Use of membrane contactors for removing and recovering dissolved methane from anaerobic reactors effluents: state-of-the-art, challenges, and perspectives

The dissolution of methane in anaerobic effluents results in energy loss, greenhouse gas emissions, and potential safety risks. Different technologies have been studied for removing or recovering dissolved methane (D-CH4) contained in anaerobic effluents. Among them, membrane contactors have been recently described as suitable for D-CH(4)recovery. This review focusses on the use of membrane contactors for D-CH(4)removal and recovery from the effluent of anaerobic reactors. Different membrane contactor configurations (e.g., pressurised and submerged modules) with diverse membrane characteristics (e.g., microporous, dense, and composite membrane) have been operated in vacuum or sweeping gas mode and with the liquid phase in the shell or lumen side, to remove or recover D-CH(4)in various anaerobic reactor configurations (e.g., anaerobic membrane bioreactors, upflow anaerobic sludge blanket, and expanded granular sludge bed reactors). Pressurised modules have demonstrated higher D-CH(4)stripping efficiencies, with values up to 98% in very compact units. Microporous membranes present lower CH(4)mass transfer resistances than dense membranes, even though similar overall mass transfers for CH(4)have been observed in both. For anaerobic effluents with high concentrations of solids, membrane fouling and module clogging are major concerns; thus, a pre-treatment has been recommended in these cases. More experiments must be performed to establish a more detailed characterisation of the recovered waste gas. Theoretical estimations, available in the literature, state that the use of membrane contactors for D-CH(4)recovery from the effluent of anaerobic reactors would be a net-energy-producing process, which should enable neutral-carbon-footprint anaerobic sewage treatment plants.