans which reduce U(VI) to insoluble U(IV). When combined with bicarbonate extraction of contaminated soil, this may provide an effective treatment for removing uranium from contaminated soil (85). 

Water Groundwater can be treated in anaerobic bioreactors that encourage the growth of sulfate reducing bacteria, where the metals are reduced to insoluble sulfides, and concentrated in the sludge. For example, such a system is in use to decontaminate a zinc smelter site in the Netherlands (95). 

Various patents (22—24) have been issued claiming the use of tetrakis(hydroxymethyl)phosphonium sulfate in, for example, water treating, pharmaceuticals (qv), and in the oil industry where this compound shows exceptional activity toward the sulfate-reducing bacteria that are a primary cause of hydrogen sulfide formation and consequent problems associated with souring and corrosion (25). 

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. 

Sulfate reducers. The best-known form of microbiologically influenced corrosion involves sulfate-reducing bacteria.- Without question, sulfate reducers cause most localized industrial cooling water corrosion associated with bacteria. Desulfovibrio, Desulfomonas, and Desulfotomacu-lum are three genera of sulfate-reducing bacteria. 

Corrosion morphologies. Sulfate-reducing bacteria frequently cause intense localized attack (Figs. 6.2 through 6.7). Discrete hemispherical depressions form on most alloys, including stainless steels, aluminum. Carpenter 20, and carbon steels. Few cases occur on titanium. Copper alloy attack is not well defined. 

TABLE 6.3 Typical Microbiological Analysis at Outlet A Main Condenser Suffering No Significant Corrosion by Sulfate-Reducing Bacteria ... 

Figure 6.2 Severely pitted aluminum heat exchanger tube. Pits were caused hy sulfate-reducing bacteria beneath a slime layer. The edge of the slime layer is just visible as a ragged border between the light-colored aluminum and the darker, uncoated metal below.

Figure 6.9 Irregular deposit and corrosion-product mounds containing concentrations of sulfate-reducing bacteria on the internal surface of a 316 stainless steel transfer line carrying a starch-clay mixture used to coat paper material. Attack only occurred along incompletely closed weld seams, with many perforations. Note the heat tint, partially obscured by the deposit mounds, along the circumferential weld.

Figure 6.10 A perforated carbon steel pipe at a weld-backing ring. The gaping pit was caused by sulfate-reducing bacteria (see Case History 6.1).

Clostridia frequently are found where sulfate-reducing bacteria are present, often in high numbers inside tubercles. A typical microbiological analysis of tubercular material removed from a troubled service water system main is given in Table 6.4. Clostridia counts above 10 /g of material are high enough to cause concern. When acid producers... 

The section was perforated in several locations due to severe, localized wastage on internal surfaces (Fig. 6.23A and B). The cooling water had a history of low-pH excursions, with documented depressions to a pH below 5. The system also had been plagued with high sulfate-reducing bacteria counts. 

Pitting had two distinct causes. Sulfate reducers had formed the large hemispherical pits. The more undercut pits were formed during a low-pH excursion involving mineral acid after the sulfate-reducing bacteria became inactive. It is likely the low-pH excursion deepened preexisting sulfate-reducer pits, causing final perforation. 

There are heat-resistant sulfate-reducing bacteria with high activity at 70°C... 

Scale deposits create conditions for concentration-cell corrosion as they do not form uniformly over the metal surface. Sulfate-reducing bacteria thrive under these deposits, producing hydrogen sulfide and, consequently, increasing the rate of corrosion. Due to the following factors, the drilling fluid environment is ideal for scale deposition [189]. These factors are as follows ... 

The presence of sulfate-reducing bacteria can be detected by using API sulfate-reducing broth. If the broth is inoculated with drilling fluid and the color changes from yellow to black, the result is positive. 

Light, sandy, well-drained soil of high electrical resistivity is low in corrosivity and coated steel or bare stainless steels can be employed. It is unlikely that the whole pipe run would be in the same type of soil. In heavier or damp soils, or where the quality of back filling cannot be guaranteed, there are two major corrosion risks. Steel, copper alloys and most stainless steels are susceptible to sulfide attack brought about by the action of sulfate-reducing bacteria in the soil. SRB are ubiquitous but thrive particularly well in the anaerobic conditions which persist in compacted soil, especially clay. The mechanism of corrosion where SRB are involved is described in Section... 

NOTE Where RW quality is poor, a booster unit is generally required on the front of the multifunctional tank, so that the concept of a single tank is lost. Additionally, where iron- and sulfate-reducing bacteria may be present, periodic sterilization of the bed using chlorine injection becomes necessary. 

Dissimilatory sulfate reduction (SO - - H2S) Sulfate-reducing bacteria... 

L. L. Barton (Ed.), Sulfate-Reducing Bacteria, Plenum Press, New York, 1995. 

Metal Effects on Sulfur Cycle Bacteria and Metal Removal by Sulfate Reducing Bacteria (O. J. Hao)... 

Yagi laid the foundation for the enzymology of CODH when he discovered an enzymatic activity in sulfate-reducing bacteria that oxidizes CO to CO2 (118). Twenty-five years later, the first CODH was purified to homogeneity (119, 120). The homogeneous C. thermo-aceticum CODH was shown to contain 2 mol of nickel, 12 iron, 1 zinc, and 14 acid-labile inorganic sulfide per afS dimeric unit (120). 

SIMPLE AND COMPLEX IRON-SULFUR PROTEINS IN SULFATE REDUCING BACTERIA... 

This chapter will focus on simple and complex iron-sulfur-con-taining proteins isolated from sulfate reducing bacteria (SRB), in order to review the following topics types and distribution of proteins metal clusters involved and their association with other centers and... 

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