Abstract
Enrichment culture has been carried out to develop microorganisms for microbial enhanced oil recovery. In the previous paper, it was reported that 49 samples were collected from places, like agricultural fields, small rivers running through cities and oil fields, where organic matters and/or hydrocarbons were thought to be present. As a result, 41 out of 49 samples developed cultures with the use of kerosene as substrates at 30°C.
It was also reported that the growth rate, pH and interfacial tension as well as salt tolerance were used as representatives of the function of bacteria for selection, and 8 cultures were finally selected.
In the present study, 4 cultures out of 8 mentioned above were chosen for isolation and 4 isolated bacteria were used for investigating the influence of concentration of metal ions of Fe2+, Mg2+, Ca2+ and Al3+ in the liquid medium. Results are summerized as follows.
1. Fe2+ increased the growth rate more or less for all four cultures tested.
2. Al3+ decreased the gorwth rate of all cultures.
3. In relation to the growth rate, there are two types of the pH-time dependency: One is the type of sharp decrease of pH after the exponential phase. Another is the type of decreasing pH on the half way of the exponential phase and keeping pH constant at the stationary phase. The metal ion seems to give the influence on the type of pH-time dependency.
4. The interfacial tension did not vary widely with the presence of metal ion except 3-H which was obtained from the drain of heavy oil tank in the oil refinary.
