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1 Erni, M.; Drechsel, Pay; Bader, H. P.; Scheidegger, R.; Zurbruegg, C.; Kipfer, R.. 2010. Bad for the environment, good for the farmer?: urban sanitation and nutrient flows. Irrigation and Drainage Systems, 24(1-2):113-125 (Special issue with contributions by IWMI authors) [doi: https://doi.org/10.1007/s10795-009-9083-9]
Sanitation ; Urban areas ; Water balance ; Nitrogen ; Phosphorus ; Nutrients ; Water pollution ; Wastewater irrigation ; Models / Ghana / Kumasi
(Location: IWMI HQ Call no: PER Record No: H042834)
http://www.springerlink.com/content/d363092w36324651/fulltext.pdf
https://vlibrary.iwmi.org/pdf/H042834.pdf
https://vlibrary.iwmi.org/pdf/H042834.pdf
(0.27 MB)
Due to poor urban sanitation farmers in and around most cities in developing countries face highly polluted surface water. While the sanitation challenge has obvious implications for environmental pollution and food safety it can also provide ‘free’ nutrients for irrigating farmers. To understand the related dimensions, a box-flow model was used to identify the most important water and nutrient flows for the Ghanaian city of Kumasi, a rapidly growing African city with significant irrigation in its direct vicinity. The analysis focused on nitrogen and phosphorus and was supplemented by a farm based nutrient balance assessment. Results show that the city constitutes a vast nutrient sink that releases considerable nutrients loads in its passing streams, contributing to the eutrophication of downstream waters. However, farmers have for various practical reasons little means and motivation in using this resource of nutrients. This might change under increasing fertilizer prices as the nutrient load will continue to increase by 40% till 2015 assuming a widening gap between population growth and investments in water supply on one side and investments in sanitation on the other. However, even a strong investment into flushing toilets would not reduce environmental pollution due to the dominance of on-site sanitation systems, but instead strongly increase water competition. Key options to reduce the nutrient load would be via optimized waste collection and investment in dry or low-flush toilets. The latter seems also appropriate for the city to meet the water and sanitation Millennium Development Goals (MDGs) without increasing water shortages in toilet connected households.
2 Erni, M.; Bader, H.-P.; Drechsel, Pay; Scheidegger, R.; Zurbrugg, C.; Kipfer, R.. 2011. Urban water and nutrient flows in Kumasi, Ghana. Urban Water Journal, 8(3):135-153. [doi: https://doi.org/10.1080/1573062X.2011.581294]
Urban areas ; Water management ; Nutrients ; Systems analysis ; Models ; Drinking water ; Wastewater ; Water use ; Water quality ; Flow discharge ; Sanitation / Ghana / Kumasi
(Location: IWMI HQ Call no: e-copy only Record No: H044001)
(0.80 MB)
Material flow analysis was applied to model different scenarios which help better identify and quantify water supply and wastewater pollution problems in the city of Kumasi, Ghana. Results show that despite a relative abundance of water resources in the surrounding area of the city, drinking water consumption will remain at a low level (from 49 + 4 l/cap/day in 2006 to 59 + 5 l/cap/day in 2015). Changing sanitation practices to using more flush toilets will require significantly more water if these toilets are to be used adequately. The water–nutrient balance shows that total nitrogen (N) and phosphorus (P) outputs of the modelled area are 10 times higher than system inputs, most of this being attributed to human wastes from sanitation. A number of possible measures to reduce nutrient flows into water bodies were identified and quantified, showing the usefulness of the applied model in providing estimates for municipal decision-makers.
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