ACCELERATED BIOREMEDIATION OF PAH-CONTAMINATED SOILS BY
PRETREATMENT WITH FENTON'S REAGENT
1
Kenneth F. Reardon and 2Shelley A. Allen
1,2
Department of Chemical and Bioresource Engineering, Colorado State University, Glover Room
100, Fort Collins, CO 80523; 1Phone: (970) 491-6505, E-mail: reardon@engr.colostate.edu;
2
Phone: (970) 491-1123, E-mail: shelley@engr.colostate.edu.
Chemical oxidation and bioremediation are two remediation techniques commonly used to treat
contaminated soil. Bioremediation can be an economically sound method of treating easily
degradable compounds. However, many pollutants are not effectively degraded by bioremediation.
Chemical oxidation, on the contrary, successfully degrades contaminants that are biologically
recalcitrant, but is considerably more expensive than the biological treatment. By combining these
two technologies, a cheaper, more effective method should result. For the most effective
combination, the optimal extent of chemical oxidation must be found.
In a laboratory-scale project, soils obtained from two different sites were used to study the
combination of chemical oxidation and bioremediation. The primary contaminants in these soils
were polycyclic aromatic hydrocarbons (PAHs) and pentachlorophenol (PCP), chosen because they
are both recalcitrant and carcinogenic. The specific chemical oxidation process utilized in this
study involved the addition of hydrogen peroxide along with a Fenton's-like reagent. This mixture
was selected because it produces hydroxyl free radicals, which have an oxidizing potential second
only to fluorine. In order to distribute the reagent properly into the soil, a Microenfractionator™,
designed by H&H Eco Systems, Inc., was used. The Microenfractionator is essentially an efficient,
rapid, and large-scale mixing device. It not only mixed the reagent homogeneously into the soil,
but also decreased the mass transfer limitations brought about by sorbed contaminants. This
decrease in mass transfer limitations increased the degradation rate by increasing the availability of
the contaminants. Once chemically oxidized and well mixed, the soil was set aside to allow the
indigenous microorganisms to biodegrade the remaining contaminants. The effect of hydrogen
peroxide was tested at three concentrations: zero, one, and two percent (by weight).
Soil samples were taken at regular intervals over a six-week period. These samples were analyzed
for pollutant levels, microbial population characteristics, and mutagenicity. The microbial
population characteristics studied include total biomass, population composition, and degradation
activity.
The highest overall degradation was achieved by the two-percent hydrogen peroxide, which was
the highest concentration of hydrogen peroxide tested. This level of hydrogen peroxide also had
the largest impact on the microbial community. The concentration of microorganisms decreased by
a factor of four after the hydrogen peroxide was added. However, the microbial population
rebounded within a week. The addition of even a small amount of hydrogen peroxide produced
better degradation than bioremediation alone.
Key words: bioremediation, oxidation, PAH, PCP, soil