Bioremediation of High Molecular Weight PAHs

Abstract

Land farming is a common treatment option for PAH-contaminated soils. The process is based on the degradation of PAHs by natural microbial communities in the presence of aeration (tilling), fertilizer addition, and physical mixing. In general, considerable degradation of total PAHs occurs but the removal of the high molecular weight (HMW) PAHs (four or more aromatic rings), those that are of most concern from a regulatory and remediation standpoint, is very problematic. This is due many times to the absence of a key metabolic activity, namely the ability to cometabolize HMW PAHs, and to the lack of availability of the PAHs to the degrading microorganisms. The problem can be corrected, we believe, by bioaugmentation with two key microorganisms; one that adds significant cometabolic capability and another that produces a biosurfactant. The characteristics of the organisms and the practicality of introducing them into soil are discussed. Although bioaugmentation will add costs to the treatment process, it is likely that the improved reliability for removing HMW PAHs to below regulatory limits will eventually justify the added cost.