Page 445 - Corrosion Engineering Principles and Practice

414 C h a p t e r 1 0 C o r r o s i o n i n S o i l s a n d M i c r o b i o l o g i c a l l y I n f l u e n c e d C o r r o s i o n 415

Organic
sulfur
compounds
Assimilatory sulfate Mineralization processes
reduction (plants (Spontaneous/
Sulfate & microorganisms) microbiological)
in marine Dissimilatory Sulfide
environments sulfate reduction Minerals
(Desulfovibrio)
Biological oxidation
with O and NO
3
2
SO 4 2– (Thiobacillus) S 2–
Dissimilatory
sulfur reduction

Biological oxidation
with O and NO 3 Spontaneous
2
(Thiobacillus) oxidation
Biological oxidation
Anaerobic photosynthetic with O (Beggiatoa
2
Oxidation (Green & purple S andThiobacillus)
sulfur bacteria) Anaerobic photosynthetic
Oxidation (Green & purple
sulfur bacteria)

Sulfur
deposits

FIGURE 10.10 The sulfur cycle showing the role of bacteria in oxidizing elemental
sulfur to sulfate and in reducing sulfate to sulfide [27].

Tests for the presence of SRB have traditionally involved growing
the organisms on laboratory media, quite unlike the natural
environment in which they were sampled. These laboratory media
will only grow certain strains of SRB, and even then some samples
require a long lag time before the organisms will adapt to the new
growth conditions. As a result, misleading information has been
obtained regarding the presence or absence of SRB in field samples.

Sulfur/Sulfide Oxidizing Bacteria This broad family of aerobic bacteria
derives energy from the oxidation of sulfide or elemental sulfur to
sulfate (Fig. 10.10). Some types of aerobes can oxidize sulfur to sulfuric
acid, with pH values as low as one reported. These Thiobacillus strains
are most commonly found in mineral deposits, and are largely
responsible for acid mine drainage, which has become an environmental
concern. They proliferate inside sewer lines and can cause rapid
deterioration of concrete mains and the reinforcing steel therein.