KOH-modified biochar enhances nitrogen metabolism of the chloroquine phosphate-disturbed anammox: physical binding, EPS modulation and versatile metabolic hierarchy

Chloroquine phosphate (CQ) poses strong biotoxicity on anammox process, and thus detoxifying is essential for the stable operation of anammox in treating CQ-bearing wastewater. Biochar has been proven to simultaneously detoxify pollutant and modulate nitrogen cycle in anammox by its shelter effect and electron exchange capacity (EEC) ability. To further improve the ability of biochar to promote the nitrogen metabolism of anammox, a KOH modification strategy was used to tailor a high-EEC biochar in this work. KOH modified biochar can bind CQ for detoxification driven by hydrogen bond, π–π interaction, and electrostatic interaction. Meanwhile, the EEC of modified biochar increased by 70% than that of pristine biochar, thus improving nitrogen removal efficiency by 55.6% and 9.5% than CQ and BC group, respectively. Besides, the microorganism regulated by modified biochar produced more α-helix configuration, improving EPS barrier ability to CQ and sludge granulation. Lastly, metagenomic analysis revealed that modified biochar can stimulate the Wood-Ljungdahl pathway, increased the relative abundance of CODH from 0.74% in CQ to 1.00% in modified BC group. It favored the proliferation of autotrophic microorganisms, especially increased the relative abundance of anammox bacteria by 86.8% than CQ group. This work will shed the light on integrating high-EEC biochar into anammox to cope with the micropollutants stress.