¹Center for Environmental Science and Technology and Department of Chemistry, University of Missouri-Rolla, Rolla, MO, 65401 and ²Environmental Affairs Division, Southern California Edison Company, Rosemead, CA, 91770
The organic wood treatment chemicals (creosotes, chlorinated phenols and associated chlorinated dioxins) are highly toxic and persistent environmental contaminants. The only widely accepted technology for destruction of these contaminants in soil is high temperature incineration. This technology, however, is very expensive and meeting increased public resistance.
A study to explore effective, low-cost alternative decontamination techniques is underway in our laboratory. One promising technique involves removal of contaminants with suitable solvents/surfactants, photodegradation of contaminants and, finally, removal of residual contaminants from solvent with activated carbon.
The present report deals with laboratory experiments designed to enhance photodegradation efficiencies of polynuclear aromatic hydrocarbons (PAHs), chlorinated phenols, and, in particular, the polychlorinated dibenzo-p-dioxins (PCDDs). All irradiation experiments were conducted in the near UV and visible regions. Enhancements resulting from the presence of suspended (solgels) and/or immobilized semiconductor photocatalysts were monitored. In addition, effects of homogeneous photocatalysts, i.e., free radical initiators such as hydrogen peroxide (H2O2) and organic peroxide, were also monitored. The results obtained showed that the presence of photocatalysts leads to a significant increase in photodegradation efficiencies. The higher efficiencies were achieved in solutions which contained homogeneous and heterogeneous catalysts. The highest transformation efficiency was achieved with titanium oxide (TiO2) and H2O2. Quantum yields in the presence of these catalysts was approximately 50 times higher than in solutions devoid of these materials.
The results of field experiments showed that soil decontamination can be obtained by coupling solvent wash with photodegradation. The most promising results were obtained with the use of binary solvent mixtures, and up to 95% of polychlorinated dibenzo-p-dioxins were removed from the soil. The technique with efficient solvent recovery and reuse should provide an economical option for remediation of contaminated soils at wood treatment sites. Detailed results for removal and destruction of major contaminant classes will be presented.
photodegradation, soil, wood treatment
This paper is from the Proceedings of the 10th Annual Conference on Hazardous Waste Research 1995, published in hard copy and on the Web by the Great Plains/Rocky Mountain Hazardous Substance Research Center.