Streamline - Spring 2012 - (Page 31)

Wastewater Math Questions 1. A DAF unit receives air at a rate of 8.53 ft3/min. How many pounds per day is that equivalent to? Hint: Air = 0.0807 lb/ft3 (at standard temperature, pressure and composition). 2. 3. A gravity thickener has a 25 ft radius and a daily flow of 68,500 gpd. What are the solids loading on the gravity thickener, if the average percent solids are 3.2%? What is the motor horsepower (mhp) of a pump with the characteristics below? Motor efficiency – 93.6% Pump efficiency – 78.8% Total head – 175 ft Flow – 4.35 MGD 4. Calculate the pounds of MLSS in an aeration tank that has a diameter of 42 ft with a sludge depth of 16 ft and an average concentration of 2,850 mg/L and a specific gravity of 1.1. 5. 7. What is the percent strength of 145 lb of ferric sulfate solution dissolved in 50 gallons of water? General Study At what temperture will the fusible plug on a chlorine cylinder begin to melt? a. 212 ° F b. 105 ° F c. 160 ° F d. 100 ° F 9. The main purpose of a check valve is to prevent water from flowing in two directions. a. True b. False 6. What is the recommended velocity range in feet per second for effective grit removal? a. 1 to 1.5 ft/s b. 0.7 to 1.4 ft/s c. 0.5 to 1.0 ft/s d. 1.5 to 2.5 ft/s 8. 10. What is the equivalent temperature in ° Celsius? a. 71.1 ° C b. 160 ° C c. 86 ° C d. 21.2 ° C The BOD/Nitrogen/ Phosphorus ratio needed for microorganism growth is: a. 100:3:2 b. 100:25:15 c. 100:5:1 d. Unknown Answers on page 32 31

Table of Contents for the Digital Edition of Streamline - Spring 2012

From the President
From the Executive Director
Where is Virginia’s Groundwater?
Basic Management Skills
Planning or Piecemeal?
CPEs and YOU
The Sludge Bag
Fracking Rapidly Becoming Unpopular
Amazing We All Learned English!
Springtime Safety – Outdoor Hazards
Spotlight on Western Virginia Water Authority’s Blue Ridge Brawler
Wastewater Math
VRWA’S 24th Annual Exposition Agenda
Throwing My Loop
eLearning Benefits
Membership Application
Do You Know What Your VRWA Benefi ts Are?
Rural Water Review
VRWA Mailbag
Welcoming New Members
Training Calendar
Board Of Directors
VRWA Committees
Index To Advertisers/Ad.Com

Streamline - Spring 2012