Key Takeaways & Executive Findings
- •• • Optimal THP conditions for corn straw: solid-to-liquid ratio 51.0–57.5 mg·mL−1, time 74–81 min, temperature 182.5–197.5 °C, yielding a 66.7% increase in cumulative methane production (from 218.0 to 362.9 mL·g−1 VS) compared to untreated straw. • • THP significantly alters biomass structure: lignin content drops from 21.5% to 8.3% and crystallinity index (CrI) from 70.83% to 61.95%, enhancing cellulose accessibility and microbial degradation. • • Inhibitory derivatives (furfural, 5-methylfurfural, phenol) are generated at concentrations up to 23.14 mg·L−1, with a theoretical combined inhibition rate of 7.26%—far lower than the 66.7% promotion effect, confirming process viability. • • Dose-response analysis reveals IC50 values for furfural, phenol, and 5-methylfurfural as 0.0471±0.0092, 0.3201±0.0732, and 0.2788±0.1101 g·L−1, respectively, indicating that derivative inhibition could be further mitigated to enhance methane yields.
Abstract
Low hydrolysis efficiency is a core bottleneck in anaerobic digestion (AD) of lignocellulosic agricultural residues, limiting methane production and resource utilization. This study optimized thermal hydrolysis pretreatment (THP) of corn straw (CS) using response surface methodology (RSM) to enhance methane yield. The optimal conditions were determined as solid-to-liquid ratio of 51.0–57.5 mg·mL−1, pretreatment time of 74–81 min, and temperature of 182.5–197.5 °C. Under the optimal combination (52.3 mg·mL−1, 78.4 min, 191 °C), cumulative methane yield increased from 218.0 to 362.9 mL·g−1 VS, a 66.7% improvement over untreated CS. Characterization via XRD, FTIR, and SEM revealed that THP disrupted the lignocellulosic structure, reducing lignin content from 21.5% to 8.3% and crystallinity index (CrI) from 70.83% to 61.95%. Inhibitory derivatives generated during THP included furfural (1.69 mg·mL−1), 5-methylfurfural (2.44 mg·mL−1), and phenol (23.14 mg·L−1), with a theoretical combined inhibition rate of 7.26%. The promotion effect on methane production (66.7%) far exceeded the theoretical inhibition (7.26%), indicating that THP under optimized conditions is effective and environmentally controllable. This study provides a systematic framework for optimizing THP parameters to maximize methane production from agricultural residues.
1. Introduction
Lignocellulosic biomass, such as corn straw, represents a vast renewable resource, yet its recalcitrant structure—characterized by lignin–carbohydrate complexes—limits hydrolysis, the rate-limiting step in anaerobic digestion. Conventional pretreatment methods (physical, chemical, biological) suffer from high energy demands, toxic byproducts, or slow kinetics, hindering commercial viability. Thermal hydrolysis pretreatment (THP) offers a chemical-free alternative, but its efficacy hinges on precise optimization of temperature, time, and solid-to-liquid ratio to maximize methane yield while minimizing energy input and inhibitory compound formation.
This study addresses the bottleneck by employing response surface methodology (RSM) to systematically optimize THP parameters for corn straw, achieving a 66.7% increase in methane yield. The research quantifies structural changes (lignin reduction, crystallinity decrease) and inhibitory byproduct generation, demonstrating that the promotion effect vastly outweighs inhibition. These findings provide a data-driven framework for scaling THP in agricultural waste-to-energy systems, balancing efficiency and environmental safety.
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LI Zhibo, XIE Juan, HAN Yongchen, LI Su, WANG Xiaochang, LI Yuyou, CHEN Rong, XING Baoshan (2026). Optimization of Thermal Hydrolysis Pretreatment of Corn Straw for Enhanced Methane Production. Chinese Journal of Environmental Engineering. https://doi.org/10.12030/j.cjee.202510029
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Frequently Asked Questions
What are the optimal THP conditions for corn straw, and how were they determined?
Optimal conditions were identified via RSM as solid-to-liquid ratio 51.0–57.5 mg·mL−1, time 74–81 min, and temperature 182.5–197.5 °C. The central point (52.3 mg·mL−1, 78.4 min, 191 °C) yielded a 66.7% increase in methane production, validated experimentally.
How does THP affect the lignocellulosic structure of corn straw?
THP reduces lignin content from 21.5% to 8.3% and crystallinity index from 70.83% to 61.95%, as confirmed by XRD, FTIR, and SEM. This disruption increases porosity and cellulose accessibility, enhancing enzymatic hydrolysis and microbial degradation.
What inhibitory derivatives are formed during THP, and what is their impact on methane production?
THP generates furfural (1.69 mg·mL−1), 5-methylfurfural (2.44 mg·mL−1), and phenol (23.14 mg·L−1). Their combined theoretical inhibition rate is 7.26%, based on IC50 values of 0.0471, 0.3201, and 0.2788 g·L−1, respectively. This inhibition is negligible compared to the 66.7% promotion effect.
What are the energy and economic implications of THP at optimal conditions?
THP operates at 191 °C and pressures up to 1.925 MPa, requiring energy input. However, the 66.7% increase in methane yield can offset energy costs, but a detailed energy balance and techno-economic analysis are necessary to confirm net energy gain at scale.
Can the findings be scaled to industrial applications?
The study provides a validated parameter range for THP, but scaling requires consideration of reactor design, heat recovery, and continuous operation. The low inhibitor levels suggest minimal downstream treatment, but pilot-scale trials are needed to assess practical feasibility and cost-effectiveness.
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