Ecologically Non-Invasive Decontamination of Natura 2000 Locality from Old Deposits of Hexavalent Chromium and Bivalent Nickel by Modular Electrocoagulation Combined with Ca(OH)2 Addition

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.

The Influence of the Duration of Exposure to Direct Current on the Treatment Efficiency of Wastewater from Soilless Tomato Cultivation in a Bio-Electrochemical Reactor

“…Tejera et al [27], who treated leachate from a municipal landfill at current densities of 5 mA•cm −2 and 10 mA•cm −2 , determined iron concentration in the treated effluent at 100 mg•L −1 and 200 mg•L −1 , respectively. In turn, Krystynik et al [28] removed chromium and nickel ions during the treatment of groundwater from a metallurgical plant and found a residual iron concentration in the effluent between 0.2 and 2.2 mg Fe•L −1 at a current density of 11.42 mA•cm −2 . In their study, they used a flow-through electrocoagulation cell with a flow rate of 350 L•h −1 .…”