Catalytic enhancement of microbial denitrification by FeVO4@biochar: Insight into the extra cellular polymeric matrix mechanism

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The biological denitrification is being considered as one of the best methods for nitrate removal from wastewaters, however it suffers with lower efficiency which needs to be improved effectively. The present study was aimed to prepare FeVO 4 @biochar and investigated its role as electron shuttle in enhancing the biological denitrification through various batch experiments. Significantly higher rates of denitrification were observed after addition of FeVO 4 @biochar in different concentrations and the highest efficiency was observed in 15 wt% FeVO 4 @biochar (BF-15) where 87.6 % denitrification was achieved after 7 days (from 100 mg/L to 12.7 mg/L of nitrate) compared to pure biochar (65.7 mg/L; 34.3 %) and sludge (72.7 mg/L; 27.3 %). FeVO 4 @biochar increased the transfer of external electron to bacteria and enhanced the denitrification activity. The variations in NAR (nitrate reductase), NIR (nitrite reductase) and ETSA (electron transport system activity) were investigated to understand the changes in microbial-community during denitrification. The FeVO 4 @biochar and extracellular polymeric substance (EPS) both acted as the media for electron transport along with the decreased repulsions between nitrate and the catalyst surface that further provides higher nitrate reduction efficiency. The electroactive bacteria could easily utilize the photogenerated electrons from FeVO 4 @biochar and facilitate excellent denitrification. The microbial-diversity analysis revealed Bacteroidota , Firmicutes , Proteobacteria , Chloroflexi , Desulfobacterota, Acidobacteriota, Actinobacteriota, and Gemmatimonadota were observed as the most predominant phyla actively participated in enhanced denitrification. This study suggested that the addition of photoactive catalyst strongly enhanced the electron transfer during denitrification and provides new ideas to the biological denitrification

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