PRESENTER: IP MOLOBELA APRIL 29, 2011

Microbiologically influenced corrosion in water infrastructures and pipe line materials College of Science, Engineering and Technology Civil and Chemical Engineering Department University 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

Involve in metal degradation How do MIC form? Do microorganisms “eat” metals? Types of Microorganisms Aerobes – oxygen consuming Anaerobes – 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

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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 materials All 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 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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