chapter 6. drinking water purificationenglish-c.tongji.edu.cn/_siteconf/files/2013/04/20/... ·...

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


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

All

above

0% 0%0%0%

3. Solids and color

4. All above

15


(3) Treatment methods: - Microorganisms disinfection


- 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


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

All

above

0% 0%0%0%

3. Air stripping

4. All above

15


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


- 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

e

Fal

se

0%0%

15

2. False


(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;


- 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 …


- 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

All

above

0% 0%0%0%

15

3. 1000 ppb

4. All above


- 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)


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;


- 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;


- 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

mat

e

THM

s

HAAs

0% 0%0%0%

15

3. THMs

4. HAAs


(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


(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;


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?



-- Design settling tank to remove heavy particlesDesign settling tank to remove heavy particles

Understand coagulation principlesUnderstand coagulation principles-- Understand coagulation principlesUnderstand coagulation principles


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);


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

le s

e...

The

larg

er p

artic

le s

et...

The

larg

er p

artic

le s

e...

0% 0%0%

15

2. The larger particle settles at the same velocity as the smaller particle

3. The larger particle settles slower than the smaller particle


(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


(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


QQHQH

A

Q

LW

Q

LHW

HQ

t

HV0


(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

wat

er d

epth

0% 0%0%

3. The water depth

15


(5) Inclined settling system (plate or tube settlers):

- Increase settling area/reduce settling depth; - Handle 3 – 6 times more flow;- Not for secondary clarifier;


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

rovi

des

more

set

tl...

It in

crea

ses

partic

le s

e...

It in

crea

ses

partic

le s

ize

0% 0%0%

15

settling distance of particles

2. It increases particle settling velocity

3. It increases particle size


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


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

ry th

e sa

me

...

All

above

0% 0%0%

15

2. They carry the same type of surface charge therefore repel each other

3. All above


(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

All

above

0% 0%0%0%

15

3. Adjusting pH

4. All above


(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

mix

ing p

ower

0% 0%0%

15

3. The mixing power



(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;



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

ticle

s

To p

reve

nt bre

akin

g u...

0%0%

15

p g p


(5) Upflow solids contact clarifier:Mixing, flocculation, and clarification in the same tank


(6) Jar test: simulate water treatment process; determine the optimum coagulants, dosage, pH; mixing intensity, reaction time;


(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.


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;


(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


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?


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 )



-- 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


5. Filtration: Remove small nonsettleable solids mandatory for surface water and shallow groundwater


(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

reta

in..

Par

ticle

s ca

n flocc

ula.

.

Par

ticle

s ca

n stu

ck b

...

All

above

0% 0%0%0%

15

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



(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


Preferred filtration mode Preferred filtration mode


(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

lter .

..

The

mul

timed

ia fi

lter .

.

The

mul

timed

ia fi

lter..

.

All

above

0% 0%0%0%

2. The multimedia filter is cheaper to build

3. The multimedia filter produces better effluent quality

4. All above

15


(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


(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



(6) Slow sand filter:



- 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

m i.

..

The

biolo

gical

laye

r o...

All

above

0% 0%0%

15

2. The biological layer on top of the filter can break down pollutants and remove pathogens

3. All above


(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.


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 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...

Colif

orm b

acte

ria a

re...

All

above

0% 0%0%

15

indicate the presence of other pathogens

2. Coliform bacteria are easy to detect

3. All above


(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;


Breakpoint chlorination process:


(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;


(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

Chlo

rine

is s

trong

and...

Chlo

rine

is s

tabl

e an

...

Chlo

rine

does

not f

o..

0% 0%0%

15

2. Chlorine is stable and maintains the effect for a long time

3. Chlorine does not form disinfection by-products


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?


Lecture #4 Objective:Lecture #4 Objective:

-- Know softening and other water treatment methodsKnow softening and other water treatment methods


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


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

It c

an fo

rm s

cale

insi

d...

It c

an h

urt peo

ple w

h..

0%0%

the boiler tube

2. It can hurt people when drinking it

15


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


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


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)


Cation exchange softening: - 2R-Na + Ca2+ R2-Ca + 2Na+

- Regeneration: R2-Ca + 2Na+ (High Concentration) 2R-Na + Ca2+


What softening method is used in our What softening method is used in our homes? homes?

1. Lime-soda ash softening method

Lim

e-so

da a

sh s

ofte

...

Ion

exch

ange

met

hod

0%0%

method

2. Ion exchange method

15


(2) Aeration: Remove gas (CO2 and H2S), oxidize iron and manganese to insoluble forms



(3) Carbon adsorption: Remove taste and odor; soluble organic matter; heavy metals; dechlorination;



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

Filt

ratio

n

Coag

ulatio

n-flocc

ulat..

.

Adso

rptio

n

0% 0%0%

15

3. Adsorption


(4) Membrane filtration:


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)


Residential unit: Residential unit:


RO equipmentRO equipment


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

Siz

e ex

clusi

on

Char

ge re

pulsio

n

All

above

0% 0%0%

15

3. All above


(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


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?


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?

chapter 6. drinking water purificationenglish-c.tongji.edu.cn/_siteconf/files/2013/04/20/... ·...

Documents