Enhanced treatment of oily ink wastewater using a modified degreaser by nano-Fe3O4/Na2S2O8: Efficient coagulation and sedimentation

Abstract

Ink wastewater is hazardous because it contains oil and refractory pollutants, with high Chroma and turbidity. There are many aromatic compounds in the wastewater, such as benzene, toluene, xylene, and phthalocyanines, azos, and nitroso, which make high chemical oxygen demand (COD) and ammonia nitrogen content. The refractory pollutants are always encapsulated in diverse oil-water systems. Usually a massive degreaser has to be used to destroy the dispersant oil forms under preferred alkaline condition, and advanced oxidation is used for good removal of refractory pollutants under preferred acid condition, which commonly lead to a bad coagulation and sedimentation as a result. In this study, the nano-Fe3O4 (MNPs) activated sodium persulfate (SPS) has been testified to enhance degrease with efficient coagulation and sedimentation. The results showed that the removal of oil, COD, ammonia nitrogen, Chroma and turbidity reached respectively 96.40%, 98.35%, 88.00%, 99.70% and 98.22%, within 40–50 min. The mechanism shows that the catalytic oxidation significantly decreased the Zeta potential of the colloidal particles in the wastewater, which destroyed the steady-state of the colloid and enhanced the effect of coagulation sedimentation. Importantly, the combination of MNPs and colloidal particles successfully promoted the simultaneous production of SO4− and a large amount of HO under weakly alkaline (pH = 7.5–8.0) conditions, which made synergistic oxidation to remove micro-oil and organic pollution efficiently.