Microwave pretreatment of glycogen-containing cyanobacteria Synechococcus elongatus UTEX 2973 to enhance enzymatic saccharification and fermentation for bioethanol production.

This study aimed to investigate whether that microwave pretreatment of glycogen-containing Synechococcus elongatus UTEX 2973 could enhance subsequent enzymatic saccharification and ethanol fermentation. The first experiment found that pretreatment with microwave was more effective than either pretreatment with ultrasound or lysozyme under the specific operational conditions examined, when a glycogen-containing cyanobacterial suspension (100 g/L) was pretreated and subjected to the saccharification assay at low biomass loading (10 g/L). Next, to investigate the appropriate microwave pretreatment time for enzymatic saccharification of glycogen in S. elongatus UTEX 2973, a cyanobacterial suspension (100 g/L) was pretreated by microwave (200 W) for 0-200 s and subjected to the saccharification assay at low biomass loading (10 g/L). The glucose yield was only 18% in the case of pretreatment for 0 s (negative control). On the contrary, the value increased to almost 100% in the case of microwave pretreatment for 100 s and more. Finally, to perform saccharification and ethanol fermentation of microwave-pretreated glycogen-containing S. elongatus UTEX 2973, a cyanobacterial suspension (100 g/L) was pretreated by microwave for 0-150 s and subjected to high biomass loading (100 g/L) enzymatic saccharification followed by ethanol fermentation. When the pretreatment time was 150 s, the glucose concentration at the end of saccharification was 44 g/L (glucose yield of 94%). The ethanol concentration was 21 g/L during the ethanol fermentation, which is 88% of the theoretical value. These results suggest that microwave pretreatment of glycogen-containing S. elongatus UTEX 2973 could facilitate the subsequent enzymatic saccharification and ethanol fermentation.