PRESENTER: IP MOLOBELAAPRIL 29, 2011

Microbiologically influenced corrosion in water infrastructures

and pipe line materials

College of Science, Engineering and Technology

Civil and Chemical Engineering DepartmentUniversity of South Africa

Outline What is MIC? How do they form and induce

corrosion? What impacts do they have in the

water industry? What kind of surface materials do

they attack? How can they be removed or

controlled?

Microorganisms – everywhere Some are bad (destructive) Some are good (non destructive)

What is MIC? MIC - causative agent of biofouling

and biocorrosion MIC - cause deterioration of metals

as a result of the metabolic activity of microorganisms-(forms by biofilms)

Biological activity modify the structural chemistry of the materials - corrosion

How do MIC form?Do microorganisms “eat” metals?Types of Microorganisms Aerobes – oxygen consumingAnaerobes – non- oxygen consuming

Groups Categorized as (Acid producing, Sulphate reducing, Nitrate reducing and Iron reducing biofilms) - (Gallionella, Sphaerotilus, Pseudomonas, Klebsiella, Eneterobacter, Acinetobacter, Bacillus, Aeromonas, and Legionella)

Cont.

Involve in metal degradation

Sulphate Reducing Biofilms (SRB) Cathodic depolarisation MIC mechanism

(proposed by Wolzgen and Vulgt, 1934) type materials steel and iron

SRB- consumes H2 through Hydrogenase enzymes depolarise cathode corrosion (end product) Equa: SO42- + 8H S2- + 4H20 Cathodic depolarisation SRB

Biocorrosion and biofouling of water pipe materials and other

infrastructures

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Sulphur Reducing Bacteria

Desulfovibrio vulgaris

Desulfuromonas acetoxidans

Impact of MIC in the water industry Cause fouling of water pipe materials

and other infrastructures loss in billions of revenues annually

Reduces efficiencies of water structures cooling towers, heat exchangers etc

Affect the quality of drinking water - health risk hazards (production of H2- not environmentally friendly)

Cont.

Causes odour Debris from corroded materials-end up

in human systems from consumption of drinking water carcinogenic and mutagenic

Type of materialsAll materials Stainless steel Iron Aluminium alloys Titanium alloys Cooper Nickel

Note: Specific bacterial group – affect – specific materials

Prevention of biocorrosion or MIC Temperature control - can reduce /

minimise corrosion enhancing bacteria (20- 350C is the most desirable temperature range for growth of most of the microbes)

Do not allow dead-spots to form in any water pipe line material or infrastructure. These stagnant environments provide the best environment for biofilms to form and bacteria to grow.

Material development more alkaline environment likely to reduce corrosion, but some of the bacteria prefer an alkaline environment, so diagnosis of the type of bacteria for the individual corrosion problem is required.

To understand biocorrosion and MIC – it is important to integrate physical and chemical phenomena with microbial physiology

Cont.

• Collaborative research on biofouling and biocorrosion (scientists from different expertise)

I thank you!!!!!!!!!

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