By comparing the actual oxygen consumption amounts with the
theoretical ones for complete oxidation, the actual oxidation rate
of the BTEX was only 10.8% for benzene, 10.5% for toluene, 5.8% for
ethylbenzene and 11.4% for p-xylene, respectively. Because BTEX
was used as the sole carbon source in the mixed culture immobilized
bead, a certain proportion of pollutants, approximately as
twice as much as the mineralized percent, were assimilated to form
biomass [28]; so, the consumption rate of the BTEX stemming from
oxidation and assimilation was about 32.4% for benzene, 31.5% for
toluene, 17.4% for ethylbenzene and 34.2% for p-xylene, respectively.
It was speculated that the ring cleavage of the BTEX occurred
to meet so high consumption rates; however, the remaining which
kept in the solution as metabolism products was needed to be
further identified. The very low oxidation rate meant that a very
limited oxygen supply could meet the biodegradation of much
more amount of BTEX, with the BTEX transforming into harmless
or low toxic metabolism products by ring cleavage under aerobic
condition. The biodegradation characteristic of the mixed culture
immobilized bead was advantageous for bioremediation of the
BTEX-contaminated groundwater due to the low required amount
of oxygen.