P.E. Civil Exam Review: Wastewater and Water Treatment. Andy Winfrey

Transcription

1 P.E. Civil Exam Review: Wastewater and Water Treatment Andy Winfrey

2 WATER QUALITY

3 WATER QUALITY CWA WQ Standards 3 Clean Water Act states that the water quality standards are set to meet the goals of streams and lakes that are fishable and swimmable. Water uses that are protected are: 1. Aquatic Life 2. Primary Contact Recreation (Swimming) 3. Secondary Contact Recreation (Wading) 4. Fish Consumption 5. Domestic Water Supply (Drinking)

4 WATER QUALITY Antidegradation Policy 4 To protect the existing uses of waters, and to protect waters with water quality levels better than necessary to support propagation of fish, shellfish and wildlife, and recreation in and on waters of the states, a set of policies called "antidegradation" comes into play. The purpose of these policies is to keep clean waters clean. States, tribes, and territories usually cover this program as part of their water quality standards regulations. Antidegradation is generally considered to have three components, or "tiers" of protection: (1) protection & maintenance of existing water uses (2) protection of high quality waters, and (3) protection of outstanding national resource waters

5 WATER QUALITY Monitoring 5 Sampling & Contaminant Analysis Impaired streams problems caused by sediment, bacteria, nitrates(eutrophic), metals, pesticides, ph, DO, ph, temp. Monitoring concentrates on these parameters. Fish & macroinvertebrates bioassays for mercury, PCBs, metals, pesticides, other. Indicators of good water quality stonefly, mayfly, gilled snail Indicators of moderate water quality- dragonfly, damselfly, crayfish Indicators of poor water quality midge or blackfly larvae, leech, worm

6 WATER QUALITY Assessment 6 Surface Water Quality Evaluation/Assessment Bacteria E. Coli and Fecal Coliform 200 mg/l Std. Habitat Banks, stream bottoms, vegetation, flow Algae Benthic (attached) - good or floating- bad Macroinvertebrates- Total, pollution-sensitive, MHBI Fish- IBI, Total, Entolerance Species, Abundance

7 WATER QUALITY Reports on Nation s Waters 7 States, tribes, and territories are required to provide the results of their monitoring efforts in the form of two reports, submitted to EPA and made available to the public, generally submitted every even-numbered year. The first report is the "305(b) Report," which includes all that which the state, tribe, or territory knows about all its waters -- healthy, threatened, and impaired. The second is the "303(d) List" and includes only those waters threatened or impaired, not healthy waters.

8 WATER QUALITY TMDL 8 TMDL - Total Maximum Daily Wasteload is the maximum amount of wasteload a body of water can receive and still meet water quality standards. Surface Water Quality Evaluation/Assessment Bacteria E. Coli and Fecal Coliform 200 mg/l Std. Habitat Banks, stream bottoms, vegetation, flow Algae Benthic (attached) - good or floating- bad Macroinvertebrates- Total, pollution-sensitive, MHBI Fish- IBI, Total, Entolerance Species, Abundance

9 WATER QUALITY NPDES Permits for Point Sources 9 NPDES Permits: Key Elements Effluent Limits Best management practices Compliance schedules Monitoring requirements Reporting requirements Standard conditions For POTWs only: Pretreatment program and sludge management requirements

10 WATER QUALITY Sect 319 for Nonpoint Sources 10 Congress chose not to address nonpoint sources through a regulatory approach, unlike its actions with "point" sources. Rather, when it added Section 319 to the CWA in 1987, it created a federal grant program that provides money to states, tribes, and territories for the development and implementation of NPS management programs. Under the Clean Water Act Section 319, states, territories, and delegated tribes are required to develop nonpoint source pollution management programs (if they wish to receive 319 funds).

11 WATER QUALITY Section 404 Dredge & Fill Permits 11 Regulates the placement of dredged or fill materials into wetlands and other waters of the United States. U. S. Corps of Engineers issues the permit jointly with EPA. Section 404 deals with one broad type of pollution -- placement of dredged or fill material into "waters of the United States". Wetlands are one component of "waters of the United States;" however, there are numerous other types -- intermittent streams, small perennial streams, rivers, lakes, bays, estuaries, and portions of the oceans..

12 WATER QUALITY Section 401 State WQ Certification 12 Section 401(a) of the CWA requires that before issuing a license or permit for any discharge to waters of the United States, a federal agency must obtain from the state in which the proposed project is located, a certification that the discharge is consistent with the CWA, including attainment of applicable state water quality standards. (Downstream states whose water quality may be affected can enter the 401 process.) CWA provisions to which Section 401 certification applies include 404 permits from the Corps of Engineers and EPA-issued NPDES permits.

13 WATER QUALITY State Revolving Loan Fund 13 EPA provides annual capitalization grants to states, who in turn provide low interest loans for a wide variety of water quality projects. States must match the federal funds with $1 for every $5 (20 percent match). As a result of federal capitalization grants, state match, loan repayments, and leverage bonds, the total amount of assets in all the CWSRFs is approaching $40 billion. Between $3 and $4 billion is loaned annually from CWSRFs nationwide. Territories must match the federal funds with a 20 percent match, while Indian tribes are not required to provide a match.

14 WATER QUALITY Treatment Plant Location 14 Wastewater Treatment Plants & Water Treatment Plants Both Require Permits from the State Both have to be protected from 100-year floods NIMBY Wastewater Treatment Plants Located downwind and away from residential areas Located at lowest elevation in sewer system to promote gravity flow Located downstream from water treatment intake Discharge at approved stream location & with approved treatment Water Treatment Plants Located near acceptable water resource Intake quantities are limited for small resources or lakes Water quality of intake varies with weather

15 WATER QUALITY Treatment Objectives 15 Wastewater Treatment Objectives by Regulation Effluent Limitations BOD5 30 mg/l TSS 30 mg/l Maximum Others ph, organics, toxicity, COD Water Treatment Objectives by Regulation Effluent Limitations 0 Fecal Coliform, pathogenic bacteria Insignificant solids very low turbidity No taste and odor problems Insignificant organics, toxicity Bottled water regulated by Food & Drug Administration

16 WATER QUALITY Water Quality Sampling 16 Water Quality Sampling Surface Water Sampling One Upstream One Downstream Treatment Plant Site Effluent Sampling Stream Flow

17 WATER QUALITY Water Quality Sampling 17 Example Problem A treatment site is bordered on the east side by one stream and on the west side by another stream. How many water quality monitoring stations would be required if discharges are to both streams? a) 1 b) 2 c) 3 d) 4 e) 5

18 WATER QUALITY Groundwater Sampling 18 Groundwater Sampling Gradient Flow Direction One Upgradient Well Three Downgradient Wells Treatment Plant Site

19 WATER QUALITY Groundwater Sampling 19 Example Problem There are no streams adjacent to a treatment site. How many groundwater monitoring stations are required? a) 0 b) 1 c) 2 d) 3 e) 4

20 WASTEWATER TREATMENT Useful Conversion Factors 1 cubic foot = 7.48 gallons 1 MGD = cfs 1 cfs = Million gallons / day 1 mg/l = 1 ppm 1 mg/l = 8.34 pounds / million gallons Design Flows MGD Average Annual Design Flow = Actual or 100 MGD for new systems Peak Hourly Design Flow = 1.5 to 4.5 times the Average Annual Design Flow Peaks occur during high groundwater and rainfall events

21 WASTEWATER TREATMENT 21 Design Flow 10 States Stds. For 100,000 pop. Plug in 100 into the below formula, and the peak ratio would be divided by = 2.0, which checks with above curve.

22 Selected 10-States Standards for Wastewater Treatment 14

23 Flow from sewers 100 gal/cap/day WASTEWATER TREATMENT Flow from Sewers 23 Actual Average Flow is 100 gal/cap/day Actual Infiltration/Inflow is an additional percent Peak flow multiplier from graph not required with actual I/I data Example Problem A city with a population of 10,000 has an additional infiltration flow of 10% and an inflow of 150%. What is the design flow for this city based on actual flows? a) 1 MGD b) 1.6 MGD c) 2.6 MGD d) 3.0 MGD e) None of the above

24 Flow from sewers 100 gal/cap/day WASTEWATER TREATMENT Basic Flow Diagram 24 Bar Screen Settling Tank Aeration Tank Clarifier Chlorinator To Stream To Sludge Treatment Recycle Biomass Clarifier required for tertiary treatment only

25 Flow from sewers 100 gal/cap/day WASTEWATER TREATMENT Bar Screen 25 Bar Screen Settling Tank Aeration Tank Clarifier Chlorinator To Stream To Sludge Treatment Recycle Biomass All racks and screens shall have openings less than 1.75 wide. The smallest opening for manually cleaned screens is 1.0, and for automatically cleaned screens is Flow velocity should be 1.25 to 3.0 fps.

26 Flow from sewers 100 gal/cap/day WASTEWATER TREATMENT Settling Tank 26 Bar Screen Settling Tank Aeration Tank Clarifier Chlorinator To Stream To Sludge Treatment Recycle Biomass Multiple units required for flows > 100,000 gpd Depth should be 7 or greater, use 10 if not given Maximum peak overflow rate 1500 gpd/ft 2 Maximum weir loading 10,000 15,000 gpd/ft Length should be 4 times width

27 WASTEWATER TREATMENT Settling Tank 27 Operational Concerns Floating Solids Solid build-up in tank bottom

28 WASTEWATER TREATMENT Settling Tank Problem 28 Formula for calculation of tank size for settling tanks and clarifiers. Surface Area of Tank = Design flow Overflow Rate

29 WASTEWATER TREATMENT Settling Tank Problem 29 Given a peak hourly design flow of 2 MGD in a conventional activated sludge plant: (Note: Peak design flow is given) Calculate the dimensions and volume of the settling tank Flow = 2 MGD; overflow rate for settling tank is 1500 gpd/ft 2 ; length 4 times width; use 10 feet deep Surface area of settling tank = Flow / Overflow Rate = 2 MGD / 1500 gpd/ft 2 = 1333 sq ft Surface area = 4x times x = 1333 sq ft; therefore, x = = width and 4x = 73 feet =length Volume = Width x length x depth = x 73 x 10 = 13,323 cu ft Volume = 13,323 cu ft x 7.48 gals/cu ft = 99,656 gals

30 WASTEWATER TREATMENT Settling Tank Problem 30 Problem What are the dimensions of a settling tank for a city of 10,000 population and a peak 2 times average daily flow? Design flow = 10,000 x 2(100 gallons/capita/day) = 2,000,000 gallons/day or 2 MGD. Surface Area of Tank = 2,000,000 gals/day = 1,333 sq ft 1500 gpd/sq ft Surface Area = 4w x w 1,333 sq ft = 4w2 w = ft l = 4 x w = ft d = 10 ft

31 Flow from sewers 100 gal/cap/day WASTEWATER TREATMENT Aeration Tank 31 Bar Screen Settling Tank Aeration Tank Clarifier Chlorinator To Stream To Sludge Treatment Recycle Biomass Activated sludge processes Conventional, Step, Contact, t D 3-8 hours Extended Aeration, t D 24 hours Aeration tank depths are feet or overflow rate t D detention time Minimum of two tanks, length 4 times width Dissolved oxygen above 2 mg/l Aeration rate 1500 cubic feet oxygen per pound of BOD 5

32 Operational Concerns Small bubbles at suface Brown Color Tan Color Black Color WASTEWATER TREATMENT Aeration Tank 32

33 WASTEWATER TREATMENT Aeration Tank 33 An 1.0 MGD activated sludge plant has an influent BOD 5 of 200 mg/l. How many cubic feet of oxygen per day is required in the aeration tank? (Note: Plant size is given, therefore, peak multiplier not required) 1.0 MGD of water weighs 8.34 lbs/gal x 1,000,000 = 8,340,000 lbs 200 mg/l BOD 5 = 200 ppm Weight of BOD 5 = 200 ppm = BOD / 8.34 million lbs BOD = 8.34 million lbs x 200 lbs/million lbs = 1668 lbs (Or use conversion factor 1 mg/l = 8.34 pounds/mg) Oxygen required = 1500 cf/lb BOD x 1668 lbs BOD = 2.5 million cf

34 WASTEWATER TREATMENT Aeration Tank Problem 34 Derivation of formula for calculation of aeration tank volume. Q (flow) = V (velocity) x A ( area) cfs = ft/sec x sq ft cfs = ft 3 /sec Flow = Volume/Time Volume = Q (Design Flow) x Time (Detention Time or t D ) Problem. What is the aeration tank volume in cubic feet for an activated sludge plant with a peak hourly design flow of 2.0 MGD? Assume 6 hour detention time. a) 77,845 b) 66,845 c) 32,750 d) 12,000,000 e) 500,000

35 WASTEWATER TREATMENT Aeration Tank Problem 35 Given a peak hourly design flow of 2 MGD in a conventional activated sludge plant: Calculate the volume of the aeration tank Use 6 hour detention time (td) and the formula Volume = Flow x td Volume = 2 MGD x 6 hours Volume = 2 x 10 6 gallons/day x cu ft / 7.48 gals x 6 hours x day/24 hours = 66,845 cu ft

36 Flow from sewers 100 gal/cap/day WASTEWATER TREATMENT Clarifier 36 Bar Screen Settling Tank Aeration Tank Clarifier Chlorinator To Stream To Sludge Treatment Recycle Biomass Required for tertiary treatment only Surface settling rate 1000 gpd/ft 2 for extended aeration Surface settling rate 1200 gpd/ft 2 for all others

37 WASTEWATER TREATMENT Aerial View of Plant 37

38 WASTEWATER TREATMENT Clarifier 38 Operational Concerns Floating Solids Foaming Pin Floc

39 WASTEWATER TREATMENT Clarifier 39 Example Problem An activated sludge plant with a 2.0 MGD peak hourly design flow requires a clarifier for tertiary treatment. What is the radius of the circular clarifier? a) 46 feet b) 14 feet c) 18 feet d) 30 feet e) 23 feet

40 WASTEWATER TREATMENT Clarifier 40 Given a peak design flow of 2 MGD in a conventional activated sludge plant: Calculate the dimensions and volume of the clarifier Settling or overflow rate = 1200 gpd/sq ft; use 7 foot depth Surface area of settling tank = Flow / Settling rate = 2 MGD / 1200 gpd/sq ft = 1667 sq ft Surface area = 3.14 r 2 ; solving for r = 23 feet radius clarifier tank with 7 foot depth Volume = Surface Area x depth = 1667 sq ft x 7 ft = 11,669 cu ft

41 Flow from sewers 100 gal/cap/day WASTEWATER TREATMENT Chlorinator 41 Bar Screen Settling Tank Aeration Tank Clarifier Chlorinator To Stream To Sludge Treatment Recycle Biomass 15 minute contact period (t D ) required 6 mg/l chlorine for tertiary plant 8 mg/l chlorine for secondary plant 10 mg/l chlorine for extended air plant

42 WASTEWATER TREATMENT Chlorinator 42 Example Problem What is the volume of the chlorinator for a 10 cfs (peak design flow) wastewater treatment plant? a) 150 cubic feet b) 748 cubic feet c) 9000 cubic feet d) 900 cubic feet e) 1500 cubic feet

43 WASTEWATER TREATMENT Chlorinator 43 Example Problem What is the volume of the chlorinator for a 10 cfs (peak design flow) wastewater treatment plant? Volume = Qt D Volume = 10cfs x 15 minutes x 60 sec/1 min = 9000 cubic feet

44 Flow from sewers 100 gal/cap/day WATER QUALITY To Stream 44 Bar Screen Settling Tank Aeration Tank Clarifier Chlorinator To Stream To Sludge Treatment Recycle Biomass Secondary treatment requires 30 mg/l TSS and 30 mg/l BOD Tertiary treatment requires 20 mg/l TSS and 20 mg/l BOD Advanced treatment requires 10 mg/l TSS and 10 mg/l BOD TSS Total Suspended Solids BOD Biochemical Oxygen Demand Toxicity LC50% Fathead Minnow (Pimephales Promelas) Water Flea ( Daphnia Magna)

45 WASTEWATER TREATMENT Sludge Treatment/Disposal 45 Sludge Source Waste activated sludge -- no primary settling Primary plus waste activated sludge Aerobic Treatment Volume/Population Equivalent ft 3 /P.E. (m 3 /P.E.) 4.5 (0.13)* 4.0 (0.11)* Waste activated sludge exclusive of primary sludge 2.0 (0.06)* Extended aeration activated sludge 3.0 (0.09) Primary plus attached growth biological reactor sludge 3.0 (0.09) Sewage sludge is treated by aerobic or anaerobic treatment Sludge drying beds requires 2 ft 2 /capita Vacuum belts are also used to dewater sludge Treated and dried sludge is disposed in sanitary landfills or may be land spread

46 WASTEWATER TREATMENT Sludge Treatment/Disposal 46 Treatment plants normally reduce the sludge volume by aerobic treatment before the waste sludge is sent to drying beds. What is the volume of aerobic treatment units for a 0.2 MGD plant? Assume primary plus waste activated sludge = 4.0 cubic feet/population Volume of aerobic digestor = 2000 population X 4.0 cf/pop = 8,000 cubic feet A 0.2 MGD plant requires how many square feet of drying beds? Equivalent population = 0.2 MGD / 100 gallons/cap/day = 2000 population Drying beds req d = 2000 pop x 2 sq ft/cap = 4,000 sq ft

47 WATER QUALITY BOD Influent/Effluent Quality 47 Biochemical Oxygen Demand (BOD 5 ) Ten 10-ml samples of wastewater are placed in 300-ml bottles, and distilled water is added to the bottles for a total of 300-ml of liquid. Five of the bottles are titrated immediately and dissolved oxygen is 7.1 mg/l. The other five bottle are incubated for 5 days, after which the average dissolved oxygen is 3.7 mg/l. What is the 5-day BOD and the ultimate BOD, assuming Kd = 0.13? What is the ultimate BOD if Kd = 0.1? 1. BOD 5 = DOi DOf = = 102 mg/l. Vs/(Vs +Vd) 10/(300) 2. BODu = BOD 5 = 102 = 131 mg/l (-Kdt) 1-10 (-0.13)(5) 3. BODu = 1.47 BOD 5 (Approximate if Kd = 0.1) = 1.47 x 102 = 144 mg/l. Note: BOD of 100 mg/l is considered a weak effluent BOD of mg/l is considered a medium strength effluent BOD above 300 mg/l is a strong effluent.

48 WATER QUALITY BOD & DO in Streams 48 BOD and Dissolved Oxygen Effluent to Streams A treatment plant discharges 15 cfs with 45 mg/l BOD5, 2.9 mg/l DO. The receiving stream has a flow of 120 cfs with 4 mg/l BOD5 and 8.3 mg/l of DO. Find the stream BOD5 and DO immediately after the wastewater effluent discharges into the stream. For BOD and DO, the final concentration = Cf = C1Q1 + C2Q2 Q1 +Q2 BOD5 final = 45x15 + 4x120 = 8.56 mg/l DO final = 2.9x x120 = 7.7 mg/l

49 WATER TREATMENT

50 WATER TREATMENT 50 Design Flows Design Flows Average Daily Flow = Actual or 165 gpcd (includes fire, ind, etc) Peak Flow = Actual peak or 1.5 to 3.5 times the ave. daily flow Average Flows (gals/cap/day) Domestic 70 Peak Month = 1.5 Average Day Commercial 25 Maximum Day = 2.0 x Ave Day Industrial 45 Peak Hour = 2-4 x Ave Day Public 15 Peaks occur during summer Losses 10 Total 165

51 Water Supply from Stream/Lakes WATER TREATMENT Flow Diagram 51 Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users

52 Water Supply from WATER QUALITY Water Supply 52 Stream/Lakes Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users Water supplies such as rivers, lakes, etc. are tested for parameters such as: Acidity and alkalinity Hardness Iron and Manganese Fluoride and Chloride Phosphorus and Nitrogen Color and Turbidity Suspended and Dissolved Solids Water-Borne Diseases

53 Water Supply from Stream/Lakes WATER TREATMENT Bar Screen 53 Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users All racks and screens shall have openings less than 1.75 wide. The smallest opening for manually cleaned screens is 1.0, and for automatically cleaned screens is Flow velocity should be 1.25 to 3.0 fps.

54 Water Supply from Stream/Lakes WATER TREATMENT Mix Tank 54 Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users Chemicals Added: Calcium Carbonate (Lime) Aluminum Sulfate (Alum) Activated Carbon Chemicals are added to a mix tank which has a detention time of seconds. Calcium carbonate is added for coagulation and ph adjustment. Aluminum sulfate is added when turbidity is high. Activated carbon is added for taste and odor problems.

55 WATER TREATMENT Mix Tank 55

56 WATER TREATMENT Mix Tank 56 Example Problem For a city of 5,000 population & peak flow of 165 gpcd calculate the following: Mix tank size and volume Flow = 165 gpcd x 5,000 pop. = 825,000 gallons per day Volume = Flow x td = 825,000 gpd x 1 minute x hour/60 minutes x day /24 hours = 573 gallons Volume = 573 gallons x cu ft /7.48 gals = 77 cubic feet Size so diameter of tank is approximately the same as height of tank or height = 2 x radius Volume = 77 cubic feet = 3.14r 2 x 2r; solving for r = 2.3 feet; diameter and height = 4.6 ft.

57 WATER QUALITY Hardness & Alkalinity 57 HARDNESS measures the presence of Mg++, Ca++, Fe++ and other multi-valent positive ions. ALKALINITY measures the presence of HCO3-,SO4--,Cl-,NO3-,OH-. If Hardness and Alkalinity are the same, then there are no negative ions present and there is no non-carbonate hardness. If hardness is greater than alkalinity, non-carbonate hardness is present. If hardness is less than alkalinity, then all hardness is bicarbonate hardness.

58 WATER TREATMENT Hardness & Alkalinity Table 58

59 WATER TREATMENT Hardness Problems 59 Hardness Removal Hardness as CaCO 3 in water is usually caused by calcium (Ca), magnesium (Mg), aluminum (Al), and iron(fe). Tables are given in water supply engineering in the Civil Engineering Reference Manual to convert these metals to calcium carbonate (CaCO 3 ) such as: Appendix A. Conversions from mg/l as a Substance to mg/l as CaCO 3. Substance Factor Al 5.56 Ca 2.50 Fe 1.79 Mg 4.10 Example problem: What is the total hardness (as CaCO 3 ) of water containing 0.5 mg/l Al, 80.2 mg/l Ca, 1.0 mg/l Fe, and 24.3 mg/l Mg? Total Hardness = Sum (Each Substance concentration X conversion factor in table). Total Hardness = 0.5x x x x4.10 = = mg/l

60 WATER TREATMENT Coagulants 60 Coagulants are chemicals added to mixing units to flocculate suspended and colloidal solids and promote settling. Alum, Al2(SO4)3.14H20 is the most common coagulant. The usual dosage is 10 mg/l to 40 mg/l. Alum reacts with alkalinity to form an aluminum hydroxide floc. Alum is commonly added to the mixing unit during periods of high turbidity, and also in clarifiers. Polymers are long-chained, charged starches and polysaccharides that attract solids and promote settling. Polymers are commonly used in clarifiers. Alum and polymers cause floating problems in high concentrations.

61 WATER TREATMENT Mix Tank 61 For a city of 5000 population, how much alum on average is required per day in pounds if concentration is 10 mg/l Flow = 5000 pop x 165 gal/cap/day = 825,000 gpd Convert 10 mg/l = 10 ppm Alum required per day = 825,000 gpd x 8.34 lbs/gal x 10 ppm = 68.8 pounds per day

62 WATER TREATMENT Water Softening 62 Water softening is accomplished with lime and soda ash to precipitate calcium an magnesium ions. Lime (CaO) or hydrated lime is added to remove calcium and magnesium. Lime is added to water that has little turbidity, while lime and alum combined is added to water with turbidity problems. Lime is added in concentrations of 10 to 50 mg/l dosages depending upon hardness levels and desired softness. Soda ash, Na2CO3, is added to remove sulfates and chlorides.

63 WATER TREATMENT Taste & Odor Removal 63 Taste and odor problems may be caused sulfides, decaying organic matter such as algae, agricultural runoff chemicals, and various other sources. Aeration is used to remove hydrogen sulfide odors. Activated carbon is commonly used to remove most tastes and odors. Activated carbon is usually added in dosages of 2 to 10 mg/l. Chlorination residuals will reduce organic odors by oxidation. However, excess chorine residual will create taste and odors.

64 Water Supply from Stream/Lakes WATER TREATMENT Settling Tank 64 Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users Settling tanks have a surface loading rate of gpd/sq ft. Length is 4 times width Depth of 10 feet

65 WATER TREATMENT Settling Tank 65 Example Problem What are the dimensions of a settling tank for a 1.5 MGD plant? Surface Area = Q/Overflow Rate = 1.5 MGD/1000 gpd/sq ft Surface Area = 1,500 square feet w x 4w = 1500 square feet 4w 2 = 1500 sq ft w = 19.4 ft l = 77.5 ft d = 10 ft

66 Water Supply from Stream/Lakes WATER TREATMENT Clarifier 66 Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users Clarifiers often have light small particles that settle slowing Too much alum can cause floating of solids Clarifiers have a settling rate of 1400 gpd / sq ft Depth of Clarifier feet

67 WATER TREATMENT Clarifier 67 Example Problem What is the radius of a clarifier for a 1.5 MGD plant? Surface Area = Q/Overflow rate = 1.5 MGD/1400 gpd/sq ft = 1071 sq ft Radius 2 = Area / 3.14 r = 18.5 feet

68 Water Supply from Stream/Lakes WATER TREATMENT Filters 68 Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users Sand and other media filters are used to remove suspended solids Slow sand filters have surface loadings of 2 gpm/sq ft Rapid sand filters have surface loadings of 4 gpm/sq ft

69 WATER TREATMENT Filters 69 Example Problem For a city of 5,000 population and a peak factor of 2 calculate the following: (b) Rapid sand filter surface area Surface Area = 5,000 pop x 165 gpcd x 2 /4 gpm/sq ft x 1 hr/60min x 1day/24hrs =286 sq ft Depth of sand filter is a minimum 3 feet

70 Water Supply from Stream/Lakes WATER TREATMENT Chlorinator 70 Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users Chlorinators add enough chlorine to provide a residual chlorine to eliminate water-borne pathogens

71 WATER TREATMENT Disinfection 71 Disinfection destroys bacteria and microorganisms. As in oxidant, it removes iron, manganese, and ammonia nitrogen. Chlorine can be added as a liquid or solid (hypochlorite). Liquid chlorine is commonly used because it is cheaper and easier to add to water. However, liquid chlorine has to be stored in an explosion proof housing, and is definitely an OSHA hazard that has caused deaths. Chlorine is added in 1 to 2 mg/l dosages, with residual chlorine maintained at 0.3 mg/l or less due to taste and odor potential. Ozone is a more powerful disinfectant, but is more expensive than chlorine. However, ozone leaves no residual. Ultraviolet light is becoming popular as a disinfectant, because it eliminates safety concerns of chlorine. UV leaves no residual and some form of chlorine has to be added at the end.

72 WATER TREATMENT Chlorinator 72 Example Problem For a peak design flow of 1 cfs, what is the volume of a chlorinator if the detention time is 20 minutes? Volume = Qt D = 1 cfs x 20 min x 60 sec/min = 1200 cubic feet How many pounds of chlorine are added per day if the concentration of chlorine is maintained at 2 mg/l? 1 cfs = MGD 1 mg/l = 8.34 pounds / MG Chlorine added = 1 cfs x MGD/cfs x 2 mg/l x 8.34 pounds /MG/mg/l = 10.7 pounds/day

73 Water Supply from Stream/Lakes WATER QUALITY To Water Users 73 Bar Screen Mix Tank Settling Tank Clarifier Filters Chlorinator 165 gal/cap/day To Water Users Design for units is 165 gal/cap/day Water should have close to 0 ppm of TSS and turbidity Water should be free of bacteria Water should not have objectionable color, odor, or taste

74 GOOD LUCK ON THE EXAM!