Abstract
Hydrothermal carbonization (HTC) is an innovative process capable of converting wet biodegradable residues into value-added materials, such as hydrochar. HTC has been studied for decades, however, a lack of detailed information on the production and composition of the process water has been highlighted by several authors. In this paper the state of the art of the knowledge on this by-product is analyzed, with attention to HTC applied to municipal and agro-industrial anaerobic digestion digestate. The chemical and physical characteristics of the process water obtained at different HTC conditions are compared along with pH, color, organic matter, nutrients, heavy metals and toxic compounds. The possibility of recovering nutrients and other valorization pathways is analyzed and technical feasibility constraints are reported. Finally, the paper describes the main companies which are investing actively in proposing HTC technology towards improving an effective process water valorization.
Highlights
IntroductionResearch in renewable energy production from bioresources, such as organic resources and waste, is constantly increasing in intensity and quality, pushed by the current rate of exploitation of fossil fuels and their related impacts and green house gases (GHGs) emissions on the environment
Research in renewable energy production from bioresources, such as organic resources and waste, is constantly increasing in intensity and quality, pushed by the current rate of exploitation of fossil fuels and their related impacts and green house gases (GHGs) emissions on the environment.The use of anaerobic digestion (AD) for the energetic utilization of agro-industrial residues and even biodegradable municipal wastes is raising year after year (Figure 1a)
While biogas is a valuable source of energy, as it can be used in combined heat and power (CHP) generators or upgraded to biomethane for vehicles fuel and immission into the natural gas grid, after undergoing an upgrading process, digestate in some contexts could represent a problem to the environment or can sometimes encounter disposal-related issues
Summary
Research in renewable energy production from bioresources, such as organic resources and waste, is constantly increasing in intensity and quality, pushed by the current rate of exploitation of fossil fuels and their related impacts and green house gases (GHGs) emissions on the environment. The use of anaerobic digestion (AD) for the energetic utilization of agro-industrial residues and even biodegradable municipal wastes is raising year after year (Figure 1a). The main products of the AD are biogas and digestate. While biogas is a valuable source of energy, as it can be used in combined heat and power (CHP) generators or upgraded to biomethane for vehicles fuel and immission into the natural gas grid, after undergoing an upgrading process, digestate in some contexts could represent a problem to the environment or can sometimes encounter disposal-related issues.
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