Optimising the sustainable circular economy of palm oil biomass with a P-graph approach to waste-to-wealth solutions

Palm oil industry generates significant amounts of biomass waste, offering opportunities to establish a circular economy (CE) framework where waste is systematically converted into value-added products. Unlike conventional linear models, this study explicitly integrates circularity as an optimisation criterion alongside profitability in designing a palm oil biomass waste-to-wealth network. This study applies the process graph (P-graph) approach to optimise a palm oil biomass waste-to-wealth network, targeting multiple outputs such as fertiliser, medium-pressure steam, electricity, and transportation fuel while ensuring both circularity and profitability. A key contribution is the formalisation of circularity metrics to evaluate network designs. Results show that the CE-optimised solution (Rank 38) achieved a 2.67% reduction in total resource costs compared to linear models, demonstrating the economic viability of closed-loop systems. However, the trade-off between circularity and profitability necessitates a balanced approach. The Rank 31 solution achieves near-optimal circularity while reducing reliance on imported resource by 28.18% and retaining competitive profitability. Sensitivity analyses further validate the robustness of CE-driven optimization, showing how circular design mitigates inflation risks. An optimal solution was identified, achieving the highest profitability and circularity with a 63.2% reduction in total resource costs and a 4% increase in gross profit. This study provides a replicable framework for embedding circularity into industrial optimisation, offering policymakers and stakeholders actionable strategies to align economic goals with CE principles.