Biodegradation Of Pyridine Under UV Irradiation

Pyridine, a complex nitrogen-containing heterocyclic compounds, used in many areas, is usually difficult to degrade by means of single biological method. The effect of UV irradiation on pyridine degrading bacterial was researched. Then the internal loop photobiodegradation reactor (ILPBR) was used for degradation of pyridine following three protocols:photolysis alone (P), biodegradation alone (B), and intimately coupled photolysis and biodegradation (P&B) to investigate the regularity of pyridine degradation, the pyridine degradation kinetic and the regularity of NH4+-N generation, in order to prove the high-efficiency of intimately coupled photolysis and biodegradation (P&B). The community analysis was adopted to find out the change of biofilm under UV irradiation and discuss microbiology mechanism in process of P&B.The pyridine degrading bacterial was enriched from the pyridine-acclimated activated sludge. Without other source of carbon and nitrogen, the pure culture bacteria (OD600of0.1) caused complete degradation of416.3mg/L of pyridine in15h at35℃and pH of6.5, giving a degradation rate constant of27.75mg/L/h. Pyridine (concentration of50,100,300,500,800,1000,1500mg/L) was respectively degraded following two protocols:biodegradation alone and photolysis and biodegradation to discuss the effect of UV irradiation on pyridine degrading bacterial. The experimental results indicated that the pyridine of which concentration is more than500mg/L caused inhibition to biofilm(OD600of0.113) at35℃and pH of6.5, however, the inhibition of pyridine to biofilm could be relieved due to UV irradiation and the time of UV irradiation longer, the inhibition of pyridine to biofilm weaker.500mg/L of pyridine was degraded completely in process of9h photolysis and biodegradation at OD600of0.1,35℃and pH of6.5, giving a degradation rate constant of41.67mg/L/h.Pyridine was degraded following three protocols:photolysis alone (P), biodegradation alone (B), and intimately coupled photolysis and biodegradation (P&B) to investigate the regularity of pyridine degradation. The experimental results indicated that pyridine removal rate by P&B was fastest among three protocols inbatch experiment, in which protocol B was faster than P. For initial pyridineconcentration of500mg/L, the pyridine removal rates in batch were respectively8.28、20.49and27.32mg/L/h corresponding to protocol P, B and P&B. Protocols P, Band P&B were also used for pyridine degradation in continuous flow and influentpyridine concentration increased from50to300mg/L, and their average removalrates were respectively15.8mg/L/h for protocol P,23.1mg/L/h for protocol B and24.9mg/L/h for protocol P&B, in which the removal rates were higher than that inbatch. Two sequential protocols P2+B3and P3+B2were used for pyridinedegradation in bath compared with P&B, and the pyridine degradation rate withP&B6obviously was faster than that by P2+B4and P3+B3, and, at the end of the6-hour,100mg/L pyridine removal by P&B6was100%, whereas the pyridineremoval was respectively35.6%by P2+B3and47.5%by P3+B2. Among threeprotocols P, B and P&B in batch experiment, as pyridine was completely degraded,the NH4+-N generated in P&B was most, in which protocol P was more than B. Forinitial pyridine concentration of100mg/L, the concentration of NH4+-N generated inbatch were respectively11.6、0.2and11.9mg/L/h corresponding to protocol P, B andP&B.Pyridine degradation kinetic equations corresponding to protocol B and P&B inbatch experiment were established based on Haldane model and Aiba model, and themaximum pyridine removal rates based on Haldane model and Aiba model are higherfor protocol P&B than protocol B. The inhibition constants based on Aiba modeldecreased from1660mg/L for protocol B to1600mg/L for protocol P&B,.Experiments suggested that the inhibition of pyridine to biofilm could be relieved dueto UV irradiation in process of intimately coupled UV photolysis and biodegradation,and biofilm had kept its bioactivity degrading pyridine and enhanced pyridineremoval rates.The DNA of the microorganisms, originating from acclimated activated sludgedegrading pyridine (sample A) and biofilm from the inside of the ceramic carriersafter the P&B (sample B), was extracted to compare16S rRNA sequences. The experimental results indicated that the bacteria composition of two samples wasdifferent. The bacterias doing work to pyridine degradation in sample A wereParacoccus denitrificans PD1222(16%) and Polaromonas sp. JS666(18%), whereasthe dominant strains in sample B were Acidovorax ebreus TPSY (10%), Cytophagahutchinsonii ATCC33406(10%), and Pseudomonas fluorescens SBW25(19%). Itsuggested that the dominant strains in activated sludge were sensitive to UVirradiation and although the bacteria composition of biofilm from the inside of theceramic carriers was changed under UV irradiation, the alive microorganisms stillkeep the ability to degrade pyridine.