The wastewater from our factories, farms, and homes is increasingly filled with stubborn organic pollutants. Substances like industrial dyes, pesticides, and leftover pharmaceuticals do not break down easily, posing a profound threat to the environment and human health. Traditional cleaning methods often fall short, especially when pollutants are mixed or in low concentrations. In a recent review published in Highlights in Science, Engineering and Technology, author Jiashuo Liu explores the progress of one promising and sustainable solution: biochar.

The potential scale of Biochar resource is massive. China, for instance, produces over 900 million tons of straw waste annually. Converting this agricultural byproduct into biochar could not only manage waste but also sequester nearly 100 million tons of carbon, helping to mitigate climate change. This process turns readily available, inexpensive waste into a powerful tool for pollution management.

The power of biochar lies in its unique structure. It has a vast surface area and is filled with small pores and active spots that can catch and hold harmful substances. Liu explains that biochar uses several mechanisms to clean water. Its surface can have a negative charge, which uses static electricity to attract and bind positively charged pollutants like methylene blue dye. It also leverages a chemical attraction known as π−π interaction. This is where the flat carbon rings in biochar’s structure “stick” to similar ring structures found in many organic pollutants. Biochar can also form hydrogen bonds or use hydrophobic (water-repelling) forces to trap contaminants.

While raw biochar is effective, researchers have found that “modified” biochar works even better. Modification techniques are designed to enhance biochar’s natural properties. Physical modifications, such as treating it with steam, can create new pores or enlarge existing ones, dramatically increasing the available surface area for pollutants to stick to. Chemical modifications introduce new functional groups onto the biochar’s surface. These groups act like custom-designed hooks, giving the biochar a more targeted ability to capture specific types of pollutants that raw biochar might otherwise miss.

The results from modified biochar studies are striking and show significant, measurable success. The review highlights one study where biochar made from rice husks and chemically treated was able to remove rhodamine B dye at an impressive capacity of 250 milligrams per gram of biochar. In some tests, this type of modification led to the removal of over 95 percent of the dye from the water. The applications are not limited to dyes. In a real-world application, a pharmaceutical factory used a magnetic biochar made from coconut shells to treat its wastewater. This material removed 93 percent of the pharmaceutical pollution. Furthermore, it proved to be both durable and cost-effective: the factory reused the same biochar five times and found it still worked well, demonstrating its potential for long-term use.

Despite this promise, Liu notes that challenges remain. The quality and effectiveness of biochar can vary greatly depending on the source material—biochar from rice husks, for example, will not perform the same as biochar from wood chips. This makes it difficult to standardize. Additionally, many chemical modification methods are costly and require strong acids or metal salts, which can be hazardous to the environment. Real-world wastewater is also a complex soup of different pollutants (organic waste, heavy metals, etc.), which all compete for the same active sites on the biochar, sometimes reducing its overall effectiveness. Finally, researchers still need to find safer and easier ways to clean, or regenerate, the biochar after it is full of pollutants.

The future of biochar research is focused on overcoming these hurdles. Scientists are exploring “green” modification methods that use enzymes or beneficial microbes instead of harsh chemicals. There is also a push to create new, multi-functional biochars that can, for instance, remove pollutants and kill germs at the same time. By using computer models and machine learning, researchers hope to design better, more targeted biochar from the ground up, making this ancient material a high-tech solution for a cleaner future.

Source: Liu, J. (2025). Research Progress on the Application of Biochar in Adsorbing Organic Pollutants from Wastewater. Highlights in Science, Engineering and Technology, 157, 194–199.