1.Determine the chlorine demand of an effluent it the chlorine dose is 10.0 mg/L and the chlorine residual is 1.1 mg/L.

2. To maintain satisfactory chlorine residual in a plant effluent, the chlorine dose must be 10 mg/L when the flow is 0.37 MGD. Determine the chlorinator setting, (feed rate) in lbs/day

3. Determine the chlorinator setting in lbs per 24 hours if 2 MG of water per day are to be treated with a desired chlorine dose of 3.0 mg/L.

4. The optimum liquid polymer dose from the jar tests is 12 mg/L Determine the setting on the liquid polymer chemical feeder in milliliters per minute when the plant flow is 4.7 MGD. The liquid polymer delivered to the plant contains 642.3 milligrams of polymer per milliliter of liquid solution.

Answers:

1. The term Residual means what is left over, so:
Chlorine Demand, mg/L =
= Chlorine Dose, mg/L – Chlorine Residual, mg/L
= 10.0 mg/L – 1.1 mg/L
= 8.9 mg/L

2. any time a question asks for the answer to be in lbs/day the formula is:
Flow, MGD X Concentration, mg/L X 8.34 lbs/gal OR a Variation could be:
Volume, MG X Concentration, ppm X 8.34 lbs/gal Note: Volume is in MG but either way you will NOT use Gallons per day AND mg/L and ppm are synonymous with each other (mean the same), So:
Chlorine Feed Rate, lbs/day
= Flow, MGD X Dose, mg/L X 8.34 lbs/gal
= 10.37 MGD X 10 mg/L X 8.34 lbs/gal
= 30.9 lbs/day

3. This one just used words instead of abbreviations we are used to seeing – it still says – find lbs/day – there are 24 hrs in a day
Chlorinator Setting, lbs/day
= Flow, MGD X Dose, mg/L X 8.34 lbs/gal DOSE is given in mg/L – same as Concentration
= 2 MGD X 3.0 mg/L X 8.34 lbs/gal
= 50 lbs/day

4. The formula for this one can be confusing from some of the formula sheets I have seen – it looks like this:
Polymer Feeder Setting, mL/min =
(Flow, MGD X Poly dose, mg/L X 3.785 L/gal X 1,000,000)/(Liq. Poly mg/ml X 24 hr/day X 60 min/hr X 1,000,000)
Or you can work it out recognizing the following things and making slight variations to the normal Loading or Pounds Formula:
Instead of using 8.34 lbs/gal we are talking about L/gal and that is 3.785 L/gal
The answer will be in Minutes NOT Days so we are going to have to do time conversion to get from MGD to Gallons/day to Minutes/Gallon
SO:
Flow, MGD X Poly Dose, mg/L X 3.785 L/gal
= 4.7 MGD X 12 mg/L X 3.785 L/gal
= 213.474 Now convert to Gallons
= 213.474 X 1,000,000 = 213,474,000 L/gal/day (or just shuffle), now convert to Minutes
= (213,474,000 gal/day) / (1440 min/day) OR you could have divided by 24 hr/day then again by 60 min/hr
= 148,245.833 gal/min Remember the problem said the polymer contains 642.3 milligrams of polymer per milliliter of liquid solution? You have to compensate by dividing that into the L/gal/min answer you just got (because it is not 100% solution), So:
= (148,245.833 gal/min) / (642.3 mg/ml)
= 231 ml/min