13 Unsaturated zone gas-phase VOC biodegradation: the importance of water potential

摘要

Bioremediation of the unsaturated zone using indigenous microorganisms holds promise as a cost-effective and environmentally-compatible cleanup option. Both field and labororatory results indicate that microbial decomposition of hydrocarbon vapors in some subsurface soils may occur~(1, 2) and that forced air advection, called bioventing, through systems increases the overall cleanup rate by enhancing volatilization and gas phase mass transfer to microbial communities.~3 More conclusive evidence of biological removal stems from carbon dioxide isotopic analysis during field studies or from measuring the percent of recovered lable in ~(14)C laboratory studies. ~4Despite the evidence supporting in situ bioremediation of volatile organic compounds (VOC's), the majority of laboroatory and field studies to date can best be described as phenomenalistic. If in siut bioremediation is to be cost-effectively engineered, a firm understanding of related process factors and an ability to control those factors must be gained. Sims et al~5. proposed five environmental factors that influence microbial activity during bioremediation: (1) available soil water, (2) oxygen, (3) redox potential, (4) pH, (5) nutrients, and (6) temperature. We propose that soil water potential is a limiting constraint, and in fact is the unifving determinant of many individual factors deemed important to VOC biodegradation in unsaturated soils.