Biological air treatment: biofiltration

Application

• Odour removal

• Removal of volatiles in relatively low concentrations (0.001 g/m³ to 1 g/m³):

  • toluene

  • aromatics (toluene, styrene,…)

  • alcohols (methanol, ethanol,…)

  • hydrocarbons (pentane, hexane,…)

  • others (aldehydes, esters, …)

Principle

In a biofilter, the waste gas is blown through a reactor which is filled with an organic carrier material, as e.g. wood root, bark or mixtures. During the start-up of the biofilter, the presence of pollutants in the waste gas will result in a shift from the natural microbial flora on the carrier material towards a predominance of the most suited groups of microorganisms that efficiently metabolise the target pollutants. Only in exceptional cases, inoculation with selected microorganisms is needed in order to minimize the start-up period.

Crucial with regard to the biofilter is the correct dimensioning of the reactor in correspondence to the air flow/pollutant load and the correct preconditioning of the incoming air. Regarding the latter, a nearly 100% humidification of the incoming air is crucial. For some waste gases, a chemical scrubber is needed in front of the biofilter in order to remove too high concentrations of e.g. ammonia or hydrogen sulphide. For other applications, a peakshaver is advised before the biofilter in order to minimise a too strong fluctuation in pollutant concentrations.

While the moisturised waste gas prevents the dry out of the biofilter material, the biofilter material serves as a carrier and as a source of missing nutrients for microorganisms. Depending on the composition of the waste gas, a pH-buffer (to counter acidification of the biofilter material) and/or slow-release nutrients can be mixed with the biofilter material to improve the long-term performance of the biofilter. In addition to this, an additional periodic dosing of nutrients using the surface irrigation of the biofilter material can be done.

Biofiltration is possible for waste gases with wet bulb temperatures till maximum 70°C.  As a result of this, thermophilic biofiltration is possible for hot waste gases coming from e.g. food processing and rendering facilities(driers, extruders,…) without the need to first cool down the gases.

For some applications, the biofilter can be equipped with a cover/roof in order to collect the purified waste gas and send it to an adjacent stack or make it suitable for sampling of the purified gases.

Scheme

Realisations