A biofilter is one of the cheapest and simplest odor control methods available. However, a good number of conditions must be met for a biofilter to work properly.
How does biofiltration work?
Biofiltration usually involves the use of a filter filling consisting of biological material in a well-defined mixing ratio, or in different layers. This natural “filter bed” or biomass is contained in an open or closed filter enclosure. This filter filling is surrounded by a thin film of water. Some of the contaminants from the gas stream already dissolve in the water film. The remaining part of the contaminants is retained on the filter material and further broken down by the microorganisms in the filter bed. The microorganisms feed partly on the remaining pollutants and partly on the filter material itself. The residual products of these degradation processes are CO2, H2O, sulfate, nitrate, etc.
What are the advantages of a biofilter?
- Simple construction
- Low investment cost
- Good result for biodegradable components in relatively low concentrations (polishing technique)
Are there disadvantages?
- Big footprint, takes a relatively large area
- Biomass needs to be replaced periodically
- Exact moisture content and pH need to be monitored accurately, a continuous aeration is vital
Most important application areas of biofiltration
- Wastewater treatment plants
- food industry
- meat and fish processing industry
Biofilter – biofiltration – emission treatment – odour treatment
The important parameters for the proper functioning of the biofilter
- Constant moisture content: Maintaining an optimal moisture content in the biomass is an essential condition for the proper functioning of a biofilter. Too much moisture can cause the biomass to clump, air resistance increases and oxygen content decreases. The filter in turn becomes a source of odor nuisance instead of combating odor nuisance.
- Constant air supply: The emission must be offered relatively continuously. If only 7 to 8 hours/day of waste gas is produced, a biofilter will not be able to provide a solution. The bacteria in the biofilter cannot survive without a constant oxygen supply. In addition, the incoming air must be free of dust and grease.
- Constant temperature: A temperature between 15 and 25 °C is ideal (max 30 °C). Lower temperatures will slow down the action, higher temperatures will unbalance the entire biomass.
- Constant load: A relatively low load is not a problem as such and will only translate into a high removal yield. With a too high and/or peak load, the biomass will clog up quickly, resulting in a lower removal efficiency.
- No toxic and/or acidifying components: Highly toxic compounds kill microbiology. Excessive concentrations of sulfur, chlorine, nitrogenous organic components and ammonia lead to acidification and reduced efficiency of the biofilter. This can be partly counteracted by adding certain additives to the biomass, by replacing the biomass more frequently or by incorporating a chemical scrubber.
- Adapted biomass: The biomass must be adapted to the offered gas flow. For certain specific applications, it may be appropriate to use more specific bacteria. In all cases, the biomass must be replaced periodically, depending on the degree of acidification, salinization and the pressure drop over the filter. The lifespan of a biofilter filling strongly varies and is situated between 6 months and 5 years.