Lecture 3 Sustainable Water Environment

ENGG1006 - Engineering for Sustainable Development

SUSTAINABLE WATER ENVIRONMENT

Dr. Kaimin Shih DEPARTMENT OF CIVIL ENGINEERING THE UNIVERSITY OF HONG KONG

Office: Rm. 5-26, Haking Wong Building • Phone: 2859-1973 • E-mail: [email protected]

PROGRESS & OUTCOMES

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Keeping sustainable water resources is to…. Provide sustainable supply of water quantity.

Protect and restore the water quality.

“Water” - The Earth's Most Important Resource

“Provide Access to Clean Water” within

The Grand Challenges for Engineering in The 21st Century (5/14) U.S. National Academy of Engineering Feb. 15, 2008

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Major Problems of Water Environment • Limited Water Resource Water is so common that we take it for granted

• Safe Drinking Water Over 1 billion people (1/6) lack access to safe drinking water worldwide

• Appropriate Wastewater Discharge Historically discarded in the cheapest method possible

Water Resources Engineering

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precipitation

Water Cycle Components 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

Storage in ice and snow: freshwater stored in the frozen form, usually in glaciers, icefields and snowfields. Precipitation: discharge of water, in the form of rain or snow, from atmosphere. Snowmelt runoff to streams: movement of water as surface runoff from snow or ice to the nearest stream channels. Infiltration: downward movement of water from the land surface into soil and porous rock. Ground water discharge: movement of water out of ground. Ground water storage: water exist for a period below the earth land surface. Water storage in ocean: saline water stored in ocean or inland sea. Evaporation: liquid to gas Condensation: gas to liquid Evapotranspiration: The process by which water is discharged to the atmosphere as a result of evaporation from soil and transpiration by plants. Water storage in atmosphere: water stored in atmosphere in as vapor, such as clouds and humidity. Surface runoff: precipitation runoff which travels over the soil surface to the nearest stream channels. Stream flow: water movement in a channel on land surface, such as river. Springs: a place where concentrated discharge of groundwater flows at the ground surface. Freshwater storage: freshwater stored on the Earth surface, such as lake or reservoirs. Sublimation: from solid phase to gas phase.

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Global Water Distribution

2.5% × 0.3% = 0.0075% !

12900 m3/c.a (1970), 9000 m3/c.a (1990), 7000 m3/c.a (2000), 5100 m3/c.a (2025).

5100 m3/c.a would be enough to meet individual human needs, if it distributes equally among the world's population.

2 1 3

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The annual precipitation in Hong Kong is about 2169 mm.

Transport of Water

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Engineering for Development: Aqueduct “Aqueduct” is a water supply channel (conduit) constructed to convey water.

r ate W g rin p S

Purposes • Irrigation • Drinking water • Transportation (More recent time, such as canals)

City A 50 km aqueduct in the South of France.

Top layer: A water conduit [1.8m H × 1.2 m W]

Pont du Gard - “Bridge of the Gard (river)”. A 275 m aqueduct constructed by the Roman Empire circa 19 BC. (World Heritage Site in 1985)

• Early Time: Time Earth or porous material

• Modern time: time Concrete, polymers, or impermeable soils

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Hoover Dam

When completed in 1936, it was the world's largest concrete structure (379 m L × 221m H). Lake Mead can store 35.2 km³ of water.

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Dedicated aqueduct from Dongjiang intake to Shenzhen Reservoir (since 2003)

: Output capacity 2.6 Mm3 per day

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Plover Cove Reservoir (1967) Storage capacity 0.22973 km3 (229.73 Mm3)

High Island Reservoir (1978) Storage capacity 0.28112 km3 (281.12 Mm3)

Alternative Water Source To conserve supplies of fresh water, Hong Kong is progressively increasing the use of sea water as an important alternative source of flushing water for buildings. Sea water, treated at seafront salt water pumping stations, is piped to end user buildings or into service reservoirs for storage. About 80 % of Hong Kong’s population uses salt water for flushing purposes. (2006)

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Functional Components of Modern-Day Water Utility

How expensive of producing drinking water ? ($$ /m3)

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Knowledge Applied in Water Resources Engineering ƒ Hydrology Sources and quantity of water ƒ Hydraulic engineering Design of wells, dams, reservoirs, transport, distribution systems ƒ Physics, Chemistry, Microbiology Water quality and treatment processes ƒ Management Policies, administration ƒ Economics Cost evaluation, pricing

Water Treatment

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Why We Need Water Treatment ? • Purification for domestic use • Treatment for specialized industrial applications

Examples • Domestic use: Thoroughly disinfected, appreciate level of mineral ions • Boiler use: Very low mineral ions but may tolerate bacteria

Common Drinking Water Treatment For drinking water from natural water source

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Application Example: Treating Well Water for Municipal Use

• • • • •

Aeration: volatile compounds (H2S, CH4, NH3,...) Lime (CaO or Ca(OH)2): pH↑, precipitate metal ions Coagulation: add Fe- or Al-sulfates to settle suspended particles CO2: pH adjustment back to neutral Cl2: disinfection

Application Example: Treating Water for Industrial Use External Treatment Basic treatment for entire water supply • Aeration, coagulation, sedimentation, sand filtration, etc.

Internal Treatment Further modify properties for specific applications • • • •

Addition of inhibitors to prevent corrosion Agents to prevent metal ions precipitation Disinfection for food processing Membrane filtration for electronic components fabrication

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Disinfection Technique: Chlorination ™ Most commonly used: Cl2(g) + H2O → H+ + Cl- + HOCl HOCl → H+ + OClHOCl and OCl- are "free available chlorine" and very effective in killing bacteria. ™ Chloramines can also be used by having ammonia: NH4+ + HOCl → NH2Cl (monochloramine) + H2O + H+ NH2Cl + HOCl → NHCl2 (dichloramine) + H2O NHCl2 + HOCl → NCl3 (trichloramine) + H2O Chloramines are "combined available chlorine", weaker disinfectants, but are more readily retained throughout the distribution system. ™ The problem is carcinogenic "disinfection by-products (DBPs)", such as trihalomethanes (THMs), produced by reacting with organic matters.

Disinfection Technique: Ozonation ™ A disinfectant in place of chlorine, particularly in Europe. Generated on site to contact water for 10-15 mins: 2O3 → 3O2(g) ™ Advantages: No order or taste left in treated water, and More destructive to viruses than chlorine. ™ Ozonation gained increased interest due to the concern over DBPs by chlorination, but it was recently discovered with the promotion of bromate (carcinogenic) formation in water. Br- + O3 → BrO3™ Disadvantages: No residual in water due to low solubility, and the potential bromate formation.

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Sewage (Wastewater) Treatment

Municipal sewage may contain... Oxygen-Demanding Materials Algal Nutrients

Hazardous Metals

Viruses Pathogenic Bacteria Pesticides

Municipal Sewage

Grease

Oil

Scum Salts Sediments

Refractory Organics

Others that were hard to image !?

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Strategy of Sewage (Wastewater) Treatment

Further purification...

Tertiary Treatment

BOD Removal...

Secondary Treatment

Insoluble matters...

Primary Treatment

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Primary Treatment Purpose: Removal of insoluble matters (solids, grease,...) • Screening out large size solids (usually the first step) • Remove settleable and floatable solids by primary sedimentation: - Add chemicals to help settling or precipitation and remove them as sludge - Remove floats known collectively as grease by skimming

Secondary Treatment (1) Purpose: Use biological process to remove BOD • BOD (Biochemical Oxygen Demand)? - Measure how fast biological organisms use up oxygen in a body of water - Pristine rivers: <1 mg/l; Moderately polluted: 2-8 mg/l; Untreated sewage: 200-600 mg/l. - Indicate how much harmful biodegradable organic matters in water

• Strategy: Using aerobic biological processes. Microorganisms provided with added oxygen to degrade organic matters in water, in order to reduce organic matters (also BOD) to acceptable levels.

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Secondary Treatment (2)

• Attached Growth Processes: - Trickling Filter Wastewater is sprayed over hard solid support covered with microorganisms, and is exposed to air. - Rotating Biological Reactor Microorganisms grow on the drums, and the drums are slowly rotated to periodically submerge the microorganisms in the wastewater to remove organic materials.

Secondary Treatment (3)

• Suspended Growth Process: - Activated Sludge Add dissolved oxygen to promote the growth of microorganisms on suspended sludge that substantially removes organic matters. The process create large surface area for reaction, but will need to settle and treat the sludge particles during the process.

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Tertiary Treatment • Sometimes called "Advanced Water Treatment" • Further remove: - Dissolved small organic compounds (potential toxicity) - Dissolved inorganic materials (algal nutrients, nitrates, phosphates, hazardous metals) • Disinfection to kill bacteria/viruses which may be harmful to human/animal health. • Examples: chlorination, ozonation, UV disinfection, activated carbon sorption, filtration, distillation, etc.

Technology Outlook: Membrane Filtration for Water Recycling

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Membrane Filtration

(Reverse Osmosis) (Nanofiltration)

(Ultrafiltration)

(Microfiltration)

ƒ

Advantages: High treatment efficiency, stable system, compact facility (low capital cost)

ƒ

Disadvantages: Energy consumption (high operational cost), cost of membranes*

* Largely decreased recently but is still a major cost for good membranes

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Orange County Water District’s Reclaimed Water [2:25]

Water Factory – 21 One of the best known projects of the Orange County Water District (OCWD), located along the Southern California coast between Los Angeles and San Diego. Water Factory 21 protects groundwater from seawater intrusion by injecting up to 5.7 x 104 m³/d of highly treated reclaimed water blended with deep-well water into four coastal aquifers. More than half the injected water flows inland and becomes potable water supplies. The treatment technique includes clarification, sand filtration, followed by reverse osmosis (RO) membrane technology and chlorination. Water Factory 21 plans to provide a reliable supply of injection water, even in times of drought period.

Water Reuse Most difficult is on the controversy swirling around the "Toilet to Tap" idea, which appears to offend the sensibilities.

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The Role of Engineered Treatment, Reclamation, and Reuse Facilities in The Cycling of Water

(Metcalf & Eddy, 4th ed, 2003)

To see may not be something you would like to believe ~

“The Water World” Lab

* Brought to you by Dr. Shih’s research group…

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Got Safe Water to Drink ?

██ Methyl Red (pH=5) ██

██ Thymol Blue (pH=9) ██

pH Acidic

Neutral

Basic

What Is It in Your Water ? NaOH(aq)

NaOH(aq)

Weak Acid

Strong Acid

pH2.5

pH2.5

0.1 M of CH3COOH(aq)

0.003 M of HCl(aq) ██ Methyl Red (pH=5) ██

CH3COOH(aq) →

HCl(aq) → H+ + Cl-

CH3COO- + H+

(Ka= 107)

(Ka= 10-4.75)

[CH3COO-][H+]/ [CH3COOH] = 10-4.75

[CH3COOH] >> [CH3COO-]

[Cl-][H+]/[HCl] = 107

pH4

pH11 [Cl-] >> [HCl]

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It Is NOT Just Water !!

? ZnCl2 (aq)

NaOH (aq) ZnCl2(aq)

⇒

Zn2+ +

Cl-

NaOH(aq)

⇒

Na+

OH-

+

Zn(OH)2(s) ↔ Zn2+ + 2OH-

(Ksp= 10-16.35)

When [Zn2+][OH-]2 > 10-16.35, precipitation of Zn(OH)2(s) will happen

Engineer’s TOOLBOX…

for our Sustainable Development…

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Henry’s Constant  Acidity Constant, (Ka) CH3COOH(aq) → CH3COO- + H+

Ka = 10-4.75

 Solubility Constant, (Ksp) Zn(OH)2(s) → Zn2+ + 2OH-

Ksp = 10-16.35

 Henry’s Constant, [KH] NH3(g) → NH3(aq)

KH = 57 (M/atm)

Solubility of Gases in Water Pg

Henry’s Law: [Dissolved Gas] [Dissolved Gas] KH Pg

=

KH Pg

[Dissolved Gas] William Henry (1775-1836), an English chemist.

= concentration of dissolved gas (M = mol/L) = Henry’s Constant (mol/L-atm or M/atm) = the pressure of the gas (atm)

Henry’s Constants (M/atm)

„ At 25oC and 1 atmosphere of pressure, what is the equilibrium concentration of O2 in water? Air is 21% of O2(g), Pg = 0.21 atm. [O2] = KH × Pg = 0.0012630 × 0.21 = 2.65 × 10-4 M = 8.5 mg/L

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Ammonia Stripping – An example of removing volatile organic chemicals from water Q:

Wastewater is contaminated by ammonia [NH3] and ammonium [NH4+] ions with a total concentration of 7.1 × 10-4 M. You are given the equilibrium condition between these two species: NH4+ = NH3 + H+

Ka = 5.5×10-10

At pH10, 25oC and atmospheric ammonia pressure is 5 × 10-10 atm, how much percentage of total dissolved ammonia (including both ammonia and ammonium) can be removed by blowing air into this wastewater when equilibrium reached? You are given Henry’s Constant of NH3 at 25oC as KH = 57 M/atm.

Dr. Shih’ Shih’s Catch & Treat Lab.

Henry’s Law: [NH3] = KH Pg

← Inject Air Pg of NH3(g) = 5 × 10-10 atm

AFTER Total NH3(aq) : [NH3] + [NH4+] =?M

START Total NH3(aq) : [NH3] + [NH4+] = 7.1 × 10-4 M

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ANS: n In equilibrium with air, [NH3]eq = KH × PNH3 = 57×5×10-10 = 2.85×10-8M o Due to: NH4+ =

NH3 +

H+

Ka = 5.5×10-10

In equilibrium with air, the concentration of NH4+ is: [NH4+]eq = [NH3]eq [H+] / Ka = 5.2×10-9M p The total dissolved ammonia (including both ammonia and ammonium), [NH3]eq, T, is : [NH3]eq, T = [NH3]eq + [NH4+]eq = 3.37 × 10-8 M

Bye, bye!

q So, the % removal is: 1 – [ (3.37 × 10-8) / ( 7.1 × 10-4) ] = 99.995%

ENGG 1006: Engineering for Sustainable Development

Dr. Shih’s Regular Office Hours QUESTIONS, learning HELP, or more DISCUSSION ? (1) In person September 7, 14, 21, 28 (Mondays) 5-7pm at Haking Wong Building Room 5-26 (2) Via phone or e-mail Call 2859-1973 or e-mail for appointment

Kaimin Shih (PhD, Stanford University)

DEPARTMENT OF CIVIL ENGINEERING THE UNIVERSITY OF HONG KONG Office: Rm. 5-26, Haking Wong Building • Phone: 2859-1973 • E-mail: [email protected]

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