# The Use of ELAN GIS-Integrated Tool for Exploring Decentralized Wastewater Management by Treatment Wetlands

Zoé Legeai, Pascal Molle, Alberto Tonda, Nicolas Forquet

► To cite this version:

Zoé Legeai, Pascal Molle, Alberto Tonda, Nicolas Forquet. The Use of ELAN GIS-Integrated Tool for Exploring Decentralized Wastewater Management by Treatment Wetlands. 11th International Symposium On Wetland Pollutant Dynamics and Control, WETPOL, Sep 2025, Gdansk, Poland. hal-05264641

HAL Id: hal-05264641

https://hal.inrae.fr/hal-05264641v1

Submitted on 17 Sep 2025

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# The Use of ELAN GIS-Integrated Tool for Exploring Decentralized Wastewater Management by Treatment Wetlands

**Zoé Legeai**¹, Pascal Molle¹, Gabrielle Favreau¹, Alberto Tonda², Nicolas Forquet¹

¹INRAE, REVERSAAL Research Unit, Villeurbanne, France

²INRAE, MIA Research Unit, Paris Saclay, France
> Identified issue : a missing decision-making support tool

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > 3. MCDA > Conclusion

How can we guarantee stakeholders **reliable decision-making support** in selecting the most suitable **sanitation** system as a **whole**, balancing **efficient** and **safe sizing** with **technical** and **local constraints**?

<figure><img src="image_3.png" /></figure>
> ELAN : a comprehensive tool under development

Issue > **ELAN Tool** > Case study > 1. pysewer > 2. wetlandoptimizer > 3. MCDA > Conclusion

<figure><img src="image_4.png" /></figure>

URBAN WATER PLANNING SCENARIOS
FOR SUSTAINABLE CITIES

Sewer module
pysewer code

<figure><img src="image_5.png" /></figure>

HELMHOLTZ
Centre for Environmental Research

<figure><img src="image_6.png" /></figure>

Process module
wetlandoptimizer
code

<figure><img src="image_7.png" /></figure>

MCDA module
Under development

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

INRAO
REDUIRE RÉUTILISER VALORISER LES RESSOURCES
DES EAUX RÉSIDUAIRES [REVERSAAL]

Interreg
Caraïbes
Fonds européen de développement régional

<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

CARIBSAN

<figure><img src="image_12.png" /></figure>
> Case study : Black Bay district in Saint Lucia, CARIBSAN project

Issue > ELAN Tool > **Case study** > 1. pysewer > 2. wetlandoptimizer > 3. MCDA > Conclusion

<figure><img src="image_13.png" /></figure>

Map legend:

<figure><img src="image_14.png" /></figure>

Houses to be connected

<figure><img src="image_15.png" /></figure>

ELAN
URBAN WATER PLANNING SCENARIOS
FOR SUSTAINABLE CITIES

<figure><img src="image_16.png" /></figure>
<figure><img src="image_17.png" /></figure>

# 1. pysewer: configuration of site-specific features

Issue > ELAN Tool > Case study > **1. pysewer** > 2. wetlandoptimizer > 3. MCDA > Conclusion

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /></figure>

HELMHOLTZ
Centre for Environmental Research

**Map legend:**

<figure><img src="image_20.png" /></figure>

Houses to be connected

<figure><img src="image_21.png" /></figure>

Outlet treatment area

**Technical informations:**

Daily water consumption : 230 L/d/capita

Average number of people per household : 2
<figure><img src="image_22.png" /></figure>

# 1. pysewer: optimized sewer results

Issue > ELAN Tool > Case study > **1. pysewer** > 2. wetlandoptimizer > 3. MCDA > Conclusion

<figure><img src="image_23.png" /></figure>

pysewer code

<figure><img src="image_24.png" /></figure>

Map legend:

<figure><img src="image_25.png" /></figure>

Houses to be connected

<figure><img src="image_26.png" /></figure>

Outlet treatment area

<figure><img src="image_27.png" /></figure>

Optimized separate sewer system
(diameter grading)

<figure><img src="image_28.png" /></figure>

Lifting station

<figure><img src="image_29.png" /></figure>

Pumping station (none)

<figure><img src="image_30.png" /></figure>

Treatment plant

<figure><img src="image_31.png" /></figure>

HELMHOLTZ
Centre for Environmental Research

<figure><img src="image_32.png" /></figure>
## 2. wetlandoptimizer: global architecture

Issue > ELAN Tool > Case study > 1. pysewer > **2. wetlandoptimizer** > 3. MCDA > Conclusion

<figure><img src="image_33.png" /></figure>

wetlandoptimizer
code

(Legeai et al., 2025)

<figure><img src="image_34.png" /></figure>
> 2. wetlandoptimizer: configuration of site-specific features

Issue > ELAN Tool > Case study > 1. pysewer > **2. wetlandoptimizer** > 3. MCDA > Conclusion

<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>

URBAN WATER PLANNING SCENARIOS
FOR SUSTAINABLE CITIES

Interreg
Caraïbes
Fonds européen de développement régional

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

CARIBSAN

<table><thead><tr><td>Parameters</td><td>TSS (mgTSS/L)</td><td>BOD<sub>5</sub> (mgO<sub>2</sub>/L)</td><td>TKN (mgTKN/L)</td><td>COD<sub>t</sub> (mgO<sub>2</sub>/L)</td></tr></thead><tbody><tr><td>Input</td><td>298</td><td>336</td><td>21</td><td>585</td></tr><tr><td>Objective</td><td>15</td><td>25</td><td>10</td><td>90</td></tr></tbody></table>

Flow = 61 m³/day

Available surface area = 15173 m²
<figure><img src="image_39.png" /></figure>

## 2. wetlandoptimizer: results...

Issue > ELAN Tool > Case study > 1. pysewer > **2. wetlandoptimizer** > 3. MCDA > Conclusion

<table><thead><tr><th rowspan="2">Treatment train number</th><th rowspan="2">Surface per stages (m²)</th><th rowspan="2">Saturated depth per stages (m)</th><th rowspan="2">Unsaturated depth per stages (m)</th><th colspan="5">Loading per stages (%)</th><th rowspan="2">Total surface (m²)</th><th rowspan="2">Total volume (m³)</th><th colspan="4">Outlet concentration (mg/L)</th><th colspan="4">Outlet to objective deviation (mg/L)</th></tr><tr><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>Hydraulic</th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th></tr></thead><tbody><tr><td>A (2 stages)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>B (1 stage)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C (1 stage)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>D (3 stages)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>E (2 stages)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>F (3 stages)</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>

<figure><img src="image_40.png" /><figcaption>1st stage French system</figcaption></figure>

<figure><img src="image_41.png" /><figcaption>2nd stage vertical system</figcaption></figure>

<figure><img src="image_42.png" /><figcaption>1st stage French system with a saturated bottom layer</figcaption></figure>
> 2. wetlandoptimizer: results...

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > 3. MCDA > Conclusion

<table><thead><tr><th rowspan="2">Treatment train number</th><th rowspan="2">Surface per stages (m²)</th><th rowspan="2">Saturated depth per stages (m)</th><th rowspan="2">Unsaturated depth per stages (m)</th><th colspan="5">Loading per stages (%)</th><th rowspan="2">Total surface (m²)</th><th rowspan="2">Total volume (m³)</th><th colspan="4">Outlet concentration (mg/L)</th><th colspan="4">Outlet to objective deviation (mg/L)</th></tr><tr><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>Hydraulic</th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th></tr></thead><tbody><tr><td>A (2 stages)</td><td>[272, 256]</td><td>[0, 0]</td><td>[0.3, 0.3]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>B (1 stage)</td><td>[272]</td><td>[0]</td><td>[0.6]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C (1 stage)</td><td>[272]</td><td>[0.4]</td><td>[0.35]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>D (3 stages)</td><td>[272, 256, 173]</td><td>[0, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>E (2 stages)</td><td>[272, 204]</td><td>[0.4, 0]</td><td>[0.3, 0.3]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>F (3 stages)</td><td>[272, 204, 174]</td><td>[0.4, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>
<figure><img src="image_43.png" /></figure>

## 2. wetlandoptimizer: results...

Issue > ELAN Tool > Case study > 1. pysewer > **2. wetlandoptimizer** > 3. MCDA > Conclusion

<table><thead><tr><th rowspan="2">Treatment train number</th><th rowspan="2">Surface per stages (m²)</th><th rowspan="2">Saturated depth per stages (m)</th><th rowspan="2">Unsaturated depth per stages (m)</th><th colspan="5">Loading per stages (%)</th><th rowspan="2">Total surface (m²)</th><th rowspan="2">Total volume (m³)</th><th colspan="4">Outlet concentration (mg/L)</th><th colspan="4">Outlet to objective deviation (mg/L)</th></tr><tr><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>Hydraulic</th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th></tr></thead><tbody><tr><td>A (2 stages)</td><td>[272, 256]</td><td>[0, 0]</td><td>[0.3, 0.3]</td><td>[89, 47]</td><td>[100, 80]</td><td>[19, 10]</td><td>[75, 100]</td><td>[54, 59]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>B (1 stage)</td><td>[272]</td><td>[0]</td><td>[0.6]</td><td>[89]</td><td>[100]</td><td>[19]</td><td>[75]</td><td>[54]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C (1 stage)</td><td>[272]</td><td>[0.4]</td><td>[0.35]</td><td>[89]</td><td>[100]</td><td>[19]</td><td>[75]</td><td>[54]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>D (3 stages)</td><td>[272, 256, 173]</td><td>[0, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td>[89, 47, 14]</td><td>[100, 80, 24]</td><td>[19, 10, 0]</td><td>[75, 100, 41]</td><td>[54, 59, 100]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>E (2 stages)</td><td>[272, 204]</td><td>[0.4, 0]</td><td>[0.3, 0.3]</td><td>[89, 50]</td><td>[100, 100]</td><td>[19, 12]</td><td>[75, 83]</td><td>[54, 81]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>F (3 stages)</td><td>[272, 204, 174]</td><td>[0.4, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td>[89, 50, 12]</td><td>[100, 100, 24]</td><td>[19, 12, 0]</td><td>[75, 83, 35]</td><td>[54, 81, 100]</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>
<figure><img src="image_44.png" /></figure>

## 2. wetlandoptimizer: results...

Issue > ELAN Tool > Case study > 1. pysewer > **2. wetlandoptimizer** > 3. MCDA > Conclusion

<table><thead><tr><th rowspan="2">Treatment train number</th><th rowspan="2">Surface per stages (m²)</th><th rowspan="2">Saturated depth per stages (m)</th><th rowspan="2">Unsaturated depth per stages (m)</th><th colspan="5">Loading per stages (%)</th><th rowspan="2">Total surface (m²)</th><th rowspan="2">Total volume (m³)</th><th colspan="4">Outlet concentration (mg/L)</th><th colspan="4">Outlet to objective deviation (mg/L)</th></tr><tr><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>Hydraulic</th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th></tr></thead><tbody><tr><td>A (2 stages)</td><td>[272, 256]</td><td>[0, 0]</td><td>[0.3, 0.3]</td><td>[89, 47]</td><td>[100, 80]</td><td>[19, 10]</td><td>[75, 100]</td><td>[54, 59]</td><td>528</td><td>158</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>B (1 stage)</td><td>[272]</td><td>[0]</td><td>[0.6]</td><td>[89]</td><td>[100]</td><td>[19]</td><td>[75]</td><td>[54]</td><td>272</td><td>163</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>C (1 stage)</td><td>[272]</td><td>[0.4]</td><td>[0.35]</td><td>[89]</td><td>[100]</td><td>[19]</td><td>[75]</td><td>[54]</td><td>272</td><td>198</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>D (3 stages)</td><td>[272, 256, 173]</td><td>[0, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td>[89, 47, 14]</td><td>[100, 80, 24]</td><td>[19, 10, 0]</td><td>[75, 100, 41]</td><td>[54, 59, 100]</td><td>701</td><td>210</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>E (2 stages)</td><td>[272, 204]</td><td>[0.4, 0]</td><td>[0.3, 0.3]</td><td>[89, 50]</td><td>[100, 100]</td><td>[19, 12]</td><td>[75, 83]</td><td>[54, 81]</td><td>476</td><td>252</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>F (3 stages)</td><td>[272, 204, 174]</td><td>[0.4, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td>[89, 50, 12]</td><td>[100, 100, 24]</td><td>[19, 12, 0]</td><td>[75, 83, 35]</td><td>[54, 81, 100]</td><td>650</td><td>304</td><td></td><td></td><td></td><td></td><td></td><td></td><td></td></tr></tbody></table>
<figure><img src="image_45.png" /></figure>

## 2. wetlandoptimizer: results...

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > 3. MCDA > Conclusion

<table><thead><tr><th rowspan="2">Treatment train number</th><th rowspan="2">Surface per stages (m²)</th><th rowspan="2">Saturated depth per stages (m)</th><th rowspan="2">Unsaturated depth per stages (m)</th><th colspan="5">Loading per stages (%)</th><th rowspan="2">Total surface (m²)</th><th rowspan="2">Total volume (m³)</th><th colspan="4">Outlet concentration (mg/L)</th><th colspan="4">Outlet to objective deviation (mg/L)</th></tr><tr><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>Hydraulic</th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th></tr></thead><tbody><tr><td>A (2 stages)</td><td>[272, 256]</td><td>[0, 0]</td><td>[0.3, 0.3]</td><td>[89, 47]</td><td>[100, 80]</td><td>[19, 10]</td><td>[75, 100]</td><td>[54, 59]</td><td>528</td><td>158</td><td>6</td><td>7</td><td>0</td><td>41</td><td></td><td></td><td></td></tr><tr><td>B (1 stage)</td><td>[272]</td><td>[0]</td><td>[0.6]</td><td>[89]</td><td>[100]</td><td>[19]</td><td>[75]</td><td>[54]</td><td>272</td><td>163</td><td>30</td><td>34</td><td>5</td><td>92</td><td></td><td></td><td></td></tr><tr><td>C (1 stage)</td><td>[272]</td><td>[0.4]</td><td>[0.35]</td><td>[89]</td><td>[100]</td><td>[19]</td><td>[75]</td><td>[54]</td><td>272</td><td>198</td><td>25</td><td>34</td><td>5</td><td>90</td><td></td><td></td><td></td></tr><tr><td>D (3 stages)</td><td>[272, 256, 173]</td><td>[0, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td>[89, 47, 14]</td><td>[100, 80, 24]</td><td>[19, 10, 0]</td><td>[75, 100, 41]</td><td>[54, 59, 100]</td><td>701</td><td>210</td><td>1</td><td>1</td><td>0</td><td>26</td><td></td><td></td><td></td></tr><tr><td>E (2 stages)</td><td>[272, 204]</td><td>[0.4, 0]</td><td>[0.3, 0.3]</td><td>[89, 50]</td><td>[100, 100]</td><td>[19, 12]</td><td>[75, 83]</td><td>[54, 81]</td><td>476</td><td>252</td><td>5</td><td>7</td><td>0</td><td>35</td><td></td><td></td><td></td></tr><tr><td>F (3 stages)</td><td>[272, 204, 174]</td><td>[0.4, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td>[89, 50, 12]</td><td>[100, 100, 24]</td><td>[19, 12, 0]</td><td>[75, 83, 35]</td><td>[54, 81, 100]</td><td>650</td><td>304</td><td>1</td><td>1</td><td>0</td><td>25</td><td></td><td></td><td></td></tr></tbody></table>
## 2. wetlandoptimizer: results...

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > 3. MCDA > Conclusion

<table><thead><tr><th rowspan="2">Treatment train number</th><th rowspan="2">Surface per stages (m²)</th><th rowspan="2">Saturated depth per stages (m)</th><th rowspan="2">Unsaturated depth per stages (m)</th><th colspan="5">Loading per stages (%)</th><th rowspan="2">Total surface (m²)</th><th rowspan="2">Total volume (m³)</th><th colspan="4">Outlet concentration (mg/L)</th><th colspan="4">Outlet to objective deviation (mg/L)</th></tr><tr><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>Hydraulic</th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th></tr></thead><tbody><tr><td>A (2 stages)</td><td>[272, 256]</td><td>[0, 0]</td><td>[0.3, 0.3]</td><td>[89, 47]</td><td>[100, 80]</td><td>[19, 10]</td><td>[75, 100]</td><td>[54, 59]</td><td>528</td><td>158</td><td>6</td><td>7</td><td>0</td><td>41</td><td>-9</td><td>-18</td><td>-10</td><td>-49</td></tr><tr><td>B (1 stage)</td><td>[272]</td><td>[0]</td><td>[0.6]</td><td>[89]</td><td>[100]</td><td>[19]</td><td>[75]</td><td>[54]</td><td>272</td><td>163</td><td>30</td><td>34</td><td>5</td><td>92</td><td>15</td><td>9</td><td>-5</td><td>2</td></tr><tr><td>C (1 stage)</td><td>[272]</td><td>[0.4]</td><td>[0.35]</td><td>[89]</td><td>[100]</td><td>[19]</td><td>[75]</td><td>[54]</td><td>272</td><td>198</td><td>25</td><td>34</td><td>5</td><td>90</td><td>10</td><td>9</td><td>-5</td><td>0</td></tr><tr><td>D (3 stages)</td><td>[272, 256, 173]</td><td>[0, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td>[89, 47, 14]</td><td>[100, 80, 24]</td><td>[19, 10, 0]</td><td>[75, 100, 41]</td><td>[54, 59, 100]</td><td>701</td><td>210</td><td>1</td><td>1</td><td>0</td><td>26</td><td>-14</td><td>-24</td><td>-10</td><td>-64</td></tr><tr><td>E (2 stages)</td><td>[272, 204]</td><td>[0.4, 0]</td><td>[0.3, 0.3]</td><td>[89, 50]</td><td>[100, 100]</td><td>[19, 12]</td><td>[75, 83]</td><td>[54, 81]</td><td>476</td><td>252</td><td>5</td><td>7</td><td>0</td><td>35</td><td>-10</td><td>-18</td><td>-10</td><td>-55</td></tr><tr><td>F (3 stages)</td><td>[272, 204, 174]</td><td>[0.4, 0, 0]</td><td>[0.3, 0.3, 0.3]</td><td>[89, 50, 12]</td><td>[100, 100, 24]</td><td>[19, 12, 0]</td><td>[75, 83, 35]</td><td>[54, 81, 100]</td><td>650</td><td>304</td><td>1</td><td>1</td><td>0</td><td>25</td><td>-14</td><td>-24</td><td>-10</td><td>-65</td></tr></tbody></table>
<figure><img src="image_46.png" /></figure>

## 2. wetlandoptimizer: results & preselection

Issue > ELAN Tool > Case study > 1. pysewer > **2. wetlandoptimizer** > 3. MCDA > Conclusion

<table><thead><tr><th rowspan="2">Treatment train number</th><th rowspan="2">Surface per stages (m²)</th><th rowspan="2">Saturated depth per stages (m)</th><th rowspan="2">Unsaturated depth per stages (m)</th><th colspan="5">Loading per stages (%)</th><th rowspan="2">Total surface (m²)</th><th rowspan="2">Total volume (m³)</th><th colspan="4">Outlet concentration (mg/L)</th><th colspan="4">Outlet to objective deviation (mg/L)</th></tr><tr><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>Hydraulic</th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th><th>TSS</th><th>BOD<sub>5</sub></th><th>TKN</th><th>COD<sub>t</sub></th></tr></thead><tbody><tr><td>A (2 stages)</td><td>[272, 256]</td><td>[0, 0]</td><td>[0.3, 0.3]</td><td>[89, 47]</td><td>[100, 80]</td><td>[19, 10]</td><td>[75, 100]</td><td>[54, 59]</td><td>528</td><td>158</td><td>6</td><td>7</td><td>0</td><td>41</td><td>-9</td><td>-18</td><td>-10</td><td>-49</td></tr></tbody></table>

<figure><img src="image_47.png" /></figure>

<figure><img src="image_48.png" /></figure>

<figure><img src="image_49.png" /></figure>

1st stage French system + 2nd stage vertical system

<figure><img src="image_50.png" /></figure>

<figure><img src="image_51.png" /></figure>

<figure><img src="image_52.png" /></figure>

1st stage French system with a saturated bottom layer

+ 2nd stage vertical system

<figure><img src="image_53.png" /></figure>

<table><tr><td>E (2 stages)</td><td>[272, 204]</td><td>[0.4, 0]</td><td>[0.3, 0.3]</td><td>[89, 50]</td><td>[100, 100]</td><td>[19, 12]</td><td>[75, 83]</td><td>[54, 81]</td><td>476</td><td>252</td><td>5</td><td>7</td><td>0</td><td>35</td><td>-10</td><td>-18</td><td>-10</td><td>-55</td></tr></table>
<figure><img src="image_54.png" /></figure>

## 3. MCDA: concept...

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > **3. MCDA** > Conclusion

<figure><img src="image_55.png" /></figure>

Treatment trains A & E

(Zolghadr-Asli et al., 2021)

<figure><img src="image_56.png" /></figure>
<figure><img src="image_57.png" /></figure>

## 3. MCDA: concept & method selection

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > **3. MCDA** > Conclusion

<figure><img src="image_58.png" /></figure>

Basic steps of an MADM method

<figure><img src="image_59.png" /></figure>

(Zolghadr-Asli et al., 2021)
<figure><img src="image_60.png" /></figure>

## 3. MCDA: Expert side

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > **3. MCDA** > Conclusion

<figure><img src="image_61.png" /></figure>
<figure><img src="image_62.png" /></figure>

## 3. MCDA: User side & results

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > **3. MCDA** > Conclusion

<figure><img src="image_63.png" /></figure>

<table><tr><td>Rate from 1 to 5 the importance you give to each criteria :</td><td>(1 = not</td></tr><tr><td>Cost</td><td>2</td><td>important /</td></tr><tr><td>Robustness</td><td>5</td><td>5 =</td></tr><tr><td>Construction & operation skills</td><td>2</td><td>important)</td></tr></table>

<figure><img src="image_64.png" /></figure>

<figure><img src="image_65.png" /><figcaption>Treatment train E</figcaption></figure>

<figure><img src="image_66.png" /></figure>

<table><tr><td>Rate from 1 to 5 the importance you give to each criteria :</td><td>(1 = not</td></tr><tr><td>Cost</td><td>5</td><td>important /</td></tr><tr><td>Robustness</td><td>1</td><td>5 =</td></tr><tr><td>Construction & operation skills</td><td>3</td><td>important)</td></tr></table>

<figure><img src="image_67.png" /></figure>

<figure><img src="image_68.png" /><figcaption>Treatment train A</figcaption></figure>

<figure><img src="image_69.png" /></figure>

<table><tr><td>Rate from 1 to 5 the importance you give to each criteria :</td><td>(1 = not</td></tr><tr><td>Cost</td><td>3</td><td>important /</td></tr><tr><td>Robustness</td><td>3</td><td>5 =</td></tr><tr><td>Construction & operation skills</td><td>5</td><td>important)</td></tr></table>

<figure><img src="image_70.png" /></figure>

<figure><img src="image_71.png" /><figcaption>Treatment train A</figcaption></figure>

<figure><img src="image_72.png" /></figure>
> Conclusion

Issue > ELAN Tool > Case study > 1. pysewer > 2. wetlandoptimizer > 3. MCDA > **Conclusion**

**3-step methodology enabling:**

* Reliable decision-making with a ranking of the treatment solution, adjustments possible at any time

* Comprehensive sanitation scenarios, from the network to the sizing and selection of a treatment plant

* Efficient and safe sizing with uncertainty analysis provided

* Context adaptive with multiples adjustable parameters

**Next steps:**

* To perform sensitivity analysis on the MCDA with new information from the partners thanks to the workshop, integration to wetlandoptimizer

* To integrate into ELAN the ability to operate MCDA on decentralized scenarios with multiple treatment plants

* To add stormwater management

* To work on user adoption of ELAN, with participatory workshops.

<figure><img src="image_73.png" /></figure>
INRAE

<figure><img src="image_74.png" /></figure>

Interreg
Caraïbes

Fonds européen de développement régional

<figure><img src="image_75.png" /></figure>

UNION EUROPÉENNE

<figure><img src="image_76.png" /></figure>

CARIBSAN

<figure><img src="image_77.png" /></figure>

Thank you for your attention !

Zoé Legeai

zoe.legeai@inrae.fr
# ELAN : a QGIS decision-support plugin

<figure><img src="image_78.png" /></figure>

<figure><img src="image_79.png" /></figure>

For urban water
management issues

Wicked and complex
problems

<figure><img src="image_80.png" /></figure>

URBAN WATER PLANNING SCENARIOS
FOR SUSTAINABLE CITIES

Facilitate issue resolution
and enlight decision
making

Scenario comparison
with preliminary
sizing

Open source
project

Open to
contributions !

<figure><img src="image_81.png" /></figure>

Training planned in
Summer 2026

<figure><img src="image_82.png" /></figure>

INRAO

<figure><img src="image_83.png" /></figure>

Interreg
Caraïbes

<figure><img src="image_84.png" /></figure>

<figure><img src="image_85.png" /></figure>

CARIBSAN

The Use of ELAN GIS-Integrated Tool for Exploring Decentralized Wastewater Management by Treatment Wetlands

9th Sept 2025 / WETPOL 2025 Gdańks / Zoé Legeai