Utilization of the saccharification residue of rice straw in the preparation of biochar is a novel strategy for reducing CO₂ emissions

Once rice straw has been bioconverted into biofuels, it is difficult to further biodegrade or decompose the saccharification residue (mainly lignin). Taking into account the pyrolysis characteristics of lignin, in this study the saccharification residue was used as a raw material for the preparation of biochar (biochar-SR), a potential soil amendment. Biochar was prepared directly from rice straw (biochar-O) with a yield of 32.45 g/100 g rice straw, whereas 30.14 g biochar-SR and 30.46 g monosaccharides (including 20.46 g glucose, 9.11 g xylose, and 0.89 g arabinose) were obtained from 100 g of rice straw. When added to liquid soil extracts as a soil amendment, almost nothing was released from biochar-SR, whereas numerous dissolved solids (about 70 mg/L) were released from biochar-O. Adding a mixture of biochar-SR and autotrophic bacteria improved soil total organic carbon 1.8-fold and increased the transcription levels of cbbL and cbbM, which were 4.76 × 10³ and 3.76 × 10⁵ times those of the initial blank, respectively. By analyzing the soil microbial community, it was clear that the above mixture favored the growth of CO₂-fixing bacteria such as Ochrobactrum. Compared with burning rice straw or preparing biochar-O, the preparation of biochar-SR reduced CO₂ emissions by 67.53% or 37.13%, respectively. These results demonstrate that biochar-SR has potential applications in reducing the cost of sustainable energy and addressing environmental issues. Copyright © 2018 Elsevier B.V. All rights reserved.