HELP: floating sludge (coagulation) 2

[red857]

i would like to inquire how come the sludge formed after a series of coagulation and floculation in our wastewater system floats and wont settle at the bottom of our hydrocone clarifier. we are currently using polyaluminum chloride and polymer which are injected in our inline mxing system. any explanations and suggestion to address this problem. i'm from a beverage industry. thanks.

 

[saxon]

red857, The settling velocity of any particle is controlled by Stokes Law, where:

V=g(Ps-Pl)d/U^2
V=settle velocity
Ps=particle density
Pl=liquid density
d=particle dia.
U=liquid velocity

By varying any of the variables in the above form that decreases the settling velcity below a critical point will lead to flotation. There are other operational variables that can affect the settling as well. Such as, temperature, agitation rate, pH, qty. of coagulant/flocculant used, time of addition, type of coagulant and flocculant used.

To go through the entire analysis required to isolate the cause of your flotation problem would require a text on sedmentation and clarification. I hope the above gives you some ideas to check into.

saxon

 

[red857]

thanks saxon. geesh, i guess i need to hit on my textbooks again! as a quick fix, i varied the dosing concentration of the coagulant and flocculant and it gave me a better result. though there are still a few fine particles floating, but its much better now than before where pratically the entire sludge floated. i guess some other parameters would need to be evaluated and tested as well. thanks again!

 

[saxon]

Whoops! My error. "U", should read liquid viscosity, not velocity.

saxon

 

[ehiatt]

Red -- what are you treating? How long is the water left in the clarifier? I would think you biggest problems are with the polymer and PAC you are using and not necessarily the dosage. Any idea what type of polymer?

 

[jproj]

red857:

You may want to check this link out... sounds like the problem is similar:

thread161-92263