Anaerobic methane oxidation coupled with anaerobic ammonium oxidation via iron-modified powdered activated carbon: Focus on nitrogen removal and microbial variation

Nitrate/nitrite-dependent anaerobic methane oxidation (n-DAMO) coupled with anaerobic ammonium oxidation (anammox) offers an effective approach for removing low-concentration nitrogen from wastewater. However, the slow growth and low metabolic activity of the involved microorganisms limit the overall efficiency of the process. This study investigated the effects of two iron-loaded modified powdered activated carbons (PACs) on synergistic microbial enrichment and nitrogen removal performance. The results showed that the optimal dosages of the unmodified PAC, iron-modified PAC (FePAC), and iron–copper-modified PAC (FeCuPAC) were 0.250 g/L, 0.250 g/L, and 0.025 g/L, respectively, achieving corresponding total nitrogen removal rates of 61.60 mg/(L·d), 68.49 mg/(L·d), and 51.72 mg/(L·d). In short-term experiments, the FePAC group exhibited the highest level of extracellular polymeric substances (134.33 mg per gram of volatile suspended solids) and protein content, which correlated with its superior nitrogen removal performance. The relative abundances of Candidatus Methylomirabilis and Candidatus Methanoperedens in the FePAC group were 45.49% and 6.40% higher, respectively, than those in the control group. This study provides insights into strategies for enhancing the synergistic enrichment of anammox and n-DAMO microorganisms.