Degradation and mineralization of 2-chlorophenol in a single-stage anaerobic fixed-bed bioreactor

Chlorophenols（CPs） have drawn great attention due to their high toxicity and ubiquitous presence in the environment. However,the practical application of anaerobic biodegradation to remove CPs is limited by low degradation rate and incomplete mineralization. This work aims to apply a single-stage anaerobic fixed-bed bioreactor（An FBR） for complete anaerobic dechlorination and mineralization of CPs. Results showed that 2-CP removal efficiency of 99.4%, chemical oxygen demand（COD）removal efficiency of 93.0%, and methane yield of 0.22 L-CH4/g-COD could be obtained for a wide range of 2-CP loading rates（3.6–18.2 mmol L–1 d–1）. Nearly complete anaerobic mineralization of 2-CP was achieved even in the absence of co-substrates,thereby greatly reducing the operation cost. This may be partly related to the attached-growth microorganisms in An FBR,allowing a higher biomass concentration and longer biomass retention time for enhanced 2-CP removal. Moreover, 16 S r RNA gene sequence analysis suggests that the An FBR harbored the potential dechlorinators（e.g., Anaeromyxobacter）, phenoldegrading microbes（e.g., Comamonas and Syntrophobacter）, and methanogens（e.g., Methanobacterium and Methanosaeta）after acclimation, which could cooperate effectively for 2-CP dechlorination and mineralization. Based on the identified intermediates, the possible mineralization pathway of 2-CP was proposed. These findings should be valuable to facilitate the engineering applications of An FBRs for removing CPs from wastewater.