Autotrophic-heterotrophic synergies in electrically stimulated denitrification anaerobic methane oxidation systems for enhanced nitrogen and methane removal

Denitrification anaerobic methane oxidation (DAMO) integrating carbon and nitrogen cycles is regarded as a promising biological process for mitigating methane emissions and achieving nitrogen removal in wastewater treatment. However, the slow reaction rate and long doubling time limit its application. This study addressed these by coupling bioelectrochemical stimulation with DAMO system to enhance extracellular electron transfer and promote microbial activity. The results showed that bioelectrochemical stimulation significantly improved system performance. Under the microbial electrolysis cell mode (MEC), the nitrate removal rate increased by 2.73 times to 6.57 ± 0.60 mg N/L/d compared to control. Methane consumption rates were also enhanced to 80.49 ± 0.59 μmol/d. The interaction between methane-oxidizing autotrophic microorganisms and heterotrophic denitrifiers was strengthened under electrical stimulation, with the relative abundance of Candidatus Methylomirabilis increasing by 4.36 and 3.91 times in the anode biofilm and suspended sludge, respectively. Key denitrification genes such as napA, nirS and norB were upregulated by 101.98 %, 149.97 %, and 208.59 % on the electrode biofilm in MEC. Additionally, the methane oxidation gene pmoA was also upregulated by 66.61 %. The upregulation genes encoded to Mtr on the electrode biofilm further indicated the extracellular electron transfer between autotrophic and heterotrophic microorganisms. In summary, electrical stimulation facilitated the formation of an autotrophic core dominated by methane-oxidizing microorganisms and a heterotrophic core dominated by nitrogen-metabolizing microorganisms and further improving pollutant removal efficiency. These findings offer a promising approach for efficient nitrogen and methane removal in autotrophic DAMO systems and improve the sustainability of wastewater treatment.