BIOFILTRATION FOR CONTROL OF AIR POLLUTION

Given by-Ashish kumar yadav M.Tech 1st year Roll No. 3140912

Department of Civil EngineeringNIT Kurukhshetra

Biofiltration Biofiltration is an air pollution control

technique which Involves bio degradation of contaminants under the action of microorganisms diffused in a thin layer of moisture known as “BIOFILM”, mainly used for elimination of malodorous gas emissions and low concentrations of Volatile Organic Compounds (VOCs).

The process of Bio Degradation is— Organic Pollutant + O2 CO2+ H2O + Heat + Biomass

History of BiofiltersThe following is a brief timeline of the development of biofilters:

1923 -- Biological methods were proposed to treat odorous emissions.

1955 -- Biological methods were applied to treat odorous emissions in low concentrations in Germany.

1960’s -- Biofiltration was used for the treatment of gaseous pollutants both in Germany and US.

1970’s -- Biofiltration is used with high success in Germany.

1980’s -- Biofiltration is used for the treatment of toxic emissions and volatile organic compounds (VOCs) from industry.

1990’s -- Today, there are more than 500 biofilters operating both in Germany and Netherlands and it is widely spreading in US.

Components Of A Bio-filter Unit MATERIALS used for bed media – peat, composted

yard waste, bark, coarse soil, gravel or plastic shapes.

SUPPORT RACK -perforated – allow air from the plenum to move into the bed media -to contact microbes that live in the bed. Perforations also permit excess, condensed moisture to drain out of the bed to the plenum.

FAN - Used to collect contaminated air, As the emissions flow through the bed media, the pollutants are absorbed by moisture on the bed media . Microbes reduce pollutant concentrations by consuming and metabolizing pollutants.

Schematic Diagram Of A Biofilter Unit

Differentiation Between Bio Filtration , Chemical oxidation & Thermal Processes

Types Of Bio Filters ON THE BASIS OF LAYOUT Open Bed : Uncovered and Exposed to all Weather conditions. Closed Bed : Enclosed with a small exhaust port for venting of cleaned

air ON THE BASIS OF SHAPE Horizontal :1. With Larger footprints2. Relatively inexpensive3. Easy maintenance Vertical :1. Designed to reduce the footprint required.2. Use less surface area compared to Horizontal3. Expensive4. Not easy to Maintain ON THE BASIS OF SUPPORT MEDIA Compost Bio Filter : Soil , Peat, Compost material is used Synthetic Bio Filter : Ceramic , Plastic .

Vertical biofilter

Open-bed biofilter

Biofiltration media The media used in biofilters

can include peat, heather, bark, composted sewage sludge, granular carbon or other suitable materials

The useful life of media is typically 5 years.

Parameters that need to be maintained

Moisture Content – Microorganisms need a moist environment. Media has a tendency to dry out because of the air flow. Optimum 20 -60%. Temperature – Microorganisms operate best between 30

°C and 40°C. 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 microorganism are 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 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. 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 partitioned between various phases.

Wastes partition out between soil and gas, so that the VOC remain in soil longer than in air.

Process Diagram of a Biofilter

Phenomena involved in the operation of biofilters

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.

Half-lives of contaminants range from minutes to months.

The oxidation of organic matter generates heat.

Typical Biofilter Operating Conditions for Waste Air Treatment

Parameter Biofilter layer height Biofilter area Waste air flow Biofilter surface loading Biofilter volumetric loading

Bed void volume Mean effective gas residence time pressure drop per meter of bed

height Inlet pollutant and/or odor

concentration Operating temperature Inlet air relative humidity Water content of the support material pH of the support material Typical removal efficiencies

Typical value 1-1.5 m 1-3000m2

50-300,000m3h-1

5-500m3m-2 h-1

5-500m3m-2 h-1

50% 15-60 s 0.2-1.0 cm water gauge (max.

10cm) 0.01-5gm-3, 500-50,000OUm-3

15-30 °C >98% 60% by mass pH 6-8 60-100%

Comparison of Biofiltration Technology

� Benefits:1. Low Operating Cost2. Does not require chemicals3. Effective removal of compounds Drawbacks:1. Break-through can occur if air flow or concentration is not

consistent2. Large area required to treat contaminated source3. Requires large acclimation time for microbial population. � Requirements:1. Requires continuous air flow2. Requires consistent loading3. Requires a humid and warm air stream

Case StudyThis case study of PPC Industry ,Texas which conducted Biofiltration as a VOC Control for Serigraph Inc.(a screen printer and sheet fed offset printer located in West Bend, Wisconsin, about 30 miles northwest of Milwaukee , US).

A Few Existing Bio Filters McMinnville, Oregon: The installation in McMinnville, Oregon perhaps best

demonstrates the capabilities as the levels of odorous compounds to be treated were among the highest ever reported from the wastewater treatment environment.

Long Sault, Ontario: Although a small (1500 cfm), indoor, container-type system, this installation demonstrates several key aspects that are relevant to any installation.

Sarnia, Ontario: This biofilter was installed in 2001 and treats 12,500 cfm of air coming from a sludge liming and drying operation.

Brookfield, P.E.I. : This biofilter was installed in 2002, at a composting plant in P.E.I., that treats 60,000 cfm of air from the composting process.

Toronto, Ontario: This biofilter was installed in 2002 in the north end of Toronto at the Toronto Mixed Waste Recycling and Organics Processing Facility.

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