**6. Conclusions**

This book chapter sheds some light on the use of low-grade biomass feedstocks as a sustainable and renewable source for the production of energy and chemicals through thermal conversion processes. The chapter assesses the availability of the feedstocks for thermal conversion and provides the sources of impurities (ash-forming elements) contained in them. Also, it emphasizes that the main challenges associated with the utilization of the feedstocks in thermal conversion systems are related to the type and concentration of the impurities in the feedstocks. Furthermore, it details the challenges of low-grade biomass combustion, gasification, pyrolysis, and liquefaction and the potential alternative options to address them. Evaluation of the existing information on the thermal conversion of these feedstocks reveals that the fast pyrolysis process is a promising thermal conversion route for these feedstocks. The pyrolysis oils from this process can be upgraded to transportation fuels or can be used for the production of high value-added chemicals. Moreover, the fast pyrolysis biochars can be returned to the soil for use as fertilizer and at the same time minimize CO2 emission through carbon sequestration. Overall, this work provides useful information for the design and development of state-of-the-art thermal conversion technologies for challenging biomass feedstocks.
