# Streamline - Spring 2013 - (Page 41)

Wastewater Math QUESTIONS BY DONNA LAWSON, WASTEWATER TECH II 1. Water is flowing through a pipe at a rate of 3.5 ft/sec. What is the flow rate in ft3/sec given that the pipe diameter is 16 inches? a. 4.6 ft3/sec b. 7.0 ft3/sec c. 4.86 ft3/sec d. 43.96 ft3/sec 4. Find the total weight in pounds of ferric chloride (SG 1.47) in a storage tank that has a diameter of 3.2 feet and with a useable height of 5.7 feet? a. 2,000 lbs b. 3,200 lbs c. 4,000 lbs d. 4,201 lbs 7. 2. 5. 8. A centrifugal pump is able to produce 260 gpm against a 30 ft total pumping head. Given this information, what is the approximate horse power of the pump? a. 2.0 HP b. 8.6 HP c. 15 HP d. 30 HP 3. Calculate the solids recovery rate of a vacuum filter using the following data: Filter area - 425 ft2 Sludge filtered – 72,000 gal Sludge solids – 4% Sludge volatile solids - 62% Cake solids – 18% Cake produced – 54 wet tons Operation hours - 8 a. 64% b. 75% c. 81% d. 90% A system’s sewer billing rate is twice the water rate. What is the total bill for a customer who used 3,500 gallons of water if the billing rate is a base rate of \$30.00 for the first 1,000 gallon and then \$0.25/1,000 gallons for additional gallons used? a. \$30.62 b. \$61.25 c. \$91.88 6. Determine the detention time in hours for a basin that is 12 feet wide, 15 feet and 20 feet deep and receives a flow of 120 gpm? a. 2.6 hrs b. 3.7 hrs c. 4.0 hrs Find the removal efficiency of a primary clarifier that received an influent BOD of 250 mg/L and reduced the BOD to 130 mg/L before reaching the RBC? a. 5.2% b. 52% c. 60% 15.0 hp is provided to a motor that is only 92% efficient. What is the available water horsepower (whp) if the pump is 85% efficient? a. 1.2 whp b. 7.4 whp c. 10.2 whp d. 11.7 whp 9. Find the average flow per day in MGD for the following flow rates: 120 gpm, 235 gpm, 175 gpm and 152 gpm. a. 0.682 MGD b. 170.5 MGD c. 0.246 MGD d. 1440 MGD 10. The pressure reading at the bottom of a water tank is 85 psi, what is the level of water in the tank? a. 36.8 ft b. 115 ft c. 196.4 ft d. 200 ft Answers on page 42 www.vrwa.org 41 http://www.vrwa.org

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# Streamline - Spring 2013

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