Study On Thermally Assisted Orifice Plate Hydrodynamic Cavitation Degradation Of Rhodamine B And Heat Production

At present,with the development of consumption demand,the production and application of synthetic dyes are expanding gradually,which results in large amounts of dye wastewater being discharged into the environment.The dye molecules are so complicated that they are difficult to remove completely using traditional wastewater treatment methods.Therefore,it is urgent to explore a new and efficient sewage treatment method.Advanced oxidation technology has attracted wide attention because of its ability to produce highly active oxygen-containing free radicals to react non-selectively with organic pollutants,resulting in effective mineralization of organic pollutants.Hydrodynamic cavitation(HC)technology,as a new advanced oxidation technology,has shown good ability to treat refractory organic wastewater in recent years,and has the advantages of no secondary pollution,simple operation and low treatment cost.However,at present,HC development in the field of environment is still in the initial stage,and there are still some problems such as poor treatment effect,low efficiency and incomplete mineralization of organic matter.Therefore,the traditional HC system still needs to be further optimized.In this study,a thermally assisted HC system was established by adding a water pre-heater in front of the cavitation device(orifice plate),which realizes the local heating of the flowing liquid,thus intensifying the HC effect and enhancing Rhodamine B(Rh B)degradation ratio and heat generation efficiency of the system.The effects of preheating temperature,Rh B initial concentration,orifice plate hole number,inlet pressure and solution volume on Rh B HC degradation and heat generation were investigated.Free radical trapping experiments were performed to explore the active substances produced by the HC effect.Based on LC-MS and TOC data,the possible Rh B degradation pathway and mechanism were proposed.The results indicate that the Rh B degradation ratio increased from 23.42%to 34.49%within 90 min cycle time,and the treatment cost decreased from 130.699 USD/m~3 to91.701 USD/m~3 when the preheating temperature rose from 10°C to 50°C.At 30min cycle time,the solution temperature rose from 45.6°C to 56.4°C,the heat production increased from 149.46 k J/L to 194.81 k J/L and the corresponding thermal efficiency increased from 47.45%to 61.84%.Further,at 60 min cycle time,under the conditions of 30°C preheating temperature,30 mg/L Rh B initial concentration,3-hole orifice plate,3 bar inlet pressure and 5.0 L Rh B solution volume,the Rh B degradation ratio was the highest(40.38%).After Fenton reagent was used,the Rh B degradation ratio and heat production both were further enhanced.At 60 min cycle time,the Rh B degradation ratio was 65.52%,solution temperature rose to 72.8°C,the heat production reached 131.83 k J/L and the treatment cost was only 45.447USD/m~3 at 30°C preheating temperature.TOC test results show that the Rh B mineralization ratio can reach 61.53%after 90 min cycle in the thermal assisted HC+Fenton system,indicating that dye molecules can be effectively degraded and mineralized.All in all,this work proves that thermally assisted HC+Fenton is an effective method to degrade organic dyes and generate heat,which can be used for large-scale treatment of organic dye wastewater.