1. Environmental Engineering CIV2257
Water Treatment
Environmental Engineering
CIV2257

2. Water Distribution

3. Water Demand Varies: Climate Economic considerations
Air conditioning, swimming pools
Economic considerations
Wealth (appliances, acreages, density)
Metering (60% of non-metered demand)
Lawn / Landscape irrigation
Can reach 50% – 75% of demand
Season & time of day / week
Water Pressure
25 psig to 45 psig increases consumption by 30%
Leaks will also affect average demand.

5. Range [litres/day/person]
Water Demand
Range [litres/day/person]
Average
Yearly Average
425
Mean Winter Consumption
380
Mean Summer Consumption
650
Maximum Daily Use
600 –
875
Maximum Hourly Use
750 –
1500
Table 6-1 Hammer & Hammer

6. Water Demand Range Laundering 75 – 150 l / load Showering
75 – 100 liters
Dish Washing
50 – 100 l / day
Toilet
10 – 30 l / flush
Lawn Watering
2.5 – 17.5 l /m²/week

9. Distribution Size
For designing wells, piping, treatment, pumping, & storage,
Typically designed for peak daily demand plus fire flow.
Hourly variations are handled by storage.
Fire flow depends on codes.
Distribution systems typically operate at 65 to 75 psig (450 –to 520 kPa)
Water at home should be 40 psig.
Minimum residual pressure of 20 psig during fire flow.

10. Fire Flow - Guideline C = 3.7F(A)0.5 Where: C = liters per second
F = Classification of construction
Class 1: F = 1.5 for wood frame
Class 2: F = 1 for ordinary
Class 3: F = 0.8 for noncombustible
A = area of building in square meters.
Maximum flows are typically 500l/s for Class 1
Sustained for 3 hours at approximately 220 l/s
p.164 Hammer & Hammer

11. Distribution Systems
Gridiron distribution system with an arterial network on a system of mains.
Avoid dead-end distribution systems.

12. Ductile Pipe Sizes

13. Burying Ductile Pipe

14. Ductile-Iron Pipe Joints

15. PVC Bell & Spigot Compression-Type Joint

16. Water Treatment

17. Water Sources Concerns: Sources:
Pollution and eutrophication depending on agricultural practices, sewer discharge, river development, season of year, & climatic conditions.
Sources:
Lakes & reservoirs
Rivers
Groundwater

18. Industrial chemicals, plastics, paints, pesticides
Contaminant
Health Effect
Primary
MCL [mg/l]
Typical Source
Aldicarb
Nervous System
0.003
Insecticide
Benzene
Possible Cancer
0.005
Industrial chemicals, plastics, paints, pesticides
Carbon Tetrachloride
Cleaning Chemicals
Endrin
0.002
Pentachlorophenol
Possible Cancer,
Liver
0.001
Wood preservative
Vinyl Chlorides
PVC pipe
Xylene
Liver, Kidney 10
Gasoline, paint, ink, detergent
Primary MCLs (organic)

19. Bitter metallic taste, staining Manganese 0.05 Taste, black staining
Contaminant
SecondaryMCL [mg/l]
Effect on Water
Aluminum
Discoloration
Chloride
250
Salty taste
Copper 1
Metallic taste
Foaming Agents
0.5
Frothy
Iron
0.3
Bitter metallic taste, staining
Manganese
0.05
Taste, black staining pH
6.5 – 8.5
Low pH – bitter taste, corrosion
High pH – slippery feel, soda taste
Total Dissolved Solids
Taste, indicator of corrosivity
Lead 5
Secondary MCLs palatability

20. Lake or Reservoir Supply

22. River Supply

23. Groundwater Supply
Deep-well supply can be disinfected for protection against potential contamination.
Dissolved iron and manganese can be removed by oxidation with chlorine or potassium permanganate and the precipitates filtered.
Excessive hardness may be removed by precipitation softening using lime or soda ash. Carbon dioxide is added to stabilized the water before final filtration.
Aeration is a common first step to strip out dissolved gases and add oxygen.

24. Groundwater Supply Potassium Permaganate can act as disinfectant.
Lime raises the pH, carbon dioxide brings it back down. Lime will react with water and precipitate out hardness as well as TDS.

26. Sludge Disposal

27. Mixing & Flocculation Mixing changer with baffles and impellers.
Suspended propeller.
Static mixing element for in-line mixing.
Hydraulic mixing upstream of a centrifugal pump.

28. Mixing & Flocculation Mixing occurs in 10 to 30 seconds
Chemical (coagulant) has positive charged sites to grab onto negatively charged dirt. Some negatively charged chemicals may be added to bind flocs together to make bigger flocs.

29. Flocculation Basins
Flow from inlet to outlet should be designed to prevent short-circuiting and destruction of the floc.
Flow should be maintained between 0.5 ft/min to 1.5 ft/min, with a detention time of at least 30 minutes.
Agitators shall have variable speeds for optimum slow speeds (0.5 – 3.0 ft/min at the paddle)

30. Baffled Flocculator

32. http://www. cityofmesa

33. Flocculation Time (based on chemical concentration)
t = V/Q = 1/k * ln (Co/Ct)
Where: V = volume of basin
Q = quantity of flow
k = rate constant
Co = influent reactant concentration
Ct = effluent reaction concentration
(remember a minimum of 30 minutes is recommended)

34. Clarification (Sedimentation)
Removes particulate matter, chemical flocs, and precipitates through gravity settling.
Detention time
Overflow rate
Weir loading
Horizontal velocity (rectangular tanks)

35. Stokes’ Law vs = g(ρs - ρ) d² / 18μ Where vs = Settling velocity [m/s]
ρs = Density of particle [kg/m³]
ρ = Density of water [kg/m³]
d = Diameter of particle [m]
μ = Dynamic viscosity [Pa*s]

36. Settling of Small Particles
Suspended
Colloidal
Dissolved
Size [mm] 10 1
sand
0.1
hair
0.01
silt
0.001
0.0001
tobacco
smoke
Polio
virus
Floc
Algae
Turbidity
Bacteria
Colloidal Clay
Colour
Virus
Molecules / Atoms
Time to settle 3m in still water
0.3 s
3 s
38 s
33 m
55 hr
230 d
6.3 y
63 y

37. Detention Time t = V / Q Where t = detention time [hours]
V = basin volume [m³]
Q = Average hourly flow [m³/hr]
(or mean daily flow / 24 hours)

38. Overflow Rate
Vo = Q / A
Where Vo = Overflow rate or surface loading [m³/m²/day] Q = Average daily flow [m³/day]
A = Total surface of the basin [m²]

39. Weir Loading Weir Loading = Q / weir length
Where Weir Loading [m³/d/m length]
Q = Average daily flow [m³/day]
Weir Length [m]

40. Sedimentation
The velocity of the solids must be greater (downward) than the upward flowing water.

41. http://www. sanitaryengineering. tudelft

42. Rectangular Sedimentation Tank

44. Clarification (Sedimentation)
General Standards:
Detention time > 4 hrs
Maximum horizontal velocity = 0.5 ft/minute
Weir Loading < 250 m³/m/d
Overflow Rate = 20 to 33 m³/m²/d
A pre-sedimentation basin to settle heavy solids before treatment typically uses a circular design with a detention time of 3 hours.

45. Flocculation – Clarifier Unit
Lethbridge plant holds 4.5 million litres (90ft x 90 ft and 20 feet deep)
Top 3ft of Lethbridge clarifier has tubes at an angle to hold down floc (as an additional filter) and extend the travel distance. “Easier to clean dirty water than clean water” due to floc acting as a filter.

46. http://web. cecs. pdx. edu/~wellss/PSU_WQ/Willamette/photog/imageC1K

47. US Filter
US Filter

48. Tube Settlers

49. Filtration
Chemically assisted filtration – add some positively charged polymers to help the sand adsorb small particles, including cysts.

50. Filtration

51. Filtration
Granular-media gravity filters remove particles that overflow during sedimentation.
Down flow at a typical rate ranging between 1.4 to 6.8 liters/m²/s
Ideally, non-settled coagulated floc is held in the bed to filter even smaller particulates
Backwash is used to clean the filter with sediments being further treated.
Backwashing aids like compressed air or mechanical agitators help break up the bed during cleaning.
Filters are commonly cleaned every day for 5 to 10 minutes at a flow of 10 liters / square meter / second.
Initial filtered water may be wasted for 3 to 5 minutes (2% to 4% of filtered water).

52. Gravity Filter Operation
1 & 4 are open during filtration. The liquid level is enough to overcome pressure drop through the filter media and piping (typically 3 to 4 feet to a maximum of 9 or 12 feet, depending on the height of the filter).
During cleaning (when the pressure drop reaches around 9 feet), 1 & 4 are closed and 2 is opened to drain the filter; 5 is then opened and backwashed through the filter media, expanding the media by about 50 per cent; once clean, 5 & 2 are closed and 1 & 3 are opened (leaving 4 closed). The first few minutes of water are disposed of, then 3 is closed and 4 opened.

53. Filtration

54. Other Types of Filters Pressure filters Mechanical filters
Water is forced through the filter media using pressure, and backwashed by reversing the flow
Used in small plants processing groundwater.
Mechanical filters
Using fabrics that can remove microscopic organisms and debris
Used in industrial treatment or final polishing of wastewater effluents.

56. Treatment Chemicals

57. Coagulation & Flocculation
Sensitive to:
Nature of turbidity-producing substances
Colloidal solids from land erosion, decaying vegetation, microorganisms, etc.
Dosage
pH of the water.
Jar tests used to estimate optimum chemical dosages.

58. Coagulants Aluminum-based: Iron-based:
0.50 mg/l alkalinity reacts with 1.0 mg/l of alum.
5 to 50 mg/l is a typical dosage, pH limits of 5.5 to 8.0
Aluminum sulfate
Sodium aluminate ($, effective for secondary coagulation).
Potash alum
Ammonia alum
Iron-based:
Effective over a wide pH range, especially lime softening.
Ferric sulfate
Ferrous sulfate
Chlorinated ferrous sulfate
Ferric chloride

59. Coagulant Aids
Polymers to stabilized fragile flocs or to coagulate slow-settling precipitates.
Typical dosage of 0.1 to 1.0 mg/l
Makes dewatering waste-sludge easier and reduces volume of waste overall.

60. Precipitation Softening
Uses lime (CaO) and soda ash (Na2CO3) to remove calcium and magnesium in solution.
Other benefits include bactericidal action, iron removal, and clarification of turbid surface waters.
CO2 can be applied for recarbonation to lower the pH.
Carbonates are removed by lime
Non-carbonate hardness (calcium & magnesium sulfates and chlorides) required soda ash.

61. Lime Softening (Single-Stage Calcium Carbonate)
Add a second flocculator-clarifier (with soda ash) and recarbonation before the filter for a two-stage excess lime softening plant

62. Corrosion
Iron pipe & valves are corroded causing degradation ($) and unaesthetic taste / discoloration.
Cathodic protection is used to reduce corrosion by:
Sacrificial galvanic anode
magnesium or zinc
Electrolytic anode energized by an external source of direct current.

63. Fluoridation Reduces dental caries. 0.6 to 1.2 mg/l an optimum range.
Too much causes dental fluorosis (mottling)
0.6 to 1.2 mg/l an optimum range.

64. Chlorination For disinfection For oxidation
destroying pathogens and nuisance microorganisms
For oxidation
iron and manganese removal and destruction of taste & odor compounds and hydrogen sulfide
Enteric bacteria and viruses may be protected in suspended and colloidal solids not filtered from the water.

65. Chlorination Effectiveness depends upon: Dosage Contact Time Turbidity
‘hides’ pathogen from chlorine
Other reactive species
like ammonia, which consumes the disinfectant pH
effective less than 7.5
Water Temperature
cooler water slows the rate of disinfection

66. Summary
Water distribution systems must be designed for demand plus fire flow.
Water treatment plants including flocculation, clarification and filtration is required to reduce alkalinity.
Chemical treatment can be used to soften water and eliminate pathogens.