Development of (NH4)2CO3-based biomass pretreatment technique and isolation of consolidated-bioprocessing microbial species for efficient cellulosic bioethanol production

Abstract

Energy insecurity and global warming are the biggest challenges for the global economy. Biomass energy is considered as an alternative energy which has numerous advantages over conventional fossil fuels. However, grains such as corns are used as the feedstock and may cause food insecurity. Therefore, it is vital to use cellulosic material from non-food biomass sources, however, these materials are quite recalcitrant to be converted into fermentable sugars due to its complex structure. In the first study, response surface methodology (RSM) was employed to optimize ammonium carbonate pretreatment condition for maximum enzymatic hydrolysis with respect to ammonium carbonate concentration (2.0-10.0%), reaction temperature (120-160°C), and pretreatment time (10-30 min). From the statistical analysis, it was revealed that all the independent variables except time significantly contributed to enzymatic hydrolysis. The maximum enzymatic hydrolysis of 79.7% was obtained at the following optimal conditions: (NH4)2CO3 loading of 10.0%, reaction temperature of 160°C, and pretreatment time of 20 min. In addition, the alteration of structure after pretreatment was verified according to the SEM, XRD, and BET analysis. In the second study, I searched for new microorganism species by isolating cellulose degraders from various environment samples. Instead of random sampling, several sources were targeted in the nature where cellulosic materials were actively decomposed such as Suncheon bay, silkwarm, and excrement of various grass-eating animals. Total 49 species were isolated by ten-fold serial dilution and cellulase activity assay with filter paper and Congo red. Several samples from grass-eating animals showed high cellulose-degrading efficiency. The strains of Nb and Nd from Nyala were determined as Pleomorphomonas sp. and Cellulomonas sp., respectively, by 16s rRNA sequencing. These strains showed highest growth rate under glucose, xylose, and carboxy-methyl cellulose (CM...