UV Irradiation For Accelerating Pyridine And Quinoline Biodegradation

Pyridine and quinoline, as represent of nitrogen-containing heterocycliccompounds, and recalcitrant and toxic maters with carcinogenic and teratogeniceffects, were widely found existing in solids and water body. Pyridine and quinolineare two common nitrogen-containing heterocyclic compounds, and approaches fordegradation of them are increasingly paid to attention, as their harm to environments.For treatment of wastewater containing pyridine and quinoline, conventionalapproaches are usually physicochemical and biological methods, but they have acetrain limitation when they are used for treatment of them. So it is a good strategy tocouple UV irradiation with biodegradation.In order to transform and degrade pyridine and quinoline effectively, in this work,UV irradiation was coupled with biodegradation for the treatment of wastewatercontaining pyridine and quinoline. At the same time, pyridine UV photolysisintermediates were analyzed to explore the mechanism how intermediates acceleratepyridine biodegradation. Based on the research, an internal circulation baffled biofilmreactor was developed and used for biodegradation of pyridine and quinoline, duringwhich pyridine and quinoline were not only biodegraded effectively, but also thenitrogen was removed simultaneously, as its function of simultaneous nitrification anddenitrification. Experimental results were gotten:(1) Many intermediates form during UV photolysis, including hydroxylpyridine,succinic acid etc. and nitrogen releases in form of NH4+. Succinate, one of mainpyridine photolysis intermediates, generates intracellular electron carirer (H), whichreacted with molecular oxygen (O2) to accelerate initial pyridine mono-oxygenation reaction, and enhance pyridine biodegradation and mineralization.(2)Pyridine removal rate was faster after UV photolysis compared with originalpyridine without photolysis. The acceleration is due to succinic acid, acceleratedpyridine biodegradation by producing intracellular electron carrier (H) to drive initialmono-oxygenation reactions.(3)Pyridine removal rates fit fractional order kinetics, and its removal rateincreased with increasing of its initial concentration.(4)Both pyridine and quinoline show inhibition to microorganism, and Aibamodel was used for describing their kinetics based on microorganism growth. But theinhibition can be relieved at a certain degree by means of UV photolysis, and theirbiodegradations were obviously increased atfer UV photolysis.(5)Different UV photolysis times were investigated in order to get optimum time,which suggested that pyridine removal rate is faster and inhibition is smaller with2hours of UV photolysis.(6)When internal circulation baffled biofilm reactor (ICBBR) was used forpyridine biodegradation, three protocols, biodegradation alone (B), biodegradationafter photolysis (P+B)，and pyridine added succinate (B+S), were employedrespectively to investigate pyridine removal rates. Total nitrogen removal percentageswere respectively38%,44%and45%corresponding to protocols B+, PB and B+S forthe same10hours. For TN removal rates, initial pyridine concentration of300mg/Lwas illuminated with UV light for2hours before biodegradation, and its removal ratewas similar to protocol B+S with the same pyridine concentration, but their TNremoval rates were faster by16%than protocol B. Therefore, UV photolysis did notonly accelerate pyridine biodegradation, but also accelerate its TN removal rates.(7)ICBBR was also used for quinoline removal, and two protocols B and P+Bwere accepted for quinoline removals, in which UV photolysis was4hours aspretreatment. For8hours of biodegradation, protocol B and P+B gave COD removalpercentages of82%and89%, and TN38%and53%respectively, e.g. protocol P+B isby8%and39%higher than protocol B corresponding to COD and TN removalpercentages. Similar to pyridine, UV photolysis did not only accelerate quinoline biodegradation, but also accelerate its TN removal rates.(8) Simultaneous nitrification and denitrification was realized by means ofICBBR，which also integrated advanced oxygenation and biodegradation at one set.Therefore a novel technology can be used for organic wastewater treatment.