Evaluation of molybdate and nitrate on sulphate-reducing bacteria related to corrosion processes in industrial systems

The sulfate-reducing bacteria growth kinetics and the biotransformation of sulfate into hydrogen sulfide were studied under laboratory conditions, using batch and continuous assays to determine the effect of molybdate and nitrate as metabolic inhibitors. The microorganisms were isolated from water coming from a natural gas dehydration plant, where they were associated with Microbiologically Influenced Corrosion (MIC) processes, and later cultured in planktonic and sessile states. The addition of 5 mM molybdate showed a growth reduction to levels of non-detectable floating cells and a six order of magnitude reduction in biofilms, concomitant with a sulfide decrease of around 100% in all cultures inhibited by this compound. The addition of 75 mM nitrate showed a four order of magnitude reduction in free bacterial cells and a two order of magnitude reduction in adhered bacterial cells, respectively, as well as a sulfide decrease of around 80%. The decreased corrosion rate detected suggests that these inorganic salts could be non-conventional biocides for an effective and environmentally non contaminant way of controlling and mitigating internal biocorrosion processes in storage tanks and pipelines in natural gas and petroleum industrial systems.