Pilot-scale hybrid system combining hydrodynamic cavitation and sedimentation for the decolorization of industrial inks and printing ink wastewater.

A pilot-scale hydrodynamic cavitation (HC) system followed by sedimentation (SED) was used for the decolorization of 5 industrial-grade inks, a fluid containing a mixture of the five industrial grade inks (MIX) and printing ink wastewater (PIW). The pilot scale HC reactor combines a Venturi tube with a 31 holes orifice plate accommodated in the vena-contracta of Venturi. The study aimed to define optimal operating conditions, i.e., hydrogen peroxide concentration (HO), pH and combined HC/SED treatment time, to achieve decolorization and reduce HC operation time. Under the optimal conditions at the proposed HC/SED system, color removal reached 92%, 91%, 90%,98% and 90%, for black, red, yellow, cyan, and green ink respectively (at pH 8 without HO addition). In the same system, color removal for PIW was 92%, whereas for MIX decolorization reached more than 90% for all the wavelengths in the selected spectrum 300-700 nm at HC/SED system (at pH 8 and 1 g L hydrogen peroxide). The suspended particles were characterized by measurements of the particle size distribution and of the respective zeta potential. The equivalent cavitation yields, electric energy consumption and operating costs were calculated. The present work's results suggested that HC combined with sedimentation has a great potential for real applications and is superior compared to other technologies (i.e., HO alone, sedimentation alone or even HC with or without HO).