Hydrothermal Carbonization as a Valuable Tool for Energy and Environmental Applications: A Review

Abstract

Hydrothermal carbonization (HTC) represents an efficient and valuable pre-treatment technology to convert waste biomass into highly dense carbonaceous materials that could be used in a wide range of applications between energy, environment, soil improvement and nutrients recovery fields. HTC converts residual organic materials into a solid high energy dense material (hydrochar) and a liquid residue where the most volatile and oxygenated compounds (mainly furans and organic acids) concentrate during reaction. Pristine hydrochar is mainly used for direct combustion, to generate heat or electricity, but highly porous carbonaceous media for energy storage or for adsorption of pollutants applications can be also obtained through a further activation stage. HTC process can be used to enhance recovery of nutrients as nitrogen and phosphorous in particular and can be used as soil conditioner, to favor plant growth and mitigate desertification of soils. The present review proposes an outlook of the several possible applications of hydrochar produced from any sort of waste biomass sources. For each of the applications proposed, the main operative parameters that mostly affect the hydrochar properties and characteristics are highlighted, in order to match the needs for the specific application.

Evaluating the Aqueous Phase From Hydrothermal Carbonization of Cow Manure Digestate as Possible Fertilizer Solution for Plant Growth

“…In particular, the HTC process takes place between 180 and 250°C and 10 and 80 bars, with residence time ranging from few minutes to several hours. The HTC process converts wet feedstock into gas (mainly CO 2 ), a carbonaceous solid fraction (termed hydrochar), and a liquid phase [termed aqueous HTC liquid (AHL); Funke and Ziegler, 2010 ; Maniscalco et al, 2020 ].…”

“…In the last 20 years, hydrochar has gained attention because of its chemical and physical properties, which can be exploited for numerous purposes ( Hu et al, 2008 ; Fang et al, 2018 ). For instance, hydrochar can be used as (i) solid fuel for energy production ( Lucian and Fiori, 2017 ); (ii) adsorbent material to remediate polluted soils and water because of toxic substances ( Elaigwu et al, 2014 ; Fornes et al, 2015 ; Fang et al, 2018 ; Parlavecchia et al, 2020 ); and (iii) organic soil amendment, being rich in carbon (C) and nutrients ( Maniscalco et al, 2020 ). Recently, it has also been suggested as either a stand-alone substrate or a constituent of growing media for plants in soilless culture systems ( Belda et al, 2016 ; Gruda, 2019 ).…”

Characteristics of Black Ginseng (Panax ginseng C.A. Mayer) Production Using Ginseng Stored at Low Temperature after Harvest

“…5-HMF can form a furfural derivative with one aldehyde group falling off. The benzene ring is then formed through polymerization and several rings are polymerized to form BAP [ 27 , 28 , 29 ]. The process of producing BAP from free sugar is shown in Figure 4 .…”

Biochar as an Eco-Friendly and Economical Adsorbent for the Removal of Colorants (Dyes) from Aqueous Environment: A Review

“…Unlike many types of biochars, it has been seen that hydrochar produced as a result of hydrothermal carbonization has low organic content and reduced mobility of heavy metals, which makes it ideal for soil amendment. Addition of hydrochar to soil has shown to improve water retention capacity, microbial community, nutrient holding capacity, and much more [69,70]. Since the use of hydrochar has grown considerably only during the last decade, research on different aspects of hydrochar is still yet to be studied thoroughly.…”