Remediation of Petroleum Contaminated Soils and Groundwater Using High Carbon Content Fly ash

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Class F fly ash, a by-product of coal-burning power plants, is generated in large quantities and occasionally contains significant amounts of unburned carbon (i.e., high loss on ignition) as a result of equipping the power plants with the low nitrogen oxide burners. The overall goal of this research was to assess the feasibility of using high carbon content fly ash (HCCFA) as a stabilizing agent for petroleum contaminated soils (PCSs) and as a reactive medium in permeable sorptive barriers (PSBs) for remediation of petroleum hydrocarbon contaminated groundwater. A battery of laboratory tests was conducted to evaluate the geotechnical and environmental suitability of stabilized PCSs. The test program included batch adsorption, compaction, long-term column leaching, column sorption-desorption, and column biodegradation tests. Naphthalene and o-xylene sorption onto seven different fly ashes and powder activated carbon (PAC) was studied in a series of batch adsorption tests. A tertiary model non-aqueous phase liquid was used as the pollutant in column leaching tests conducted on PCS-fly ash mixtures. Retardation performance of HCCFA or PAC mixed with sand was investigated through column sorption-desorption and column biodegradation experiments to study the mass transfer behavior of the medium in a PRB application.

Batch sorption tests demonstrated a nonlinear sorption behavior for naphthalene and o-xylene onto HCCFA. Sorption was strongly correlated with carbon content of the ashes. Compaction test results indicated that the maximum unit weights and optimum liquid contents of the stabilized soils satisfy the limits set for highway embankment construction. Column leaching test results indicated that the naphthalene and o-xylene concentrations in the effluents collected from the stabilized PCS columns were lower than those collected from the control (soil only) columns. Column sorption-desorption tests revealed a retardation capacity of 48 to 78% for naphthalene and 15 to 48% for o-xylene. The biodegradation tests showed that high levels of biodegradation occurred when fly ash was employed as reactive medium. The study indicated that HCCFA can be effective in remediation of PCSs, and has good hydraulic and adsorption properties which may justify its potential use as a PSB material in remediation of groundwater contaminated with petroleum residues.