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 temperatures from 200 degrees C to 350 degrees 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 torrefaction at 250 degrees 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 degrees C could remove methylene blue from an aqueous solution, in fast adsorption test with a contact time of only 3 s, with efficiencies higher than 50%. (C) 2016 Elsevier Ltd. All rights reserved.