Background
Lignocellulose represents the most abundant renewable carbon source on Earth. However, lignin, one of its three major components, is often burned as waste due to extremely low utilization efficiency, resulting in resource waste and environmental pollution. Although lignin serves as an excellent precursor for the production of activated carbon (AC), pure carbon materials exhibit weak surface activity. Their adsorption performance typically requires heteroatom (e.g., nitrogen) doping processes relying on external chemical reagents and high energy consumption, which severely restricts their green and sustainable applications.
Meanwhile, Bacillus coagulans, an industrially competitive strain, generates a large amount of nitrogen-rich waste microbial biomass during the fermentative production of lactic acid from lignocellulosic hydrolysates. Therefore, exploring the direct use of such waste biomass as a natural, low-cost nitrogen source for reagent-free in-situ co-pyrolysis with lignin residues has become a highly promising strategy to break through the bottleneck of green modification of activated carbon and achieve high-value full-component utilization of biomass.
Biorefinery Strategy for Lignocellulosic Biomass
Lignocellulosic biomass is the most abundant renewable resource on Earth, but traditional biorefinery processes suffer from low lignin utilization and microbial inhibitor toxicity in hydrolysates, limiting economic and ecological benefits. To address these issues, the research team from Beijing University of Chemical Technology published a study in Separation and Purification Technology, proposing an innovative closed-loop strategy of "turning waste into treasure and in-situ recycling".
The core strategy involves in-situ co-pyrolysis of lignin residues (from enzymatic hydrolysis) and nitrogen-rich waste cells ofBacillus coagulans (the main strain for lactic acid fermentation) at 800°C, without any external chemical reagents. This process successfully synthesizes high-performance nitrogen-doped activated carbon (N-NAC), which is directly reused for in-situ detoxification of biomass hydrolysates.
Key results: The optimal N-NAC (8-3-NAC) has a BET specific surface area of 696.42 m²/g, a total pore volume of 0.7455 cm³/g, and a nitrogen doping content of 2.04%. It exhibits excellent adsorption capacity for gallic acid (a typical phenolic inhibitor) up to 686.98 mg/L, with superior cyclic stability (2 more adsorption-desorption cycles than commercial activated carbon). After detoxification with 8-3-NAC, the hydrolysate significantly relieves microbial inhibition, shortening the fermentation cycle by 40 hours, increasing xylose utilization by 31.43%, and raising lactic acid titer to 155.45 g/L (17.0% higher than the non-detoxified group).
The closed-loop system achieves full-component, zero-waste utilization of lignocellulosic biomass: 1000 kg of dry corn stover produces 449 kg of lactic acid and 72.3 kg of high-performance activated carbon, eliminating emissions of 241 kg of lignin residues and 125 kg of microbial waste. This strategy verifies the feasibility of green co-production of high-value chemicals and functional carbon materials, establishing a sustainable paradigm for zero-waste biorefinery.
Full text link:https://doi.org/10.1016/j.seppur.2025.136012