Pilot-scale fermentation of aqueous-ammonia-soaked switchgrass.
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 degrees 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.
Isci
Asli
A
Department of Agricultural and Biosystems Engineering, Iowa State University, Ames, IA 50011, USA. isci@iastate.edu
Himmelsbach
Jennifer N
JN
Strohl
John
J
Pometto
Anthony L
AL
Raman
D Raj
DR
Anex
Robert P
RP
D000641:Ammonia / Q000737:chemistry*; D064753:Ammonium Hydroxide; D019149:Bioreactors; D000431:Ethanol / Q000378:metabolism; D005285:Fermentation / Q000502:physiology*; D006878:Hydroxides / Q000737:chemistry; D008897:Panicum / Q000254:growth & development / Q000378:metabolism*; D013696:Temperature; D014867:Water / Q000737:chemistry*
D006878:Hydroxides; D014867:Water; D000431:Ethanol; D064753:Ammonium Hydroxide; D000641:Ammonia