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34
Figure 12a:
Is reuse of wastewater a benefit or a threat for agri-
culture?
Figure 12b
looks at what one litre of wastewater might
contain in terms of pathogens.
Wastewater in urban agriculture
Resource or threat?
Inefficent crops
No need of added fertilizers
Costs of treatment
Low quality output
Eutrophication
Soil enrichment
Ecosystem
destruction
Waterborne
disease risk
Wastewater
treatment
Heavy metals
Nutrients
Nutrients
Pharmaceuticals
Source: Drechser, P.
,
et al.Wastewater Irrigation and Health. Assessing and
Mitigating Risk in Low-Income Countries,
IWMI-IDRC, 2009.
Wastewater reuse in agriculture:
blackwater and graywater discharge
Food provision
Contamined food provision
Pollutant discarge on soils and ecosystems
A look inside
Concentrations of micro-organisms excreted
in one litre of wastewater
Cryptosporidium
parvum
Entamoeba
histolytica
Giardia
intestinalis
Enteric visuses
Rotavirus
Ascaris
lumbricoides
Anchilostoma
duodenale
Trichuris
trichiura
Salmonella
Shighella
Vibrio cholerae
Source: WHO,
Guidelines for the Safe Use of
Wastewater, Excreta and Greywater, Volume
2 Wastewater use in agriculture,
2006.
Number of organisms
Logaritmic scale
1 000
10
100 000
100
10 000
1 000 000