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#groundwater cleanup

2 public questions tagged with this topic.

Bioremediation

Biosparging involves:

Biosparging constitutes in situ groundwater remediation targeting dissolved and sorbed petroleum hydrocarbons in saturated zone where natural oxygen typically depleted below 1 mg per L. Technology injects air, pure oxygen or microbubble oxygen-emitters at pressures slightly above hydrostatic 5 to 15 psi through wells placed 5 to 10 feet below plume. Bubbles rising dissolve oxygen up to 8 to 10 mg per L per Henry's law and partition volatile BTEX upward to vadose zone for capture by soil vapor extraction. Aerobic bacteria Pseudomonas putida and Rhodococcus carrying xylene monooxygenase and catechol pathways exploit oxygen for initial ring activation otherwise rate-limiting. Design accounts for air channeling due to heterogeneity by using closely spaced points 20 to 50 feet apart, pulsed injection preventing biofouling and monitoring dissolved oxygen, oxidation-reduction potential and contaminant concentrations to verify radius of influence. Unlike bioventing treating unsaturated zone, biosparging prevents plume migration and protects downgradient receptors while promoting aerobic mineralization rather than slower anaerobic routes.

Ref: EPA Biosparging Design Guidance 1994; Leeson et al. Air Sparging Principles; PubMed biosparging review PMID 10463012.

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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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