| In recent years,a large amount of antibiotics were discharged into coastal waters through river runoff,sewage discharge and mariculture,cauzing resistance genes that seriously threaten human health and safety.At present,chlorine,ozone and other conventional oxidants are difficult to mineralize antibiotics,and easy to produce toxic by-products.Advanced oxidation technology with hydroxyl radical(·OH)as the core can mineralize organics such as antibiotics without selectivity and secondary pollution,and it becomes an international research hotspot.This research based on the technology that combination of atmospheric pressure ionization discharge and water jet cavitation to efficiently generate ·OH,studied the mineralization of tetracycline antibiotics such as oxytetracycline.The main research contents include:(1)On the basis of EPA Method 1694,optimization was carried out from three aspects of liquid chromatography parameters,mass spectrometry detection parameters and solid phase extraction(SPE)process.Finaly a method was established for simultaneous detection of tetracycline and sulfonamide antibiotics.The linear range of the standard operating curve was 10-1000 μg/L,and the correlation coefficients were greater than 0.999.The minimum detection limit of the instrument was 0.004-0.294μg/L,and the recovery rate was 90-110%with the relative standard deviation less than 10%.In addition,the improved extraction conditions are more mild to the extraction column,which can be reused and reduce the cost of detection.(2)Atmospheric pressure ionization discharge was used to ionize and dissociate O2 to generate oxygen active particles of a high concentration,which produced ultra-fine bubbles in the aid of water jet cavitation.As those bubbles expanded with high-speed and adiabatic condition,·OH was generated efficiently in pipeline at the moment bubbles rupture,mineralizing tetracycline antibiotics in situ.Based on this,the "timeresponse" and "agent response" relationships of ·OH and tetracycline antibiotics were studied.Combined with the full scan of mass spectrometry and total organic carbon analysis,it demonstrated that the time of tetracycline antibiotics complete mineralized by ·OH was only 3 s,when the concentration ratio of ·OH solution(TRO)to antibiotics was 7:1.(3)The charge distribution,bond strength and other parameters of oxytetracycline were analyzed by quantitative calculation to determine the initial reaction site of oxytetracycline by ·OH.ESR method was used to verify the direct effect of ·OH on oxytetracycline.Based on liquid mass spectrometry analysis and literature review,·OH mineralized oxytetracycline mainly through the following three reaction pathways:1)·OH attacks the tricarbonyl group,resulting in its separation from the parent structure;2)·OH attacks phenolic diketone group,causing the cleavage of oxytetracycline intermediate double ring;3)·OH replaces the dimethylamino group.These three paths all produce hydroxyl benzocyclobutene(m/z=121),of which the conjugated structure inside the benzene ring would be destroyed by ·OH.Then its rings open to small molecules such as alcohols and acids,finally mineralized into CO2 and H2O.(4)The reaction time required by ·OH,O3,ClO2,KMnO4 and H2O2 to degrade oxytetracycline was compared at the same oxidant concentration.When the oxidant concentration was 1 mg/L,it only took 3 s for ·OH to completely degrade oxytetracycline,while other oxidants could not.The degradation rate was 96.3%after 15 s of O3 reaction,96.1%after 10 min of ClO2 reaction,and less than 9%after 2 h of KMnO4 reaction.H2O2 had no degradation effect after 2 h reaction.·OH could degrade oxytetracycline to the state that no macromolecular products canbe detected at 3 mg/L oxidant concentration,while in the O3,ClO2 and KMnO4 reaction,there still were byproducts detected,and H2O2 still had no degradation effect.Especially in the ClO2 reaction,there were many toxic chlorine products detected.(5)A ·OH treatment system for mariculture water of Epinephelus coioides,consist of sand filter-reservoir-·OH equipment-aquaculture tank-filter-foam separator-biological filter,was established in the demonstration base of Grouper seed Industry Innovation and Industrialization in Fujian Province to demonstrate how-OH degrade antibiotics and treat cultured seawate.·OH equipment produced the high concentration·OH solution(10 mg/L),which was injected into the pipeline mixed with pretreated aquaculture water to produce Img/L ·OH solution in the pipeline.With a reaction time of 6 s,tetracycline,oxytetracycline,chltetracycline,sulfadiazine,sulfamethazine and sulfamethoxazole as respective concentration of 100 μg/L could be degraded to an undetected level.Discharging ·OH solution into the aquaculture tank to maintain the concentration of ·OH at 0.3 mg/L for 10 min,all cryptocaryon irritants could be killed.No bromate was produced after ·OH treatment,and the amount of bromomethane(4.87μg/L)was far lower than the standard limit of 100 μg/L.The water quality meets the requirements of the second class of Seawater Water Quality Standard(GB 3097-82). |
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