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Overview of the utility:
The recharge system of Sant Vicenc dels Horts (near Barcelona) is located in the Low Llobregat delta, which is one of the pioneer zones in Spain in terms of artificial or managed aquifer recharge (MAR). In this area, several measures are taken to improve the quality and the quantity of the groundwater, e.g. scarification of river beds, deep well injection, and infiltration in ponds. The system at Sant Vicenc dels Horts was built in 2007 and started operation in 2008/09, managed by the Catalan Water Agency (ACA). The pond system is designed to receive water from the Llobregat River and reused water from the WWTP Baix Llobregat for artificial infiltration into the aquifer.
Description of current system design and key figures:
The system includes a decantation pond (4 000 m³) and an infiltration pond (5 600 m³) for pre-treatment of the infiltrating water. The infiltration rate reaches 1 m³/(m²*d) on an infiltration area of 5 600 m² (see Figure 1). It is operated seasonally (140-170 d/a).
Figure 1: Aerial picture of groundwater recharge system at Sant Vincenc dels Horts
Experience shows that the processes which take place between the recharge water and the soil enhance the quality of the groundwater resources, e.g. denitrification or removal of organic matter which are both boosted by the microbial activity in the un-saturated zone. However, these processes require sufficient residence time and the presence of easily degradable organic carbon to facilitate the growth of micro-organisms. In this case, the river water has low content of dissolved organic carbon (DOC = 4 mg/L), providing non-optimum conditions for microbial growth.
New system design and removal mechanism:
To overcome this limitation in microbial activity and improve the capacity of the system to remove organic compounds and especially micropollutants, a reactive organic layer (60 cm of compost, mixed with local soil and adsorptive material such as clay and iron oxides) has been installed at the bottom of the infiltration basin (see Figure 2). This layer should promote the release of easily degradable organic carbon to enhance microbial activity and increase sorption processes to remove micropollutants from recharge water. This system has been installed during the EU project ENSAT (2010-2012, http://www.life-ensat.eu), and the monitoring showed an enhanced removal of selected organic micropollutants (carbamazepine-epoxy, gemfibrozil) and improved denitrification.
Figure 2: Proposed design for the reactive layer
The relevant application area for managed aquifer recharge systems with enhanced micropollutant removal by the introduction of an organic layer is groundwater recharge for aquifer replenishment in quality and quantity, to finally enhance available resources for production of drinking water or irrigation purposes.