Exploring the functional significance of novel cellulolytic bacteria for the anaerobic digestion of rice straw

The purpose of this study is to evaluate the potential of isolated novel bacterial strains for rice straw (RS) hydrolysis in terms of total sugar and COD (chemical oxygen demand) solubilization to improve overall biomethane yield. Four out of seven pretreatment setup with isolated bacterial strains i.e., Bacillus paralicheniformis VKVVG3 (CDf), Perlucidibaca piscinae VKVVG6 (CDd1), Bacillus clausii VKAK2 (RSa1) and Bacillus mojavensis VKAK1 (CDb1) exhibited higher saccharification compared to untreated RS. The CDf pretreated RS showed highest efficiency with 137% COD solubilization and 320% sugar accumulation at optimal dosage of 109 CFU/mL within 4-day of incubation. The batch reactor (20L) study with CDf pretreated RS produced 476 mL/g VSsubstrate compared to 310 mL/g VSsubstrate for untreated RS which corresponds to 53.6% higher than untreated RS. The FESEM, FTIR, and XRD analysis also support the overall results, indicating excellent degradation of the structural morphology of the RS microcrystalline structure. Furthermore, the fitting error in bio-kinetic parameters using modified Gompertz, Fitzhugh, and Monomolecular models were 5.47, 2.44, and 4.28% respectively, with R2 values above 0.99, also supports the experimental data. The results of this study revealed many positive interpretations concerning the future expansion of the existing system for bacterial pretreatment of RS.