BIOAUGMENTATION FOR MTBE REMEDIATION - Bioaugmentation for Groundwater Remediation - page 302

vendor that is currently providing MTBE-degrading cultures with well-documented activity for
use in bioaugmentation for MTBE remediation applications.
In cases where MTBE-degrading cultures are not commercially available or are too costly,
it is possible to obtain MTBE-degrading organisms from sites where biodegradation is known
to occur naturally, and then to grow sufficient quantities of the culture. Sediment and/or
groundwater from the site with known MTBE-degrading activity can be seeded into a properly
designed reactor (high solids retention time is critical) which is then fed with MTBE and
nutrients (Salanitro et al., 2000 ; Wilson et al., 2002 ).
10.8 FUTURE PROSPECTS FOR MTBE BIOAUGMENTATION
Bioaugmentation with MTBE degrading organisms is likely to remain a minor field of
endeavor. The costs and time associated with generating enough biomass to seed a barrier
system has proven to be prohibitive for most applications, and generally not necessary for
effective aerobic treatment. Homogeneous microbial distributions can be achieved only in
homogeneous materials. Stable and robust zones of oxygenation, however, are achievable in
somewhat more complex lithologic systems, making biostimulation a feasible alternative for
many MTBE-impacted sites.
It still can be difficult to evaluate if bioaugmentation may, in fact, be beneficial at a
specific site. Although indigenous MTBE degraders can be detected at many sites, this
information alone is not sufficient to ensure the success of biostimulation. The native microbial
population's degrading activity also must increase to a level that is sufficient to achieve the
desired MTBE concentration reduction. At this time, it is not clear how to determine if this will
be the case on a site-specific basis except through trial and error in the field.
The potential need for bioaugmentation of MTBE and TBA sites led to a burst of research
activity. This research has led to valuable improvements in the tools available to monitor and
diagnose MTBE biodegradation. These tools can be helpful at MTBE sites because MTBE/TBA
biodegradation can be difficult to demonstrate and quantify, although it is vital to natural
attenuation decisions. For example, molecular tools and genetic analyses of MTBE and TBA
biodegraders offer the potential to quickly detect and quantify specific bacterial strains known
to degrade MTBE (Hristova et al., 2003 ; Kane et al., 2007 ). However, to be useful on a routine
basis, molecular probes still need to be developed for more strains of MTBE-degrading
organisms, or for targeted regions that are conserved in most or all MTBE and TBA degraders.
Another powerful technique is CSIA. CSIA can be used to demonstrate MTBE and TBA
biodegradation and the potential need for augmentation or engineered bioremediation (Wilson
et al., 2005 ).
REFERENCES
Borden RC, Daniel RA, LeBrun IV LE, Davis CW. 1997. Intrinsic biodegradation of MTBE and
BTEX in a gasoline-contaminated aquifer. Water Res 33:1105-1115.
Braunschneider S. 2000. Visualization Studies of Microbial Delivery Methods for In Situ
Bioaugmentation. MS Thesis. Arizona State University, Tempe, Arizona, USA.
Busch-Harris J, Sublette K, Roberts KP, Landrum C, Peacock AD, Davis G, Ogles D, Holmes
WE, Harris D, Ota C, Yang X, Kolhatkar R. 2008. Bio-Traps coupled with molecular
biological methods and stable isotope probing demonstrate the in situ biodegradation
potential of MTBE and TBA in gasoline-contaminated aquifers. Ground Water Monitor
Remediat 28:47-62.