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Homework answers / question archive / HOMEWORK 8 1

HOMEWORK 8 1. What is the CT required for 2.0 log of inactivation of Giardia at 20 degrees C, at a pH of 6.5, and 1.2 ppm of free chlorine? a. 24 b. 32 c. 7 d. 41 2. A treatment plant is using alum to dose at 12 mg/L a flowrate of 35 MGD. The alum solution is 11.02 lbs/gal and is 48.25% by weight. How many gals per minute are being fed? a. 0.2367 gpm b. 0.4575 gpm c. 0.7855 gpm d. 0.1065 gpm 3. A well is pumping water into a water system at a rate of 650 GPM and 90 mg/L nitrate. This water is blended with 7100 GPM purchased water that contains 4mg/L nitrate. Find the nitrate blend of these two sources. a. 8.2 mg/L b. 9.2 mg/L c. 10.2 mg/L d. 11.2 mg/L 4. A well must be disinfected at 50 ppm chlorine concentration using 65% HTH. The well casing is 10 inches in diameter and is 775 feet deep. The static water level in the well is 75 feet below ground level. How many pounds of 65% HTH are required to disinfect the well? a. 1.19 lbs b. 1.34 lbs c. 1.57 lbs d. 1.83 lbs 5. Express 2.4% concentration in terms of mg/L concentration. a. 24,000 mg/L b. 240 mg/L c. 24 mg/L d. 240,000 mg/L 6. Convert 6700 mg/L to percent. a. 6.7 % b. 0.24 % d. 0.67 % c. 0.76 % 7. Express 22% concentration in terms of mg/L. a. 22,000 mg/L b. 220 mg/L c. 220,000 mg/L d. 22 mg/L 8. Express 141bs/MG concentration as mg/L. a. 3.72 mg/L b. 2.76 mg/L c. 1.68 mg/L d. 5.51 mg/L 9. Express 23 Lbs/MG concentration as mg/L concentration. a. 3.72 mg/L b. 2.76 mg/L c. 1.68 mg/L d. 5.51 mg/L 10. Calculate the percent fluoride ion present in hydrofluosilicic acid, H2SiF6. (The atomic weights are as follows: H = 1.008; Si = 28.06; F = 19.00) a. 66.7 % b. 49.2 % c. 99.9 % d. 79.1 % 11. A fluoride dosage of 1.5 mg/L is desired. How many lbs/day dry sodium silicofluoride will be required if the flow to be treated is 980,000 gpd. The commercial purity of the sodium silicofluoride is 98% and the percent of fluoride ion is 60.6%. (Assume the raw water contains no fluoride.) a. 28.3 lbs/day b. 62.2 lbs/day c. 99.9 lbs/day d. 20.6 lbs/day 12. A fluoride dosage of 1.2 mg/L is desired. How many lbs/day dry sodium silicofluoride will be required if the flow to be treated is 1.68 MGD? The commercial purity of the sodium silicofluoride is 98% and the percent of fluoride ion is 60.6%. (Assume the water to be treated contains no fluoride.) a. 28.3 lbs/day b. 49.2 lbs/day c. 99.9 lbs/day d. 20.6 lbs/day HOMEWORK 8 13. A flow of 2,796,000 GPD is to be treated with sodium silicofluoride. The raw water contains no fluoride. If the desired fluoride concentration in the water is 1.6 mg/L, what should be the chemical feed rate (in lbs/day)? The manufacturer's data indicates that each pound of contains 0.6 lbs of fluoride ion. (Assume the raw water contains no fluoride.) a. 28.3 lbs/day b. 62.2 lbs/day c. 99.9 lbs/day d. 20.6 lbs/day 14. A flow of 3.06 MGD is to be treated with sodium fluoride, NaF. The raw water contains no fluoride and the desired fluoride concentration in the finished water is 1.0 mg/L. What should be the chemical feed rate in lbs/day? (Manufacturer's data indicates that each pound of NaF contains 0.44lbs of fluoride ion.) a. 58.0 lbs/day b. 62.2 lbs/day c. 99.9 lbs/day d. 20.6 lbs/day 15. A flow of 775,000 gpd is to be treated with sodium fluoride, NaF. The raw water contains 0.09 mg/L fluoride and the desired fluoride level in the finished water is 1.3 mg/L. What should be the chemical feed rate in lbs/day? (Manufacturer's data indicates that each pound of NaF contains 0.45 lbs of fluoride ion.) a. 38.0 lbs/day b. 22.2 lbs/day c. 17.4 lbs/day d. 20.6 lbs/day 16. If 8 lbs of sodium fluoride (NaF) are mixed with 50 gal of water, what is the percent strength of the solution? (The commercially available sodium fluoride is 98% pure.) a. 6.7 % b. 1.2 % c. 2.7 % d. 1.8 % 17. If 15 lbs of sodium fluoride, NaF, are dissolved in 75 gallons of water, what is the percent strength of the solution? (Assume the chemical used is 100% pure) a. 6.7 % b. 1.2 % c. 2.7 % d. 2.3 % 18. How many pounds of sodium fluoride (98% pure) must be added to 200 gallons of water to make a 1.5% solution of sodium fluoride? a. 28.3 lbs b. 25.9 lbs c. 39.9 lbs d. 20.6 lbs 19. If 10 lbs of sodium fluoride are mixed with 50 gal water, what is the percent strength of the solution? (The commercial sodium fluoride is 98% pure.) a. 6.7 % b. 1.2 % c. 2.7 % d. 2.3 % 20. How many pounds of sodium fluoride (98% pure) must be added to 150 gallons of water to make a 2% solution of sodium fluoride? a. 28.3 lbs b. 26.1 lbs c. 39.9 lbs d. 20.6 lbs 21. A flow of 4.12 MGD is to be treated with a 22% solution of hydrofluosilicic acid. The acid has a specific gravity of 1.2. If the desired fluoride level in the finished water is 1.1 mg/L, what should be the solution feed rate (in gpd)? The raw water contains no fluoride. (The percent fluoride ion content of H 2 SiF6 is 79.2%.) a. 16.5 GPD b. 25.9 GPD c. 39.9 GPD d. 21.7 GPD 22. A flow of 2.8 MGD which contains no natural fluoride is to be treated with a 20% solution of hydrofluosilicic acid which weighs 9.8 lbs/gal. The desired concentration is 1.1 mg/L. What should be the solution feed rate (in gpd)? The AFI is 79.2%. a. 18.5 GPD b. 25.9 GPD c. 39.9 GPD d. 16.5 GPD HOMEWORK 8 23. The desired solution feed rate has been determined to be 90 gpd. What is this feed rate expressed as mL/min? a. 216.5 ml/min b. 236.6 ml/min c. 239.9 ml/min d. 321.5 ml/min HOMEWORK 8

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