Isha Ray
Energy & Resources Group, UC Berkeley
isharay@berkeley.edu
Waste not, want not
Wastewater re-use for urban /
peri-urban irrigation
March 25 2011
Cities Conference | New Delhi
1
“The sewer is the conscience of the city”
(Victor Hugo, Les Miserables)
March 25 2011
Cities Conference | New Delhi
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The sewer is the conscience of the city

2 million tons of human waste dumped untreated in water
bodies *every day* (UNESCO 2003)

Lancet, v 368, 2006: Investments in sewer systems in 20th
century led directly to massive reductions in mortality
British Medical Journal 2007 poll: sanitation voted ‘greatest
medical advance’ in 166 years

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Sanitation & collection / treatment of human waste is as critical
to public & environmental health as is water supply (recognized by
HPEC Report 2011 chaired by Isher Judge Ahluwalia)
March 25 2011
Cities Conference | New Delhi
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Indian cities treat very little of the
wastewater they generate

Access to improved sanitation in urban India, 2008: 54%

Urban India generates >26 million liters of ww/day

Official capacity to treat is 27% of that volume. In reality, (e.g.)
Delhi treats less than 20% of its wastewater (HDR 2006)

Cost of treatment types vary hugely; construction $15 - $75
/person and O&M $1 - $10 / person/year. Variation depends on
technology, population density, climate, end-use (Nelson & Murray
2008).
March 25 2011
Cities Conference | New Delhi
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This is true for most cities in most of the
world
Accra, Ghana. Photo: Ashley Murray
March 25 2011
Cities Conference | New Delhi
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But partially treated wastewater is a
valuable resource

Biogas recovery
Irrigation (food & non-food crops, with differences in quality of
treated water; landscaping)
Aquaculture
Groundwater recharge; Streamflow recharge
Industrial uses

Therefore financial costs of treatment can be partially recouped
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(Murray, Ray & Nelson 2009)
(also HPEC 2011 p53, tho’ irrigation not discussed)
March 25 2011
Cities Conference | New Delhi
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Urban & peri-urban agriculture needs
water and nutrients
QuickTime™ and a
decompressor
are needed to see this picture.
March 25 2011
Cities Conference | New Delhi
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Sewage-fed aquaculture is well-known in
Kolkata
QuickTime™ and a
decompressor
are needed to see this picture.
March 25 2011
Cities Conference | New Delhi
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Seasonal / vegetable crops are especially
suited to peri-urban agriculture
QuickTime™ and a
decompressor
are needed to see this picture.
Photo: CGIAR
March 25 2011
Cities Conference | New Delhi
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Why aren’t more cities designing their
ww tx for re-use?
1)
Planning: Usually compartmentalized (also HPEC
2011 p 62) ‘Waste’water systems -- when they exist
-- designed for disposal, not for re-use.
2)
Economic / environmental: does wastewater
irrigation make sense for the city? For the farmer?
IS IT WORTH IT?
[Also: cost recovery? health risks? Consumer acceptance?]
March 25 2011
Cities Conference | New Delhi
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A model of wastewater irrigation:
assess, simulate, select

Coupled performance assessment and optimization model for
wastewater systems for re-use in agriculture (Murray & Ray WR
2010)

Three steps:
1)
Assess: performance of current agriculture in catchment area
of city (with current level of irrigation)
Simulate: multiple feasible re-use scenarios
Select: optimal wastewater re-use design & scenario -- based
on what is “optimal”. Make trade-offs *transparent*
2)
3)
March 25 2011
Cities Conference | New Delhi
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Pixian and its farm economy

Peri-urban district in Sichuan province, south west China

25,000 m3/d wastewater, usually discharged untreated

127,000 farmers; average landholding < 0.5 acres

4 irrigation canals: Xuyan, Zouma, Baitiao, Jiangan

Main crops: rice, winter wheat, rapeseed, fall vegetables, spring
vegetables, cabbage, green onion, garlic, chuanxiong
March 25 2011
Cities Conference | New Delhi
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Model results: freshwater can be saved
by irrigating with urban wastewater
QuickTime™ and a
decompressor
are needed to see this picture.
March 25 2011
Cities Conference | New Delhi
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Model results: agricultural incomes benefit
from wastewater irrigation

Zouma irrigation system with conventional irrigation
supplemented by wastewater: farm profits change
between 0% and +13%

Zouma irrigation system with conventional irrigation
replaced by wastewater: farm profits change between
-3% and +16%

Head-tail asymmetry on canal system also declines
March 25 2011
Cities Conference | New Delhi
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Financing could partially be covered by
back-end users of sanitation

For Pixian, regional farm profits could rise by $20
million / year with ww supplement
(or treated water could be conserved for other purposes)

This approach needs demand analysis of re-use as
part of planning process, not afterthought

Needs coordinated sanitation and irrigation planning - traditionally these are completely separated (Murray
and Ray, JPER 2010)
March 25 2011
Cities Conference | New Delhi
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Wastewater re-use simultaneously
addresses sanitation and irrigation

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Mainly a planning strategy for high-density urban areas where
it’s feasible to collect and treat large volumes of wastewater
Urban sanitation usually treated as disposal problem, not re-use
opportunity
Irrigation in urban periphery usually faces water shortage;
“competes” with domestic needs
Wastewater re-use is potential solution to *both*
Hence: waste not, want not
HPEC 2011: “…build synergies between urban & rural parts of
the economy…” (p5)
March 25 2011
Cities Conference | New Delhi
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Wastewater re-use: barriers

Monitoring and regulation are critical -- handling waste is
hazardous

Sewers (even if low cost sewers) have to be built to transport
waste away towards treatment sites.

It’s expensive to build sewers & treat waste

Water & sanitation agencies have to be “decompartmentalized”. Possibly expensive. Definitely political.
-- None of this is trivial -March 25 2011
Cities Conference | New Delhi
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Wastewater re-use: advantages
On the other hand:
1.
4.
5.
Significant public health benefits
Significant urban environment benefits
Can be achieved through low-energy treatment systems such
as stabilization ponds
Potential to reduce peri-urban water constraints
Potential for partial cost recovery
6.
Potential to “generate urban-rural synergy”
2.
3.
(HPEC 2011, p22)
-- And don’t forget Victor Hugo -March 25 2011
Cities Conference | New Delhi
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Wastewater re-use: conclusions

Design for re-use, not for disposal
(Murray/Nelson/Ray 2009)

Consider the lack of wastewater infrastructure as an
opportunity to design for re-use

Assess, simulate, select: Conduct market analysis.
Calculate the costs & benefits of alternative forms of
wastewater treatment at the design stage
(What is the user demand? How / how much to treat depending on end use?
What do different sewer + treatment systems cost? Can water agencies adapt to
unconventional strategies? )
March 25 2011
Cities Conference | New Delhi
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Thank you
(and to my colleagues Dr. Ashley Murray, Dr. Kara Nelson)
QuickTime™ and a
decompressor
are needed to see this picture.
Photo: Kibera by breathedreamgo
WW fed fish pond, Ghana. Photo: Ashley Murray
March 25 2011
Cities Conference | New Delhi
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