Activated Sludge Process
Activated Sludge Process
(OP)
We have a lightly loaded (BOD5 -100 mg/L) municipal extended sludge plant (1500 m3/d) that sees almost zero flows during the off peak times. (3- 5 hrs/day ). As a practice we run the RAS pumps continuously throughout the day. In order to save energy is it okay to shut off the pumps when there is no flow to the plant. Would this impact the bugs?
Thanks in advance.
Thanks in advance.





RE: Activated Sludge Process
When RAS flow rates are too low, thick sludge blankets in the final clarifier can result. The operator will see gas bubbles (from nitrogen gas) and rising/floating sludge clumps on the clarifier surface. The clarifier may go anaerobic.
RE: Activated Sludge Process
Some plants flow pace the RAS pumps against the inlet flow so that when the flow reduces so does the RAS rates. However they probably do not go to zero.
Some SBR designs have unaerated periods of 2-4 hours without any problems. Sludge sitting in a clarifier for several hours wont affect the bugs. But if it compacts and thickens and is a long time before it is collected then it may go anaerobic as bimr suggests and then you will have problems.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
RE: Activated Sludge Process
We were able to develop a control system that allowed the blowers to shut down for 15 min intervals. We had aeration/no aeration cycles. After some experimentation, the operators settled on 1/2 hr on, 1/2 hour off through most of the day with 15 min intervals during normally high flow levels. The foam disappeared. The pH came up. The D.O. floated around 2.0 during aeration cycles. The sludge began to settle better and the hypochlorite use dropped. The BOD removal rates remained above 90%. There is no significant accumulation of solids in the aeration basins.
The high efficiency blowers were already reducing the energy bill and this dropped the energy use by about 35% more.
You didn't say what type of blower system you are using, but, if they could handle on/off cycles, you might look into this type of control.