Improving the fermentable sugar yields of wheat straw by high-temperature pre-hydrolysis with thermophilic enzymes of Malbranchea cinnamomea.

BACKGROUND: Enzymatic hydrolysis is a key step in the conversion of lignocellulosic polysaccharides to fermentable sugars for the production of biofuels and high-value chemicals. However, current enzyme preparations from mesophilic fungi are deficient in their thermostability and biomass-hydrolyzing efficiency at high temperatures. Thermophilic fungi represent promising sources of thermostable and highly active enzymes for improving the biomass-to-sugar conversion process. Here we present a comprehensive study on the lignocellulosic biomass-degrading ability and enzyme system of thermophilic fungus Malbranchea cinnamomea N12 and the application of its enzymes in the synergistic hydrolysis of lignocellulosic biomass. RESULTS: Malbranchea cinnamomea N12 was capable of utilizing untreated wheat straw to produce high levels of xylanases and efficiently degrading lignocellulose under thermophilic conditions. Temporal analysis of the wheat straw-induced secretome revealed that M. cinnamomea N12 successively degraded the lignocellulosic polysaccharides through sequential secretion of enzymes targeting xylan and cellulose. Xylanase-enriched cocktail from M. cinnamomea N12 was more active on native and alkali­pretreated wheat straw than the commercial xylanases from Trichoderma reesei over temperatures ranging from 40 to 75 °C. Integration of M. cinnamomea N12 enzymes with the commercial cellulase preparation increased the glucose and xylose yields of alkali­pretreated wheat straw by 32 and 166%, respectively, with pronounced effects at elevated temperature. CONCLUSIONS: This study demonstrated the remarkable xylanase-producing ability and strategy of sequential lignocellulose breakdown of M. cinnamomea N12. A new process for the hydrolysis of lignocellulosic biomass was proposed, comprising thermophilic enzymolysis by enzymes of M. cinnamomea N12 followed with mesophilic enzymolysis by commercial cellulases. Developing M. cinnamomea N12 as platforms for thermophilic enzyme mixture production will provide new perspectives for improved conversion yields for current biomass saccharification schemes.

[Effect of pretreatment on storage and biogas production of baling wheat straw].

Long-term storage of crop straw is very important for biogas plant while pretreatment is always used to improve biogas production of crop straw. Feasibility of integrating the storage with pretreatment of baling wheat straw was studied. Changes of physicochemical properties and the biogas productivity of wheat straw obtained before and after 120 days storage were analyzed. The results showed that it was feasible to directly bale wheat straw for storage (control) and storage treatment had little effect on the physicochemical properties, structure and biogas productivity of wheat straw. After 120 day's storage, biogas production potential of the surface wheat straw of pile was decreased by 7.40%. Integrating NaOH pretreatment with straw storage was good for biogas production of wheat straw and the total solid (TS) biogas yield was increased by 7.02%-8.31% (compared to that of wheat straw without storage) and 5.68% -16.96% (compared to that of storage without alkaline pretreatment), respectively. Storage with urea treatment was adverse to biogas production of wheat straw and the contents of cellulose and hemicellulose of wheat straw were decreased by 18.25%-27.22% and 5.31%-16.15% and the TS biogas yield was decreased by 2.80%-7.71% after 120 day's storage. Exposing wheat straw to the air during the storage process was adverse to the conserving of organic matter and biogas utilization of wheat straw, but the influence was very slight and the TS biogas yield of wheat straw obtained from pile surface of control and urea treatment was decreased by 7.40% and 4.25%, respectively.

[Effect of alkaline post-treatment on physicochemical property of digested Spartina alterniflora].

Alkaline treatment is widely used for improving biogas production for lignocellulosic materials. This study was conducted to investigate the effect of alkaline treatment on physicochemical property of digested Spartina alterniflora (DSA). Fourier Transform Infrared Spectroscopy (FTIR), X-Ray diffraction patterns, proton Nuclear Magnetic Resonance Spectroscopy (1H-NMR), solid-state 13C-NMR Spectroscopy and some general indicators were used to analyze changes of the lignocellulosic structure and composition of NaOH-treated digested Spartina alterniflora. The results showed that, after NaOH treatment, surface lignin and some carbohydrate were destructed into lignin fragment, organic acids and some other small molecular organic matter, but the skeleton structure of lignin and cellulose of DSA were not destructed significantly. The crystalline of cellulose of DSA was transferred into biodegradable forms and content of crystalline of DSA and cellulose were increased after NaOH treatment. The results of 13C-NMR showed that methyl (CH3) and carboxylic C(COOH) groups of DSA were decomposed significantly.

[Effect of NaOH-treatment on dry-thermophilic anaerobic digestion of Spartina alterniflora].

In order to improve the biotransformation rate of lignocellulosic materials, sodium hydroxide (NaOH) was widely used to pretreat lignocellulosic materials. Effect of NaOH-treatment on dry-thermophilic anaerobic digestion of Spartina alternflora was studied by batch model under the temperature of 55 degrees C +/- 1 degrees C, at the initial total solid loading (TSL) of 20%. The results indicated that biogas production was inhibited by NaOH-treatment and improved by NaOH-treatment with water washed. The cumulative biogas yield of control (CK), NaOH-treated and NaOH-treated with water washed (NaOH + water) were 268.35 mL/g, 205.76 mL/g and 299.97 mL/g, respectively. The methane content of CK and NaOH + water treatments kept stable while fluctuation of NaOH-treated treatment during anaerobic digestion process was observed. Compared with CK and NaOH + water treatments, methane content of NaOH-treated treatment was improved by 5.30%. The content of hemi-cellulose and cellulose of S. alternifora decreased while content of lignin of S. alterniflora increased after 51-day anaerobic digestion. The crystallinity of cellulose of S. alterniflora increased after NaOH-treatment which was consistent to the result of FTIR. The lignocellulosic structure was destroyed and the biodegradability of S. alterniflora was increased by NaOH pretreatment. However, the amount of Na+ was taken into the anaerobic system, besides the high Na+ content in the plant itself which inhibited the anaerobic microorganisms. Therefore, NaOH-treatment is considered to be unsuitable for the anaerobic digestion of S. alterniflora.

[Effect of NaOH-treatment on advanced anaerobic biogasification of Spartina alterniflora].

In order to improve the biotransformation rate of Sparnina alterniflora, effect of NaOH-treatment on anaerobic dry-mesophilic digestion of Spartina alterniflora and feasibility of NaOH-treatment as a pretreatment of biogas residues of Spartina alterniflora for advanced anaerobic biogasification were conducted under lab-scale conditions. The results indicated that there was less improvement to biogas yield with NaOH-treatment and the cumulative biogas yield of Spartina alterniflora was 358.94 mL/g TS which was 92.42% to that of control (CK). However, the average methane content was improved slightly with 1.84% improvement. After solid-state pretreatment with 5% NaOH solution for 48 h, the biogas residue of Spartina alterniflora was used for advanced biogasification. This experiment was conducted under 35 degrees C +/- 1 degrees C with initial total solid loading of 8%. The cumulative biogas yield was 209.73 mL/g TS with 70.78% of average methane content, but the biotransformation rate was only 23.29% which was much lower than that of Spartina alterniflora. The fermentation type was propionic acid type fermentation. After two-phase fermentation treatment, cellulose content was decreased significantly while lignin and hemicellulose content were increased. The crystalinity of cellulose of biogas residue decreased after two-phase anaerobic fermentation which was consistent to result of FTIR. The comprehensive analysis of experiment indicated that biogas residue of Spartina alterniflora was still a good material for biogas production and NaOH-treatment was a good pretreatment for biogas production.