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

Abstract

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.