Anaerobic biodegradation of phenol in structured-bed reactors under methanogenic and sulfate-reducing conditions: performance assessment and microbial community analysis

Phenol biodegradation was investigated in anaerobic fixed-structured bed reactors, namely, R1 and R2, treating synthetic wastewaters simulating the soluble fraction of sugarcane vinasse. Exclusively methanogenic conditions were applied in R1, whilst combined methanogenic and sulfate-reducing conditions were established in R2. Next-generation sequencing was used to further characterize the microbial communities in both systems. Phenol was completely and stably degraded in R1 after a short biomass acclimation period (˜55 days). Conversely, phenol removal in R2 required a longer period (˜125 days) to reach levels equivalent to R1. VFA accumulation in R2, most likely due to the inhibition of the aceticlastic biomass by sulfide, may have limited phenol removal in the initial operating phases, as intermediate steps from phenol degradation are thermodynamically dependent on the removal of acetate, hydrogen and bicarbonate. Overall, the results indicated the potential for anaerobically removing phenol from complex wastewaters, even at low phenol/COD ratios, which could kinetically limit the process. 16S rRNA gene sequencing analysis showed a low correlation of taxonomic profile between R2 and inoculum, whereas, a higher correlation was observed from R1 and the inoculum samples. Functional inference further indicated that, possibly, Methanospirillum, Desulfonauticus, Syntrophus, Bacillus, and, Clostridium genus played a key-role in phenol degradation.