Circular Bioenergy Production from Heavy-Metal-Contaminated Biomass: An Integrated Biorefinery Optimization Approach

Abstract

The increasing prevalence of heavy-metal-contaminated biomass in industrial, agricultural, and remediation processes poses challenges for the environment and the bioenergy sector. This paper elaborates and analyzes a risk-conscious integrated bio-refinery optimization model for circular bioenergy generation from contaminated biomass, enabling the production of both biodiesel and biogas while accounting for heavy-metal fate and associated environmental risks. System performance was evaluated based on low, moderate, and high levels of contamination (10–1,000 mg·kg⁻¹) using deterministic multi-objective optimization, global sensitivity analysis, Monte Carlo propagation of uncertainty, and multivariate regime classification. Findings indicate that total energy recovery decreased from 13,610 to 6,665 MJ·t⁻¹ biomass with increasing contamination; nevertheless, anaerobic digestion gradually replaced energy production, with a maximum contribution of 75.2 percent to total output at high contamination. Biodiesel production went down to 172.4 to 44.6 kg·t⁻¹, and still, the amount of metals in biodiesel was at a quarter of the previous range, 0.5 mg·kg⁻¹. The fraction of incoming heavy metals immobilized in the digestate exceeded96 percent, and it met regulatory limits for land application in all situations, with compliance rates over 90 percent under stochastic uncertainty. Pareto-optimal solutions have shown obvious trade offs in terms of energy recovery, metal risk index (0.07-0.18), and circularity performance (0.79 0.92). In contrast, principal component and cluster analysis revealed operation regimes influenced by contamination. The investigation introduces a system-level approach and reinvigorates the concept of heavy-metal contamination as a manageable design constraint, offering a significant pathway to sustainable bioenergy recovery from polluted landscapes within the circular bioeconomy.