NOVELTY - Converting a feed gas comprising syngas into a liquid product under anaerobic conditions, comprises e.g. (a) passing an aqueous seeding solution comprising a monoculture of microorganisms into contact with a gas contacting side of hydrophilic membrane, passing the liquid portion of the solution through the membrane, and retaining on the gas contacting side of the membrane microorganisms consisting essentially of a monoculture of an anaerobic microorganism with the gas contacting side serving as an exclusion surface to inhibit penetration of the microorganisms into the membrane.    USE - The process is useful for converting a feed gas comprising syngas and containing at least one of carbon monoxide or a mixture of carbon dioxide and hydrogen into a liquid product under anaerobic conditions, where the liquid product is ethanol, n-butanol, hexanol, acetic acid and butyric acid (all claimed), which are useful as liquid motor fuels and diesel motor fuels, and for blending with conventional gasoline.    ADVANTAGE - The process provides liquid products with high yield in an economical manner.    DETAILED DESCRIPTION - Converting a feed gas comprising syngas and containing at least one of carbon monoxide or a mixture of carbon dioxide and hydrogen to a liquid product under anaerobic conditions, comprises: either (a) passing an aqueous seeding solution comprising a monoculture of microorganisms into contact with a gas contacting side of hydrophilic membrane, passing the liquid portion of the solution through the membrane, and retaining on the gas contacting side of the membrane microorganisms consisting essentially of a monoculture of an anaerobic microorganism with the gas contacting side serving as an exclusion surface to inhibit penetration of the microorganisms into the membrane, (b) growing a biofilm comprising the immobilized microorganisms of the monoculture on the surface of the gas contacting side of the membrane by passing a feed gas comprising carbon monoxide or a mixture of carbon dioxide and hydrogen into contact with the monoculture of microorganisms on the gas contact side of the membrane, and permeating a fermentation liquid from the liquid contacting side through the membrane and into contact with the immobilized microorganisms, where the gas contacting side of the membrane serves as an exclusion surface to inhibit penetration of the biofilm into the membrane, and the feed gas has an oxygen concentration of less than 1000 ppm, (c) producing liquid products under autotrophic conditions by contacting the biofilm with the feed gas, permeating the fermentation liquid from the liquid contacting side through the membrane and into contact with the biofilm, and permeating liquid products from the biofilm across the membrane and into the fermentation liquid, where a liquid retention chamber retains the fermentation liquid into contact with the liquid contacting side of the membrane, and the fermentation liquid has a redox potential of less than -200 mV, and (d) collecting fermentation liquid containing liquid products from the liquid retention chamber to recover liquid products from the process; (a1) passing a seeding solution comprising a monoculture of microorganisms into contact with the outside side surface of a hydrophilic hollow fiber membrane having a central lumen, draining the liquid from the outside surface of membrane through the lumens, and retaining microorganisms consisting essentially of monoculture of anaerobic microorganisms on the outside surface of the membrane which serves as an exclusion surface to inhibit penetration of the microorganisms into the membrane, (b1) growing a biofilm comprising the immobilized microorganisms of the monoculture on the outside surface of the membrane by passing a feed gas comprising carbon monoxide or a mixture of carbon dioxide and hydrogen into contact with the monoculture of microorganisms on the outside surface of the membrane, and permeating a fermentation liquid from the outside surface through the membrane and into contact with the immobilized microorganisms, where the outside surface of the membrane serves as an exclusion surface to inhibit penetration of the biofilm to no more than 10 mu m beyond the membrane surface into the membrane, (c1) producing liquid products under autotrophic conditions by contacting the biofilm with the feed gas, permeating the fermentation liquid from the lumen of the membrane through the membrane and into contact with the biofilm, and permeating liquid products from the biofilm across the membrane and into the fermentation liquid, where a liquid retention chamber retains the fermentation liquid, the step (d) as above per se, and (d1) periodically increasing the pressure of the fermentation liquid to create liquid flow form the lumen through the membrane to and its outside and purge microorganisms from the biofilm; or (a2) passing a seeding solution comprising a monoculture of microorganisms to a feed gas chamber that comprises hydrophilic hollow fiber membranes and into contact with the outside side surface of hollow fiber membrane, raising the pressure on the outside of the membranes relative to the lumens to drain the liquid from feed gas chamber through the lumens of the hollow fibers, and retaining microorganisms consisting essentially of monoculture of an anaerobic microorganism on the outside surface of the membrane, which has pores size of 0.5 mu m or less for inhibiting penetration of the microorganisms into the pores such that the membrane surface provides an exclusion surface to inhibit penetration of the microorganisms into the membrane, the steps (b1), (c1), and (d) as above per se, and the step (d1) as above per se.