Anaerobic formation of volatile acids in a chemostat

Summary If anaerobic digestion of waste can be performed as a two-step fermentation it becomes possible to optimize the separate steps. As the CH₄ formation is assumed to be the slower step and the step more sensitive to substrate composition, an improvement of the overall process could be achieved by control of the effluent from the preceding step, in which volatile acids are formed. In this paper it is demonstrated that the composition of volatile acids from a chemostat varies to a great extent with dilution rate, so that, if an optimal composition of volatile acids exists for the CH₄-forming step, it might be obtained by proper choice of dilution rate. The best substrate for CH₄-formations is discussed.