The present invention is generally related to systems and methods to permit the growth of anaerobic, ethanol-producing bacteria using pretreated biomass such as cellulose in a manner to facilitate the efficient conversion of cellulose to ethanol. The valve thus achieves an opening and closing characteristic with negative overlapping and so provides gentle switching processes, so that switching impacts with high pressure peaks do not arise. A keyboard and display is carried by the housing and connected to the processor.