| Summary: | A modular electrocoagulation unit, supported by Ca(OH)<sub>2</sub> addition to treated water, was operated in the vicinity of a Natura 2000 site for the removal of Cr<sup>6+</sup> or Ni<sup>2+</sup> from contaminated groundwater. The process was performed at a constant flow rate of 350 L/h. Day 0 concentrations of Cr<sup>6+</sup> and Ni<sup>2+</sup> started at 91.6 mg/L for Ni<sup>2+</sup> and 43 mg/L for Cr and during testing, were decreased by 15%–25%. Residual concentrations of Cr<sub>tot.</sub> and Ni<sup>2+</sup> below the required limits of 0.5 mg/L for Cr<sub>tot.</sub> and 0.8 mg/L for Ni<sup>2+</sup> can be achieved with the electrocoagulation unit and total removal efficiencies often exceeded 98%. The overall economic assessment showed its feasible application for removal of Cr<sup>6+</sup> and Ni<sup>2+</sup> on sites with requirements of high environmental protection standards. The polluted area was about 150 × 150 m (22,500 m<sup>2</sup>), and it contained approximately 78,750 m<sup>3</sup> of water contaminated with Cr<sup>6+</sup> and Ni<sup>2+</sup> (over 41 and 91 mg/L, respectively). The modular arrangement might allow a scaling up. The process’ output could be thus increased according to the number of EC modules in operation.
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