Biodegradation Of 1H-1,2,4-triazole In Aerobic And Anoxic Conditions

In this study,a novel 1H-1,2,4-triazole(TZ)degrading strain capable of utilizing TZ as carbon and nitrogen source was isolated from activated sludge acclimated by TZ and was identified as Raoultella sp.,named Raoultella sp.NJUST 42 by 16S r RNA sequence analysis.The degradation performance and degradation mechanism were investigated under aerobic and anoxic conditions.The similarities and differences of degradation under the two conditions were compared and analyzed.The aerobic biodegradation sequencing experiment showed that 100 mg L^-1 TZ was completely removed within 288 h at incubation temperature of 30°C and initial p H of 7.0,which was accompanied by obvious TOC removal,NH₄⁺release,p H increase,biomass growth,biotoxicity reduction and excitation emission matrix(EEM)variation.TZ biodegradation profile by Raoultella sp.was well fitted by the first-order degradation kinetic model,confirming that substrate concentration,temperature,initial p H and additional carbon source all could effect on TZ degradation.The degradation of 100 mg L^-1 TZ at 30°C and p H=7.0 was optimal.In addition,the addition of 500 mg L^-1 glucose had a positive effect on degradation.Based on HPLC/MS analysis,TZ biodegradation pathway including hydroxylation,carbonylation,carboxylation and ring cleavage was proposed for the first time.In the anoxic sequencing degradation experiment:the degradation rate of NJUST42 to50mg L^-1 TZ in 132h was 80.06%,accompanied by the release of NH₄⁺,the increase of p H,the increase of biomass,the removal of TOC,the release of N₂ and the changes of EEM during the degradation process.These results illustrated the mineralization and conversion of intermediates during the TZ removal.The degradation of TZ was also fitted by the first-order degradation kinetics model.The results showed that substrate concentration,temperature,initial p H and C/N all would influence TZ degradation.The optimal degradation conditions for 50 mg L^-1 TZ were culture temperature of 30°C,p H=7.0 and C/N=2.0.In addition,the denitrification products are different at different substrate concentrations.When the substrate concentration were 30 mg L^-1 and 50 mg L^-1,NO₃-N could be finally converted to N₂-N;at 100 mg L^-1 and150 mg L^-1,most of NO₃-N was converted to NO₂-N and accumulated in solution,which further inhibited the conversion to N₂-N;when the concentration of TZ was 200 mg L^-1,the utilization of NO₃-N was inhibited and little NO₃-N was converted to NO₂-N.By fluorescence spectroscopy and mass spectrometry analysis,different degradation pathways are proposed,which were different from aerobic degradation.By comparing and analyzing the aerobic degradation and anoxic degradation process of TZ by NJUST42,the degradation rate of the same substrate concentration under aerobic condition was higher.TZ could be completely degraded under this condition,and the substrate concentration range was wider.In addition to the higher removal rate of TZ,the removal rate of TOC was also significantly higher than the removal rate of anoxic condition,which might be related to its degradation mechanism.The degradation products under the two experimental conditions were partially identical,but most of them were different,which lead to different degradation pathways.Under aerobic conditions,three degradation pathways were produced,and two degradation pathways were produced under anoxic condition.However,due to the low degree of mineralization and the presence of fluorescence peaks in the fluorescence spectrum under anoxic conditions,it indicated that TZ has not only undergone degradation but also transformation.In a certain concentration of anoxic degradation process,not only the TZ could be removed,but also the NO₃-N in the solution could be converted into N₂-N to reduce the pollution at the same time.