Detailed Study on Biofiltration In Controlling Air Pollution – Seminar Presentation
by Shreyash Gupta & Avichal Sharma
- Industries, agriculture transport many more modern socio-economic practices pollute our environment.
- Gas Bio-filtration is a relatively new technology used to purify contaminated air from volatile organic and inorganic compounds VOC’S and VIC’S, aromatic compounds and other toxic and odorous compounds.
- Our main aim is to study use of bio filters for controlling air pollution in industries having above mentioned pollutants.
- The experience gained from monitoring exercise carried out during the last 25 years and adoption of appropriate strategy for air quality control have been discussed in this paper presentation.
Bio filtration is air pollution control technique which Involves bio degradation of contaminants under the action of microorganisms diffused in a thin layer of moisture known as “BIOFILM” ,Mainly used for elimination of malodorous gas emissions and low concentrations of Volatile Organic Compounds (VOCs).
The process of Bio Degradation is :
Organic Pollutant + O2 CO2 + H2O + Heat + Biomass
Brief Timeline Of Development Of Bio Filters
1923 – Biological methods were proposed to treat odorous emissions
1955-Biological methods were applied to treat odorous emissions in low concentrations in Germany
1960’s-Bio filtration was used for the treatment of gaseous pollutants both in Germany and US.
Why Is Bio-filtration Important
Bioreaction is a green process
Thermal and catalytic control units consume large volumes of expensive fuel.
Bioreactors only use small amounts of electrical power to drive two or three small motors.
Normally, bioreactors do not require full-time labor and the only operating supplies needed are small quantities of macronutrients.
Types Of Bio Filters
ON THE BASIS OF LAYOUT
- Open Bed : Uncovered and Exposed to all Weather conditions.
- Closed Bed : Enclosed with a small exhaust port for venting of cleaned air
ON THE BASIS OF SHAPE
- With Larger footprints
- Relatively inexpensive
- Easy maintenance
- Designed to reduce the footprint required.
- Use less surface area compared to Horizontal
- Not easy to Maintain
ON THE BASIS OF SUPPORT MEDIA
- Compost Bio Filter : Soil , Peat, Compost material is used
- Synthetic Bio Filter : Ceramic , Plastic ( BTX )*
How do Bio-reactors Work
Microbes’ life cycle –they breed, feed, eat, die. Their diet is based primarily on carbon-based compounds, water, oxygen (for aerobic reactions) and macronutrients.
Components Of A Bio-filter Unit
MATERIALS used for bed media – peat, composted yard waste, bark, coarse soil, gravel or plastic shapes ( Reference 2 from EPA PDF )
Oyster shells (for neutralizing acid build-up) and fertilizer (for macronutrients) are mixed with bed media.
SUPPORT RACK -perforated – allow air from the plenum to move into the bed media -to contact microbes that live in the bed. Perforations also permit excess, condensed moisture to drain out of the bed to the plenum.
FAN – used to collect contaminated air, As the emissions flow through the bed media, the pollutants are absorbed by moisture on the bed media.Microbes reduce pollutant concentrations by consuming and metabolizing pollutants. During the digestion process, enzymes in convert compounds into energy, CO2 and water. Material that is indigestible is left over and becomes residue.
Design and Performance Parameters
- Contact Time and Air Flow
- Moisture Content
- Microorganism Seeding
- Health and Safety Concerns
TEMPERATURE: Most microbes can survive and flourish in a temperature range of 60 to 105 /F (30 to 41/C) (Ref. 3 of EPA PDF). When emissions are too hot, humidifiers are used which cools gases down by evaporative cooling.
MOISTURE: Moisture creates the bio-film that removes (absorbs) pollutants from an air stream so that they can be assimilated by microbes. Humidifiers made from an old FRP (fiber reinforced plastic) tank are used to increase moisture.
CARE AND FEEDING : Microbes need a diet of balanced nutrients to survive and propagate. Pollutants provide the main source of food and energy, but microbes also require macronutrients to sustain life. Microbes use nitrogen to build cell walls. some nitrogen products form water-soluble compounds and are leached out of the system with condensing water. Nitrogen, phosphorus, potassium added by incorporating agricultural fertilizer into bed media.
ACIDITY: Most bioreactors perform best when the bed pH is near 7, or neutral. hydrogen sulfide, organic sulfur compounds, and halogens (chlorine, fluoride, bromine and iodine) are acidic in nature and lower the pH.
Oyster Shells may be added to neutralize the pH. a Dilute solution of soda ash (sodium carbonate, Na2 CO3) may be introduced by a garden hose periodically.
- Odor and hydrogen sulfide reductions up to 95%.
- Ammonia reductions up to 80%.
- Uses Microorganisms
- Absorbs And Oxidizes
- Oxidisable Inorganic Gases and Vapors
- Water, Carbon di oxide, Salts
- Microbial Biomass
BIOFILTERS – A Viable Option
- Effective at emission reduction.
- Biological system requiring management.
- Design, installation and operation will impact building ventilation and bio-filters effectiveness.
Review Of Researches
- In research on Transient Behavior of Biofilter , Marc A. Deshusses describes the aerobic biodegradation of VOC mixtures from effluent air streams in laboratory scale compost based biofilters. Bio filters had degraded and absorbed Hexane , Acetone , MIBK , propane and MEK in different proportions. Established a fundamental description of pollutant removal in biofilters.
Biofiltration-an Innovative Technolgy For The Future
- different types of biofilters’ support media
- the various biofilters operations adopted in industry.
- waste compounds treatable by biofiltration
- commercial potential of biofiltration.
- The paper concludes that when compared to other available technologies, biofilters have significant technical and economical advantages.
A Few Existing Bio Filters
McMinnville, Oregon: The installation in McMinnville, Oregon perhaps best demonstrates the capabilities as the levels of odorous compounds to be treated were among the highest ever reported from the wastewater treatment environment.
Long Sault, Ontario: Although a small (1500 cfm), indoor, container-type system, this installation demonstrates several key aspects that are relevant to any installation.
Sarnia, Ontario: This biofilter was installed in 2001 and treats 12,500 cfm of air coming from a sludge liming and drying operation.
Brookfield, P.E.I. : This biofilter was installed in 2002, at a composting plant in P.E.I., that treats 60,000 cfm of air from the composting process.
Toronto, Ontario: This biofilter was installed in 2002 in the north end of Toronto at the Toronto Mixed Waste Recycling and Organics Processing Facility.