The journal Processes featured a critical review by Elena Olivera-Begue, Daniel Gonzalez, and Antoni Sanchez exploring how biochar acts as a powerful additive to improve the environmental performance of composting. As the world moves toward a circular economy, biotechnological processes for managing organic waste are becoming more prominent. Composting is a key technology in this transition, but its implementation is often limited by the release of odors and greenhouse gases. Biochar offers a sustainable solution to these challenges. By adding this stable form of charcoalCharcoal is a black, brittle, and porous material produced by heating wood or other organic substances in a low-oxygen environment. It is primarily used as a fuel source for cooking and heating.   More to the composting mass, facility operators can significantly reduce the environmental footprint of waste management while creating a superior organic amendment for sustainable agriculture.

Research indicates that biochar possesses a unique combination of high 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 and surface area that makes it an exceptional adsorbent for a variety of gases. One of the most significant findings involves the reduction of ammonia, which is the primary gas emitted during composting. Excessive ammonia release not only causes odor nuisance but also decreases the quality of the compost by depleting essential nitrogen. Studies have documented ammonia reductions ranging from as low as 10 percent to as high as 89 percent, depending on the 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 used and the ratio of biochar to waste. Furthermore, biochar has demonstrated a remarkable ability to mitigate volatile organic compounds, with some experiments showing a 70 percent decrease in emissions. These compounds are often responsible for the unpleasant smells associated with large-scale waste treatment facilities, and their reduction is vital for public acceptance.

The mitigation of greenhouse gases like methane and nitrous oxide is another critical benefit of using biochar in composting. Methane typically forms in anaerobic zones where there is a lack of oxygen in the composting matrix. Biochar helps solve this problem by increasing the physical porosity of the mixture, which improves air circulation and oxygen transport throughout the pile. This shift in the physical environment limits the activity of methane-producing bacteria. For nitrous oxide, a potent greenhouse gas with nearly 300 times the global warming potential of carbon dioxide, biochar helps by influencing the biological nitrogen cycle. It encourages the complete transformation of nitrogen into harmless nitrogen gas, thereby preventing the escape of harmful nitrous oxide into the atmosphere. This dual effect helps composting plants achieve a much lower overall carbon footprint.

Beyond gas mitigation, biochar contributes to the physical and biological efficiency of the composting process itself. In large-scale trials, biochar has been observed to help retain heat, leading to higher process temperatures that can more effectively break down organic matter and eliminate pathogens. It also acts as a stabilizer for nutrients, increasing the ion exchange capacity of the final compost. This means the finished product can better hold onto essential minerals, making it a more effective substitute for synthetic mineral fertilizers. While most current research has been conducted in small laboratory settings, these initial findings suggest that biochar could transform composting from a basic waste treatment method into a sophisticated biorefinery process that produces high-value, eco-friendly soil conditioners.

Despite these clear benefits, the review highlights that further research is needed to standardize the use of biochar in the waste management sector. Scientists emphasize the need for consensus on the optimal dosage and a better understanding of the underlying microbiological mechanisms. Many current studies use different units to report biochar ratios, which makes it difficult for other researchers to reproduce results or for industry professionals to calculate the economic feasibility of the practice. Moving forward, the focus must shift toward full-scale industrial trials to understand how biochar behaves in massive composting piles over long periods. As these technical challenges are overcome, biochar co-composting stands ready to become a reliable, scalable technology that bridges environmental remediation with the productive reuse of agricultural and municipal waste.

Source: Olivera-Begue, E., Gonzalez, D., & Sanchez, A. (2025). A critical review of the role of biochar in mitigating atmospheric emissions during the composting of organic waste. Processes, 14(71).