Performance tests of the Mycobacterium sp. CHXY119 and
Pseudomonas sp. YATO411 immobilized beads to determine
their efficiency for in situ bioremediation of BTEX-contaminated
groundwater in a PRB were needed to evaluate their potential
applications in the field. Fig. 6 shows the time course of BTEX
removal and DO change in a PRB using ORCs as slow release source
for oxygen supply. It was found that during the first stage from
day 0 to day 7, no degradation of BTEX occurred in the absence
of the Mycobacterium sp. CHXY119 and Pseudomonas sp. YATO411
immobilized bead. In the second stage from day 8 to day 47, which was initiated by addition of both the immobilized bead and ORCs;
for each pollutant of the BTEX, biodegradation efficiency gradually
increased up to the maximum because of continuous growth
of Mycobacterium sp. CHXY119 and Pseudomonas sp. YATO411,
followed by a rather stable duration of bioremediation efficiency
owing to the maximum biomass of Mycobacterium sp. CHXY119
and Pseudomonas sp. YATO411, and then a continuous decline in
biodegradation efficiency occurred due to the shortage of oxygen
supply and slow accumulation of intrinsic microorganisms. In
the third stage from days 48 to 72, which was initiated by a
replacement of spent ORCs with the fresh ones, a similar pattern of
BTEX biodegradation with the second stage was observed except
that biodegradation efficiency was lower. Although the fresh ORCs
supplied enough oxygen, the strong accumulation of intrinsic
microorganisms adversely affected the growth and activity of the
Mycobacterium sp. CHXY119 and Pseudomonas sp. YATO411 immobilized
bead, leading to the lower remediation efficiency. In the
fourth stage from days 73 to 86, which was initiated by a removal
of the immobilized bead, biodegradation efficiencies were lower
than those in the third stage. The results showed that the Mycobacterium
sp. CHXY119 and Pseudomonas sp. YATO411 was required
for the higher remediation efficiency, although the intrinsic
microorganisms also had remediation ability to some degree.