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 k(R1) = 0.5553 min(-1) and k(R2) = 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, zonation, etc.) for the removal of cyanide from wastewaters with low organic loads or even drinking waters.