Direct potable Reuse: The next frontier

Direct potable Reuse:
The next frontier
WORKSHOP ON CRITERIA FOR
DIRECT POTABLE REUSE
Los Angeles, CA
August 29, 2012
George Tchobanoglous
Department of Civil and Environmental Engineering
University of California, Davis
Overview of Presentation
• Take Home Message
• How to Think About Wastewater
• Definition of Indirect and Direct Potable Reuse
• Driving Forces for Direct Potable Reuse
• Definition of Direct Potable Reuse
• The Future: The Southern California Example
• Challenges and Opportunities for
Wastewater Treatment and Water Purification
1

Take Home Message
Ultimately, if a significant amount of
wastewater is to be recycled from large
(coastal) cities, direct (and indirect)
potable reuse is inevitable in urban areas
and will represent an essential element of
sustainable water resources management.
• Must think of wastewater differently.
• To make it a reality, bold new planning
must begin now!!
How to Think About Wastewater
in the 21 st Century
W t t i bl
Wastewater is a renewable
recoverable source of energy,
nutrients, and potable water
2

Driving Forces for Direct Potable Reuse
• The value of water will increase significantly in the
future (and dramatically in some locations)
• Impact of global trends: urbanization and population
p
demographics
• De facto indirect potable reuse is largely
unregulated (e.g., secondary effluent, ag runoff,
urban stormwater, highway runoff)
• Existing and new technologies can and will meet the
water quality challenge
• Population growth and global warming will lead to
severe water shortages in many locations. A
reliable alternative supply should be developed
• Stringent environmental regulations
Impact of Urbanization on Agriculture Reuse
3

Population Demographics:
Urbanization Along Coastal Areas
• By 2030, 60 percent of world’s population
p
will near a coastal region
• Withdrawing water from inland areas,
transporting it to urban population centers,
treating it, using using it once, and
discharging it to the coastal waters is
unsustainable.
Impact of Coastal Population Demographics
on Water Reuse
4

Definition of
Direct and Indirect
Potable Reuse
Proven and Conceptual
Engineered Buffer Systems
5

Opportunities for the Future:
The Southern California Example
Water Use By County in Southern CA
Quantity, Mgal/d
Item
Los
Angeles
Orange
San
Diego
Riverside
San
Bernardino
Population,
1000’s
9,935 2988 2933 1946 1964
Groundwater 331 49 75 86 77
Surface water 1529 335 356 349 287
Total 1860 384 431 435 364
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Electric Power Consumption
in Typical Urban Water Systems
System
Power consumption, kWh/Mgal
Northern
California
Southern
California
Supply and
conveyance
150 8,900
Water treatment 100 100
Distribution 1200 1200
Wastewater treatment 2,500 2,500
TOTAL 3,950 12,700
Opportunities for the Future:
The Southern California Example
7

Wastewater Management Infrastructure -
Potential Locations for Water Plants
Benefits of the Southern California Example
• Reliable alternative source of supply, more secure
from natural disasters
• Lower cost and reduced energy usage
• 30 billion for Bay-Delta tunnels versus 5 billion for
purification treatment
• More water available for agricultural use, especially
during drought periods
• Environmental benefits for bay delta habitat
restoration
8

Challenges and Opportunities for
Wastewater Treatment and Water Purification
• Source Control (Batch or Continuous, Response)
• Energy Recovery
• Modification of Raw Wastewater Characteristics
• Elimination of Untreated Return Flows
• Flow Equalization
• Operational Mode for Biological Treatment
• Improved Design and Monitoring
• Ongoing Pilot Testing
• Ongoing Management (24 hours per day)
• New Treatment Process Flow Diagrams
Energy Content of Wastewater
Heat energy
Specific heat of water = 4.1816 J/g •°C at 20°C
Chemical oxygen demand (COD)
C 5 H 7 NO 2 + 5O 2 5CO 2 + NH 3 + 2H 2 O
(113) 5(32)
Chemical energy (Channiwala,1992)
HHV (MJ/kg) = 34.91 C + 117.83 H - 10.34 O
- 1.51 N + 10.05 S - 2.11A
9

Energy Content of Wastewater
Constituent Unit Value
Wastewater, heat basis MJ/10°C•10 3
m 3 41,900
Wastewater, COD basis MJ/kg COD 12 - 15
Primary sludge, dry MJ/kg TSS 15 - 15.9
Secondary biosolids, dry MJ/kg TSS 12.4 - 13.5
Required and Available Energy for
Wastewater Treatment, Exclusive of Heat Energy
• Energy required for secondary wastewater
treatment
1,200 to 2,400 MJ/1000 m 3
Energy available in wastewater for treatment
(assume COD = 5.0 g/m 3 )
Q = [500kg COD/1000 m 3 ) (1000 m 3 ) (13 MJ/ kg COD)
6,000 MJ/1000 m 3
• Energy available in wastewater is 2 to 4 times
the amount required for treatment
10

Alternative Technologies for
Primary Treatment and Energy Recovery
Impact of Recycle Flows on
Nitrogen Removal
Return
flows
contain
nitrogen
11

New Biological Treatment Processes
Ambient Temperature Anammox Process
Treatment Process Flow Diagram
Pure Cycle Corporation (c.a. late 1970s)
12

Conceptual Future WWTP Schematic
Energy and product recovery
Solids processing
Preliminary treatment
Primary Effluent treatment
Must Develop New Treatment Process
Flow Diagrams to Avoid Incremenatism
13

Closing Thoughts
• Technology is now available to produce water for
direct potable reuse
• Must resolve disconnect between existing
standards and regulations and scientific findings
• In promoting direct potable reuse, the profession
must speak with a unified vocabulary
• In the future, direct and indirect potable reuse
will be a critical element in the development of
sustainable strategies for water resources
management
THANK YOU
THANK YOU
FOR LISTENING
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