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Wastewater irrigation - hazard or lifeline?

Wastewater irrigation - hazard or lifeline?. Background. Information drawn from a 3 year, DFID funded study: Improving irrigation in peri-urban areas . Collaborators: University of Science & Technology, Kumasi, Ghana.

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Wastewater irrigation - hazard or lifeline?

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  1. Wastewater irrigation - hazard or lifeline? Background • Information drawn from a 3 year, DFID funded study: Improving irrigation in peri-urban areas. • Collaborators: • University of Science & Technology, Kumasi, Ghana. • Smallholder Irrigation Scheme Development Organisation, Nairobi, Kenya. • August 1998 - March 2001

  2. Wastewater irrigation - hazard or lifeline? Summary • What they do • - Water management - sources and application • The water they use • - Water quality • The returns they get • - Financial returns • The trade-offs • - risks and benefits • So what? • - The need for interim water quality standards

  3. Wastewater irrigation - hazard or lifeline? Water sources SourceNairobiKumasi River/stream 51% 38% Dugout 4% 46% Sewage 34% - Council 3% 3% Other (well, pool, etc) 8% 13%

  4. Wastewater irrigation - hazard or lifeline? Water sources Kumasi - dugout Nairobi - sewage

  5. Wastewater irrigation - hazard or lifeline? Water conveyance & application MethodNairobiKumasi Manual carrying 26% 78% Motor pump 38% 19% Gravity 42% - Council 6% 3%

  6. Wastewater irrigation - hazard or lifeline? Application Kumasi - watering can

  7. Wastewater irrigation - hazard or lifeline? Application Nairobi - furrow & beds

  8. Wastewater irrigation - hazard or lifeline? Application Kumasi - “spraying”

  9. Wastewater irrigation - hazard or lifeline? Water quality - Nairobi

  10. Wastewater irrigation - hazard or lifeline? Water quality - Kumasi

  11. Wastewater irrigation - hazard or lifeline? Incomes and profit -Kumasi

  12. Wastewater irrigation - hazard or lifeline? The extent of informal, urban & peri urban irrigation Area Study area irrigated (ha) No. of HHs (ha) Kumasi 502,700 12,700 11,900 Nairobi 125,700 3,700 2,220

  13. Nairobi Kumasi Kale, tomato, spinach, green maize, cabbage Tomato, garden egg, okra, chilli Main crops Av. Revenue US$ / ha 1,770 (annual) 544 (7 months) Total value of production US$ 3.9 million US$ 6 million Wastewater irrigation - hazard or lifeline? Positive impacts

  14. Wastewater irrigation - hazard or lifeline? What are the trade-offs Benefits Costs • HH income • Urban food supply • Nutrient recycling • Managed waste disposal • Chronic ill-health • Wide-scale disease outbreaks • Damage to soils & groundwater Where is the greatest ‘public good’ secured?

  15. Wastewater irrigation - hazard or lifeline? ‘Interim’ water quality standards • Current WHO guidelines: • Apply to TREATED wastewater • Aim to secure “no measurable excess risk of infection” • Use of UNTREATED wastewater iswidespread. Under these conditions: • “No risk” standard seems unrealistic • A single threshold is unhelpful - all wastewater is not equal • Are there acceptable levels of risk & what do they imply? • Can we provide greater guidance - risk assessment scales? • Can quantitative microbiological risk assessment models provide these answers?

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