An EOQ-based inventory model for circular economy implementation in municipal solid waste management

Rapid urbanization has intensified municipal solid waste (MSW) management challenges in developing regions. Tamil Nadu exemplifies this trend, with MSW generation increasing from approximately 9,000 tons per day in 2005 to 17,843 TPD in 2024 and projected to reach 18,300 TPD by 2025.

To address this growing pressure, this study develops a circular economy-based Economic Order Quantity (EOQ) model to optimize windrow composting systems for sustainable fertilizer production. A circularity index θ (0 ≤ θ ≤ 1) is introduced to quantify material recovery and reuse and is explicitly linked to demand and unit profit through linear and nonlinear functional forms. The model integrates ordering, holding, shortage, and carbon emission-related costs to evaluate their combined effect on total profit under controllable emissions. Optimal solutions are derived using Lagrangian optimization and Karush–Kuhn–Tucker (KKT) conditions.

Numerical results and sensitivity analysis demonstrate exceptional parameter stability, with ±0.1% variations in key parameters causing negligible changes in total profit, while optimal order quantity and green technology levels remain unchanged. Among the examined cases, logarithmic and logistic functional forms yield higher profits, with improvements exceeding 8–12% compared to linear structures.

Increased circularity and green technology investment simultaneously enhance profitability and reduce landfill dependency and carbon emissions. Overall, the proposed model provides a practical decision-support tool for municipal authorities to strengthen 3R (Reduce-Reuse-Recycle) strategies, improve resource efficiency, and advance toward a sustainable circular MSW management system.