Multi-response Optimization of Nauphoeta cinerea Residues Torrefaction for Biocoal Production: Advancing Waste-to-Energy and Circular Bioeconomy Pathways

Abstract

This study provides an original assessment of Nauphoeta cinerea residues, an unconventional and largely unexplored biomass, as feedstocks for biocoal production via torrefaction. By addressing a novel insect-derived resource, the work advances waste-to-energy strategies beyond traditional lignocellulosic and agro-industrial residues. Raw cockroach (RC) and defatted cockroach (DC) biomasses were processed under a Central Composite Design, comprising 26 experiments within 155–325 °C and 12–68 min. Response Surface Methodology was applied to optimize solid yield (SY), energy yield (EY), higher heating value (HHV), and atomic ratios (H/C, O/C). RC achieved superior performance, with SY of 63.66–99.33%, EY of 98.33–134.46%, and HHV up to 27.92 MJ kg –1 . DC presented SY of 69.55–93.19%, EY of 86.84–106.90%, and HHV of 16.21–19.46 MJ kg –1 . Optimal conditions were 180 °C for 60 min for RC (99.10% SY, 24.14 MJ kg –1 HHV, 129.84% EY) and 269 °C for 20 min for DC (87.05% SY, 18.44 MJ kg –1 HHV, 104.53% EY). These results confirm the decisive role of temperature in carbon densification and oxygen depletion, with clear improvements in energy quality. Although nitrogen and ash contents constrain direct combustion, nitrogen-enriched biocoal offers agronomic value through soil fertility improvement and pollutant immobilization. The study reinforces insect residues as potential resources for decentralized energy and circular bioeconomy strategies, contributing directly to the UN Sustainable Development Goal 7 (Affordable and Clean Energy) and Goal 12 (Responsible Consumption and Production).

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