Search

Hydrothermal carbonization (HTC) was evaluated as a promising treatment to enhance the biomethane potential during anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). The OFMSW was carbonized at different conditions and HTC products were tested for biomethane potential into AD. Results proved that the use of HTC liquid and slurry into AD led to an increase in biomethane production up to 37% and 363%, respectively, compared to OFMSW. Methane production increased as the HTC process severity decreased, reaching its maximum at 180 °C, 1 h for both HTC products. Energy assessment demonstrated that the combustion of biogas produced by AD of HTC liquid and slurries covers up to 30% and 104% of the HTC thermal demand, respectively. When the energy from hydrochar and biogas combustion was recovered, the process efficiency reached 60%. Hence, HTC coupled with AD demonstrates to be an efficient way to valorize OFMSW., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

This study describes the main features of a novel industrial-scale continuous operating hydrothermal carbonization (HTC) developed by Carborem srl named C700. The C700 industrial-scale HTC plant is a highly compact, modular and containerized system capable of treating more than 5 kton per year of sludge. The results of HTC operated with C700 plant at 190 °C and 1 h of residence time of three different high moisture content residues (sewage sludge, agro-industrial sludge, and organic fraction of municipal solid waste digestate) demonstrate the efficiency and versatility of the process. C700 system is capable of promoting dewaterability of sludge residues, producing solid residues (hydrochars) upon centrifugation of HTC slurries with improved phosphorus content. Results show that the system allows concentrating P into the solid residue up to 3.6 wt% on a dry basis and leads to hydrochars with a total solid content, upon centrifugation of 34.6, 38.6 and 41.0 wt% for sewage and agro-industrial sludge and organic fraction of municipal solid waste digestate, respectively. Moreover, while hydrochars show good potential as soil fertilizers, when excess heavy metals like copper and zinc are removed, recirculation of the high carbon content liquid residue to the anaerobic digestion system offers the opportunity to enhance biogas production in the waste management plant thus lowering the total external energy demand of the process. [ABSTRACT FROM AUTHOR]

Hydrothermal carbonization (HTC) is considered as an efficient and constantly expanding eco-friendly methodology for thermochemical processing of high moisture waste biomass into solid biofuels and valuable carbonaceous materials. However, during HTC, a considerable amount of organics, initially present in the feedstock, are found in the process water (PW). PW recirculation is attracting an increasing interest in the hydrothermal process field as it offers the potential to increase the carbon recovery yield while increasing hydrochar energy density. PW recirculation can be considered as a viable method for the valorization and reuse of the HTC aqueous phase, both by reducing the amount of additional water used for the process and maximizing energy recovery from the HTC liquid residual fraction. In this work, the effects of PW recirculation, for different starting waste biomasses, on the properties of hydrochars and liquid phase products are reviewed. The mechanism of production and evolution of hydrochar during recirculation steps are discussed, highlighting the possible pathways which could enhance energy and carbon recovery. Challenges of PW recirculation are presented and research opportunities proposed, showing how PW recirculation could increase the economic viability of the process while contributing in mitigating environmental impacts. [ABSTRACT FROM AUTHOR]