Engineered biochar as a powerful tool for microplastics removal from wastewater: a critical review

Microplastics (MPs) pollution in aquatic environment is considered as a critical environmental issue because of widespread and increasing use of plastics worldwide. Hence, engineered biochar known for its superior surface characteristics, enhanced surface area, greater porous structure and versatility has appeared as a sustainable and potential material for effective MPs removal from wastewater. To date, engineered biochar for MPs removal has received limited attention in reviews. Therefore, this article systematically summarizes the biochar production from low-cost and nature-friendly materials and potential modification methods to develop engineered biochars with improved performance for MPs adsorption from wastewater. Engineered biochar shows significantly higher adsorption compared to raw or pristine biochar. In this review, we critically examine emerging and novel biochar modification methods-including treatment with acid/bases, oxidizing agents, metallic oxides, non-metal compounds, clay minerals and nanomaterials which are typically applied for enhanced MPs removal from wastewater. Moreover, the discussion provides insights into the MPs removal mechanisms and the environmental factors that impact the adsorption performance of engineered biochar. We also discuss the costs of producing biochar and regeneration methods to restore its effectiveness thus revealing its viability and economic feasibility. It is anticipated that this critical review will provide comprehensive scientific breakthroughs for resolving the hot issue of MPs contamination in wastewater by proving engineered biochar application as an economical and nature-friendly solution. At the end, review outlines the present scientific knowledge, research gaps, and recommendations needed to advance technologies for mitigating MPs pollution from wastewater using engineered biochar.