Bio Corrosion 2 Ppt

SANDEEP K PSANDEEP K P

AEM 10AEM 10

1ENVIRONMENTAL MICROBIOLOGY

What is corrosion?

Corrosion of metal in an oxygenated aqueous environment is an electrochemical phenomenon in which the metal ions go into solution (anodic reaction) leaving electron that combine with oxygen to produce hydroxyl ions (cathodic reaction)

In anaerobic environments, oxygen is replaced by hydrogen ions or water as cathodic reactants


The deterioration of metal due to microbial activity Biocorrosion or microbial corrosion or

microbiologically influenced corrosion (MIC) may be defined as an electrochemical process where the participation of microorganisms is able to initiate, facilitate or accelerate the corrosion

Biocorrosion refers to the accelerated deterioration of metals owing to the presence of biofilm on their surface

The detailed mechanisms of biocorrosion are poorly understood


http://en.wikipedia.org/wiki/File:Titanic-bow_seen_from_MIR_I_submersible.jpeg

Biocorrosion means the processes at metal surfaces which are associated with microorganisms, or the products of their metabolic activities like enzymes, exopolymers, organic and inorganic acids, as well as volatile compounds such as ammonia or hydrogen sulphide

These can affect cathodic and/or anodic reactions, thus altering electrochemistry at the biofilm/metal interface


Biocorrosion is a process in which metabolic activities of microorganisms associated with metallic materials (e.g. manganese oxidation by bacteria) supply insoluble products (e.g. manganic oxides/hydroxides), which are able to accept electrons from the base metal

Pitting corrosion on 316S stainless steel, an example of MIC 5ENVIRONMENTAL MICROBIOLOGY

Recent investigations in biocorrosion have focused on the influence of biominerilization process taking place in metallic surfaces & the impact of extracellular enzymes, active within biofilm matrix and on the electrochemical reactions at the biofilm-metal interface

The two component system (metal + solution) characteristics of abiotic corrosion changes to a three component system (metal + solution + microorganism) in biocorrosion

The subsequent behavior of metal / solution interface will be conditioned by the interactions between these three components


A thick biofilm develops, an anaerobic zone develops adjacent to the colonized surface

Microorganisms develop colonies and complex consortia

These trap ions and create localized chemical and physical gradients at the metal surface

An electrochemical cell is set up and metal dissolves, causing pit formation beneath the affected area


Bacteria are considered as the primary colonizers of inanimate surfaces in both natural and manmade environment

Bacterial biofilm on Fe, Cu, Al and their alloys The main types of bacteria associated with metals in

terrestrial and aquatic habitats are sulfate reducing & oxidizing

bacteria, iron oxidizing & reducing bacteria, manganese oxidizing bacteria and bacteria secretes organic acids, slime

A consortium of bacteria coexists in naturally occurring biofilm complex


Biofilms consist of microbial cells, their EPS, which facilitate irreversible attachment of cells to the surface, inorganic precipitates derived from the bulk aqueous phase &/or corrosion products of the metal substratum

EPS consist of a complex mixture of cell-derived polysaccharides, proteins, lipids and nucleic acids.


EPS

FeS SRB CELLS

FeS

SRB Cell surface

SRB on mild steel10ENVIRONMENTAL MICROBIOLOGY

1.Free-floating /planktonic bacteria encounter a submerged surface and within minutes can become attached. They begin to produce slimy extracellular polymeric substances (EPS) and to colonize the surface.

2.EPS production allows the emerging biofilm community to develop a complex, three-dimensional structure that is influenced by a variety of environmental factors.

3.Biofilms can propagate through detachment of small or large clumps of cells, or by a type of "seeding dispersal" that releases individual cells 11ENVIRONMENTAL MICROBIOLOGY


Bacteria, Yeast and Fungi The synergistic effects of several properties of the

microorganisms such as their growth rate, varied metabolic products and their high surface to volume ratio allow them to interact very actively

Biofilm Gallionella, an iron-oxidising bacterium and Pedomicrobium

manganicum, a manganese-oxidising bacterium Hyphomicrobium, Sphaerotilus, Crenothrix, Leptothrix,

Siderocapsa. Thiobacillus thioparus and Thiobacillus thiooxidans.


Acidithiobacillus bacteria produce sulphuric acid; Acidothiobacillus thiooxidans frequently damages sewer pipes.

Ferrobacillus ferrooxidans directly oxidizes iron to iron oxides and iron hydroxides

aerobic bacteria like Thiobacillus thiooxidans, Thiobacillus thioparus, and Thiobacillus concretivorus

anaerobic bacteria especially Desulfovibrio and Desulfotomaculum


Sulphate-Reducing Bacteria (SRB) Anaerobes which carry out reduction of sulphur

compounds such as sulphate, sulphite, thio-sulphate and even sulphur itself to sulphide

Oil, gas and shipping industries are seriously affected by the sulphides generated by SRB

Biogenic sulphide production leads to health and safety problems, environmental hazards and severe economic losses due to reservoir souring (increased sulphur content) and the corrosion of equipment

Desulfovibrio alaskensis, Desulfovibrio vulgaris


Metal-Depositing Bacteria (MDB) Bacteria of the genera Siderocapsa, Gallionella,

Leptothrix, Sphaerotilus, Crenothrix and Clonothrix participate in the biotransformation of oxides of metals such as iron and manganese

Iron-depositing bacteria (e.g., Gallionella and Leptothrix) oxidize Fe2+, either dissolved in the bulk medium or precipitated on a surface, to Fe3+

Bacteria of the genera given above are also capable of oxidizing manganous ions to manganic ions with subsequent deposition of manganese dioxide

These bacteria have been typically associated with formation of tubercles 16ENVIRONMENTAL MICROBIOLOGY

Slime-producing bacteria Slime-forming microorganisms on stainless steels

include Clostridium spp., Flavobacterium spp., Bacillus spp., Desulfovibrio spp., Desulfotomaculum spp. and Pseudomonas spp

Fungi produce organic acids Hormoconis resinae, Aspergillus spp., Penicillium

spp. and Fusarium spp


Enzymes such as catalases, peroxidases and superoxide dismutases are involved in reactions of oxygen reduction, therefore facilitate corrosion by accelerating the overall cathodic reaction

Extracellular catalase produced by Pseudomonas species

SEM image of a mild steel surface after the removal of bacterial biofilm, revealing changes in surface characteristics 18ENVIRONMENTAL MICROBIOLOGY

Destroys the metal distribution pipes Water quality deterioration, environmental

contamination Economic losses in water distribution systems Damage to sewage systems by acid deterioration MIC of carbon steel in cooling water system in

power plants Losses in oil and gas companies Approximately 20% of all corrosion damage to

metallic materials is microbially influenced



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Bio Corrosion 2 Ppt