Technical Committee Fuel Oils
Microbiological contamination of biogenic fuels
The project’s aim was to clarify, which microorganisms can occur in heating oil EL, in FAME
and in their mixtures (heating oil EL A bio) and in how far the risk of microbiological load is
increased by using biogenic fuels. Various field systems with a FAME share of up to 20 %
(V/V) could be investigated and microbes could be isolated and identified. Moreover, the
chemical-physical characteristics of heating oil EL, FAME and their mixtures could be determined
in more detail by means of laboratory investigations. The hygroscopic characteristics
of fuels and their emulsion formation or degradation as well as the corrosive characteristics
could be investigated in detail. On the basis of the collected data, exposure tests could be
carried out afterwards. Purposefully, the different fuels and their mixtures were microbiologically
contaminated and incubated under various storage conditions. As inoculum a mixed
population, which was isolated from a diesel fuel, was used. It could be shown that FAME is
decisive for an increased water absorption capacity of the fuel phase because of its hygroscopic
effect. The general formation of a micro-emulsion due to FAME-admixture could not
be shown. Due to the increased water absorption capacity and the reinforced nutrients inflow
through FAME an increased microbiological growth could be demonstrated. The formation of
a free aqueous phase is essential for the growth of microorganisms. During the incubation
biofilms were formed; i.e. a mixed population of different microorganisms. In the course of
the project different microorganisms could be isolated and identified. Yarrowia lipolytica could
be identified as yeast most frequently. The genres Pseudomonas, Burkholderia und
Sphingomonas were the most frequent bacteria. All isolated or identified organisms were
able to exploit FAME. Investigating microbiologically contaminated fuels in an electron microscope,
a micro-emulsion with a drop size of about 100 nm could be proven. The steel pin
corrosion test showed that none of the steel pins had corrosive conspicuities, as long as no
free water was present in the testing apparatus. A free aqueous phase reinforces the introduction
of copper into the fuel. By means of a pump test bench, the influence of the fuels on
the operating safety in customary fuel pumps from typical heating oil fuel systems was investigated.
The used heating oil EL with 20 % (V/V) FAME did not show any disorders over 500
operating hours. During the trial period, the micro-emulsion set up by a detergent and a
dehazer lead to water accumulations in the filter in dependence of the flow conditions. The
used pumps did not show any significant effect in their starting torques.
The IGF project 16596 N of the Research Association for Petroleum, Natural Gas and Coal was funded by the Federal Ministry of Economics and Technology via the AiF within the framework of the programme for the promotion of joint industrial research and development (IGF) on the basis of a resolution of the German Bundestag.