Mechanism Of Pyridine Degradation And Denitrification In Co-metabolic Reactors And Microbial Community Analysis

Pyridine,a representative nitrogen-containing heterocyclic organic compound,is a kind of toxic and refractory pollutant.The aerobic co-metabolism is an effective technology for degradation of toxic and refractory organic compounds and has the advantages of high degradation efficiency and stable operation.In this study,aerobic co-metabolism was used to degrade pyridine,and the degradation performance and sludge performance in reactors were investigated with different co-metabolic substrates.Besides,the nitrogen removal performance in the reactor was also explored.Furthermore,the reaction mechanism was proposed by batch experiments,microbial biomass and acticities.HPLC-MS was used to deterimined the intermediates of pyridine in the systems and analyzed the possible degradation pathways.Furthermore,the high-throughput sequencing was carried out to exhibit the effect of co-metabolic substrates on the shifts of microbial communities and founction genes and provide more evidences for reaction mechanism.Three sequential batch reactors were established.P was the blank control reactor,PG with glucose and PP with phenol were cometabolic reactors.The pyridine concentration in influent increased from 200 mg/L to 400 mg/L during the operation of the reactor.The concentration of pyridine and TOC in the effluent of three reactors were all below 10 mg/L,the total nitrogen(TN)concentration in the effluent of P,PG and PP were about 53 mg/L,1 mg/L and 35 mg/L,respectively.Above results indicated all three reactors had good abilities for pyridine degradation.Basides,the addition of co-metabolic substances enhanced the nitrogen removal capabilities of reactors.In addition,the sludge concentrations(MLSS)in the three reactors increased from about 3000 mg/L to 4685 mg/L,6324 mg/L,and 5102 mg/L respectively within 36 days.Among the reactors,PG had highest SVI value of 132.8 m L/g,which might be due to the high concentration of EPS(51 mg/g MLVSS).The removal mechanism of pyridine and nitrogen in three reactors were investigated using batch experiments.The results exhibited that P reactor had pyridine degradation and nitrification,meantime,hao no denitrification.However,the microorganisms used phenol as the carbon source for denitrification in PP reactor.Besides,the bacterial in PG used pyridine as nitrogen source to proliferate,and thereby denitrify efficiently.9 intermediates were detected by HPLC-MS detecting.Based on this,three metabolic pathways(A,B and C)were further inferred.Pyridine in A and B were first hydroxylated and followed with ring opening.It in C was first hydrogenated and then reduced.According to the detected intermediate products,it was speculated that P might have three degradation pathways,indicating P reactor might had varied functional degraders.Degradation pathway B which was the fastest ring-opening pathway of pyridine might contribute to the rapid proliferation of bacteria in PG.PP might have both B and C,revealing that the microorganism which could degrade phenol and pyridine simultaneously might enrich in PP reactor.High-throughput sequencing provided more microbial information for the mechanism of pyridine degradation and denitrification in three reactors.The microbial communities of four sludge samples(the seeded sludge S,the sludge RP,RPG and RPP in P,PG and PP reactors)were investigated.The results exhibited that different cometabolic substrates could greatly change the microbial communities and founction genes.Paracoccus(13.68%),Thauera(6.78%)and Chryseolinea(6.61%)enriched in RP and contributed to the degradation of pyridine through various degradation pathways and nitrification in P reactor.Paracoccus(10.69%)and Saccharibacteria(15.54%)in RPG provided the abilities of pyridine degradation and rapid bacteria proliferation in PG reactor,thereby pyridine was degraded through pathway B,and then nitrogen was efficient removed through bacteria proliferation.Besides,Thauera(30.77%)which accounted for high proportion in RPP provided great capacities of efficient denitrification and degradation of pyridine and phenol in PP reactor.Functional gene prediction based on KEGG fourther confirmed the reaction mechanism.In this study,the mechanism of pyridine degradation and denitrification in the cometabolic reactors with glucose and phenol were investigated in detail.The reaction mechanism was further confirmed by HPLC-MS and high-throughput sequencing,which provided a certain theoretical basis and technical support for the biodegradation of pyridine wastewater.