Good Morning Mr. Chinenye ...

Good Morning Mr. Chinenye Justin Nwaogwugwu,

Although aluminum based coagulants can be quite effective, I have found here at our water plants in Canada with similar conditions (it sounds like anyways) that iron based coagulants are much more effective...the downside is that they cost more money (at least where I live).   Coagulants as you already know are very finicky and require the right balance between pH, Temperature, and the size of particles in the water.  I am sorry that there isn't an easy answer for you but jar testing as the others have mentioned is crucial in determining which coagulant might work.  However, and this is the annoying part, the bench scale tests almost always need to be tweaked in the full scale system. 

At one of our plants we were using an aluminum based coagulant and after a few years of finding increased aluminum in the treated water (there was zero aluminum in the raw water) we had determined that the coagulant had been carrying over through the treatment process into the treated water chamber.  Aluminum based coagulants (or any coagulant for that matter) must have some kind of detention system in order for the chemistry to take place and the detention time for us ranges between 30 - 90 minutes before we take that water to the second stage in the treatment process otherwise the aluminum will carry over.  I hope this helps.  Please feel free to contact me for further details as this is a complex issue that I could write pages and pages about!

Respectfully,

Kurt Rasmussen, P.Eng.

SaskWater