Microbiologically influenced corrosion (MIC): Which organisms can contribute to corrosion problems in pipelines, tanks, and distribution systems?

Introduction / Context:
Corrosion is not purely electrochemical; microbial activity can accelerate or initiate material degradation. Microbiologically influenced corrosion (MIC) involves diverse consortia that alter local chemistry, produce corrosive metabolites, and create differential aeration cells under biofilms. Recognizing culprits is vital for mitigation.

Given Data / Assumptions:

• Iron-oxidizing and iron-depositing bacteria create tubercles and differential aeration.
• Sulfur bacteria, including sulfate-reducing bacteria (SRB), produce sulfides that attack metals.
• Slime formers generate biofilms that trap corrosive species and maintain microenvironments.

Concept / Approach:
MIC typically results from synergistic communities. Iron bacteria oxidize ferrous to ferric iron, forming deposits that facilitate under-deposit corrosion. SRB reduce sulfate to sulfide, generating hydrogen sulfide and metal sulfides that are aggressive to steel. Slime-formers provide the matrix for gradients in pH, oxygen, and ions, amplifying corrosion cells.

Step-by-Step Solution:
List microbial groups known to foster corrosion.Explain their mechanisms (iron cycling, sulfide production, biofilm gradients).Acknowledge multi-species biofilms are common in practice.Select the inclusive answer reflecting real systems.

Verification / Alternative check:
Inspection of corroded lines often reveals biofilms with SRB markers (e.g., Desulfovibrio) and iron bacteria deposits; mitigation includes biocides, pigging, and materials selection.

Why Other Options Are Wrong:

• Single-group choices ignore the multi-factorial nature of MIC.
• None of these: contradicts extensive field evidence.

Common Pitfalls:
Blaming corrosion solely on SRB; overlooking the role of oxygen gradients and under-deposit corrosion maintained by slime matrices.

Final Answer:
All of these.