Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech Physicochemical, structural and combustion characterization of food waste hydrochar obtained by hydrothermal carbonization Najam Ul Saqib a , Saeid Baroutian b , Ajit K. Sarmah a, ⁎ a Department of Civil & Environmental Engineering, Faulty of Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand b Department of Chemical & Materials Engineering, The Faculty of Engineering, The University of Auckland, Private Bag 92019, Auckland 1142, New Zealand GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Hydrothermal carbonisation Food waste Hydrochar Co-combustion Energy ABSTRACT A solid carbon-rich product hydrochar, was prepared using hydrothermal carbonisation of food waste at tem- peratures of 200, 250 and 300 °C. To acquire detailed insight into physicochemical and structural properties, hydrochar samples were characterised using a range of techniques. The carbon content and higher heating value of food waste increased considerably from 39 to 73% and 15 to 31 MJ/kg corresponding to the heating tem- perature. The blends of hydrochar and coal prepared in three different ratios (5%, 10% and 15%) exhibited different thermal behaviour. The overall results of co-combustion study showed that the activation energy of hydrochar samples decreased from 56.78 KJ/mol to 29.80 KJ/mol with increase in temperature. Hydrochar prepared at 300 °C with coal blending ratio of 10% exhibited the lowest activation energy of 19.45 KJ/mol. Additionally thermal gravimetric analysis of the samples showed that high temperature carbonization can in- crease the combustion properties of hydrochar. 1. Introduction As the world energy crisis looms, alternative sustainable green en- ergy option has been the main focus in many parts of the world. The burgeoning world population coupled with shortage of fossil fuel based energy could result in catastrophic situation with shortage of energy required in diverse sectors in the future. This high requirement of en- ergy has forced researchers to seek other means of producing energy from renewable sources to fulfil energy demand (Mafakheri & Nasiri, 2014). Biomass is the leading source of energy in rural areas for many centuries (Liu & Balasubramanian, 2012). Biomass provides about 10–14% of total energy consumption of the world while coal, gas and electricity provide 12–14%, 14–15% and 14–15% respectively (Saqib et al., 2015). All non-fossil biological materials are the source of bioe- nergy. As a matter of fact, bioenergy has the ability to solve the global https://doi.org/10.1016/j.biortech.2018.06.112 Received 10 May 2018; Received in revised form 29 June 2018; Accepted 30 June 2018 ⁎ Corresponding author. E-mail address: a.sarmah@auckland.ac.nz (A.K. Sarmah). Bioresource Technology 266 (2018) 357–363 Available online 02 July 2018 0960-8524/ © 2018 Elsevier Ltd. All rights reserved. T