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DEMEAU Technology:
Overview of the utility:
In 1954, Dunea (Dutch water utility) started the infiltration of surface water as an additional source for rain water to restore and maintain the fresh water lens under the dune area. The surface water is transported towards the dune area, infiltrated by infiltration ponds or deep infiltration wells and abstracted by shallow (17 m below sea level) and deep wells (50 m below sea level). Before the surface water is suitable for infiltration, it needs to be pre-treated to remove suspended solids (especially for deep well infiltration to prevent rapid clogging of the well surface) and, in case of open infiltration, high concentrations of nutrients (e.g. phosphate).
Description of current system design and key figures:
The treatment applied by Dunea is a typical multiple barrier treatment, characterized by an extensive infrastructure and subsequent treatment steps (Figure 1). The water is first collected in a dead end side stream of the Meuse River, acting as a process reservoir. In the beginning of this side stream, coagulation, flocculation and sedimentation take place through dosing of ferrous sulphate (FeSO4) in combination with aeration. At the water intake, the water is treated by microsieves (sieve width 35 μm) and transported for 27 km to Bergambacht where the water is filtered by dual media rapid filters and transported by two transport pipelines to the dune area, with a length of 46 and 57 km, respectively. In the dune area, mainly open infiltration takes place. There is also a deep well infiltration facility which is used incidentally. After a residence time in the dunes of at least 20 days, but on average 120 days, the water is abstracted and post-treated at three different locations (Scheveningen, Katwijk and Monster). Post-treatment consists of softening, dosing powdered activated carbon, cascade aeration, rapid sand filtration, and finally slow sand filtration. The water is distributed without post-disinfection.
Figure 1: Flow chart of existing drinking water treatment scheme at Dunea
However, the source water of river Meuse contains a variety of organic micropollutants (mainly pesticides) as a result from upstream activities. Dunea has performed research to extend the current multiple barrier treatment (e.g. pre-treatment, artificial recharge and recovery (ARR), post-treatment) with an advanced oxidation processes (AOP), situated at the pre-treatment location in Bergambacht, before ARR. The degradation of organic micropollutants as a result of advanced oxidation using different combinations of hydrogen peroxide, ozone, low pressure (LP) UV lamps has been assessed by means of pilot-scale (5 m³/h) experiments. The combined AOP (O3/H2O2/UV) prove to deliver the best removal efficiency for all target compounds at reasonable costs. Other advantages of the combined AOP are limited by-product formation, especially bromate, and a future barrier against OMPs encompassing a broad spectrum of properties.