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Filter Loading and Backwash Rates Well Yields and Chlorine Dosage in Waterworks Operation

Filter Loading and Backwash Rates Well Yields and Chlorine Dosage in Waterworks Operation. Math for Water Technology MTH 082 Lecture Chapter 4 & 8- Applied Math for Water Plant Operators Loading Rate Calculations (pg 62-66); Well yield (163-177)

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Filter Loading and Backwash Rates Well Yields and Chlorine Dosage in Waterworks Operation

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  1. Filter Loading and Backwash Rates Well Yields and Chlorine Dosage in Waterworks Operation Math for Water Technology MTH 082 Lecture Chapter 4 & 8- Applied Math for Water Plant Operators Loading Rate Calculations (pg 62-66); Well yield (163-177) Mathematics Chapter 19-20 &23- Basic science Concepts and Applications (pg 183-190; 197-203)

  2. Objectives Reading assignment: Chapter 4 & 8- Applied Math for Water Plant Operators Loading Rate Calculations (pg 62-66); Well yield (163-177) Mathematics Chapter 19-20 &23- Basic science Concepts and Applications (pg 183-190; 197-203) • Filter overviews • Filter loading and backwash rates • Well yield • Chlorine dosage for a new well

  3. Conventional Treatment • Conventional Treatment– common treatment steps used to remove turbidity from the initial source water. Chlorination Ozone UV 5. Clear Well Disinfection 1. Coagulation 2. Flocculation 3. Sedimentation 4. Filtration Raw Water Distri bution Fast Pretreatment Slow Rapid or flash Mixing Alum, polymer Clearwell Backwash pumps Sludge Washwater

  4. High Rate Filter Dual or Multi Media Filter -4 times faster then rapid sand -granular activated carbon -anthracite coal -garnet sand and gravel -backwash ready (70 hr longevity) -excellent water quality

  5. High Rate Filters Anthracite Coal Fine sand Garnet sand

  6. High Rate Filter Monomedia Filter Dualmedia Filter Anthracite Coal Monomedia Coarse sand Fine sand Garnet sand

  7. Dual-media and multimedia filters • Require an extremely deep bed • Can operate at three or four times the rate of sand filters • Cannot reduce turbidity • Do not require backwashing

  8. When mixed media filters composed of garnet, sand, and crushed anthracite coal are used, which of the following describes their placement in the filter bed? • Anthracite coal on top, garnet in the middle, and sand on the bottom • Garnet on top, anthracite coal in the middle, and sand on the bottom • Sand on top, anthracite coal in the middle, and garnet on the bottom • Anthracite coal on top, sand in the middle, and garnet on the bottom

  9. In a filter using gravel, anthracite, and sand, the anthracite should be? • The top layer of media • Beneath the gravel • Between the sand and the gravel • Mixed with the sand

  10. Pilot Filters Anthracite Coal Fine sand Garnet sand

  11. The main action of a mixed media filter is: • Straining • Disinfecting • Coagulating • None of the above

  12. Backwash • Suspended particles entrapped by filter media. • Accumulation occurs: • head loss within the filter to reach excessively high levels (6 to 8 feet of hydraulic head). • Particles pass through the filter, water turbidities reach unacceptable levels • Rule Backwash at 0.1 NTU • SWTR Allows 0.3 NTU.

  13. Head Loss • Clean filter =0 psi= one foot of head loss on a new filter • As filter clogs more negative pressure • Pressure builds in a linear fashion -2.5 to -4.0 psi = 6 to 10 ft of head loss • More clogged greater the head loss • Remember 1 ft of water column = 0.433 psi • 2.31 ft of water for 1 psi change

  14. Filter Backwash • Some plants use head loss, some use time • Some plants use operator knowledge and turbidity • Each operator has their own scheme!! • Parents and diapers--

  15. The most critical criterion for determining when a mixed media filter should be backwashed is: • Filter effluent quality • Flow rate • Head loss • Visual inspection of the filter surface

  16. Filtration Rate Calculation Unit Filter Run= (Total gal filtered gal) Filter Area (sq ft) Filtration Rate= (flow gpm) Area (sq ft) Units will be gpm ft2! Backwash Rate = (flow gpm) Area (sq ft) Units will be gpm ft2! Downward Upward

  17. The total water filtered during a filter run (between backwashes) is 2,950,000 gal. If the filter is 15 ft by 20 ft, What is the unit filter run volume (UFRV)? • 9.833 g/ft2 • 101.7 g/ft2 • 9833 g/ft2 • 0.9833 g/ft2 Given Formula Solve: L= 15 ft, W=20 ft; Rate 2,950,000 gal A=L X W UFVR= (Total gallons filtered g) Area (sq ft) A= 20 ft X 15 ft = 300 ft2 UFVR= (2,950,000 gal) 300 (sq ft) UFVR = 9833 g/ft2

  18. The total water filtered during a filter run (between backwashes) is 4.8 MG. If the filter is 20 ft by 30 ft, What is the unit filter run volume (UFRV)? • 96000 g/ft2 • 8000 g/ft2 • 800 g/ft2 • 0.008 g/ft2 Given Formula Solve: L= 20 ft, W=30 ft; Rate 4.8 MG A=L X W UFVR= (Total gallons filtered g) Area (sq ft) A= 20 ft X 30 ft = 600 ft2 UFVR= (4,800,000 gal) 600 (sq ft) UFVR = 8000 g/ft2

  19. A filter 20 ft by 25 ft receives a flow of 1940 gpm. What is the filtration rate in gpm/ft2? • 3.9 gpd/ft3 • 3.9 gpm/ft2 • 0.25 gpm/ft2 • 0.25 gpd/ft3 Given Formula Solve: L= 20 ft, W=25 ft; Rate 1940 gpm A=L X W Filtration Rate= (flow gpm) Area (sq ft) A= 20 ft X 25 ft = 500 ft2 Filtration Rate= (1940 gpm) 500 (sq ft) Filtration Rate = 3.9 gpm/ft2

  20. A filter 20 ft by 35 ft receives a flow of 1530 gpm. What is the filtration rate in gpm/ft2? • 2.2 gpm/ft2 • 2.2 gpm/ft3 • 0.45 gpm/ft2 • 0.45 gpd/ft3 Given Formula Solve: L= 20 ft, W=35 ft; Rate 1530 gpm A=L X W Filtration Rate= (flow gpm) Area (sq ft) A= 20 ft X 35 ft = 700 ft2 Filtration Rate= (1530 gpm) 700 (sq ft) Filtration Rate = 2.2 gpm/ft2

  21. A filter 25 ft by 30 ft receives a flow of 3.3 MGD. What is the filtration rate in gpm/ft2? • 3.1 gpm/ft3 • 0.32 gpm/ft2 • 3.1 gpm/ft2 • 0.32 gpd/ft3 L= 25 ft, W=30 ft;Rate 3.3 MG1,000,000 gal1 Day D 1MG 1440 min A=L X W Filtration Rate= (flow gpm) Area (sq ft) A= 25 ft X 30 ft = 750 ft2 Filtration Rate= (2292 gpm) 750 (sq ft) Filtration Rate = 3.1 gpm/ft2 Given Formula Solve:

  22. A filter 25 ft by 10 ft has a backwash rate of 3400 gpm. What is the filter backwash rate in gpm/ft2? • 13.1 gpm/ft3 • 0.074 gpm/ft2 • 13.6 gpm/ft2 • 136 gpd/ft3 Given Formula Solve: L= 25 ft, W=10 ft; Rate 3400 gpm A=L X W Backwash Rate = (flow gpm) Area (sq ft) A= 25 ft X 10 ft = 250 ft2 Filter Backwash Rate= (3400 gpm) 250 (sq ft) Filter Backwash Rate= 13.6 gpm/ft2

  23. A filter 20 ft by 15 ft has a backwash rate of 4.5 MGD. What is the filter backwash rate in gpm/ft2? • 10.4 gpm/ft3 • 0.01 gpm/ft2 • 10.4 gpm/ft2 • 0.01 gpd/ft3 Given Formula Solve: L= 20 ft, W=15 ft; ft;Rate 4.5 MG1,000,000 gal1 Day D 1MG 1440min A=L X W Backwash Rate = (flow gpm) Area (sq ft) A= 20 ft X 15 ft = 300 ft2 Filter Backwash Rate= (3125 gpm) 300 (sq ft) Filter Backwash Rate= 10.4 gpm/ft2

  24. Well Problems • Drawdown ft = pumping water level – static water level ft • Well yield = Flow gallons duration of Test, min • Specific yield, gpm/ft = (Well yield gpm) (Drawdown ft) • Well casing disinfection lbs= (dose mg/L Cl2)(water in well casing MG)(8.34 lb/gal) Chlorine lbs = chlorine lbs % available chlorine 100

  25. Before the pump is started the water level is measured at 140 ft. The pump is then started. If the pumping water level is determined to be 167 ft, what is the drawdown in ft? • 307 ft • -27 ft • 27 ft • 0 ft Given Formula Solve: Static WL= 140 ft, Pumped WL=167 ft Drawdown ft = pumping water level – static water level ft Drawdown = 167 ft- 140 ft Drawdown = 27 ft

  26. During a five minute test for well yield, a total of 740 gallons are removed from the well. What is the well yield in gpm? • 67 gpm • 148 gpm • 3700 gpm • 0 gpm Given Formula Solve: total = 740 gal, time = 5 minutes Well yield = Flow gallons Duration of Test, min Well yield = 740 gallons = 148 gpm 5 min

  27. How many lbs of calcium hypochlorite (65% available chlorine) is required to disinfect a well if the casing is 18 inches in diameter and 220 ft long, with water level at 100 ft from the top of the well? The desired dose is 50 mg/L? • 2 lbs • 1 lbs • .02 lbs • 0.65 lbs Given Formula Solve: Cl= 65/100 D=18 in=1.5 ft Well 220-100 =120 ft 220 ft - 100 ft = 120 ft water in well (0.785)(D2)(H) = ft3 (0.785)(1.5 ft)(1.5 ft) (120 ft)(7.48 gal/ft3)= 1585 gal (50 mg/L)(.001585 MG)(8.34 lb/gal) = 1.01lbs 65/100

  28. Today’s objective: Filter Loading Rates, Filter Backwash Rates, Well yield and chlorine dosage of new wells been met? • Strongly Agree • Agree • Neutral • Disagree • Strongly Disagree

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