TECHNOLOGY FOCUS - BIOLOGY - Preferred Components: The microorganisms in the bioreactor comprises a mono-culture of one of Clostridium ragsdalei, Butyribacterium methylotrophicum, Clostridium ljungdahlii, Clostridium autoethanogenum, Clostridium woodii and Clostridium carboxydivorans. The biofilm exclusion surface comprises a skin having a thickness of no more than 5 mu m on the outside of a membrane layer, and the skin has a pore size of less than 0.5 mu m.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Process: In the process: a feed gas chamber in fluid communication with the gas contacting side of the membrane supplies the feed gas to the membrane; a gas stream is passed along the gas contacting side of the hollow fiber membrane while it is in the flooded condition to create turbulence in the liquid adjacent to the biolayer to remove the biolayer or control its thickness; and a continuous flow of feed gas having an oxygen concentration of less than 100 ppm passes across the gas contact side of the hydrophilic membrane. The hydrophilic membrane comprises hollow fiber membranes with the fermentation liquid and liquid product flowing through the lumens of the hollow fiber membranes and the feed gas flowing over the outside of the hollow fiber membranes. The feed gas passes serially through multiple assemblies of hollow fiber membranes, at least one feed gas chamber supplies feed gas for each hollow fiber membrane assembly, and carbon dioxide is removed from the gas as it passes between assemblies through the system. The gas contacting side of the hollow fiber membrane is temporarily flooded with liquid to remove at least a portion of the biolayer or material from the biolayer. The pressure difference between the liquid stream and the feed gas is regulated to control the liquid flow through the membrane to the biofilm and control its thickness. The feed gas chamber comprises the hollow fiber membrane and the feed gas chamber is occasionally flooded with liquid to remove at least a portion of the biofilm or material from the biolayer and while the chamber flooded a gas stream is passed through the feed gas chamber along the membrane to sparge the biofilm and control its thickness. Preferred Components: The biofilm exclusion surface has pores with effective diameters of no greater than 0.5 mu m to inhibit penetration of the biofilm into the pores. The biofilm exclusion surface has pores with a sufficient tortuosity to inhibit penetration of the biofilm into the pores. The biofilm extends into the biofilm exclusion surface by no more than 10 mu m. The hydrophilic membrane comprises a monolayer having a thickness of 0.05-0.8 mm and an effective pore diameter of 0.01 to 0.5 mu m. The feed gas is synthesis gas having an oxygen concentration of less than 100 ppm, the biofilm comprises microorganisms that produce ethanol, and a liquid recovery chamber retains an ethanol containing liquid. The hydrophilic membrane comprises a composite having a biofilm support layer and a liquid contacting layer of two different materials.    TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The hydrophilic membrane comprises polyvinylidene fluoride, polyethylene, polypropylene, PVC, polysulfone, and polyethersulfone.