DE Settling Tank

[RedBauer]

Our firm as been asked to complete a preliminary design for a diatomaceous earth settling tank. Currently, the client has several DE tanks for their water treatment process and they backwash them periodically into the waster water sewer. By doing this, they are coating the sewer lines with DE. We are proposing to install an underground settling tank before the discharge into the sewer. The tank would then be pumped periodically.

I'm in the process of obtaining back flush data, frequency, and amount of DE used from the client. However, I'm trying to find resources about DE settling characteristics. Does anyone have resources or data that may be helpful in the my design process?

 

[bimr]

Is this a batch or continous process? Are you trying to collect the other residual waste or just the DE.

 

[RedBauer]

I talked to the water plant operator. They apparently backwash roughly every 3 to 5 days. So there is variability in the frequency. However, I'll design for 3 days to be conservative.

I think the main goal will to settle out the DE and in the process we will also capture residual waste. Thank you for point out the fact that there will be residual waste, I overlooked that factor initially.

 

[bimr]

You can size the tank for 1-2 backwash volumes. The solids will settle out in an hour or two and then you can drain the tank.

 

[RedBauer]

Theoretically, I think that would work for smaller systems. However, my peak backwash volume is 40,000 gallons.

 

[bimr]

On the other hand, it is not practical to design a contiuous treatment system for backwash flow because the backwash period is typically only a 10-15 minute duration per filter module.

If you are only interested in removing the DE, you can use the sizing methods for grit chambers in Metcalf & Eddy. The specific gravity of the DE is close to that of grit.