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Recirculation of process water (PW) from hydrothermal carbonization (HTC) has revealed as an effective strategy for the residual aqueous phase valorization in order to make the process energetically more efficient while reducing its environmental footprint. The effects of temperature, solid load and consecutive conversion phases on PW recirculation were assessed by using Ferula Communis plant residues as feedstock in HTC experiments. Recirculation of solvent promoted strong synergistic interactions between biomass and PW aimed at increasing hydrochar mass recovery. Hydrochar yield increased by 4-12 wt% on a dry basis (d.b.) according to reaction conditions. Biomass degradation was catalyzed by the reactive intermediates dissolved in the PW. The energy balance results showed that the energy recovery almost doubled by recycling PW when compared to the experiments carried out using only deionized water as HTC solvent. [ABSTRACT FROM AUTHOR]

In this study fresh carob tree fruits (CF), a very widespread botanical species in the Mediterranean basin, were hydrothermally carbonized (HTC) at 200, 230, 250, and 280 °C for a residence time of 0.5 h and a biomass-to-water mass ratio (B/W) of 0.1. CF hydrochars were characterized in terms of elemental and proximate analysis for their possible valorization as solid biofuels. Increased reaction severity showed a decrease in solid mass yield recovery but an increase in hydrochar fixed carbon content and energy density. Hydrochars showed a high heating value (HHV) up to about 27.7 MJ/kg with a corresponding energy densification ratio (EDR) higher than 150%. CF hydrochars were also investigated as potential carbon-dense material as fillers in bio-plastic. Therefore, the CF hydrochar particles, at different concentrations, have been introduced in biopolymer matrices, such as PolyButylene Adipate Terephthalate (PBAT), by melt mixing and the rheological and mechanical behaviour of the bio-composites have been evaluated considering their potential application in the packaging sector. [ABSTRACT FROM AUTHOR]

In this study, hydrothermal carbonization (HTC) of Ricinus Communis (RC) (seeds and husks) has been carried out at a temperature range of 120-250 °C, 1 h of residence time, and corresponding autogenous water pressures (2-40 bar) to investigate the production of energy-dense solid (hydrochar) and liquid (bio-crude) biofuels. RC, an oilseed and phyto-depurant plant, exhibits high resistance to drought and climatic variations, and abilities to adapt to polluted and low fertility environments. RC, although is originally from tropical Africa, is also widespread and spontaneously grown in the south of Italy and in particular in the Sicilian region. Dried hydrochars were extracted with acetone (7.5 ml/gr), leading to a bio-crude fraction and a solid residue. The results showed that the bio-crude mass yield increased with increasing HTC temperature up to 47.6% at 250 °C. The bio-crude showed no significant changes in higher heating value (HHV) which was of 35.3 MJ/kg on average. The hydrochar mass yield varied between 78 and 63% at 120 and 250 °C, respectively, and the corresponding acetone-extracted hydrochars showed HHVs of 19.47 and 23.72 MJ/kg. Hydrothermal carbonization proved to be an efficient thermochemical treatment for the production of valuable bio-char and energy-dense bio-crude. [ABSTRACT FROM AUTHOR]

Hydrothermal liquefaction (HTL) is a thermochemical processing technology for the conversion of waste biomass in the presence of water near critical condition. HTL is typically carried out between 250 and 350 °C and corresponding water-saturated pressures between 4 and 16 MPa, respectively. The process target product is a high viscous hydrophobic bio-oil called bio-crude. Bio-crude added value has been primarily recognized from bio-fuels perspective as a replacement for bio-diesel and bio-based aviation fuels, however, it can also upgraded into high added value products for the green chemistry and bio-based industries. The present study describes the design and set up of a new HTL experimental apparatus to investigate agro-waste biomass liquefaction at lab scale. The HTL apparatus was tested using tangerine peel waste and castor seeds as feedstock. Raw substrates, solid residues (hydrochars) and bio-oils were characterized in terms of proximate analysis and higher heating value while aqueous liquid residues were analyzed in terms of pH and total organic carbon content (TOC). Preliminary results obtained confirmed that the lab scale HTL apparatus, developed in this work, represents a valuable tool for the study of waste biomass conversion into high-energy dense solid and liquid bio-fuels. [ABSTRACT FROM AUTHOR]

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) of sewage sludge has been investigated in this study to demonstrate its capability to segregate phosphorous element and produce a solid energy dense material, i.e. hydrochar, which could find application as solid bio-fuel and/or soil amendment. In this study, centrifuged anaerobically digested sewage sludge (total solid content: 21 wt.%) from Trento North (Italy) waste water treatment plant was hydrothermally carbonized at 190 and 210 °C at 1 and 3 h of residence time. Hydrochars, recovered via filtration, were leached using 4 M HCl solution at room temperature to transfer phosphorous (P) and inorganic elements into the aqueous solution. Recovery of P was achieved via phosphate salt precipitation by alkalinisation, up to pH 9, of the acidic leachate using a 5 M NaOH solution. Sewage sludge and the corresponding hydrochars, before and after acid leaching, were characterized in terms of energy properties (HHV) by calorimetric analysis, P and inorganic elements content via ICP-OES. Results showed that HTC promotes segregation of P element in the hydrochar (up to 90 wt.% of the initial content on a dry basis at 190 °C, 1 h). The study demonstrated that P can be effectively recovered via precipitation via acidic leaching and subsequent alkalization with total recovery yields higher than 70 wt.%. The hydrochar residues, after leaching, showed inorganic elements content and energy properties compatible with their possible use as soil amendment in agriculture and/or as solid biofuel. [ABSTRACT FROM AUTHOR]