Removal of cyanide from water by means of plasma discharge technology

Abstract

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.