Assignment 14: Bacteria and Disinfection

Each question is worth 10 points. Partial credit may be awarded.

This assignment will give you practice with the math introduced in lesson 12. You will need to have your formulas in front of you, along with any tables (ie Periodic Table or Formula Table) used within the lesson. Be sure to keep in mind significant figures. This assignment also includes questions pertaining to the chlorine lab, so make sure you have viewed the virtual lab before doing the assignment.

1. Determine the chlorinator setting (lbs/day) needed to treat a flow of 2.5 MGD with a chlorine dose of 3.7 mg/L.

(mg/L Cl2) (MGD Flow) (8.34 lb/gal) = lbs/day Cl2

(                           ) (                       MGD) (8.34 lb/gal) = lbs/day Cl2

lbs/day Cl2 = _______________________________

2. A flow of 745,000 gpd is to receive a chlorine dose of 8.4 mg/L. What should the chlorinator setting be (in lbs/day)?

(mg/L Cl2) (MGD Flow) (8.34 lb/gal) = lbs/day Cl2

(                           ) (                       MGD) (8.34 lb/gal) = lbs/day Cl2

lbs/day Cl2 = _______________________________

3. A chlorinator setting is 25 lbs per 24 hours. If the flow being chlorinated is 1.89 MGD, what is the chlorine dosage expressed as mg/L?

(mg/L Cl2) (MGD Flow) (8.34 lb/gal) = lbs/day Cl2

(mg/L Cl2) (                       MGD) (8.34 lb/gal) = (                         lbs/day Cl2) 4. A water is tested and found to have a chlorine demand of 2.3 mg/L. If the desired chlorine residual is 0.9 mg/L, what is the desired chlorine dose in mg/L?

Chlorine Dose = Chlorine Demand + Chlorine Residual

Chlorine Dose = (                             mg/L) + (                             mg/L)

Chlorine Dose = _____________________________mg/L

5. What should the chlorinator setting be, in lbs/day, to treat a flow of 2.85 MGD if the chlorine demand is 2.9 mg/L and a chlorine residual of 0.7 mg/L is desired?

Chlorine Dose = Chlorine Demand + Chlorine Residual

Chlorine Dose = (                             mg/L) + (                             mg/L)

Chlorine Dose = _____________________________mg/L

6. If the chlorine dose is 2.8 mg/L to treat a flow of 2.25 MGD, what is the dosage (feed rate) in lbs/day?

(mg/L Cl2) (MGD Flow) (8.34 lb/gal) = lbs/day Cl2

(                          mg/L Cl2) (                       MGD) (8.34 lb/gal) = (lbs/day Cl2)

lbs/day Cl2 = ___________________________

This section of the assignment deals with the chlorine virtual lab.

7. The titration method for analyzing free chlorine is called ______________________________.

8. After the stirring bar is inserted, 1 mL of pH 7 ______________________ buffer solution is added to the sample.

9. Next the operator sets the digital readout until it reads ________________________.

10. The end point reading for free chlorine in the finished water of this virtual lab is ______________________.