Influence of aqueous phase on electrochemical biocorrosion tests in diesel/water systems

Abstract

Storage tanks containing microbially contaminated diesel oil are susceptible to corrosion. This process may be evaluated electrochemically in the laboratory using simulated storage systems containing diesel oil and an aqueous phase. The simulated aqueous phase must supply mineral nutrients for microbial growth, together with adequate electrical conductivity, without, however, being too corrosive, so as to allow the aggressive nature of the microbial metabolites to be detected. In this investigation, microbial growth was measured in six electrically conductive media overlaid with metropolitan diesel oil containing an additive package. The microorganisms were the filamentous fungi, Hormoconis resinae, Paecilomyces variotii and Aspergillus fumigatus, the bacterium Bacillus subtilis and the yeast Candida silvicola, all previously isolated from contaminated diesel oil. After 60 days incubation with pure or mixed inocula of these microorganisms, pH, conductivity and viable microorganisms were measured. The electrochemical behaviour of carbon steel ASTM 283-93-C was determined in each of the six media (uninoculated) and in selected inoculated medium via measurements of open circuit potential and potentiostatic polarization curves. The uptake of phosphate (corrosion inhibitor), microbial growth, pH, conductivity and anodic and cathodic polarization curves were assessed in the water phase after 30 and 60 days of incubation with each single species Aspergillus fumigatus and Hormoconis resinae and with the consortium. The medium which proved most appropriate was Bushnell-Haas medium modified by the omission of chlorides, which allowed satisfactory microbial growth and had low aggressivity towards the steel. The performance of electrochemical tests in aerated, rather than deaerated, electrolyte solutions is suggested to be important to allow the detection of microbial influence on passive film formation and stability.

Growth of Paecilomyces variotii in B0 (diesel), B100 (biodiesel) and B7 (blend), degradation and molecular detection

“…The microbial contamination of stored fuels, mainly diesel oil, is a major problem in refineries and distribution systems (Bento andGaylarde, 1996, 2001;Bento et al, 2004).…”

“…Many factors, such as the presence of water in the bottom of the tanks during storage, have been cited as increasing microbial growth in the systems and can lead to blocking of pipelines and filters, affecting the final quality of the fuel and corrosion of the tanks (Bento and Gaylarde, 2001;Bento et al, 2004;Bücker et al, 2011;White et al, 2011;Cazarolli et al, 2012Cazarolli et al, , 2014Zimmer et al, 2013;Passman, 2013). A concentration of only 1% water in a storage system is sufficient for the growth of aerobic and anaerobic bacteria and yeasts, as well as for the development of fungal biomass at the oil/water interface (Gaylarde et al, 1999;Chesneau, 2000;Bento and Gaylarde, 2001;Bento et al, 2004;Bücker et al, 2011;Sørensen et al, 2011;Cazarolli et al, 2012Cazarolli et al, , 2014Zimmer et al, 2013;Passman, 2013).…”

“…A concentration of only 1% water in a storage system is sufficient for the growth of aerobic and anaerobic bacteria and yeasts, as well as for the development of fungal biomass at the oil/water interface (Gaylarde et al, 1999;Chesneau, 2000;Bento and Gaylarde, 2001;Bento et al, 2004;Bücker et al, 2011;Sørensen et al, 2011;Cazarolli et al, 2012Cazarolli et al, , 2014Zimmer et al, 2013;Passman, 2013). Numerous microorganisms have been isolated from fuels (Atlas, 1981;Gaylarde et al, 1999;Bento and Gaylarde, 2001;Bento et al, 2004;Bücker et al, 2011;White et al, 2011).…”

“…Biodegradability of biodiesel compared to mineral diesel it is a problem specially when occurs microbial contamination during storage which may lead to blocking of pipelines and filters, affecting the final quality of the fuel and corrosion of the tanks (Bento and Gaylarde, 2001;Bento et al, 2004Bento et al, , 2006Passman and Dobranick, 2005;Bücker et al, 2011;White et al, 2011;Cazarolli et al, 2012Cazarolli et al, , 2014Zimmer et al, 2013;Passman, 2013).…”

Impact of micelles on the biocidal efficiency in a diesel–water interface

“…good house keeping practices, treatment with biocides to limit their growth, the use of special tank linings, etc. 26 The present authors feel that the bacteria should be killed at the interface, which will be useful to stop the production of the emulsion 25 and diesel degradation. Therefore, the identification of inhibitors/biocides that could act at the interface is needed in pipelines transporting petroleum.…”