Synergistic enhancement of pollutant removal from high-salt wastewater using coagulation-flotation combined process

Sufficient treatment of industrial organic wastewater with high salt and large amounts of suspended particulate matter remains a challenge worldwide. In this work, a novel coagulation-flotation combined process was developed to treat the suspended particles as well as significantly reduce organic pollutants content in the actual high-salt organic wastewater. Four typical inorganic and organic flocculants (poly aluminum chloride (PAC), poly ferric sulfate (PFS), polyacrylamide (PAM), and modified cationic starch (CS)) were selected for compounding to obtain an optimized flocculation system for high-salt wastewater. The results showed that the PAC-PAM with a 10:1 ratio in mass exhibited the best coagulation behaviors with the removal efficiency of turbidity and chemical oxygen demand (COD) being 95.33% and 9.21%, respectively, under the optimal operation conditions, and the sedimentation process of coagulant conformed to the quasi-second-order kinetics. The PAC-PAM flocs exhibited stronger netting, sweeping, and adsorption bridging capabilities, which were conducive to removing suspended particles. When the flotation was conducted after coagulation, the COD decreased significantly by 20.82%. In addition, this combined process could reduce the treatment time by 50% compared to the process with only coagulation treatment. During the flotation process, floc particles companies with hydrophobic polycyclic aromatic hydrocarbons could collide and adhere to microbubbles and be floated to the surface, resulting in an effective reduction of COD. This work could provide a novel strategy and step forward to design and optimize the pretreatment process engineering for organic high-salt wastewater. • The organic-inorganic compound flocculant for high-salt wastewater was optimized. • The novel coagulation-flotation combined process was proposed. • The combined process could decrease COD and reduce treatment time significantly. • The sedimentation process and model of coagulant were established. • Bubbles could remove hydrophobic organics companied with flocs by flotation.