**5. Conclusions**

**5. Conclusions** The pre-feasibility of a multi-product biorefinery for the extraction of EOs and the production of biomethane was discussed and assessed considering current technical and economic conditions. In particular, the production of EOs (2900 L/y) was studied using the steam distillation of forestry biomass, while biomethane production was explored using the gasification of the spent biomass (30.4 kg/h) combined with the AD of WWTP The pre-feasibility of a multi-product biorefinery for the extraction of EOs and the production of biomethane was discussed and assessed considering current technical and economic conditions. In particular, the production of EOs (2900 L/y) was studied using the steam distillation of forestry biomass, while biomethane production was explored using the gasification of the spent biomass (30.4 kg/h) combined with the AD of WWTP sludge (5.3 kg/h) to maximize renewable gas production for different applications.

sludge (5.3 kg/h) to maximize renewable gas production for different applications.

The pre-feasibility analysis showed that the intended multi-product biorefinery concept is promising and delivers positive economic benefits in the conditions studied. From the investor's perspective, results for the main financial indicators showed an NPV of EUR 4342.6, an IRR of 18.1%, and a PB of 6 years, values that are above current financial benchmarks in biomass projects.

Overall, this work demonstrated the conceptual viability of a multi-product biorefinery to produce EOs and biomethane from forestry wastes and sludge, therefore showing that the investment opportunity warrants further study. The next steps should include a comprehensive cost and benefit analysis, including detailed technical analysis, investment appraisal, and sustainability assessment, in order to ensure social and environmental benefits from the implementation of biorefineries in rural areas.

**Author Contributions:** Conceptualization, L.C.-C. and P.B.; Methodology, L.C.-C. and R.M.-P.; Validation, C.N.; Formal Analysis, C.N. and G.L.; Investigation, L.C.-C., A.C.A., R.M.-P., O.A. and G.L.; Writing—Draft Preparation, L.C.-C., R.M.-P. and A.C.A.; Writing—Review and Editing, C.N. and G.L.; Visualization, G.L. and O.A.; Supervision, P.B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Fundação para a Ciência e a Tecnologia, I.P. (Portuguese Foundation for Science and Technology), under the project UIDB/05064/2020 (VALORIZA—Research Centre for Endogenous Resource Valorization), by the Regional Operational Program of Alentejo (Alentejo2020) under Portugal 2020 (Operational Program for Competitiveness and Internationalization) grant ALT20–05–3559–FSE– 000035, and by project PigWasteBiorefinery with grant ALT20-03- 0246-FEDER-000054.

**Conflicts of Interest:** The authors declare no conflict of interest.
