Pressure drop SAND filter

Dear all

I have a gravity sand filter,
height of sand  1.1 m, depth of sand 0.96 mm
height of water above sand 1.5 m
in order to choose the total pressure head filter backwash pump, I would like to  know how we can calculate the pressure drop of sand,

waiting for reply,

thank you

Taxonomy

• Sand Filter
• water treatment
• Pressure Management

2 Answers

1. Read the article "Design and management of conventional fluidized sand biofilters" by Steven T Summerfelt (available - just Google) where they note that for a sand with SG of 2.65, effective size of 0.1 to 1.0 mm (yours is 0.96 I assume), and a uniformity coefficient of 1.3 to 1.8, the pressure drop required across the sand bed to ensure fluidization of at least 20 to 30% is 0.87 to 0.98m for every meter of static sand depth.  So in your case the pressure drop across the bed will need to be approximately 1 to 1.1m, plus the total static head of 1.1m + 1.5m (assuming your overflow launders are at the maximum water depth of 1.5m).  Summerfelt's article gives good information to determine pressure drop in the underdrain system, etc.

2. It's not that simple, what is the effective size of the sand (d10) and what is the uniformity coefficient of the sand (d60/d10) and how much head loss is there through support gravel and the under drain system and what flow rate per unit area are you running. There are too many variables to simply give you a number.