Rotating dissolved air flotation (RDAF) has been utilized for several decades in paper‐recycling wastewater treatment; however, it has rarely been addressed in the literature, which makes research into this system challenging and complicated. However, in this work, a full‐scale industrial wastewater treatment system for a paper‐recycling mill in Mazandaran province, Iran, was evaluated. Experiments indicated that under the same wastewater and chemical conditions, there are differences in the removal efficiencies. This finding was investigated by conducting simulation in ANSYS CFX R18.0 and experimentation simultaneously. Thus, the main purpose of this research was to optimize the operation to achieve the highest removal efficiencies in a cost‐effective manner. For simulation, the flow was considered as a two‐phase homogeneous flow with a continuous solid–fluid phase, which discharges into the separation zone at different scenarios. Particles with diameters of 250, 500 and 1000 μm were introduced at four frame rotating speeds of 0.125, 0.25, 0.5 and 0.75 rpm. Measured qualitative parameters of the effluent included COD, BOD, TSS, TDS, conductivity and turbidity, whose removal efficiency ranges were (32.2%–54.8%), (32.7%–54.47%), (94.5%–97.1%), (0.47%–0.55%), (0.48%–0.59%) and (more than 55%), respectively. Moreover, the optimum rotating speeds of the frame for particles with diameters of 250, 500 and 1000 μm were obtained as 0.25, 0.5 and 0.125 rpm, respectively; these values were compared and found to agree with the experimental results.

Paper-recycling mills are serious environmental threats due to their high consumption of water and highly polluted wastewater. Particles are the most common issue of paper-recycling wastewater, and their removal is important for recycling. Rotating dissolved air flotation (RDAF) is a system for separating particles, and the mixing zone of this system, where particles collide with air bubbles, is the most important part that has not been studied. In this work, the mixing zone of a full-scale RDAF in the paper-recycling mill wastewater treatment was investigated to predict particle-bubble collision efficiency and the diameter of the formed particles in different turbulence conditions. ANSYS CFX R18.0, mathematical modeling, and experimental analysis were simultaneously conducted in this research. Based on experimental operation, four scenarios including flow rates and the discharge condition of effluent into the mixing zone were studied. Bubbles with sizes of 60, 80 and 100 µm and the turbulences were calculated. The particle-bubble collision efficiencies indicated the output particles diameter ranging from 50 to 300 µm. Also, an experimental particle size test (SLS) was performed. The modeling and experimental results both showed that the collision efficiency was higher with the production of larger particles when valves #3 and #4 were opened in the mixing zone.

Paper-recycling mills are serious environmental threats due to their high consumption of water and highly polluted wastewater. Particles are the most common issue of paper-recycling wastewater, and their removal is important for recycling. Rotating dissolved air flotation (RDAF) is a system for separating particles, and the mixing zone of this system, where particles collide with air bubbles, is the most important part that has not been studied.In this work, the mixing zone of a full-scale RDAF in the paper-recycling mill wastewater treatment was investigated to predict particle-bubble collision efficiency and the diameter of the formed particles in different turbulence conditions. ANSYS CFX R18.0, mathematical modeling, and experimental analysis were simultaneously conducted in this research. Based on experimental operation, four scenarios including flow rates and the discharge condition of effluent into the mixing zone were studied. Bubbles with sizes of 60, 80 and 100 μm and the turbulences were calculated. The particle-bubble collision efficiencies indicated the output particles diameter ranging from 50 to 300 μm. Also, an experimental particle size test (SLS) was performed. The modeling and experimental results both showed that the collision efficiency was higher with the production of larger particles when valves #3 and #4 were opened in the mixing zone.