Dunea’s drinking water treatment plants (DWTPs) want to reach the new arsenic (As) companytarget of < 1 µg/L, due to uncertainties on toxicity at the current WHO, European and Dutch guideline of 10 µg/L. The aim of this research was to lower the As concentration in Dunea’s effluent
to < 1 µg/L by improving our system understanding and exploring novel techniques for As(III) oxidation. Fieldwork was performed to assess whether each well section contributed to the elevated As concentrations. In order to enhance As(III) oxidation at Dunea’s DWTP, the use of electrochemical advanced oxidation processes (eAOPs) with a RuO2/IrO2-coated anode was examined during laboratory experiments. Fieldwork results showed that in each monitoring point the measured As concentration was > 1 µg/L, indicating that each well section contributed to the elevated As concentrations. The combination of strongly fluctuating groundwater tables, infiltration of oxygenated water, the observed pH decrease and synchronous mobilisation of several TEs, indicated that As was most probably mobilised by pyrite oxidation. It was observed that the As-bearing layer was present between -2.5 and -8.5 m NAP. With an average filter depth from -1.6 to -7.4 m, water was being extracted from the As-bearing layer. Laboratory results showed complete As(III) oxidation by eAOPs at a current density (i) of 7.5 A/m2, with a corresponding charge dosage (q) and hydraulic retention time (HRT) of 30 C/L and 1.4 min, respectively. At the aforementioned condition, the energy consumption of the eAOP cell was 0.066 kWh/m3 with operational costs of 0.04 e/m3. Free chlorine formation was minimized by reducing q, HRT and i. During the optimal anodic configuration of 7.5 A/m2, the estimated cathodic OH− production was sufficient to replace the dosed chemicals for pellet softening (PS). However, it was not sufficient to buffer for the anodic pH decrease. It was proposed to implement the eAOP cell at Dunea’s DWTP after PS and before aeration and rapid sand filtration.