Pilot-Scale Fermentation of Aqueous-Ammonia-Soaked Switchgrass

• Published in: Applied biochemistry and biotechnology Vol. 157; no. 3; pp. 453 - 462
• Main Authors: Isci, Asli, Himmelsbach, Jennifer N., Strohl, John, Pometto, Anthony L., Raman, D. Raj, Anex, Robert P.
• Format: Journal Article
• Language: English
• Published: New York Humana Press Inc 01.06.2009; Springer; Springer Nature B.V
• Subjects: Acetic acid; Agricultural biotechnology; Ambient temperature; Ammonia; Ammonia - chemistry; Ammonium; Ammonium Hydroxide; Biochemistry; Biofuels; Biological and medical sciences; biomass; Bioreactors; Biotechnology; Cellulose; Chemistry; Chemistry and Materials Science; Ethanol; Ethanol - metabolism; ethanol production; Fermentation; Fermentation - physiology; Fundamental and applied biological sciences. Psychology; Grasses; growth & development; Hydroxides; Hydroxides - chemistry; laboratories; lactic acid; metabolism; Methods. Procedures. Technologies; Microbial engineering. Fermentation and microbial culture technology; Panicum; Panicum - growth & development; Panicum - metabolism; Panicum virgatum; physiology; pretreatment; Reactors; saccharification; Saccharomyces cerevisiae; Temperature; Water; Water - chemistry; Yeast; Simultaneous saccharification and fermentation (SSF); Aqueous ammonia soaking; Pilot scale; Switchgrass; Ethanol production; Ammonia; Ethanol; Production; Saccharification; Fermentation; Pilot plant scale
• ISSN: 0273-2289; 1559-0291; 1559-0291
• DOI: 10.1007/s12010-008-8235-y

Aqueous-ammonia-steeped switchgrass was subject to simultaneous saccharification and fermentation (SSF) in two pilot-scale bioreactors (50- and 350-L working volume). Switchgrass was pretreated by soaking in ammonium hydroxide (30%) with solid to liquid ratio of 5 L ammonium hydroxide per kilogram dry switchgrass for 5 days in 75-L steeping vessels without agitation at ambient temperatures (15 to 33 °C). SSF of the pretreated biomass was carried out using Saccharomyces cerevisiae (D 5 A) at approximately 2% glucan and 77 filter paper units per gram cellulose enzyme loading (Spezyme CP). The 50-L fermentation was carried out aseptically, whereas the 350-L fermentation was semiaseptic. The percentage of maximum theoretical ethanol yields achieved was 73% in the 50-L reactor and 52–74% in the 350-L reactor due to the difference in asepsis. The 350-L fermentation was contaminated by acid-producing bacteria (lactic and acetic acid concentrations approaching 10 g/L), and this resulted in lower ethanol production. Despite this problem, the pilot-scale SSF of aqueous-ammonia-pretreated switchgrass has shown promising results similar to laboratory-scale experiments. This work demonstrates challenges in pilot-scale fermentations with material handling, aseptic conditions, and bacterial contamination for cellulosic fermentations to biofuels.