Environmental Engineering Reference
In-Depth Information
has drained away. More simply, this is the moisture content 2 to 3 days after
a soaking rain. It is also known as the normal field capacity, the normal
moisture capacity, or the capillary capacity. The original POPILE soil deliv-
ered to the pilot facility had an FMC of 23%. Land-farming protocols (U.S.
Army Corps of Engineers, 1996) state that the moisture content be main-
tained between 30 and 90% of the FMC in order to sustain microbial growth.
For POPILE soil, this correlates to 6.9 to 20.7% moisture.
Soil pH affects the contaminant chemistry and interactions with the soil
particles. The initial pH of POPILE soil was 9, but this decreased rapidly
with treatment and was maintained throughout the project at an average of
7.7.
7.3.3 Flask (bench-scale) experimental design
Building on research begun with composting systems and bioslurries, we
isolated and characterized from various PAH-contaminated site soils bacteria
that could produce biosurfactant or degrade PAHs, directly or cometaboli-
cally. Biosurfactant production by our chosen microorganism,
Pseudomonas
aeruginosa
strain 64, was examined for toxicity to PAH-degrading bacteria
and its effectiveness in increasing the extractability of PAHs in water. A
relatively low-cost, solid carrier system (vermiculite) was developed for
delivery and maintenance of the bacteria in the contaminated soil environ-
ment. The effect on PAH removal of various nutrient sources and bulking
agents was evaluated. An 11-month microcosm study was conducted using
contaminated site soil to evaluate PAH removal under biostimulation and
bioaugmentation conditions.
7.3.4 Flask (bench-scale) materials
7.3.4.1 Bacteria
Many soils contaminated with different toxicants (i.e., hydrocarbons, TNT,
PAHs, PCBs, etc.) were screened for biosurfactant and bioemulsifier produc-
ers.
Pseudomonas aeruginosa
strain 64 was originally isolated in enrichment
cultures of TNT-contaminated soil by Dr. Doug Gunnison of the U.S. Army
Corps of Engineers (USACE)-ERDC in Vicksburg, MS.
P. aeruginosa
strain 64
was notable in its production of both surfactant and a biomarker pigment,
pyocyanin. This microorganism was also found to survive and grow in
PAH-contaminated soils but did not degrade PAHs.
P. aeruginosa
strain 64
was grown in Luria-Bertani broth (Bacto) supplemented with 0.3% (v/v)
glycerol at room temperature. The glycerol is an energy source and promotes
pyocyanin pigment (blue-green color) production. Broth cultures were
shaken at 150 rpm on a gyratory shaker at room temperature.
7.3.4.2 Amendments
Ground rice hulls used as the bulking agent were purchased from Rice Hull
Specialty Products, Inc. (Stuttgart, AR). The rice hulls were purchased with
