Printing Ink Wastewater Treatment Using Hydrodynamic Cavitation and Coagulants/Flocculants

Raw printing ink wastewater (PIW) was treated with various inorganic coagulants and organic flocculants (anionic and cationic polyacrylamides). These processes were also examined as post treatment step following hydrodynamic cavitation. Treatment effectiveness was assessed through color, chemical oxygen demand (COD) and total suspended solids (TSS) removal. The addition of 4500 mg L^-1 polyaluminum chloride coagulant in undiluted PIW (COD: 17000 mg L^-1) resulted in 99% color removal, 96% COD and TSS removal, after settling for 2 h. The addition of 10 mg L^-1 of anionic polyacrylamides in the sample reduced settling time to only 5 min, with concomitant 96-98% removal efficiency. The addition of a 4 min hydrodynamic cavitation pretreatment step reduced coagulant addition by 33%, for the treatment of undiluted PIW (with 10 mg L^-1 anionic polyacrylamide), while removals were ranged between 96 and 98%. Economic analysis for the undiluted PIW showed that costs were reduced by ca. 20% with the hydrodynamic cavitation pretreatment step. Moreover, sludge characterization showed the presence of maghemite, aluminum chloride and potassium aluminum silicate. Finally, toxicity tests revealed a significant attenuation of the toxic potential of undiluted PIW, thus indicating the enhanced efficiency of the proposed combined process (hydrodynamic cavitation and coagulation/flocculation).