Water resources in China

WANG Hongtao, Ph.D., Associate ProfessorCollege of Environmental Science and Engineering, Tongji University

hongtao@tongji.edu.cn

Sustainable Development in China

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

Outline

Question:Which technology is “sustainable?” Why?

Drinking water treatment

Conventional scheme of water cycle

Sludges

Effluents

reject

WW treatment plantAdequate sanitation

Production of drinking water

To protect the quality of the environment

Assume a safe water

Open system-closed system

5

SourceWater Coagulation Filtration

PumpCustomer

Coagulant

Sedimentation Clean water

Cl2

Conventional treatment process of drinking water

Disinfection

Distribution

Source: US EPA

Coagulation

Source: SNF FLOERGER (2003)

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.

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.

Following coagulation, flocculation, a gentle mixing stage, increases the particle size from submicroscopic microfloc to visible suspended particles.

flocculation

Coagulation

Coagulation

agitator

Jar tester, Nairobi, 1938

Coagulation

Poly Aluminum Chloride for Drinking Water

IndexLiquid Solid

High-class product First-class product High-class product First-class product

Al2O3 Content %≥ 10.0 10.0 30.0 28.0

Basicity % 40-85 40-80 40-90 40-90

Density (20%)/(g/cm3) ≥ 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 3.5-5.0As /%≤ 0.0001 0.0002

Pb /%≤ 0.0005 0.001Cd /%≤ 0.0001 0.0002Hg /%≤ 0.00001 0.00001Cr6+ /%≤ 0.0005 0.0005

Heavy metal in the coagulant!

Ore: calcium aluminate

• Jar test • Raw water turbidity: >500 NTU• Treated water turbidity:1-2 NTU

Drinking water treatment in Ethiopia

WTP PAC-SDD PAC-CFII ALUMNG’ETHU 97.7% 98% 89.8%SASUMUA 81.9% 84% 75%KABETE 91.8% 92% 89%

Drinking water treatment in Kenya

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

Sand

Gravel

Influent

DrainEffluent Wash water

Anthracite

Size(mm)0.70

0.45 - 0.55

5 - 60

SpecificGravity

1.6

2.65

2.65

Depth(cm)30

45

45

Rapid Sand Filter (Conventional US Treatment)

Sand

Gravel

Influent

DrainEffluent Wash water

Anthracite

Backwash

• Wash water is treated water!

Filtration

Pollution?

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.

Disinfection

What is the problem of disinfection?

Disinfection Byproducts(DBPs)

Cl2+natural organic matter——trihalomethanes （ THMs,

carcinogenic ）

24

Source

WaterCoagulation Oxidation

Pump Customer

O3Coagulant

Sedimentation

Activated carbon Clean water

Advanced treatment process of drinking water

Filtration

Ozone biological activated carbon technology

Chlorine

25

Oxidation

• Oxidation- complete or partial loss of electrons or the gain of oxygen.

• Reduction- complete or partial gain of electrons or loss of oxygen

Oxidation and Reduction

Oxidizing Strength of ·OH

·OH oxidizing properties are comparable to Fluorine (F2) the most electronegative element in the periodic table

26

Oxidizing agent Half reactions Standard-State Reduction 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

Oxidation

hydroxyl radical

• Taihu Lake algae crisis(2007):

Oxidant:potassium permanganate (KMnO4)

Oxidation

What is the problem of KMnO4 addition?

Erosion to the pipelines (Fe)

Hazardous to human health

Adsorption

Increasing magnification

Adsorption

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.

Adsorbent: activated carbon

Adsorption (Fixed Bed Absorber).

Efflu

ent

Con

cent

ratio

n Co

CE

CB

Volume of EffluentVB VE

Breakpoint

Exhaustion point

Breakthrough Curve

Breakthrough of Adsorbent

What is the problem of Adsorption?

expensive

regeneration

Pollutants transferred, not degraded

Wastewater treatment

Wastewater treatment ratio in Shanghai

wastewater treatment in Shanghai

Wastewater treatment plants in Shanghai

一级处理Primary treatment

二级处理Secondary treatment

三级处理Tertiary treatment

Conventional activated sludge

BNR

Biological phosphorus removal

Biological nitrogen &phosphorus removal

MBR

RO

Bar Screen

Biofilm

Dischargeor Reuse

Disinfection

Ecological treatment

Filtration

How to Choose the Process

Primary sedimentation

Grit chamber

Enhanced primary sedimentation

Coagulation

BNR: Biological Nutrient RemovalMBR: Membrane BioreactorRO: Reverse Osmosis

Wastewater treatment process in China

General concept and process of wastewater treatment plant

WastewaterBar screen

Smell treatment Exhaust

Primary treatment

Secondary treatment

Advanced treatmentSludge treatment

Drainage/ reuse

Disposal

How to Choose the Process

Case study: Shidongkou WWTP,Shanghai,China

项 目 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

Treatment technologies of Shidongkou WWTP,Shanghai

进水泵房

粗格栅细格栅

沉砂池计量槽

一反体应化池加氯消毒

出水泵房

栅渣压干机 栅渣压干机 砂水分离器 剩余污泥泵

排放进水

栅渣 栅渣 砂 剩余污泥

至剩余污泥处理段栅渣外运

主体工艺Influent

FineScreen

LiftPump

GritChamber

CoarseScreen

Flowmeter

UnitankChlorination Disinfection

Effluent

GridResidue Sand Surplus sludge

Presser Presser Separator Sludge Pump

Landfill To Sludge treatment

鼓风机房 Aeration station

Effluent: Discharged to Yangtze River; Reclaimed and reused for road flushing, firefighting, irrigation

Effluent discharge Reclaimed water

Case study: Shidongkou WWTP,Shanghai,China

Sludge treatment

Thickening;

Dewatering;

incineration;

LandfillSludge dewatering Incineration

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 WetlandsConstructed 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 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

Shanghai

Tai Lake

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 Ducks swim in the algae-rich Tai Lake

Tai Lake turns green after an algae bloom

• Algae collection

• Algae separation

Algae Separation from Tai Lake

2,000 m3/dDesigned 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

Algae Separation from Tai Lake

A B C ED

A1 C1B1 D1

A1:algae slurry B1:+absorbent modified with chitosan C1: +poly aluminum chloride (PACl) D1: +alum

(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)

Algae Separation from Tai Lake

Energy producing and carbon sequestration

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

element C H N S P

content（ %

） 37.63 3.453 3.050 0.94 0.57

Table 1. Elementary analysis table of algae sludge

Energy producing and carbon sequestration

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

Algae Separation from Tai Lake

Reuse of Wastewater: Desalination

Example: wastewater reuse in Tongji University

Source: Prof. XIA Siqing

Wastewater reuse-Desalination in Libya

Project profile

Sirte City

Chlorine injection

To sea

filtrationChemical treatmentSedimentation tankBiological treatment

((activated sludge))

Grit and insolublematerial removal

Return sludge

Sludge digestion

Sludge to dryers

Sand filterSample 1

Sample 2

Sample 3

Tertiary treatment

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/LCurrent TDS in S WWTP: 2500 mg/LDesalination is needed!

Wastewater reuse-Desalination in Libya

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