Degradation Of Fluoroquinolone Using UV/Chlorine In Aqueous Solution: Direct Photodegradation,Chlorine Oxidation And Their Combined Degradation

The continuous detection of fluoroquinolones?FQs?antibiotics in the water environment has aroused widespread concern.Due to the poor removal of traditional drinking water treatment processes,advanced oxidation processes?AOPs?have become a better choice.As an emerging AOP,UV/chlorine has unique advantages in drinking water treatment,but there are still many gaps in basic research on the degradation of FQs.Therefore,this paper studies the basic kinetics of chlorine oxidation and UV direct photodegradation of FQs in the degradation mechanism of UV/chlorine AOP.In view of the difficulty of accurately measuring the UV dose,the alignment and optimization of the Quasi-collimated beam apparatus?QCBA?was simulated.In addition,the effects of UV/chlorine AOP,UV direct photodegradation and chlorine oxidation degradation of FQs were compared,and the acute toxicity changes during UV direct photodegradation and chlorine oxidation degradation of FQs were studied.The main conclusions are as follows:?1?Using Computational Fluid Dynamics?CFD?to optimize the construction parameters of the photoreactor.The QCBA of the baffle structure is superior to the barrel structure.The structure where the relative position of the two layers of baffles is located above and below can realize the quasi-parallel beam with the highest parallelism?PF?=0.950?;The number of lamps has almost no effect on the parallelism of the beam,and multiple lamps placed next to each other can increase the UV fluence rate?FR?;The size of the UV lamp unit FR has no effect on the beam parallelism,and the unit FR is linearly related to the highest point FR;The measured value of PF?of the actually constructed three-layer structure QCBA is 0.973,which is higher than the simulation optimal result?PF?=0.964?.?2?Explore the basic kinetics of UV light degradation of FQs and the acute toxicity changes during degradation.The direct photodegradation of the selected five FQs conforms to pseudo-first-order kinetics.The pH of the solution has a great influence on the molar absorption coefficients???of FQs,fluence-based photolysis rate constant?k'?and quantum yield???,which mainly depends on the dissociation form of FQs.The relationship between?,k'and?in different forms of FQs is FQ⁰>FQ^->FQ⁺.Temperature can promote the degradation of FQs,but the effect is small,and the calculated activation energy range of FQs is 13.26—23.14kJ/mol;SO₄^2-,Cl^-,NO₃^-and HCO₃^-/CO₃^2-both promote and inhibit the degradation of five FQs;FQs have basically no acute toxicity to aquatic organisms,but the chronic toxicity to Daphnia is between toxic and non-toxic;Photodegradation has the potential to weaken toxicity at a certain dose,but the conventional UV disinfection dose of 40mJ·cm^-2 has little effect on the acute toxicity changes during the degradation of FQs.?3?To explore the basic kinetics of chlorine oxidation degradation of FQs and the acute toxicity changes during degradation.pH affects the process of free chlorine oxidizing FQs by affecting the form of FQs and free chlorine.The molecular state Enrofloxacin?ENR?reaction rate is the highest,the degradation of Lomefloxacin?LOM?is almost only related to the anionic state,and the degradation of Ofloxacin?OFL?is almost independent of the anionic state;The increase in temperature increases the reaction rate of the three FQ,and the apparent activation energy range of FQs is calculated to be 26.80—84.27kJ/mol;SO₄^2-,Cl^-,NO₃^-and HCO₃^-/CO₃^2-almost all promote the oxidative degradation of chlorine in FQs,except that Cl^-has a slight inhibitory effect on OFL degradation;Chlorine oxidation is difficult to reduce the acute toxicity during the degradation of FQs,and even the intermediate products generated may be more toxic than the parent.?4?The effects of UV/chlorine,UV direct photodegradation and chlorine oxidation degradation of FQs were compared.UV/chlorine AOP shows a strong oxidative degradation ability for the three selected FQs,almost complete degradation of FQs under the conditions of UV dose within 40mJ·cm^-2 and chlorine dose within 10?M.Compared with chlorine oxidation alone and UV direct photodegradation,UV/chlorine AOP achieves the same removal effect,the required UV dose and chlorine dose are greatly reduced.