Effect of flow rate on phosphate removal in HGMS
Flow rate is an important parameter in the HGMS as it determines the retention time of particles in the magnetic field. In this experiment, the flow rate was varied from 1.0 to 3.8 L/min, while keeping the magnet working current at 160 A and the magnetic seed dosage and coagulant dose at 100 and 50 mg/L, respectively. The effect of flow rate on the removal of phosphate from aqueous solution is shown in Fig. 8. An obvious effect of flow rate on the removal of phosphate from aqueous solution was observed. Specifically, an increase in flow rate resulted in a decrease in phosphate removal efficiency. When the flow rate of HGMS was less than 1.5 L/min, the final effluent phosphate was lower than 0.02 mg/L. However, when the flow rate of HGMS was higher than 1.5 L/min, the final effluent phosphate increased sharply and the quality of wastewater decreased to levels that did not satisfy the effluent standards. This was likely because the drag force on the trapped magnetite flocs particle became great enough to shear some of the phosphate precipitates from the magnetite particles as the flow rate increased, resulting in lower phosphate removal efficiency [30]. Li et al. [24] also found that a higher flow rate and relative motion velocity between water and magnetic flocs was associated with greater amounts of pollutant flocs being sheared.