Failure Analysis of Microbiologically Influenced Corrosion in Storage Tanks Containing B20 Biodiesel

Abstract

Ultra-low sulfur diesel (ULSD) in the United States contains up to 5% v/v biodiesel, which is used as an additive to improve lubricity and to reduce emissions. Biodiesel blends containing up to 20% biodiesel (i.e.,, B20 biodiesel) further reduce emissions and can be used with most current engines and fuel infrastructure without changes in performance. There are downsides to biodiesel: it is more hygroscopic than ULSD, absorbing and entraining more water from the atmosphere, and it is also more readily degraded by microorganisms. After several U.S. military bases converted storage tanks to B20 biodiesel, operators soon began reporting the presence of particulates in the fuel and frequent fouling of filters. The root cause of the decline in fuel quality and increase in corrosion was presumed to be microbiological in origin. Fuel degradation and corrosion were monitored in two B20 biodiesel storage tanks located at an air force base in the southeastern United States. We determined that a member of the filamentous fungal genus Byssochlamys was directly related to periods of heavy contamination, low fuel quality, and increased susceptibility to microbiologically influenced corrosion (MIC). Corrosion rates were higher in tanks containing heavily contaminated fuel, which is a considerable risk to infrastructure storing product for long periods. Controlled laboratory experiments with fungi and bacteria isolated from contaminated tanks further linked microbiological biomass with the observed fouling and corrosion. Mass loss measurements and surface analysis of “witness” coupons inserted into the tanks linked microbial population density and the location of biofilm formation with the highest rates of degradation and corrosion. Proliferation of microorganisms in B20 biodiesel storage tanks was detrimental to both fuel and infrastructure. The lessons learned by this failure analysis should be used to enhance the prevention, detection, and mitigation of microbial contamination in ULSD and B20 storage systems worldwide.