Key Takeaways & Executive Findings
- •• • Biochar addition at 1 g/L increased total VFAs concentration to 2150 mg/L, a 30.2% improvement over the control (1651 mg/L), demonstrating a direct yield enhancement in a 7-day fermentation. • • The biochar-amended system maintained pH stability, preventing excessive acidification, which is critical for sustaining acidogenic microbial activity and avoiding process inhibition. • • Biochar's porous structure adsorbed soluble ions, leading to lower electrical conductivity compared to the control, indicating a modified ionic environment that may favor microbial metabolism. • • Microbial community analysis showed that biochar enriched key acidogenic genera (Defluviitoga and norank_f__Family_XI) while reducing Streptococcus abundance, optimizing the microbial consortium for VFAs production.
Abstract
This study investigated the effects of biochar on volatile fatty acids (VFAs) production, biogas composition, physicochemical properties of the fermentation broth, and microbial community structure through batch anaerobic fermentation experiments using food waste as the substrate. The results demonstrated that the addition of biochar (1 g/L) significantly enhanced VFAs production, with the total VFAs concentration reaching 2150 mg/L in the biochar group, which was 30.2% higher than that of the control group (1651 mg/L). Acetic acid, propionic acid, and butyric acid were identified as the primary VFAs components. In the fermentation system, biochar exhibited a notable pH-buffering effect, stabilizing the fermentation environment. Additionally, its porous structure adsorbed ions during the fermentation process, resulting in a slightly lower electrical conductivity compared to the control group. Microbial community analysis revealed that biochar addition enriched key acidogenic bacteria, such as Defluviitoga and norank_f__Family_XI, optimizing the microbial community structure, and thereby facilitating organic acid production. In summary, biochar effectively promoted the efficient accumulation of VFAs during anaerobic fermentation of food waste by improving the fermentation microenvironment, enhancing system buffering capacity, and regulating microbial community composition. These findings provide theoretical support for sustainable enhancement of resource utilization of food waste.
1. Introduction
The escalating generation of food waste (FW), exceeding 100 million tons annually in China, poses significant environmental and economic burdens. Conventional disposal methods, such as landfilling and incineration, are increasingly untenable due to greenhouse gas emissions and resource inefficiency. Anaerobic digestion offers a promising route for FW valorization, yet its efficiency in producing volatile fatty acids (VFAs)—key precursors for biodegradable plastics and carbon sources for biological nutrient removal—is often limited by low yields and process instability. This bottleneck hinders the industrial adoption of FW fermentation for VFAs recovery.
Biochar, a carbonaceous porous material, has emerged as a cost-effective additive to enhance anaerobic digestion. Prior studies have demonstrated its efficacy in boosting methane production, but its role in the acidogenic phase, particularly for VFAs accumulation, remains underexplored. This study addresses this gap by systematically evaluating the impact of biochar on VFAs yield, fermentation broth properties, and microbial community dynamics in FW fermentation. The findings elucidate the mechanisms by which biochar improves process performance, offering a strategic approach to enhance FW resource recovery.
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SHI Fangying, CHEN Jingting, YANG Wanli, XU Qiyong, WANG Ning (2026). Mechanism of Biochar for Enhancing Volatile Fatty Acids Production during Anaerobic Fermentation of Food Waste. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202607019
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Frequently Asked Questions
What is the optimal biochar dosage for maximizing VFAs yield, and how does it compare to other reported additives?
In this study, a biochar dosage of 1 g/L resulted in a 30.2% increase in total VFAs concentration (2150 mg/L vs. 1651 mg/L control). This dosage is relatively low compared to other studies, suggesting a cost-effective enhancement. However, the optimal dosage may vary with substrate composition and reactor configuration; further optimization is recommended.
How does biochar addition affect the pH profile and buffering capacity of the fermentation system?
Biochar exhibited a notable pH-buffering effect, preventing a sharp decline in pH that typically inhibits acidogenic bacteria. This stabilization is attributed to the alkaline nature of biochar and its ion-exchange capacity, which helps maintain a favorable pH range for VFAs production.
What are the implications of reduced electrical conductivity in the biochar-amended system?
The lower electrical conductivity in the biochar group suggests that biochar adsorbed soluble ions, potentially reducing osmotic stress on microbial cells. This could enhance microbial activity and stability, contributing to higher VFAs yields.
Can the observed microbial community shifts be attributed solely to biochar addition, and what is the functional significance?
Biochar addition enriched key acidogenic genera (Defluviitoga and norank_f__Family_XI) and reduced Streptococcus, indicating a selective pressure that favors efficient VFAs producers. This shift likely enhances metabolic pathways for VFAs generation, as evidenced by the increased yields.
What are the scalability prospects of this biochar-enhanced fermentation process for industrial application?
The use of low biochar dosage (1 g/L) and the demonstrated yield improvement suggest potential for cost-effective scale-up. However, continuous-flow studies and techno-economic analyses are needed to assess long-term stability, biochar recycling, and overall process economics.
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