Performance of a polypropylene membrane contactor for the recovery of dissolved methane from anaerobic effluents: Mass transfer evaluation, long-term operation and cleaning strategies

A polypropylene membrane contactor was used for the recovery of dissolved methane from an anaerobic reactor effluent. Effect of operational parameters, operation mode and fouling on long-term operation was studied using vacuum pressure or N2 as sweep gas. Results were analyzed based on the mass transfer estimations. Lower performance was observed in the shell-side mode due to the lower liquid velocity and the probable channeling. Membrane pore wetting was observed with the increase in QL in the vacuum-pressure mode. This was confirmed with mass transfer resistance analysis, resulting in an estimated wetted pore fraction of between 0.25 and 0.53. The highest removal efficiencies were obtained with the liquid flowing in the lumen side and sweep-gas operation (between 98% and 67% for QL between 4.1 and 27.2 L h-1), with negligible effect of the N2 flow rate. In the long-term operation, the impact of membrane fouling was less intense in the lumen side, with longer operation time and more reversible fouling. A complete characterization of the fouling based on water sample analysis concluded that both inorganic and organic foulants were present, probably with higher biofouling presence. A combination of water and chemical cleanings resulted in a recommended protocol based on daily water cleaning.