Pumping Water Treatment Works Sludge

[tipp79]

Hello,

I've been asked for advise regarding the range of acceptable pipeline velocities for pumping sludge generated at a WTW. I've had an internet trawl and have been through the usual textbooks (MWH, Twort) to see whether I could find any details. Most specs give guidance for wastewater sludges and recommend velocities within a range of approx within the range 0.76m/s and 1.8 m/s. However, the characteristics of sewage sludge is obviously very different to water works chemical sludge.

The sludge I've been asked about is consists of superpulsator sludge and settled filter washwater sludge. These feed a balance tank where the sludges are mixed and this balanced sludge (which has a range of 0.1 - 0.6 %D.S.) is then forwarded to a set of WRc Thickeners where it is thickened up to 3-5% D.S. The project is proposing a new set of balanced sludge pumps (due to an increase in sludge production at the works due to deteriorating raw water quality) and its the velocity in the pipeline from the balanced sludge pumps to the thickener that has been questioned. The only reference I've found to velocity of balanced sludge is the below

"The thickeners shall be designed in accordance with the WRc Application Guide with the addition that the flow velocity in the feed launder should not be less than 0.24 m/s to avoid settlement should the thickener be sized to a maximum solids loading of 4 kg/m2/h."

Is there a range of line velocities which would be acceptable? The turndown on the pumps is quite high and it is expected that in the short term the pumps will be operating towards the lower end of their range with a line velocity of 06-0.7 m/s. If we experienced this low line velocity, what would the potential consequences be?

Any help or reference would be much appreciated!

 

[bimr]

The sludge from clarifiers is relatively dilute. Most textbooks recommend minimum velocities of 0.6-0.7 m/s, thus insuring turbulent flows. Try Pumping Station Design by Garr M. Jones for a reference.

 

[justanoperator]

It may be a good idea to add a 2 inch connection behind pump for a fire hose connection just in case the line gets plugged with sludge you can flush with high pressure water. I have seen pumps like this in a sump set together and valves set so the discharge from one can be used to backflow through another. Hopefully you will never need either modification but if there is operator neglect and pump is off several days solids will thoroughly plug lines quickly.