Printing ink wastewater treatment using combined hydrodynamic cavitation and pH fixation

Printing ink wastewater (PIW) carries a heavy load of pollutants, the composition of which makes treatment difficult, especially when trying to minimize the pollution load. According to the latter, the present study aims to investigate PIW treatment with different various methods and to determine the maximum color, COD (chemical oxygen demand) and TSS (total suspended solids) removal. First, hydrodynamic cavitation (HC) was tested and the effect of hydrogen peroxide dosage (0-10 g L^-1), and pH (3, 5, 8, 10) was examined concerning the removal of PIW initial COD concentrations 4000 and 8000 mg L^-1. Removal was high (more than 81%) only at pH 5 in HC reactor. The second method involved treatment with separate pH fixation of the undiluted PIW (COD 17000 mg L^-1, actual pH 8 ± 0.2). This treatment, maximized removals, reaching reduction of the initial values more than 91%, at pH 5. Finally, PIW was treated with a combination of the above methods, leading to 93-97% removals for 8000 mg L^-1 PIW treatment and 97-99% for 17000 mg L^-1 PIW respectively. Process cost calculations showed that the latter method is an effective and affordable treatment method for PIW streams, while toxicity tests of the treated PIW showed substantial toxicity reduction.