Rust dissolution and removal by iron-reducing bacteria: A potential rehabilitation of rusted equipment

• The present study demonstrated the high reductive capacity of both strains: the collection S. oneidensis and the wild strain Geobacter spp. (soil isolate).
• The experimental strains were successful in Fe3+ reduction for both states: soluble and crystalline (originally prepared from rust).
• Rust dissolution can be improved by: addition of AFC at low concentration (0.2 g/l), increasing bacterial initial inoculum and rust reactive surface.
• Both experimental IRB strains were able to completely remove previously formed rust on carbon steel coupons.
• Additional results (not showed) revealed that culture S. oneidensis and the environmental isolate Geobacter spp., apparently have a different mechanism of iron reduction that requires further study.

Iron reducing bacteria (IRB), to be used in rust dissolution and removal, have been isolated and enriched from different environmental sources. Comparative measurements revealed that a soil isolate (Geobacter sulfurreducens sp.) had the highest reductive activity equivalent to Shewanella oneidensis (strain CIP 106686, pure culture). Both reductive microorganisms can use Fe3+ ions as electron acceptors from soluble as well as from crystalline sources. In nutrient medium containing soluble Fe3+, the highest reductive activity obtained for G. sulfurreducens sp. and S. oneidensis was 93 and 97% respectively. Successful removal of rust from carbon steel coupons has been achieved with both experimental bacteria.

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