Environmental Engineering Reference
In-Depth Information
The Flask to Field PAH project (Flask, for short) focused on the first of
these objectives, increasing the availability of PAH compounds for biological
degradation and increasing the overall biodegradation of the high-molecu-
lar-weight homologues.
7.1.2 Available treatment options
Treatment of PAH-contaminated soil can be performed either
ex situ
or
in
situ
, and each of these has both abiotic and biotic technologies available. Of
the
ex situ
treatments, the abiotic choice is a destructive technology — incin-
eration. Biotic options include slurry bioreactors and compost reactors. The
available abiotic
in situ
treatments include soil flushing and stabilization.
Electrokinetic (E-K) separation is in preliminary development. Biotic treat-
ments performed
in situ
include bioventing, phytoremediation (on soils with
low PAH concentrations), and land farming. These options generally sepa-
rate into either of two treatment approaches: highly engineered solutions
such as solid phase or slurry phase treatment, and minimally engineered
in
situ
treatment. Examples of each strategy are presented in Table 7.3, along
with a summary of the inherent benefits and limitations associated with each
technology. The difficulties associated with the use of biotreatments have
been analyzed in Talley and Sleeper (1997), with reviews of pertinent tech-
nologies. Detailed information including cost summaries and case studies
can be obtained at http://www.frtr.gov
7.1.3 Thrust area: early studies
The approach taken during the Flask studies separated the objective into two
broad tasks: (1) isolating and characterizing a microorganism, or consortium
of microorganisms capable of degrading the higher-molecular-weight PAHs,
and (2) selecting a means of releasing the PAHs from the soil into the sur-
rounding soil pore spaces where it would, presumably, be available to degra-
dation. Each of these tasks was further separated into smaller research areas.
In order to find an organism that would degrade higher-molecular-weight
PAHs, a new isolation method was developed. New and existing strains were
characterized and metabolic pathways have been described. It became neces-
sary to explore the potential of cometabolism for the degradation of these
PAHs. At the same time, the effects of chemical surfactants on soil-PAH bind-
ing were studied. Bacteria that are natural surfactant producers were isolated
and the biosurfactant activities were compared to the chemical surfactants.
When a decision for bioaugmentation had been made, a method had to be
found to deliver the chosen microorganisms into the contaminated soil.
Several different technologies contributed to the Flask portion of the study,
as illustrated in Figure 7.1: slurry reactors, land farming, and composting. The
project began with an examination of available treatment options. Three prom-
ising technologies were selected: a high-technology system of slurry bioreac-
tors and two low-technology soil treatment systems — composting and land
