Dynamics of fermentation quality, physiochemical property and enzymatic hydrolysis of high-moisture corn stover ensiled with sulfuric acid or sodium hydroxide
Introduction
Corn stover is one of the most common cereal residues with an annual biomass yield of over 1.13 billion tons around the world (FAOSTAT, 2017), the utilization of which in biofuel/livestock production would eminently help to combat with energy crisis and feed shortage. Meanwhile, its resource utilization would accelerate the rotation of crops, increase the utilization efficiency of limited land resource and avoid open burning causing environmental problems (Sun et al., 2019, Zhao et al., 2019). Large amounts of studies prove that fresh corn stover with relatively high WSC content and low buffer capacity is favorable for ensiling storage (Mcdonald et al., 1991, Sun et al., 2019). However, its high moisture (>75%) might cause large dry matter loss due to leachate formation and the activity of undesirable organisms like Clostridia. Meanwhile, the resistant structure of lignocellulosic biomass is the main obstacle for its industrial utilization (Venturin et al., 2018a, Venturin et al., 2018b). Thus, an economically feasible pretreatment and storage method would eminently promote the utilization of corn stover.
Other than a preservation method, ensiling is also a beneficial pretreatment for lignocellulosic materials (He et al., 2019a, He et al., 2019b, He et al., 2019c, He et al., 2019d), which could carry out the effects of kinds of pretreatments by combination with chemical reagents, fibrolytic enzymes or microbes. Of the alternatives, ensiling with addition of acids or alkalis seems to be a good choice given that the addition of chemical reagents would directly change the pH thus inhibiting microbial activity as well as break down bond linkages of lignocellulose whereby increasing biomass usability (He et al., 2019a, He et al., 2019b, He et al., 2019c, He et al., 2019d, Shetty et al., 2016, Singh et al., 2015, Venturin et al., 2018a, Venturin et al., 2018b). However, though such “solid state” chemical pretreatments are not as efficient as the common “wet state” pretreatments in a short time, where the treatment time is negatively related to chemical dose (Zheng et al., 2009), they own the advantages of no waste liquid, less nutrient loss and no additional infrastructure (Pang et al., 2008). Thus, to figure out the best dose of agents and optimum unsealing time, it is necessary to monitor the dynamic changes during ensiling preservation.
So far, pretreating lignocellulosic biomass with acids or alkalis has been largely studied, but little information about the dynamics of physiochemical property and usability of the materials, especially in solid state pretreatment, is available, the illustration of which would help to make decisions in practical production. Therefore, high-moisture corn stover was ensiled with addition of H2SO4 (0.3% and 0.6% on a fresh matter basis) and NaOH (0.5% and 1.0%) in the present study, and ensiling characteristics, carbohydrate components and lignocellulosic structure as well as enzymatic saccharification were analyzed on day 3, 7, 15, 30 and 60 of ensiling storage.
Section snippets
Raw material and silage preparation
Fresh corn stover (dough stage) was manually harvested on the experimental field of South China Agricultural University (Guangzhou, China) and immediately chopped into 1–2 cm by a handy cutter in lab. Then the prepared material was allocated to the ensiling treatments either with addition of 0.3%, 0.6% H2SO4 (on a fresh matter basis; H1, H2) or 0.5%, 1.0% NaOH (Na1, Na2), meanwhile blank silage without addition was set as control (CK). Specifically, 200 g materials (mainly based on the capacity
Characteristics of the fresh corn stover before ensiling
The corn stover used in the present study had a DM content (16.38%), far below the ideal value (30%-35%) for good silage (Guyader et al., 2018). In general, high moisture is believed to be not beneficial to good silage production in that it would benefit the activities of plant enzymes and microorganisms at the early stage of ensiling whereby resulting in more DM loss, other than potential effluent loss (He et al., 2019a, He et al., 2019b, He et al., 2019c, He et al., 2019d). On the contrary,
Conclusions
The present results showed that the addition of 0.6% H2SO4 reduced dry matter loss and ammonia-N content of high-moisture corn stover during ensiling, whereas it was converse for 0.5% or 1.0% NaOH treatment. Chemical and structural analyses indicated that hemicellulose content was dramatically decreased by the addition of 0.6% H2SO4 or 1.0% NaOH. Enzymatic hydrolysis revealed that H2SO4 and NaOH treatments improved saccharification with the most WSC yield in 0.6% H2SO4 treatment. This study
CRediT authorship contribution statement
Liwen He: Conceptualization, Methodology, Writing - review & editing. Hongjian Lv: Methodology, Investigation. Cheng Wang: Investigation, Resources. Wei Zhou: Data curation, Writing - original draft. Ruiqi Pian: Investigation, Formal analysis. Qing Zhang: Conceptualization, Methodology, Visualization. Xiaoyang Chen: Validation, Supervision.
Declarations of Competing Interest
We wish to confirm that there are no known conflicts of interest associated with this publication and there has been no significant financial support for this work that could have influenced its outcome.
Acknowledgements
This work was financially supported by 2018 Big Pig-producing County Reward Funds (Research and promotion of key technologies for healthy feeding of pigs and resource utilization of manure pollution), Guangdong Young Innovative Talents Project (Grant No. 218220), National Key Research & Development Projects (Grant No. 2017YFD0502102-02), Guangzhou Science Forestry Technology and Innovation Commission (Grant No. 2018KJCX001).
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