CHEMICAL OXIDATION OF MGP RESIDUALS AND DICYCLOPENTADIENE AT A FORMER MGP SITE

摘要

The Sempra Energy Utilities former MGP site in Los Angeles, California was the site of a number of industrial activities following the termination of MGP operations. The site contains vadose and saturated zone soils contaminated with mixed-use contaminants, including MGP residuals, predominantly polynuclear aromatic hydrocarbons (PAHs) and dicyclopentadiene (DCPD) in a hydrocarbon mixture similar to diesel fuel. The site also contains volatile organic compounds (VOCs) such as aromatic hydrocarbons, tetrachloroethene (PCE) and its daughter products. In general, these compounds have low solubility and are recalcitrant. Additionally, DCPD has an extremely low odor threshold (~3μg/cm cm3), and is of particular concern to ongoing site operations. ), A treatability study was performed on vadose and saturated zone soils from the site in order to determine the efficacy of using ozone (O O3) and/or sodium persulfate (Na ) Na2S2O8) as an in situ treatment on vadose and saturated zone soils, respectively. Vadose zone soil columns were treated with both continuous ozone and pulsed ozone over a 14-day reaction period. Vadose zone soil/distilled water slurries were treated with heat activated (using hydrogen peroxide [H ) H2O2]) sodium persulfate over a 14-day reaction period. Corresponding controls were tested in order to determine if any non-oxidative processes were occurring in the reaction systems. ]) One vadose zone soil column was treated with a continuous stream of approximately 5% ozone in oxygen. One vadose zone column was treated with a continuous stream of approximately 5% ozone in oxygen for 4 hours/day and a continuous air stream for 20 hours/day. The corresponding control was treated continuously with air. Following 7 days of reaction, a total of ~173g and 22g was delivered to the continuous and pulsed columns respectively. The soil treated with continuous ozone exhibited a concentration decrease of 100% of VOCs and greater than 99% decrease in total semivolatile organic compounds (SVOCs) and DCPD. The pulsed ozone soil exhibited an 87% decrease in VOCs, an 81% decrease in DCPD, and a 52% decrease in SVOCs. Following 14 days of treatment (315g and 40g of O O3 delivered, respectively), 100% of all compounds were treated in the continuous column, while greater than 98% of all compounds were treated in the pulsed column. Vadose zone soil/distilled water slurries were treated with hydrogen peroxide in order to increase the slurry temperature, followed by sodium persulfate as an oxidant. The corresponding control was treated with peroxide, only. Peroxide and persulfate were added periodically during the 14-day reaction period. Following 14 days of reaction, the slurries were analyzed for the constituents-of-concern. 97% of the total VOC mass, 100% of the DCPD mass, and 78% of the total SVOC mass were treated in the reaction slurry.