Volatile fatty acid fermentation of AFEX-treated bagasse and newspaper by rumen microorganisms

Abstract

The anaerobic digestion of bagasse and newspaper by rumen microorganisms was studied. A one-half replicate of a 2 5 factorial design was used to evaluate the effect of type of substrate (bagasse and newspaper), AFEX (Ammonia Fiber Explosion) pretreatment, liquid residence time (LRT), solid/liquid residence time ratio (SRT/LRT), and loading rate (LR) on volatile fatty acid (VFA) yield, productivity, and acid composition. A fermentor for the continuous culture of rumen microorganisms, which allows solids to be retained longer than liquid (SRT/LRT> 1), was used. Yields averaged 8.8 mmoles and 5.8 mmoles VFA per g volatile solids (VS) in bagasse and newspaper fermentations, respectively. The propionic acid molar percent was 52% higher in bagasse fermentation (19%) than in newspaper fermentation (12.5%). AFEX pretreatment increased VFA yield by 21% and decreased propionic acid molar percent by 9.1 %. The best reactor performance (i.e., high VFA yield and high VFA productivity) was achieved with AFEX-treated material at a LR of 14.1 g substrate per 1 day, LRT of 11 h, and SRT of 44 h. At these experimental conditions, productivity and yield were 163 mmoles VFA per 1 per day and 0.64 g VFA/g VS in bagasse fermentation, and 81 mmoles per 1 per day and 0.31 g VFA/g VS in newspaper fermentation. The rumen fermentation product yields are significantly higher than the sugar yields from extracellular cellulase/hemicellulase. A promising application of the rumen fermentation is to produce mixed VFA calcium salts which may be used to remove sulfur from coal-fired boilers. It is estimated that these salts may be produced from municipal solid waste for $119–137/tonne.