Circular Economy: Principles, Design and Industrial Metabolism

Circular economy (CE) is the most comprehensive framework for rethinking modern society's relationship with material resources. The linear 'take-make-dispose' economy of the 20th century saw the environment as an endless source of raw resources and garbage. In contrast, the circular economy reduces waste and pollution, maximizes product and material value, and restores the ecological systems on which all economic activity depends. This chapter covers circular economy principles, methods, and implementation from molecular material design to industrial system architecture. Start with the Circular Economy framework's theoretical foundations, then develop its three core principles with scientific and engineering rigor. This chapter examines circularity technologies including reuse and remanufacturing, mechanical and chemical recycling, biological nutrient cycling, and energy recovery as the last resort in the waste hierarchy. Industrial symbiosis and metabolism examine and design material and energy flows in industrial systems at the facility, eco-industrial park, and regional economy levels. This chapter discusses digital facilitators of circularity (digital product passports, blockchain traceability, IoT-enabled reverse logistics, AI-driven material sorting), governance mechanisms promoting circular economy adoption (Extended Producer Responsibility, eco-design regulation, the EU Circular Economy Action Plan), and quantitative methods for systemic circular economy performance assessment. Case studies of the Kalundborg Symbiosis network, rare earth element recycling in electronics, and circular material transition in architecture inform the analysis.