Sand Filters 1

[ozfish]

Not sure how to specify the pressure requirement of a pump when sizing a pump for a deep bed pressurized sand filter (Total bed depth 2 metres in six graded layers) with a desired flow rate of 120-180litres per min. The pump is for duty only. The filter is 1.8m in dia. In addition am I correct to assume that the backwash pump will need to be atleast double the flow rate and similar pressure?

The filter is to be used as tertiary stage of ground water treatment to pick up any break through of iron or manganese oxide.

Can anybody recommend some literature to assit me in learning more about sizing and specifying sand filters for ground water treatment?

 

[waterexpert]

I use a paper by Amithrajah and Cleasby for determining headloss through multi-media filters in the clean state. Practically however, the design point for the feed pumps usually ends up being the backpressure at which a backwash is initiated, usually around 1 bar.

Regards
Seán

http://www.seanmoran.co.uk

 

[bimr]

You can use the Kozeny equation. This is outlined in the book Water Quality and Treatment by the AWWA.

For the system that you are proposing, the throughput headloss will probably vary from .14-.35 bar for a clean filter to 1-1.3 bar for a dirty filter.

The backwash headloss is actually lower than the throughput headloss because you will be fluidizing the media at a much higher velocity. The backwash pump should be sized to deliver 37.5 m/h.