Diesel fuels with 5 % (V/V) FAME and Micro-organisms
Since FAME has been used as a fuel component in diesel fuels, varying incidents were observed, such as deposit formation in storage tanks and filter clogging at service stations. 150 samples of fuels and materials of the logistic chain were analysed, whether a microbial contamination was the cause for the occurrence of filter plugging at service stations. Bacteria (aerobic and anaerobic) and/or fungi were detected in about 95 % of all cases in the filters/filter elements and non return valves of the investigated service stations. These were always metabolically active, reproducible micro-organisms, i.e. living biological substance. In particular, partly massive contaminations by fungi were detected. The investigations show that micro-organisms are involved in the filter clogging at service stations to a considerable extent. In subsequent tests of samples of fall 2007 and 2008, numerous different species of bacteria, filamentous fungi and yeast were identified. This shows that a broad multitude of ubiquitously occurring micro-organisms is capable to colonise on the surfaces of filters and valves. The identified fungi and bacteria are classified not higher than risk group 1 according to TRBA 460 and TRBA 466, respectively. According to these technical rules, “it is unlikely that they cause any infectious disease in mankind”. In vitro tests were carried out, in order to investigate, whether the presence of water or the fuel composition have any effect on the growth of micro-organisms. The test results prove a tendency towards a higher gain of biomass in the presence of a free water phase. It could be demonstrated that the gain of biomass is higher, if the samples contain FAME. Furthermore, the kinetics of the formation of biomass is accelerated.