1. MTU Department of Civil & Environmental Engineering
CE3503
Environmental
Engineering
Water Treatment
Dr. Martin T. Auer
MTU Department of Civil & Environmental Engineering

2. Drinking Water Treatment Objectives
Potable: safe to drink - may be consumed with low risk of immediate or long term harm.
Palatable: pleasant to taste

3. London
1854

4. Philadelphia

5. Milwaukee
Cryptosporidium
,000 – 104 Dead

6. U.S. EPA Standards National Primary Drinking Water Regulations
Microorganisms
Disinfectants & Disinfection Byproducts
Inorganic Chemicals
Organic Chemicals
Radionuclides
Enforceable

7. U.S. EPA Standards National Primary Drinking Water Regulations
Microorganisms
Viruses: hepatitis A, gastroenteritis
Bacteria: cholera, dysentery, legionellosis, typhoid
Protozoa: Giardia and Cryptosporidium
Turbidity: standard is 1 NTU; microorganism contamination is associated with turbidity; particles also shield microorganisms from agents of disinfection.
Indicator organisms: standard for microbial contamination is based on E. coli , a species of bacteria originating from animal or human fecal material. Most strains of E. coli are not pathogenic, but their presence indicates the presence of fecal material and thus, potentially, pathogenic microbes. No E. coli may be present in finished drinking water.

8. U.S. EPA Standards National Primary Drinking Water Regulations
Chemicals
Inorganic: arsenic, cadmium, copper, lead, mercury, nitrate
Organic: herbicides (e.g. atrazine), insecticides (methoxychlor), industrial residues (e.g. polychlorinated biphenyls, dioxin)
Radionuclides:  and  particles, radium, uranium
MCLs: Maximum Contaminant Levels

9. U.S. EPA Standards National Primary Drinking Water Regulations
Disinfectants
Chlorine
Chlorine dioxide
Chloramines
Disinfectants & Disinfection Byproducts
Trihalomethanes

10. U.S. EPA Standards Secondary Drinking Water Regulations
Cosmetic Effects (tooth color, excess fluoride)
Total Dissolved Solids (chloride, sulfate)
Taste, Odor, Color
Non-Enforceable (federally)

11. U.S. EPA Standards National Primary Drinking Water Regulations
Microorganisms
Viruses: hepatitis A, gastroenteritis
Bacteria: cholera, dysentery, legionellosis, typhoid
Protozoa: Giardia and Cryptosporidium
Turbidity: standard is 1 NTU; microorganism contamination is associated with turbidity; particles also shield microorganisms from agents of disinfection.
Indicator organisms: standard for microbial contamination is based on E. coli , a species of bacteria originating from animal or human fecal material. Most strains of E. coli are not pathogenic, but their presence indicates the presence of fecal material and thus, potentially, pathogenic microbes. No E. coli may be present in finished drinking water.

12. Drinking Water Process Train
Basic treatment for turbidity and pathogens

13. Particle Settling Velocities
Diameter (mm)
Velocity (m/s)
Sand
1.0
2x10-1
Fine sand
0.1
1x10-2
Silt
0.01
1x10-4
Clay
0.001
1x10-6
Source: Vesilind & Morgan
Stokes Law
Thus, the small, clay particles settle extremely slowly.

14. Coagulation +
Particle populations are stable because their net negative charge repels one another.
Chemicals such as alum
are added to neutralize the negative charge and destabilize the particle populations and allow them to come together, i.e. coagulate.
Addition of the chemical occurs in a flash mix of 1-3 minutes where the chemical dissolves and mixes with the raw water.
+++

15. Flocculation
The alum reacts with calcium bicarbonate naturally present in most waters to form a precipitate or floc, aluminum hydroxide.
Destabilzied smaller particles can be attracted to the floc or simply swept up by the larger particles (sweep floc) as they settle and removed from the system.
Flocculation proceeds through a slow mix of minutes.

16. Sedimentation
Sedimentation takes place over a period of 1-4 hours.

17. Disinfection Chlorination sorption
Thus above HOCl dominates below pH 7.5
and OCL- dominates above pH 7.5

18. Disinfection Design Chick’s Law sorption
The Surface Water Treatment Rule
Requires a 4-log or 99.99% removal
and

19. Disinfection Design Ct = concentration, time It = irradiance, time
The Surface Water Treatment Rule
Requires a 4-log or 99.99% removal
Design Ct = concentration, time It = irradiance, time

20. Disinfection
Residual

21. Disinfection Disinfection By-products (DBPs)
Formed through reaction of chlorine and natural organic matter (NOM) e.g. trihalomethanes such as chloroform,
Design – reduce NOM through pre-oxidation with ozone.

22. Iron and Manganese

23. Hardness Primarily Ca2+, Mg2+ Limestone: calcium carbonate, CaCO3
Dolomite: calcium magnesium carbonate, CaMg(CO3)2
The limestone formation underlying much of Miami, Florida

24. Lime – Soda Ash Process
Adding lime, Ca(OH)2
Adding soda ash, Na2CO3

25. Millenium Inorganic Chemicals
Granular Activated Carbon
The most commonly used adsorbent is granular activated carbon (GAC). These irregular particles, mm in diameter, are a char of carbon material (wood or coal). They are ‘activated’ or made more porous by exposure to steam at high temperature. Activated carbon has 1000 m2 of adsorbing surface area per gram (~ 1 teaspoon) or equivalent to that of a 40 acre farm in one handful!
Source:
Chemviron Carbon
Source:
Millenium Inorganic Chemicals
Source:
Sontheimer et al. 1988

26. The Adsorption Process
Organic chemicals are typically removed from a water supply prior to distribution through the process of adsorption:
the physical-chemical attraction of a solid material for a chemical in solution.
In adsorption, the chemical being adsorbed is termed the adsorbate and the solid to which it sorbs is the adsorbent.
Influent
stream
Effluent
stream

27. … tendency to sorb
For adsorption to be effective, the chemical must sorb strongly. Poorly soluble (hydrophobic) compounds (e.g. the components of gasoline) adsorb more strongly than highly soluble (hydrophilic) compounds (e.g. table salt). 2 4 6 8
Time (d)
Concentration
(mg/L)
Poorly sorbed
Strongly sorbed

28. … application in water treatment
In drinking water treatment, adsorption with GAC is accomplished using a packed bed column. The untreated water is introduced at the top of the column and trickles down through the GAC. Contaminants are removed en route and clean water emerges at the bottom of the column. In application, columns 6 feet in diameter and 30 feet in height are not uncommon.
Carbon
Bed
GAC columns

29. … column operation Cout
Water flows thru the column and contaminants are adsorbed. With time, the GAC becomes saturated (sorption capacity is reached) and contaminants exit the bed (breakthrough). The exhausted carbon must then be replaced.
Cin
exhaustion
Cout
Ceq
breakthrough

30. Asbestos/Arsenic/Metals Removal
Sorption with Ferric sulfate: asbestos, arsenic, cadmium, chromium, copper, lead, mercury, molybdenum, selenium, silver
Coagulation with Alum: asbestos, nickel, uranium

31. Membrane Processes

32. Ultrafiltration
polypropylene fiber
300 µm ID
500 µm OD

33. Ultrafiltration
0.2 µm nominal pore size

34. Ultrafiltration
permeate flow
raw
water in
epoxy seal

35. Ultrafiltration
contaminants
banks of fiber bundles
backwashing

36. Ultrafiltration
contaminants
backwashing

37. Home Water Treatment Reverse osmosis unit (salt) Softening by
ion exchange
(hardness)

38. Home Water Treatment Three step process:
sieve and bottom filter – rust, sand, turbidity
activated carbon filter – chlorine, color and SOCs
ion exchange resin – metals
Bottled Water: $8 /gallon
Tap Mount: $0.25 / gallon
Municipal: $ / gallon
Achieves 99.99% removal of Giardia
and Cryptosporidium cysts, but does not
remove all pathogenic organisms.