water

Report
Sustainable Development in China
Water resources in China
WANG Hongtao, Ph.D., Associate Professor
College of Environmental Science and Engineering, Tongji University
[email protected]
Outline
Drinking water treatment
 Conventional treatment process
 Advanced treatment process
Wastewater treatment





Wastewater situation in China
Wastewater treatment process
Case Study of wastewater treatment plant
Algae separation
Reuse of wastewater
Question:
Which technology is “sustainable?”
Why?
Drinking water treatment
Conventional scheme of water cycle
Production of
drinking water
To protect the
quality of the
environment
reject
Assume a
safe water
Effluents
WW treatment plant
Adequate sanitation
Sludges
Open system-closed system
Conventional treatment process of drinking water
Coagulant
Cl2
Disinfection
Source
Water
Coagulation
Sedimentation
Filtration
Clean water
Distribution
Customer
Pump
5
Source: US EPA
Coagulation
Physical-chemical process involved in Coagulation-Flocculation
Coagulation-flocculation: The use of chemical reagents to destabilise and increase the
size of the particles; mixing; increasing of flocs size.
Source: SNF FLOERGER (2003)
Coagulation destabilises the particles’ charges. Coagulants with charges opposite to
those of the suspended solids are added to the water to neutralise the negative
charges on dispersed non-settable solids such as clay and organic substances.
Once the charge is neutralised, the small-suspended particles are capable of sticking
together.
flocculation
Following coagulation,
flocculation, a gentle
mixing stage, increases
the particle size from
submicroscopic
microfloc to visible
suspended particles.
Coagulation
Coagulation
agitator
Jar tester, Nairobi, 1938
Coagulation
Poly Aluminum Chloride for Drinking Water
Liquid
Index
Solid
Al2O3 Content %≥
High-class
product
10.0
First-class
product
10.0
Basicity %
40-85
Density (20%)/(g/cm3) ≥
High-class product First-class product
30.0
28.0
40-80
40-90
40-90
1.15
1.15
-
-
Non-dissolved Substances /%≤
0.1
0.3
0.3
1.0
pH(1% aqueous suspension)
3.5-5.0
3.5-5.0
3.5-5.0
3.5-5.0
0.0001
0.0002
Pb /%≤
0.0005
0.001
Cd /%≤
0.0001
0.0002
Hg /%≤
0.00001
0.00001
Cr6+ /%≤
0.0005
0.0005
As /%≤
Ore: calcium aluminate
Drinking water treatment in Ethiopia
• Jar test
• Raw water turbidity: >500 NTU
• Treated water turbidity:1-2 NTU
Drinking water treatment in Kenya
WTP
NG’ETHU
SASUMUA
KABETE
PAC-SDD
97.7%
81.9%
91.8%
PAC-CFII
98%
84%
92%
ALUM
89.8%
75%
89%
Questions:
 Do you think COAGULATION is a “sustainable?” technology?
 What do you think of the advantages and disadvantages of
COAGULATION?
Chemical consumption: coagulant
Energy consumption: agitator
Residual coagulant dissolved in water: Al
Safety issue: heavy metals
Sedimentation/Settling
Sludge
 What is the problem of sedimentation/settling?
 Pollutants separated from water to sludge(not degraded);
Sludge is a problem.
 Residual coagulant in sludge (Al, Fe, PAM);
Filtration
Rapid Sand Filter (Conventional US Treatment)
Size
(mm)
Anthracite
Influent
Sand
Gravel
Drain
Effluent
Specific Depth
Gravity (cm)
0.70
1.6
30
0.45 - 0.55
2.65
45
5 - 60
2.65
45
Wash water
Filtration
Backwash
• Wash water is
treated water!
Anthracite
Influent
Pollution?
Sand
Gravel
Drain
Effluent
Wash water
Disinfection
Chlorine Disinfection (Cl2):
one of the most commonly used disinfectants for water disinfection.
can be applied for the deactivation of most microorganisms and it is relatively
cheap.
Advantages:
efficient oxidant and disinfectant
effectively eliminates unpleasant taste and odors
featured with aftereffect (Free chlorine residual of 0.2-0.5 mg/L)
prevents and controls growth of algae, biological slimes and microbes
decomposes organic contaminants (phenols, etc.)
oxidizes iron and magnesium
decomposes hydrogen sulfide, cyanides, ammonium and other nitrogen
compounds.
Disadvantages:
strict requirements for transportation and storage ;
potential risk to health in case of leakage;
formation of disinfection by-products, such as trihalomethanes.
Disinfection
Sodium hypochlorite (NaClO):
Advantages:
effective against most of pathogenic microorganisms
relatively safe during storage and use
when produced on site does not require transportation and storage of hazardous
chemicals
Disadvantages:
looses its activity during long-term storage
ineffective against cysts (Giardia, Cryptosporidium)
produces disinfection by-products, such as trihalomethanes
generated on-site requires immediate use
Other disinfectants:
Chlorine dioxide; Chloramine; Ozone; Ultraviolet
Solar Disinfection(SODIS)
Heating water to 65°C (149°F) in a solar cooker will pasteurize the water and
kill disease causing microbes.
What is the problem of disinfection?
Disinfection Byproducts(DBPs)
Cl2+natural organic matter——trihalomethanes(THMs, carcinogenic)
Advanced treatment process of drinking water
Coagulant
O3
Source
Water
Coagulation
Sedimentation
Oxidation
Filtration
Chlorine
Activated
carbon
Clean water
Pump
Customer
Ozone biological activated carbon technology
24
Oxidation
Oxidation and Reduction
• Oxidation- complete
or partial loss of
electrons or the gain
of oxygen.
• Reduction- complete
or partial gain of
electrons or loss of
oxygen
25
Oxidation
Oxidizing Strength of ·OH
Oxidizing agent
Half reactions
Standard-State
Potentials, Eo
MnO2
MnO2(s)+4H++2e- =Mn2++2H2O2
1.23
Cl2
Cl(g)+2e-=2Cl-
1.36
ClO2
ClO2+2e-= Cl-+ O2
1.50
H2O2
H2O2+ 2H++2e-=2 H2O
1.77
O3
O3+2H++2e-= H2O+ O2
2.07
·OH
·OH+ H++2 e-= H2O
2.80
F2
F2(g)+ 2H++2e-=2HF
3.06
·OH oxidizing properties are comparable to Fluorine (F2)
the most electronegative element in the periodic table
Reduction
hydroxyl radical
26
Oxidation
• Taihu Lake algae crisis(2007):
Oxidant:
potassium permanganate (KMnO4)
What is the problem of KMnO4 addition?
 Erosion to the pipelines (Fe)
 Hazardous to human health
Adsorption
Adsorption
Increasing magnification
Adsorbent: activated carbon
Applications in water treatment usually involve
adding AC as a media to the filtration unit. In
some cases a contactor is added just before the
final chlorination step.
Breakthrough of Adsorbent
Effluent Concentration
Adsorption (Fixed Bed Absorber).
C
CoE
Breakthrough Curve
Exhaustion point
Breakpoint
CB
Volume of Effluent
VB
VE
What is the problem of Adsorption?
 expensive
 regeneration
 Pollutants transferred, not degraded
Wastewater treatment
wastewater treatment in Shanghai
Wastewater treatment ratio in Shanghai
Wastewater treatment
plants in Shanghai
How to Choose the Process
Wastewater treatment process in China
一级处理
Primary treatment
Bar Screen
二级处理
三级处理
Secondary treatment
Tertiary treatment
Conventional
activated sludge
Grit chamber
Disinfection
Coagulation
BNR
Primary sedimentation
Enhanced primary
sedimentation
Biological
phosphorus
removal
Biological nitrogen
&phosphorus
removal
Biofilm
BNR: Biological Nutrient Removal
MBR: Membrane Bioreactor
RO: Reverse Osmosis
Filtration
MBR
RO
Ecological
treatment
Discharge
or Reuse
How to Choose the Process
General concept and process of wastewater treatment plant
Exhaust
Smell treatment
Wastewater
Bar screen
Primary
treatment
Secondary treatment
Disposal
Sludge treatment
Advanced treatment
Drainage/
reuse
Case study: Shidongkou WWTP,Shanghai,China
COD
BOD5
SS
NH3-N
TP
Influent
(mg/L)
400
200
250
30
4.5
Effluent
(mg/L)
60
20
20
8(15)
1.5
项
目
Treatment technologies of Shidongkou WWTP,Shanghai
鼓风机房
Coarse
Lift
Fine
Screen
Pump
Screen
粗
格
栅
进
水
泵
房
细
格
栅
进水
Influent
Grit
Flow
Chamber meter
沉
砂
池
计
量
槽
Aeration station
Chlorination
Disinfection
Unitank
一反
体应
化池
加
氯
消
毒
出
水
泵
房
排放
Effluent
主体工艺
Grid
Residue
栅渣压干机
Presser
栅渣外运
Landfill
栅渣
栅渣
栅渣压干机
Presser
砂
Sand
砂水分离器
Separator
剩余污泥
Surplus sludge
剩余污泥泵
Sludge Pump
至剩余污泥处理段
To Sludge treatment
Case study: Shidongkou WWTP,Shanghai,China
Reclaimed water
Effluent discharge
Effluent:
 Discharged to Yangtze River;
 Reclaimed and reused for road flushing, firefighting, irrigation
Sludge treatment
Sludge dewatering
Incineration

Thickening;

Dewatering;

incineration;

Landfill
What is your opinion on the technologies adopted
in Shidongkou Wastewater Treatment Plant?
 Efficient to remove pollutants from water
 Energy consumption
 Air pollution (incineration)
 Landfill leachate pollution
Wetland wastewater treatment system in Nanhui District, Shanghai
Benefits of Treatment Wetlands
Constructed and natural treatment wetlands provide several major benefits
compared to more conventional treatment alternatives:
• less expensive to construct than traditional secondary and tertiary
wastewater treatment systems.
• less maintenance and are less expensive to operate than traditional
treatment systems.
• may provide important wetland wildlife habitat, as well as human
recreational opportunities such as birdwatching, hiking, and picnicking.
• Treatment wetlands are viewed as an asset by regulatory agencies in
many regions and as a potentially effective method for replacing natural wetlands
lost through agricultural practices, industrial and municipal development, and
groundwater withdrawal.
Case study: Separation of Algae from Tai Lake
Tai Lake
Shanghai
Tai Lake to Shanghai: 130 km
Shanghai is located in the downstream of
Yangtze River
Huangpu River and entrance of Yangtze River
provide raw water for Shanghai.
Tai Lake is in the upstream of Huangpu River
Introduction of Tai Lake
China's famous scenic spot
Algae bloom in Tai Lake
Blue-green algae is seen on the surface of Tai Lake
Blooming algae fills large areas of the Tai Lake
Tai Lake turns green after an algae bloom
Ducks swim in the algae-rich Tai Lake
Algae Separation from Tai Lake
• Algae collection
• Algae separation
Algae Separation from Tai Lake
2,000 m3/d
Designed by
Tongji University
Solid content: 0.5-1%
Algae Separation from Tai Lake
Coagulant:150 ppm
A:algae slurry
B:+absorbent modified with chitosan
C:+poly aluminum chloride (PACl)
D:+poly ferric sulfate
E: +alum
A
B
C
D
E
A1:algae slurry
B1:+absorbent modified with chitosan
C1: +poly aluminum chloride (PACl)
D1: +alum
A1
B1
C1
D1
Algae Separation from Tai Lake
(a)SEM of modified fly ash coagulant(10 um)
(b)SEM of modified fly ash coagulant(2 um)
(c) SEM of the algae cell after treatment(5 um)
(d) SEM of the algae cell after treatment(2 um)
Energy producing and carbon sequestration
Energy producing and carbon sequestration
Table 1. Elementary analysis table of algae sludge
element
C
content(%) 37.63
H
N
S
P
3.453
3.050
0.94
0.57
1ton algae(dry)=600 m3 methane
+100 kg N
+10 kg P
Carbon sequestration=0.85~3.39 ton carbon/d
Energy producing and carbon sequestration
Algae Separation from Tai Lake
 Algae bloom is a serious problem in Tai Lake
 Algae can be separated from water by
coagulation/adsorption and dewatering
 Algae can produce energy and fertilizer
 Significant for carbon sequestration
Reuse of Wastewater: Desalination
Example: wastewater reuse in Tongji University
Source: Prof. XIA Siqing
Wastewater reuse-Desalination in Libya
Wastewater reuse-Desalination in Libya
Sirte City
Project profile
Tertiary treatment
Grit and insoluble
material removal
Biological treatment
Sedimentation tank
Chemical treatment
filtration
((activated sludge))
Sample 2
Sand filter
Sample 1
Return sludge
To sea
Sample 3
Sludge to dryers
Chlorine injection
Sludge digestion
Wastewater reuse-Desalination in Libya
Sirte Wastewater Treatment Pant:
•Constructed in 2001
•Capacity: 30000m3/d
•Treatment Process: activated sludge
Existing Problem:
TDS (Total Dissolved Solid) is too high!
Acceptable TDS for irrigation: 600~1000 mg/L
Current TDS in S WWTP: 2500 mg/L
Desalination is needed!
Reuse of Waste Water for Forest Plantation Irrigation project in Libya
Sampling in Sirte City, Libya
Preliminary scheme of tertiary treatment and reuse of wastewater in Sirte City, Libya
Libya-Desalination
What is your opinion on the wastewater reuse?
 Save water
 Cost-effective? Too expensive!
 Reliability (power system; infrastructure; solar power?)
thanks for your attention

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