The gliding arc discharge, which is a source of
nonthermal plasma, was used to enhance the biodegradation
of crystal violet (CV), a triphenylmethane nonbiodegradable
organic dye. The determination of the
biodegradability index, i.e., biochemical oxygen demand
(BOD
5)/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 × 10
8 -
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
BOD
5/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 nonbiodegradable
dyes.
