Study On Degradation Of Bisphenol F By Pseudomonas Sp.ZH-FAD

A lot of bisphenols are used in industrial manufacturing,resulting in their wide distribution in the environment.As bisphenols are a class of endocrine disruptors,even at low doses they are harmful to human and animals.Thus,extensive attentions have been focused on these compounds by domestic and foreign scholars in recent years.Many studies have shown that bisphenols can be efficiently degraded under aerobic conditions.However,there is low removal efficiencies of bisphenols and no information is available on their degradation products under anaerobic conditions.Based on this,characteristics of bisphenol F(BPF)degradation by Pseudomonas sp.ZH-FAD and its degradation pathway were studied under aerobic and anaerobic conditions,respectively.These studies provides a theoretical basis for the biodegradation of bisphenol compounds.Under the aerobic conditions,strain ZH-FAD could realize the simultaneous removal of BPF and nitrate.The removal efficiencies of total organic carbon and nitrogen could reach100% and 96.19% at 35 oC with 150 rpm,respectively.According to GC and GC-MS analyses,the pathway of BPF degradation was proposed: BPF was firstly hydroxylated to bis(4-hytroxyphenyl)methanol,and dehydrated to 4,4’-dihydroxybenzophenone(DHBP),then oxidized to 4-hydroxyphenyl 4-hydroxybenzoate,which was hydrolyzed to 1,4-hydroquinone and 1,4-Hydroxybenzoate,followed by mineralization to CO2.Nitrogen balance analysis showed that 53.9% of NO3-N was converted to intracellular N,and 39.7% of NO3-N was converted to N2.During this process,less than 0.01 mg/L nitrite was accumulated,NO and N2 O were not detected.In addition,in the presence of additional carbon sources,strain ZH-FAD could efficiently degrade 1 mg/L BPF.Among these carbon sources,the addition of sodium citrate resulted in the maximum degradation rate of BPF.The enzyme inhibitors experiment showed that the addition of a cytochrome P450 inhibitor metyrapone resulted in the decreased degradation rate of BPF.This results showed that a cytochrome P450 system was involved in initial BPF degradation.Under anaerobic conditions,strain ZH-FAD can remove BPF when nitrate was used as an electron acceptor.When the initial inoculation amount was 0.071 g/L,the removal efficiency of BPF reached the highest.When the temperature was 25-35,pH 7.0,the nitrate concentration was 100 mg/L and BPF was used as the only electron donor,the removal rates of BPF and nitrate could reach maximum.Additional carbon source such as formate,acetate,pyruvate and glucose so on,inhibited BPF degradation.Under the optimal conditions,20mg/L BPF and 100 mg/L KNO3 could be completely removed in 36 h,the removal rates ofBPF and KNO3 was 0.80 mg/(L·h),and 4.16 mg/(L·h),respectively.Under anaerobic conditions,strain ZH-FAD could remove BPF up to 40 mg/L.GC-MS analysis showed that BPF was converted to bis(4-hytroxyphenyl)methanol,followed by DHBP,which could not be further degraded.Meanwhile,nitrate was reduced to nitrite and then nitrite was accumulated,which could not be further denitrified.Different from aerobic degradation of BPF,anaerobic transformation of BPF was not inhibited by metyrapone,indicating that anaerobic conversion process from BPF to DHBP was not related with cytochrome P450.The localization experiments of enzymes showed that anaerobic transformation enzymes of BPF are mainly located on the cell membrane.