Waste not, want not Wastewater re-use for urban / peri-urban irrigation

1. Isha RayEnergy & Resources Group, UC Berkeleyisharay@berkeley.edu Waste not, want not Wastewater re-use for urban / peri-urban irrigation Cities Conference | New Delhi

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

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

7. Urban & peri-urban agriculture needs water and nutrients Cities Conference | New Delhi

8. Sewage-fed aquaculture is well-known in Kolkata Cities Conference | New Delhi

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

10. Why aren’t more cities designing their ww tx for re-use? • Planning: Usually compartmentalized (also HPEC 2011 p 62) ‘Waste’water systems -- when they exist -- designed for disposal, not for re-use. • Economic / environmental: does wastewater irrigation make sense for the city? For the farmer? IS IT WORTH IT? [Also: cost recovery? health risks? Consumer acceptance?] 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: • 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* 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 Cities Conference | New Delhi

13. Model results: freshwater can be saved by irrigating with urban wastewater 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 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) 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) 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 -- 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 • Potential for partial cost recovery • Potential to “generate urban-rural synergy”(HPEC 2011, p22) -- And don’t forget Victor Hugo -- 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? ) Cities Conference | New Delhi

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