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
Corroded section
Corroded section
Corroded section
Corroded section
Corroded section
Corroded section
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!!!!!!!!!
Cartoons