The inhibition of anammox system under Cu2 + stress and mechanisms of biochar-mediated recovery.

Copper (Cu2+)-containing wastewater has proven difficult to effectively treat using the anammox process. In this study, the nitrogen removal efficiency (NRE), sludge characteristics, microbial community and recovery mechanisms of biochar-mediated anammox under Cu2+ stress were elucidated. At a Cu2+stress of 5 mg/L, a 73.52 % decrease in NRE (from 99 % to 25.48 %) was observed within the control setup (no biochar). The highest average NH4+-N removal for 36.28 % was observed at a reduced Cu2+ concentration of 3 mg/L with biochar addition compared to only 16.63 % in control reactor. The differences in the protein/polysaccharide (PN/PS) content in sludge from different biochar systems under long-term Cu2+ stress was a key factor influencing overall nitrogen removal performance, with the sludge predominantly displaying tightly bound extracellular polymeric substances (TB-EPS). The relative abundance of Candidatus Brocadia increased from 2.61 % to 15.28 % in the nitric acid-modified bamboo biochar group following cessation Cu2+ addition, while the control group only recovered to 0.76 %. The Cu2+ inhibition alleviation effect of biochar, facilitated via enhanced EPS secretion and selective proliferation of key functional microorganisms, has thus been demonstrated.