Microbiological aspects of biodiesel and biodiesel/diesel blends biodeterioration

The present work consisted of evaluating and comparing, at bench scale, the biodeterioration processes of diesel oil, soy biodiesel (B100 soy), beef tallow biodiesel (B100 beef tallow) and the resulting blends containing 5% biodiesel and 95% diesel oil (B5), throughout 42 days storage. Fuels were stored with and without the inoculation of a microbial consortium from a water drainage tank, under conditions that simulated service station storage. Oxygen consumption and carbon dioxide production were more pronounced in the presence of microbial inoculum, especially for B100 and B5 beef tallow. Diesel oil instead was the least subject to chemical and/or biological oxidation. A trend of increase in acid number was also observed and for B100 soy and B5 beef tallow the regulatory limits were exceeded. Residues deposition was observed in all inoculated fuels, especially in B5 beef tallow. Communities' differentiation depended on biodiesel feedstock and occurred during storage time. Among all microcosms, 18 microbial genera (8 fungal and 10 bacterial) were identified by DNA sequencing, being 17 of them directly linked to: fuel microbial contamination and/or biodegradation (74%); biofuel production or related enzymes expression (26%); biofilm formation and/or exopolysaccharide production (26%), emulsifying properties (11%) and nitrogen fixation (5%). Finally, despite the biodeterioration events in all the fuels, such phenomenon had small magnitude, even in inoculated samples.