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#bioventing

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Bioremediation

Bioventing works by:

Bioventing achieves remediation by supplying air as oxygen source directly into unsaturated vadose zone above capillary fringe where soil pores partially air-filled but contaminated with sorbed fuel in smear zone. Operational layout uses injection wells screened in contaminated interval with oxygen, carbon dioxide and hydrocarbon analyzers plus extraction vents creating pressure gradient drawing atmospheric air at low velocity 0.5 to 5 cfm, ensuring oxygen above 2 percent while limiting volatilization below 20 percent. Indigenous heterotrophs use oxygen for alkane hydroxylase and aromatic dioxygenase initiating mineralization and as electron acceptor for complete oxidation to carbon dioxide via TCA cycle. Biological activity evidenced by O2 drop from 21 to 5 percent and CO2 rise to 5 to 10 percent above background, plus increased microbial counts. Moisture sensors prevent clogging. Unlike biosparging injecting air below water table, bioventing specifically targets unsaturated zone avoiding aggressive stripping, focusing on biological transformation as primary removal, proven cost-effective across thousands of fuel sites under EPA guidance since 1990s.

Ref: EPA Bioventing Manual 1994; Hinchee et al. Bioventing case studies; PubMed bioventing mechanism EA/2.

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Bioremediation

Bioventing is mainly used for remediation of:

Bioventing has emerged over past three decades as leading cost-effective in situ technology for vadose zone soils contaminated with mid-range and light petroleum hydrocarbons such as diesel, jet fuel, gasoline and BTEX compounds frequently leaked from underground storage tanks. Unsaturated soils typically harbor indigenous populations of hydrocarbonoclastic genera Alcanivorax, Pseudomonas, Rhodococcus and Mycobacterium carrying genes alkB alkane monooxygenase, CYP153 cytochrome P450, and catechol dioxygenases requiring molecular oxygen both as terminal electron acceptor and as cosubstrate for initial activation via insertion of one oxygen atom into alkane forming alcohol and aromatic ring forming catechol. Low-flow air injection typically 1 to 2 cubic feet per minute per well provides just enough oxygen to maintain aerobic respiration rates measured by oxygen utilization 0.1 to 1 percent per hour while minimizing stripping and need for off-gas treatment, contrasting with soil vapor extraction designed primarily for volatilization. Nutrients such as ammonium nitrate and phosphate salts and moisture optimization to 40 to 70 percent field capacity further accelerate rates. Heavy metals, radionuclides and chlorinated plastics lacking oxidizable C-H bonds not amenable to oxidative bioventing and require alternative strategies.

Ref: Leeson & Hinchee EPA Bioventing Principles and Practice 1997; EPA Bioventing design manual; PubMed BTEX bioventing.

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