Force main blockage

[loganco]

thread161-237329 I've read this thread on the problem with force main blockage and have experienced the same identical problem. On one of the posts it was mentioned that there is a bioxide holding tank in the pump room. If you are feeding bioxide (Calcium Nitrate) into a long force main, it will eventually lock it up. Mind you, it takes time....but it will lock it up. I went through the same senario you are going through with pump calculations, force main design, air relief...etc. If you can, look at the discharge of the force main and see if you have a scum matt forming. If so, that is a sure indication of calcium nitrate. Bioxide application is good odor control, but is tricky because the need to have a detention time long enough to work but not to long as may be your problem. It won't cost you a dime to just shut off the bioxide feed and flush your force main good. If this is the problem, you will notice the gpm rise within a week or so...we did.

 

[bimr]

As i recall from that other blog, there was little information provided and a lot of time spent guessing at solutions.

I have a hard imagining that adding calcium nitrate is going to "lock up" a force main. It would seem that calcium nitrate may make an existing force main problem such as low velocity worse, but will not cause the problem outright.