Water and Wastewater.com Help Forums - Can a centrifugal pump destroy pin flocc?

kyleallenpearson

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Can a centrifugal pump destroy pin flocc?
Aug 31^st, 2012, 9:29am

We are currently adding a coagulant preceding a centrifugal pump as the wastestream is transfered to our DAF unit. A polymer is added after the wastestream passes the centrifugal pump but before reaching the flocculation tubes leading to the DAF.

I have heard one opinion that the centrifugal pump helps to mix the coagulant in the wastestream. I have also heard that the vigorous action of the centrifugal pump impedes the pinn flocc process and that and air diaphram pump would better serve a process like this. Thoughts?

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NorCal_Wastewater1 God Member Offline "Wastewater rules! Give sludge a chance!!!" Posts: 1780 CA. Gender: Company or Organization: Wastewater	Re: Can a centrifugal pump destroy pin flocc? Reply #1 - Aug 31^st, 2012, 11:34am Certainly a diaphram pump is probably less likely to cause floc issues but centrifical pumps can be used, it really depends on the rate of rotation of the pump. You might want to consult with the forums DAF expert Dan Keys of Keys Tech Inc. Dallas
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Water Boy

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Re: Can a centrifugal pump destroy pin flocc?
Reply #2 - Sep 3^rd, 2012, 2:13am

Interesting question - I hope a few more people will post their thoughts.

My two cents - I think the centrifugal pump would aid coagulation by increasing the mixing energy but it depends on your floc size, you mention pinn floc so I would think that would be OK- if it was a floculant you were adding that would most likely impeed the process as you would most likely either damage the floculant (assuming long chain polymer floculant) or damage the flocs.

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Chromo Full Member Offline Water and Wastewater.com is the best! Posts: 128 Gender: Company or Organization: Koundakjian	Re: Can a centrifugal pump destroy pin flocc? Reply #3 - Sep 3^rd, 2012, 6:24am Depends on the RPM of the pump.. The higher the speed the higher the velocity in the volute of the pump allowing possibility of the distruction of the floc. The floc will hit the volute and the impeller/vanes and break up.
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Jeff Naumann God Member Offline I love Water and Wastewater.com Posts: 1133 Torrance, California Gender: Company or Organization: Jeff Naumann & Associates	Re: Can a centrifugal pump destroy pin flocc? Reply #4 - Sep 3^rd, 2012, 7:17am I think that a centifugal pump is fine for the "flocculation" stage; but, not good for the "coagulation" of the floc. What you want in the flocculation is "rapid mix," and the pump certainly provides that. For coagulation, you want a "gentle" mixing of the floc formed in flocculation.
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zxmonday YaBB Newbies Offline I love Water and Wastewater.com Posts: 3 Gender: Company or Organization: EPU	Re: Can a centrifugal pump destroy pin flocc? Reply #5 - Sep 7^th, 2012, 3:34am i am agree with Jeff's opinion.
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argfin

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Re: Can a centrifugal pump destroy pin flocc?
Reply #6 - Sep 7^th, 2012, 5:24am

Hiya,

So are you having problems with pin-floc in the DAF still? You haven't said if the process is actually working or not?

The setup you have sounds OK to me on the surface of it. The coagulant is well mixed by the pump and then the more delicate floc forming part is carried out after the pump.

If your flocs are breaking up still then maybe you have too much turblent flow into the DAF?

Once the polymer is dosed it does need to be a bit calmer for the floc to stay together, depending on the binding strength and once broken up probably wont refloc to the same extent.

Regards,
argfin

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DS

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Re: Can a centrifugal pump destroy pin flocc?
Reply #7 - Sep 7^th, 2012, 9:35am

Hi,

first is coagulation (destabilisation of colloids or fine SS, often with Fe(III) or Al(III), or others), succeeded by floc forming or flocculation in which the smaller (destabilised) parts are bound into a larger floc that settles (floats in this case) well. This is done with Poly-electrolytes (PE).

efficient coagulation requires intense mixing whereas flocculation requires much more quiscent flow conditions ("gentle stir") to let things aggregate without disrupting them..

In well designed/operated DAF's the flow conditions are quiscent enough to not disrupt the floc. If this happens, you should try another combination of dosing levels or even other chemicals that do satisfy your requirements. Maybe you might be overdosing, which may have an adverse effect on the coagulation/flocculation/flotation ?

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SludgeHound Senior Member Offline Water and Wastewater.com is the best! Posts: 388 Gender: Company or Organization: Nalco Company	Re: Can a centrifugal pump destroy pin flocc? Reply #8 - Sep 11^th, 2012, 10:53am DS is correct in the distinction between coagulation and flocculation. Centrifugal pumps tend to be more problamatic in controlling the mixing environment that can lead to breaking down the coagulated particles if the rpm is too high.
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