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The chemical-physical processes controlling hydrothermal carbonization (HTC) are still not completely understood. This paper focuses on two aspects: the influence on the hydrochar formation of the particle size of the feedstock and the presence of solved compounds in the feedwater. To address these, brewer’s spent grains were crushed to 250 μm proved by HPLC analysis of liquid byproducts, particularly when rPW, containing readily condensable/polymerizable intermediates, is added. This has a positive effect on the yield and carbon content of the hydrochars caused mainly by an increase in its secondary char fraction. The reaction pathways involved are discussed in detail.

This study evaluates the effects of thermal hydrolysis (TH) pretreatment on anaerobic digestion (AD), through results obtained by biochemical methane potential (BMP) tests under mesophilic conditions (35 °C). Thickened sludge from a wastewater treatment plant (WWTP) was thermally treated under two different temperatures (150 and 170 °C) and reaction times (30 and 60 min). Results show a significant increase in soluble COD, compared with the untreated sludge, when sludge was treated at 170 °C for 60 min. Moreover, the following BMP tests point out that TH pretreatment of sludge accelerated the AD rate and increased the biogas yield contributing to an increase in methane production, ranging between 17 and 24% compared with the raw sludge. Furthermore, the hydrolysis constant was estimated and methane production and degree of disintegration of the TH pretreated sludge were correlated, in order to deep the knowledge on the hydrolysis as the AD rate-limiting step. Further, the combined effects of TH pretreatment and AD on sludge show a reduction of total and volatile solids up to 19% and 24%, respectively.

The present work reports a case study for the industrialization of a biorefinery aimed at valorizing fish processing residues in order to obtain ω-3 concentrates for the nutraceutical sector. The biorefinery includes a series of processes: oil extraction from fish waste, fish oil transesterification with ethanol, ω-3 concentration based on supercritical CO2 fractionation. The biorefinery is at first designed and then modeled by Aspen Plus™: this allows for a comprehensive picture (mass and energy flows, processing costs and costs for investment) of the overall process. In accordance with the zero-waste concept, all the biorefinery by-products are valorized: fish proteins as fishmeal, and glycerol, saturated fatty acids and short chain unsaturated fatty acids as liquid biofuel. In addition, fish oil transesterification with ethanol is also experimentally tested in different operational conditions in order to maximize fish oil conversion to fatty acid ethyl esters. A trout processing company located in Trentino Province, Italy, represents the case study. The company produces 870 t/year of fish waste. Mass balances allow estimating a production of 26.6 t/year of ω-3 rich oil (income: 1.3 M€), 160 t/year of fish proteins (income: 0.27 M€), and 160 t/year of liquid biofuel. The biofuel, fed to a 100 kWel CHP unit, allows to produce 720 MWhe/year and 870 MWhth/year, covering the total electricity consumption of the plant and providing more than 45% of the thermal energy needs. This translates into a reduction in utility costs of about 0.12 M€ and avoids the emission of 416 t/year of CO2. Finally, the total investment costs for the whole biorefinery amount to about 3.34 M€. In conclusion, this study demonstrates that the production of ω-3 rich fish oils in a bio-refinery concept could become a good opportunity for valorizing fish by-products and increasing the competitiveness of the fish processing industry.

In this paper the attention is focused on the energetic exploitation of grape marc, the main biomass remaining from the vine-making process. Three different scenarios have been analyzed: a typical combustion process coupled with a steam cycle for cogeneration, an air gasification process and, finally, a steam gasification process with indirect heating. The syngas from gasification has been intended to fuel a gas turbine and its utilization in fuel cells has been considered as well. Considering the simulation results, it seems that the combustion process coupled with a steam cycle should be preferred to both air and steam gasification processes coupled with a gas turbine; this, in view of the greater simplicity of the combustion scheme. Differently, even if undoubtedly more complex, the steam gasification process coupled with fuel cells seems competitive with the combustion scheme. In fact, in this case, a noticeably larger electric efficiency corresponds to a greater process complexity.