Coagulation performance and floc properties for synchronous removal of reactive dye and polyethylene terephthalate microplastics

As a new type of pollutant, microplastics are widely distributed in printing and dyeing wastewater. Coagulation performance, floc characteristics and mechanisms for synchronous removal of reactive orange and polyethylene terephthalate (PET) microplastics using magnesium hydroxide and polyacrylamide (PAM) were investigated in this paper. The floc properties were evaluated by laser particle size analysis and on line intelligent photometric dispersion analysis. Coagulation mechanism was investigated by scanning electron microscope (SEM), Fourier transform infrared spectroscope (FTIR) and Zeta analyzer. The results showed that the removal efficiencies for reactive orange and PET were 98 a/o and 93 a/o under the optimal conditions of magnesium ion 100 mg/L, PAM 4 mg/L with pH value 11.75. The increase of pH, coagulant and PAM dosage would significantly enhance the removal efficiency. The average floc size reached 61.90 mu m and these flocs aggregated together for fast sedimentation. Meanwhile, electrical neutralization and adsorption for reactive orange by magnesium hydroxide, PAM bridging for PET were the main mechanisms. The removal behavior of reactive orange and PET microplastics during coagulation has potential applications for the removal of printing and dyeing wastewater.