The bioconversion of gas feedstreams to liquid products by direct contact with a layer of microorganism obtains enhanced productivity through the regular cycling of liquid across a substrate that supports a biolayer of microorganisms while separating the gas and liquid phases. Such processes produce liquid products such as ethanol, butanol and other chemicals from syngas components by contacting CO or a mixture of CO2 and H2 with a highly porous side of an asymmetric membrane under anaerobic conditions and transferring these components into contact with microorganisms contained within bio-pores of the membrane. A periodic laving of liquid from the liquid contact side to and away from the microorganisms can increase nutrient flow to the microorganisms while enhancing the recovery of liquid products. The process effects laving by temporarily raising the liquid phase pressure relative to the gas phase pressure to periodically surge liquid toward the microorganisms and then restoring the original pressure differential to urge liquid away from the microorgaisms.