Untersuchungen des mikrobiologischen Wachstums in Mischungen aus mineralölstämmigem Heizöl und Fettsäuremethylestern(FAME)

  • Growth of microorganisms in the blends of mineral oil based heating oil and fatty acid methyl ester (FAME)

Xie, Wei; Blank, Lars Mathias (Thesis advisor); Schäffer, Andreas (Thesis advisor)

Aachen (2017, 2018)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2017

Abstract

Microbial contaminations are generally problematic in domestic heating oil tanks. They are supposed to be a hazardous factor to the investment in terms of filter clogging, corrosion, biodegradation etc. In this thesis, different methods were applied to isolate and identify the microorganisms present in heating oil tanks. Both, in old oil samples which had been stored for more than 5 years and in 10 newly sampled oil plants, microorganisms were identified in all oil-phases. Due to the tank-design, the entry of germs from the environment and the accumulation of water at the tank bottom cannot be completely excluded. Additionally, the heating oil is no barrier for oxygen diffusion. The microorganisms use the water phase as a niche for their proliferation and even a minor volume of water can be enough for an initial growth when a certain minimum germ density had been reached. More water is potentially produced by the metabolism of the organisms with heating oil or FAME (fatty acid methyl ester). Once the microbes have entered the oil phase, they can survive for years without using the oil as nutrient. By decanting and through logistics, the contaminated oil could infect other plants. However, it is very expensive to carry out a complete tank cleaning which is legally not required by today. A lot of microorganisms like molds, yeasts and bacteria are capable of metabolizing heating oil and FAME. Although FAME / Biodiesel is easily degradable C-sources for the microbes compared to mineral heating oil, the microbial growth was limited by another element in the oil. However, no confirmation of this limiting factor could be found within this study. Nevertheless, a significantly reduced bacterial growth was observed in the case of phosphor-deficiency. In addition, FAME is responsible for the indirect promotion of microbial growth due to its physical and chemical properties such as water absorption and product aging. In contrast, the yeast Yarrowia lipolytica showed a better growth in mineral medium supplemented with mineral heating oil than with FAME. This means, the mineral heating oil is also a good C-source, if the microbes have previously been adapted to it. To identify and to analyze the microbial community in heating oil samples, the NGS-technique was evaluated to be the best method. 86 prokaryotic and 41 eukaryotic genera were identified in tanks. From these, only a small portion has already been described in publications. There are apparently more microorganisms responsible for the oil-contamination in tanks. NGS identification and the additional DGGE analysis are tools for observing the microbial abundance and diversity dynamics in different environments. Even in identical oil tanks the microbial diversity was different from phase to phase. In order to detect the microorganisms playing the essential role during “contamination of fuels” and to develop appropriate measures for their reduction, the investigation of several oil plants is required.

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