Electric field coupled with Fe3O4 modified biochar to enhance anaerobic degradation of phenolic compounds in coal gasification wastewater (CGW)

Abstract

Anaerobic treatment of coal gasification wastewater is usually limited by the inhibition of high concentration of phenolics. In this study, the Fe3O4 loaded biochar (FeBC) coupled with electric field (E-FB) was used to enhance anaerobic phenolics degradation. E-FB significantly accelerated anaerobic removal of phenol, p-cresol and 3,5-xylenol with methane production improved by 84.2 % compared to the control, where FeBC contributed most. E-FB improved anodic oxidation capacity, adsorption-biodegradation and Fe (III) reduction process, which resulted from the synergistic effects between electric field and FeBC. E-FB significantly enhanced the microbial activity and extracellular electron transfer (EET) in the suspended sludge with the maximum electron transfer system activity (132.9 %), cytochrome C (7.2 nmol/g MLSS) and adenosine triphosphate contents (87.8 nmol/ g MLSS) obtained. Compared with FB, E-FB stimulated the secretion of proteins and humic acid-like substances in extracellular polymeric substance, which could contribute to higher EET efficiency. More abundant phenol degrading bacteria, dissimilatory iron reducing bacteria, electroactive bacteria and potential direct interspecies electron transfer (DIET) partners (e.g., Geobacter and Methanobacterium) were enriched in E-FB especially on the anode. The benzoyl-CoA pathway on the anode and CO2-reduction methanogenesis (possibly via DIET) in the suspended sludge and anode were improved in E-FB.