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

A field pilot-scale. test was conducted to determine if the use of citric acid-stabilized hydrogen peroxide (H2O2) is effective in reducing dissolved concentrations of petroleum hydrocarbon compounds (PHCs) and the additive methyl tert-butyl ether (MTBE) in impacted high salinity groundwater. The test was carried out adjacent to an operational hydrocarbon fuel facility in Western Saudi Arabia. The pilot test was based on the results of laboratory tests, which suggested that hydrogen peroxide stabilized with citric acid (C6H8O7) would enhance the degradation of the dissolved PHCs and associated MTBE within a saline groundwater. A 7.5 weight percent hydrogen peroxide solution was injected into a series of injection wells positioned to target a PHC-impacted plume within an unconfined aquifer. The plume contains total benzene, toluene, ethylbenzene, and xylenes (BTEX) at concentrations up to 6.890 micrograms per liter (mu g/L). The MTBE concentration within the groundwater was detected at concentrations of up to 55.182 mu g/L, whereas the groundwater salinity was approximately 7,000 milligrams per liter (mg/L). A total of 9,012 liters of citric acid-stabilized hydrogen peroxide solution was injected over three events spaced over a 1-month period. The results of the pilot test indicated that injection of stabilized hydrogen peroxide was effective in reducing the concentration of dissolved PHCs within the plume, including BTEX and other aromatic hydrocarbons. The average concentration decrease for total BTEX was 72% with up to 97.4% reduction being measured in a sample collected from one key monitoring well during the treatment period. MTBE was also effectively treated during the pilot test with an average MTBE degradation of 50% being realized during the test and up to 86% concentration decrease being measured in some groundwater samples. While reductions in MTBE concentrations were noted, no increase in tertiary butyl alcohol was measured, which is a promising finding. The general water quality did not fluctuate significantly between pre- and postinjection with the pH, oxidation-reduction potential, and dissolved oxygen remaining relatively constant. The dissolved iron, nitrate, and sulfate concentrations vary during the injection period with nitrate decreasing to below detection limits following the final injection, whereas sulfate decreased in two of the three monitoring wells following the injection. Dissolved iron concentrations remained relatively constant in two of the three monitoring wells (NJBP45 and NJBP46) during the injection events, whereas dissolved iron in monitoring well NJBP44 decreased from a baseline concentration of 1.03 mu g/L to 0.09 mu g/L, suggesting that the ferrous iron in solution was being oxidized to ferric iron. Measurements of the preinjection microbiological community indicated that the community is diverse within the injection area based on deoxyribonucleic acid extraction by polymerase chain reaction as well as sequencing and clustering. Subsequent analyses of the microbiological community postinjection indicated that the community diversity and biomass was reduced with a shift to a more aerobic population, at least over the short term. Results of compound specific isotope analyses are consistent with the concentration data and show petroleum hydrocarbon and MTBE was degraded by the citric acid-stabilized hydrogen peroxide treatment.