Dual Media Filter

Dual media filters are used in places where the raw water contains suspended particles, turbidity and iron. Dual media filters provide very efficient particle removal under the conditions of high filtration rate. These filters use layers of anthracite and garnet particles as the filter medium, with filtration rate of 98% down to 2 microns. The dual media filters employ an automatic backwashing feature, which employs a combination of air and water to maintain unit efficiency.


Design
Internally, the dual media filter is fitted with an inlet distributor and a bottom collecting system. Externally, the system is fitted with frontal pipe work and isolation valves. Sand is used to remove the suspended particles and anthracite is used to remove the odor and color etc. to make the water fit for different applications. Gravels and pebbles are provided to support to both the media. The filter is required to be backwashed after accumulation of suspended solids, however, before carrying out the backwash, air scouring is also to be done for loosening of suspended solids and dirt. Limit for the backwash in these filers is regulated by differential pressure across the filter.

Working
The stream of waste water enters at the top of filter bed. As the solution permeates through the porous upper bed, the bigger suspended particles are trapped in and on the surface of activated coal or carbon. Smaller particles that are not trapped continue into the lower bed of rocks / sand.

Advantages
Some of the important advantages of dual media filters include -

• Automatic self backwashing
• High filtration efficiencies
• Able to operate at very high flux rates
• Protection of downstream absolute (cartridge) filters
• Custom designed packages

Applications
Some of the important applications of dual media filters include -

• Side stream filtration of cooling water and in potable water treatment.
• Waste water treatment.
• Pre-treatment of reverse osmosis
• Water injection systems
• Boiler feed water