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Pump solids handling capacity behind a grinder?

Pump solids handling capacity behind a grinder?

Pump solids handling capacity behind a grinder?

I'm looking at a fairly high head wastewater pumping application for a realitively small flow (~350 GPM @ 365' TDH).

I can find traditional solids handling pumps that would work connected in series. However, given the pump station is collecting flow from an entire small town I'm thinking a bar screen, or more likely a grinder, may be a necessity. That said, I'd like to hear some thoughts on using a pump behind the screen or grinder that passes a smaller solid in order to get a more efficient pump and maybe eliminate the second set of pumps.



RE: Pump solids handling capacity behind a grinder?

Call some pump vendors.

Richard A. Cornelius, P.E.

RE: Pump solids handling capacity behind a grinder?

I had a breif discussion with my most trusted pump rep around here. We had some good pro & con thoughts, but he'd seen it done in practice. Figured I might find someone on here who's has seen it in practice and have some considerations to share that we havent thought of.

RE: Pump solids handling capacity behind a grinder?

It is a reasonable concept. However, there are additional considerations such as the length of the forcemain and the operation of the forcemain. You should consider the effect of the solids on operating the forcemain.

RE: Pump solids handling capacity behind a grinder?

Agreed Bimr,

At 350 GPM I'm looking at a 6" FM which would operate ~ 4 fps. I figure that shoud keep macerated solids suspended prety well. I'd maybe be thinking of a mechanical screen except for the issue of odors where the pump statin has to go.

RE: Pump solids handling capacity behind a grinder?

That is an excellent idea to keep the velocity high. It will also help to move air bubbles downstream and eliminate the need for air release valves except for maybe on system startup.

There are some screens that will wash the removed solids and eliminate the odors:


But that will involve a larger lift station and operating labor.

You might also consider using a trench type self cleaning lift station and fertilizer based odor removal agents.

RE: Pump solids handling capacity behind a grinder?

Good input so far to this rather unique application. During my time as consultant and manufacturer I have never really seen any good guidelines or examples regarding solids handling requirements after a grinder. Better than a pump manufacturer may be the grinder/macerator manufacturers. One other approach would be a solids separation system, which is become increasingly common in Europe and catching on here in the states. Details on such a system can be found here http://amads.ksb.com/en/home.html . I personally am not involved with this equipment but find the concept very interesting and it seems well suited for just this kind of application.

Disclosure, I do work for manufacturer of this equipment.

RE: Pump solids handling capacity behind a grinder?

Screens and grinder pumps add a lot of unnecessary complexities. Since you are handling normal residential wastewater, I suggest you use the traditional approach of using solids pumps connected in series. This is time tested.

Your attempt to make a better mousetrap has a lot of things that could go wrong -- such as how are you going to clean the upstream screens. And no one knows if wastewater passed through a grinder pump is not going to be a problem for a "clean water" centrifugal pump. Rags and hair from barber shops seem to always cause clogging.

RE: Pump solids handling capacity behind a grinder?

You will have difficulty in finding a pump that can give you the head and also passing some solids after a bar screen or grinder.

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