In the batch experiments, the Mycobacterium sp. CHXY119 and
Pseudomonas sp. YATO411 immobilized bead possessed very high
bioremediation ability towards BTEX and almost 100% of removal
was attained for each pollutant of the BTEX. In contrast, the same
immobilized bead in the PRB system removed 97.8% of benzene,
94.2% of toluene, 84.7% of ethylbenzene and 87.4% of p-xylene
in the stable duration of the second stage from days 29 to 39.
A partial explanation could be the continuous treatment by PRB
process. However, further study is needed. As for the difference
in biodegradation efficiency with different pollutants in the same
stage and with different stages of the PRB system, gradually accumulated
intrinsic microorganisms might play an important role
for it, although the detailed mechanism was still unknown. However,
despite the lower biodegradation efficiency of the BTEX in
the PRB system compared with the batch experiments, the bioaugmentation
process based on the Mycobacterium sp. CHXY119 and
Pseudomonas sp. YATO411 immobilized bead indeed exhibited
much higher bioremediation capacity compared to biostimulation
when facing the high-concentration contaminated groundwater.
By addition of exogenous oxygen and inorganic nutrients to stimulate
the activity of the intrinsic microorganisms, biostimulation
achieved only 60% of biodegradation efficiency for benzene, 80%
for toluene, 86% for ethylbenzene, and 78% for p-xylene [16]. An
efficiency increase of 37.8% for benzene, 14.2% for toluene and 9.4%
for p-xylene was achieved using the bioaugmentation PRB process
except for a slight decline of 1.3% for ethylbenzene. The high
concentration BTEX-contaminated groundwater around the world
highlighted the importance of the present studies, although there
were still a lot of works to do for further improving the bioremediation
efficiency of the PRB system based on the Mycobacterium sp.
CHXY119 and Pseudomonas sp. YATO411 immobilized bead.