Biochar applications in microplastic and nanoplastic removal: mechanisms and integrated approaches

Microplastics (MPs) and nanoplastics (NPs) are increasingly present in aquatic environments due to their widespread use across various sectors. These contaminants can cause adverse effects on exposed organisms, exacerbated by their potential for bioaccumulation and their ability to transport other pollutants. Conventional water treatment plants are ineffective at removing MPs and NPs, highlighting the need for alternative solutions. In this context, biochar emerges as a promising material for removing MPs and NPs from water due to its advantageous properties, such as high specific surface area, large pore volume, abundance, and versatility. Additionally, producing biochar from biomass waste ensures a low-cost and environmentally sustainable material. This review explores the application of biochar and its composites in the removal of MPs and NPs from water, exploring its applications in adsorption, filtration, and aggregation. The discussion extends to the environmental factors that influence the performance of biochar in water treatment, such as pH, temperature, and the presence of competing contaminants. Furthermore, the potential synergies between biochar and other water treatment technologies, such as coagulation–flocculation and anaerobic granular sludge, are discussed along with methods for regenerating biochar to restore its effectiveness. Notwithstanding, emphasis is also given to the possible drawbacks of negligent use of biochar, such as harmful contaminants such as polycyclic aromatic hydrocarbons (PAHs) and metal that may leach from the material. Despite these hindrances, biochar remains a valuable tool in enhancing the efficiency of water treatment systems for MPs and NPs removal, offering a sustainable and efficient approach to water treatment.