Biofilters use microorganisms to capture and degrade air pollutants. They come in open or closed bed designs with various support media like compost or synthetic materials. A biofilter unit contains a bed of media that hosts pollutant-degrading microbes. As contaminated air passes through the bed, pollutants are absorbed and broken down. Biofilters have low costs but require space and stable conditions to maintain microbial health for effective treatment of some pollutants.

1. Use of Biofilters for Air Pollution
Control
By: Ishanee Sharma
Roll No. 15/252
7th Semester

2. Introduction
• pollution control technique using a bioreactor
containing living organisms to capture and
biologically degrade pollutants
• Microorganisms are diffused in thin layer known as
“biofilm”
• Importance of biofiltration:
1. Green process
2. Use small amounts of electrical power

3. Types of
Biofilters
On the basis
of layot
Open Bed Closed Bed
On the basis
of Shape
Horizontal Vertical
On the basis
of support
media
Compost
Biofilter
Synthetic
Biofilter
Classification of Biofilters

4. Components of Biofilter Unit

5. • Biofilter Components- Usually a rectangular box that contains
an enclosed plenum on the bottom, a support rack above the
plenum, and several feet of media (bed) on top of the support
rack.
• Materials used for bed media – Peat, composted yard waste,
bark, coarse soil, gravel or plastic shapes, Oyster shells (for
neutralizing acid build-up) and fertilizer (for macronutrients)
are mixed with bed media.
• Support Rack – perforated to allow air from the plenum to
move into the bed media to contact microbes that live in the
bed.
• Fan – It is used to collect contaminated air.

6. Purpose of a Biofilter Media
• To provide a large surface area for the absorption and
adsorption of contaminants.
• To serve as a nutrient source for the microbial population.

7. Considerations for Filter Material
• Ability to retain moisture to sustain biofilm layer;
• Large surface area, both for contaminant absorption and
microbial growth;
• Ability to retain nutrients and supply them to microbes as
required;
• Low resistance to air flow (minimizes pressure drop and
blower power requirements);
• Physical characteristics, such as physical stability and ease of
handling.

8. Working
• In a biofilter the to-be-cleaned gas stream is passed upwards
through a filter bed. The filter material carries a thin film of
water which is home to micro-organisms. The pollutants in
the gas stream are retained in the filter material via
adsorption and absorption, and are then decomposed by the
present micro-organisms. The degradation products for
conversion are carbon dioxide, sulphate, nitrate etc.
• A humidifier is implemented in advance, in order to prevent
the filter from drying out.

9. • In case of substances that are more difficult to degrade, the
filter can be injected with special cultures in order to realise
faster filter start-up. The addition of minerals and nutrients
may be desired if there is insufficient nutrient-release in the
filter material.
• When the packing is being introduced, one must ensure that
the filter material is well distributed and that there are no
solid of loose zones. These could lead to open streams,
causing sub-standard air treatment and reducing the effective
filter surface and filter dries out quickly.

10. Design Parameters
• Space Constraints – 25 square feet size
• Temperature – 30 to 41 degree Celsius
• Chemical Constituents and Concentration – low concentration
less than 1000 ppm
• Residence Time – 30 seconds to 1 minute
• Humidity – 95% relative humidity

11. • pH Control – Generally 7, In case of H₂S pH= 1-3
• Biofilter Media – Peat, Heather, Bark, Granulated Carbon
• Pressure Drop – 1 to 10 Pa
• Maintenance – Biweekly or monthly

12. Advantages and Disadvantages
• Advantages
1. Low capital cost, low operating cost, low chemical usage and
no combustion source
2. versatile enough to treat odours, toxic compounds, and
VOCs. The treatment efficiencies of these constituents are
above 90% for low concentrations of contaminants (<1000
ppm)
3. Different media, microbes and operating conditions can be
used to tailor a biofilter system for many emission points.

13. • Disadvantages:
1. cannot successfully treat some organic compounds, which
have low adsorption or degradation rates
2. Contaminant sources with high chemical emissions would
require large biofilter units or open areas to install a
biofiltration system
3. Sources with emissions that fluctuate severely or produce
large spikes can be detrimental to the biofilter’s microbial
population and overall performance
4. Acclimation periods for the microbial population may take
weeks or even months

14. Applicability of Biofilters
Company Name Location Application
Monsato Chemical Co. Springfield, Mass., USA Ethanol and Butyraldehyde
removal from dry air
Dow Chemical Co. Midland, Mich., USA Chemical Process Gas
Esso of Canada Sarnia, Ontario, Canada Hydrocarbon vapours from
fuel storage tanks
Mobil Chemical Co. Canandaigua, N.Y., USA Pentane from polystyrene
foam moulding
Uphohn Co. Kalamazoo, Mich., USA Pharmaceutical Production
odours

15. Microbial Degradation of Pollutants
Pollutants Microbes Degradation Product
Hydrogen Sulphide Thiobacillus thiooxidans H2SO4
NOx Nitrobacter
Denitrifying Bacteria
Nitrates
N2
Dimethylamines P. aminovorans Methylamine and
formaldehydes
Phenol P. putida Acetaldehyde and
puyrate
Aniline Pseudomonas spp. Pyrocatechol
Benaldehyde Acetobacter acendens Benzyl alcohol and
Benzoic acid

16. Conclusion
• Biofiltration plays a very important role in air pollution control.
• Biofilter is successful only when microbial system is healthy
• Optimum working of biofilter depends on temperature,
pressure, pH, biofilter media and humidity conditions
• Overall, biofilter has low capital and operating costs but
requires lots of space
• Biofilter cannot treat pollutants with low adsorption or
degradation rates