Plasmachemical degradation of azo dyes by humid air plasma: Yellow Supranol 4 GL, Scarlet Red Nylosan F3 GL and industrial waste.

Abstract A recent non-thermal plasma technique (i.e., a gliding arc discharge which generates reactive species at atmospheric pressure) is tested for pollution abatement of dyes dispersed in synthetic solutions and industrial effluents. Yellow Supranol 4 GL (YS) and Scarlet Red Nylosan F3 GL (SRN) are toxic synthetic dyes widely used in the Algerian textile industry and frequently present in liquid wastes of manufacture plants. Classical removal treatment processes are not efficient enough, so that the presence of dyes in liquid effluents may cause serious environmental problems, in connection with reusing waste waters for irrigation. The degradation processes achieved by the oxidising species formed in the plasma are followed by UV/VIS spectroscopy and by chemical oxygen demand measurements. They are almost complete (i.e., 92.5% for YS and 90% for dilute SRN) and rapidly follow pseudo-first-order laws, with overall estimated rate constants 3×10 −4 and 4×10 −4  s −1 for YS and SRN, respectively. The degradation rate constant for the industrial mixture (i.e., k =1.45×10 −3  s −1 ) is a mean value for two consecutive steps (2 10 −3 and 6×10 −5  s −1 ) measured at the absorption peaks of the major constituent dyes, YS and SRN.