Biological functionalization of a sol-gel coating for the mitigation of microbial-induced corrosion

The addition of biocides to water systems has been the most direct attempt to limit or mitigate the formation of surface biofilms that lead to the development of microbial-induced corrosion (MIC), a process that costs industry millions of pounds annually. The efficacy of this approach is dependent upon a) the biocide being delivered to all water-metal substrate interaction sites and b) the biocide remaining active, therein preventing biofilm development/growth. Anti-fouling biocide additions to water supplies, or anti-fungal additives in paints, have an adverse impact upon the environment, for example, tri-butyl tin is toxic to aquatic life. An alternative non-toxic approach currently being pursued by the authors involves localizing a biologically active reagent close to the metal substrate. Localization in this case is achieved by synthesizing a hybrid functional sol-gel coating and encapsulating a suitable non-pathogenic biological component within the sol-gel matrix. Distribution within the sol-gel coating of vegetative bacteria or spores has been confirmed using various microscopy techniques. Electrochemical data in the form of polarization resistance, impedance spectroscopy, and electrochemical noise all show that the presence of either P. fragi or P. polymyxa within a sot-gel coating leads to a corrosion resistance improvement at least 10 times that of an equivalent abiotic coating. Confirmation of this improvement is derived from six months of field trial testing conducted in a tidal estuarine environment. Comparative tests that use a control sol-gel coating immersed within nutrient poor artificial seawater that contained freely suspended R polymyxa reveal no marked improvement over a control sample in the absence of the endospores.