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March 25 2011Cities Conference | New Delhi1 Waste not, want not Wastewater re-use for urban / peri-urban irrigation Isha Ray Energy & Resources Group,

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Presentation on theme: "March 25 2011Cities Conference | New Delhi1 Waste not, want not Wastewater re-use for urban / peri-urban irrigation Isha Ray Energy & Resources Group,"— Presentation transcript:

1 March Cities Conference | New Delhi1 Waste not, want not Wastewater re-use for urban / peri-urban irrigation Isha Ray Energy & Resources Group, UC Berkeley

2 March Cities Conference | New Delhi2 “The sewer is the conscience of the city” (Victor Hugo, Les Miserables)

3 March Cities Conference | New Delhi3 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)

4 March Cities Conference | New Delhi4 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).

5 March Cities Conference | New Delhi5 This is true for most cities in most of the world Accra, Ghana. Photo: Ashley Murray

6 March Cities Conference | New Delhi6 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)

7 March Cities Conference | New Delhi7 Urban & peri-urban agriculture needs water and nutrients

8 March Cities Conference | New Delhi8 Sewage-fed aquaculture is well-known in Kolkata

9 March Cities Conference | New Delhi9 Seasonal / vegetable crops are especially suited to peri-urban agriculture Photo: CGIAR

10 March Cities Conference | New Delhi10 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?]

11 March Cities Conference | New Delhi11 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*

12 March Cities Conference | New Delhi12 Pixian and its farm economy  Peri-urban district in Sichuan province, south west China  25,000 m 3 /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

13 March Cities Conference | New Delhi13 Model results: freshwater can be saved by irrigating with urban wastewater

14 March Cities Conference | New Delhi14 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

15 March Cities Conference | New Delhi15 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)

16 March Cities Conference | New Delhi16 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)

17 March Cities Conference | New Delhi17 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 --

18 March Cities Conference | New Delhi18 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 --

19 March Cities Conference | New Delhi19 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? )

20 March Cities Conference | New Delhi20 Thank you (and to my colleagues Dr. Ashley Murray, Dr. Kara Nelson) Photo: Kibera by breathedreamgo WW fed fish pond, Ghana. Photo: Ashley Murray

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