Calculating Alum and Polymer Dosages?

[KWTPOP]

Is there a formula that can be used to calculate how much Alum and Polymer will be needed for a clarifier with a capacity of 249,000 gals and 1000 gpm coming in? I want to have a good sludge blanket and clear up a heavy floc that is starting to develop but not settle out. It sounds like from what I've been told it is just a case of experimenting with different amounts. That doesn't sound right to me. My plant went from 7hrs detention time @ 600 gpm to 4 hrs detention time @ 1000 gpm. Has to be a scientific solution to this. Any help would be appreciated.

 

[hydrae]

yes, the solution is a jar test, standard units have six jars with stirrers, you vary the dose of alum, cat poly, acid, bleach, caustic, stir rate and stir time (one at a time) to find out which dose of each item works best with the current water as a batch process, let settle then filter through a filter paper for a overall process.
Treatment training books get into detial on the procedure, methods and evaluation.

Hydrae

 

[KWTPOP]

My plant had a jar test done last week but the company only checked the effectiveness of various polymers and the one we are currently using. When I asked what amount we would need he said we would have to try different amounts. he didn't solve my problem. We had run the same feed settings for years without any problems until we came back with a high aluminum level on our primarys. We lowered the alum, but at the same time the licensed op. wanted to increase well output to 1000gpm from 600gpm. I don't think the chemicals are enough to handle that increase.

 

[hydrae]

Anytime something is different a good operator will perform a whole suite of jar tests to see how the treatment can be optimized, nearly doubling the flow is a significant change to a treatment process even from a well the chemistry of the water can be very different at 1000 gpm vs 600 gpm
Hydrae

 

[semo]

Hydrae is correct that it will take several jar tests to see what the optimum dosage is. Your pH will also have an effect on the sludge formation, so you will have to throw that into account as you perform jar tests.

Just because the well will output 1000 gpm does not mean the clarifier is sized for that flow. The surface area of the clarifier will allow you to determine your upflow rate. Increasing the upflow rate too much will keep the sludge suspended and not allow it to settle. If this is the case, varying the chemical dosages may not help develop a sludge blanket.

 

[KWTPOP]

Thanks for the response hydrae and semo. I personally think the plant is not deigned for that amount of flow. We almost doubled our well output from previous years and it really increases the amount of iron the clarifier has to settle out. Its getting harder and harder to get the filters clean.