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In the recent past, especially after the addition of biodiesel, more disturbances and failures ofDiesel fuel systems occurred as a result of microbial contamination. The aim of the presentresearch project was the identification of factors, which improve microbial growth in heating oil, achemically similar product. In addition, the influence of contamination on materials andcomponents of heating oil burners was examined. Furthermore, contaminating microorganismswere identified. In all experiments, the impact of the addition of FAME (Fatty Acid Methyl Ester), abiofuel that is supposed to be used in the future for blending heating oil, was investigated. Theresults could improve the tank safety by identifying factors that inhibit or even avoid microbialgrowth.To achieve this, experiments were performed which simulated highly contaminated storage tanksusing a mixed microbial culture originating from the Diesel sector. These cultivations imitated theprocesses in heating oil storage tanks realistically. Working with the hydrophobic medium heatingoil as well as the microbial growth in solid biofilms at the fuel-water-interphase required theestablishment of methods for cultivation, for verification of growth and DNA isolation.Within the project time, samples from several unsuspicious heating oil storage tanks were takenand analyzed regarding their microbial diversity. In these examinations, a high diversity oforganisms, which are generally able to degrade heating oil, were discovered. In addition to theseself-sampled tanks, a heating oil sample originating from a contaminated heating system which ledto a failure of the system was provided. Additionally to the identifications of microbes, different purecultures from different heating oil sources were isolated and integrated into the institute’s ownstrain collection.The existence of a free water phase has been identified as an essential factor for microbial growth.Thereby, even smallest volumes of water were sufficient to allow growth. In contrast to that, aminimum cell concentration had to be given. The addition of FAME to the fossil fuel resulted inhigher final biomasses as well as a reduction of the needed initial cell concentration.Different storage temperatures, which are typical for heating oil storage, influenced only the growthrate, but not the final biomass. It was proven in theoretical calculations as well as in practicalapproaches that oxygen can pass a layer of heating oil, resulting in aerobic conditions in all areasof the tank.Microbial growth often occurred together with the formation of solid biofilms within some weeks.During growth, the production and secretion of metabolites, especially acids and emulsifiers, wereobserved. These fostered the corrosion of metallic components of the burner systems or led to theformation of water-in-oil as well as oil-in-water (micro)emulsions.To prevent biomass gain, experiments with phosphorous-reduced FAME, the addition of copper orbiocides and the deprivation of carbon dioxide were performed. Except of the phosphorousreduction, all approaches were appropriate to prevent microbial growth under laboratoryconditions. |
