City Speak XII - Water We Drink: Bevis Mak of Aecom
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City Speak XII - Water We Drink: Bevis Mak of Aecom



Where does the water we drink come from? Is there enough for everyone? Where will it come from? ...

Where does the water we drink come from? Is there enough for everyone? Where will it come from?

Hong Kong's water supply comes from two sources: the rainfall we collect in our reservoirs (20-30%) and water we buy from the Mainland (70-80%). The current agreement for water from the Dongjiang, a tributary of the Pearl River, will expire in 2015. With demand for water growing sharply throughout the Pearl River Delta and the supply of water compromised by pollution and climate change, Hong Kong's future access to clean water is far from certain.

In our drive to become a sustainable city, should Hong Kong become self-sufficient? Should we increase the size of our reservoirs? Follow Singapore and recycle our waste water? Build plants to desalinate seawater? What other possible methods are there? Who's going to pay?

CitySpeak invites you to join Hong Kong officials, academics and planners in this discussion about our water issues.

The keynote speaker is Mr. LT Ma, Director of the Water Supplies Department, who will set the scene and outline the current situation in Hong Kong. The discussion will be moderated by Mr. Mike Kilburn, Environmental Programme Manager, Civic Exchange.

Background reading
"Liquid Assets -- Water security and management in the Pearl River Basin and Hong Kong" by Civic Exchange, November 2009 ( For more information about water in China, visit Civic Exchange is a Hong Kong independent non-profit think tank. See:

Designing Hong Kong is a not-for-profit organisation focused on sustainable urban planning. See:



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City Speak XII - Water We Drink: Bevis Mak of Aecom City Speak XII - Water We Drink: Bevis Mak of Aecom Presentation Transcript

  • City Speak - The Water We Drink: Water Treatment Technology and Demand Management Bevis Mak Executive Director, Water, AECOM 15 May 2010
  • From Source to Tap – How Does It Work?
    • A brief history of water treatment
    • What is in our raw water?
    • Treatment philosophy and method
    • Sustainable water resources planning
      • Demand management
      • New water sources: Seawater
      • New water sources: Reuse
    • Conclusion
  • A Brief History of Water Treatment
  • Historical Development of Water Treatment (1)
    • 1676: Microorganisms found under microscope
    • 1746: First patent for a filter design. Commercial product in 1750 consisting sponge, charcoal and wool
    • 1804: First treatment plant in Scotland using filters
    • 1854: first report case tracing a terrible epidemic of cholera due to contamination of water by a cholera victim recently returned from India
    • 1931: Virus identified by electron microscope
  • Historical Development of Water Treatment (2)
    • 1930s: With filtration and chlorination, no more waterborne disease outbreak in US
    • 1950-80: Major improvements in cost effective treatment design:- clarification + filtration
    • 1974: Chlorine + organics in raw water = trihalomethanes + other carcinogens (DBP disinfection by-products)
    • 1993: Outbreak in Milwaukee identified a new organism: cryptosporidium and giardia (C&G) [54 deaths, 700+ ill; False alarm in Sydney in1998]
    • 1990s: Advanced treatment technology - membranes, ozone and UV
    Page Giardia (4-14 micron) Cryptosporidium (4 - 6 microns)
  • What is in our raw water?
  • Our Water
    • Source water from rivers, lakes, groundwater  reservoirs
    • Many inorganic, organics and biological matters in raw water
    • Inorganics : calcium, magnesium, sodium, potassium, carbonate, sulphate, chloride, nitrogen,
    • phosphorus, iron, manganese etc
    • Organics : mostly natural decomposition of plant and animal material, + synthetic (industrial and agricultural)
    • Biological : bacteria, viruses, algae, other micro-organisms (protozoans such as C&G etc, helminths etc)
  • Particles in Water – How dirty does it look?
    • Finely divided solids not generally distinguishable by the unaided eye
    • Mainly from soil weathering processes and biological activities
    • Potential absorption sink for toxic substances such as heavy metal and DBP
    • Can cause strong scattering of incident light and leads to degradation of visibility
    • Clear water < 1NTU; runoff with sediment 40+ NTU
  • Treatment Philosophy and Method
  • World Health Organization (WHO) “Guidelines for Drinking-water Quality” 2006 (WHO 2006)
    • … Securing the microbial safety of drinking-water supplies is based on the use of multiple barriers , from catchment to consumer, to prevent the contamination of drinking-water or to reduce contamination to levels not injurious to health. Safety is increased if multiple barriers are in place…
    • Impounding reservoirs - self cleaning and dilution
    • Treatment processes – minimum 2 processes, and each process enhances efficiency of next process
  • Our Water Sources
    • 30% local catchment water and 70%+ Dongjiang water
    • Reservoirs:
      • Local catchment with excellent water quality: High Island, Shek Pik, Tai Tam, Kowloon and Aberdeen Groups of Reservoirs
      • Local catchment with partial mixing by Dongjiang water: Tai Lam Chung, Shing Mun Reservoirs
      • Main storage for Dongjiang water: Plover Cove Reservoir
    • Most major treatment plants treats Dongjiang water direct, eg, Sha Tin Water Treatment Works handles 40% of supply daily
    • Quality of Dongjiang water affects treatment options
  • What Are the Key Concerns in Our Water?
    • 5 most “difficult” parameters:
      • Avoid DBP formation (health) – oxidant / dosing point
      • Ammonia (health) – oxidation, biological
      • Manganese (aesthetics, brown water) - oxidation
      • Turbidity (health and aesthetics) – clarification + filtration
      • 4 log (99.99%) removal/reduction of C&G (health) – advanced treatment needed
    • What’s in Dongjiang water:
  • Conventional Treatment Approach
    • Soluble organics / inorganics: chemical reaction to make them insoluble [Mn 2+ -> Mn 4+ (MnO 2 )]
      • Ozone if available (chlorination no long practiced)
    • Insoluble particles – make them stick and bigger, carry with them the micro-organism and other toxic substance, and settle out faster
      • Addition of alum at pH 6.0-6.5 (polymer optional)
    • After most organics are removed in above process, add chlorine for oxidation if needed to avoid formation of DBP
    • Finer particles are removed by filtration
    • Chlorine added for final disinfection
  • The Process Diagram Page
  • Before and After Clarification Page Solids formed after coagulation and flocculation
  • Traditional Clarifiers Page
  • Filtration Page
    • Dual media
    • Biofilters
  • Site Utilization – When Land Becomes An Issue
    • Traditional clarifiers robust and stable
    • Gravitation, with minimum energy
    • But they are slow with large land intake
    • Can they be more efficient?
  • Clarification Process Foot Print
    • Proprietary systems are smaller, but are more energy and/or chemical intensive
    • Long term O&M cost
    Conventional 100% Solids Contact - 40 % Superpulsator - 17% DAF - 14% DensaDeg - 10% Adsorption Clarifier - 6% Actiflo - 3%
  • C&G Treatment
    • Mainly from human and animal waste pollution
    • Can cause serious gastrointestinal problems to immuno-compromised population: 54 death and 700+ ill in Milwaukee 1993
    • 4-log removal of C&G required for new WTW built after 2003
    • Conventional treatment (clarification + filtration) inadequate: either by membrane (replacing clarification+filtration) or addition of ozone/UV disinfection
    • Not a major problem for Hong Kong
  • How’s Our Treated Water Like?
    • Treated Water Quality Standards:
      • Primarily WHO Guidelines 2006
      • USEPA standards
      • EC standards
    • WSD samples regularly:
      • 4 Microbiological parameters
      • 92 Chemicals of health significance
      • 15 other parameters
    • Full compliance based on the annual average of monitoring data in accordance with international practice
  • Sustainable Water Resource Planning
  • Sustainable Water Resources Planning Portfolio Conservation Reuse Desalination Groundwater Surface Water Brackish Water Sea Water General Indirect Potable Direct Potable
  • Sustainable Water Resource Planning Demand Management
  • Water Demand Management – Conserve What We Have
    • Education on water conservation: good practices on use of water and water savings
    • Promotion on use of water saving devices
    • Leakage control – pressure management and replacement of aging pipes
    • Extension on use of sea water for toilet flushing
  • Sustainable Water Resource Planning New Water Source – Seawater Desalination
  • Seawater Desalination – Thermal Process
    • Not quality or salinity dependent
    • Multi-stage systems with heat recovery
    • Much more efficient than the 1973 system but still significantly more expensive than membrane system; viable only co-locate with power plant
    Page Photo from: WSD “Water for a Barren Rock” Completed 1976 Demolished 1992
  • Seawater Desalination – Thermal Process Page Al Hidd MED Plant, Bahrain (273 ML/d)
  • Seawater Desalination – Reverse Osmosis Membrane Process
    • A membrane is like a paper filter, a physical barrier, but holes are much smaller, and is designed to take much higher pressure
    • Latest material: Polyvinylidene Difluoride (PVDF)
    • Pore size/ Pressure
      • Micro/ultra filtration (MF/UF)
      • Nanofiltration (NF)
      • Reverse osmosis (RO)
    Page 4 to 6 micron 0.1 micron pore size
  • Membrane Pore Size Smaller than Most Microorganisms 0.0001 0.001 0.01 0.1 1 10 100mm hair Crypto- sporidium smallest micro-organism polio virus MF/UF: -0.2 to 2.0 bar (1 bar = 10m depth of water) NF: 5 to 9 bar RO: 10 to 100 bar Suspended solids Parasites Bacteria Org. macro. molecules Viruses Colloids Dissolved salts Sand filtration Microfiltration Ultrafiltration Nanofiltration Reverse Osmosis
  • Seawater Desalination
    • All membrane units are VERY expensive; so is energy cost
    • Many contaminants in seawater will cause fouling:
      • Some contaminants can precipitate on the membrane surface
      • Microrganisms can grow on the membrane surface
      • Some chemicals can chemically degrade the membranes
    • Must have good pre-treatment and screening: Normally MF/UF + RO
    • RO cannot completely eliminate boron ; second pass RO needed
  • Process Diagram Page
  • Pilot Testing of Desalination in Hong Kong
    • WSD conducted pilot testing of sea water desalination at Tuen Mun and Al Lei Chau
    • At Tuen Mun – dilution from Pearl River but seasonal variations and organics increase bio-fouling
    • At Ap Lei Chau – higher salinity but more consistent seawater quality
  • Sustainable Water Resource Planning New Water Source – Reclamation / Reuse
  • Water Reclamation / Reuse
    • Treated secondary effluent is a major water source
    • Technologically, easier to treat than seawater – more consistent quality
    • Australia, California, Singapore – indirect potable or industrial use using MF/UF + RO, similar to seawater desalination
    • Public acceptance is a major obstacle
  • Water Reclamation / Reuse – Hong Kong Applications
    • Ngong Ping: Sand filtration + UV after secondary treatment
    • Shek Wu Hui STW Pilot Scheme: MF/UF + chlorine disinfection after secondary treatment
    • Water used for irrigation, toilet flushing and water features
  • Summary and Conclusion
  • Conclusion
    • Technology has an important role to play in
      • providing a safe drinking water, and
      • Tapping into new water sources
    • There is a price tag to new technology:
      • Higher capital cost of more expensive equipment
      • Higher energy and chemical cost because of higher level of treatment
      • Higher maintenance cost because of expensive spares and replacements
      • Higher carbon footprint
  • To put the numbers into perspective: O&M Cost (Process +power / maintenance / staffing)
    • * high cost due to high membrane replacement cost against small production/demand]
    • There is a price to be paid!
    Page   O&M Cost Power Only Conventional $0.16/m 3 $0.02/m 3 Desalination (MF+RO) $4.0/m 3 $1.8/m 3 Reuse (MF+Cl 2 )* $5.2/m 3 $0.8/m 3
  • But …we do not wish to see this again! Page So, conserve now!
  • Thank You