High-field narrow-gap electrochemical treatment of chloride-containing industrial wastewater: Organic contaminant transformation and foam-mediated phase separation

A high-field narrow-gap electrochemical process was investigated for the treatment of moderately mineralized gas-processing wastewater containing chloride ions and a chemically heterogeneous organic fraction. Before the experiments described here, residual sulfide species were removed by conventional upstream conditioning; the present study therefore focused exclusively on the treatment of organic contaminants. The work combined industrial and patent-supported flow-through data with a separate laboratory series designed to clarify the effects of millimetre-scale electrode spacing. In the industrial series, preliminary spray aeration followed by undivided electrolysis decreased permanganate oxidizability by 96.0% in real wastewater; the corresponding maximum decrease in model water was 96.9%. Preliminary aeration increased the reported treatment efficiency of real wastewater from 87.8 to 96.0%. In the laboratory reactor, ten commercial high-alloy stainless-steel blade electrodes were operated at a nominal voltage of 5 V with interelectrode gaps of 2.0, 1.5, and 1.0 mm. Decreasing the gap increased the measured current from approximately 0.9 to 1.4 and 1.9 A, corresponding to nominal potential gradients of 25, 33, and 50 V cm −1 . The increase in current was accompanied by intensive gas evolution, rapid clarification, and accumulation of a removable brown foam-associated phase at the liquid surface. The treatment effect is interpreted as a combination of direct and possibly mediated electrochemical transformation, destabilization and redistribution of organic matter, bubble-assisted transport, and interfacial phase separation. The results show that a compact narrow-gap reactor can integrate organic-contaminant treatment and foam-mediated separation, although complete mineralization and the chemical composition of the floating phase were not established.