Bioventing

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Bioventing belongs to the in situ bioremediation technologies. Additional examples of such 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 compounds like gasoline, diesel and jet fuel as well as other biodegradable chemicals. Typically, these pollutants will be biodegraded in 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 so the oxygen supply rate meets the demand by the microorganisms and minimizes volatilization of contaminants. Image:principle_of_bioventing.gif

Applicability

It is recommended to use bioventing only when the groundwater table is found deeper than 3 m below surface. In addition, it should be noted that the method will have none or little effect when the original oxygen content in the soil air exceeds 5% (v/v).

Prior to bioventing, it is recommended to perform tests and measurements. These should include an 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 contaminants in question. This will provide information about biomass abundance and specific degradation rates.

Bioventing is not recommended in case of limited 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 take place at low rates.

Supplementing technologies

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

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