Enhanced Microbial Degradation And The Related Mechanisms Of Tetrabromobisphenol A With Nanoscale Pd/Fe Bimetal

Tetrabromobisphenol A?TBBPA?,a flame retardants,which is one of the broadly applied and most effectively in the world,however,the seriousness of its environmental pollution and the severity of threats to human health are increasingly prominent due to its lipophilicity,low volatility,low solubility,hard-degradation,bio-enrichment and persistence,thus,seeking a cost-effective measure to control the pollution is extremely imminent.Owing to TBBPA is mainly accumulated in the deep water bodies,soil,water/sediments and bottom mud in the environment.Therefore,it's urgent to search an efficient,sustainable and ecologically feasible degradation technology for in-situ biological enhanced decomposition of water/sediments.In this study,the microbiological implantation of nano-palladium/iron bimetallic particles was used to investigate the enhanced biodegradation efficiency and mechanism of TBBPA in water.Determing the influences of each factor,such as temperature,pH value,Pd loading rate,Fe dosage,etc.,to the debromination efficiency,decomposition pathway and reaction kinetics of TBBPA via optimize the various factors in the reductive decomposition system.combining with the 16S rRNA high-throughput sequencing to analyze the changes of microbial community structure before and after implantation of nano-Pd/Fe bimetallic particles,and investigating the related molecular mechanisms of nano-Pd/Fe bio-enhanced reductive decomposition of TBBPA in water.The experimental results show that under the conditions of 30°C and pH 7.2,the debromination period of TBBPA(initial concentration:20?molL^-1)for anaerobic microbial enrichment solution was 29 days,The pseudo firstorder rate constant?k?is 5.21×10^-1 d^-1,half-lives(t_1/2)is 1.33 d,and the final product is bisphenol A.and the complete debromination time of TBBPA is shortened to 10days after the nano-palladium/iron bimetal is added,the k of TBBPA is 6.72×10^-1 d^-1,and t_1/2 of 1.03 d.Compared with the pure anaerobic microbial reduction system,the debromination cycle is shortened by nearly 2/3,and the final product-bisphenol A,can be further hydrodegraded.By optimizing the amount of nano-palladium/iron bimetallic particles,it was found that when the palladium/iron dosage was controlled at 1.12 g L^-1 and the palladium loading rate was 0.5 wt%,the k of TBBPA raised to1.16 d^-1,t_1/2 for 0.59 d and TBBPA completely debrominated in only 6 days.Adding too much amount will produce microbial toxicity will inhibit the microbial degradation of TBBPA,and the excessive low amount of palladium/iron leads the insufficient hydrogen production,which is not enough for the reduction debrominated microorganisms to utilize.16S rRNA high-throughput sequencing revealed that there are several types of reducing debromination functional bacteria in the microbially enriched bacterial fluid,such as Pseudomonas,Geobacter,ect.the abundance of some bacterial genus has changed after the long-term addition of nano-palladium/iron bimetallic into the composite system,for example,the relative abundance of Pseudomonas decreased from 4.83%to 2.63%,and the relative abundance of Geobacter decreased from0.67%to 0,while the relative abundance of Acinetobacter,which might be involved in the debromination of TBBPA,decreased from 7.11%to 3.56%,and the relative abundance of Citrobacter decreased from 12.64%to 6.24%.The proportion of degrading genus which can degrade TBBPA that has been found or proven is reduced.It may be the toxic causes of repeated addition of high concentrations of TBBPA poisons into the bacteria,but the degrading bacteria which is capable of degrading TBBPA still exist,suggesting that the addition of nano-Pd/Fe bimetallic particles to the sediment can supply TBBPA degrading bacteria for electron donor H₂ and suitable growth conditions,so that it can survive under the poisoning effect of high concentration of TBBPA.Combined with comparative experiments,it is presumed that the further degradation of bisphenol A in nano-palladium-iron bimetallic-microorganism composite system is due to further hydrogenation reduction of nano-palladium iron.The addition of nano-Pd/Fe bimetallic particles can not only participate in the direct reduction debromination of TBBPA,But also its Hydrolyzed H₂ products can provide additional electrons for the reductive debromination of microorganisms in the enrichment system.Thus,it can effectively activate the metabolic activity of halogenated respiratory microbes and further promote the degradation of tetrabromobisphenol A,The above studies provide tetrabromobisphenol A and other emerging refractory organic pollutants with theoretical and technical basis in terms of enhanced bioremediation in deep-water bodies and sediments.