Vol.:(0123456789) 1 3 Waste Biomass Valor DOI 10.1007/s12649-017-9914-0 ORIGINAL PAPER Process Water from the Hydrothermal Carbonization of Biomass: A Waste or a Valuable Product? Harpreet Singh Kambo 1  · Jamie Minaret 1  · Animesh Dutta 2   Received: 2 July 2015 / Accepted: 25 March 2017 © Springer Science+Business Media Dordrecht 2017 run). Most importantly, the HHV of hydrochars increased from 18.9 (raw biomass) to 26.6 MJ/kg (maximal value) during recirculation of process water. As a result, the recir- culation of process water can increase the overall system’s efciency and reduce both the operating costs and environ- mental impact of a commercial HTC plant. Keywords Hydrothermal carbonization · Organic acids · Recirculation · Process water Introduction The abundant amount of biomass on earth plays a sub- stantial role in global energy production as it has been widely consumed as an alternative to fossil fuels for the purpose of generating heat and power. Lignocellulosic biomass wastes (agricultural and forest residues) and pur- pose grown energy crops (miscanthus, switchgrass, etc.) are favored over frst generation biomass because of their nonedible characteristics; hence they do not compete with food shortage when the waste-biomasses are con- sumed for producing energy [1]. Therefore, the consump- tion of lignocellulosic biomass wastes as a resource of fuel has gained remarkable attention in the development of a clean, green renewable energy society. However, lignocellulosic biomass has inferior physicochemical properties when compared to coal, which include poor homogeneous nature, high moisture content and hydro- philic nature, poor grindability, low bulk energy density, and high alkali and alkaline earth metal content. There- fore the utilization of raw lignocellulosic biomass can be highly inefcient and expensive [2]. Treatment processes can be applied to biomass to overcome the aforemen- tioned limitations [3]. Torrefaction, a thermal treatment Abstract Hydrothermal carbonization (HTC) is a prom- ising method for the production of energy dense coal-like material from low quality lignocellulosic biomass. The pro- cess takes place in the presence of water and therefore is unafected by feedstocks containing a high moisture con- tent. However, the substantial water requirement and dis- posal concerns for a large scale HTC plant may outweigh its advantages from an economical and environmental point of view. The work presented in this study proposes a solu- tion to the aforementioned problem. Miscanthus feedstock was treated hydrothermally at three diferent reaction tem- peratures (190, 225, and 260 °C) for 5 min with a solid load ratio of 1:6. The liquid by-product from each experiment was characterized for chemical composition. The results show that the HTC process water was rich in organic acids (acetic, formic, levulinic, and glycolic acid), Hydroxy- methyl-furfural (HMF), and total organic carbon (TOC). The acidity and the concentration of intermediate products in the HTC process water increased with an increase in reaction temperature. The HTC process water produced at 260 °C was examined for the recirculation of process water. The results show that, during successive recirculation of HTC process water, the mass yield of the hydrochar sam- ples increases by 5–10% and the energy yield of the hydro- char samples increased up to 15% compared to the HTC- reference sample (hydrochar sample produced at initial * Animesh Dutta adutta@uoguelph.ca 1 School of Engineering, University of Guelph, Guelph N1G 2W1, Canada 2 Mechanical Engineering Program, School of Engineering, University of Guelph, Room No RICH 3509, 50 Stone Road East, Guelph, ON N1G 2W1, Canada