Chemical oxidation using stabilized hydrogen peroxide in high temperature, saline groundwater impacted with hydrocarbons and MTBE

Abstract

In situ chemical oxidation (ISCO) of petroleum hydrocarbons (PHCs) within groundwater is considered a proven approach to addressing PHC-impacted groundwater in nonsaline environments. One of the most common oxidants used for oxidation of PHCs in groundwater is hydrogen peroxide (H2O2). Due to its highly reactive nature, H2O2 is often stabilized to aid in increasing its reactivity lifespan. Limited research and application of ISCO has been completed in warm, saline groundwater environments. Furthermore, even fewer studies have been completed in these environments for ISCO using stabilized H2O2. In this research, stabilized H2O2 was examined to determine its effectiveness in the treatment of PHCs and the additive methyl tert-butyl ether (MTBE). Three stabilizers (citrate, phytate, silica [SiO2]) were tested to determine if the stabilizers could enhance and extend the treatment life of H2O2 within saline groundwater. To determine the effect of salinity on the three stabilizers, groundwater and aquifer samples were collected from two saline locations that had different salinity (total dissolved solids of about 7,000 mg/L and 18,000 mg/L). Specific target chemicals for treatment were water soluble, mobile components of gasoline including benzene, toluene, ethylbenzene, xylenes, (BTEX) and MTBE. Previous studies using unactivated persulfate indicated that the PHCs within the groundwater could be oxidized, however, only limited oxidation of the MTBE could be affected. The results of the laboratory tests indicated that greater than 95 percent of the target hydrocarbons were removed within 7 days of treatment. Microcosms with citrate-stabilized H2O2 demonstrated a significantly faster and greater decline with most hydrocarbon concentrations reaching 400 mg/L to 90 percent) being measured in the citrate-stabilized microcosms. Unfortunately, H2O2 oxidation in the microcosms also resulted in production of up to 40 mg/L TBA or approximately 10 percent of the MTBE oxidized.