Degradation Of Typical Brominated Flame Retardants In Water With Dithionite Method

Brominated flame retardants are widely used and ubiquitous in the environment due to their excellent flame retardant ability and refractory biodegradation,which has brought about the certain environmental risks and hazards.Nowadays,the reduction method has been drawn more attention because of its effective dehalogenation and detoxification in the degradation of halogen-containing organic pollutants.Among of them,sodium dithionite?DTN?had great potential in degrading pollutants based on its high reduction.This study attempts to degrade two typical brominated flame retardants,namely tetrabromobisphenol A?TBBPA?and decabromodiphenyl ether?BDE209?,and explores the economical and convenient method coupled with DTN to achieve effective degradation of the brominated flame retardants.We have conducted the experiment to explore the degradation ability of two brominated flame retardants by sodium dithionite system and obtain the optimal reaction conditions.Additionally,the effect of typical coexisting substances on the degradation performance were investigated.The results have shown that TBBPA can be effectively degraded by sodium dithionite alone with the concentration of TBBPA and DTN,pH,temperature of 1?M,200?M,7 and 30°C,respectively.Under the optimal condition,we have detected the rate of TBBPA degradation,debromination and mineralization of 83.7%,76.4%,and 14.4%,respectively,and calculated the activation energy of 45.2 kJ/mol.However,it was noticeable that sodium dithionite could not degrade BDE209 effectively.In terms of BDE209 degradation,we applied iron coupled with DTN to enhance the reducing capacity to degrade two brominated flame retardants.In particular,we have optimized the reaction conditions and investigated the effect on the degradation performance by the typical coexisting matters.The results have demonstrated that Fe³⁺/DTN can effectively degrade TBBPA and BDE209.When the concentration of TBBPA,DTN and Fe³⁺were 1?M,100?M,and 25?M,respectively,with the pH and temperature of 7 and 30°C,the rate of TBBPA degradation,debromination and mineralization were 87.5%,83.9%,and 19.8%,respectively.In addition,we have calculated the activation energy of 20.4 kJ/mol.Similarly,we have achieved the rate of BDE209 degradation,debromination,and mineralization of 81.1%,6.6%,and 13.7%,respectively,with the concentration of BDE209,DTN and Fe³⁺of 1?M,200?M and 75?M,respectively,and the same condition of pH and temperature.Moreover,the activation energy of BDE209 degradation process is 43.3 kJ/mol.Based on GC-MS to analyze the possible intermediate,we have proposed the degradation pathways of TBBPA and BDE209 mainly including debromination,hydroxylation,methylation,and mineralization.Compared with DTN alone,there is also a carbon-carbon bond cleavage with the debromination during TBBPA degradation by DTN/Fe³⁺,and the final debromination rate and mineralization rate also have been further improved.Therefore,we speculated that there were several active substances producing in the two systems by decomposition,hydrolysis and reaction between Fe³⁺and DTN.In addition,we considered that the amount of oxidizing active groups in DTN/Fe³⁺system is larger than DTN alone based on the degradation performance.