Global applications of biochar in sustainable cities of the future: a perspective

As urbanization intensifies, cities are facing escalating challenges related to environmental degradation and resource management, necessitating innovative and sustainable solutions. Biochar, a carbon-rich material derived from the pyrolysis of organic waste, has emerged as a versatile tool for advancing urban sustainability. This perspective synthesizes key findings regarding the global applications of biochar in promoting sustainable urban development, demonstrating its efficacy across multiple domains, including air quality improvement, waste valorization, carbon sequestration, soil regeneration, and water purification. By converting organic waste into a stable form of carbon, biochar provides a practical strategy to reduce landfill use and mitigate greenhouse gas emissions. Notably, biochar also contributes to reducing airborne pollutants. Recent studies have shown that certain metal-rich biochars can adsorb volatile organic compounds emitted from asphalt surfaces (up to 76%). Asphalt represents a less recognized yet significant source of urban air pollution, and this finding highlights an additional pathway through which biochar can improve air quality and extend infrastructure longevity. In the construction sector, the incorporation of biochar into cement and concrete not only enhances mechanical properties but also enables long-term carbon sequestration via carbonation processes. For soil regeneration, biochar improves porosity, water retention, and nutrient availability, increasing crop yields (e.g., 50% for chili in field trials). In water and wastewater treatment, biochar removes heavy metals (> 70% Pb2+), dyes (up to 95%), nutrients, and emerging contaminants such as PFAS. Additionally, it boosts methane yields in anaerobic digestion by 27%–42%. Furthermore, the potential of biochar in renewable energy systems and decentralized water treatment solutions underscores its value in building more resilient urban infrastructure. When integrated into circular economy models, biochar can facilitate the closure of resource loops, reduce environmental footprints, and support regenerative city planning. Despite its promising prospect, the large-scale adoption of biochar is hindered by several challenges, including technical limitations, economic constraints, and the lack of supportive policies and standards. By synthesizing current research findings and emerging applications, this perspective positions biochar as a versatile and foundational component in the transition toward climate-resilient, sustainable cities.