Biofiltration: natural odour controlWalker Environmental Group

What is biofiltration used for?• Biofiltration is an air pollution control

technology.

• Biofiltration is successfully being used for odour control in a variety of industries, including wastewater treatment plants, food processing plants, composting & organics processing facilities, and pulp & paper industries.

Nature-inspired engineering

How does biofiltration work?• Biofilters use microorganisms to remove air pollution.

• Biofilter operation involves growing a colony of micro-organisms on filter media (wood).

• Biofilters come in various designs, but the ones on our site are called open cell biofilters, incorporating root wood as packing material.

• Process air flows through a wood-packed bed.

• The pollutants are transferred into a thin biofilm on the surface of the wood.

• Microorganisms, including bacteria and fungi, grow in the biofilm and remove pollutants and odour.

• Microorganisms convert the pollutants to CO2, water and organic material.

• Conditions such as temperature, humidity and pH are essential to ensure the microbes survive and prosper.

• The biofilters used on our site are engineered components of our on-site air treatment systems and are operated as part of our Ministry of the Environment approvals.

Biofilter construction

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Advanced odour controlThe biosolids plant is equipped with an air treatment system. Odour is controlled at each step of the process.

Walker Environmental Group

1. Hooded receiving binsHooded receiving bins have large fans that vacuum the air over the load and convey it into the rotary dryer.

2. Enclosed mixing room and conveyorThe mixing room is fully enclosed. Air from that area of the plant is conveyed to the rotary dryer through the enclosed conveyor system.

3. CycloneThe air passes through the dryer and passes through a cyclone. The cyclone uses centrifugal force to clean the air. Heavier solids drop from the bottom of the cyclone while lighter dusts and air move up and pass through a baghouse.

4. Baghouse The baghouse is a large filter that acts like a vacuum to remove dust from the air stream. The dust is shaken out of the baghouse and is reintroduced into the product stream.

5. Scrubber The vacuumed air from the baghouse then moves to the scrubber. The scrubber also treats the air collected over the heat pulse cells.

6. Biofilter The air from the scrubber then moves to the biofilter. The biofilter uses nature to treat the odour in the air stream. The filter is full of micro-organisms, including bacteria and fungi, that consume the pollutants and odour causing agents.

How the scrubber scrubs the air• The scrubber removes ammonia

from the air stream.

• It “washes” the air using a mixture of sulphuric acid and water.

• The solution is sprayed over packing material.

• As air flows through the packing material, the sulphuric acid reacts with the ammonia in the air stream and creates ammonium sulphate.

• The acid solution is recirculated until it reaches a specific concentration.

• Then the solution is removed from the scrubber and is sold as a product to a fertilizer manufacturer. Bag house

Scrubber

Scrubber

Biofilter

Receiving bins

Enclosed conveyor

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