Environmental Engineering Reference
In-Depth Information
used. The method consists of a single extraction using a dilute acid solution.
Extraction fluid used to determine the leachability of soil from a site that is
in the east of the Mississippi River consists of a 60/40 weight percent mixture
of sulfuric and nitric acids diluted with reagent water to a pH of 4.20 ± 0.05.
6.6 Conclusions
Bioremediation can potentially result in dechlorination of PCBs and possibly
even in mineralization of the contaminant. Energy costs are lower than other
forms of treatment. Slurry phase treatment usually requires less time than
solid phase biological treatment due to the increased rates of contaminant
mass transfer. Furthermore, it is relatively simple to maintain either aerobic
or anaerobic conditions in the reactor and to switch between these two
conditions. As noted previously, this characteristic process is especially ben-
eficial when treating PCBs. Anaerobic conditions can be maintained to allow
for reductive dechlorination of the highly chlorinated congeners. After this
stage is complete, aerobic conditions can be established to allow the resulting
lightly chlorinated congeners to be metabolized aerobically.
Principal drawbacks to preexisting bioremediation schemes are slow
rates of the anaerobic Aroclor dechlorination in sediments and the inability
of naturally occurring biphenyl-degrading organisms to dechlorinate and
grow on lower-chlorinated PCB congeners resulting from the anaerobic
phase. We have addressed these principal barriers and developed processes
that resolve the above problems via enhancing rates of anaerobic dechlori-
nation and allowing aerobes to grow on the products from anaerobic Aroclor
dechlorination.
Although results of the currently ongoing pilot test are yet to be deter-
mined, flask- and laboratory-scale soil remediation experiments indicate that
the designed two-phase enhanced anaerobic dechlorination of Aroclor cou-
pled with GEM-based enhanced aerobic degradation/mineralization of
lower-chlorinated PCBs could be very beneficial as a remediation technology.
6.7 Recommendations for further transitional research
The results of our research indicated that the developed bioremediation
scheme could be beneficial in future technologies. However, much more
research is needed to resolve remaining questions as well as improve current
results by gaining knowledge on how the degradative processes affect and
are being affected within the given metabolic networks in microbial com-
munities. Recent developments in genomic sequencing and DNA microarray
technology create opportunities for transferring these approaches to com-
munity and populational studies. The latter would allow for rapid advances
in our understanding of the complex processes involved in successful bio-
degradation within a given microbial population, naturally occurring or
engineered by the introduction of foreign members. Success in this direction
