Gliding arc discharge-assisted biodegradation of crystal violet in solution with Aeromonas hydrophila strain

The gliding arc discharge, which is a source of nonthermal plasma, was used to enhance the biodegradation of crystal violet (CV), a triphenylmethane non-biodegradable organic dye. The determination of the biodegradability index, i.e., biochemical oxygen demand (BOD5)/chemical oxygen demand (COD) ratio, and the total organic carbon measurement were used to assess the biodegradability. For the biological treatment alone, a bacterial strain of Aeromonas hydrophila (8 × 108 CFU mL−1) bleached 42 % of CV solution (50 mg L−1) after 12-h incubation. The bleaching rate was enhanced by increasing the initial bacterial concentration; however, a drop in the bleaching rate was noted when CV concentration was increased. For the plasma process alone, a 15-min treatment resulted in a color removal of 49.7 %, at a mineralization rate of 12.2 %, thereby increasing the BOD5/COD ratio from 0.11 to 0.23. There was an increase in the bleaching rate in temporal post-discharge conditions (i.e., self-continuity of reaction after the discharge was switched off): For 2 h of temporal post-discharge reaction, the color removal of the 15-min plasma-pre-treated CV increased to 55 %. The disappearance of color during each treatment method followed the first-order kinetics. With regard to the combined plasma/biological treatment process, the 15-min plasma-pre-treated sample was bleached at 92 % by A. hydrophila after 2-h incubation and completely bleached for 6 h. Therefore, there is a positive synergism of bacterial and plasma treatments. This combined treatment is useful in reducing the energy involved in complete mineralization of wastewater containing non-biodegradable dyes.