Rapid expansion within the traditional Chinese medicine industry has generated massive volumes of spent herb residues, creating substantial disposal challenges for municipal waste management networks. Concurrently, aquatic and soil environments face growing risks from persistent heavy metal contamination and complex organic pollutants like pharmaceuticals, synthetic dyes, and pesticides. Because traditional herbal waste contains an average lignocellulosic content of 68.2 percent—a level comparable to common agricultural residues like wheat straw and sugarcane bagasse—it serves as an exceptional feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More for high-value carbon materials. Transforming these waste streams into functional carbon frameworks aligns with global circular economy goals and low-carbon remediation strategies.

Thermal conversion processes, including slow pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More and hydrothermal carbonization, convert raw herbal dregs into porous biochars with high specific surface areas often exceeding 500 square meters per gram. Production temperatures between 200 and 800 degrees Celsius govern the final carbon structure: higher temperatures increase ashAsh is the non-combustible inorganic residue that remains after organic matter, like wood or biomass, is completely burned. It consists mainly of minerals and is different from biochar, which is produced through incomplete combustion.   Ash Ash is the residue that remains after the complete More content, pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More, and micropore volume while lowering overall product yield and elemental hydrogen-to-carbon ratios. The resulting materials possess abundant oxygen-containing surface functional groups, such as phenolic hydroxyl and carboxyl groups, which provide primary active sites for contaminant binding.

Engineered modifications further enhance the performance, selectivity, and recovery of herbal biochars. Impregnating biochar matrices with magnetic iron oxides simplifies solid-liquid separation from treated water using external magnetic fields. Nanomaterial hybridizations, such as titanium dioxide loading or nitrogen doping, create highly active catalytic sites capable of generating reactive oxygen species. In advanced oxidation systems, these modified biochar catalysts activate peroxymonosulfate to achieve over 99 percent degradation of antibiotics like tetracycline within 60 minutes. Furthermore, because herbal residues retain 30 to 50 percent of their original bioactive compounds after decoction, tailored carbonization processes can yield multifunctional carbon dots with inherent antibacterial and antioxidant capabilities.

Heavy metal removal proceeds primarily through surface complexation, cation exchange, and electrostatic attraction, alongside reduction-precipitation pathways that convert toxic high-valence ions like hexavalent chromium into insoluble forms. Organic contaminant removal relies on synergistic physical and chemical interactions, including pi-pi electron donor-acceptor interactions, hydrogen bonding, and pore filling. While lab-scale evaluations demonstrate extraordinary sorption capacities, expanding herbal biochar applications requires further research into competitive multi-pollutant dynamics, long-term environmental stability, and full life-cycle safety assessments.

Source: Tan, Y., Liu, Y., Chu, T., Wang, C., Gu, Y., Chen, C., Fu, W., Yuan, J., Chen, H., & Peng, C. (2026). From waste to resource: TCM herb residue-derived biochar as a multifunctional material for environmental remediation. Biochar X, 2, e010.