Bacterial growth in process pipelines happens when operating and material conditions allow microorganisms to attach, survive, and multiply (often as biofilms). The main causes can be grouped as follows:
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1️⃣ Water & Nutrient Availability (Primary Cause)
Bacteria need water + food to grow.
Presence of water or moisture (especially stagnant or low-flow zones)
Organic matter (oils, hydrocarbons, sugars, proteins)
Inorganic nutrients (iron, sulfur, nitrogen, phosphorus)
Dissolved oxygen (for aerobic bacteria) or sulfates (for SRB)
📌 Even “clean” water can support bacteria if nutrients are present at low levels.
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2️⃣ Flow Conditions
Poor hydraulic conditions strongly promote growth.
Low flow velocity
Dead legs, blind branches, unused connections
Stagnant zones (shutdowns, batch operation)
Laminar flow instead of turbulent flow
➡ These allow bacteria to settle and attach to pipe walls.
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3️⃣ Pipe Material & Surface Condition
Some materials promote attachment more than others.
Carbon steel & cast iron → rough surface, iron acts as nutrient
Corroded or pitted pipes
Weld seams and gaskets
Rubber liners and elastomers
🦠 Rough surfaces make it easier for bacteria to form biofilms.
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4️⃣ Temperature Range
Most process bacteria thrive in:
20–45 °C → ideal for many bacteria
<60 °C → biofilm still possible
>70 °C → many bacteria die (not all)
⚠ Thermophilic bacteria can survive at higher temperatures in some systems.
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5️⃣ Chemical Conditions
Certain chemistry favors bacterial growth:
Low disinfectant residual (chlorine, biocide, ozone)
Neutral pH (6–8) → optimal
Low salinity (some bacteria tolerate high salinity)
Sulfates → support sulfate-reducing bacteria (SRB)
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6️⃣ Lack of Proper Disinfection / Biocide Control
No continuous or periodic biocide dosing
Incorrect biocide type or concentration
Poor mixing or contact time
Biocide neutralized by organic load
➡ Bacteria adapt and form resistant biofilms.
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7️⃣ Oxygen Conditions
Different bacteria dominate depending on oxygen presence:
Aerobic bacteria → oxygen present
Anaerobic bacteria → oxygen-free zones (dead legs, deposits)
Sulfate-reducing bacteria (SRB) → major cause of MIC corrosion
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8️⃣ Contamination Sources
Bacteria can be introduced from:
Makeup water
Poorly cleaned new pipes
Maintenance activities
Open tanks and vents
Recycled or reused process water
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9️⃣ Deposits & Fouling
Sediments, scale, corrosion products
Sludge and oil films
These shield bacteria from disinfectants and create micro-environments.
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⚠ Consequences of Bacterial Growth
Microbiologically Influenced Corrosion (MIC)
Flow restriction and pressure drop
Product contamination
Heat transfer loss
Bad odor (H₂S)
Reduced pipe life
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✅ Typical Prevention Measures
Eliminate dead legs
Maintain minimum flow velocity
Proper material selection (e.g., stainless steel, plastics)
Regular pigging / flushing
Correct biocide selection & dosing
Maintain disinfectant residual
Control nutrients and deposits