# Streamline - Summer 2013 - (Page 43)

Wastewater Math Questions BY DONNA LAWSON, WASTEWATER TECH II 1. A wastewater treatment plant treats 1,500,000 gpd with a 12.5% sodium hypochlorite solution. If the necessary feed rate dose is 3.0 mg/L and the specific gravity of the hypochlorite is 1.03, how many gallons per day of sodium hypochlorite are required? 2. What is the F/M ratio for a treatment plant that treats a flow of 2.0 MGD with a BOD concentration of 150 mg/L and an aeration basin with a volume of 1.85 MG with a MLVSS concentration of 3,000 mg/L? 3. What would the motor horsepower be if the brake horsepower is 75 HP and the motor efficiency is 89%? 4. An operator fed 6.7 gallons of saturated sodium fluoride while treating 120,000 gallons of water over a 24-hr period. What is the calculated fluoride dose in mg/L? 5. A sedimentation basin has a weir which is 87 feet long. Water flows through the basin at a rate of 1.0 MGD. What is the overflow rate in gallons per day per foot of weir for the basin? 6. 2.75 MGD of water was treated with a fluoride dose of 1.0 mg/L. Find the sodium fluorosilicate feed rate in pounds per day. Note: AFI, decimal = 0.607 Purity, decimal = .985 7. A water treatment plant has four (4) sedimentation basins. The basins are 100 feet long, 30 feet wide and 12 feet deep. One of the basins has been taken out for routine maintenance. Find the surface overflow rate in gallons per day per square foot with a daily flow of 8.25 MGD. 8. A tank holds 1,000,000 gallons and has a flow of 8 MGD flowing through the tank. What is the detention time in hours? 9. Find the operating cost (\$/hr) of a 50 hp pump, if the power cost is \$0.055/kWhr. 10. 40 pounds of chlorine was used to treat 3,250,000 gpd of effluent. If the chlorine residual is 0.5 mg/L, what is the chlorine demand, mg/L? Answers on page 44 www.vrwa.org 43 http://www.vrwa.org

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# Streamline - Summer 2013

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