Enhanced 1h-1,2,4-triazole Degradation During Tertiary Wastewater Treatment:Role Of Nitrifiers

In this paper,the enhanced 1H-1,2,4-triazole biodegradation through nitrifying activated sludge(NAS)co-metabolism was studied,exploring the optimal operation conditions and the mechanism by analyzing main metabolites,which is of great significance for the comprehensive understanding of the ammonia oxidizing bacteria and the development of new tertiary wastewater treatment.Several sets of batch tests were conducted to explore the biodegradation conditions,the assays suggested that optimal pH,substrate concentration and initial 1H-1,2,4-triazole were 7.0,50mg/L and 50mg/L respectively.The controlled trials demonstrated that the the enhanced biodegradation potential of nitrifying activated sludge towards 1H-1,2,4-triazole,this enhanced biodegradation seems to be related to the activity of ammonia oxidizing bacteria which could co-metabolize these compounds using one of its key enzymes,ammonia monooxygenase(AMO),responsible for ammonia oxidation.Long term experiments by continuous aerobic biological fluidized bed reactor were also conducted to verify the enhanced pollutants biodegradation through NAS,the reactor performance and microbial composition were monitored with conventional parameters and molecular techniques such as 16S rRNA gene cloning and sequencing,denaturant gradient gel electrophoresis(DGGE),quantitative PCR(qPCR)and high-throughput analysis et al.The results suggested 1 H-1,2,4-triazole inhibited the nitrification activity,nitrifying rate approached to 0 after 10th day of continuous influent and gradually recovered at the end of acclimation period,dominant bacteria phylas included Proteobacteria、Fircumates、Acidobacteria、Bacteroidetes、Plantctomycetes、Chloroflexi and Nitrospirae.1H-1,2,4-triazole led to quantity differences of bacterial.Besides,the diversity of microbial communities decreased and the difference increased at OUT level.After 30th day,nitrification activity gradually came back to the initial level,this may be a consequence of selection for bacteria utilizing or resistant to SMX during the dosing period.The composition and changes of fluorescent substances were analyzed via EEM during the acclimation period,the results showed that aromatic proteins was an important part of the composition,the peak of 1H-1,2,4-triazole located near λex/λem=220/290nm,belonging to the aromatic proteinl.Accompanied by biodegradation of pollutants,the fluorescence intensity decreased from 436.771 to 70.22,a new fluorescence peak which belonged to aromatic protein Ⅱ appeared,it was speculated as the intermediate products of 1H-1,2,4-tri azole.The main metabolites were analyzed by GC-MS and LC-MS,biodegradation pathway of 1H-1,2,4-triazole by NAS was proposed:with the continuing attack of OH,3-and 5-formed C=O,the probability of ring-opening reaction occurred,eventually carbazic acid,formaldehyde and alcohols were generated.