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Isha Ray Energy & Resources Group, UC Berkeley [email protected]. Waste not, want not Wastewater re-use for urban / peri-urban irrigation. “The sewer is the conscience of the city” (Victor Hugo, Les Miserables). The sewer is the conscience of the city. - PowerPoint PPT Presentation
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March 25 2011 Cities Conference | New Delhi 1
Waste not, want not
Wastewater re-use for urban / peri-urban irrigation
Isha RayEnergy & Resources Group, UC Berkeley
March 25 2011 Cities Conference | New Delhi 2
“The sewer is the conscience of the city”(Victor Hugo, Les Miserables)
March 25 2011 Cities Conference | New Delhi 3
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
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 4
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 5
This is true for most cities in most of the world
Accra, Ghana. Photo: Ashley Murray
March 25 2011 Cities Conference | New Delhi 6
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(Murray, Ray & Nelson 2009)
(also HPEC 2011 p53, tho’ irrigation not discussed)
March 25 2011 Cities Conference | New Delhi 7
Urban & peri-urban agriculture needs water and nutrients
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March 25 2011 Cities Conference | New Delhi 8
Sewage-fed aquaculture is well-known in Kolkata
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March 25 2011 Cities Conference | New Delhi 9
Seasonal / vegetable crops are especially suited to peri-urban agriculture
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Photo: CGIAR
March 25 2011 Cities Conference | New Delhi 10
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 11
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)
2) Simulate: multiple feasible re-use scenarios
3) Select: optimal wastewater re-use design & scenario -- based on what is “optimal”. Make trade-offs *transparent*
March 25 2011 Cities Conference | New Delhi 12
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 13
Model results: freshwater can be saved by irrigating with urban wastewater
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March 25 2011 Cities Conference | New Delhi 14
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 15
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 16
Wastewater re-use simultaneously addresses sanitation and irrigation
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 17
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 “de-compartmentalized”. Possibly expensive. Definitely political.
-- None of this is trivial --
March 25 2011 Cities Conference | New Delhi 18
Wastewater re-use: advantages
On the other hand:1. Significant public health benefits
2. Significant urban environment benefits
3. Can be achieved through low-energy treatment systems such as stabilization ponds
4. Potential to reduce peri-urban water constraints
5. Potential for partial cost recovery
6. Potential to “generate urban-rural synergy” (HPEC 2011, p22)
-- And don’t forget Victor Hugo --
March 25 2011 Cities Conference | New Delhi 19
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 20
Thank you(and to my colleagues Dr. Ashley Murray, Dr. Kara Nelson)
Photo: Kibera by breathedreamgo
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WW fed fish pond, Ghana. Photo: Ashley Murray