Sand Filter

[CathyJiang]

Please give me some information of the function and principle of sand filter. It's very urgent for me. I will feel very appreciated if you can give me any suggestion and information!

 

[quark]

Cathy!

Sand filters are used to remove suspended solids and debris out of water. (primarily) It's a cheaper option to do so. The top fine silica bed does the filtration action, while the increasing sized media do the support work. You have to backwash it when the pressure drop across the filter bed exceeds the manufacturer specification. (generally kg/sq.cm)

Regards,

Truth: Even the hardest of the problems will have atleast one simple solution. Mine may not be one.

 

[gibfrog]

Quark is right on the money. You really need to refine your question.

Consider the sand filter as just another porous media. You have some control over the average pore size and pore length and head loss by the sand gradation, particle uniformity coefficient and depth of sand.

Sand filters are cheap. The sand may be completely or partially confined via a fabric and or a vessel.

As Quark stated, sand filters are usually intermittantly backwashed (forcing a semi-batch type operation) and wasting some fluid as backwash.

As Quark stated, these filter's are commonly used to filter water. We civil engineers use them in swimming pools, septic tank drain fields, polishing WWTP effluent (for tertiary treatment, use dual media - sand & activated charcoal for lagoon effluent polishing just sand), sludge drying beds, stormwater treatment ponds effluent filtration , etc...

The filters are usually design based on Darcy's Law. Q = K * I * A. with Q = flow of filtrate, K = tranmissivity of the sand in units of length per time. I = vertical drop divided by the length of the flow (dimensionless) and A is the cross sectional flow area. K's are available from the manufacturer of the sand. K may be divided by the safety factor.

 

[misterd]

I would suggest that you take a look in "Wastewater engineering - treatment and reuse" by Metcalf and Eddy. You will get a complete review of the process and all the basic criterias.

Have fun...

 

[Piperap]

I posted this thread under another forum. I am in the process of hydrostatic testing for a new sand filter. The walls are 1ft6in the dims are 100ft x 12ft x 9ft.I am lookinf for a calc to figure the leakage rate of the concrete which will include evaporation rate,absortion rate,
Is there a formula? Dollarbill