Comparative study of degassing membrane modules for the removal of methane from Expanded Granular Sludge Bed anaerobic reactor effluent

The feasibility of an emergent technology for in situ removal/recovery of methane from the effluent of an Expanded Granular Sludge Bed (EGSB) anaerobic reactor has been studied. For this purpose, the performances of two commercial hollow fibre degassing contactors with different membrane materials - microporous (polypropylene, PP) and non-porous (polydimethylsiloxane, PDMS) - were compared. The influence of water fluxes (QL/Amembrane ranging from 22.6 to 377.4 L h−1 m−2), vacuum pressure (140-800 mbar), sweep gas fluxes (QN2/Amembrane ranging from 0.14 × 103 to 4.44 × 103 L h−1 m−2), and mode of operation (liquid flowing in the lumen side or the shell side) was studied. Both materials showed different behaviours with the variations in operational conditions. In liquid flowing in the lumen mode operation, PP microporous membrane was slightly more efficient under soft or mild operational conditions (low liquid flow and/or vacuum pressure) but showed a wetting phenomenon when operational conditions were harder. In shell side mode, PDMS was more efficient and no wetting phenomenon was observed with this contactor. The differences have been explained, taking into account the material properties (porosity, material resistance …) of the membrane and structure (packing density, fibre diameter …) of the modules. Methane removal efficiencies of up to 98% could be achieved, showing the viability of methane removal/recovery using this technology. Simultaneous degassing of CO2 was also monitored in both modules, showing that the removal efficiency of this gas was considerably lower than for methane. In general terms, the removal of dissolved CO2 followed a quite similar behaviour from that described for methane. Experimental overall mass transfer coefficients were also obtained.