Role of Manganese Depositors on Ennoblement Process: Evidences for Adsorption Theory

Abstract The process of ennoblement has been correlated with extracellular polymers (enzyme theory) and biogenic manganese dioxide deposition by many investigators. In the present study, to find out the role of cations and polymers on ennoblement process investigation has been undertaken on materials such as 6XN-SS (UNS NO8387); C 276 (UNS NO10276); Titanium gr2 (UNS NOR50250) for microbiological characterization and electrochemical studies. The quantum of manganese depositing heterotrophic bacteria was 1.31 × 106 CFU / cm2 on 6XN-SS. Bacillus, Arthobacter, Propionibacterium were acting as manganese depositors in the biofiim. Ethylene diamine tetra acetic acid (EDTA) has been used to eliminate all cations in biofilm., The ennoblement could not be observed in EDTA treated biofilm. The present study reveals that without the presence of cations in the biofilm ennoblement does not take place on passive materials. Polarisation study reveals that even though cathodic current is increased by biofilm during ennoblement, biofiim decreases passivation current (ip). It is due to the presence of anodic inhibitors like phosphates, nitrates, nitrites in the biofilm matrix. The present study explains the nature of cathodic curves of various n/p type semiconducting oxide films in presence of biofilm.This present study also supports the MnO2 theory and contradicts the enzyme theory. Moreover, it gives additional supporting evidences for adsorption theory proposed by Central Electro Chemical Research Institute, Karaikudi,lndia.