It is well established that metabolic pathways in the fermentation of organic waste are primarily controlled by dissolved H-2 concentrations, but there is no reported study that compares observed and predicted shifts in fermentation pathways induced by manipulating the dissolved H-2 concentration. A perfusion system is presented that was developed to control dissolved H-2 concentrations in the continuous fermentation of glucose by a culture highly enriched towards Thermoanaerobacterium thermosaccharolyticum (86 9% relative abundance) from an originally diverse consortia in the leachate of a laboratory digester fed with municipal solid waste. Media from a 2.5 L CSTR was drawn through sintered steel membrane filters to retain biomass, allowing vigorous sparging in a separate chamber without cellular disruption. Through a combination of sparging and variations in glucose feeding rate from 0.8 to 0.2 g/L/d, a range of steady state fermentations were performed with dissolved H-2 concentrations as low as an equivalent equilibrated H-2 partial pressure of 3 kPa. Trends in product formation rates were simulated using a H-2 regulation partitioning model. The model correctly predicted the direction of products redistribution in response to H-2 concentration changes and the acetate and butyrate formation rates when H-2 concentrations were less than 6 kPa. However, the model over-estimated acetate, ethanol and butanol productions at the expense of butyrate production at higher H-2 concentrations. The H-2 yield at the lowest dissolved H-2 concentration was 2.67 0.08 mol H-2/mol glucose, over 300% higher than the yield achieved in a CSTR operated without sparging. (C) 2014 Wiley Periodicals, Inc.