**4. Conclusions**

This chapter explored the possibility of using postprocess residues as abundant biorenewable and low-cost resources in future waste biorefineries. Available waste streams have a complex and varied composition according to its source, requiring new logistic platforms of assortment and valorization. With the exhaustion of the "collection and disposal" linear economy, new waste handling methods are unavoidable in the long term. As such, waste biorefineries that produce green energy and make virtually zero-waste high-value products in a "closed loop" and "up-cycling" approach are the "landfills" of the future. They are expected to be crucial in taking sustainable waste management into the real world allowing game-changing economic growth under the concept of circular economy. However, from the reviewed technologies, it can be concluded that single WtL and WtE processes are almost always limited in their scope, producing many times unwanted products. In this regard, the technology with more potential and scope in single applications is by far gasification; nonetheless, even this process has drawbacks such as reactor design, feeding system, and tar production that require costly posttreatment and/or further technological developments. Conversely, combining multiple WtE and WtL processes in an integrated waste biorefinery will allow the mitigation and elimination of each single process drawbacks. In gasification, for example, some of the unwanted substances generated may be utilized and valued by subsequent chemical processing, and even syngas can be upgraded. This novel waste valuation pyramid will create opportunities

**47**

**Author details**

Portugal

provided the original work is properly cited.

*Review of Biofuel Technologies in WtL and WtE DOI: http://dx.doi.org/10.5772/intechopen.84833*

**Acknowledgements**

SFRH/BDE/111878/2015.

for niche technologies such as explosive decompression and torrefaction to make it into practical application by enhancing other technologies that are already well established when used in an integrated approach. Future research should primarily focus on the establishment of a hierarchy of processes to produce the highest value products and then progress gradually to low-cost products and energy production. For this vision to be a reality, however, an increased effort on the part of the researchers will be required with a combined continuous and sustained support from all potential stakeholders. More demonstration projects at pilot or semipilot scale should materialize in the upcoming years, focusing on aspects such as energy balance and

cost-benefit analysis guaranteeing the viability of the proposed solutions.

Authors acknowledge the financial support received by the projects 0008\_ECO2CIR\_4\_E and 0049\_INNOACE\_4\_E co-funded by ERDF – European Regional Development Fund through INTERREG V-A Spain-Portugal Cooperation Programme (POCTEP). G. Lourinho also gratefully acknowledges FCT - Fundação para a Ciência e Tecnologia - for financial support within the scope of the grant

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

VALORIZA—Research Center for Endogenous Resource Valorization, Portalegre,

Bruno B. Garcia, Gonçalo Lourinho, Paulo Brito\* and Pedro Romano

\*Address all correspondence to: pbrito@ipportalegre.pt

*Review of Biofuel Technologies in WtL and WtE DOI: http://dx.doi.org/10.5772/intechopen.84833*

for niche technologies such as explosive decompression and torrefaction to make it into practical application by enhancing other technologies that are already well established when used in an integrated approach. Future research should primarily focus on the establishment of a hierarchy of processes to produce the highest value products and then progress gradually to low-cost products and energy production. For this vision to be a reality, however, an increased effort on the part of the researchers will be required with a combined continuous and sustained support from all potential stakeholders. More demonstration projects at pilot or semipilot scale should materialize in the upcoming years, focusing on aspects such as energy balance and cost-benefit analysis guaranteeing the viability of the proposed solutions.
