Domestic wastewaters and industrial wastewaters from food processing industry, pulp industry, pharmaceutical and organic synthesis industries, coalmines and mines contain various inorganic and organic substances in the form of fine suspension, emulsions, colloids, etc. In particular, the microplastics contained in wastewater pose a potential threat to the environment and human health due to their small particle size, high hydrophobicity and easy adsorption of toxic substances.
There are several methods for treating wastewater containing microplastics, among which the dissolved air flotation (DAF) process using microbubbles has attracted special attention. DAF process is one of the wastewater treatment methods for accelerating gravity separation by adhering microbubbles to solid particles in wastewater and increasing the density difference between continuous and dispersed phases.
Most of the previous studies have paid a great deal of attention to the structure of DAF tanks and fluid flow characteristics, and little effort has been directed to the effect of liquid properties on flotation efficiency.
Since the objective of the DAF process is to increase the efficiency of impurity removal under constant hydraulic surface loads, it is also important to have a correct understanding of the interaction characteristics between particles to be removed, bubbles and liquid phases.
Kim Kwang Jun, a researcher at the Institute of Nano Science and Technology, has simulated the process of dissolved air flotation (DAF) to remove microplastics from various wastewaters by the computational fluid dynamics (CFD) method.
First, he injected a solution with a resin particle concentration of 0.2 g/L at a flow rate of 20 mL/min. Then, he injected a solution with a water-to-microbubble volume ratio of 4:1 at a flow rate of 300 mL/min. The simulation results showed that the kinematic and distribution characteristics of the resin particles and microbubbles were in good agreement with the experimental results.
Based on the simulation system to analyze the behavior of particles in flotation solutions, he evaluated the flotation performance by varying the concentration of NaCl solution and the pH value of 10-2 M salt solution. The calculation results showed that the flotation performance improved with increasing NaCl concentration and pH, and the concentration of NaCl had a greater effect.
These results provide some basic information for designing industrial wastewater treatment processes for removing microplastics from wastewater of different properties.
For further details, you can refer to his paper “CFD Simulation of DAF processing for removal microplastic in different flotation solution” in “Water Science & Technology” (SCI).