An integrated strategy for the utilization of rice straw: Production of plant growth promoter followed by ethanol fermentation

Abstract The aim of this study was to investigate the effects of bioactives derived from rice straw on tomato growth and develop an integrated process for utilization of straw. The humic substances (HS) was obtained from rice straw in this study. To investigate the effect of HS on tomato growth, tomato seedlings were sprayed with HS and the changes in morphology were measured. Compared with the control, the relative stem heights and leaf numbers of the tomato plants increased by 17.05% and 23.47% for polyphenols in HS and by 28.27% and 17.66% for polysaccharides in HS, respectively. Moreover, the inhibition of HS on cellulase activity and ethanol fermentation were confirmed in this study. When HS was added, the activities of FPase, CMCase and β-glucosidase decreased by 37.29%, 11.54% and 30.70%, respectively. Essentially, the production of HS could be considered as a removal step prior to the bioconversion of the straw into ethanol, and it increased the productivity of ethanol fermentation by 29.39%. The findings demonstrated that HS from rice straw could be successfully used as an environmentally friendly product to increase plant yield and, the residue after HS removal exhibited an improved efficiency of bioconversion to ethanol, making biofuels more attractive.