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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