Bioventing

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Bioventing belongs to the in situ bioremediation technologies. Additional examples of in situ bioremediation approaches include bioaugmentation, biostimulation, and biosparging. These methods can usually be applied without much disturbance of the activities on the site.

Contents

Principle

Bioventing is an in-situ bioremediation process that promotes aerobic biodegradation of organic contaminants in the unsaturated (vadose) zone. The method is suitable for sites contaminated with fuel compunds like gasoline, diesel and jet fuel as well as other biodegradable chemicals. Typically, these pollutants will be biodegraded at aerobic conditions by indigenous heterotrophic microorganisms naturally occurring in the soil. Thus, in order to promote microbial degradation, air or poor oxygen is delivered to anaerobic and permeable polluted soil zones at a low flow rate such that the oxygen supply rate meets the demand by the microorganisms and minimizes volatilization of volatile contaminants. Image:Biofinal2.gif


Applicability

It is recommend to use bioventing only when the grounwater table is found deeper than 3 m below surface. In addition, it should be noted that the method will have no or little effect when the original oxygen content in the soil air exceeds 5% (v/v).

Prior to onset of bioventing, it is recommended to perform tests and measurements. These should include in situ respiration test, in situ air permeability test and measurements of pH, bioavailable nutrients and soil moisture. Furthermore, it is relevant to carry out biomass determinations (DAPI staining, SIR etc.) and batch/column biodegradation experiments in the laboratory using the contaminant in question. This will provide information about biomass abundance and specific degradation rates.

Bioventing is not recommended in case of limiting air transport conditions (fine texture or saturated layers) or inhibited bioactivity (extreme pH, very low soil temperature, oligotrophic environment etc.). Under such conditions, indigenous microorganisms will be present in a limited number and their growth and metabolism will be slow.

Supplementing technologies

Bioventing is often combined with vacuum extraction in order to control the transport of the injected air. Furthermore, biostimulation using addition of nutrients can be applied. However, infiltration of dissolved nutrients may increase moisture content in the unsaturated zone, leading to enhanced gas transport properties.


External links:

Overview (USEPA)

A Guide for Corrective Action Plan Reviewers (USEPA)

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