Global plastic accumulation presents an escalating threat to aquatic ecosystems, as microscopic plastic particles smaller than five millimeters disperse across freshwater and marine environments. These persistent pollutants act as secondary pollution vectors by absorbing heavy metals, antibiotics, and toxic organic compounds, subsequently transferring hazardous payloads into aquatic food webs and human water supplies. Conventional municipal and industrial wastewater treatment processes struggle to eliminate these microscopic particles, typically achieving removal rates between forty and seventy-eight percent while demanding significant energy inputs and generating secondary waste. To address this environmental challenge, research into low-cost, circular-economy adsorbents has expanded rapidly, positioning biochar as a leading candidate for large-scale water purification.

Biochar is a carbon-rich porous material produced through the oxygen-limited thermal breakdown of 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 such as agricultural waste, wood chips, sewage sludge, and microalgae. Unmodified or pristine biochars exhibit modest baseline microplastic removal efficiencies due to limited surface functionality and negative surface charges that cause electrostatic repulsion against weathered plastic particles. However, surface-engineering techniques fundamentally transform material performance. By modifying biochar through chemical activation, surface oxidation, magnetic particle impregnation, and heteroatom doping, scientists create specialized architectures tailored for targeted contaminant capture. Amine functionalization using coupling agents reverses negative surface charges, allowing for strong electrostatic attraction alongside hydrophobic interactions and physical pore filling.

The review highlights that physical entrapment and pore-scale filtration dominate the capture of larger microplastics, whereas smaller microplastics and nanoplastics are primarily bound through complex interfacial chemical interactions. Aromatic ring structures on high-temperature biochars enable strong electron interactions with synthetic polymers like polystyrene, while oxygenated functional groups foster hydrogen bonding with polar or weathered plastics. Beyond simple particle capture, advanced nanocomposite biochars incorporate metal oxides like iron or manganese to achieve simultaneous removal of microplastics and dissolved heavy metals. Other hybrid systems integrate titanium dioxide to enable photocatalytic degradation, using light to break down retained organic contaminants directly on the adsorbent surface.

Operational factors such as water acidity, ionic strength, temperature, and dissolved organic matter significantly influence remediation outcomes. Neutral to mildly acidic conditions optimize particle capture, whereas highly alkaline environments intensify charge repulsion and decrease performance. Dissolved organic matter presents a key field challenge by competing for active binding sites on the biochar surface. Despite these natural water variations, fixed-bed column systems utilizing engineered biochar routinely demonstrate superior performance over batch setups, achieving continuous microplastic removal efficiencies above ninety-five percent with long operational lifespans. Furthermore, magnetically engineered biochars allow operators to rapidly retrieve loaded adsorbents using external magnetic fields, maintaining high performance across multiple regeneration cycles.

Life-cycle evaluations demonstrate that biochar-based remediation provides substantial environmental and economic advantages over commercial activated carbon. Utilizing agricultural residues converts waste streams into valuable adsorbents while sequestering atmospheric carbon in stable solid structures, yielding a net-negative carbon footprint. Raw biochar production costs remain significantly lower than standard commercial adsorbents, though extensive chemical functionalization adds manufacturing expense that must be balanced against extended material lifespan and regeneration capacity. As research moves from laboratory batch tests toward pilot-scale wastewater installations, establishing standardized testing protocols and data-driven material design will be essential to fully deploy engineered biochar as a sustainable cornerstone of global water infrastructure.

Source: Rasool, A., Heviánková, S., Halfar, J., Brožová, K., Chromíková, J., Pertile, E., Malíková, P., Motyka, O., Drabinová, S., & Čabanová, K. (2026). Engineered biochar for microplastic remediation in aquatic environments: Interfacial mechanisms, modification strategies, and future perspectives. Journal of Hazardous Materials, 143085.