A foundation for the risk-based treatment of gasoline-contaminated soils using modified Fenton's reactions

The relative oxidation of representative aromatic and aliphatic hydrocarbon s found in gasoline was evaluated to provide the foundation for risk-based treatment of petroleum-contaminated soils and groundwater using modified Fe nton's reagent (catalyzed hydrogen peroxide). Aromatic components of gasoli ne are considered more hazardous than the aliphatic fractions due to their higher mobility in the subsurface and their higher acute and chronic toxici ties. Benzene, toluene, and mixed xylenes (BTX) were selected as aromatic c ompounds representative of unleaded gasoline, while nonane, decane, and dod ecane (NDD) were used as model aliphatic compounds. The effects of hydrogen peroxide (H2O2) concentration, iron catalyst concentration, and pH on the degree of treatment of the model compounds were investigated using central composite rotatable experimental designs. Oxidation of the aromatic compoun ds required less iron and less H2O2 than did oxidation of the aliphatic com pounds, while proceeding more effectively at near-neutral pH. Greater than 95% of the BTX was treated at near-neutral pH using 2.5% H2O2 and 12.5 mM i ron (III), while only 37% nonane, 7% decane, and 1% dodecane oxidation was achieved under the same conditions. The results show that the more toxic an d mobile aromatic fraction was more effectively oxidized using less H2O2 an d more economical conditions, including near-neutral pH, compared to the al iphatic fraction. A process design based on treating only the aromatic frac tion of petroleum may provide significantly lower costs when using modified Fenton's reagent for the treatment of contaminated soils and groundwater. (C) 2000 Elsevier Science B.V. All rights reserved.