Understanding the anaerobic BTEX removal in continuous-flow bioreactors for ex situ bioremediation purposes

This work aimed to understand the anaerobic BTEX removal in continuous-flow bioreactors for ex situ bioremediation purposes, evaluating the effect of some operational parameters on efficiency, stability and microbial community structure. The influence of the hydraulic retention time, effluent recirculation and co-substrate (ethanol) concentration was investigated on a mesophilic UASB bioreactor operated under methanogenic conditions. The changes on the bacterial and archaeal communities were evaluated in terms of diversity, evenness and richness. Good BTEX removal (∼63%) and reactor stability could still be reached at a HRT of 24 h. The impact of the effluent recirculation on BTEX removal was not evident at high co-substrate (ethanol) concentrations, but it was significant when low concentrations were applied. The reduction of ethanol concentration had a positive impact on BTEX removal (from 80% to 86%), especially for benzene (from 51% to 62%). The optimal degree of evenness likely contributed to the relatively high stability of the system in terms of BTEX removal. Changes observed in bacterial and archaeal richness did not match with the functioning of the system. However, dynamics and evenness parameters seemed to be of importance in maintaining a stable reactor performance.