Impact of treated wastewater on soil

Scientific leader: Eric Michel <eric.michel@inrae.fr> (INRAE, EMMAH, Avignon).

The VSoil platform has been used to simulate the transport of water and contaminants in soil to assess the impact of treated wastewater on soil.

Details of the work carried out under this theme are presented below.

• Suhaila Díaz and Rafael Márquez (PhD students since the second semester of 2022)

Suhaila Díaz and Rafael Márquez are PhD students at the National Autonomous University of Mexico (UNAM, Mexico City) under the supervision of Dr Blanca Prado. They started using the VSoil platform in the last semester of 2022 as modelers. They will model the transport of water (Rafael) and pharmaceuticals (Suhaila) in undisturbed one-cubic meter soil monoliths (picture here) located at the lysimeter station of UNAM inaugurated in 2019 (more details here). These soils, extracted from agricultural fields in the Mezquital Valley, have been irrigated for 100 years with raw waste-water from Mexico City. What will happen now, in terms of water and contaminant transfer, that a waste-water treatment plant has been constructed and that irrigation will take place with treated waste-water? Both PhD students will contribute to answer these questions, by monitoring the lysimeters and modeling their behavior. This collaborative work between France and Mexico is supported by the 4-years French-Mexican scientific cooperation program ECOS-NORD (project M18AU01 led by Eric MICHEL in France) and SEP-CONACYT-AUIES (project FONCICYT 296672 led by Blanca PRADO in Mexico).

In November and December 2023, Rafael spent a month and a half at EMMAH. He received an extensive hands-on training on the use of the VSoil platform by Nicolas Beudez (INRAE, EMMAH, Avignon) and got acquainted with the parameter estimation tools included in VSoil. He used the official water_flow_Richards_Pastis model together with the Levenberg-Marquardt's algorithm (minpack.lm R package) included in VSoil to estimate soil hydraulic properties from time-varying water content and matrix potential data measured in two of the lysimeters mentioned above. He will visit EMMAH again in the second semester of 2024 to finish this task.

• Hamza Chaif (postdoctoral fellow from September 2021 to December 2022)

Hamza Chaif (INRAE, EMMAH, Avignon) did his postdoctoral research as part of the SmartFertiReuse project. The goal of this project was to develop and implement, on an experimental scale, a management tool for irrigation and ferti-irrigation of agricultural plots using treated wastewater while ensuring the safety of the environment and the population.

Hamza’s contribution to this project consists in studying and modelling the transfer in the soil of water and contaminants present in the treated wastewater. For this, he used a 1D soil transfer model based on the PASTIS model and implemented in the VSoil platform. The model considers crop development, canopy water transfer, root water uptake, water flow and balance (Richards model) and colloids transport and retention.

Most of the parameters required to run this model were obtained during earlier phases of the project. However, soil hydraulic properties need to be determined. A bayesian approach was used to estimate these parameters using inverse modelling of temporal series of matrix potential and soil water content measured in the experimental site of the project. To this end, the DREAMzs bayesian parameter estimation method (from BayesianTools R package) was added in the list of R parameter estimation methods available in VSoil.