Air | Biofilter

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Biological air treatment: biofiltration

Purpose

  • Odour removal
  • Removal of solvents (VOS) in relatively low concentrations (0,1 g/m³ à 1 g/m³):
    • toluene
    • esters
    • styrene
    • hexane
    • ethanol
    • methanol
    •  …

Principle

In biofiltration the gas to be treated is first humidified to 100% saturation and then sent through a bed of organic material (bark, compost, peat, ...). This causes biodegradation of pollutants by means of the micro-organisms which develop in this organic support material. While the moisturized air prevents that the biofilter will dry out, the organic material serves as a carrier and as a source of nutrients (which are non-existent in the gaseous effluent) for the present micro-organisms. In order to counter acidification of the biofilter material in some cases a pH-buffer is added. In addition nutrients are also periodically dosed into the biofilter through surface irrigation.

In a number of cases a chemical scrubber is placed in front of the biofilter to be able to deal with (very) high concentrations of ammonia, organic sulfur compounds, hydrogen sulfide, etc. This scrubber then serves as a pre-treatment step and the biofilter then takes care of the degradation of the other compounds.

Scheme

Humidifier prior to biofilter

Applications

  • Odour removal:
    • composting
    • rendering and slaughterhouses
    • aroma-industriy
    • driers
    • stable air
    • manure treatment air
    • water treatment
  • Solvents (VOS):
    • chemical industry
  • Thermophilic biofiltration (45 till 65°C)
    • drying plants
    • bake ovens
    • tobacco industry

The most common ways of implementing biofiltration are:

  • Container units for treating low flow rates
  • Concrete basins in agriculture
  • PP insulated panels with lining for use in industry

Realisations

Biofilter

Biofilter

Humidification prior to biofilter

Operational costs

Operating costs at biofiltration are rather low in terms of water and electricity. In addition the biofilter must be replaced on a regular basis, typically after about 2 to 4 years.