Microbial sludge formation in Brazilian marine diesel oil (B0) and soybean methylic biodiesel blends (B10 and B20) during simulated storage

Abstract Biofuels are renewable alternatives to fossil fuels mainly due to the lower impact they have in terms of release of air pollutants. Brazilian diesel oil must be composed of 10–15% biodiesel, while the addition of biodiesel to marine diesel oil has not yet been authorized. This paper aimed to evaluate the impact of the addition of biodiesel to marine diesel oil. The biotic and abiotic degradation of pure (B0) marine diesel oil and that with the addition of 10% (B10) and 20% (B20) of soybean methyl biodiesel were evaluated in simulated storage in an aqueous phase of Bushnell Haas mineral medium for 28 days. An uncharacterized inoculum (adapted from the ASTM E1259-16 standard) was prepared from a microbial population found in the marine diesel oil storage tank of a ship. For 28 days, microbial growth was monitored by gravimetry and the composition of the fungal microbial community was determined by next-generation sequencing (NGS). In the aqueous phase of the tests, the nature of the metabolites (pH measurements, headspace-solid phase microextraction [HS-SPME], gas chromatography with mass spectrometry (GC–MS), detection of the lipase enzyme (Rhodamine B Medium) and production of biosurfactants (surface tension measurements) were assessed. The oil phase was evaluated by gas chromatography (GC) and infrared spectroscopy. Higher biomass was observed in the B20 condition and the microbial community analysis revealed the dominance of the genus Pseudallescheria. No significant pH decreases were observed in the aqueous phase; however, the analyses by HS-SPME and GC–MS showed the presence of organic acids, alkanes, and phenols in both conditions, with and without microorganisms. The infrared results with the mixtures (10 and 20%) showed degradation of the biodiesel fraction. GC analysis showed that the linoleic acid methyl ester was the most susceptible to degradation by microorganisms. Thus, the results found showed the impact of adding biodiesel to marine diesel, calling attention to the need for maintenance routines, which will guarantee the final quality of the stored fuel.