Fe-loaded biochar facilitates simultaneous bisphenol A biodegradation and efficient nitrate reduction: Physicochemical properties and biological mechanism

The simultaneous removal of nitrate and bisphenol A (BPA), two highly concerning contaminants in fluvial systems, is limited due to the low activity of the denitrifying community and poor degradability of BPA. Iron-loaded biochars (FeBCs) are efficient in promoting electron transfer efficiency and accelerating redox active processes, e.g., nitrate reduction and pollutant degradation. Nevertheless, the physicochemical properties of FeBCs and their potential strengthening mechanism during simultaneous removal of nitrate and BPA from aquatic systems are largely unknown. This study explored the potential of FeBCs to accelerate the simultaneous removal of nitrate and BPA. The FeBCs were prepared at 300–700 °C, with a BET surface area that increased from 10.78 to 207.97 m2 g−1 and oxygen content that decreased from 12.16% to 3.89%. Maximum nitrate and BPA removal of 99.0% and 74.1%, respectively, was achieved when the biochar was pyrolyzed at 500 °C (FeBC5). FeBC5 increased the levels of nicotinamide adenine dinucleotide (NADH), 5′-adenylate triphosphate (ATP), and electron transport system activity (ETSA) of the microbes, which were 485.50%, 371.88%, and 68.85% higher than the control values. After adding 0.05 g L−1 FeBC, the denitrifying enzyme activity and the level of nitrate-reducing genes increased by 48.22% and 45.6% respectively, and the genera responsible for denitrification and BPA degradation were increased by 5.56% and 33.33%, respectively. The BPA degradation pathway analysis suggested that the enhanced biotransformation of BPA resulted from co-metabolic degradation by denitrifying bacteria. The ferric-containing functional groups and their types were significantly correlated with nitrate-reducing enzymes and metabolic activities, facilitating the simultaneous removal of nitrate and BPA.