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

2

Project Region: Cuvelai-Etosha Basin

3

Sanitation and Water Reuse Concept

Biogas

4

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

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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

11 www.cuvewaters.net

Thank you for your attention !