Biochar as a protagonist in sustainable city: Bridging green technologies and the circular economy

Biochar is a climate-positive green material that has proven its potential application in various sectors related to the circular economy, including waste management, wastewater treatment, global climate change mitigation, sustainable agriculture, and the construction industry. Although many hundreds of studies have explored the applications of biochar, the existing literature remains highly segregated, largely focused on isolated or specific sectoral applications due to the diverse properties. To date, no comprehensive review has conceptualized biochar as a protagonist in the circular economy of cities. An approach is urgently needed to assess how biochar can contribute holistically to sustainable city development—bridging production, utilization, and long-term urban planning for resilience. This includes examining both economic and environmental returns, establishing sustainable supply chains for scaling up biochar solutions. Since biochar has diverse properties and context-dependent applications, it is also suitable to propose a model biochar-integrated city at a pilot scale to investigate real-world problems, limitations, and transformative potential. This demonstration can serve as a blueprint for future urban sustainability planning worldwide. Thus, by highlighting biochar as a crucial component of urban resilience, this article seeks to promote the idea of a sustainable city supported by the ideas of the circular economy.