Waste water flow rate in small municipal wastewater treatment packages.

Question

In small wastewater treatment packages working through extended aeration process, inlet water flow rate is more than average produced wastewater due to limited flow rate of submersible pumps used to transfer raw waste water to the package and pump should start and stop periodically. Since the automation system used in these packages is the least and can not control flow rate properly, What consequences does this issue has? Does semi-intermittent (on-off pattern) working of the package has any adverse effect on the process?

Ademar Cesar Ferreira · Answer

One alternative is to use bigger pump station as already indicated but install speed control in the pumps to have a more smooth flow variation to the aeration tank.

Ali Cheraghi · Answer

Hi Reza
in small waste water treatment is designed for peak flow and the raw waste water transfer pump should be selected for peak flow.(peak flow>normal flow).in your statement "inlet water flow rate is more than average produced wastewater due to limited flow rate of submersible pumps used to transfer raw waste water to the package" ,this show design is correct.Have you any promblem in quality of treatment?

Hossein Akhgari · Answer

because of long detention time, extended aeration is a shock resistance process. 
for better  performance, you can use a bigger pump station as an equalization tank

AGGASIT DAD · Answer

Intermittent operation is used for Domestic wastewater which contain N because NO3 will change to N2 in Anoxic phase. But for Extanded AS if you operate intermittently 3hr Aerate/1hr stop or , 5/1, 7/1 is OK. BUT If you have bigger Vol of EQ that will be good because this can make wastewatertreat run stable and smoothly.

Kumar Packiakumar · Answer

Normally pumps are designed for peak wet weather flow and the aertaion tank is designed to cater for the average flow but checked for peak loading.

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