Different amounts of cell-immobilized bead (1, 5, 10, 15 and 20 g) were placed in 250 ml sealed brown flasks containing 100 ml of oxygen-saturated (about 7–8 mg l−1 of dissolved O2) simulated BTEX-contaminated groundwater with total dose of 95 mg l−1 as sole carbon sources, in which 24.68 mg l−1 for benzene, 23.67 mg l−1 for toluene, 21.97 mg l−1 for ethylbenzene and 24.68 mg l−1 for p-xylene. The immobilized bead-inoculated flasks were incubated in a shaker at 25 ◦C at 150 rpm. In the course of biodegradation of BTEX, the headspace gas of flasks was sampled
periodically for gas chromatography with flame ionization analysis (GC-FID, GC-14B, Shimadzu, Japan) to measure the remaining concentration of BTEX in the contaminated groundwater.