In the journal Biochar, Wu et al. explore the promising potential of biochar-supported microbial systems as a solution for remediating persistent organic pollutants. These pollutants, which include polycyclic aromatic hydrocarbons (PAHs), pesticides, and chlorinated solvents, are widespread toxicants that pose serious threats to the environment and human health. Conventional methods for remediation, such as physicochemical treatments, are often expensive and inefficient, while traditional bioremediation struggles with low microbial survival rates and sensitivity to environmental changes. The novel strategy reviewed by the authors overcomes these challenges by combining the excellent adsorption capacity of biochar with the catalytic power of pollutant-degrading microorganisms.

Biochar offers a porous structure and various functional groups that effectively immobilize pollutants. More importantly, it acts as an ideal microhabitat and protective carrier for microbial communities, promoting their growth and degradation capabilities. This symbiotic relationship, where biochar concentrates nutrients and substrates while sheltering the microbes from environmental stressors like high toxicity or desiccation, is the core of the system’s enhanced performance. For instance, the degradation efficiency of atrazine was improved by approximately 20−40% compared with using free strains alone when applied in soil.

Different techniques are used to construct these biochar-supported microbial systems, each with distinct advantages for various scenarios. The simplest and most common method is adsorption, which relies on non-specific forces between the microbes and the biochar matrix. While cost-effective and operationally simple, adsorption suffers from weak binding strength, making microbes prone to desorption under high environmental stress. To address this, covalent bonding uses chemical reactions between the functional groups on the biochar surface and microbial cells to create a high stability and strong binding strength. This makes it particularly suitable for continuous-flow reactors or high-toxicity wastewater. For highly toxic or unstable environments, entrapment is a widely used protective technique, embedding microorganisms within the porous structure of biochar or high-molecular-weight organic compounds like sodium alginate gels. This technique protects the microbes and extends their biodegradation lifespan, although mass transfer blockage can occur for large-molecule pollutants. Lastly, biofilm formation allows microorganisms to naturally attach and proliferate on the biochar surface, providing enhanced resistance to external stress and often showing higher pollutant removal efficiency; for example, a biochar-loaded functional bacterial biofilm removed over 99% of atrazine within 48 hours.

The system’s effectiveness is influenced by multiple factors. The physicochemical properties of the biochar are key, as they determine both pollutant adsorptionBiochar has a remarkable ability to attract and hold onto pollutants, like heavy metals and organic chemicals. This makes it a valuable tool for cleaning up contaminated soil and water.   More capacity and microbial colonization. The 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 temperature is critical, as increasing it generally enhances surface area and porosityPorosity of biochar is a key factor in its effectiveness as a soil amendment and its ability to retain water and nutrients. Biochar’s porosity is influenced by feedstock type and pyrolysis temperature, and it plays a crucial role in microbial activity and overall soil health. Biochar More. Environmental conditions also play a significant role. Biochar’s inherent alkalinity allows it to buffer and stabilize soil 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, which is particularly beneficial since most degrading microorganisms thrive in a near-neutral pH range of 6.0−8.0. While higher temperatures generally accelerate microbial metabolism, biochar provides a stable microenvironment, enabling functional microorganisms to maintain high degradation efficiency even at temperatures like 40∘C, demonstrating better thermal adaptability than free cells. Furthermore, while a moderate initial pollutant concentration promotes microbial growth by providing abundant carbon sources, excessively high concentrations can be toxic, inhibiting microbial activity.

Biochar-supported microbial systems have been successfully applied to remove pollutants in both aquatic and soil environments, addressing industrial wastewater, domestic sewage, and agricultural contamination. For instance, a chitosan-biochar composite carrier successfully encapsulated a microbial consortium for crude oil-contaminated soil remediation, achieving nearly 75% crude oil degradation and improving the soil microecosystem within 45 days.

Despite these demonstrable successes, challenges remain, including the need for large-scale economic feasibility evaluation, ensuring long-term microbial viability in the field, and managing potential antagonistic relationships between coexisting microbial species. Additionally, the strong adsorption of certain organic pollutants by biochar may sometimes inhibit their bioavailability for the immobilized microorganisms, highlighting the need for optimization. Future research should focus on engineering novel biochar materials with specific functionalities and using synthetic biology to enhance microbial strains for complex field conditions. By addressing these gaps, biochar-supported microbial systems can become a scalable and sustainable strategy for environmental rehabilitation, supporting circular economic goals.

Source: Wu, H., Huo, Y., Qi, F., Zhang, Y., Li, R., & Qiao, M. (2025). Biochar-supported microbial systems: a strategy for remediation of persistent organic pollutants. Biochar, 7(1), 113.