Settling model to predict microplastics removal efficiency in wastewater treatments

Microplastics (MPs) are plastic particles less than 5 mm and become a good carrier and vectors for contaminants in the environment. Current wastewater treatment technologies, including preliminary treatment, primary treatment, secondary treatment, and tertiary treatment, have a certain removal efficiency for MPs or nano-scale plastic particles. The settling treatment is employed in several wastewater treatment processes. This work built a settling model based on the Reynolds number, drag coefficient, and settling mechanism to predict the microplastics removal efficiency. Microplastics with larger density difference with wastewater, larger size, and CSF closer to 1 are easily captured and have a higher removal efficiency. The calculated removal efficiency according to density, size distribution, different shapes, and the surface loading rate in the operation of wastewater treatment is in a reasonable removal efficiency range. The removal efficiency increases when the surface loading rate decreases.