CS#5 - Aquifer recharge for water reuse in Belgium

This case study consists of a Demonstrator Site. It does not have any Follower Site.

DS#5 - "Blue Horizon Limburg" (Belgium)

The case study in 5 minutes

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Location

The demonstration site Blue Horizon Limburg is located in Flanders, Belgium.

CS5a — *©Arial photograph of the Sint-Truiden WWTP – possible site for the CS5 ASR pilot*

Description of the area

Biogeographical region: Atlantic
Landscape context: Urban agglomerations interspersed with rural zones
Area coverage: ~2 427 km²
Water supply: Groundwater is the main source of water for South Limburg (Mid-East region)
Hydrology: Drained by two river systems (Meuse/Maas and Schelde)

Climatic Challenges

Climatic

Planned activities

The use of alternative water sources (e.g. WWTP effluent, industrial process water) can complement groundwater as a source of drinking water. In urbanised areas, some of this surface water is discharged effluent from WWTPs. The indirect use of effluent from surface water is thus already a reality in many urbanised locations. For example, it has been estimated that globally about 65% of the irrigation water is already impacted by urban wastewater flows.

Applications of designed wastewater reuse for drinking water are also already available today (e.g. Torreele, Belgium), although these are exceptional. Using municipal wastewater effluent has advantages. For instance, its composition and flow rate are fairly constant, making design and operation of treatment easier. In addition, it is a secure source, less dependent on weather conditions for minimum flows. In the context of circular thinking, this also contributes to retaining water in the water system, thus reducing pressure on external sources.

The treatment objectives regarding the use of alternative water sources are similar or more challenging than surface water, with specific challenges towards microbial safety, chemical safety and salt load. However, the current state of treatment technology makes it possible to address these challenges to achieve drinking water quality in a direct or indirect way.

In this case, we want to simulate indirect reuse as an alternative water source, whereas the nature-based system is located sub ground. A confined aquifer system will act as a water reservoir creating a omitted buffer. The injected water is enriched with minerals because of the water already present in the cretaceous aquifer and the soil composition. Moreover, long residence times improve the microbial quality and diminish the operational requirements in case of calamities. This will enable indirect reuse of the treated wastewater effluent whenever it is needed. The injection of water into an aquifer for later recovery and use is called Aquifer Storage Recovery (ASR). In this case the water is injected in the cretaceous layer. The capacity of the Cretaceous aquifer to conditions the warer for reuse water by ASR approach will be assessed as part of the DS#5 actions.

Progress

The focus in the first year was on the preparation and planning of our case study. As an essential first step, a three-dimensional MODFLOW model was developed to assess the storage and transfer potential of the Cretaceous chalk aquifer. This model tested a range of injection and extraction scenarios, with rates varying between 10 m³/h and 100 m³/h, and explored different configurations of the ASR well field. The modelling work also considered the uncertainties in aquifer properties, providing valuable input for the design and setup of the pilot system.

CS5Progress1

Building on these insights, a comprehensive pilot test plan was formulated. This involved a series of meetings to discuss and evaluate the feasibility of various well field designs and pilot configurations. The pilot is structured into different stages, each targeting specific tasks aligned with the research objectives.

CS5Progress2

Ambition

Ambition during the project

Obtain a better idea of the feasibility of ASR for drinking water supply and/or replenishment of groundwater reserve. Gaining initial experience with the possibilities but also complexities around indirect reuse, preferentially starting from an alternative water source

Ambition after the project

If the implementation of the ASR is successful, the intention is to implement the technology at large scale (100 m3/h). Moreover, there is a replication potential at other sites.

Questions

Ever wondered how nature can help us tackle climate change? NBS are “Solutions inspired and supported by nature, which are cost-effective, simultaneously provide environmental, social and economic benefits and help build resilience.” European Commission, 2015.

An aquifer is an underground layer of porous rock or sediment that holds groundwater. It is a vital source of freshwater for many regions, but there are challenges such as over-exploitation, declining groundwater levels, or pollution (mainly from agricultural nutrients or pesticides).

Wastewater is never injected directly into the aquifer, since this is a pristine layer. In this case study, raw groundwater and RO water (simulating purified reuse water) are injected into the Cretaceous layer. The potential of the Cretaceous aquifer to accept and transport such water qualities is investigated.

The idea is that the injected water will remain in the aquifer for a certain period of time before being pumped out again for reuse. The water will be conditioned to raw groundwater quality. This quality is ideal to produce drinking water after normal treatment.