Mixing Efficiency In A Rotating Bar Reactor And Application In Wastewater Treatment

A rotating bar reactor（RBR）is a novel process intensification reactor consisting of a rotating shaft arranged on the inside and a fixed cylinder on the outside concentrically.For a liquid-liquid system,there are two feeding modes,radial feeding and tangential feeding modes.The rotation of the rotating shaft enhances the flow and mixing of liquids to achieve intensification of application processes,such as wastewater treatment.The mixing behavior of the novel rotating bar reactor was first studied on a fundamental basis in this dissertation.Using the reaction system of iodide-iodate,the micromixing performance of RBR under different operating conditions was studied,and the characteristic micromixing time（t_m）was calculated using the agglomeration model based on experiments.Then for the first time,the axial macroscopic mixing behavior of RBR was investigated using the conductivity technique to acquire the concentration field.In the Fenton oxidation system,RBR was used to increase the effective contact between H₂O₂ and Fe²⁺to achieve an enhanced wastewater treatment process.And the feasibility of using activated carbon in the Rhodamine B removal process was further investigated.The main research results are shown as follows:1.Different rotational speeds,flow rates,viscosities,volumetric flow ratios and hydrogen ion concentrations and feed patterns have important effects on the micromixing performance.The results showed that the micromixing performance of tangential RBR was better than that of radial RBR.Higher rotational speed had a positive effect on the micromixing efficiency,and the micromixing performance decreased with increasing viscosity,volumetric flow ratio,and hydrogen ion concentration.Based on the experimental study,the t_mwas calculated,and the micromixing time of RBR with tangential feed mode was between 5.00×10^-6-1.13×10^-5 s,which is favorable for the process intensification of fast and complex reactions.2.A method to calculate the intensity of segregation by measuring the conductivity of the solution was developed,and the axial mixing performance in RBR was investigated.The results showed that the mixing effect in RBR gradually became better along the axial direction from the bottom to the top,and the segregation intensity decreased from 6.53×10^-5 to 1.57×10^-7.As the rotational speed increased from 0 to 700 r/min,the segregation intensity at the bottom and top decreased from 4.27×10^-3 to 7.10×10^-5 and from 1.93×10^-3 to7.29×10^-7,respectively.3.Applied studies were investigated for the degradation of Rhodamine B（RhB）as a model of wastewater in a rotating bar reactor.The purpose is to improve the generation rate and utilization rate of hydroxyl radicals in the Fenton oxidation system.The results showed that the degradation efficiency of RhB increased when the flow rate was reduced,and the degradation efficiency increased as the flow rate ratio decreased.The initial pH of the RhB solution,the concentration ratio of Fe²⁺to H₂O₂ and the concentration of H₂O₂ had important effects on the degradation efficiency and the apparent reaction rate constant.The degradation efficiency and apparent reaction rate constants increased with decreasing initial pH and increased with increasing H₂O₂concentration.In addition,the reaction time required in this study was shorter compared to other Fenton processes under the same treatment conditions.4.The effect of activated carbon（AC）coupled with the Fenton oxidation process on the degradation efficiency of RhB was investigated.The effects of reagent amount and operating conditions on the RhB degradation efficiency were investigated.The results showed that the removal rate of dye increased from 28%to 82.5%with the increase of activated carbon amount.The removal efficiency increased with the increase in contact time.The degradation efficiency increased when the flow rate decreased.The RhB degradation efficiency increased with decreasing flow rate ratio and reached the maximum efficiency at a flow rate ratio of 5.The RhB degradation efficiency increased with decreasing the initial pH of the solution and increased with increasing the H₂O₂ concentration.In this study,the optimum operating conditions were:rotational speed of 500 r/min,initial pH of 4.5,AC concentration of 0.5 g/L,and H₂O₂ concentration of 0.24 mmol/L.The degradation efficiency of the activated carbon coupled Fenton oxidation process was increased by 57.5%compared to the ordinary Fenton oxidation process.Compared with other wastewater treatment processes,the RBR-based activated carbon coupled Fenton oxidation process could achieve cost-effective and efficient degradation of RhB,with a degradation efficiency of 99.4%in less than two minutes.