Hydrothermal Carbonization of Digestate Produced in the Biogas Production Process

Abstract

In agricultural biogas plants, besides biogas, the by-product digestate is also produced. Due to its high moisture content and organic origin, it can successfully be applied in the hydrothermal carbonization process to avoid the fate of landfilling. This paper reviews the properties of agricultural digestate and its hydrothermal conversion (HTC) into hydrochar and process water. The type of feedstock and the parameters of the HTC process, such as temperature, pressure and residence time, affects the physical and chemical characteristics of hydrochar. Therefore, its possible application might be as a biofuel, fertilizer, soil improver, adsorber, or catalyst. In this paper, the properties of hydrochar derived from agricultural digestate are widely discussed.

Insights into hydrothermal treatment of biomass blends: Assessing energy yield and ash content for biofuel enhancement

“…These agricultural residues, characterized by relatively high initial ash content, demonstrated consistent trends reflecting the observed ash percentages, suggesting inherent characteristics rendering them more amenable to ash reduction under specific process conditions. Recently, HTC of organic waste produced in biogas conversion processes, where the HHV of the hydrochar range was between 14 and 27 MJ/kg, values similar to those achieved in blends with high cellulose and lignin levels in the present study [64].…”

Biohythane, Biogas, and Biohydrogen Production from Food Waste: Recent Advancements, Technical Bottlenecks, and Prospects

“…Among the thermochemical processes, HTC is considered a promising technology for high-moisture biomass due to its unique advantages, such as no pre-drying process, milder reaction conditions, fast reaction rates, and low energy input [138]. HTC is a specific type of hydrothermal treatment process of biomass in a liquid environment, employing elevated temperatures (180-350 • C) and pressures [137][138][139][140]. The procedure yields a solid substance known as hydrochar, which is assumed to mimic the natural coal formation.…”

“…The procedure yields a solid substance known as hydrochar, which is assumed to mimic the natural coal formation. Hydrochar is frequently utilised as a solid fuel for combustion, but it also serves multiple other purposes, such as soil amendment, energy storage, and absorption [29,138]. Furthermore, the HTC process yields a byproduct known as process water.…”