Re-use of treated wastewater for irrigation and groundwater recharge: feasibility and effects on groundwater quantity at the experimental site in Kinrooi, Belgium.

It took several consecutive years of devastating droughts sweeping through Europe, causing substantial economic losses, for many to realise how urging it is to improve the water directives, making critical sectors like agriculture more resilient to a changing climate. Shrinking water supplies and growing demand further forced stakeholders to seek alternative sources, drawing their attention to projects previously considered economically unjustified. Therefore, water re-use and reclamation became one of the EU’s priorities fulfilling the ambitions of the European Green Deal to implement circular water management strategies. To facilitate the transition and support new legislation, in-depth research in the feasibility and environmental impacts of aquifer recharge with reclaimed wastewater is essential. The GROW project investigates this issue on multiple levels, among which the effect of reclamation of wastewater through aquifer recharge on local and regional scale groundwater levels.

At the experimental site in Kinrooi, Belgium, the groundwater levels are closely monitored with automatic submersible data loggers installed in 21 monitoring wells distributed on the investigated agricultural field and its vicinity. Data on water levels in the underlying Quaternary, porous aquifer are collected hourly and are verified through monthly manual measurements taken to ensure an unhindered operation of the infrastructure.

A distributed, transient-state flow model is used to simulate the groundwater table’s response to the effluent sub-irrigation at the desired rate. The model’s flexibility also allows making predictions of the aquifer behaviour under changing climatic conditions by augmenting the soil-water balance model with revised weather data. The model’s performance is tested against the high temporal resolution dataset obtained from the monitoring network. Attention is also paid to the experiment’s effect on the water levels in the adjacent hydrological network, while the effluent is partly rerouted from the hitherto used surface water discharge to the sub-irrigation system.

The data collected in our experiment is used to determine the capability of the aquifer to store and recover the reclaimed wastewater during drought periods. That would reduce the demand for traditional, inefficient surface irrigation and increase the climate resilience of the agricultural sector in Flanders. Together with data from similar projects carried out throughout Europe, our results can be used to facilitate long-expected EU legislation enabling circular water use. To support this process, we also investigate the impact of the re-use of treated wastewater for agriculture on groundwater quality and the public perception of this sensitive issue.