Methane utilization in aerobic methane oxidation coupled to denitrification (AME-D): theoretical estimation and effect of hydraulic retention time (HRT)

Even though aerobic methane-oxidation coupled to denitrification (AME-D) has been extensively studied, the exact estimation of CH₄ utilization during this process still requires better understanding because effective utilization of CH₄ is essential in denitrification performance, CH₄ emission and economy. This study presents the effect of hydraulic retention time (HRT) on CH₄ utilization in an AME-D bioreactor. Stoichiometries for AME-D were newly established by using the energy balance and the thermodynamic electron equivalent model. The theoretically determined CH₄ utilized/NO₃⁻ consumed (C/N) ratio from the stoichiometry was 2.0. However, the C/N ratios obtained from the experiment varied with increasing tendency as the HRT increased. Specifically, the C/N ratio increased from 1.38 to 2.85 when the HRT increased from 0.5 to 1.0 days, which placed the theoretical C/N ratio at the HRT between 0.5 and 1.0 days. The higher C/N ratio at the longer HRT was associated with a larger CH₄ utilization by methanotrophs than denitrifiers. The results obtained in this study together with those obtained in previous studies clearly illustrated that a variety of conditions affect the utilization of CH₄ which is essential for optimizing the AME-D process.