Modeling methane and oxygen diffusion and nitrogen and carbon dioxide back diffusion in a bubble-less membrane gas transfer system

Back diffusion of N2 and CO2 can significantly affect the behavior of membrane-aerated bioreactors. In this study, a mathematical model was developed to describe the dynamics of long-term diffusion of CH 4, O2 and back-diffusion of N2 and CO2 in an experimental bubble-less membrane bioreactor. The system consisted of CH4 and O2 in the gas phase, while dissolved N 2 was present in groundwater flowing past the membrane. The transfer of CH4 and O2 through the membrane to the aqueous side promoted growth of CH4-utilizing bacteria. The consumption of CH 4 and O2 by the methanotrophic bacteria led to the formation of CO2. Both N2 and CO2 back diffused through the membrane to the gas side. The model predicted that CO2 back diffusion would be low compared to N2 back diffusion at high aqueous flow rates, but high compared to N2 back diffusion at low aqueous flow rates.