Microorganisms can grow in different types of fuels. The presence of water in the fuel is crucial for the growth of bacteria, fungi and yeasts. Microorganisms may grow in the presence of oxygen (aerobic) or in its absence (anaerobic), feeding primarily on hydrocarbon fuel, minerals and other impurities in the water. The amount of water required for microbial growth is very small. A fuel containing only 1% of water presents favorable conditions for the development of microbial colonies and spores can survive in the presence of only 5 -80 ppm of water. In practice, the bottoms of storage tanks of fuel or even tanks of buses and trucks have enough water for microbial growth. Microbial growth results in the production of biomass (fouling), which is deposited at the bottom of the tank. Moreover, the microbial oxidation of hydrocarbons produces corrosive metabolites, such as organic and inorganic acids. Biomass, metabolic products and corrosion products result in problems such as filter and pipelines clogging, production of emulsion, change in fuel quality and corrosion of metal tanks. The detection and quantification of microorganisms in industrial samples are traditionally based on culture techniques such as the most probable number (MPN) and colony forming units (CFU). However, the slow growth of strictly anaerobic sulfate-reducing bacteria (SRB) complicates the detection and isolation of these microorganisms in culture media. The cultivation of SRB requires a long incubation period (28 days) to obtain the results. In some cases, the extended time for the detection of microorganisms retards the preventive and corrective actions which aggravate the corrosive process. In this work, the results of SRB quantification in bottom water from fuel tanks analyzed by real-time PCR are shown.
Microorganisms can contaminate a wide variety of petroleum-derived fuels, from crude oil to gasoline. This kind of contamination can cause severe operational problems of high cost for both suppliers and distributors and for end-consumers such as airlines companies, ships, buses, trucks and power generators. It is estimated that the damage caused by microbiologically influenced corrosion (MIC) in production, transport and storage of oil and its derivatives totalizes hundreds of millions of dollars a year just in the oil industry in the United States 1. Storage tanks of a refinery are the first possibility of microbial contamination of a fuel. Fuel tank vents allow entry of moisture, dust and associated microorganisms (bacteria and fungi). Some types of vent even allow the entry of rainwater. Water that enters the tank may condense and accumulate on the ceiling and tank walls or precipitate at bottom of the tank, allowing microbial growth. A storage tank severely contaminated with microorganisms can lead to degradation of fuel, increased turbidity, emulsion formation, fuel “souring”, filter plugging, corrosion of the tank with possible leak, causing serious economic and environmental problems worldwide. The presence of water in the fuel is crucial for the growth of bacteria, fungi and yeasts. However, the amount of water required for microbial growth is very small.
