Control of fermentation types in continuous-flow acidogenic reactors: effects of pH and redox potential

The experiments were carried out in continuous-flow acidogenic reactors with molasses used as sub strate to study the effects of pH and redox potential on fermentation types. The conditions for each fermentation type were investigated at different experimental stages of start-up, pH-regulating and redox potential-regulating.The experiments confirmed that butyric acid-type fermentation would occur at pH ＞ 6, the propionic acid-type fermentation at pH about 5.5 with Eh ＞ - 278 mV, and the ethanol-type fermentation at pH ＜ 4.5. A higher redox potential will lead to propionic acid-type fermentation because propionogens are facultative anaerobic bacteria.