Heavy metal contamination in water is a major environmental and public health concern, with sources ranging from industrial wastewater to agricultural runoff. Traditional cleanup methods like ion exchange and precipitation are often costly and difficult to implement on a large scale. However, a new review in Discover Chemical Engineering by Anu Kumari, Meenu Yadav, Archna Bhatia, and Rachna Bhateria presents a promising, sustainable, and cost-effective alternative: biocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More.

While biochar is an eco-friendly and effective adsorbent for heavy metals, its natural form has limitations due to a low specific surface area and limited functional groups. The review highlights that modifying biochar can significantly enhance its ability to adsorb heavy metals, with a remarkable increase in removal efficiency from 75% to 95% on average. Modification techniques are categorized into three main types: physical, chemical, and biological. Physical is simple and cost-effective, involving processes like ball milling and steam activation. Ball milling, for example, uses kinetic energy to create nanosized biochar, increasing its surface area and improving its adsorption capacity. Steam activation uses high temperatures (400-800°C) without oxygen to create more pores on the biochar’s surface, enhancing its capacity to adsorb heavy metals. One study found that steam-activated biochar was nearly twice as effective at removing lead ions as its non-activated counterpart. Chemical modification is a more common approach, though it can be more complex and expensive due to the use of reagents. This method treats biochar with acids, bases, or metal oxides to improve its 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, surface area, and functional groups. For instance, modifying biochar with a 1:1 solution of nitric and sulfuric acid can increase carboxyl functional groups, which improves its ability to adsorb cadmium ions. Base treatments, such as with potassium hydroxide (KOH), can lead to a larger surface area and higher oxygen content. A study showed that KOH-activated biochar from chicken feathers boosted cadmium and lead adsorption capacities by a striking 7.07 and 26.52 times, respectively, compared to pristine biochar.

Biological modification is a promising, cost-effective, and straightforward approach, especially for low concentrations of heavy metals. This method uses microorganisms like algae, bacteria, and fungi, which have functional groups like hydroxyl, carboxyl, and amino groups on their surfaces that can bind to heavy metals. When microbial biofilms from oil sand processed water were colonized on biochar, they increased arsenic adsorption by 6-7 times compared to unmodified biochar. While the efficiency of biological modification is lower than chemical treatments alone, combining the two creates a sustainable and green adsorbent.

The enhanced heavy metal removal by modified biochar is attributed to several mechanisms, including electrostatic attraction, ion exchange, and complexation. For example, the study found that modified biochar’s functional groups, like carboxyl and hydroxyl groups, can exchange ions with heavy metal cations or form strong complexes, effectively pulling them out of the water. The study also highlights the importance of biochar regeneration and reusability, which are critical for lowering operating costs and promoting sustainable development.

The review concludes that modified biochar is a highly effective and sustainable solution for heavy metal remediation, aligning with the United Nations Sustainable Development Goal 6 for Clean Water and Sanitation. While challenges remain, such as scaling up production and optimizing for complex wastewater conditions, the research presented provides a clear roadmap for future efforts to make water treatment more efficient and environmentally friendly.

Source: Kumari, A., Yadav, M., Bhatia, A., Sharma, M., & Bhateria, R. (2025). A review and bibliometric analysis on recent modification of biochar for effective and sustainable remediation of heavy metals in aqueous medium. Discover Chemical Engineering, 5(21).