טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKamari Ravit
SubjectRemoval of Rust from Metal Surfaces by Iron Reducing
Bacteria
DepartmentDepartment of Civil and Environmental Engineering
Supervisors Professor Robert Armon
Dr. Jeanna Starosvetsky
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

Iron is the most prevalent element on earth and the fourth most abundant one in the earth's crust. In soils and sediments it can make up a few percent per weight of the total dry mass, therefore ferric iron is by mass the most important electron acceptor for microorganisms under anoxic conditions, especially in water-logged soils, natural wetlands and freshwater lake sediments. Only in marine sediments, the high sulfate content (28 mM in seawater) counterbalances the dominance of ferric iron as electron acceptor.

The ubiquity and phylogenetic diversity of iron reducing bacteria, combined with the elemental abundance of iron in the earth's crust, establishes the global significance of the reduction process.

Iron reducing bacteria directly use insoluble Fe(III) oxides as an electron acceptors, therefore they are faced with the dilemma of how to transfer electrons to an extracellular electron acceptor. It has been shown that iron reducing bacteria such as Shewanella putrefaciens and several Geobacter species contain membrane-bound

Fe(III) reductase activity and that electron carriers such as cytochromes, capable of transferring electrons to Fe(III), are located in the membranes of these organisms. Organisms that must deal directly with these solid substrates must have unique physical or biochemical attributes, which might include the ability to solubilize the substrate, the ability to attach to substrate and directly transfer electrons to it, or the ability to transport this substrate into the cell as a solid.

Corrosion causes dramatic economic losses. Currently, widely used corrosion control strategies have disadvantages of being expensive, subject to environmental restrictions,  and sometimes inefficient. Rust on iron surfaces is usually removed by treatment with concentrated mineral acids or by mechanical polishing. In acid treatment, iron is dissolved in the acid solutions and forms salts which gradually decrease the capacity of the acids for rust removal. Therefore it is necessary to renew the solution or to supplement acids to sustain efficient rust removal.

Furthermore, rust removal by mineral acids is undesirable from the viewpoint of environmental pollution. A solution is required that may have the ability to constantly remove rust in a cyclic system. We have studied in the present work the biochemical rust removal from iron surfaces in a batch system using Geobacter sulfurreducens and Shewanella oneidensis and searched for the optimal conditions (pH, temperature, electron acceptors, medium) for the reduction process.