1. Source of Water

2. Sources of Water Hydrological Cycle
- Rain – Surface runoff – water storage - infiltration – ground water – evaporation – transpiration -
Rain
Surface Water
Groundwater
Aquifer
Quality of Water Supply in Hong Kong
Quality Monitoring
The quality of treated water supply in Hong Kong must conform both chemically and bacteriologically to the Guidelines for Drinking Water Quality (WHO, 1984). An extract of the relevant WHO guideline is given in table 1 and a typical analysis of treated water in Hong Kong is given in table 2.
The following groups of parameters are being analysed :
) physical : e.g. pH, conductivity, turbidity, colour, etc.
)chemical : a) inorganics e.g. nurients, ions, heavy metals etc.
b) organic e.g. trihalomethane, pesticides etc.
)biological : e.g. algae, zooplankton, macroinvertebrate, fish,
)bacterialogical : total coliform, E. Coliform, plate count
) radiological : e.g. gamma emitters.

3. Choice of Source Location of source Quantity of water available
Quality of water
Cost of the entire scheme

4. Surface water Surface water source may be further classified as:
-         lakes
-         Impounding reservoirs
-         River, streams, irrigation canals
The area where water is collected for water supply purpose is called catchment or watershed.

5. Ground Water
Aquifer
An aquifer is a layer of pervious material beneath the ground surface and underlied by impervious stratum.
Water table
The free surface of water in the aquifer is called water table
Sources
- Spring
- Wells

6. Characteristics of Ground Water
Generally ground water is clear and colorless. When water seeps down into ground, it dissolves inorganic salts.
Therefore, sometimes harmful

7. Sources of Water in Hong Kong
natural catchment
Guangdong Province of China.
Administration by Water Authority
Responsible for supply, treatment and distribution

8. Quality of Water Quality of Water Supply in Hong Kong
Quality Monitoring
The quality of treated water supply in Hong Kong must conform both chemically and bacteriologically to the Guidelines for Drinking Water Quality (WHO, 1984). An extract of the relevant WHO guideline is given in table 1 and a typical analysis of treated water in Hong Kong is given in table 2.
The following groups of parameters are being analysed :
) physical : e.g. pH, conductivity, turbidity, colour, etc.
)chemical : a) inorganics e.g. nurients, ions, heavy metals etc.
b) organic e.g. trihalomethane, pesticides etc.
)biological : e.g. algae, zooplankton, macroinvertebrate, fish,
)bacterialogical : total coliform, E. Coliform, plate count
) radiological : e.g. gamma emitters.

9. Quality Monitoring
conform both chemically and bacteriologically to the Guidelines for Drinking Water Quality (WHO, 1984).
Parameters:
Physical
Chemical : a) inorganics
b) organic
Biological
Bacterialogical
Radiological
Quality of Water Supply in Hong Kong
Quality Monitoring
The quality of treated water supply in Hong Kong must conform both chemically and bacteriologically to the Guidelines for Drinking Water Quality (WHO, 1984). An extract of the relevant WHO guideline is given in table 1 and a typical analysis of treated water in Hong Kong is given in table 2.
The following groups of parameters are being analysed :
) physical : e.g. pH, conductivity, turbidity, colour, etc.
)chemical : a) inorganics e.g. nurients, ions, heavy metals etc.
b) organic e.g. trihalomethane, pesticides etc.
)biological : e.g. algae, zooplankton, macroinvertebrate, fish,
)bacterialogical : total coliform, E. Coliform, plate count
) radiological : e.g. gamma emitters.

10. Physical : e.g. pH, conductivity, turbidity, colour, etc. Chemical :
a) inorganics e.g. nurients, ions, heavy metals etc.
b) organic e.g. trihalomethane, pesticides etc.
Biological : e.g. algae, zooplankton, macroinvertebrate, fish,
Bacterialogical : total coliform, E. Coliform, plate count
Radiological : e.g. gamma emitters.

11. Consumer Complaints
Consumers can file complaints regarding the quality of water. Typical complaints on the quality of water in Hong Kong are :
discoloured water
tastes and odours
cloudy, milky or chalky water

12. Introduction to Water Treatment

13. Why water need treatment
The water is polluted by the people inhabiting the catchment.
Water carries bacteria, some of which are pathogenic, and can cause water-borne diseases.
Factories let off water into rivers and pollute the water.
Surface run-off dissolve and minerals.

14. Impurities Physical impurities Chemical impurities
Bacteriological impurities

15. Physical impurities can affect the color, taste, odour and turbidity to the water.
Chemical impurities cause hardness in water. Excess quantities of metals and dissolved gases cause corrosion to pipes and fittings.
Bacteriological impurities are due to pathogenic bacteria which spread diseases.

16. Objectives of Water Treatment
To remove colour, objectionable taste and odour
To remove dissolved gases, dissolved and suspended impurities and harmful minerals
To remove suspended and dissolves organic impurities
To remove harmful bacteria
To make the water safe and attractive for drinking and domestic purposes

17. Components of a Treatment Plant
Intake work including pumping plant
Plain sedimentation tank
Clairifier-flocculator: (coagulation & flocculation)
Filter
Disinfecting plant
Water storage reservoir.
Pumping plant
Distribution system
Other processes Hardness (Colour, Iron and manganese, Fluoride, )

18. Treatment processes Source Pre-chlorination Flocculation Sedimentation
Filtration
Post-chlorination
Storage and pumping
Distribution system

19. Plain Sedimentation
Suspended and colloidal impurities that are settleable are separated in the sedimentation tanks by gravitation.

20. Principle of Sedimentation
The main principle of sedimentation is to allow water to rest or flow at a very slow velocity so that the heavier particles settle down due to gravity.

21. Types of Sedimentation Tanks
Sedimentation tanks can be
Horizontal flow tanks
Vertical flow tanks

22. Horizontal Flow Tanks
The direction of flow in the tank is essentially horizontal.
(a) Rectangular tanks
(b) Circular tanks
Radial flow tanks
Circumferential flow tanks

23. Vertical Flow Tanks

24. Sedimentation with coagulation
Colloidal particles which are fine particles of size finer than mm carry electrical charges on them. These are continuously in motion and will never settle down under gravity.

25. Coagulation
The process of adding certain chemicals to water in order to form an insoluble, gelatinous, flocculent precipitate for absorbing and entraining suspended and colloidal matter is called coagulation.

26. Purpose of Coagulation
The fine particles are removed rapidly and turbidity is reduced to about 20 ppm. The bacterial load also is reduced by 5%.

27. Principle of Coagulation
Floc Formation
Electric Charges
forming of a thick gelatinous precipitate which is insoluble in water and settle.
Colloidal particle possess negatively charged ions. The floc thus attracts the colloidal particles and makes settle down.

28. Coagulants The common coagulants used are: Salts of aluminium:
alum (明礬), filter alum, Sodium aluminate
Salts of iron:
Ferrous sulphate, Ferric sulphate, Ferric chloride

29. Chemistry of Coagulation
When alum is added to water, Al3+ ion will hydrolyze to different charged hydrolysis products depending on the pH :
Al(H2O)6 3+ < == > [Al(H2O)5OH] 2+ < == > [Al(H2O)3 (OH)3] (s) < ==> Al(H2O) 2(OH)4]-

30. Polyelectrolytes
Polyelectrolytes are increasingly used in water treatment as primary coagulant, flocculant coagulant aid or filter aid.
They are synthetic long-chain organic compounds which contain different monomers.
They can exhibit either positive (cationic), negative (anionic) or nonionic charge.

31. Advantages of polyelectrolytes
increase process stability and efficiency
improve water quality
improve sludge quality and reduce sludge quantity

32. Limitations of polyelectrolytes
expensive products
require careful control
improper dosing can cause serious filter problems filter blockage
require efficient mixing

33. Process of Coagulation and Sedimentation
Feeding
Mixing
Flocculation
Clarification.

34. Flocculation
Agglomeration of particles involve 3 separate mechanisms :
1. Brownian motion
2. stirring/agitating
3. Differential settling

35. Clarifying
After flocculation, the floc is allowed to settle down in basins called clarifiers. The clear water is drained out for further purification. The detention period is about 1*1/ hours.

36. Filtration
The process of filtration involves allowing the water to pass through a layers of sand called media which acts as strainers. The water is then collected by means of drains placed under the sand bed.

37. Objectives of Filtration
Remove colloidal and suspended matter remaining after sedimentation
Remove bacterial load

38. Theory of Filtration Mechanical straining Sedimentation or adsorption
Biological Metabolism
Electrolytic changes

39. Filter Sand The characteristics of the sand
Effective size : The effective size of a sand is the size of sieve, in mm, through which 10% of the sand (by weight) passes. It is usually denoted by D10.
Uniformity coefficient : This is the ratio of the size of sieve through which 60% of the sample of sand passes to the effective size of sand.

40. Classification of Filters
Gravity filters
Slow sand filters
Rapid sand filters
Pressure filters

41. Types of Filter Media configuration in Hong Kong
In Hong Kong, only rapid sand filter is used. Filtering materials can be single media filter or dual media filter.

42. Disinfecting
 The process by which harmful bacteria are destroyed to make it safe for drinking is called Disinfecting.
Chemicals used for this purpose are called disinfectants.

43. Criteria for a Good Disinfectant
Capable of destroying pathogenic organisms within the contact time available.
Should NOT change the physical and chemical characteristics
Should not be toxic
Available at reasonable cost
Should have residual concentration
Detectable in the water by simple tests
Easy in transportation and application

44. Methods of Disinfecting
Boiling water
Ozone gas treatment
Excess lime treatment
Iodine and bromine treatment
Ultraviolet rays treatment
Potassium permanganate treatment
Chlorination 

45. Chlorination The process is economical and cheap
It is harmless to human beings
It is reliable and effective
Residual chlorine can be maintained in the water
Easy to apply and ease to measure
Disadvantages of Chlorination
Formation of trihalomethanes (THMs) such as carcinogen chloroform (CHCl3)
To avoid the formation of THMs, water should be removed of organic impurities as much as possible before chorination.

46. Chemistry of Chlorination
Cl2 + H2O < == > HOCL + H+ + Cl- 
The hypochlorous acid is the prime disinfecting agent.
Depending on the pH, the following reaction can also take place
HOCl < == > H+ + OCl-
Together, HOCl and OCl- are called free available chlorine.

47. Chlorine Demand
Chlorine and its compounds are consumed by a variety of organic and inorganic materials present in water due to its oxidising power before disinfecting is achieved.
The difference between the amount of chlorine added to the water and the residual chlorine is called chlorine demand.
This depends on the amount of chlorine added, time of contact, pH and temperature.

48. Breakpoint Chlorination
Chlorine acts as oxidising agent to remove bacterial and organic matters
When chlorine is applied, it first kills the bacteria Any further addition will appear as residual chlorine increases.
After a certain point, the residual chlorine suddenly decreases with emanation of bad smell and objectionable taste. This indicates that chlorine is being used for oxidising the organic impurities.

49. Breakpoint Chlorination
Again, after some time, there is a sudden increase in residual chlorine indicating that oxidation of impurities is over.
The point at which both the demands are satisfied and residual chlorine increases is called breakpoint.
Beyond the breakpoint, any further dose of chlorine only gets accumulated. The process of adding chlorine beyond the breakpoint is called breakpoint chlorination.

50. Hardness of Water

51. Problem with Hardness in water
˙ Corrosion and incrustations in pipes
˙ Consumption of more soap
˙ Scales in boiler
˙ Bad taste in water
˙ Difficulties in dyeing industry
˙Creates bubbles in the manufacturing posses of paper making, textile finishing, ice making, etc.

52. Types of Hardness
˙Temporary hardness
˙Permanent hardness

53. Temporary hardness
˙is caused by the presence of bicarbonates of calcium and magnesium.

54. Permanent hardness is caused by the presence of sulphates,
chlorides and nitrates of calcium and
magnesium

55. Removal of Hardness Temporary hardness is removed by:
˙Boiling the water
˙Adding lime to the water

56. Removal of Hardness Permanent Hardnes ˙Lime-soda process
Zeolite process

57. Lime-soda Process
Ca(HCO3) 2+Ca(OH)2 2CaCO3 + 2 H2O

58. Zeolite Process Ca(HCO3) 2 + Na2Z  CaZ + 2NaHCO3 Reverse Process
CaZ + 2NaCl  Na2Z + CaCl

59. Miscellaneous Treatments
Removal of Iron and Manganese
Removal of Fluorides
Taste and Odour
Colour