Characteristics of Cellulose from Lespedeza stalks Steam Pretreated with Low Severity Steam and Post-Treatment by Alkaline Peroxide for Energy Production

Lespedeza crytobotrya is a shrub species with properties of substantial biomass and widely distributes in the desert region of China. The cellulose separated from Lespedeza after pre-treatment can be enzymatic hydrolyzed into glucose for ethanol or other chemicals production, which are important renewable fuels or raw material for other material synthesis. Moreover it also can be used for cellulosic material production. So it is necessary to evaluate the cellulose of Lespedeza crytobotrya before its utilization. In this study four cellulosic fractions were isolated by pretreatment with low severity steam and post-treatment with alkaline peroxide. They were comparatively studied by sugar analysis and the average degree of polymerization. After alkaline peroxide post-treatment, the hemicelluloses in the cellulosic fractions were removed markedly. The treatment intensity had a profound effect on the average degree of polymerization, which was increased firstly and then decreased. A combination of low severity steam pretreatment and alkaline peroxide post-treatment is an effective method for Lespedeza stalks to obtain high glucose yield.

Delignification with Alkaline Peroxide from Lespedeza Stalks Steam-Pretreated at Low Severity

A steam pretreatment method with low severity and post pretreatment with alkaline peroxide were investigated in this study with respect to the factors affecting delignification efficiency of Lespedeza Stalks. In alkaline peroxide procedure, four factors were compared to evaluate the lignin removal: substrate concentration (w/w), the ratio of peroxide to substrate (w/w), temperature and time. The remaining lignin of fractions from Lespedeza stalks steam pretreated at low severity was apparently reduced by post treatment with 1 g H2O2/g substrate at the substrate concentration of 1.67% under 60°C for 72h. Scanning electron microscopy images show that the samples with alkaline peroxide treatment have the smoother surface because of the elimination of lignin droplets and the fiber bundles individualized.

Production of Lactic Acid by Simultaneous Saccharification and Fermentation Using Steam Pretreated Lespedeza Stalks as Inexpensive Raw Materials

The lespedeza stalks with steam pretreatment were fermented to lactic acid by simultaneous saccharification and fermentation (SSF) in this study. Orthogonal design methodology was used to evaluate the optimum SSF conditions that give maximum lactic acid yield. We have investigated the following relative factors, such as temperature, loading of cellulase, calcium carbonate and concentration of substrate. The optimum operating conditions were found to be temperature of 43 °C, cellulase loading of 30 FPU/g substrate, calcium carbonate of 3 % and substrate of 6 %. Comparisons of different steam pretreated conditions on lactic acid yield from lespedeza stalks were also made. The results showed that lactic acid yields from lespedeza stalks with 4 min pretreatment at pressure of 1.0, 1.25, 1.5 and 2.0 Mpa were 41.8 %, 42.5 %, 50.6 % and 64.0 % of the theoretical, respectively. The lactic acid yield from steam pretreated lespedeza stalks was much higher than that of lespedeza stalks without pretreatment (23.9 %). It can be concluded that the lactic acid yield was remarkably improved by steam pretreatment. The yield of lactic acid from steam pretreated lespedeza stalks was 1.68 times higher than that of untreated ones. Additionally, the lactic acid yield could be further promoted from 64.0 % to 89.4 % by washing pretreated stalks with water, which suggested that water processing is a promising method to remove inhibitors in broth to improve lactic acid yield.