Biofiltration of Chlorinated VOCs

8/12/2019 Biofiltration of Chlorinated VOCs

http://slidepdf.com/reader/full/biofiltration-of-chlorinated-vocs 1/29

BIOFILTRATION OF CHLORINATED

VOC’S Literature survey

Presented By: Mudit Chauhan (2010A1PS349P)

Presented To: Dr. Smitha Raghuvanshi



VOCS: DEFINITION

General definition is very broad.

VOCs are organic chemicals that have a high vapor

pressure/low boiling point at ordinary room

temperature.

VOC have an initial boiling point less than or equal to

250 °C.

Examples:

1. Benzene

2. Ethylene glycol

3. Methylene chloride

4. Perchloroethylene

5. Xylene



VOCS: H ARMFUL EFFECTS

Presence of VOCs in the atmosphere creates a

number of problems for human health as well asenvironmental quality

1. They take part in photochemical reactions and smog

formation.

2. Long term exposure leads to increased risk of

developing health issues like cancer, Liver damage

and nervous system damage.

3. Short term effects include are eye irritation, noseirritation, throat irritation, headache, nausea ,

dizziness, asthma exacerbation etc



VOCS: SOURCES

Various industrial sites, such as plants manufacturing

organic chemicals, polymers or synthetic fibers.

VOCs emission are present in different industries,

such as petrochemical, paint and coating industries

and steel manufacture.

Major VOC emission sources are automobiles

exhaust.

Solvent emissions from products and industrial

operations is also one of the significant sources ofVOC emissions.



METHODS CURRENTLY USED FOR

CONTROLLING VOCS

o Condensation• Cooling & compression condense contaminant vapor

from air.

• Disadvantage:

1. Cost involved is very high2. Corrosion problems

3. Effluent liquid may create water pollution problem




CONTROLLING VOCS

Adsorption

• Pollutants are adsorbed onto adsorbents like

activated carbon

• Disadvantages:1. Requires regeneration when adsorbent becomes

saturated using steam or other hot gases which

increases operating costs.

2. It is not a destruction technology with difficultrecovery which means spent adsorbents such as

solid waste need to be land-filled or incinerated.




CONTROLLING VOC

Absorption/Scrubbing• Pollutants from the air are absorbed into a scrubbing

solution such as water or solvents

• Disadvantages:

1. Chemical costs are high.

2. Liquid waste needs further treatment.

3. High operating cost, complex chemical feed and

control systems.




CONTROLLING VOC

Incineration• When contaminant in gas stream is oxidizable to an inert

gas, combustion is a possible method of control.

• Can be direct flame or catalytic.

• Disadvantages:

1. An expensive method due to high energy requirements

2. Not economical if concentration levels are low & largeairflow volumes need treatment

3. Produces large amount of greenhouse gases

4. Catalysts engaged to VOC combustion aredeactivated in a short time due to chlorine poisoning



BIODEGRADATION

Biodegradation is the chemical dissolution ofmaterials by bacteria or other biological means.

Micro-organisms use these compounds as source

of carbon and electron donor for production of

energy and growth.

Types:

1. Aerobic

2. Anaerobic

Requirements for bio-degradation:I. Capable organism

II. Synthesis of requisite enzymes

III. Suitable environmental conditions



STEPS IN BIODEGRADATION

1. Uptake of compound

2. Manipulation of substrate for ring cleavage

3. Ring cleavage

4. Conversion of cleaved products into standardmetabolics.

5. Use of metabolics for Growth and energy.



BIODEGRADATION OF VOCS

Recalcitrance of Organic compounds increases

with increasing halogenation.

Cleavage of halogen-carbon bond is the critical(rate

determining) step.

Extent and rate of Bio-degradation of VOCs

depends on:

1. Structure of chemical compounds2. Micro-organism (Bacteria strain)

3. Conditions( temperature, PH, flow rates)



BIO-DEGRADATION OF VOCS

Biodegradation of chlorinated VOC’s may require

reductive dehalogenation by anaerobic bacteria

in addition to aerobic digestion.

Mixed microbial communities have the most

powerful bio-degradable potential because the

genetic information of more than one organism is

necessary to degrade the complex mixture of VOCs



BIO-FILTRATION

A bio-filter is a bioreactor system in which micro-

organisms are attached to a solid support medium

Off-gases containing biodegradable VOCs and

other toxic or odorous compounds are passed

through this biologically active bed of peat, soil, or

other media

Naturally occurring microorganisms in the bio-filter

convert the air pollutants into harmless by-products

that are primarily carbon dioxide (CO2) and water(H2O).



BIO-FILTRATION MECHANISM



TYPES OF BIO-FILTERS FOR CONTROLLING

VOCS

Four classes of bio-filters, classified on the

relationship of the biofilm to the water, are:

(1) Two phase systems (bio-scrubbers),

(2)

Trickling filters,(3) Natural medium bio-filters,

(4) Engineered medium bio-filters.



BIO-FILTER: SCHEMETIC



BIO-FILTRATION OF CHLORINATED VOCS:

ADVANTAGES

Lower capital and operating costs. Offer economicadvantages in applications where the air streamcontains contaminants at relatively lowconcentrations and high flow rates.

Bio-filtration does not require large quantities of

energy during operation . Produces a relatively low-volume, non-hazardous

waste stream.

Removal efficiencies of greater than 90% havebeen demonstrated.

Bio-filtration is based on a process that occursnaturally in soils & water and thus represents asafe, environmentally friendly "green" technology.



VOC CONTROL METHODS: OPERATING

COST COMPARISON



VOC CONTROL METHODS: CAPITAL COST

COMPARISON



CHLORINATED VOCS

These are the chlorine containing volatile organic

compounds.

They are amongst the most recalcitrant of all VOCs.

Examples includePCE, Trich loroeth ylene,

Trich loroethane (TCA), Viny l ch lor ide.

Major sources of chlorinated VOCs are chemical

and petroleum industries, polymer manufacture,

solvent industy.




PROBLEMS

Most chlorinated compounds of environmental

concern exhibit recalcitrance and cannot serve as

sole carbon and energy sources for heterotrophic

bacteria under aerobic conditions.

The presence of chlorinated compounds among

VOC mixtures creates a challenge to bio-filter

performance since biodegradation of these

xenobiotic compounds requires pathways normallynot associated with heterotrophic bacteria.




PROBLEMS

Chlorinated VOCs like PCE are not soluble in water

and therefore not easy to biodegrade.

Co-metabolism and substrate inhibition associated

with chlorinated VOCs in bio-filters have not been

elucidated.

Gaining insights into these aspects is significant in

the optimization of bio-filters for treatment of

industrial emissions containing mixtures of both

easily biodegradable and recalcitrant compounds



LAB ORIENTED PROJECT Work to be done



To carry out batch based studies for the bio-filtration

of chlorinated VOCs by varying parameters like

inlet concentration, flow rate, bed height,

composition of nutrient medium, moisture content in

bio-filter bed etc..

Carry out one set of experiment on a continuous bio

filter.

Kinetic modeling of bio-filter column using the

obtained experimental results.



Thank You

Biofiltration of Chlorinated VOCs

Documents

Transcript of Biofiltration of Chlorinated VOCs