Abstract
A modular electrocoagulation unit, supported by Ca(OH)2 addition to treated water, was operated in the vicinity of a Natura 2000 site for the removal of Cr6+ or Ni2+ from contaminated groundwater. The process was performed at a constant flow rate of 350 L/h. Day 0 concentrations of Cr6+ and Ni2+ started at 91.6 mg/L for Ni2+ and 43 mg/L for Cr and during testing, were decreased by 15%–25%. Residual concentrations of Crtot. and Ni2+ below the required limits of 0.5 mg/L for Crtot. and 0.8 mg/L for Ni2+ 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 Cr6+ and Ni2+ on sites with requirements of high environmental protection standards. The polluted area was about 150 × 150 m (22,500 m2), and it contained approximately 78,750 m3 of water contaminated with Cr6+ and Ni2+ (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.
Highlights
As it is commonly known in the EU, Natura 2000 is a network of nature protection areas in EU states
The process can be supported by the addition of Ca(OH)2 as it is beneficial for low concentrations of Ni2+ in treated effluent [16]. It does not serve for precipitation of Cr(OH)3 as this is ensured during the electrocoagulation step
Due to industrial activities spanning from the 1860s to the 1980s, there is a high occurrence of hexavalent chromium (Cr6+ ) deposits
Summary
As it is commonly known in the EU, Natura 2000 is a network of nature protection areas in EU states. It allows the water treatment to be carried out with no or significantly reduced amounts of coagulant chemicals that can potentially exhibit health and safety risks during transportation, handling, process use, or storage. It offers the potential for reduced sludge volumes or much higher removal efficacy [14,15]. The process can be supported by the addition of Ca(OH) as it is beneficial for low concentrations of Ni2+ in treated effluent [16] It does not serve for precipitation of Cr(OH) as this is ensured during the electrocoagulation step. It is highly effective and capable to “fulfil the task” of decontamination of the locality in a reasonable time and for a competitive cost
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