Dissolved methane recovery from anaerobically treated wastewaters using solvent-based membrane contactor: An experimental and modelling study

Abstract

Recovery of dissolved methane from anaerobic effluents has long been a challenge. We conduct an experimental and modelling study to assess the potential of solvent-based membrane contactor (SMC) for dissolved methane recovery from anaerobically treated wastewater. In this process, dissolved gas (methane) in an aqueous solution is extracted into an organic solvent that has a high solubility of the gas across an omniphobic (non-wetting) microporous membrane. Accounting for different gas solubilities in disparate solvents, we developed a mass transfer model that describes methane transfer and its enrichment from the low (aqueous solvent) to the high concentration phase (organic solvent). With the excellent agreement between experiments and our mass transfer model, we investigate the impact of membrane properties, and solution and operating conditions on the methane recovery efficacy. We show that the amount of recovered methane is higher at a lower temperature, methane flux across the membrane is unaffected by presence of carbon dioxide (another major constituent of biogas), and the process has a considerable fouling tolerance. Finally, we show that producing a biogas with a higher methane fraction is attainable from anaerobic effluents at a higher pH, lower temperature or using a larger feed-to-draw volume ratio in the SMC system. When combined with a low-temperature anaerobic treatment system, the SMC process has the great potential for methane harvesting from anaerobic effluents, even in cold climates.