Bioventing is an in situ remediation technology that uses indigenous microorganisms to biodegrade organic constituents adsorbed to soils in the unsaturated zone. Soils in the capillary fringe and the saturated zone are therefore not affected. In bioventing, the activity of the indigenous bacteria is enhanced by inducing air (or oxygen) flow into the unsaturated zone (using extraction or injection wells) and, if necessary, by adding nutrients.

When extraction wells are used for bioventing, the process is similar to soil vapour extraction (SVE). However, while SVE removes constituents primarily through volatilisation, bioventing systems promote biodegradation of constituents and minimise volatilisation (generally by using lower air flow rates than for SVE).  In practice, some degree of volatilisation and biodegradation occurs when either SVE or bioventing is used.

Application

All aerobically biodegradable contaminants can be treated by bioventing. In particular, bioventing has proven to be very effective in remediating releases of petroleum products including petrol, jet fuels, kerosene, and diesel. Bioventing is most often used at sites with mid-weight petroleum products (i.e., diesel fuel and jet fuel), because lighter products (i.e., petrol) tend to volatilise readily and can be removed more rapidly using SVE. Heavier products (e.g., cutting/ lubricating oils) generally take longer to biodegrade than the lighter products.

Bioventing is not appropriate for sites with groundwater tables less than 1 metre below ground level. Special considerations must be taken for sites with a groundwater table located less than 3 metres below ground level because groundwater upwelling can occur within bioventing wells under vacuum pressures, potentially occluding screens and reducing or eliminating vacuum-induced soil vapour flow. This potential problem is not encountered if injection wells are used instead of extraction wells to induce air flow.