Co-hydrothermal carbonization of food waste with yard waste for solid biofuel production: Hydrochar characterization and its pelletization Hari Bhakta Sharma, Brajesh K. Dubey ⇑ Environmental Engineering and Management, Department of Civil Engineering, Indian Institute of Technology Kharagpur, Kharagpur, West Bengal 721302, India article info Article history: Received 5 April 2020 Revised 6 August 2020 Accepted 3 September 2020 Keywords: Food waste Co-hydrothermal carbonization Biofuel pellets Coal replacement Pelletization abstract In this study, Co-HTC of food waste with yard waste was conducted for biofuel pellets production, and also to understand any possible synergy between two feedstock types. The calorific value of blended raw feedstock was 13.5 MJ/kg which increased to 27.6 MJ/kg after Co-HTC at 220 °C for 1 h. Energy yield and fuel ratio calculated was 45% and 0.65 respectively. Hydrochar produced demonstrated a stable com- bustion profile as compared to reactive combustion profile for raw samples. The blend of food and yard waste hydrochar was easily pelletized, and its pellets showed improvement in mechanical properties as compared to pellets made from mono-substrate((food waste) hydrochar. Pellets produced from the blend of food and yard waste hydrochar showed higher energy (46.4 MJ/m 3 ) and mass density (1679 kg/m 3 ) as compare to the pellet produced from food waste hydrochar alone. Tensile strength obtained for the blended hydrochar pellet was 2.64 MPa while same for the pellets produced from food waste hydrochar alone was 1.30 MPa. In addition to improving hydrophobicity, soften lignin from yard waste also helped in binding the food waste hydrochar particles together within the pellets matrix during heated pelletiza- tion. The results presented in the study indicated that in the presence of all favorable conditions, there is a potential that approximately 11% of the global coal consumption could be replaced by the combustion of hydrochar produced from food and yard waste globally. Ó 2020 Elsevier Ltd. All rights reserved. o1. Introduction It has become important than ever to address the growing con- cern of mismanaged Municipal Solid Waste (MSW) in developing nations. The issue has become even more imperative for the organic fraction of MSW (food and other green waste), generation of which is inevitable and is ever increasing. Nearly 3 billion tonnes of food is wasted every year of which an estimated 1.3 billion ton- nes ends up rotting in the bins of consumers and retailers due to poor transportation and harvesting practices (Kaza et al., 2018). Furthermore, unmanaged food waste disposal have negative envi- ronmental impacts at the end of its life, as it is mostly associated with greenhouse gas emission (mostly methane), which has a glo- bal warming potential of 25 times greater than carbon dioxide on a 100-year time scale (Kaza et al., 2018). If we adopt a market based approach to tackle the aforementioned issue, the MSW (including organic fractions) recycling and resource recovery approach could generate estimated US $410 billion annually (Nizami et al., 2017). In a resource recovery and market based approach for the organic fraction of MSW, biofuel production is most preferred lately. Despite liquid and gaseous biofuel production approach being fol- lowed predominantly, lately, production of solid biofuel pellets has gain tremendous attention (Wang et al., 2018a; Yilmaz and Akçay, 2018; Zhai et al., 2018; Zhao et al., 2014). As compared to the chips and powder, pellets has more commercial value mainly due to higher mass and energy density, apart from being easy to handle, store and transport. However, moisture laden, high volatile organic waste creates considerable challenges during pellet production. Moisture and high volatile matter not only deteriorate pellets qual- ity but also increase the risk of fire hazard during storage and transportation due to microbial activity promoted by the presence of moisture. To overcome aforementioned challenge, organic waste in often treated using the treatment techniques like pyrolysis and torrefac- tion. These treatment methods requires waste condition to be dry; moisture laden waste is not suitable, hence requires energy inten- sive pre-drying step (Sharma et al., 2019a). Hydrothermal car- bonization (HTC), which is a wet waste conversion technique is being widely used/studied to tackle moisture laden waste in a recent time (Kambo and Dutta, 2014; Funke et al., 2010; Saqib et al., 2019a). The HTC takes advantage of high moisture in the waste and converts it into a carbon rich hydrochar by the series of reaction such as; hydrolysis, dehydration, de-carboxylation, https://doi.org/10.1016/j.wasman.2020.09.009 0956-053X/Ó 2020 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: bkdubey@civil.iitkgp.ac.in (B.K. Dubey). Waste Management 118 (2020) 521–533 Contents lists available at ScienceDirect Waste Management journal homepage: www.elsevier.com/locate/wasman