I am a student and am preparing my final project. My topic is the comparative study of coagulants: aluminum sulfate, PAC, and polyDADMAC for clarification of drinking water.
I would like to know if you have any information on this topic: commonly used doses, optimal conditions, aluminum residue from PACs, etc., knowing that the water to be treated has low turbidity (8 NTU).
Treatment rates depend on the type of coagulant used, and even if turbidity is low, rates can differ for a given coagulant.
In other words several parameters affect the optimum rate in addition to turbidity such as temperature, conductivity, DOC, and to a lesser extent pH.
For example; for PACs, at 8 UNF, the treatment rate could be 20 g/m3 with DOC of 1 mg/l. But it could reach 60 to 80 g/m3 with DOC greater than 5 mg/l.
This is not a golden rule, however, because it depends on the nature of the organic matter present. The example is true when the predominant molecules are humic or fulvic acids, less so when the molecules are smaller or more hydrophilic.
Another example with aluminum sulfate: for a given water quality, the treatment rate will be 10 g/m3 at 20 °C and 30 g/m3 at 8 °C.
As you can see, coagulation is a complex process, and the notion of dosing is pretty case specific.