Physicochemical Characterization of Rice Straw Pretreated with Sodium Hydroxide in the Solid State for Enhancing Biogas Production

Abstract

The biogas yield of rice straw during anaerobic digestion can be substantially increased through solid-state sodium hydroxide (NaOH) pretreatment. This study was conducted to explore the mechanisms of biogas yield enhancement. The chemical compositions of the pretreated rice straw were first analyzed. Fourier transform infrared (FTIR), hydrogen-1 nuclear magnetic resonance spectroscopy ( 1 H NMR), X-ray diffraction (XRD), and gas permeation chromatography (GPC) were then used to investigate the changes of chemical structures and physical characteristics of lignin, hemicellulose, and cellulose. The results showed that the biogas yield of 6% NaOH-treated rice straw was increased by 27.3-64.5%. The enhancement of the biogas yield was attributed to the improvement of biodegradability of the rice straw through NaOH pretreatment. Degradation of 16.4% cellulose, 36.8% hemicellulose, and 28.4% lignin was observed, while water-soluble substances were increased by 122.5%. The ester bond of lignin-carbohydrate complexes (LCCs) was destroyed through the hydrolysis reaction, releasing more cellulose for biogas production. The linkages of interunits and the functional groups of lignin, cellulose, and hemicellulose were either broken down or destroyed, leading to significant changes of chemical structures. The original lignin with a large molecular weight and three-dimensional network structure became one with a small molecular weight and linear structure after NaOH pretreatment. The cellulosic crystal style was not obviously changed, but the crystallinity of cellulose increased. The changes of chemical compositions, chemical structures, and physical characteristics made rice straw become more available and biodegradable and thus were responsible for the enhancement of the biogas yield.

Comparative Study of the Preparation of Reducing Sugars Hydrolyzed from High-Lignin Lignocellulose Pretreated with Ionic Liquid, Alkaline Solution and Their Combination

“…After pretreatment with 1% NaOH and regeneration, the diffraction intensity of substrates was typical of cellulose I. Cellulose I properties are close to those of cellulose, with a high crystallinity and distinct peaks at the angles (16 o , 22 o and 35 o ) described above. These results were similar and comparable to previously published reports [19][20][21][22][23]. The increase in the crystalline index of substrate pretreated with NaOH was mainly caused by the liquefaction of the amorphous parts (lignin and hemicellulose).…”

“…Enzymatic hydrolysis was carried out as described previously [10,11,12,20]. A suspension solution was prepared by mixing sodium acetate buffer (pH 3, 30 mL, 0.1 M) and coconut coir dust (1 gram, 120 mesh) inside an Erlenmeyer reactor.…”

Increasing biogas production from sugar cane baggase by anaerobic co-digestion with animal manure

“…Pretreatment before anaerobic digestion process has proven to be one simple and effective method to increase the biodegradability and biogas yield from lignocellulose materials [23]. Figure 1 shows the surface bagasse as seen in SEM image.…”

Effect of Drying Method of Corn Stover on Sugar Recovery during Dilute Sulfuric Acid Pretreatment

“…The bands at 3340 and 2930 cm -1 were associated with hydrogen bonds and methylene of cellulose, which were related to typical cellulose [18]. The absorption peak of ODCS was weaker than ADCS, which implied that ODCS had less content of crystalline cellulose and explained the lower crystallinity.…”