Surface culture of torulopsis candida on supernatant from anaerobically fermented swine manure

Abstract

A process for treating swine manure to produce single cell protein was studied. Anaerobic fermentation of diluted swine manure produced volatile fatty acids (VFA) with lowering the pH value of supernatant from 6.8 to 6.3. VFA production increased about two times as the temperature was raised by $10\,^\circ\!C$ from $20\,^\circ\!C$ up to $40\,^\circ\!C$. VFA composition, on the average, was acetic 43\%, propionic 15\%, butyric 23\%, valeric 9\%, isovaleric 6\% and isobutyric 4\% on the weight basis. The supernatant from the fermentor was used as a medium for the surface culture of Torulopsis candida. The growth of bacterial population, which existed naturally in supernatant, was inhibited by adjusting pH to acidic region before inoculation of the yeast. T. candida grew well in the medium with VFA concentration of 0.08-0.18 M, utilizing acetate predominantely. The optimum temperature for the growth of T. candida was $35\,^\circ\!C$. A thick pellicle was formed on the medium with low pH. Doubling time of the yeast in the exponential growth phase was 2.6 hr when the yeast was cultured at $32\,^\circ\!C$ on the medium with initial VFA concentration of 0.11 M and pH 5.4. The yield of the yeast was 0.44 g dry cell weight per gram of VFA. T. candida did not form a stable pellicle in the supernatant diluted after the anaerobic fermentation.