Abstract
This work fits in the general research area of organic waste conversion to chemicals and fuels using anaerobic digestion. In particular this study investigates the ability of undefined mixed microbial cultures to ferment cellulose to ethanol and organic acids without any chemical or physical pretreatment of the feed. The anaerobic conversion of microcrystalline cellulose was investigated in four batch experiments, carried out at 25 °C without any pretreatment of the cellulose. The mixed culture effectively fermented the substrates, however cellulose degradation only occurred after the microorganisms had been acclimated to cellulose in continuous runs, while cellulose was not degraded by unacclimated microorganisms. Acetic acid was the main metabolic product while ethanol, butyric acid and propionic acid were also present in low concentrations. Within 100 days from the start of the batch tests, the cellulose removal was in the range 40-50 %. The maximum concentration of acetic acid observed was 8.8 g/L while the maximum ethanol concentration was 0.6 g/L.
The experimental results demonstrates the capability of open mixed microbial culture to ferment cellulose under mild conditions. Even though the rates observed in this study are still too low for industrial exploitation, they indicate the potential of mixed cultures to biodegrade cellulose even in the absence of any pretreatments. The next step of the study will be aimed at finding the conditions that increase the cellulose biodegradation rate.
