Sequential Reduction And Oxidation Of Tetrabromobisphenol A (TBBPA) In A Three-dimensional Biofilm Electrode Reactor

Tetrabromobisphenol A（TBBPA）in water is a new persistent organic pollutant,which has the characteristics of persistence,bioaccumulation and biological toxicity,threatening the public health.Traditional biological technologies exhibite poor performances in TBBPA degradation for the accumulation of toxic intermediate products,incomplete degradation of TBBPA and a very long degradation cycle.Three-dimensional biofilm electrode reactor（3D-BER）is a novel bioelectrochemical wastewater treatment technology.The particle electrodes such as granular activated carbon and zeolite are filled in 3D-BER,that become amounts of micro-electrolytic cells by applying an electric field.These particles also act as suitable carriers for microbial growth,thereby accelerating the degradation process of the pollutants.3D-BER integrates the advantages of electrochemical and biological technologies,exhibiting promising potentials in remediation of refractory organic pollutants.In this work,we developed a continuous-flow 3D-BER filled with granular activated carbon as particle electrodes to degrade simulate TBBPA wastewater by a sequential reduction-oxidation.The influence of hydraulic retention time（HRT）on TBBPA degradation was explored.The biofilm on the particle electrodes was characterized.The degradation intermediates of TBBPA in the 3D-BER was analyzed to investigate the possible degradation mechanisms.The main results of are as follows:1.The sequential reduction-oxidation of TBBPA was realized in the 3D-BER,and the applied current promoted the reduction of bromine in TBBPA.Compared to the bioreactor（3D-BR）without current application,3D-BER showed a better performance in debromination at different HRTs.The debromination rate of 3D-BER was 5%¹0% higher than that of 3D-BR.The degradation of TBBPA in 3D-BER was significantly improved by increasing the HRT value.When HRT was extended from 4 h to 48 h,the TBBPA concentration in 3D-BER effluents decreased from 1.35².88 mg/L to 0.38⁰.87 mg/L,and the debromination rate increased from 17.70²2.70% to 78.27% 87.40%.The concentration of total organic carbon in 3D-BER effluents also decreased from 6.25⁷.89 mg/L to 3.06³.21 mg/L.2.Sponge iron was beneficial to the reduction of TBBPA.Under the operation condition of HRT 4 h,the concentration of bromine ion in Fe-3D-BER（3D-BER filled with sponge iorn）effluent was 0.48¹.05 mg/L higher than that of 3D-BER.However,TBBPA removal efficiency decreased significantly for Fe-3D-BER.The average concentration of TBBPA in the effluent of the anaerobic zone was 6.35⁶.97 mg/L higher than that of 3D-BER,and the effluent of the aerobic zone was 2.70 2.89 mg/L higher than that of 3D-BER.Sponge iron originated oxides and hydroxides deposited on the surface of the particle electrodes,hindering the removal of TBBPA.3.The electric current stimulated the growth of microorganisms in the bioreactor and secreted more extracellular polymer substance（EPS）,that promoted attachment of biofilm onto the particle electrodes.The amount of the microorganisms in 3D-BER significantly increased by applying electric current,which was 2.79².85^*10⁶/g higher than that in 3D-BR.In addition,the current also influenced the communities of the microorganisms and the relative abundance of each colony in the reactor.In 3D-BER,Proteobacteria was the dominant phylum,enriching the bacteria such as Cupriavidus,Sphingomonas,Desulfuromonas and Pseudomonas that were related to the degradation of TBBPA.4.In 3D-BER,the primary degradation intermediates of TBBPA were aromatic hydrocarbons containing benzene ring structures.The other intermediates were straight chain alkanes containing hydroxyl groups and ester groups.Two possible degradation pathways of TBBPA in 3D-BER were proposed: one is that TBBPA was debrominated by dehalogenated bacteria in the anaerobic zone of 3D-BER,and the generated BPA intermediates were decomposed into monocyclic organic compounds in the aerobic zone.Then,the benzene ring was opened through oxidation reaction to form straight-chain hydrocarbon,following with finally mineralization into CO₂ and H₂O;the other is that electrochemical oxidation ruptured the C-C bond in the middle of TBBPA into two bromophenols,and then debromination,benzene ring opening and mineralization occurred.