Improving PAH Biodegradation in Contaminated Soil by Adding Surfactant After Conventional Biological Treatment

Polycyclic aromatic hydrocarbons (PAHs) are a class of compounds which occur frequently at polluted sites and are known or suspected to be toxic and genotoxic. Bioremediation is one option for the treatment of PAH-contaminated soil, but PAHs are often strongly bound to soil and may be unavailable to degrading microorganisms. Limited PAH desorption can be particularly problematic for weathered soils or soils which have undergone treatment but fail to meet cleanup goals. Additionally, bioremediation does not always lead to a reduction in soil (geno)toxicity. This dissertation addresses these limitations by screening nonionic surfactants enhanced desorption and biodegradation of residual PAHs remaining in soil after conventional slurry-phase bioreactor-treatment. Surfactant doses were chosen to be below the critical micelle concentration in the soil-slurry system. The effect of surfactant-amended treatment on soil (geno)toxicity was also evaluated. The best performing surfactant was selected for use in a second-stage bioreactor to evaluate the reproducibility of surfactant-amended treatment and to investigate the effect of varying residence time. In screening experiments, further treatment of the soil with all surfactants resulted in modest increases in PAH desorption. Four out of 5 surfactants increased PAH biodegradation relative to further treatment without surfactant. The most effective surfactants significantly enhanced the biodegradation of 5 of the 7 PAHs considered probable human carcinogens by the Environmental Protection Agency (individual PAH removals up to 80%). Further treatment without surfactant significantly reduced the genotoxicity of the soil, while treatment with surfactant had varying effects. Increased PAH removal, however, did not always coincide with a reduction in soil toxicity and genotoxicity. For the two-stage bioreactor system using polyoxyethylene sorbitol hexaoleate surfactant, substantial amounts of the PAHs and oxygenated-PAHs remaining after conventional bioreactor-treatment were removed in the second stage, including more than 80% of residual 4-ring PAHs. The most substantial PAH removal in the second stage occurred within the first week of treatment. Surfactant-amended treatment consistently made the soil less cytotoxic, but in most trials increased the genotoxicity of the soil. With further optimization of the treatment system, surfactant-enhanced treatment may increase the applicability of bioremediation as a means of meeting soil remediation goals.Doctor of Philosoph