Coagulation process was applied to treat wastewater generated from the cleaning process of production and printing equipments of water-based printing ink under without pH adjustment. Polyaluminum chloride (PACl), aluminum sulfate (Al2(SO4)3) and ferrous sulfate (FeSO4) were used as coagulants, polyscrylamide (PAM) and FeSO4 were selected as coagulant aids. Coagulation efficiency was evaluated in terms of the transmittance value of supernatant and the chemical oxygen demand (COD) removal of treated water. The results showed that three coagulants exhibited similar performances at the dosage of 1000-1400 mg/L. Coagulant aid, especially PAM, could accelerate the formation of flocs and subsequently enhanced the settling ability of flocs. The combination of PACl (1000 mg/L) and PAM (25 mg/L) removed 86.3% of COD and 96.4% of color. This study provides an effective and convenient method for pretreatment of water-based printing ink wastewater. It is worth mentioning that the treated water was transparent and might be recycled to cleaning process.
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