Use of biofilters for air pollution control

This presentation is about the use of biofilters in air pollution control. Working principle of biofilters, where it is used, its advantages and disadvantages have been discussed in this presentation. Various design parameters are also discussed.

References:
1. https://www.rpi.edu/dept/chem-eng/Biotech-Environ/MISC/biofilt/biofiltration.htm
2. https://www3.epa.gov/ttncatc1/dir1/fbiorect.pdf
3. https://civildigital.com/detailed-study-biofilters-controlling-air-pollution-seminar-presentation/
4. https://emis.vito.be/en/techniekfiche/biofilter-0
5. https://www.slideshare.net/AabidMir/biofilters-and-air-pollution-controll/25

1. Use of Biofilters for Air Pollution Control By: Ishanee Sharma Roll No. 15/252 7 th 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 : Green process Use small amounts of electrical power

3. Classification of Biofilters

4. Components of Biofilter Unit

5. Biofilter Components - U sually 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, I n 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 Low capital cost, low operating cost, low chemical usage and no combustion source 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 ) Different media, microbes and operating conditions can be used to tailor a biofilter system for many emission points.

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

14. Applicability of B iofilters 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