Volatile Organic Compounds (VOCs) Volatile Organic Compounds (VOCs) and its removal techniquesand its removal techniques

Presented by:Presented by:Dr. C. B. MajumderDr. C. B. Majumder

VOLATILE ORGANIC VOLATILE ORGANIC COMPOUNDSCOMPOUNDS

Volatile organic compounds are Volatile organic compounds are organicorganic chemicalschemicals that have a high that have a high vapourvapour pressure pressure and easily form and easily form vapoursvapours at at normal temperature and pressurenormal temperature and pressure. More . More precisely, if an organic compound has a vapour precisely, if an organic compound has a vapour pressure greater than 0.1 mm Hg at 20 °C, it is pressure greater than 0.1 mm Hg at 20 °C, it is considered volatile. Hundreds of VOCs can be found considered volatile. Hundreds of VOCs can be found in the air and have been documented from a variety in the air and have been documented from a variety of sources.of sources.

Source of VOCs:Source of VOCs:

Sources of volatile organic compounds Sources of volatile organic compounds

can be classified into 2 types:can be classified into 2 types:

1.1. Man madeMan made

2.2. AnthropogenicAnthropogenic

MAN-MADE VOLATILE ORGANIC MAN-MADE VOLATILE ORGANIC COMPOUND EMISSIONSCOMPOUND EMISSIONS

• TransportationTransportation• Petroleum and petrochemical industryPetroleum and petrochemical industry• Solvents, coatings and miscellaneous sourcesSolvents, coatings and miscellaneous sources• Fuel marketing (gasoline transfers from Fuel marketing (gasoline transfers from

refinery to bulk stations, build stations to gas refinery to bulk stations, build stations to gas stations, gas stations to vehicles)stations, gas stations to vehicles)

• Electrical power generationElectrical power generation• Chemical process industriesChemical process industries

Industrial Sources of VOC emissionIndustrial Sources of VOC emission

Industry VOCs emittedAcetate finish coating Silicate Solution

Alcohol synthesis Cl, C2, C3, C6 Hydrocarbons

Automobile coating Ketones, Xylene, Toluene, Phenols

Bakery ovens Ethanol

Can coating Ketones, Alcohols, Aromatic Hydrocarbons, Ethers

Coffee roasting Heavy Oils From Coffee Beans

Coil coating Phosphates, Solvesso, Cyclohexanol, Alcohols, Hydrocarbons

Electronic components Butyl Acetate, Xylene, MEK, Cellosolve

Fiberglass coating Teflon Emulsion, Fiberglass, Synthetics, Styrene

Lithographic print/ paint

Butyl Cellosolve, Ciacetone Alcohol, Solvesso, Cellosolve Cetate, Xylene, MIBK

Metal coating Alcohols, Cellosolve Acetate, Phthalates, Solvesso

Paper coating High-Boiling Organics, Latexes

Pharmaceuticals Isoproponol, Toluene, Hydrocarbons

Phthalic anhydride Organic Acids

Resin plant Formaldehyde, Phenols, Phthalic Anhydride

Soil remediation Benzene, Toluene, Ethylene, Xylene

Sterilizers Ethylene Oxide

Vinyl surgical glove

Polyvinyl Chloride, Cioctyl Phathalate

Wire enameling Cellosolve Acetate*Source: http://www.anguil.com/vochand2.php.

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Sl No.Sl No. Volatile Organic CompoundVolatile Organic Compound Mol. WeightMol. Weight Boiling point (Boiling point (ooC)C) Vap. Pr. (mm-Hg) @ 23 Vap. Pr. (mm-Hg) @ 23 ooCC

11 PropanePropane 44.144.1 -44-44

22 N-ButaneN-Butane 58.1258.12 -0.48-0.48

33 N-OctaneN-Octane 114.23114.23 125.8125.8 12.55412.554

44 EthaneEthane 28.0528.05 -104-104

55 1-Butene1-Butene 56.1156.11 -6.1-6.1

66 StyreneStyrene 104.15104.15 145.3145.3 5.4085.408

77 BenzeneBenzene 78.1178.11 80.280.2 86.55486.554

88 TolueneToluene 92.1492.14 110.8110.8 25.64125.641

99 AcetyleneAcetylene 26.0426.04 -84-84

1010 MethanolMethanol 32.0432.04 64.764.7

1111 Isobutyl AlcoholIsobutyl Alcohol 74.1274.12 82.682.6 36.79536.795

1212 Acrylic AcidAcrylic Acid 72.0672.06 139139

Sl No.Sl No. Volatile Organic CompoundVolatile Organic Compound Mol. WeightMol. Weight Boiling point (Boiling point (ooC)C) Vap. Pr. (mm-Hg) @ 23 Vap. Pr. (mm-Hg) @ 23 ooCC

1313 Propionic AcidPropionic Acid 74.0874.08 141.1141.1

1414 FormaldehydeFormaldehyde 30.0330.03 -18.95-18.95 3652.8423652.842

1515 AcetaldehydeAcetaldehyde 44.0544.05 20.520.5 835.88835.88

1616 AldehydeAldehyde 86.1486.14

1717 AcroleinAcrolein 56.0656.06 52.8452.84 252.631252.631

1818 Methyl Ethyl KetoneMethyl Ethyl Ketone 72.1172.11 79.879.8 86.95286.952

1919 Methyl Isobutyl KetoneMethyl Isobutyl Ketone 100.16100.16 116.7116.7 17.71617.716

2020 PhenolPhenol 94.1194.11 182182 0.4530.453

2121 NitrobenzeneNitrobenzene 123.11123.11 210.9210.9

2222 Vinyl ChlorideVinyl Chloride 62.562.5 -13.4-13.4

2323 Methyl BromideMethyl Bromide 94.9594.95 3.63.6

2424 ChloroformChloroform 119.39119.39 74.174.1

2525 TLEV Exhaust-LPGTLEV Exhaust-LPG 14.8614.86 -42.1-42.1

2626 TLEV Exhaust-CNGTLEV Exhaust-CNG 15.2215.22

EFFECTS OF VOCSEFFECTS OF VOCS

• Photochemical smog Photochemical smog • Health effectsHealth effects• Global warmingGlobal warming• Odour Odour • CarcinogenicityCarcinogenicity

VOCs AND HEALTH EFFECTS

VOC Hazard summaryAcrolein Extremely toxic to humans in inhalation and dermal exposure.  Acute (short-

term) inhalation exposure may result in upper respiratory tract irritation and congestion.  

Acrylonitrile Acute (short-term) exposure of workers to acrylonitrile has been observed to cause mucous membrane irritation, headaches, dizziness, and nausea.

Benzene Acute (short-term) inhalation exposure of humans to benzene may cause drowsiness, dizziness, headaches, as well as eye, skin, and respiratory tract irritation, and, at high levels, unconsciousness.  Chronic (long-term) inhalation exposure has caused various disorders in the blood, including reduced numbers of red blood cells and a plastic anemia, in occupational settings. 

Chlorobenzene The major effect from acute (short-term) inhalation exposure to chloroform is central nervous system depression.  Chronic (long-term) exposure to chloroform by inhalation in humans has resulted in effects on the liver, including hepatitis and jaundice, and central nervous system effects, such as depression and irritability. 

Ethylidene Dichloride(1,1-Dichloroethane)

Acute (short-term) inhalation exposure to high levels of ethylating dichloride in humans results in central nervous system (CNS) depression and a cardio-stimulating effect resulting in cardiac arrhythmias

Formaldehyde Acute (short-term) and chronic (long-term) inhalation exposure to formaldehyde in humans can result in respiratory symptoms, and eye, nose, and throat irritation. 

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Hexane Acute (short-term) inhalation exposure of humans to high levels of hexane causes mild central nervous system (CNS) effects. Chronic (long-term) exposure to hexane in air is associated with polyneuropathy in humans, with numbness in the extremities, muscular weakness, blurred vision, headache, and fatigue observed

Styrene Acute (short-term) exposure to styrene in humans results in mucous membrane and eye irritation, and gastrointestinal effects.  Chronic (long-term) exposure to styrene in humans results in effects on the central nervous system (CNS), and peripheral neuropathy.

Tetrachloroeth—ylene(Perchloroet-hylene)

The main effects of tetrachloroethylene in humans are neurological, liver, and kidney effects following acute (short-term) and chronic (long-term) inhalation exposure.

Xylenes (Mixed Isomers)

Acute (short-term) inhalation exposure to mixed xylenes in humans results in irritation of the eyes, nose, and throat, gastrointestinal effects, eye irritation, and neurological effects.  Chronic (long-term) inhalation exposure of humans to mixed xylenes results primarily in central nervous system (CNS) effects, respiratory, cardiovascular, and kidney effects

Polycyclic organicmatter (POM)*

Cancer is the major concern from exposure to POM.  Epidemiologic studies have reported an increase in lung cancer in humans exposed to coke oven emissions, roofing tar emissions, and cigarette smoke; all of these mixtures contain POM compounds. 

* The term polycyclic organic matter (POM) defines a broad class of compounds that includes the polycyclic aromatic hydrocarbon compounds (PAHs), of which benzo[a]pyrene is a member.  POM compounds are formed primarily from combustion and are present in the atmosphere in particulate form

Harmful effects of some common VOCsHarmful effects of some common VOCs

►BenzeneBenzene can enter our body through our lungs, gastrointestinal tract,

and across our skin when we are exposed to high levels. In the bloodstream,

benzene travels throughout the body and can be temporarily stored in the bone

marrow and fat. ►It is converted to products, called metabolites, in the liver and bone marrow.

People who breathe benzene for long periods may experience harmful effects

in the tissues that form blood cells, especially the bone marrow. These effects

can disrupt normal blood production and cause a decrease in important blood

components.►TolueneToluene in the air combines with oxygen and form benzaldehyde and cresol,

which are harmful to humans. A serious health concern is that it may have an

effect on our brain. Toluene can cause headaches, confusion, and memory

loss.►Low-to-moderate, day-after-day exposure in our workplace can cause

tiredness, confusion, weakness, drunken-type actions, memory loss, nausea,

and loss of appetite

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►XyleneXylene can also cause a number of effects on the nervous system, such as

headaches, lack of muscle coordination, dizziness, confusion, and changes in

one's sense of balance.►Short-term exposure of people to high levels of xylene can cause irritation of

the skin, eyes, nose, throat; difficulty in breathing; impaired function of the

lungs; delayed response to a visual stimulus; impaired memory; stomach

discomfort; and changes in the liver and kidneys.►PhenolPhenol in Short-term causes respiratory irritation, headaches, and burning

eyes. Chronic effects of high exposures include weakness, muscle pain,

anorexia, weight loss, and fatigue; effects of long-term low-level exposures

include increase in respiratory cancer, heart disease, and effects on the

immune system.►Exposure to high concentrations for several weeks results in paralysis &

severe injury to the heart, kidneys, liver, and lungs, followed by death in some

cases. Effects reported in humans following dermal exposure include liver

damage, diarrhea, dark urine, and RBC destruction.

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► PyridinePyridine: Most important health concern for humans exposed to it is damage

to the liver. Other health concerns for humans may be neurological effects, renal

effects, and irritation of the skin and eye. Effect of pyridine as cancer or birth

defect is not known

►ChloroformChloroform affects the central nervous system (brain), liver, and kidneys after

a person breathe air or drinks liquids that contain large amounts of chloroform.

Breathing about 900 ppm or 900,000 ppb for a short time causes fatigue,

dizziness, and headache. Elevated levels of chloroform, over a long period may

damage liver and kidneys.

►Methyl Ethyl KetoneMethyl Ethyl Ketone concentrations above the TLV may cause headache,

dizziness, nausea, shortness of breath, and vomiting. Higher concentrations may

cause central nervous system depression and unconsciousness.

►It may produce abdominal pain, nausea. Aspiration into lungs can produce

severe lung damage.

Regulations on VOC emission:Regulations on VOC emission:Regulations on controlling organic vapour pollutants in air have been Regulations on controlling organic vapour pollutants in air have been issued world-wide. Many countries have implemented various regulatory issued world-wide. Many countries have implemented various regulatory norms for its control. Some of the norms are:norms for its control. Some of the norms are:

1.1. In the ambient air quality standards produced by the US Environmental In the ambient air quality standards produced by the US Environmental Protection Agency, the maximum 3-hour concentration of hydrocarbon Protection Agency, the maximum 3-hour concentration of hydrocarbon content is 1.6 kg/mcontent is 1.6 kg/m33 (0.24 ppm), not to be exceeded for more than a year. (0.24 ppm), not to be exceeded for more than a year.

2.2. Reduction of VOCs emissions that exceeds the current national ambient air Reduction of VOCs emissions that exceeds the current national ambient air quality standard for ozone of 0.12 ppm is mandated under Title I of the US quality standard for ozone of 0.12 ppm is mandated under Title I of the US Clean Air Act Amendment of 1990Clean Air Act Amendment of 1990

3.3. Title III of the amendments requires reduction of the emissions of 189 Title III of the amendments requires reduction of the emissions of 189 hazardous air pollutants, most of which are included under the definition of hazardous air pollutants, most of which are included under the definition of VOCs as wellVOCs as well

4.4. The recently passed European Community stage emissions limit is 35 The recently passed European Community stage emissions limit is 35 grams total organic compounds (TOC) per cubic meter gasoline loaded (35 grams total organic compounds (TOC) per cubic meter gasoline loaded (35 g TOC/mg TOC/m33))

5.5. The United States Environmental Protection Agency Standard 40 CFR Part The United States Environmental Protection Agency Standard 40 CFR Part 63 has established an emission limit of 10 g TOC/m3.63 has established an emission limit of 10 g TOC/m3.

6.6. The German TA-Luft Standard, the most stringent known gasoline emission The German TA-Luft Standard, the most stringent known gasoline emission regulation, has set an emissions limit to 150 mg TOC (excluding methane) regulation, has set an emissions limit to 150 mg TOC (excluding methane) per cubic meter of loaded product (0.15 g TOC/mper cubic meter of loaded product (0.15 g TOC/m33))

VOC removal Technologies

Destruction

Membrane separation

Thermal incineration

Catalytic incineration

Photo-catalytic oxidation

Add on Control technologies

Process and equipment modification

Recovery

Condensation

Adsorption

Absorption Plasma technology

Electron beam technology

Biofiltration

Flares

Refrigeration condensation

Cryogenic condensation

Regenerative

Recuperative

Classification of VOCs Control Technology

VOC removal techniques:VOC removal techniques:

1.1. Process and equipement modificationProcess and equipement modification

2.2. Add on control techniquesAdd on control techniques

a. Destructiona. Destruction

i. Oxidationi. Oxidation

ii. Bioremovalii. Bioremoval

b. Recoveryb. Recovery

i. Absorptioni. Absorption

ii. Adsorptionii. Adsorption

A) Zeolite based B) Activated carbon A) Zeolite based B) Activated carbon basedbased

iii. Condensationiii. Condensation

iv. Membrane separationiv. Membrane separation

Various destruction processes:Various destruction processes:

1. Oxidation1. Oxidation

i. Thermal oxidationi. Thermal oxidation

ii. Catalytic oxidationii. Catalytic oxidation

iii. Reverse flow reactorsiii. Reverse flow reactors

2. Bioremoval2. Bioremoval

i. Biofiltrationi. Biofiltration

ii. Bio Trickling filterii. Bio Trickling filter

iii. Bioscrubberiii. Bioscrubber

Process and equipment modification:Process and equipment modification: Process and equipment modifications are usually Process and equipment modifications are usually

the most preferred alternative for reducing the most preferred alternative for reducing emissions. Modifications include:emissions. Modifications include:

1.1. Substitution of raw material to reduce VOC inputSubstitution of raw material to reduce VOC input

2.2. Changes in operating condition to reduce Changes in operating condition to reduce formation of VOCformation of VOC

3.3. Modification of equipment to minimize escape of Modification of equipment to minimize escape of VOCs VOCs

The first two mechanisms vary with the process The first two mechanisms vary with the process being addressed. Equipment modification can being addressed. Equipment modification can take many forms, but the objective is always to take many forms, but the objective is always to prevent the escape of VOCsprevent the escape of VOCs

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An overall approach to develop collection and An overall approach to develop collection and

control strategies to reduce VOCs emissions is control strategies to reduce VOCs emissions is

via a stepwise analysisvia a stepwise analysis

1.1. The first step is to quantify the release by The first step is to quantify the release by

developing an understanding of the process developing an understanding of the process

steps and material balancessteps and material balances

2.2. It is followed by sampling, measuring or It is followed by sampling, measuring or

estimating vent flowsestimating vent flows

3.3. Then significant sources can be identified and Then significant sources can be identified and

strategies and designs are developed to address strategies and designs are developed to address

the issuesthe issues

Add on Control Techniques:Add on Control Techniques:

• Secondary control involves treatment of the waste Secondary control involves treatment of the waste stream after it has been produced.stream after it has been produced.

• The choice of the technology is often dictated by The choice of the technology is often dictated by economical and ecological constraints. Such economical and ecological constraints. Such constraints arise for the nature of the compound constraints arise for the nature of the compound being treated, the concentration, the flow rate and being treated, the concentration, the flow rate and the mode of emission of the waste.the mode of emission of the waste.

• Combination of the various technologies may Combination of the various technologies may often be required to meet the regulatory often be required to meet the regulatory standards. standards.

Absorption:Absorption:

• Absorption removes the waste gas contaminat withAbsorption removes the waste gas contaminat with a scrubbing solution. a scrubbing solution.

• The gases enter a large contactor where the gaseous pollutants are The gases enter a large contactor where the gaseous pollutants are

transferred to a liquid phase. Efficient gas-liquid mass transfer may be transferred to a liquid phase. Efficient gas-liquid mass transfer may be

accomplished through the use of packed or bubble column or a venturi accomplished through the use of packed or bubble column or a venturi

contactor. contactor.

• Success is dictated by the affinity of the pollutant for liquid phase. Water Success is dictated by the affinity of the pollutant for liquid phase. Water

is the most frequently used scrubbing solution and the pH can be is the most frequently used scrubbing solution and the pH can be

adjusted to increase the solubility acidic or basic gases. For hydrophobic adjusted to increase the solubility acidic or basic gases. For hydrophobic

pollutants organic solvents such as silicon oil may be used as scrubbing pollutants organic solvents such as silicon oil may be used as scrubbing

solution. solution.

• Once the pollutant transfer has occurred, additional treatment of the Once the pollutant transfer has occurred, additional treatment of the

liquid phase may be necessary. This may be achieved by desorbing the liquid phase may be necessary. This may be achieved by desorbing the

pollutant at high temperatures and incinerating the vapors. pollutant at high temperatures and incinerating the vapors.

• If the scrubbing solution is water, the wastewater may be directed to a If the scrubbing solution is water, the wastewater may be directed to a

treatment plant.treatment plant.

Adsorption:Adsorption:• Adsorption generally occurs on a fixed or fluidized bed of Adsorption generally occurs on a fixed or fluidized bed of

material such as active carbon or zeolite and is most material such as active carbon or zeolite and is most efficient for treatment of low concentration vapors.efficient for treatment of low concentration vapors.

• The effectiveness of an adsorption system for a particular The effectiveness of an adsorption system for a particular waste stream is function of the air flow rate, the total VOC waste stream is function of the air flow rate, the total VOC loading of the stream and the individual components of the loading of the stream and the individual components of the VOC stream. Moisture is also one of the crucial parameters VOC stream. Moisture is also one of the crucial parameters to dictate the efficiency and effectiveness of adsorption. to dictate the efficiency and effectiveness of adsorption.

• Adsorption is generally used for controlling VOCs with low Adsorption is generally used for controlling VOCs with low vapor pressure and high molecular weight.vapor pressure and high molecular weight.

• Physical adsorption has been found to be more significant Physical adsorption has been found to be more significant in the case of separation processes. Physical adsorption is in the case of separation processes. Physical adsorption is again classified into Thermal Swing Adsorption (TSA) and again classified into Thermal Swing Adsorption (TSA) and Pressure Swing Adsorption (PSA). Pressure Swing Adsorption (PSA).

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• Activated carbon is a good adsorbent due to its large Activated carbon is a good adsorbent due to its large surface area and micropores. surface area and micropores.

• There are three types of nonmicroporous carbons that are There are three types of nonmicroporous carbons that are very promising as adsorbents and catalyst carriers: very promising as adsorbents and catalyst carriers: nanotubes (CNT), nanofibres (CNF), high surface area nanotubes (CNT), nanofibres (CNF), high surface area graphites (HSAG). graphites (HSAG).

• CNTs consists of grapheme layer rolled coaxially into CNTs consists of grapheme layer rolled coaxially into cylinders of nanometric diameter. cylinders of nanometric diameter.

• CNFs differ from CNTs in the absence of hollow cavity and CNFs differ from CNTs in the absence of hollow cavity and the diameters of CNFs are generally higher than the diameters of CNFs are generally higher than nanotubes. nanotubes.

• But the surface area recorded for CNT is significantly But the surface area recorded for CNT is significantly greater than that of CNFs. Typical value of surface area for greater than that of CNFs. Typical value of surface area for CNTs are around 200 mCNTs are around 200 m22/g and for CNFs they range from 10 /g and for CNFs they range from 10 to 200 mto 200 m22/g/g

• hydrophobic zeolite is now considered an alternative hydrophobic zeolite is now considered an alternative adsorbent since it has good properties such as thermal adsorbent since it has good properties such as thermal stability and hydrophobicity stability and hydrophobicity

VOC laden air

Adsorber 1 Adsorber 2

Separator

Treated air

Filter

Pr. Regulator

Condenser

Typical activated carbon VOC Removal SystemTypical activated carbon VOC Removal System for for gasesgases

Adsorption controlling parameters:Adsorption controlling parameters:

1.1. Retentive abilityRetentive ability

2.2. Pressure Pressure

3.3. ConcentrationConcentration

4.4. Particulate concentrationParticulate concentration

5.5. Type of adsorbentType of adsorbent

6.6. Desorption methodDesorption method

7.7. Fire suppressionFire suppression

8.8. Steam recoverySteam recovery

Condensation:Condensation:• The driving force for condensation is over-saturation, The driving force for condensation is over-saturation,

which is achieved by chilling or pressurisation (or both) of which is achieved by chilling or pressurisation (or both) of the waste gas stream.the waste gas stream.

• Waste gas contaminantsWaste gas contaminants that are concentrated and have a that are concentrated and have a high boiling point may be partially recovered by high boiling point may be partially recovered by simultaneous cooling and compressing of the gaseous simultaneous cooling and compressing of the gaseous phase. phase.

• This technique is only economical for concentrated vapour This technique is only economical for concentrated vapour where there is some recycle or recovery value. where there is some recycle or recovery value.

• If the waste gas is a mixed pollutant stream, recycling will If the waste gas is a mixed pollutant stream, recycling will be virtually impossible and incineration of the condensed be virtually impossible and incineration of the condensed liquid may be required. liquid may be required.

• This technique must often be followed by additional This technique must often be followed by additional removal technologies for compliance with regulatory removal technologies for compliance with regulatory emission standards.emission standards.

Membrane separation:Membrane separation:• Membrane separation system can be used to Membrane separation system can be used to

transfer VOCs from various stream to a water transfer VOCs from various stream to a water phase. phase.

• In a membrane separation system for gases, In a membrane separation system for gases, compression and condensation of the emission compression and condensation of the emission stream is followed by membrane separation.stream is followed by membrane separation.

• This pressure differential drives the membrane This pressure differential drives the membrane separation process. separation process.

• Air stream is passed across the surface of a Air stream is passed across the surface of a microporous hydrophobic membrane constructed microporous hydrophobic membrane constructed of material such as polyethylene and of material such as polyethylene and polypropylene polypropylene

• The membrane provides high VOC permeability The membrane provides high VOC permeability without allowing bulk permeates transport across without allowing bulk permeates transport across the membrane the membrane

• The process then requires treatment of the liquid The process then requires treatment of the liquid permeate for final VOC disposal or recycling permeate for final VOC disposal or recycling

Pump

VOC laden

Air

Filter

DemisterMist

Membrane Cell

Treated Air

Recovered VOC

Simple Schematic diagram of Simple Schematic diagram of Membrane Separation TechniqueMembrane Separation Technique

Membrane separation controlling Membrane separation controlling parameters:parameters:

1.1. Adaptibility to the range of organicsAdaptibility to the range of organics

2.2. Cost of membraneCost of membrane

3.3. Maintenance of membraneMaintenance of membrane

4.4. Process rateProcess rate

5.5. Rechargeable or reusable Rechargeable or reusable

membranemembrane

6.6. Presence of liquidPresence of liquid

7.7. Flow patternFlow pattern

OxidationOxidation

• Oxidation is the most widely used secondary Oxidation is the most widely used secondary

technique, but costs are high for low technique, but costs are high for low

concentration pollutant vapours because of the concentration pollutant vapours because of the

need for large amount of fuel. need for large amount of fuel.

• Regenerative or recuperative heat systems are Regenerative or recuperative heat systems are

often used as an attempt to reduce these fuel often used as an attempt to reduce these fuel

operating costs. operating costs.

• Production of nitrogen oxides and some dioxins is Production of nitrogen oxides and some dioxins is

also possible during oxidation. also possible during oxidation.

• In general this technology is more suitable for In general this technology is more suitable for

concentrated stream with moderate flow rates. concentrated stream with moderate flow rates.

Thermal Oxidation:Thermal Oxidation:

• Thermal oxidation systems, also known as fume incinerators, are not simple Thermal oxidation systems, also known as fume incinerators, are not simple

flares or afterburners. flares or afterburners.

• The modern thermal oxidiser is designed to accomplish from 95% to 99% The modern thermal oxidiser is designed to accomplish from 95% to 99%

destruction of virtually all VOCs. These systems can be designed to handle a destruction of virtually all VOCs. These systems can be designed to handle a

capacity of 1,000 to 500,000 cfm (cubic feet per minute) capacity of 1,000 to 500,000 cfm (cubic feet per minute)

• VOC concentration ranges from 100 to 2,000 ppm. VOC concentration ranges from 100 to 2,000 ppm.

• Nominal residence time ranges from 0.5 to 1.0Nominal residence time ranges from 0.5 to 1.0

• Thermal oxidation systems combust VOCs at temperatures of 1,300–1,800°F.Thermal oxidation systems combust VOCs at temperatures of 1,300–1,800°F.

• Actual operating temperature is a function of the type and concentration of Actual operating temperature is a function of the type and concentration of

material in the vent stream and the desired Destruction and Removal Efficiencymaterial in the vent stream and the desired Destruction and Removal Efficiency

• Two types of thermal energy recovery systems are in common use Two types of thermal energy recovery systems are in common use

today, regenerative and recuperativetoday, regenerative and recuperative

VOC laden air

Heater

Thermal Oxidizer Heat Storage

Cold and clean air

Schematic diagram of Thermal Schematic diagram of Thermal OxidationOxidation

Catalytic Oxidation:Catalytic Oxidation:

• Catalytic oxidation systems directly combust VOCs in a Catalytic oxidation systems directly combust VOCs in a manner similar to thermal oxidisers.manner similar to thermal oxidisers.

• The main difference is that the catalytic system operates at The main difference is that the catalytic system operates at a lower temperature, typically about 700–900°F. a lower temperature, typically about 700–900°F.

• This is made possible by the use of catalysts that reduce This is made possible by the use of catalysts that reduce the combustion energy requirements.the combustion energy requirements.

• Catalyst systems can be designed to handle a capacity of Catalyst systems can be designed to handle a capacity of 1,000 to 100,000 cfm and VOC concentration ranges from 1,000 to 100,000 cfm and VOC concentration ranges from 100 to 2,000 ppm.100 to 2,000 ppm.

• The catalytic system is well suited to low concentration The catalytic system is well suited to low concentration operations or those that operate in a cyclic manneroperations or those that operate in a cyclic manner

• Destruction efficiencies in excess of 90% are common with Destruction efficiencies in excess of 90% are common with a maximum Destruction Recovery Efficiency of 95%a maximum Destruction Recovery Efficiency of 95%

VOC laden air

Recovery heater

Catalytic Oxidizer

Cold and clean air

Schematic diagram of Catalytic Schematic diagram of Catalytic OxidationOxidation

Reverse Flow ReactorReverse Flow Reactor• A Reverse Flow Reactor (RFR) is an adiabatic packed bed A Reverse Flow Reactor (RFR) is an adiabatic packed bed

reactor in which the direction of the feed flow is reversed reactor in which the direction of the feed flow is reversed periodicallyperiodically

• RFR is becoming a strong alternative for the removal of RFR is becoming a strong alternative for the removal of VOCs from polluted air because unsteady-state reactor VOCs from polluted air because unsteady-state reactor operation can be profitable for the chemical processoperation can be profitable for the chemical process

• For the RFR the dynamics of the system should be well For the RFR the dynamics of the system should be well defined and not influenced by its surroundingsdefined and not influenced by its surroundings

• The best way of achieving adiabatic conditions and The best way of achieving adiabatic conditions and minimising the influence of surroundings is making use of minimising the influence of surroundings is making use of an evacuated jacket with the provision of a radiation shield an evacuated jacket with the provision of a radiation shield at higher operating temperatureat higher operating temperature

• RFR is influenced by Cycle period, VOC velocity, adiabatic RFR is influenced by Cycle period, VOC velocity, adiabatic temperature, components, pressure, inlet concentrationtemperature, components, pressure, inlet concentration

Biodegradation/ BioremovalBiodegradation/ Bioremoval• Biotechniques are relatively cheap because of the low Biotechniques are relatively cheap because of the low

investment and operational costs and can show a good investment and operational costs and can show a good operational stability, are environment friendly and require operational stability, are environment friendly and require ambient conditions for destruction of pollutants.ambient conditions for destruction of pollutants.

• Biological reactors utilize microbial metabolic reaction to Biological reactors utilize microbial metabolic reaction to treat contaminated stream. treat contaminated stream.

• The treatment is carried out at ambient temperature and it The treatment is carried out at ambient temperature and it does not generate secondary waste stream. does not generate secondary waste stream.

• VOC containing streams are transported to the air/ biofilm VOC containing streams are transported to the air/ biofilm interface where they are absorbed into the biofilm and interface where they are absorbed into the biofilm and employed as carbon or energy source by microorganism employed as carbon or energy source by microorganism

• The by-products of microbial oxidation are primary water, The by-products of microbial oxidation are primary water, carbon dioxide, mineral salts, some volatile organic carbon dioxide, mineral salts, some volatile organic compound and microbial biomass. compound and microbial biomass.

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In general the microbes used for biological treatment are organisms that are naturally occurring. These microbial populations may be dominated by one particular microbial species or may interact with numerous species to attack a particular type of contaminant.The particular contaminants of interest must be biodegradable and non toxic for biological treatment to be successful. The most successful removal in bioreactors occur for low molecular weight and highly soluble organic compounds with simple bond structures.Biodegradation was the major mechanism for the removal of nonchlorinated VOCs including toluene, benzene, ethylbenzene and methylene chloride. Some compounds that show moderate to slow degradation include phenols, chlorinated hydrocarbons, polyaromatic hydrocarbons and highly halogenated hydrocarbons. Inorganic compounds such as hydrogen sulfide and ammonia are also biodegraded well.

Biofilter:Biofilter:• Biofiltration is a result of a complex combination of different Biofiltration is a result of a complex combination of different

physicochemical and biological phenomenaphysicochemical and biological phenomena

• It is a systems that uses a combination of basic processes: absorption, It is a systems that uses a combination of basic processes: absorption, adsorption, degradation and desorption of gas-phase contaminants. adsorption, degradation and desorption of gas-phase contaminants.

• Biofiltration uses microorganisms fixed to a porous medium to break Biofiltration uses microorganisms fixed to a porous medium to break down pollutant present in an stream. The microorganisms grow in a down pollutant present in an stream. The microorganisms grow in a biofilm on the surface of a medium or are suspended in the water phase biofilm on the surface of a medium or are suspended in the water phase surrounding the medium particlessurrounding the medium particles

• The filter bed medium consists of relatively inert substances (Compost, The filter bed medium consists of relatively inert substances (Compost, peat etc) which ensure large surface attachment areas, high porosity, peat etc) which ensure large surface attachment areas, high porosity, compressive strength and additional nutrient supply. Natural packing compressive strength and additional nutrient supply. Natural packing materials such as compost, peat and soil have been widely used materials such as compost, peat and soil have been widely used

• The overall effectiveness of a biofilters is largely governed by the The overall effectiveness of a biofilters is largely governed by the properties and characteristics of the support medium which include properties and characteristics of the support medium which include porosity, degree of compaction, water retention capabilities and the porosity, degree of compaction, water retention capabilities and the ability to host microbial population ability to host microbial population

• Biofilters usually incorporate some form of water addition Biofilters usually incorporate some form of water addition to control moisture content and add nutrientsto control moisture content and add nutrients

• Interphase mass transfer occur which leads to interfacial Interphase mass transfer occur which leads to interfacial equilibrium so that gas phase resistance can be neglected. equilibrium so that gas phase resistance can be neglected. Here oxygen is subjected to diffusional resistance Here oxygen is subjected to diffusional resistance

• The overall effectiveness of a biofilters is largely governed The overall effectiveness of a biofilters is largely governed by the properties and characteristics of the support by the properties and characteristics of the support medium which include porosity, degree of compaction, medium which include porosity, degree of compaction, water retention capabilities and the ability to host microbial water retention capabilities and the ability to host microbial population population

• Critical biofilters operational and performance parameters Critical biofilters operational and performance parameters include the microbial inoculum, medium pH, temperature include the microbial inoculum, medium pH, temperature and the medium moisture and nutrient content and the medium moisture and nutrient content

• Moisture control of the packing material has been Moisture control of the packing material has been identified as the most critical parameter to control in identified as the most critical parameter to control in biofilters biofilters

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Waste AirParticulate,

Temp and Load Control

Humidifier

Clean Air

Leachate

BiofilterReactor

Blower

Nutrient, Buffer(Discontinuous)

Discontinuous Water Addition

Water Influent

Schematic diagram of a biofilterSchematic diagram of a biofilter

Biotrickling filter: Biotrickling filter: • In biotrickling filter gas contaminants are absorbed in a free liquid In biotrickling filter gas contaminants are absorbed in a free liquid

phase prior to biodegradation by either suspended or immobilized phase prior to biodegradation by either suspended or immobilized

microorganisms microorganisms

• For biotrickling filters suspended microbes fixed to an inorganic For biotrickling filters suspended microbes fixed to an inorganic

packing material and suspended microbes in the water phase degrade packing material and suspended microbes in the water phase degrade

the absorbed contaminants as they pass through the reactor the absorbed contaminants as they pass through the reactor

• As the water is recirculated, nutrients, acids or bases may be added by As the water is recirculated, nutrients, acids or bases may be added by

the operator to regulate the environment for optimal pollutant removal the operator to regulate the environment for optimal pollutant removal

• Most importantly a biotrickling filter reactor must host a thriving Most importantly a biotrickling filter reactor must host a thriving

microbiological population while avoiding conditions that promote microbiological population while avoiding conditions that promote

excessive biomass growth and clogging conditionsexcessive biomass growth and clogging conditions

• The free water phase benefits both biotrickling filter by providing a The free water phase benefits both biotrickling filter by providing a

continuous supplycontinuous supply of nutrients, removing possible toxic degradation of nutrients, removing possible toxic degradation

by-products, suspending biomass for continual reseeding of the by-products, suspending biomass for continual reseeding of the

system and aiding in the diffusion of hydrophilic pollutants into biofilmsystem and aiding in the diffusion of hydrophilic pollutants into biofilm

Particulate, Temp and

Load Control

Waste Air Blower

Biotrickling Filter

Clean Air

Wastewater Purge

Recycled Water

Water Nutrient

BufferWater Influent

Pump

Schematic diagram of a biotrickling filterSchematic diagram of a biotrickling filter

Bioscrubber:Bioscrubber:• In bioscrubbers also gas contaminants are absorbed in a In bioscrubbers also gas contaminants are absorbed in a

free liquid phase prior to biodegradation by either free liquid phase prior to biodegradation by either suspended or immobilized microorganisms suspended or immobilized microorganisms

• In a bioscrubber after initial contaminant absorption In a bioscrubber after initial contaminant absorption occurs, the degradation of the contaminants is performed occurs, the degradation of the contaminants is performed by a suspended consortium of microbs in a separate by a suspended consortium of microbs in a separate vessel vessel

• Absorption may be achieved in a packed column, spray Absorption may be achieved in a packed column, spray tower or bubble column tower or bubble column

• The free water phase benefits bioscrubbers by providing a The free water phase benefits bioscrubbers by providing a continuous supplycontinuous supply of nutrients, removing possible toxic of nutrients, removing possible toxic degradation by-products, suspending biomass for degradation by-products, suspending biomass for continual reseeding of the system and aiding in the continual reseeding of the system and aiding in the diffusion of hydrophilic pollutants into biofilm diffusion of hydrophilic pollutants into biofilm

• The water is transferred to a separate vessel where The water is transferred to a separate vessel where optional environmental conditions for degradation are optional environmental conditions for degradation are maintained maintained

Criteria for Choice of an Optimal Criteria for Choice of an Optimal Filter Medium:Filter Medium:

1.1. Inorganic Nutrient ContentInorganic Nutrient Content

2.2. Organic ContentOrganic Content

3.3. Chemical and Inert AdditivesChemical and Inert Additives

4.4. Water ContentWater Content

5.5. pHpH

6.6. Sorption characteristics and PorositySorption characteristics and Porosity

7.7. Bacterial AttachmentBacterial Attachment

8.8. Mechanical PropertiesMechanical Properties

9.9. Odour of the PackingOdour of the Packing

10.10. Packing cost and LifetimePacking cost and Lifetime

Biodegradation Controlling Factors:Biodegradation Controlling Factors:

1.1. Water contentWater content

2.2. TemperatureTemperature

3.3. pHpH

4.4. NutrientNutrient

5.5. Contaminat loadContaminat load

6.6. Oxygen limitationOxygen limitation

A natural process of VOC and A natural process of VOC and odour removalodour removal

BIOFILTRATIONBIOFILTRATION

• Biofiltration is an easy and cost-effective technologyBiofiltration is an easy and cost-effective technology• Biofiltration has a very high VOC and odour removal Biofiltration has a very high VOC and odour removal

efficiency efficiency • Biofilters have low investment and operation costsBiofilters have low investment and operation costs• The biofiltration process results in a complete The biofiltration process results in a complete

decomposition of the pollutants, creating no decomposition of the pollutants, creating no hazardous byproductshazardous byproducts

• The biofilter material is an organic, nontoxic, The biofilter material is an organic, nontoxic, biodegradable material that can be readily composted biodegradable material that can be readily composted after useafter use

• Above all, biofiltration has been accepted by residents Above all, biofiltration has been accepted by residents and regulators as an environment friendly and cost-and regulators as an environment friendly and cost-effective odour and air pollution control technology. effective odour and air pollution control technology.

ADVANTAGES OF BIOFILTRATIONADVANTAGES OF BIOFILTRATION

MethodMethod Application areaApplication area AdvantagesAdvantages Disadvantages Disadvantages

Biofilter Biofilter

Odours and low VOC Odours and low VOC concentrations concentrations

VOC concentration less VOC concentration less than 0.5 g/m3 Flow rates than 0.5 g/m3 Flow rates of 500 to over 200,000 mof 500 to over 200,000 m33/h, /h, depending on filter designdepending on filter design

Low capital costsLow capital costs

Low operating costsLow operating costs

Degrades a wide range of Degrades a wide range of compoundscompounds

Can handle insoluble VOCsCan handle insoluble VOCs

Easy to operate and Easy to operate and maintain maintain

Low specific productivityLow specific productivity

Control of operating Control of operating conditions requiredconditions required

Large area requiredLarge area required

Biomass bed is heavy and Biomass bed is heavy and bulky to replacebulky to replace

Long retention time Long retention time

Susceptible to channeling Susceptible to channeling

Biotrickling filterBiotrickling filter

Low/ medium VOC Low/ medium VOC concentrationsconcentrations

VOC concentration less VOC concentration less than 3 g/mthan 3 g/m33

Flow rates of 500 to Flow rates of 500 to 50,000 m50,000 m33/h /h

Medium capital costsMedium capital costs

Low operating costsLow operating costs

Low retention time/high Low retention time/high volume throughputvolume throughput

Small size and weight Small size and weight

Requirement to design Requirement to design system for fluctuating system for fluctuating concentrationsconcentrations

BioscrubberBioscrubber

Low/ medium VOC Low/ medium VOC concentrationsconcentrations

VOC concentration less VOC concentration less than 3 g/mthan 3 g/m33

Flow rates of 10,000 to Flow rates of 10,000 to 50,000 m50,000 m33/h/h

Able to deal with high flow Able to deal with high flow rates and severe fluctuationsrates and severe fluctuations

Good control of reactions Good control of reactions conditionsconditions

Treats only water soluble Treats only water soluble compoundscompounds

Can be complicated to Can be complicated to operate and maintainoperate and maintain

Extra air supply may be Extra air supply may be neededneeded

Excess sludge will require Excess sludge will require disposal disposal

Comparison of Biofilter, Biotrickling filter and Bioscrubber

FUNDAMENTALS OF FUNDAMENTALS OF BIOFILTRATION PROCESSBIOFILTRATION PROCESS

• BiofilmBiofilm

• Mechanisms of VOC RemovalMechanisms of VOC Removal

• Kinetics Kinetics

Industries using biofiltration to abate VOCIndustries using biofiltration to abate VOCApplication VOC/OdourCable productionplant

Xylene

Chemical plant Formaldehyde

Coach works Formaldehyde, Ethanol

Composites plant Cyclohexanone, Methyl ethyl ketone

Furniture factoryHexane, Ethanol, Acetone, Styrene, Ethyl Acetate,Toluene, Xylene

Glass fiber plant Styrene, Epichlorhydrin

Leather factoryEthyl acetate, Butyl acetate, Acetone, Toluene,Ethanol

Meat processing plant Odorous Aldehydes, Acids

Rubber factory Ethyl acetate, Butyl acetate, Acetone

Shoe factory Ethyl acetate, Butyl acetate, Acetone

Printing Ethyl acetate, alcohols

DESIGN AND OPERATIONAL DESIGN AND OPERATIONAL CONSIDERATIONSCONSIDERATIONS

• Packing materialsPacking materials

• Media selectionMedia selection

• Moisture content Moisture content

• pH pH

• Temperature and Temperature and

• Nutrients Nutrients

Conclusion:Conclusion:11.. OxidationOxidation is the most commonly used technique, though it destroys the is the most commonly used technique, though it destroys the

valuable VOCs. Further, the oxidation process with heat recovery is a good valuable VOCs. Further, the oxidation process with heat recovery is a good

economical option. However, this process requires specific operating economical option. However, this process requires specific operating

conditions and design of incinerator depending upon the composition of the conditions and design of incinerator depending upon the composition of the

VOCs. It may also generate toxic combustion products. the Reverse Flow VOCs. It may also generate toxic combustion products. the Reverse Flow

Reactor is the best alternative to oxidation in today’s context of energy Reactor is the best alternative to oxidation in today’s context of energy

managementmanagement

2.2. Oxidation (catalytic)Oxidation (catalytic) It is concluded that it is a good option when VOCs It is concluded that it is a good option when VOCs

recovery is not important (both in terms of efficiency and cost)recovery is not important (both in terms of efficiency and cost)

3.3. AdsorptionAdsorption is the next most favoured technique. It has good removal is the next most favoured technique. It has good removal

efficiency, though it requires higher capital investment and operating costs. efficiency, though it requires higher capital investment and operating costs.

Activated carbon, though a cheap adsorbent, has many limitations. If VOCs Activated carbon, though a cheap adsorbent, has many limitations. If VOCs

recovery is important, then adsorption is a good technique to be recovery is important, then adsorption is a good technique to be

implementedimplemented

4.4. AbsorptionAbsorption process involves high initial investment as well as process involves high initial investment as well as

difficulties in design, due to the lack of availability of vapour liquid difficulties in design, due to the lack of availability of vapour liquid

equilibrium data. Moreover, stripping of VOCs from the absorbing equilibrium data. Moreover, stripping of VOCs from the absorbing

solvent requires further separation, and thus costs. This technique solvent requires further separation, and thus costs. This technique

though has some advantages, e.g. the ability to handle a wide range though has some advantages, e.g. the ability to handle a wide range

of concentrations, simple process and equipment, and good of concentrations, simple process and equipment, and good

efficiencyefficiency

5.5. CondensationCondensation is a safe alternative for VOCs recovery. It does not is a safe alternative for VOCs recovery. It does not

involve any second component and thus not much separation involve any second component and thus not much separation

technology. It is simple. But it suffers from many limitations such as technology. It is simple. But it suffers from many limitations such as

it requires high concentration, extreme-operating conditions it requires high concentration, extreme-operating conditions

(temperature and pressure), high boiling VOCs, high operating costs (temperature and pressure), high boiling VOCs, high operating costs

etcetc

66.. Bio-filtrationBio-filtration is a cheap and most effective alternative for VOCs is a cheap and most effective alternative for VOCs

elimination. This process does not generate any secondary waste elimination. This process does not generate any secondary waste

stream as m.o’s consume the waste as energy source. stream as m.o’s consume the waste as energy source.

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