Aims: Most of the over 250,000 t.y⁻¹ of organic municipal waste generated in Al-Nasiriyah is landfilled, which raises the risk of leachate and methane emissions. This study explores sustainable waste valorization strategies through energy recovery and coproduct use.
Materials & Methods: Anaerobic digestion (AD) and hydrothermal carbonization (HTC) were combined to develop and evaluate an integrated pathway. Response-surface and Gompertz models, alongside pilot-scale feedstock characterization, were used to predict hydrochar yields, increased heating values, and methane production under various operating conditions. To assess environmental impacts, such as eutrophication and global warming potential, as well as financial metrics, including net present value (NPV), internal rate of return (IRR), and payback period, a bottom-up techno-economic analysis and a cradle-to-gate life-cycle assessment (ISO 14040/44) were performed.
Findings: Compared to standalone AD, the coupled HTC–AD system reduced greenhouse gas emissions by 67%, generated 6.5 GJ.t⁻¹ of net energy, and demonstrated financial viability with an 18% internal rate of return and a four-year payback period.
Conclusion: The results confirm that the integrated HTC–AD pathway offers a practical, climate-friendly, and sustainable waste-management solution for arid subtropical urban areas like Al-Nasiriyah.