Copper’s dual role in aerobic methane oxidation coupled with aerobic denitrification: Boosts CH4-derived carbon for denitrification but inhibits it via methanobactin competition

Aerobic methane oxidation coupled with aerobic denitrification (AME-AD) has the capability to remove nitrate and reduce methane (CH 4 ) under aerobic conditions. However, the impact of copper as a cofactor in wastewater and its underlying mechanism in the AME-AD process remains unexplored. This study conducted a series of batch experiments, examining the influence of copper concentrations (ranging from 0 to 20 μM Cu 2+ ) on denitrification, CH 4 oxidation, nitrous oxide (N 2 O) generation, and the expressions of key functional genes within a synthetic AME-AD community. The results revealed that Cu 2+ concentrations significantly affected the denitrification capacity of the AME-AD system. Specifically, the 10 μM Cu 2+ treatment exhibited optimal AME-AD performance, achieving a denitrification rate of 0.031 mg·h -1 and a CH 4 oxidation efficiency of 98%. However, this treatment had a high proportion of N 2 O generation (4.79%), ultimately resulting in a decrease in the overall reduction of total greenhouse gases to 802.5 mg CO 2 -e. Moreover, the Cu 2+ concentrations had a significant impact on the expression of crucial genes associated with aerobic denitrification ( napA, nosZ ) and CH 4 oxidation ( pmoA ). Specifically, the highest abundance of functional genes related to denitrification was observed in 15 μM Cu 2+ treatment, with napA reaching 3.75 × 10 10 copies·g -1 and nosZ attaining 1.32 × 10 9 copies·g -1 at 192 h. Conversely, the peak pmoA copy number of 4.8 × 10 9 copies·g -1 was noted in 10 μM Cu 2+ treatment. These discoveries enhance our comprehension of how copper modulates the AME-AD process and facilitate its application in treating low-C/N wastewater and mitigating greenhouse gas emissions.