80 巻 (2015) 6 号 p. 465-469
We are considering the possibility of application of an anaerobic bacterium which degrades long-chain hydrocarbons preferentially and induces oil viscosity reduction to Microbial Enhanced Oil Recovery (MEOR) in an oilfield in North Sea Oil. In this study, we estimated lower grade nitrogen sources which were effective for stimulating the growth of the bacterium and its ability to lower the oil viscosity.
The bacterium was incubated in the culture medium consisting of synthetic sea water, crude oil and lower grade nitrogen sources such as ammonium nitrate, urea, flower fertilizer, and agricultural fertilizer. The flower fertilizer contained 3 % of nitrogen and 16 kinds of amino acids according to the manufacturer. The agricultural fertilizer was made from beer yeast cell wall and contained 3.5 % of nitrogen according to the manufacturer. Retail prices of ammonium nitrate, urea, the flower fertilizer and the agricultural fertilizer are approximately 38 USD/kg, 25 USD/kg, 25 USD/kg and 1 USD/kg respectively while that of yeast extract which is usually used for incubating microorganisms as a rich nitrogen source is about 350 USD/kg.
Growth of the bacterium was clearly found in the culture solution containing the agricultural fertilizer at the concentration ≥ 0.5 g/L. Cell number of the bacterium increased more than 10 times as large as the initial cell number in the culture solution containing the fertilizer at the concentration of 2.0 g/L. This result suggests that the fertilizer can be utilizable as a growth promoter of the bacterium. Although the reduction of oil viscosity was found in all the culture solution containing the agricultural fertilizer, the reduction of oil viscosity in those culture solution was not so much. It can be assumed that the bacterium degrades not only heavier components but also lighter components of the crude oil in the culture medium containing the agricultural fertilizer.