Waste Gas; Types and Treatments

Outline

• Overview• Air pollutants• Waste gas treatmens• Biofilters

Definition

Air pollution may be defined as:-the presence in the air (outdoor atmosphere) of one or more contaminants or combinations there of in such quantities and of such durations- as may be or tend to be injurious to human, animal or plant life, or property, -unreasonably interferes with the comfortable enjoyment of life or property or conduct of business.

The Composition of Atmosphere

I ndex Value

PSI Descriptor

General

Health

Effects

Cautionary Statements

Up to 50 Good None for the general population.

None required.

50 to 100 Moderate Few or none for the general population.

None required.

100 to 200

Unhealthful Mild aggravation of symptoms among susceptible people, with irritation symptoms in the healthy population.

Persons with existing heart or respiratory ailments should reduce physical exertion and outdoor activity. General population should reduce vigorous outdoor activity.

200 to 300

Very Unhealthful

Significant aggravation of symptoms and decreased exercise tolerance in persons with heart or lung disease; widespread symptoms in the healthy population.

Elderly and persons with existing heart or lung disease should stay indoors and reduce physical activity. General population should avoid vigorous outdoor activity.

Over 300 Hazardous Early onset of certain diseases in addition to significant aggravation of symptoms and

Elderly and persons with existing diseases should stay indoors and avoid physical exertion.

Air Pollution Index Value

Outline

• Overview• Air pollutants• Waste gas treatmens• Biofilters

Outline

• Overview• Air pollutants• Waste gas treatments• Biofilters

-may reduce quality

- Increase cost

Waste gas

treatments

Waste Gas Treatments

Source control:

a.Raw product substitution

b.Reductionc. Recycle

Secondary control:

Treatment after it has

been produced

Choice of tech dictated by:

-Economic-Ecological const.

Types of waste gas treatments

a. Condensationb. Incinerationc. Adsorptiond. Absorptione. Membrane systemsf. Biological Treatments

1. Condensations

• Applicable for waste contaminant that are: -> concentrated and have a high boiling point -> have recycle or recovery value -> recovery is impossible for mixed pollutant

stream• Mechanism: -> waste gas are treated by simultaneous cooling

and compressing

2. Incineration

• Widely used, suitable for moderate flow rate waste

• Mechanism: -> thermal incineration involves combustion at

tempt of 700-1400 0C

-> catalytic incineration (used platinum, palladium, rubidium) at 300-7000C

• Drawbacks: -> high cost esp for low conc. Waste -> need a large amount of fuel -> produce another pollutant (Nox, dioxins)

3. Adsorption

• Most efficient for: -> low concentration vapour -> low vapour pressure -> high molecular weight waste gas• Common methods: -> fixed or fluidized bed of material such as

activated carbon or zeolite• Function of effectiveness: -> air flow rate -> total VOC loading

3. Adsorption • Limitations: -> misjudgment of bed saturation often

encountered, bed maybe renewed before it is necessaru

-> the saturated bed materials are often treated as hazardous material

-> increasing operational cost for its treatment

-> generaly it is treated by: a. Desorption with steam or hot air b. Disposal c. incineration

4. Absorption

• Process: -> removes contaminant with a scrubbing

solutions (water mostly used) -> gas enters a large contactor -> gas are transferred to a liquid phase -> silicon oil maybe used for hydrophobic

pollutant -> after gas are transfered to liqiud, additional

treatment need to be apllied.• Drawbacks: -> need additional treatment for liquid phase (incineration. Additional wwtp)

Vertical Venturi Scrubber

Packed Bed Scrubber

5. Membrane Systems• The subsequent process of condensation • Process:

-> gas stream are compressed to 310-1400 kPa

-> the pressure diferential drives the membrane separation process

-> the membrane pores remain filled with water -> the organic vapour transfered through the

membrane -> the process than requires treatment of liquid

permeate for final VOC disposal

6. Biological treatments

• Utilize microbial metabolic reactions• Effective and economical for low

concentrations of contaminant in large quantities of air.

• The contaminant maybe used as energy or carbon source for microbial growth

• Most succesfull for low molecular weight and highly soluble organic compound with simple bond structure (H2S or Ammonia)

6. Biological treatments

• The appropiate industries: - Animal husbandary (slaugterhouse) - Composting - Crematorium - Food Processing - Fragnance - Furniture - Landfill gas extraction - Pulp and paper - Petroleum industries

6. Biological treatments

Biofilter

• Fixed Microorganism

• Stationary water phase

Biotrickl-

ing

• Fixed Microorganism

• Flowing water phase

Bioscrub-ber

• Suspended Microorganism

• Flowing water phase

Operational Concerning Factors

• Characteristics of supporting medium (porosity, degree of compaction, water retention capability, ability to host microbial populations)

• Microbial inoculum• Medium pH• Temperature• Medium moisture• Nutrient content

Operational Cost

• include: 1) nutrients and water expenses 2) electricity for the blower and the recycle

pump and miscellaneous electrical equipment

3) maintenance4) costs associated with controlling the

growth of biomass 5) capital costs

Applicability of various air pollution control

Case Studies

- 98% H2S RE

- 50-70% (toluene, benzene, xylene)

Case Studies

- 85-99% H2S RE

Case Studies- >90 % H2S

RE- >90 % RE

aromatic compounds

- >95% RE ketones

Thank You