Environmental Engineering Reference
In-Depth Information
4.1.2 PAHs
PAHs include industrial wastes such as petroleum and fuel residues, tars,
and creosote that contaminate soils and sediments. Land farming is a com-
mon treatment option for PAH-contaminated soils, but the removal of the
high-molecular-weight (HMW) PAHs by this method is often problematic.
The goal of this project, coordinated by Dr. Hap Pritchard Navel Research
Laboratory (NRL), was to modify land farming by using bioaugmentation
to improve degradation of PAHs. Bioaugmentation involved the addition of
a biosurfactant-producing bacterium (strain Pa 64), a bulking agent (rice
husks), and a carbon/nitrogen source (dried-blood fertilizer) (Pritchard et
al., 1999). Microcosm studies conducted at NRL validated the method and
determined the degradation kinetics.
Lance Hansen conducted a pilot-scale study at the U.S. Army Engineer
Research and Development Center (ERDC) in Vicksburg, MS, implementing
bioaugmentation technology for PAH remediation. The study consisted of
three metal pans (10 feet long ×
3 feet wide × 2 feet deep), each filled with
approximately 1 cubic yard of PAH-contaminated soil. One pan was
untreated, one received bulking agent and dried blood, and the third
received bulking agent, dried blood, and the bacteria. The pan study was
designed to define the sampling strategy required to measure the effective-
ness of bioaugmentation and to provide a realistic cost estimate for the
bioaugmentation treatment (U.S. Army Corps of Engineers, 1996). Methods
were developed and refined to monitor the progress and effectiveness of
bioremediation. These included molecular biological techniques to monitor
the presence of the inoculated organisms and their
in situ
activity (White
and Ringelberg, 1998; Balkwill et al., 1988), respirometric techniques that
monitor relative microbial activity based on CO
2
production, and genetic
techniques that monitor the presence or absence of enzymes involved in
nitrogen use and PAH degradation (Perkins et al., 2001). These techniques
were correlated to standard contaminant analytical chemistry methods and
were applied to the cost optimization of land-farming PAHs.
4.1.3 PCBs
Research on microbial degradation of PCBs has been ongoing for more than
25 years and has shown that bioremediation requires a more sophisticated
technology than the simplistic attempts that have been tried so far. The
project conducted by Dr. Jim Tiedje at Michigan State University addressed
key barriers to bioremediating PCBs:
•
Developing microorganisms that will grow on the major congeners
produced by anaerobic dechlorination of PCBs
•
Improving bioavailability of PCBs through the use of surfactants
•
Optimizing field delivery of anaerobic or aerobic PCB bioremediation
technologies
