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

Nkechi Blessing Chinedu, ORCID, Gospel Effiong Isangadighi, ORCID, Goodness Effiong Isangadighi, ORCID, Jessica Gospel Isangadighi, ORCID, Oyerinde Oluwole Joshua

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 exceeded , 96 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.

Keywords

Integrated biorefinery; Circular bioenergy; Heavy-metal-contaminated biomass; Biodiesel–biogas co-production; Multi-objective optimization; Anaerobic digestion; Environmental risk management; Circular

References

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