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Wastewater irrigation - hazard or lifeline?

Wastewater irrigation - hazard or lifeline?. Gez Cornish & Neeltje Kielen HR Wallingford Ltd. UK. Wastewater irrigation - hazard or lifeline?. Summary:. Based on field studies in Nairobi and Kumasi The need for a typology of wastewater irrigation

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Wastewater irrigation - hazard or lifeline?

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  1. Wastewater irrigation - hazard or lifeline? Gez Cornish & Neeltje Kielen HR Wallingford Ltd. UK

  2. Wastewater irrigation - hazard or lifeline? Summary: • Based on field studies in Nairobi and Kumasi • The need for a typology of wastewater irrigation • Variations in microbiological water quality • Positive impacts of wastewater irrigation • What are the trade-offs? • The need for “interim” water quality standards

  3. Wastewater irrigation - hazard or lifeline? The need for a typology of wastewater irrigation : • Great variation exists in wastewater: • sources • conveyance systems • treatment • in-field management • A typology is essential to guide discussion of practice or the formulation of guidelines or regulations.

  4. Wastewater irrigation - hazard or lifeline? A proposedtypology Conveyance Treatment Disposal Source Formal collection network River or surface water body Conventional Industrial Groundwater recharge Road tankers Natural / Biological Municipal Natural drainage None Irrigation Informal Backyard Informal or formal use Indirect use Direct use Indirect use Direct use Informal use Formal use = Use of wastewater with a certain level of permission and control by state agencies Informal use = Use of wastewater lacking permission and control by state agencies Direct use = Wastewater conveyed to a defined area for irrigation Indirect use = Wastewater discharged into water bodies with scattered and uncontrolled downstream abstraction

  5. Wastewater irrigation - hazard or lifeline? Examples - Mau Mau Bridge, Nairobi Informal, indirect. Untreated municipal waste. Natural drainage channels running to river. Surface & overhead irrigation of vegetable crops sold in local Nairobi markets.

  6. Wastewater irrigation - hazard or lifeline? Examples - Maili Saba, Nairobi Informal, indirect. Untreated municipal waste diverted from sewer to fields. Surface irrigation of vegetable crops grown for home consumption and sold in local Nairobi markets.

  7. Wastewater irrigation - hazard or lifeline? Examples - Asago, Kumasi Informal, indirect. Untreated municipal & industrial waste. Natural drainage to river + dumping by vault emptying tankers. Overhead irrigation of vegetable crops, grown mainly for Kumasi market.

  8. Wastewater irrigation - hazard or lifeline? Variations in water quality - Nairobi

  9. Wastewater irrigation - hazard or lifeline? Variations in water quality - Kumasi

  10. Area Study area irrigated (ha) No. of HHs (ha) Kumasi 502,700 12,700 11,900 Nairobi 125,700 3,700 2,220 Wastewater irrigation - hazard or lifeline? Positive impacts

  11. Wastewater irrigation - hazard or lifeline? Positive impacts 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

  12. Profit $US Plot area ha Revenue $US Cost $US Farmer 1 2 3 4 5 6 Overall 237 232 -4 0.109 417 1,802 1,385 0.143 60 68 8 0.041 33 196 162 0.088 1 63 62 0.032 0 60 60 0.069 124 403 279 0.080 Wastewater irrigation - hazard or lifeline? Positive impacts - revenue + profit, Nairobi

  13. Farm profit $US 500 400 300 200 Average = $US 152 100 0 34 15 25 27 11 22 32 13 26 24 35 21 31 36 17 33 37 12 14 16 23 -100 Wastewater irrigation - hazard or lifeline? Positive impacts - profits, Kumasi

  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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