Study On The Subcritical Hydrothermal Degradation Of Chloramphenicol In Water And The Degradation Of Persulfate Catalyzed By Biochar

As one of the typical antibiotics,chloramphenicol（CAP）has attracted public attention due to its adverse biological effects and the potential to induce resistance genes.For the degradation and transformation of chloramphenicol,this paper uses subcritical hydrothermal reaction and persulfate advanced oxidation technology to discuss the removal effect and degradation mechanism of CAP under the two systems.Subcritical hydrothermal reaction is used to remove CAP in high-concentration pharmaceutical wastewater,and cobalt/iron double-doped biochar is used to catalyze the removal of persulfate from CAP in low-concentration pharmaceutical wastewater.The research results are as follows:（1）Research on subcritical hydrothermal reaction shows that CAP can be effectively degraded in subcritical hydrothermal reaction.The removal rate of CAP increases with increasing temperature.When the temperature increased from 140°C to 240°C,after 30minutes of reaction,the removal rate of CAP increased from 31%to 96%.At the same time,the removal rate of CAP also increases with the extension of the reaction time.When the temperature is 160℃and the reaction time is extended from 0 min to 150 min,the removal rate of CAP increases from 40%to 93%.TOC is only reduced to a certain extent,and the removal rate of TOC can only be reduced to 88.3%of the pre-reaction under optimal conditions.This shows that only a small part of CAP is mineralized,and most of it exists in the reaction liquid in the form of other organic matter.The increase of subcritical hydrothermal reaction temperature and the increase of time can promote the conversion of organic nitrogen in CAP to NH₄⁺,and NH₄⁺comes from the imino group in CAP,and the nitro group remains in the product.The organochlorine in CAP can be effectively converted to Cl^-in the subcritical hydrothermal reaction.The increase in temperature and time of the subcritical hydrothermal reaction is conducive to the conversion of organochlorine to Cl^-,and the effect of temperature is more significant.According to the product identification results combined with the conversion of nitrogen and chlorine in CAP,it is speculated that in the subcritical hydrothermal reaction of CAP,the C-Cl bond will be broken and converted to Cl^-;the two C-N bonds on the imino group will be broken successively to generate NH₄⁺;the C-C bond outside the benzene ring will break and eventually form nitrobenzene.（2）Using camellia seed hulls as biomass raw materials,a co-precipitation-pyrolysis method was used to prepare a cobalt/iron bimetal doped biochar catalyst to activate persulfate to degrade CAP.Through SEM（with energy spectrum）,XRD,XPS,Raman spectroscopy,specific surface area and pore size distribution determination,a series of characterization of the catalyst,these characterizations verified the successful synthesis of the catalyst.Experimental studies on catalytic degradation show that the higher the pyrolysis temperature of the prepared catalyst,the better the catalytic effect on CAP degradation.As the pyrolysis temperature increased from 500°C to 900°C,the CAP removal rate within 10 minutes increased from 15%to 41.4%.The cobalt/iron doping ratio also has a significant impact on the catalytic effect of the catalyst.As the cobalt/iron doping ratio increases from 2:1 to 1:4,the catalytic effect of the catalyst gradually increases,and the CAP removal rate within 10 minutes Increased from 58.5%to 90.1%.In addition,the effects of catalyst dosage,PS concentration,initial CAP concentration,and initial p H on the degradation of CAP were also explored.Through free radical quenching experiments,the role of free radicals in the reaction process was explored,and it was proved that·OH played a major role in the catalytic degradation of CAP.Finally,the intermediate products of the reaction were detected by LC-MS and GC-MS,and seven possible intermediate products were obtained,and the degradation path of CAP in the advanced oxidation of persulfate was inferred.