On-line extraction of volatile fatty acids in acidogenic chemostat culture using a supported liquid membrane

An on-line extraction of volatile fatty acids (acetic and butyric acids) from acidogenic fermentation in chemostat cultures using a supported liquid membrane (SLM) was investigated in order to overcome end-product inhibition. By using SLM, the high-cell-density retaining dilution rate of the chemostat could be increased, thus enhancing the microbial acidogenesis. To further understand this phenomenon, the growth and extraction kinetics were studied. The effect of substrate concentration was found to obey the Haldane equation. Regarding the inhibition by volatile fatty acids, it turned out that undissociated butyric acid rather than acetic acid severely inhibited the growth, corresponding to non-competitive kinetics. The extraction rates of the acids were proportional to their undissociated concentration as well as to the SLM area/broth volume, and butyric acid extraction was easier than that of acetic acid.