Removal of cyanide from water by means of plasma discharge technology

Two different nonthermal plasma reactors at atmospheric pressure were assessed for the first time for cyanide removal (1 mg L−1) from aqueous solutions (0.025 M NaHCO3/NaOH buffer, pH 11) at laboratory scale. Both devices were dielectric barrier discharge (DBD) reactors; one of them was a conventional batch reactor (R1) and the other one was a coaxial thin falling water film reactor (R2). A first-order degradation kinetics was proposed for both experiments, obtaining kR1 = 0.5553 min−1 and kR2 = 0.7482 min−1. The coaxial reactor R2 yielded a removal of 99% within only 3 min. Energy efficiencies (G) were calculated, yielding 1.74 mg kW−1 h−1 for R1 and 127.9 mg kW−1 h−1 for R2. When the treatment was applied to industrial wastewaters, cyanide elimination was confirmed, although at a lower rate (above 92% removal in 90 min with R2). Therefore, plasma reactors could be a relevant alternative to established advanced oxidation techniques (UV, H2O2, ozonation, etc.) for the removal of cyanide from wastewaters with low organic loads or even drinking waters.

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► Cyanide aqueous solutions (1 ppm) were treated in two dielectric barrier discharge reactors.
► A maximum removal of 99% was attained within 3 min (127.9 mg kW−1 h−1).
► A first-order degradation kinetics is proposed with k 0.5553–0.7482 min−1.
► Lower efficiency was observed in complex wastewater (>92% removal in 90 min).
► Plasma reactors could be an alternative to established advanced oxidation processes.