1. Environmental Engineering 343
Philadelphia University
Faculty of Engineering
Department of Civil Engineering
First Semester, 2013/2014
Environmental Engineering 343
Lecture 8:
Water Treatment (3)
Filtration & Disinfection

2. Filtration
Filtration is a process for separating suspended or colloidal impurities from water by passing through a porous medium, usually a bed of sand or other medium.
Settled water (Sedimentation effluent) turbidity range 1-10 TU – due to residue of flocs particles. So turbidity need to be reduce to less than 0.3
Common materials for granular bed filters:
Sand (slow, rapid or high)
Anthracite coal
Dual media (Coal plus sand)
Mixed media (coal, sand & garnet)

3. Filtration- Filter media
Loading rate
Where,
Vo = water velocity (m/s)
Q = water flow (m3/s)
Ac= cross surface area (m2)
Example
Installing a Sand filter after the sedimentation tank . The design loading rate to the filter is 200m3/d.m2 How much filter surface area should be provided for the design flow rate of 0.5 m3/s

4. Filtration
Purpose to reduce the turbidity from TU to less than 0.3 TU
Slow sand filters
Low filtration rate with the use of smaller sand
Filter sand is less uniform
Particles are removed on the surface of the filter (forming a mat of materials , called schmultzdecke)
Schmultzdecke forms a complex of biological community that degrade some organic compounds.
Pretreatment is not important
Require large area of land and are operator intensive
Loading rate m3/d.m2

5. Filtration Rapid sand filters ( most common)
Graded (layered) within the bed to optimize the passage of water while minimizing the passage of particulate mater
Cleaned in place by backwashing process
Pretreatment to destabilize particles is essential
Loading rate 120 up to 235 m3/d.m2
For larger loading rate, a minimum of 4 filters is suggested

6. Filtration

7. Filtration

8. Filtration Dual-media Filters
Constructed of silica sand and anthracite coal.
Depth of sand is about 0.3m and coal 0.45 m. Size and uniformity is selected to produce a distinct separation after backwashing
Disadvantage is that filtered materials are held loosely in the anthracite layer and can dislodge with sudden changes in hydraulic loading. The material can then bind to the sand layer
Loading rate up to 250 m3/d.m2 or more

9. Filtration Mixed Media Filters
The perfect filter is composed of a grading of large media at the top to small at the base. This is best achieved by the use of 3 or more media with ranging size, density and uniformity coefficient
Typical installation – Overall bed depth 0.75m; 60% anthracite; 30% silica sand; 10% garnet sand
Size range from 1.0mm anthracite to 0.15 garnet sand
Filtration rates range from 10 to 20m/hr

10. Filtration
Terminal head loss: As the filter clogs, it become very hard to force water through the bed and the filter bed must be cleaned for backwashing process
Head loss: (pressure drops) that occurs when clean water flows through a bed of clean filter media. It is important in design value to determine the overall head require to operate the filter
Backwashing process; allowing large flow of water (clean water) to be pumped to enter the filter bed. This forces the sand bed to release the colloidal particles that trapped in the pores and released and escaped with the washwater.

11. Filtration Design Key Elements
Hydraulics
Parameters to be measure during operation
The head loss across the filter
The turbidity of the effluent

14. Disinfection
Disinfection is used in water treatment to reduce pathogens (diseases-producing microorganisms) to an acceptable level

15. Disinfection- Introduction
Treatment of water with chemicals to kill bacteria”
Two objectives:
Primary disinfection : Kill any pathogen in water
Secondary (residual) disinfection : Prevent pathogen re growth in the water.
Method use :
Should be harmless and unobjectionable to the consumer
Should be able to retain a residual disinfecting effect for a long period

16. Disinfection- properties
Destroy bacteria / pathogens within a practicable period of time, over an expected range of water temperature
Effective at variable compositions, concentration and conditions of water treated.
Neither toxic to humans and domestic animals nor unpalatable
Not change water properties
Have residual in a sufficient concentration to provide protection against recontamination

17. Disinfection- properties-con’d
6) Can be determined easily, quickly, and preferably automatically.
7) Dispensable at reasonable cost
8) Safe and easy to store, transport, handle and supply
10) Not form toxic by-products due to their reactions with any naturally occurring materials in water.

18. Disinfection- Methods
Chlorination- chlorine
Ultra violet Radiation
Ozonation

19. DISINFECTION METHODS-CHLORINATION
Free chlorine disinfection
Effective and the most common application
Available in granular, powdered, liquid or gases form
Developed by using chlorine gas (Cl2), sodium hypochlorite (NaOCl) or calcium hypochlorite (Ca(OCl)2).
Reacts in water to produce dissolved chlorine gas(Cl2(aq)), hypochlorous acid (HOCl) and hypochlorite (OCl-).  

20. Disinfection –water reaction
H2O+Cl2 (g) H+ + HOCl + Cl-
HOCl H++ OCl- (pH > 8)
H++ OCl HOCl (pH < 7)
HOCl= hypochlorous acid
OCl- = hypochlorite ion
HOCl is more effective than OCl-
Chlorine gas will be injected for water pH less than 3

21. Chlorination- Ammonia Reaction
Ammonia chlorine
HOCl+NH H2O+NH2Cl (Monochloramine)
HOCl+NH2Cl H2O+NHCl2 (Dichloramine*)
HOCl+NHCl H2O+NCl3 (Trichloramine)
*These reactions depend on :
Low pH
Low Temp
Time
high Cl2 : NH3 initial concentration
In favor of dicloramine

22. Ammonia Reaction Con’d
The proportion of chloramines depends on
pH.
Temperature
Time
Initial chlorine to ammonia ratio
*Combined chlorine: Combination of chlorine with ammonia nitrogen or organic nitrogen compounds. Combined chlorine is less reactive.

23. Chlorination- Advantage
Provide chlorine residual for secondary disinfection.
Chlorine residue must be maintained in the treated water to the end user. This secondary disinfection functioned to control pathogen distribution during water distribution.
Increase lifetime of chlorine residual by adding ammonia to treated water.
Ammonia reacts with free chlorine to form chloramines (NH2Cl, NHCl2 and NCl3) which are termed combined chlorine.-
Chloramines less effective as oxidants than HOCl, seldom used as primary disinfectant. However, more persistent than free chlorine and maintain secondary disinfectant.

24. Chlorination- Disadvantage
Effectiveness is less with protozoan cysts, Giardia lamblia and Crytosporidium and virus.
Formation of halogenated disinfectant by- products (DBPs). Includes trihalomethanes (THMs) such as chloroform (CHCl3) and haloacetic acids (HAAs).
- THMs and HAAs created when free chlorine combines with natural organic substances that may still be present in the water.

25. Chlorine Effectiveness -Factors
1.Dosage – Sufficient high concentration to inactive pathogen 2.Contact time – Physical contact with pathogen for sufficient time to achieve inactivation. 3.Turbidity – Present particles (turbidity) hides pathogen from the disinfectant. 4.Other reactive species – Consume disinfectant, reduce concentration available for inactivation. 5. pH – Most effective at pH values less than Water temperature – Disinfection increases, however chlorine become less stable.

26. Disinfection - Ozone
Sweet smelling, unstable gas-Form of oxygen in which three atoms of oxygen combined to form the molecule O O+O2 O3
Air in generating equipment contain up to 13% ozone.
 Most powerful disinfectant and widely used in water
More effective against cysts and viruses than free chlorine.
Leaving no taste or odor problems.
Faster contact time
No residual remain
Not forming THM
Unaffected by the pH or the ammonia content of the water
 High cost – Construction, Operation and Maintenance

27. Disinfection - UV
Employed by submerged UV lamps into the water to be treated
Energy is absorbed by genetic material in the microorganism, interfering with their ability to reproduce and survive.
Multiple lamps used to provide greater coverage
Ability of UV lights to pass through the water to get the target organism.
Much higher energy level than visible light
Potential to inactivate pathogens.
Performs well against both bacteria and viruses.
Leaves no residual protection for distribution system.
High cost