Hydrolysis and acidogenic fermentation of gelatin under anaerobic conditions in a laboratory scale upflow reactor

Summary Gelatin was dissolved in a mineral salts medium for growth under carbon limitation and fed to a mixed population of bacteria in a lab-scale upflow reactor for hydrolysis and acidogenic fermentation under anaerobic conditions, at pH=7 and 30°C.With the shortest applied liquid retention time (30 min), 84% of the protein was hydrolysed. The majority (85%) of the hydrolysed protein was fermented. The ammonia concentration in the reactor was about 1,400 mg N·l^-1.The fermentation products were mainly acetate, propionate, and valerate. Iso-butyrate, butyrate, and iso-valerate were formed to a limited extent. Gas production was very low and consisted of carbon dioxide and methane. The product composition was independent of the retention time applied. The sludge formed was slimy. No granules were formed, however a hold-up factor of 46 could be obtained.