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

isharay@berkeley.edu

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“The sewer is the conscience of the city”(Victor Hugo, Les Miserables)

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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

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)

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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).

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This is true for most cities in most of the world

Accra, Ghana. Photo: Ashley Murray

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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(Murray, Ray & Nelson 2009)

(also HPEC 2011 p53, tho’ irrigation not discussed)

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Urban & peri-urban agriculture needs water and nutrients

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Sewage-fed aquaculture is well-known in Kolkata

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Seasonal / vegetable crops are especially suited to peri-urban agriculture

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Photo: CGIAR

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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?]

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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)

2) Simulate: multiple feasible re-use scenarios

3) Select: optimal wastewater re-use design & scenario -- based on what is “optimal”. Make trade-offs *transparent*

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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

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Model results: freshwater can be saved by irrigating with urban wastewater

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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

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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)

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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)

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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 “de-compartmentalized”. Possibly expensive. Definitely political.

-- None of this is trivial --

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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 --

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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? )

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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