Biosorption And Biodegradation Mechanisms Of Polychlorinated Biphenyls (PCBs) By Ensifer Adhaerens

Due to the good flame retardancy,thermal stability,chemical inertness and high resistivity,polychlorinated biphenyls(PCBs)have been mass-produced and widely used in industrial production.PCBs are one of the twelve priority controlled persisted organic pollutants,because of the characteristics,such as persistence,toxicity,carcinogenicity,and bioaccumulation.PCBs in the environment were affected by various factors,transporting in different media and finally tended to reach a balance.Water pollution of PCBs has significant impact on human production and life.This study researched on the ability of the Ensifer adhaerens to remove 2,4,4’-trichlorobiphenyl(2,4,4’-TCB,PCB28)from water in different tested periods,also the optimum experiment was set up.The mechanism of bacteria on the removal of 2,4,4’-TCB was investigated.The changes of the ratios between the biosorption and biodegradation under different conditions were studied,including different inbubation time,and different PCBs congerners.The results showed as blow:1.The alive and dead bacteria were capable to remove 2,4,4’-TCB and the dead biomass had better effects on the 2,4,4’-TCB dissipation.The removal rate reached a plateau in 2hr.The test conditions,such as temperature,optical density and metal ions,could affect the removal rates.2.Both biosorption and biodegradation contributed to the removal of 2,4,4,-TCB by liveE.Adhaerens in water,while biosorption dominated in 24hr.Biosorption was the only contribution to the removal of TCB by dead bacteria biomass and adsorption percentage of dead bacteria was obviously higher that of live bacteria.The removal efficiency reached a plateau after 2h incubation.The highest adsorption rate of live strain was occuring at pH of 6.0,temperature of 35℃,OD of 0.8,cell pretreated with 1mol/L metal ion.The optimal degradation efficient of live strain was under the condition of 7.5pH,30℃and biomass pretreated with 0.05mol/L metal ion.3.In a 16-d incubation,biosorption was dominated in the early period,while biodegradation gradually increased with the incubation time.Biodegradation played an important role.Polysaccharides,proteins,lipids were all involved in adsorption of 2,4,4’-TCB.With the increase of incubation time,the content of soluble polysaccharides increased while the content of insoluble polysaccharides and proteins decreased.Antioxidant enzymes of bacterias played an important role in biodegradation.Superoxide dismutase(SOD)and peroxidase(POD)activities increased with time and the highest value were up to 575.21 U/g,1052.63 U/(g·min),respectively.The polyphenol oxidase(PPO)activity increased to 2631.58 U/(g·min)and then kept consistent.2-(p-indophenols)-3-(p-nitrophenyl)-5-phenyl-tetrazoliumChloride(INT)activity was increased and then slightly reduced.4.The results showed that the degree of chlorination of PCBs had a significant impact on the ability of Ensifer adhaerens on removing them from the aqueous environment.With the higher number of chlorine substitution,the pollutant was sopposed to be more difficult to be degraded,while the absorption rate increased.