The scientific community has long recognized biochar as a versatile carbon-rich material capable of enhancing soil fertility, managing biomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More waste, and trapping atmospheric carbon dioxide. When mixed into agricultural lands, this material enhances structural stability, provides a hospitable habitat for beneficial microbes, and helps alleviate the severe stress caused by salt accumulation. Traditionally, researchers believed that the properties of the material and its associated chemical risks were almost exclusively dictated by the choice of plant or animal waste used as 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 and the maximum temperatures reached during the heating process. However, this comprehensive review published in Preprints.org by Omotayo E. Ojewumi, Gang Chen, and Modupe E. Ojewumi shifts the focus toward process engineering, demonstrating that the structural design of the processing equipment is just as critical for determining final safety and performance.

A significant hurdle preventing the widespread adoption of biochar in commercial farming is the inadvertent generation of polycyclic aromatic hydrocarbons, which are highly persistent and potentially carcinogenic environmental toxins. The authors highlighted a pivotal shift in understanding how these contaminants develop during the oxygen-free heating process known as 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. While older assumptions implied that these toxins formed directly within the solid carbon phase, recent evidence confirms that they actually originate from gas-phase reactions when volatile vapors recombine. As the entire system cools down after processing, these vaporized pollutants deposit directly onto the surfaces and lock inside the open pores of the newly formed 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.

Because these dangerous chemical compounds condense during the cooling phase, the amount of time the hot vapors spend interacting with the solid carbon determines the final level of contamination. If volatile gases are allowed to linger inside the processing chamber for extended periods, they undergo secondary reactions that drastically increase the concentration of toxins. Systems engineered to actively strip away volatile organic compounds and prevent the stagnation of gases can drastically minimize the accumulation of hazardous residues. This insight dispels the common scientific belief that modifying temperature alone is the only way to control pollution, proving instead that smart engineering can bypass the typical trade-offs between agricultural efficacy and ecological safety.

When applied safely, high-quality biochar provides exceptional benefits for heavily degraded environments, particularly salt-affected agricultural zones. The material alters critical ion dynamics by absorbing soluble salts and facilitating the leachingLeaching is the process where nutrients are dissolved and carried away from the soil by water. This can lead to nutrient depletion and environmental pollution. Biochar can help reduce leaching by improving nutrient retention in the soil.   More away of excess sodium, which otherwise stunts plant growth. It simultaneously releases essential plant nutrients like calcium and magnesium, which rebalance soil chemistry and reduce overall salt stress indicators. This structural support fosters healthier microbial ecosystems, which speeds up natural nutrient cycling and boosts overall crop yields.

Despite these clear agronomic advantages, the long-term environmental impacts of applying contaminated materials to food-producing soils require careful management. Most existing regulatory frameworks fail to account for the complex differences in chemical structures, creating an urgent need for multi-objective optimization strategies that weigh fertilization benefits against toxicological risks. Moving forward, the development of safe-by-design production technologies that couple gas-stripping mechanisms with specific local soil conditions will allow farmers to utilize this powerful material safely, securing sustainable agricultural yields without introducing unintended ecological hazards.

Source: Ojewumi, O. E., Chen, G., & Ojewumi, M. E. (2026). Biochar production: Toward safe, effective, and sustainable agriculture. Preprints.org.