Because supply of oxygen was crucial for the aerobic bioremediation
of contaminated groundwater [26], further investigations
were performed to elucidate the detailed relationships between
biodegradation efficiencies and oxygen consumption rates. Fig. 5
presents the time courses of BTEX removal and oxygen consumption
rates. It was observed that for each pollutant of BTEX, there
was almost no oxygen utilization in the early stage of several
hours, followed by growing oxygen consumption until that oxygen consumption rate reached the maximum, and then it sharply
declined to zero again, even though that dissolved oxygen was
not depleted. Accordingly, the BTEX concentration also remained
unchanged for early several hours, followed by active biodegradation
up to zero. The experimental results confirmed that BTEX
biodegradation is highly dependent on oxygen consumption.