BIOFILTERS: AND CONTROLL OF AIR
POLLUTION.Aabid Bashir Mir.
M.Sc. 4th sem.Roll No. 8258.
Department of Environmental Science.University of Kashmir.
OUTLINEDefinition.History.Design.Parameters to be maintained.Microbial ecology.Mechanism.Extreme biofilters.Applicability.Comparison.Conclusion.
Biofiltration Involves passing a
contaminated air streamthrough a media bedthat is porous and moist.
As the air passesthrough the media, thecontaminants are
adsorbed into the waterwithin the media.
Bacteria that are presentwithin the media
continuously consumethe absorbed
Contaminants.
80-95% odor reduction of air through biofilter.
History of Biofilters:
• 1923: The first proposition to use biological methods to treat odorous compounds was as early as 1923. Bach thought of using a biologically active biofilter to control emissions of H2S from a waste water treatment plant.
• 1955: Biological methods were first applied to treat odorous emissions in low concentrations in Germany.
• 1959: A soil bed was installed at a sewage treatment plant in Nuremberg for the control of odors from an incoming sewer main.
• 1960's: Biofiltration was first used for the treatment of gaseous pollutants both in Germany and US; research was intensified.
• 1970's: Biofiltration becomes widespread in Germany.
• 1980's: Biofiltration is used for the treatment of toxic emissions and volatile organic compounds (VOCs) from industry.
• 1990's: There are more than 500 biofilters operating both in Germany and Netherlands, and it is spreading in the US.
Schematics of a Biofilter
Air with H2S
Clean air
Packing Material Supporting Biofilm
Biological Reaction
Water with nutrients
Water with oxidation products
The major reactors are:-
• Biofilters.
• Biotrickling filters.
• Bioscrubber.
Classification of bioreactors for waste gas purification.
Reactor type Microorganisms Water phase
Biofilter Fixed Stationary
Biotrickling filter Fixed Flowing
Bioscrubber Suspended Flowing
Biotrickling filter
Gas contaminants are absorbed in a free liquid phase prior to biodegradation by microbes.
Operate with the air and water phase moving either counter-currently or co-currently, depending on specific operation.
Offer greater performance than biofilters at higher contaminant loadings.
Bioscrubber
The degradation of contaminants is performed by a suspended consortium of microbes in separate vessel.
Absorption achieved in packed column, spray tower.
Water transferred to separate vessel , where optimum environmental conditions for biodegradation are.
Biofilter Designs
Biofilter Designs Description Feature velocity
First Piles and Pits Compost mixed with wood chips Erratic Performance 3-4 cfm/ft2Generation
Second Enclosed Vessels Similar media as used in "Piles and Improved Performance, 10 cfm/ft2Generation Pits" but included enclosures around Difficult Expansion and
all sides of the biofilter. Better Maintenanceirrigation and better flow into media
Third Modular Systems Moved from organic medias to Easy 25 cfm/ft2Generation inorganic medias. Since media is no Installation and Expansion,
longer water soluable, longer media life Easy Media Replacement,and more aggressive irrigation systems Less Footprintused, improved mass transfer
A biofilter can be:
open or enclosed.
built directly into the ground or in a reactor vessel.
single or multiple bed.
Vertical biofilter Open-bed biofilter
Schematic diagrams of above-ground closed biofilter
Schematic diagrams of below-ground open biofilter
Multiple level biofilter
Biofiltration Medias Simple Media
Peat, Compost, Mulch, Wood Chips, etc.
Low Initial Cost .
Prone to Settling, Erratic Performance
Engineered Media
Specific Composition and Preparation
Process
Higher Initial Cost .
Superior Physical Characteristics .
Superior, Consistent Performance
The useful life of the media is typically up to 5 years.
Fluffing, or turning, of the media material in the biofilter may be required at shorter intervals to prevent excessive compaction and settling.
source: Devinny J.S. et al. (1999) “Biofiltration for air pollution control”, Lewis Publishers.
Summary of Important propertiesof Common Biofilter Materials
Indigenous microorganisms population densitySurface areaAir permeabilityAssimilable nutrient contentPollutant sorption capacity
Lifetime (year)CostGeneral applicability
Compost
H
MMHM
2-4L
E, cost effective
Peat
M-L
HH
M-HM
2-4 LM, watercontrol
problems
Soil
H
L-MLHM
>30Very L
E, low-
activitybiofilters
Activated carbon,perlite, and otherinert materials
None
HM-HNoneL-H
>5M-H
Needs nutrient,may be expensive
Synthetic material
None
HVery HNone
None to H very H
>15Very H
Prototype only or biotrickling
filters
Parameters that need to be maintained
Moisture Content –
Temperature –
Microorganisms operate best between 30 degrees C and 40 degrees. Oxygen Level -
Most of degradations are aerobic. Oxygen is not used directly in the gas form but the microorganisms use
the oxygen present in dissolved form in the media.
pH –
For better results must maintain a pH where the microorganismsare the most efficient.
Nutrient Supply:
For aerobic microorganisms, the O/N/P ratio is estimated as 100/5/1. These are typically nitrogen, phosphorous, and some trace metals.
Microorganisms need a moist environment. Media has a tendency to dry out because of the air flow. Optimum 20 -60%.
Pretreatment of Gas Streams
• Besides humidification, heating, or cooling, other pretreatment necessary may include removing particulates.
• Though the biofilter is capable of removing particulates, the solid matter can cause clogging of the biofilter and gas distribution system.
Microorganisms• Fungi, Bacteria, and Actinomycetes.
• Start up of a biofilter process requires some acclimation time for the microorganisms to grow specific to the compounds in the gaseous stream.
• For easily degradable substances, this acclimation period is
typically around 10 days.
• The biomass has been shown to be able to be viable for shut downs of approximately 2 weeks.If inorganic nutrient and oxygen supplies are continued, the biomass may be maintained for up to 2 months.
Mechanism:
Movement of the contaminants from the air to the water phase occurs according to the physical laws.
The contaminants in the gas are either adsorbed onto the solid particles of the media or absorbed into the
water layer that exists on the media particles.
Concentration of contaminants decreases from inlet to outlet as they partionised between various phases.
Mechanism cont.. Wastes partition out between soil and gas, so that the
VOC remain in soil longer than in air.
Soil – gas partition coefficients indicate the relative strength of retention.
The coefficients increase with VOC molecular weight and the no. of oxygen, nitrogen and sulphur functional groups in the VOC molecules.
In dry soils the coefficients for VOC is 1 for methane to 10,000 for octane.
Mechanism cont..• Diffusion occurs through the water layer to the
microorganisms in the slime layer on the surface of the media particles.
• Through biotransformation of the food source, end products are formed, including carbon dioxide, water, nitrogen, mineral salts, and energy.
• Biotransformation act along with adsorption, absorption, and diffusion to remove contaminants from the gaseous stream.
Biotransformation and transport processes in biofilters
Mechanism cont..
• The media of the filter functions both to supply inorganic nutrients and as a supplement to the gas stream being treated for organic nutrients.
• The sorbed gases are oxidized by the microorganisms to CO2.
• The volatile inorganics are also sorbed and oxidized to form calcium salts.
Mechanism cont..
• Half-lives of contaminants range from minutes to months. Aliphatics degrade faster than aromatics.
• Adsorption sites are continually becoming available as oxidation by microorganisms occur.
• Overloading of the biofilters results when adsorption is occurring faster than oxidation..
• HAPs
Mechanism cont..
• The oxidation of organic matter generates heat.
• The difference between the amount being degraded and the amount represented by carbon dioxide release from the biofilter gives an indication of how much carbon is being incorporated in biomass (Medina et al., 1995).
Common Biofilters
Pollutants: BTEX, NH3, Trirmethylamine, Ethanol, Organic acids, etc.
Emission sources: Various industrial systems
Microorganisms: Pseudomonas, Bacillus, etc.
Abundant water and oxygen.
Aerobic metabolism.
Temperature: 15-40 ºC, pH: 6-8.
Metabolic product: CO2 , H2O, Biomass
Biofilter 의 종류 Low pH Biofilters for Sulfide Oxidation
Pollutants: H2S .
Emission sources: various industrial systems, wastewater collection and treatment facilities .
Microorganisms: Thiobacillus thiooxidans, Thiobacillus spp.
pH: 1-3, Temp.: 15-40 ºC.
Abundant water and oxygen.
Aerobic metabolism.
Metabolic product: H2SO4
Biofilter 의 종류 Low-Water-Content Biofilters
Pollutants: VOCs, Odorous materials.
Microorganisms: Filamentous fungi (Xeromyces bisporous).
Degradation of pollutants at low water .
Aerobic metabolism.
Applications: Bench biofilters for treatment of Tounlene, Ethylbenzene, o-Xylene
Biofilter 의 종류
High-Temperature Biofilters
Thermophilic Microorganisms: 45-60 ºC. Advantages:
Higher degradation rate More economical treatment processes.
Disadvantages: Fast decomposition of degradable support media Reduction of the solubility of pollutants.
Applications: Deshusses et al. (1997): 100 g- ethyl acetate/m3•h,
45-50 ºC van Groenestijn et al. (1995):
Hot gases containing ethanol, 50-70 ºC
Biofilter 의 종류 NOx Biofilters
Microorganism: genus Nitrobacter:
Nitric oxide Nitrite Nitrate Denitrifying bacteria: NO N2.
Aerobic / Anaerobic Processes.
Applications: Apel et al. (1995): Anaerobic removal of nitrogen
oxides from combustion gases using denitrifying bacteria (NO N2 in thick biofilm ).
Biosaint (1999): Removal of ammonia using Nitrobacter:95-98% removal at 50-1000 ppm
Biofilters using cometabolism Biofilter 의 종류
Growth substrate (CH4, toluene, phenol, etc.)
M.O. (TCE) CO2, H2O Biomass
Microorganism: no energy or other benefits from degrading co substrate fortuitously degrade unrelated compounds (similar shape to the active site of the enzyme)
Typical Biofilter Operating Conditionsfor Waste Air Treatment
Parameter
Biofilter layer heightBiofilter areaWaste air flowBiofilter surface loadingBiofilter volumetric loadingBed void volumeMean effective gas residence timepressure drop per meter of bed heightInlet pollutant and/or odor concentrationOperating temperatureInlet air relative humidityWater content of the support materialpH of the support materialTypical removal efficiencies
Typical value
1-1.5 m1-3000m2
50-300,000m3h-1
5-500m3m-2 h-1
5-500m3m-2 h-1
50%15-60 s0.2-1.0 cm water gauge (max. 10cm)0.01-5gm-3, 500-50,000OUm-3
15-30 C>98%60% by masspH 6-860-100%
Source: Deshusses, M.A., biodegration of mixtures of ketone vapours in biofilters for the treatment of waste air, Swiss Federal institute of technology, Zurich, 1994.
Applicability Company Location application
S. C. Johnson and Son, Inc. Racine, Wis. Propane and butane removal from room air.
Monsanto chemical Co. Springfield, Mass. Ethanol and butyraldehyde removal from dry air. 99% efficiency.
Dow chemical Co. Midland, Mich. Chemical process gas.
Hoechst Celanese corp. Coventry, R.I. Process gas.
Sandoz. Basel, Switzerland. Chemical process gas.
Esso of Canada. Sarnia, Ontario. Hydrocarbon vapors from fuel storage tanks.(proposed)
Mobil chemical co. Canandaigua, N. Y. Pentane form polystyrene foam molding (proposed)
Uphohn CO. Kalamazoo, Mich. Pharmaceutical production odors: 60000 cfm (proposed)
Source: H. Bohn, 1992, Consider biofiltration for decominating gases, Chem. Eng. Prog. (April)
Investment costs vs. air flow rate for variousair pollution control technologies
Operating costs vs. air flow rate for variousair pollution control technologies
Full-Scale Biofilters in ParallelSurface Area = 2,556 ft2 each
Comparison of Biofiltration Technology
� Benefits:
� Low Operating CostDoes not require chemicalsEffective removal of compounds
� Drawbacks:
� Break-through can occur if air flow or concentration is notconsistent
� Does not remove ammonia or amines
� Relatively large footprint required
� Requirements:
� Requires continuous air flow
� Requires consistent loading
� Requires a humid and warm air stream
� Often requires an acclimation period for the media
Microbial degradation of substances with intense odors.
Substrate Microbe Degradation product
Methanol Pseudomonas Water, carbon dioxide
Dimethylamines P. aminovorans Methylamine and formaldehyde.
Phenol P. putida Acetaldehyde and puyrate.
Benaldehyde Acetobacter ascendens Benzyl alcohol and benzoic acid.
Aniline Nocardia spp. And pseudomonas spp.
Pyrocatechol
Indole Chromobacterium violaceum Pyrocatechol
Camphor P. putida Lactonic acid
CONCLUSION.• Biofiltration plays very important role in control of air
pollution
• Biofilter, like all systems follows laws of conservation & mass balance
• Biofilter is successful only when microbial ecosystem is healthy & vigorous
• The design of biofilter system requires a detailed understanding of site,conditions,site limitations, system components & costs
• Monitoring of BF is very important
REFRENCES. Head, I. M., Singleton, I., and Milner, M. (2003). Bioremediation: A critical
review horizon scientific press Norfolk. Devinny, J. S. ;Deshusses, M. A.,& Webster, T. S.Biofiltration for air
pollution control. Lewis publishers London. Sincero, A. P. and Sincero, G. A. Environmental engeenering.:PHI learning
Private Limited. N. Delhi. Evans, G. M. and Furlong, J. C. Environmental Biotechnology.: Wiley &
Sons. Liu, D. H. F. and Liptak, B. G. Environmental engineers handbook. (2nd ed.). Nathonson, J.A. Basic Environmental Technology.4th Ed. Brown, C. A. ,Karl, B. Air pollution control technology handbook. http://www.mega.cz/electrodialysis.html. www.globalspec.com/../air biofilter www.gnest.org/journal/vol 11_no2/218. www.ambio.ca/operation.php
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