Good use of grinder? 1

[sjohns4]

Our client wants to remove a mechanical bar screen & install a grinder in one of their pump stations. The station has two GR T-10 pumps. The FM exiting the station is 12", the gravity line intering the station is 18". I sales rep I work with quite a bit said he doesnt think a grinder is such a great idea because of the large materials that could come through the 18" line, i.e. bricks. I guess it would be better for a brick to chew up some grinder teeth than a pump impeller though.

Any thoughts? Leave the bar screen, install the grinder, or remove the bar screen with out a grinder?

Thanks,

Mike

 

[jmrosell]

I would personally stick with what you have. The only grinder stations that we use are for maybe a couple of homes. The largest i know of using services only 10 homes.

 

[sjohns4]

They are wanting to install a grinding device in front of the GR pumps, not a grinder pump.

Mike

 

[redbridge]

I have designed grinders in front of lift stations several times. They make grinders that will grind bricks and even bed sheets. The brand I last specified was muffin monster, we used at a prison. It worked great and we have never had any problems. I would contact a grinder representative to help you pick the right grinder for your application.

 

[CivEnvEng98]

I echo Lburg's comments.

I have also seen the muffin monster installed upstream of prison lift stations. Inmates intentionally flush anything they can down the toilets to cause as much of a headache for the warden as possible: shoes, bedsheets, etc. We tossed several golf balls into one of them at once and it chewed them up like a hot knife through butter. Bricks however....I would contact muffin monster and check with them.

 

[sjohns4]

I've been doing a little research on grinders. If you like the JWC muffin monster, check out Franklin Miller. Dont know what the difference in cost is, but I like the features of the FM personally.

Mike

 

[SteveWag]

I generally don’t like grinders but sometimes they have a place. Both JWC and F-M make good units, around central PA JWC is favored, maybe a better sales agent. Don’t trust the head loss charts in the JWC book, I have seen them as much as 20-25% low. The grinder should be mounted so as to allow removal and I usually ask for a “box” with coarse holes to slide in place of the grinder during those times the grinder is removed for repair. Keep in mind that the inside of a manhole/wetwell is a hazardous area and you need either: an explosion proof motor; hydraulic drive; or extended motor and shaft. Although they will grind up stones, I have a client with four Channel Monsters and after three years they spent $45,000 in rebuild/replacement. The culprit seems to be 1 to 4-inch stones. Don’t ask why, we can’t find the source, but when dewatering the channel we find stones that show signs of being “chewed” on. I have no idea how many have gotten chewed up.

Steve Wagner

 

[FiltrationEngineer]

Assuming your grinder works great and you turn all your big peices of trash into little ones, make sure that downstream processes are not affected. This can be a major headache at the WWTP if they aren't set up to remove this stuff.

 

[bimr]

If you remove the bar screen, the grinder is going to chop up the stuff into particles that may settle out in your pipes downstream.

You would be better off with a mechanical screen that would remove the stuff rather than just chopping it up.

Don't think that the grinder is the "easy button" that your clients are looking for. Leave the bar screen, or think about installing a mechanical screen. Forget the grinder.

 

[CivEnvEng98]

Dumb question maybe....but does your client already have one of these muffin monsters in their system?

If not, why did they tell you to not look at other options?

 

[sjohns4]

The client wants to get rid of the bar screen for what I understand because of oddor issues with the dumpsters - not sure they arent just trying to cut back on some labor. Apparently the bar screen has been a bit problematic, but it's got some years on it too. They have both JWC & Franklyn Millers & like the Franklyn Millers better. It looks like we're about do dive in to this a bit deeper. First I want to talk to the operators to see just what sort of stuff ended up in the dumpster & go from there.

Mike

 

[JoePr]

Does this bar screen have a screenings washer? If the client is complaining about odor, maybe a washer unit is needed.

 

[DMStahl]

Our WWTP has both barscreens and grinders; the grinders macerate the debris stream from the screens before it goes through a washer-compactor.

We originally had only grinders (comminutors) in the influent stream, and had terrible problems with debris clogging downstream equipment. The barscreens have done us a great service in that respect.

Our grinders are Muffin Monsters; there is a relatively small rock trap upstream of the grinders which in our case seems to take care of some of the geological problems others have mentioned. (Rocks do show up there, and sometimes they're pretty big!)

Heavy grease loads can partially blind the muffin monster-style grinders, though. In some sewage systems -- ours included -- grease "bergs" build up in wetwells or lines and break loose during high flow periods. These bergs get chewed into grease-butter by the grinders; the teeth become packed with the stuff, and then the remaining bergs won't go through and form a dam upstream of the grinders.

Odor is a terrible problem with screenings, though, especially if your pump station is in or near a residential neighborhood. Rats love 'em as well; they're a vermin magnet.

One further thought -- depending on the hydraulic flushing of the wetwell it could be that ground rags and sticks could agglomerate into wads or mats and cause ugly pump problems periodically.

Good luck --