Effect of black carbon on the migration and biodegradation of pentabromodiphenyl ether (BDE-99) during natural groundwater recharge with treated municipal wastewater

• The attenuation effect of BDE-99 was in the order of BCA > SC which followed a first-order kinetic.
• The residual BDE-99 in different depths of BCA column were much higher than in SC column.
• Three major genera Halomonas, Pseudomonas and Shewanella were considered to be PBDE degradation-associated bacteria.
• The higher bacterial diversity and adsorption capacity in BCA system were able to mitigate the migration of BDE-99.

When using treated municipal wastewater for recharging river-based natural groundwater, pentabromodiphenyl ether (BDE-99) pollution might be a potential threat to underground aquifers. Due to their strong affinity for black carbon (BC), the migration and bioavailability of PBDEs may be decreased in aquifer media with a high BC content. To properly examine the effect of black carbon on the migration and biodegradation of BDE-99, a lab-scale column was set up to simulate the recharge process. The filler media of the two columns mainly comprised silty clay (SC) and black carbon amendment silty clay (BCA). The results showed that the attenuation effect of BDE-99 was in the order of BCA > SC. The attenuation rate constants of BED-99 in the SC and BCA systems were 0.12 and 0.18 m−1, respectively, which followed first-order kinetics. The two turning points of the BDE-99 percentage with depth in the leachate were 0.15 m and 0.45 m due to fast sorption and biodegradation, respectively. The primary debrominated metabolites were not the only lower brominated ether congeners; high-brominated diphenyl ethers and isomers of BDE-99 were also produced during the biotransformation process. The accumulation of BDE-99 and PBDEs in the soil was higher in BCA soils than in the SC system. The bacterial community in the upper layer was more diverse than in the bottom layer. Five known bacterial classes (Gammaproteobacteria, Alphaproteobacteria, Betaproteobacteria, Acidobacteria and Clostridia) and seventeen known bacterial genera (three major genera: Halomonas, Pseudomonas and Shewanella) were considered to be PBDE-degradation-associated bacteria. The bacterial community diversity and percentage of PBDE-degradation-associated bacteria in the BCA system were marginally greater than those in the SC system. The higher bacterial diversity and adsorption capacity in the BCA system were able mitigate the migration of BDE-99 into groundwater.