Study On The Removal Effect And Mechanism Of Doxycycline Hydrochloride By Hydrodynamic Cavitation Combined With Photocatalytic Technology

Antibiotics are one of the most widely used drugs,however,due to the long-term abuse of antibiotics and the difficulty of degradation of antibiotics themselves,untreated or incomplete disposal can cause serious environmental problems.Antibiotic wastewater usually has the characteristics of difficult degradation,complex components,and a large amount of water.Therefore,it is urgent to develop new environmentally friendly and efficient technologies to reduce antibiotic pollution.Photocatalytic oxidation has become a new research focus and attracted extensive attention from researchers.However,the traditional photocatalytic degradation technology is limited by mass transfer,and catalyst surface agglomeration and is difficult to recover,which hinders its large-scale application in actual wastewater treatment.In addition,hydrodynamic cavitation,as a new advanced oxidation technology,has the advantages of simple operation and green pollution-free,but a single hydrodynamic cavitation system can not completely remove the pollutants in the water body.Therefore,the combination of hydrodynamic cavitation and photocatalytic technology can strengthen the efficiency of wastewater treatment.In this paper,doxycycline hydrochloride（DOX）was taken as the research object,and the self-made hydrodynamic cavitation combined with a photocatalytic device was used to investigate the effects of different influencing factors on its degradation effect,and the mechanism of the hydrodynamic cavitation combined with photocatalytic technology for the degradation of doxycycline hydrochloride（DOX）was discussed,which provided an effective idea for the research on antibiotic wastewater treatment technology.（1）The N-doped TiO₂ catalyst was prepared by the sol-gel method.The optimal doping amount of N-doped TiO₂ catalyst and its dosage was confirmed through the results of X-ray diffraction（XRD）analysis,ultraviolet-visible diffuse reflection spectroscopy（UV-vis DRS）,and photocatalytic degradation experiment.The results show that when the molar ratio of N/Ti is 0.01:1.00 and the catalyst dosage is 0.5 g/L,the degradation rate of doxycycline hydrochloride（DOX）can reach 26.96%.Therefore,the following experiments all adopt 0.5 g/L N-doped TiO₂（N/Ti=0.01:1.00）photocatalyst.（2）A single hydrodynamic cavitation system,a single photocatalysis system,and a combined hydrodynamic cavitation photocatalysis system are used for degrading doxycycline hydrochloride（DOX）,and the effects of anions(Cl^-,NO₃^-and CO₃^2-),humic acid and initial pH on the degradation rate of doxycycline hydrochloride（DOX）are explored.The specific research contents are as follows:For a single hydrodynamic cavitation system,Cl^-,NO₃^-,humic acid,and a low concentration of CO₃^2-inhibited the degradation of doxycycline hydrochloride（DOX）,while a high concentration of CO₃^2-promoted the degradation.When the initial pH of the solution was 3.0,a maximum of 52.78%was obtained.For a single photocatalytic system,Cl^-had little effect on the degradation of doxycycline hydrochloride（DOX）.NO₃^-promoted the degradation of doxycycline hydrochloride（DOX）,but after the addition of CO₃^2-at a high concentration,DOX was significantly inhibited.Low concentration of humic acid played a promoting role,while high concentration had an inhibiting effect.At the initial pH of 7.0,the degradation rate of doxycycline hydrochloride（DOX）reached 41.66%.For the hydrodynamic cavitation combined with the photocatalysis system,Cl^-has little effect on the degradation of doxycycline hydrochloride（DOX）.NO₃^-,CO₃^2-,and humic acid played an inhibitory role;At the initial pH of 5.0,the degradation rate of doxycycline hydrochloride（DOX）was 86.01%.（3）By comprehensively comparing the degradation performance of each system,the feasibility of degradation of doxycycline hydrochloride（DOX）by hydrodynamic cavitation combined with photocatalytic technology was analyzed,and the free radical quenching experiment was conducted.In addition,a possible mechanism of hydrodynamic cavitation combined with photocatalytic degradation of doxycycline hydrochloride（DOX）was proposed.The results showed that the degradation rate of a single hydrodynamic cavitation system was 44.49%,and that of a single photocatalytic system was only 26.96%,while the combination of hydrodynamic cavitation and photocatalytic method had significant synergistic and strengthening effects,with the degradation rate reaching 80.32%,and all the systems were following the first-order reaction kinetics.Finally,the direction of future work is briefly discussed.