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Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Lecture #1 Objectives:Lecture #1 Objectives:
-- Overview water treatment process Overview water treatment process
Understand water quality parametersUnderstand water quality parameters-- Understand water quality parameters Understand water quality parameters
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
1. Water treatment overview:
(1) Water sources: ….- Deep wells - relatively clean – maybe hard; - Shallow wells; rivers; lakes; reservoirs –; ; ; need more treatment.
(2) Water quality concern: - Appearance - color; odor; turbidity; solids; - Pathogens: bacteria; protozoa; viruses; helminthes; - Organic pollutants – pesticides; - Inorganic pollutants - heavy metals (Pb; As; ...); - Disinfectants and disinfection by-products; - Radionuclides;
What are major concerns of the drinking What are major concerns of the drinking water quality? water quality?
1. Bugs
2. Toxic materials
3. Solids and color
Bugs
Toxi
c m
ater
ials
Solid
s an
d col
or
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above
0% 0%0%0%
3. Solids and color
4. All above
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Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(3) Treatment methods: - Microorganisms disinfection
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Debris screening
- Heavy particles settling
- Colloid and suspended solids and some soluble pollutants p coagulation + flocculation + clarification
- Small, non-settleable particles sand filtration
- Hardness (mostly for groundwater) softening
- Dissolved organic pollutants; odors Activated carbon adsorption; air stripping; biological treatment
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Which method is used to remove small, Which method is used to remove small, nonnon--settleable particles at the end of the settleable particles at the end of the
treatment process? treatment process?
1. Sand filtration
2. GAC adsorption
San
d filtr
atio
n
GAC a
dsorp
tion
Air
strip
ping
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3. Air stripping
4. All above
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Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
2. Safe drinking water act:
(1) Drinking water standards: - To make sure the drinking water is safe;
- Only apply for public water systems y pp y p y= 15 connections or >25 people for > 60 days/year;
- Primary standards: for harmful substances; - The maximum contaminant level (MCL)Enforceable for regulated substances; Treatment technique (TT) requirements; - The maximum contaminant level goal (MCLG)= no adverse effect level; 0 for all carcinogenic chemicals
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Secondary standards: for non-critical parameters such as color, odor; not enforceable;
True or false:True or false:Federal drinking water standards apply Federal drinking water standards apply
to the water supply to every home to the water supply to every home
1. True
Tru
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2. False
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(2) Primary MCLs: - For potentially toxic chemicals
- 2 L per day consumption for lifetime + other sources 10-6 chance of effect
- Organic chemicals, inorganic chemicals, microorganisms, disinfectants, disinfection byproducts, and radionuclides
- For carcinogens:Normally the minimum detectable level;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Organic chemicals: mostly from human activity;
Table 6.1 (page 152);
ppm = parts per million = mg/L
1 ppm = 1000 ppb = 1000 µg/L
Benzene – cancer – 0.005 mg/L – industrial chemicals ..
TCE – cancer – 0.005 mg/L – dry cleaning …
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Inorganic chemicals: from human activity and the natural world; Table 6.2 (page 153)
Arsenic (As) – nervous system effects – 0.01 mg/L; groundwater; coal fly ash (leaching); pesticides; g ; y ( g); p ;industrial wastes
Nitrate – blue-baby effect – 10 mg/L – fertilizers; wastewater;
Cadmium – kidney effects – 0.005 mg/L – metal finishing; natural mineral deposits
Lead/Copper – action levels – 0.015/1.3 mg/L
For water contaminants, 1 mg/L equals For water contaminants, 1 mg/L equals to to
1. 1 ppm
2. 1000 µg/L
1 p
pm
100
0 µg/
L
100
0 ppb
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3. 1000 ppb
4. All above
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Microorganisms:
Total coliform; fecal coliform
Cryptosporidium; Giardia
….
Turbidity – directly indicates the overall water quality; Nephelometric turbidity units (NTU)
always <1 NTU; 95% of time < 0.3 NTU
Mostly based on the technology used for treatment (TT)
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
E. Coli O157:H7 is pathogenic to humans contaminated ground beef, raw milk, fruit juices
Cryptosporidium Cryptosporidium
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Disinfectants: from disinfection activities;
Chloramines – MRDL=4.0 mg/L;
Chlorine – MRDL=4.0 mg/L;
Chlorine dioxide – MRDL=0.8 mg/L;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Disinfection byproducts: from disinfection activities;
Bromate – 0.01 mg/L; from ozone disinfection
Chlorite – 1.0 mg/L; from chlorine dioxide disinfection −1 Cl− chloride+1 ClO− hypochlorite +3 ClO2
− chlorite+5 ClO3
− chlorate +7 ClO4
− perchlorate
Haloacetic acids (HAA5) – 0.060 mg/L;
Total Trihalomethanes (TTHMs) – 0.080 mg/L;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Radionuclides: from natural sources;
Alpha particles - 15 picocuries per Liter (pCi/L)
Beta particles and photon emitters;
Radium 226 and Radium 228 (combined);
Uranium;
Which of the following disinfection Which of the following disinfection byproduct will be produced if ozone is byproduct will be produced if ozone is
used for disinfection? used for disinfection?
1. Chlorite
2. Bromate
Chlo
rite
Bro
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e
THM
s
HAAs
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3. THMs
4. HAAs
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(3) Secondary guidelines: suggested levels (not MCL!)
- Table 6.3 (page 155)
- chloride, color, iron, odor, pH, ….
(4) Drinking Water Contaminant Candidate List (CCL):
- Microorganisms and chemicals
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(5) Sampling, record keeping, and reporting:
- Need to follow required procedures when taking samples;- Detailed information for the sample and the quality parameters;p ;- Public notification within 48 hours if primary MCLs are not met;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Review questions:
• What are the major water quality concerns?• What is the conventional drinking water treatment
process?• Why is groundwater cleaner than surface water?y g• How to remove heavy particles? • What is MCL? What is MCLG? How are these
parameters determined?• What is the major difference between primary
standards and secondary standards?• What is turbidity? Why is it the most important
parameter for the overall drinking water quality? • What are side effects of disinfection?
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Lecture #2 Objectives:Lecture #2 Objectives:
-- Design settling tank to remove heavy particlesDesign settling tank to remove heavy particles
Understand coagulation principlesUnderstand coagulation principles-- Understand coagulation principlesUnderstand coagulation principles
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
3. Sedimentation: A process to remove heavy and large particles
(1) Settling process:- Sedimentation tank = settling tank = clarifier
- Settling velocity is related to the specific gravity and particle size
- Setting types: Discrete settling (free settling);Flocculent settling;Zone settling (hindered settling);
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
For two clay particles with different For two clay particles with different sizes, sizes,
1. The larger particle settles faster than the smaller particle
The
larg
er p
artic
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The
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artic
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The
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artic
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2. The larger particle settles at the same velocity as the smaller particle
3. The larger particle settles slower than the smaller particle
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(2) Detention time: = settling time- Longer settling time = better particle removal
- 2 – 4 hours; T = V/Q
- Example 6.1 (page 157) for detention time calculationp (p g )
- Example 6.2 (page 157) for tank dimension calculation
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(3) Free settling of discrete particles: - Only the particles that have settling velocity greater than a specific value can be removed; - Overflow rate = surface loading = upflow velocity V0 = Q/AS
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
QQHQH
A
Q
LW
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LHW
HQ
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HV0
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(4) Settling tank design: - Overflow rate determine the tank area: to make sure particles with certain settling velocity can are removed;
- Detention time determine the volume therefore the depth of water: to make sure water to receive certain pperiod of treatment time (not to disturb the tank);
- Example 6.4 (page 158):For average Q = 6 ML/dDetermine: Diameter; SWD (water depth)
Design criteria: HRT = 4 h (detention time)Overflow rate = 20 m3/m2-day
What is the most critical design What is the most critical design parameter defining the clarifier parameter defining the clarifier
efficiency?efficiency?
1. The detention time
2. The overflow rate
3. The water depth
The
deten
tion ti
me
The
overfl
ow rate
The
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epth
0% 0%0%
3. The water depth
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Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(5) Inclined settling system (plate or tube settlers):
- Increase settling area/reduce settling depth; - Handle 3 – 6 times more flow;- Not for secondary clarifier;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Adding inclined tubes/plates in clarifiers Adding inclined tubes/plates in clarifiers can enhance particle removal. Why? can enhance particle removal. Why?
1. It provides more settling area thus reduces the
It p
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It in
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It in
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ses
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ize
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settling distance of particles
2. It increases particle settling velocity
3. It increases particle size
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
4. Coagulation and flocculation: Remove turbidity, color, and bacteria
(1) Colloid stability: - Colloid particles are very small; normally they are negatively charged repel each other g y g p
- Coagulant: neutralize the surface charge when particles are in contact, they stick together form large settleable size
- Too much coagulant reverse the charge re-stabilization
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Why do colloid materials not settle? Why do colloid materials not settle?
1. They are too small and the settling velocity caused by the gravity force is negligible
They
are
too
smal
l an...
They
car
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2. They carry the same type of surface charge therefore repel each other
3. All above
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(2) Coagulants: Usually aluminum and iron salts
Aluminum sulfate (alum): Al2(SO4)3.14H2O Al3+ + H2O Al(OH)x + H+
Best pH range: 4.5 – 8.0; higher pH creates larger flocs
Ferric sulfate and ferric chloride: Fe2(SO4)3 and FeCl3Fe3+ + H2O Fe(OH)3 + H+
Best pH range: 4 – 12 (wider than above)
Coagulant aids:- Activated silica, clay, return sludge, and polymers; - Alkalinity addition/pH adjustment: need alkalinity to neutralize the acidity Lime (slaked lime; hydrated lime) and soda ash
Which of the following process can help Which of the following process can help the coagulation process? the coagulation process?
1. Adding clay
2. Adding polymers
3. Adjusting pH
Addin
g cl
ay
Addin
g pol
ymer
s
Adju
stin
g pH
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3. Adjusting pH
4. All above
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(3) Rapid mix: - To quickly disperse the chemical to particle surface for surface charge neutralization;
- Degree of mixing is measured by the velocity gradient:
PW
- Mechanical mixers: G = 700 - 1000 s-1; retention time: 20 – 60 sec; power requirement: 0.85 – 1.0 horsepower per MGD;
- In-line static mixers:mixing time 1 – 3 s, head loss 2 – 3 ft;need a screen to prevent clogging;
V
PWG
Which is the parameter that directly Which is the parameter that directly defines the mixing intensity? defines the mixing intensity?
1. The turbulence
2. The velocity gradient
3. The mixing power
The
turb
ulence
The
velo
city
gra
dient
The
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ower
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3. The mixing power
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(4) Flocculation:Slow mixing, allow particles to form large flocs
- Paddle flocculators: Gt = 104 – 105;G = 30 – 60 s-1; ;t = 15 – 45 min;
- Baffled channels: Velocity in channels 0.3 – 1.3 m/s; Detention time: 15 – 20 min;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Compared to the coagulation, a smaller Compared to the coagulation, a smaller GG is used for flocculation. Why? is used for flocculation. Why?
1. To destabilize particles
2. To prevent breaking up flocs
To d
esta
bilize
par
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s
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p g p
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(5) Upflow solids contact clarifier:Mixing, flocculation, and clarification in the same tank
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(6) Jar test: simulate water treatment process; determine the optimum coagulants, dosage, pH; mixing intensity, reaction time;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(7) Sedimentation in water treatment:
Pre-sedimentation:- Used when surface contains high turbidity; - HRT > 3 h; - Chemical addition may be required; y q ;
Sedimentation after flocculation:- HRT = 2 - 4 h; - Overflow rate = 500 – 1000 gpd/ft2 (20 – 41 m/day); - Horizontal velocity < 0.5 m/min; - Max weir loading: 20,000 gpd/ft.
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Example: Design one water treatment clarifier to handle a flow rate of 1.5 MGD maximum daily flow at the design year.
Design criteria: average overflow rate = 800 gpd/ft2; minimum side-water depth = 10 ft; peak weir loading < p ; p g20,000 gpd/ft.
Solution:(a) Calculate diameter: The max daily flow rate to each unit is 1.5 MGD; Choose surface overflow rate = 800 gpd/ft2;A = 1.5 x 106/800 = 1875 ft2; D = 2 (1875/3.14)0.5 = 48.87 ft Choose design 50 ft;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(b) Choose side water depth 10 ft;
(c) Check peak weir loading:Total length of the weir = 3.14 x 50 = 157 ft Weir loading = 1.5 x 106/157 = 9,554 gpd/ft < 20,000 gpd/ft OKgp
(d) Check HRT:Total tank volume: 3.14 x 252 x 10 = 19,625 ft3 = 146,795 gallon HRT = 146,795/(1.5 x 106) = 0.098 day = 2.3 h Ok
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Review questions: • Why is the settling velocity related to the particle size?• What is the overflow rate? Why is it the most important
parameter for clarifier design?• Why can adding inclined tubes and plates enhance the
clarifier performance for water treatment?p• Why do colloid particles not settle in water? How to
destabilize them?• What are major coagulants for water treatment? • What are coagulant aids?• Why do we need to rapidly mix the coagulant with water? • What is the parameter of the mixing intensity? • What is flocculation? Why should we reduce the mixing
intensity during flocculation?
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Homework #5: Due Thursday
1. Please tell the differences between the US drinking water standards and Chinese drinking water standards, and offer some explanations.
2. Practice problems #5 (page 181)p (p g )
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Lecture #3 Objectives:Lecture #3 Objectives:
-- Design sand filtersDesign sand filters
Understand disinfection and its side effectsUnderstand disinfection and its side effects-- Understand disinfection and its side effectsUnderstand disinfection and its side effects
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
5. Filtration: Remove small nonsettleable solids mandatory for surface water and shallow groundwater
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(1) Sand filtration principle: - Straining: particles are too large to pass through the sand medium;- Interception: particles are attached to the medium;- Flocculation: particles attached to each other when contact; Straining FlocculationStraining Flocculation;- Settling;
gStraining
SedimentationInterception
gStraining
SedimentationInterception
Sand filter can remove very small Sand filter can remove very small particles. Why? particles. Why?
1. Particles can be retained by the sand surface
Par
ticle
s ca
n be
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Par
ticle
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n flocc
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.
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2. Particles can flocculate and grow larger
3. Particles can stuck between sand medium
4. All above
Typical gravity filter system Typical gravity filter system
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Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(2) Single media rapid sand filters: - Sand is graded for easy backwashing;
- Effective size (10 percentile diameter) = 0.45 – 0.55 mm; bed depth = 2 – 3 ft (~0.75 m);
- Backwashing process: pump water back through the media; sand bed expends; particles are removed;
- Loading rate: Q/A = 120 m3/day.m2 or above;
- At least 2 units; size of each unit up to 100 m2;
- Backwash: use 2 – 4% of treated water;
Single media filter filtration modeSingle media filter filtration mode
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Preferred filtration mode Preferred filtration mode
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(3) Multimedia filter: - Several media including sand, anthracite, and/or garnet; media are graded largest and lightest on top;
- Similar effluent quality;
- Anthracite size 0.9 – 1.1 mm;
- Reduced the resistance and increase the capacity due to the use of large anthracite medium;
- Loading rate up to 300 m3/day.m2;
- Backwash: use air and water mixture;
Why are multimedia filters more Why are multimedia filters more frequently used than single media frequently used than single media
filters?filters?
1. The multimedia filter has larger capacity thus longer filter run
2 The multimedia filter is cheaper
The
mul
timed
ia fi
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..
The
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.
The
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2. The multimedia filter is cheaper to build
3. The multimedia filter produces better effluent quality
4. All above
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Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(4) Filter design: - The total filter depth is about 3 m, but the medium thickness is about 0.75 m;
- The area is calculated based on the filtration rate, or loading rate (similar to the overflow rate of the clarifier);g ( );
- Multimedia filters can handle 2 – 3 times of the flow per unit filter area; 1.4 L/m2.s vs. 3.5 L/m2.s
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(5) Filter operation:
Initially particles are retained on the top layers of the medium;
after a while the water velocity increase (due to the y (particle collection), break the particle, and force the particles move down to deep layers of the medium;
when penetrate the medium, the effluent turbidity increase
back washing
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(6) Slow sand filter:
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
- Use very small sand medium; flow rate is very low;
- Can effectively remove all particles especially biological particles (Giardia cysts and Cryptosporidium oocysts) due to the formation of biologically active layer on top; y p;
- Manual cleaning; once every several months;
- Need large area; suitable for small communities;
- Flow rate of water applied per unit area of the filter, or loading rate (Q/A) = 2.9 – 7.6 m3/day.m2.
Slow sand filters produce better effluent Slow sand filters produce better effluent than rapid filters becausethan rapid filters because
1. The filtration medium is finer than rapid filters
The
filtra
tion m
ediu
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2. The biological layer on top of the filter can break down pollutants and remove pathogens
3. All above
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(7) Deep filter:
- Larger medium size = 1.0 – 1.5 mm diameter;
- Thick filter bed: 1.5 – 2.5 m deep;
- Loading rate up to 8000 m3/day.m2.
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
6. Disinfection: Kill pathogens
(1) Pathogens:Microorganisms that cause the waterborne disease -bacteria, viruses, protozoa, and helminthes;
Coliform bacteria as indicator organisms: - Easy to detect; - Their presence indicates the pollution by feces the presence of pathogens;
Limitations:Coliform bacteria die off rate is faster than viruses and protozoa without coliform does not mean that there is no other pathogens.
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Why do we use coliform bacteria as an Why do we use coliform bacteria as an indicator for water biological quality?indicator for water biological quality?
1. Coliform bacteria can indicate the presence of
Colif
orm b
acte
ria c
a...
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indicate the presence of other pathogens
2. Coliform bacteria are easy to detect
3. All above
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(2) Chlorine disinfection: strong oxidant
- Cl2(g) + H2O = HOCl + H+ + Cl-
- HOCl = H+ + OCl- (hypochlorite); pKa = 7.54
- Chlorine react with ammonia form chloramines a weaker disinfectant; also called combined chlorine;
- Free chlorine: HOCl + OCl-; pH < 7.54 is more effective;
- Residue chlorine: ~ 2 mg/L before entering the distribution system;
- > 0.2 mg/L in distribution system;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Breakpoint chlorination process:
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(3) Disinfection by products (DBPs):
- Formed between chlorine and organic matter in water;
- Trihalomethanes (THMs): chloroform; bromodichlorimethane; ; ;dibromochloromethane, and bromoform;
- Haloacetic acids (HAA5): monochloroacetic acid; dichloroacetic acid; trichloroacetic acid; monobromoacetic acid, and dibromoacetic acid;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(4) Chlorine dioxide (ClO2):
- Weaker, not forming THMs/HAAs; - Form chlorate and chlorite toxic;
(5) Ozonation: ( )
- Kills everything instantly;- Not stable (half life 10 – 30 minutes); - Form bromate toxic;
(6) UV:
- Kills pathogen on a specific location;
Why is chlorine a commonly used Why is chlorine a commonly used disinfectant for drinking water disinfectant for drinking water
disinfection?disinfection?
1. Chlorine is strong and kills all pathogens quickly
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2. Chlorine is stable and maintains the effect for a long time
3. Chlorine does not form disinfection by-products
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Review questions:
• Why can a sand filter remove very small particles?• What are the differences between single-mediia sand
filter, multi-media filtration system, deep bed filter, and slow filter?
• Why is sand graded when used in the filter?• How do we clean up the above filters?• What are pathogens? Why are coliform bacteria used as
indicator organisms? What are their limitations?• Why is Cl2 commonly used to disinfect drinking water? • Why is chlorine disinfection more effective when pH is
less than 7.54? • What are the major disinfection by-products?
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Lecture #4 Objective:Lecture #4 Objective:
-- Know softening and other water treatment methodsKnow softening and other water treatment methods
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
7. Other treatment processes(1) Water softening:
Hardness: = Sum of all polyvalent cations especially Ca2+ and Mg2+;
TH = Ca2+ + Mg2+; unit: mg/L as CaCO3g ; g 3
60 – 120: moderately hard
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
What is the problem associated with What is the problem associated with hard water? hard water?
1. It can form scale inside the boiler tube
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2. It can hurt people when drinking it
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Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Example: Water has 20 mg/L Ca2+ and 10 mg/L Mg2+; what is the hardness (in mg/L as CaCO3)?
Solution: change everything in meq/L, then add up and convert to mg/L as CaCO3: g 3
For Ca2+: atomic weight = 40 g/mole; equivalent weight = 20 g/eq.; calcium hardness = 20/20 = 1 meq./L;
For Mg2+: atomic weight = 24 g/mole; equivalent = 12 g/eq; magnesium hardness = 10/12 = 0.83 meq./L;
Total hardness:1 + 0.83 = 1.83 meq./L = 1.83 x 50 = 91.5 mg/L as CaCO3
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Hardness composition:
- Carbonate hardness: Ca(HCO3)2; Mg(HCO3)2;This hardness decreases with the increase of temperature temporary hardness; p p y ;
- Noncarbonate hardness (NCH), or permanent hardness: calcium/magnesium sulfate, chloride, nitrate, ...
- TH = CH + NCH
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Lime-soda ash softening:
(1) Lime neutralize CO2 in water:CO2 + Ca(OH)2 = CaCO3(s) + H2O
(2) Lime remove all carbonate hardness (CH): ( ) ( )Ca(HCO3)2 + Ca(OH)2 = 2CaCO3(s) + 2H2OMg(HCO3)2 + Ca(OH)2 = CaCO3(s) + MgCO3 + 2H2OMgCO3 + Ca(OH)2 = Mg(OH)2(s) + CaCO3(s)
(3) Lime convert Mg2+ NCH to Ca2+ NCH: MgSO4 + Ca(OH)2 = Mg(OH)2(s) + CaSO4
(4) Soda ash remove calcium NCH:CaSO4 + Na2CO3 = Na2SO4 + CaCO3(s)
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Cation exchange softening: - 2R-Na + Ca2+ R2-Ca + 2Na+
- Regeneration: R2-Ca + 2Na+ (High Concentration) 2R-Na + Ca2+
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
What softening method is used in our What softening method is used in our homes? homes?
1. Lime-soda ash softening method
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Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(2) Aeration: Remove gas (CO2 and H2S), oxidize iron and manganese to insoluble forms
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(3) Carbon adsorption: Remove taste and odor; soluble organic matter; heavy metals; dechlorination;
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Breakthrough curve:
In drinking water treatment, what method In drinking water treatment, what method is used to remove colloid materials? is used to remove colloid materials?
1. Filtration
2. Coagulation-flocculation-clarification
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3. Adsorption
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(4) Membrane filtration:
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
RO: pore size: 0.1 nm; remove salts and synthetic organic compounds (SOCs); size exclusion and charge repulsion;
NF: pore size: 1 nm; soften fresh water and remove DBP precursors; size p ;exclusion and charge repulsion;
UF and MF: pore size: 0.01 and 0.1 m; remove turbidity, pathogens, and particles from fresh waters; size exclusion only;
Uncharged small organic molecules such as THMs and dissolved gases can not be removed.
Filtration SpectrumFiltration Spectrum Reverses osmosis (RO)Reverses osmosis (RO)
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Residential unit: Residential unit:
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
RO equipmentRO equipment
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Electrodialysis (ED)Electrodialysis (ED)
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification RO membrane removes contaminants RO membrane removes contaminants through through
1. Size exclusion
2. Charge repulsion
3 All above
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3. All above
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
(5) Corrosion control: Add chemicals to water to control pipe corrosion;Sodium silicate; sodium phosphate
(6) Fluoridation: Add fluoride to some water that lacks it
(7) Desalination: Using evaporation methods or membrane methods
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Review questions:
• What is the temporary hardness? What is the permanent hardness? What is the unit of hardness?
• Why can lime remove temporary hardness?• What is the principle of the ion exchange softening?p p g g• What are the purposes of carbon adsorption and
aeration in drinking water treatment?• What is the principle of the RO processes?
Chapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water PurificationChapter 6. Drinking Water Purification
Homework #6: Due Thursday
1. Explain why the multimedia filter is more commonly used than the mono-media filter for water treatment.
2. Why is chlorine more commonly used for drinking water y y gdisinfection than other disinfectants? What are their side effects?
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