Studies On The Characteristics Of Aerobic Biodegradation Of Tetrabromobisphenol A By Irpex Lacteus F17

Tetrabromobisphenol A(TBBPA)is widely used in the printed circuit boards of electronic products as the most widely used brominated flame retardants,and has become a typical pollutant in electronic waste dismantling area as the rapid upgrading of electronic products and the increasing of e-waste.TBBPA exhibits the characteristics of persistent organic pollutants in the environment,which bring harm to the ecological environment and human health.Microbial degradation is an effective way to remove organic pollutants from environment,and white rot fungi showed a broad application prospect in bioremediation of organic pollutants due to its broad-spectrum degradation ability and unique ligninolytic enzymes system.However,at present,the researches on biodegradation of TBBPA mainly focus on bacteria,little work has been down on the biodegradation of TBBPA by white rot fungi.Therefore,in present study,Irpex lacteus F17,a new model strain of white rot fungi,was chosen as the experimental strain to investigate its characteristics of aerobic biodegradation of TBBPA,and preliminarily discussed the biodegradation pathway of TBBPA by I.lacteus F17.The results presented as follows:The biodegradation of TBBPA was affected by the growth conditions of I.lacteus F17.Firstly,single factor experiments were carried out to determine the optimal conditions for I.lacteus F17 growth,and the results were as follows:initial p H 5.0,shaking speed of 160 r/min,and temperature of 30?.Secondly,the effects of co-metabolism substrates on TBBPA biodegradation were investigated by adding different concentrations of phenol,glucose,sodium pyruvate,sodium citrate and yeast into degradation systems,respectively.And the results showed that the addition of proper concentration of phenol,glucose,sodium pyruvate and sodium citrate could promote the degradation efficiency of TBBPA,and the most significant effect could be achieved when glucose was used as the co-metabolism substrate,and the highest degradation efficiency of 76.0%was obtained with 8 g/L of glucose in degradation system.The experimental results showed that I.lacteus F17 could degrade TBBPA to some extent,however,the addition of appropriate co-metabolism substrates could significantly improve the biodegradation efficiency of TBBPA.On the basis of glucose as the optimal co-metabolism substrate,single factor experiments were carried out to investigate the effect of the initial p H value,inoculum volume,and the initial concentration of TBBPA on the biodegradation of TBBPA by I.lacteus F17.It was concluded that I.lacteus F17 could effectively degrade TBBPA in a wide p H range(4?8),and the optimal conditions were as follows:8 g/L of glucose,p H 5.0,inoculum volume of 5%,TBBPA concentration of 5 mg/L.Under the optimal degradation conditions,78.4%of TBBPA was degraded after 12 days.In addition,the presence of Mn²⁺(10-80?mol/L)could significantly increase the degradation efficiency of TBBPA.When Mn²⁺was in low concentration range(10-50?mol/L),the degradation rate of TBBPA increased with the increase of Mn²⁺concentration and the highest degradation efficiency of 77.9%was achieved with 50?mol/L Mn²⁺.However,higher concentration of Mn²⁺(80?mol/L)could inhibit the growth of I.lacteus F17 and the secretion of degrading enzymes,which resulted in the decrease of degradation efficiency of TBBPA.The optimal concentration of Mn²⁺in degradation system was 50?mol/L.Further experiments were conducted to investigate the relationship between Mn P activity and the degradation efficiency of TBBPA,and it was found that Mn P activity would affect the biodegradation efficiency of TBBPA.Seven intermediate products were detected by GC-MS,including 1-(3-bromo-4-hydroxyphenyl)ethanone,4-hydroxybenzoic acid,bisphenol A,2,5-dihydroxyacetophenone,2,5-dihydroxybenzoic acid,2,4-dihydroxyacetophenone,and 2,4-dihydroxybenzoic acid.By analyzing the structure of the products,two degradation pathways of TBBPA by I.lacteus F17were proposed.First route,TBBPA was debrominated,?-scission,hydroxylation,deprotonation or oxidation to form 1-(3-bromo-4-hydroxyphenyl)ethanone and 4-hydroxybenzoic acid.For another route,TBBPA was debrominated completely to generate BPA,then the bond between two benzene was broken to form 2,5-dihydroxyacetophenone and 2,4-dihydroxyacetophenone,and 2,5-dihydroxyacetophenone and 2,4-dihydroxyacetophenone can further reacts to form 2,5-dihydroxybenzoic acid and 2,4-dihydroxybenzoic acid,which could effectively avoid the accumulation of BPA.