Impact of torrefaction and low-temperature carbonization on the properties of biomass wastes from Arundo donax L. and Phoenix canariensis Ricardo Correia ⇑ , Margarida Gonçalves, Catarina Nobre, Benilde Mendes Mechanical Engineering and Resource Sustainability Center, Department of Science and Technology of Biomass, Faculty of Sciences and Technology, New University of Lisbon, Campus de Caparica, 2829-516 Caparica, Portugal highlights  Torrefaction and carbonization of A. donax L. and P. canariensis was studied.  Temperature was the parameter that most affected yield and biochar composition.  A strong linear correlation between mass and energy yields was found.  Grindability of the biochars was strongly improved for thermal treatments above 250 °C.  Raw biomasses and biochars produced at 200 °C were able to adsorb methylene blue. article info Article history: Received 20 August 2016 Received in revised form 14 October 2016 Accepted 16 October 2016 Available online 18 October 2016 Keywords: Arundo donax L. and Phoenix canariensis Torrefaction and carbonization Mass and energy yields Grindability Dye adsorption abstract The impact of torrefaction and low-temperature carbonization on the properties of biomass wastes from Arundo donax L. and Phoenix canariensis was studied. Thermal treatments were performed at tempera- tures from 200 °C to 350 °C during 15 to 90 min and temperature was the parameter that more influenced mass and energy yields as well as biochar composition. Torrefaction reduced moisture, volatile matter, O/C and H/C ratios of the biomass, while increasing heating value, ash content and fixed carbon. For tor- refaction at 250 °C or higher temperatures grindability of the biochars was significantly improved. The low volatile matter contents and high ash contents of these biochars restricts their use as solid fuels but they can be valorized otherwise. Raw biomasses and the biochars torrefied at 200 °C could remove methylene blue from an aqueous solution, in fast adsorption test with a contact time of only 3 s, with effi- ciencies higher than 50%. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Biomass wastes are available in substantial amounts from dif- ferent sources and activities, but a significant fraction does not pre- sent the appropriate characteristics for energetic or material valorization. Their high moisture content, heterogeneity and low bulk density increases transportation and storage costs (Arias et al., 2007), decreases their heating value (McKendry, 2002) and negatively affects combustion (Hellwig, 1985). Moreover, their water content facilitates enzymatic and microbiological degrada- tion (Tumuluru et al., 2011). For some types of biomass, such as perennial grasses, their fibrous nature hinders the milling opera- tions (Bergman et al., 2005a) and their high ash content limits their use as biofuels, especially for low melting point ashes, that lead to the formation of deposits and incrustations in the boilers (Coulson et al., 2004). Some biomass wastes can also be affected by diseases or pests that prevent their valorization as biomaterials. The dis- posal of the contaminated biomass wastes in landfills should also be avoided because it contributes to the dissemination of these pests. Torrefaction is a thermochemical process in which raw biomass is heated under atmospheric pressure, at a temperature range of 200–300 °C, in the absence of oxygen or under low oxygen concen- trations (Rousset et al., 2011). The torrefied materials have a higher calorific value, a lower O/C ratio and a lower moisture content, than the raw biomass, also becoming hydrophobic, which improves their resistance to biological degradation during storage (Wilk et al., 2015). Torrefaction also improves grindability, because it breaks the bonds between lignocellulosic polymers and http://dx.doi.org/10.1016/j.biortech.2016.10.046 0960-8524/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: rjc07189@campus.fct.unl.pt (R. Correia). Bioresource Technology 223 (2017) 210–218 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech