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 < 5 μg/L. The exceptions were ethylbenzene and m‐xylene, which were slightly decreased to about 30 and 20 μg/L, respectively. Initial mean concentrations of the BTEX compounds within the citrate‐stabilized microcosms were 10,554 μg/L, 9,318 μg/L, 6,859 μg/L, and 14,435 μg/L, respectively. The silicate‐stabilized H2O2 microcosms showed no significant benefit over the unstabilized control microcosms. The better performance of citrate‐stabilized microcosms was confirmed by increasing δ13C values of remaining hydrocarbons. MTBE declined from > 400 mg/L to < 100 mg/L in all microcosms, again with the best removal (> 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.

The in situ treatment of BTEX, MTBE, and TBA in saline groundwater

“…Previous laboratory experiments by Kashir et al () on groundwater collected from the site indicated that no significant δ 13 C shift occurred for benzene during oxidation by sodium persulfate until benzene concentrations declined by at least 50%. During the pilot test, a shift in the δ 13 C occurred before a decrease in the benzene concentration suggesting a more complex relationship between the benzene sorbed to the soil and groundwater.…”

“…Previous laboratory studies using site‐specific groundwater showed greater hydrogen enrichment relative to δ 13 C during biodegradation of benzene (Kashir et al, ). During the ISCO phase of the pilot test, δ 13 C and δ 2 H in benzene data indicated similar magnitudes of enrichment.…”

“…To determine if a similar approach could be used in a saline aquifer, a series of laboratory tests were conducted to evaluate combining ISCO and EBR in a saline environment (Kashir & McGregor, ; Kashir, McGregor, Gusti, & Shouakar‐Stash, ). Challenges with using ISCO in saline aquifers is the potential for the oxidant(s) to be consumed by scavengers such as carbonate( ), chloride (Cl − ), and bromide (Br − ; Saeed, ).…”

Stabilized hydrogen peroxide for the remediation of hydrocarbons and MTBE in high temperature and saline groundwater

“…Laboratory microcosm testing using site media and a variety of stabilization reagents including silica dioxide, phytate, and citrate indicated that greater than 95% of the target hydrocarbons were removed within 7 days of treatment (Kashir & McGregor, ). Microcosms with citrate‐stabilized H 2 O 2 demonstrated a significantly faster and greater concentration decrease with most hydrocarbon concentrations reaching <5 micrograms per liter (μg/L).…”

“…MTBE declined from >400 milligrams per liter (mg/L) to <100 mg/L in all microcosms, again with the best removal (>90%) being measured in the citrate‐stabilized microcosms. Unfortunately, H 2 O 2 oxidation in the microcosms also resulted in production of up to 40 mg/L TBA or approximately 10% of the MTBE oxidized (Kashir & McGregor, ).…”