Introduction of Depth Filtration

Depth Filtration is a process which involves removal of particulate matter suspended in a liquid. To remove particulate matter liquid is passed through a filter bed comprised of a filter media. Filtration is used to remove suspended particulate matter from potable water, filtration of effluents from wastewater. Filtration is used to achieve supplemental removal of suspended solids (incl particulate BOD) from wastewater. Filtration is also used as pre-treatment for membrane separation.

Filtration Process:

Following is the basics of the depth filtration

  1. Physical features
  2. Filter media
  3. Filtration process
  4. Backwash process

Physical features of Depth Filter: As shown in figure, Filter bed is supported on gravel layer. Depth FilterThe water to be filtered enters the filter from an inlet channel. Filtered water is collected in the treated water chamber/ under-drain system. Filtered water also used to backwash the Filter.

Filter Media: Particle is is the principal filter media characteristic that affects filtration operation. Media particle size affects both the clear water head loss and the headloss during filter run. Particle size of media is too small, then headloss or driving force will be more. On the other hand if particle size is too large, many of the small particles in the influent will passed through the bed.

Filtration Process: During service/ filtration run of filter, water containing suspended particle is retained to the top of the filter media bed. As time passes during service cycle, suspended particle in the water is retained by filter media. After accumulation of dirt on filter media filter must be cleaned by means of Backwash

Backwash Process: At the end of service/ filtration run, suspended solids in treated water starts to increase beyond design outlet limit/ acceptable level or headloss/ pressure drop increases across the filter bed. If either of these conditions is reached, filtration is stopped and the filter must be backwashed to remove the accumulated suspended particle.

Read more about Filtration.

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