CS#5 - Aquifer recharge for water reuse in Belgium

"Blue Horizon Limburg" (Belgium)

The demonstration site Blue Horizon Limburg is located in Flanders, Belgium. The demonstration site concerns an urban area (biogeographical type: Atlantic) with an approximate area of 2427km2­.

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

The study area is located in South Limburg in Flanders, Belgium. The drinking water supply in southern Limburg (Mid-East region) consists exclusively of groundwater pumping. Supply and demand seem reasonably balanced in size and spatial distribution. The permitted groundwater abstraction exceeds 23 million m3 and the effective drinking water production is 17.5 million m3. However, there are concerns such as drought sensitivity of the aquifers from which groundwater is extracted. With implications for available water resources and other potential problems for people and nature. The groundwater extractions in southern Limburg are among the most vulnerable extractions in Flanders.

© Confined and phreatic layers in Flanders                                                                                                                       © VMM, 2021. Strategisch Plan Openbare drinkwatervoorziening

De Watergroep thus faces challenges around maintaining the balance between demand and supply. We see that climatically, drought periods are becoming more intense and longer. Because of the above reasons, it also becomes more difficult and complex to renew existing environmental permits. It can also be said that, for this region, there is a clear lack of diversification in drinking water supply as groundwater is the sole source for the region.

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.   

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.