Bio-scrubbers for odour control applications - Air and Climate - Indoor Air
Many industrial processes like food, drink and milk plants, slaughtering, rendering and industrial and municipal wastewater treatment plants can generate odours which create an unpleasant working environment and possible health and safety issues for plant operators as well as being a nuisance to the public in the surrounding area.
Odours are caused by a variety of chemical species, the commonest of which are:
- reduced sulphur compounds such as hydrogen sulphide, mercaptans and organic sulphides
- nitrogen compounds like ammonia tertiary amines and quaternary ammonium compounds
- volatile fatty acids including formic, acetic and butyric acids
- aldehydes and ketones including formaldehyde, acetaldehyde and acetone
- solvents such as toluene
There are several approaches to odour mitigation based on chemical or biological treatment, and selection depends on the specific chemical species present.
The simplest process is biological or chemical scrubbing in which water-soluble species like hydrogen sulphide or ammonia are the source of the odour. The contaminated air from process is collected and is blown upwards through a column filled with media while a recirculated liquid phase flows counter-currently down the scrubber. In a chemical scrubber, dilute acid is used for ammonia removal, dilute alkali for hydrogen sulphide and sodium hypochlorite for oxidizable organics. In a biological scrubber ammonia and sulphides are oxidised and VOC’s broken down by bacteria and the cleaned air is discharged to atmosphere from the top of the column. The media provides an interface contact between the gas and liquid phases and should provide a high surface area but low gas phase pressure drop. Bioball and Biopipe+ is an appropriate media for this application.
Advantages of Warden Biomedia
- Simple technology
- Small footprint
- Efficient removal of water-soluble gases
- Ease of maintenance
Where odour-causing species are mostly organic, biological filtration has a proven track record. The air passes through a bed of media on which a biomass grows. As the air flows upwards through the bed it encounters a variety of microorganisms. The specific population depends on the nature of the odour but will typically include sulphur oxidising bacteria for hydrogen sulphide and mercaptan removal, nitrifying bacteria for ammoniacal odours and heterotrophs for VFA degradation. The media is continuously irrigated with water containing selected nutrients for optimum bacterial growth. The key to success is a high surface area for biomass growth combined with low pressure drop since the air flow is natural draught. The typical media is wood chip, mussel shells, rocks, etc but this requires replacement every 3 to 5 years, although the use of bio-media avoids this. Bioflo+ and Biomarble are appropriate media.
Advantages of Warden Biomedia
- Treats a variety of contaminants
- No Replacement cost of media
- No hazardous chemicals
- Low energy consumption
- Cost effective