Protein degradation in anaerobic digestion: influence of volatile fatty acids and carbohydrates on hydrolysis and acidogenic fermentation of gelatin

Summary The hydrolysis and fermentation of gelatin in the presence of a carbohydrate by gelatin-adapted mixed anaerobic bacterial populations in putatively carbon-limited chemostat cultures is investigated. It was shown that the degradation of the protein is progressively retarded with increasing dilution rates, as well as with increased concentrations of carbohydrates present in the feed as a second substrate. That this is not due to high concentrations of fermentation products in the reactor was established. Moreover, the carbohydrate is totally fermented at all dilution rates. It is concluded that for optimal performance of an anaerobic digestion system purifying waste waters containing carbohydrate/protein mixtures, fermentation of carbohydrates should be spatially separated from hydrolysis and fermentation of the protein.