Public Services and Procurement Canada
Bioventing consists of increasing soil aeration to stimulate in situ biological activity and enhance the aerobic biodegradation of residual contamination in the unsaturated (vadose) zone. This technique is suitable for all chemical compounds that are biodegradable under aerobic conditions.
The objective of a bioventing system is to enhance contaminant biodegradation by injecting air in the subsurface soils while minimizing contaminant volatilization. The rate of air injection or extraction is calculated and monitored in order to provide the required volume of air for optimal bacterial activity. There are two methods of bioventing: air injection and air extraction. The advantages of an air injection system over an air extraction system are: a reduction of contaminant volatilization; augmentation of the radius of influence; and, lower costs. However, an air injection system is not recommended when there are buildings and/or underground structures within or near the contaminated site.
Occasionally, bioventing systems may include the use of water irrigation (with or without the use of nutrients), gaseous nutrients (nitrous oxide [N2O], triethyl phosphate [TEP]), moisture addition or the use of gases other than air (methane [CH4], propane [C3H8], hydrogen [H]). Such applications are rare. Methane injection in order to stimulate the cometabolic destruction of chlorinated solvents (tetrachloroethene/perchloroethylene [PCE], trichloroethene [TCE], 1,1,1-trichloroethane [TCA] and 1,2-cis dichloroethylene [DCE] for example) has been demonstrated, but is unusual.
Bioventing using air extraction is not to be confused with soil vapour extraction (SVE) which uses relatively large amounts of energy to create relatively high subsurface vacuums and gas flow rates, stripping volatile contaminants out of the soil (refer to the SVE Technology Factsheet for more information). Bioventing uses lower energy inputs to refresh the subsurface supply of oxygen to stimulate biodegradation. Low energy “passive” bioventing systems and solar-powered bioventing systems have been successfully demonstrated. Passive bioventing utilizes the difference between gas pressure in unsaturated soil and in the atmosphere to move air into or out of vent wells.
Bioventing induces the flow of air (sometimes mixed with another gas), in the subsurface soils, above the water table (vadose zone), to stimulate the biodegradation of contaminants. Bioventing systems may include the following:
The vast majority of bioventing systems use air as the working gas. However, cometabolic remediation of chlorinated solvents has been demonstrated using injected methane or propane gas.
Bioventing is based on adapted monitoring well and gas-handling technologies. Pre-assembled systems complete with air emissions controls are commonly available in trailers, shipping containers or on skids. Bioventing systems may require only electrical power and fresh air for operation.
Wells, trenches, permeable drains or other structures are used to extract or inject air. If air is injected, monitoring points should be used to verify that deleterious vapour migration is not occurring. If air is extracted, it is typically subjected to treatment and then, once treated, discharged into the atmosphere. Since extracted air is typically moist, it is directed through an air/water separator before treatment. Treatment systems are commonly comprised of combustion (thermal oxidation, catalytic oxidation) or filtration/sorption (activated carbon, biofiltration) units.
Bioventing typically require very little on-site storage. Storage could include auxiliary fuel (such as natural gas or propane for thermal oxidizers) or air treatment media (i.e. sorbent which is usually granular activated carbon).
Tests examining the effect of temperature change on hydraulic conductivity and
establishing the zone of freezing with a pilot scale tubing system are recommended to
properly design the full-scale containment system.
The bioventing remediation technology is suitable when the following conditions are met:
Few to none.
Biodegradation of organic contaminants does not typically generate any deleterious secondary by-products or metabolites, as it results in innocuous by-products including carbon dioxide and water.
Although, vinyl chloride and cis -1,2-dichloroethylene are produced in the biodegradation of trichloroethylene (TCE) and tetrachloroethylene/perchloroethylene (PCE).
Application examples are available at these links:
The treatment time to lower contaminant concentrations required by a bioventing system is highly variable and depends upon many parameters including: contaminant properties, the natural bacterial population, the physical and chemical properties of the soil and vadose zone and the design of the bioventing system. Bioventing systems are more effective when treating low molecular weight, less hydrophobic contaminants.
Unavailable for this factsheet
Composed by : Serge Delisle, Eng. M.Sc., National Research Council
Updated by : Karine Drouin, M.Sc., National Research Council
Updated Date : January 1, 2008
Latest update provided by : Daniel Charette, P.Eng., eng., Jan McNicoll, M.Sc., P. Geo., exp Services Inc.
Updated Date : March 31, 2017