Effects of microbiological contamination in the quality of biodiesel fuels.

The introduction to the European Market of biodiesel blends along with the minimization of the sulphur content in automotive diesel has rejuvenated the research interest on the microbial stability of diesel fuel. Several microorganisms are able to metabolize hydrocarbons contained in conventional fuels and particularly in diesel and jet stocks. With the advent of FAME (Fatty Acid Methyl Esters) as a diesel fuel substitute there has been an increase in the number of samples suspect of microbial contamination with confirmative results. The aim of this study was to investigate the microbiological stability of FAME/diesel blends and consequently the impact of microbial proliferation on their quality. A commercially available FAME was blended with Ultra-Low Sulphur (ULSD) and Low Sulphur (LSD) conventional automotive diesel fuels in mixing ratios of 5, 10 and 20 % v/v. The resulting blends were contaminated with bottom-water of known viable microbial colonies and were stored for a period of 16 weeks. During storage the microbiological growth was evaluated by employing both semi-quantitative and quantitative methodologies. At the same time the devolution of certain quality parameters, namely oxidation stability and acid number, which could be influenced by microbial growth was examined. The overall results reveal the need to establish a scheduled inspection plan adapted to the diesel fuel supply chain infrastructure aiming to control and remedy efficiently the microbiological growth issues.