Application of biochar-based permeable reactive barriers in environmental remediation: A critical review

Groundwater contamination has become an increasingly severe global challenge. Traditional in situ remediation technologies generally suffer from high energy consumption, susceptibility to secondary pollution, and long treatment cycles. Permeable reactive barriers (PRBs), as a passive and low-energy in situ remediation technology, offer unique advantages. Among these, biochar-based permeable reactive barriers (BC-PRBs) have attracted considerable attention due to the wide availability of biochar raw materials, low cost, and high adsorption capacity. This review systematically evaluates the research progress of BC-PRBs in environmental remediation, covering biochar preparation, modification strategies, and the synergistic coupling mechanisms with inert skeleton materials. The optimal pyrolysis temperature for biochar typically lies in the medium-to-high range (600-800 °C), where the specific surface area can reach 600-1000 m²/g. Composite media can achieve a favorable balance between adsorption performance and hydraulic conductivity through appropriate media ratios. Engineering case studies demonstrate that under controlled hydraulic retention times of 0.2-0.3 m/d and with optimized graded media, BC-PRBs can achieve removal efficiencies exceeding 99% for organic pollutants and heavy metals, with construction costs significantly lower than those of activated carbon-based systems. Despite these promising results, long-term operation still faces challenges such as media aging, permeability loss, and risks associated with intermediate by-products. Future research should focus on developing anti-aging biochar modification materials, integrating intelligent monitoring systems to enable real-time control of operational parameters, and establishing standardized design frameworks to support the large-scale application of this technology. By overcoming these bottlenecks, BC-PRBs are expected to become a robust and sustainable solution for in situ groundwater remediation.