Pollution Control & Sustainable Environment

Biography

Biography: Mansor Kashir

Abstract

A series of laboratory microcosm experiments and a field-pilot test was performed to evaluate the potential for the in situ chemical oxidation of aromatic hydrocarbons and methyl tertiary butyl ether (MTBE), in saline, high temperature (greater than 30) groundwater. Groundwater samples from a site in Saudi Arabia were amended in the laboratory portion of the study with the chemical oxidants persulfate, percarbonate and stabilized hydrogen peroxide to evaluate the changes in select hydrocarbons and MTBE concentrations with time. Almost complete degradation of the aromatic hydrocarbons, naphthalene and trimethylbenzene was found in the groundwater samples amended with persulfate and stabilized hydrogen peroxide whereas the percarbonate-amended samples showed little to no degradation of the target hydrocarbon compounds in the laboratory. Isotopic analyses of the persulfate-amended samples suggested that C-isotope fractionation for xylenes occurred after approximately 30% reduction in concentration with a decline in the δ13C values of xylenes of about 1%. Based on the laboratory results, pilot-scale testing at a Saudi Arabian field site was carried out to verify the persulfate laboratory results. Results obtained from the pilot test indicated that all the target compounds decreased substantially with time. pH of the groundwater remained neutral following injections whereas oxidation-reduction potential remained anaerobic throughout the injection zone with time. Nitrate concentrations decreased within the injection zone suggesting that the nitrate may be consumed by denitrification reactions while sulfate concentrations increased as expected within the reactive zone suggesting that the persulfate was being reduced to sulfate. Overall, the injection of the oxidant persulfate was shown to be an effective approach to treating dissolved aromatic and associated hydrocarbons within the groundwater. The generation of sulfate as a byproduct was an added benefit as the sulfate could be utilized by sulfate-reducing bacteria (SRBs) presents within the subsurface to further biodegrade any remaining hydrocarbons. The results of the pilot-study using stabilized hydrogen peroxide as an oxidant suggested that the hydrogen peroxide was not stabilized by citric acid but instead the citric acid enhanced the oxidation of the target compounds including the oxidation of BTEX and MTBE. It appears that the citric acid may be chelating natural metal activators, such as ferric iron, and enhancing their activation function. Analysis of the BTEX compounds indicated a degradation percent of greater than 99% over the course of the study whereas MTBE was degraded by greater than 50%. Analysis of the TBA prior to and post injection suggested that TBA was not generated and in most cases TBA was degraded by greater than 75% during the pilot test. CSIA analysis indicated the 13C within the MTBE and benzene was enriched during the oxidation process. Bacterial analysis showed a dramatic change.