Immobilization and ferrous iron bio-oxidation studies of a Leptospirillum sp. mixed-cell culture

Immobilization of a mixed bacterial culture (predominantly Leptospirillum sp.) on mechanically modified graphite surfaces and different types of activated carbon fiber supports (felt and textile; both silicated and non-silicated) was studied experimentally. Maximum cell coverage on graphite samples occurred on a surface roughness of 2.08 μm (3.9 × 104 cells/mm2). In non-silicated samples the activated carbon fiber support with the greatest surface area per gram (felt) lead to the greatest number of immobilized microorganisms over a 10 h period (2.2 × 104 cells/mm2). The silication significantly increased surface area in the fibrous matrix voids and thereby increased the number of immobilized microorganisms on both modified activated carbon felt and fabric. The silicated felt exhibited the greatest number of immobilized Leptospirillum sp. cells of all activated carbon fiber cathodes studied (2.9 × 104 cells/mm2). Physical property and elemental analyses of silicated samples indicated that other methods of augmenting bacterial immobilization should be explored as silication increased electrical resistance of the samples 100 fold. Leptospirillum sp. immobilized on unmodified activated carbon felt yielded the maximum experimentally observed rate of ferrous iron bio-oxidation (∼900 mg/L h).