connecting the water, food and energy nexus with water...
TRANSCRIPT
In cooperation with
Industry partners
Connecting the water, food and energy nexus with water
reuse for urban agriculture in Namibia: Modeling water,
nutrient and salt flows
Woltersdorf, L.*, Felmeden, J.*, Müller, K.**, Liehr, S.*
*Institute for Social-Ecological Research ISOE, Germany
**Technische Universität Darmstadt, Germany
Sustainability in the Water-Energy-Food Nexus
19. May 2014, Bonn
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Connected settlements, wwtp and agriculture
Total: ~1500 users Source: Google 2014 and CNES/ Astrium 2014, Google Earth (Version 7.0.2): Outapi,
Namibia. 17° 30' 05.06'' S 14°59'24.45''O, elevation 1114 m. Available online at
http://www.google.com/earth/index.html, checked on 1/5/2014.
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Water:
Water supply, sanitation and water reuse
Water supply and sanitation in sparsely built, partly
informal settlements
Wastewater is collected with vacuum sewer
Advanced wastewater treatment (anaerob/aerob) with
microsieve (removal of helminth eggs) and UV-
disinfection
Water is hygienically save for reuse in agriculture
Nutrients (N, P, K) are left in the water for fertigation
6
Food:
Water reuse for irrigation of food crops
Fertigation of 1.5 ha of food crops (maize, spinach, tomato,
pumpkins, watermelon, etc.)
Production: ~ 5 t/ year of fruits and vegetables
Revenues: ~ 30,000 Euro/ year (potential)
The steady supply of nutrient rich water means a high
reliability for farmers
Local food production for food security and import
substitution
The Town Council sells the reuse water to local farmer
Achieved revenues subsidize drinking water and sanitation
tariffs affordability for local users
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Energy:
Biogas production
The wastewater treatment plant produces biogas:
anaerobic pre-treatment of the wastewater
anaerobic digestion of sewage sludge and co-
digestion of crop residues
Produced biogas covers:
Heat demand coverage (design): 100%
Electricity demand coverage (design): ~ 50%
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Modelling of water, nutrient, salt flows
Water
Wastewater
Wastewater
Wastewater
Irrigation water
Precipitation
Precipitation
ETAgricultural products
Agricultural products
Food
Drained water
FoodFood
Treated water
Excretion
Excretion
Excretion
Wastewater
Water
Excretion
ExcretionExcretion
Water
Water
Water
WastewaterWastewater
Wastewater
ExcretionExcretion
Excretion
Water
Evaporation
Evaporation
Excretion
Water
Water
Water
Percolation
Groundwater flow
Water
Channeled water
Food
Food
Food
Inflow
Water
HH Individual
Cluster
Community
Sewer
WWTP Agriculture
Storage pond Drainage pond
Distributor
External consumers Atmosphere
HH
HH
Latrine
Water grid
EnvironmentGroundwater
Ephemeral river
"Individual"
"Cluster"
"Community"
Mathematical Material Flow Analysis with SIMBOX
System chart:
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Modelling of water, nutrient, salt flows
Nutrient requirements are met, no additional fertilizer is needed
Excess salts are controlled with leaching, drainage and collection in drainage pond
Crop water requirements: nearly met in case 1, half met in case 2
Amount of substances solved in reuse water applied on 1.5 ha field/ yr
0
5,000
10,000
15,000
20,000
25,000
30,000
H2O
m³/
year/
1.5
ha
0
500
1000
1500
2000
2500
3000
3500
4000
4500
N P K Na Ca Mg
kg/ ye
ar/
1.5
ha
Case 1: ideal utilisation of sanitation units (potential)
Case 2: low utilisation of sanitation units
Requirement of cultivating 1.5 ha
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Conclusion
The new sanitation and water reuse facility increases water productivity
compared to the situation before its implementation
Nutrient requirements of crops can be met by leaving nutrients in the
treated water and reusing it for fertigation
The behavior of sanitation users needs to be taken into consideration when
calculating the available amount of water and nutrients for fertigation and
organic load for biogas production
Revenues subsidize
Creation of external effects such as job creation and development of skills