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

Abstract

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.