Microorganisms in diesel and in biodiesel fuels

The presence of microorganisms in tanks used for petroleum products iscaused by contamination, i.e. fouling of petroleum products when replenishing stocks by adding new fuel. The presence and growth of microorganisms results in the creation of sediments, sludge and slime, and consequently leads to deterioration of the quality of fuel and damage to the tank farm fuel-handling facilities such as the storage tanks, pipelines, pumps, filters and valves, and indirectly also causes difficulties when using contaminated fuel. Of the basic categories of fuels comprising automotive gasoline, middle distillates (diesel and domestic heating oil) and aviation fuel JET-A1, the group containing middle distillates is the most sensitive to the growth of microorganisms. Specifically with the introduction of biodiesel blended fuel, the exposure of this group to microorganisms has increased. In this study analytical results are presented for cases where there is a possibility for growth of microorganisms in unblended diesel fuels and in the combination with biodiesel, both in the medium free of water and in the medium containing water, as well as in the presence and absence of biocides in the samples. The results obtained indicate that the most significant criterion for the prevention of microorganisms in fuels is the absence of water. In the case when microorganisms have started to grow, adding a biocide can inhibit their growth.