Agricultural systems require sustainable alternatives to chemical pesticides for controlling crop pathogens. This study evaluated biochar derived from grape pomace, a major winery byproduct, as an antimicrobial agent against tomato root pathogens (Fusarium oxysporum f. sp. lycopersici, Phytophthora infestans, Verticillium dahliae and Rhizoctonia solani). Under in vitro conditions, pathogens were exposed to biochar, washed biochar, and aqueous extracts in solid and liquid media. Biochar significantly inhibited fungal growth, whereas aqueous extracts showed no antifungal activity. Similar effects of washed and unwashed biochar indicate that inhibition is associated with the solid biochar structure rather than soluble compounds, and pH alone did not explain the effect. F. oxysporum and R. solani were most sensitive at lower concentrations. Metabolomic analysis identified 59 differential metabolites linked to stress responses. These findings highlight grape pomace-derived biochar as a promising sustainable strategy for managing tomato root pathogens.

This study explores hydrothermal carbonization (HTC) of garden and park waste, sewage sludge and food waste as a sustainable alternative for waste management, focusing on the enhancement of hydrochar properties and phytotoxicity reduction through post-treatments such as washing and aging. Additionally, co-HTC of lignocellulosic waste mixed with the other two raw materials using several mixing ratios (1:3, 1:1, 3:1 wt:wt in dry basis) were carried out to assess potential beneficial effects on hydrochars characteristics. HTC reactions were done at 180 °C for 1 h. Pyrolysis of individual feedstocks, at 650 °C for 1 h, was also performed to compare biochar with hydrochars and co-hydrochars. Ultimate analysis reported high ash content in sewage sludge-derived chars, along with lower volatile matter and higher ash content in biochars respect to hydrochars, regardless of feedstock or mixing ratio in co-HTC. Hydrochars exhibited acidic pH, and those derived from sewage sludge and, especially, food waste showed electrical conductivity values remarkably higher than those from garden and park waste. Biochars displayed fewer surface functional groups and higher mineral concentration than hydrochars. Regarding leachates, those from food waste-derived hydrochars released higher concentrations of organic compounds, including potentially phytotoxic molecules, compared to those from lignocellulosic waste or sewage sludge. Nevertheless, phytotoxicity assays revealed that fresh hydrochars from sewage sludge and food waste inhibited tomato seed germination, whereas hydrochars from garden and park waste were not phytotoxic. Overall, co-HTC offers a promising approach for integrated waste valorization, enabling the production of hydrochars suitable for use as soil amendments.

Hydrothermal carbonization (HTC) offers a promising pathway for valorizing food waste into hydrochar for soil amendment applications; however, the release of toxic compounds during post-application leaching remains a key concern. This study evaluated how feedstock composition and HTC conditions influence the ecotoxicity of hydrochar wash waters generated under laboratory-simulated washing conditions designed to represent potential rainfall or irrigation-driven leaching. Wash water composition and toxicity (via Escherichia coli and Aliivibrio fischeri assays) were measured. Food wastes (e.g., fruit, vegetable, grain, meat and dairy/confectionery products) were carbonized at 200-250 °C across multiple residence times. All hydrochars were sequentially washed to simulate rainfall or irrigation events. Across all conditions, cumulative washing was the strongest factor associated with toxicity, with the first wash producing the most toxic leachates and toxicity declining rapidly with subsequent washes, indicating that inhibitory compounds are largely water soluble. Feedstock composition appeared to significantly influence toxicity magnitude, with fruit-derived hydrochars consistently producing the least toxic wash waters, while vegetable- and grain-derived materials exhibited higher and more variable toxicity. A generalized linear model indicated that hydrogen richness was among the most influential feedstock properties associated with toxicity, with lower H:C values associated with reduced E. coli toxicity and higher A. fischeri EC50 values across the evaluated conditions and O:C ratio exerting a comparatively minor influence. Overall, these results provide a screening-level assessment of potential ecotoxicity risks associated with hydrochar-derived leachates.

In this work, the adsorption of imidazolium-based ionic liquids containing the bis(trifluoromethanesulfonyl) imide anion (NTf2−) from aqueous phase was evaluated using different activated carbons (ACs). Three commercial Acs and two Acs prepared from grape seeds (one produced by pyrolysis and the other by hydrothermal carbonization (HTC), both activated with potassium hydroxide) were tested, assessing the adsorption of both the cation and the anion. For commercial ACs, similar adsorption performances were observed, with maximum adsorption capacities ranging from 0.85 to 1.08 mmol g−1. These values increased under acidic conditions (pH 4), reaching 1.74 mmol g−1 for the 1-butyl-3-methylimidazolium cation (Bmim+) and 1.87 mmol g−1 for NTf2−. Among the prepared ACs, the HTC-derived AC showed slightly higher capacities than the commercial samples, while the pyrolysis-derived AC exhibited the highest adsorption capacity for BmimNTf2 (3.36 mmol g−1 at pH 4). In terms of reusability, the pyrolysis-derived AC maintained 84% of its initial adsorption capacity between the third and fifth regeneration cycles. These results highlight the high adsorption performance and recyclability of grape-seed-derived activated carbons, demonstrating their potential for the removal of ionic liquids from aqueous environments.

Dark fermentation (DF) of food waste (FW) is a promising and sustainable alternative for valorization, where a carbohydrate-rich substrate is converted into value-added products such as hydrogen (H2) and volatile fatty acids (VFA). In this work, several combinations of hydrogen-producing bacteria (Clostridium butyricum and Clostridium beijerinckii) along with lactic acid bacteria (Lactobacillus plantarum and Lactobacillus pentosus) were evaluated for H2 production using sterile FW as a substrate in DF batch tests as follows: 10

The management through co-hydrothermal carbonization (co-HTC) of swine manure (SM) and soybean hulls (SH), a by-product of animal feeding, is established as a strategy for their material and/or energy recovery. The effect of hydrothermal carbonization (HTC) temperature (210–240 °C) and mass ratio (1:0, 1:1, 1:3, 0:1) on hydrochar characteristics revealed that an improved hydrochar (C (51–59%), HHV (21–24 MJ/kg), N (~2%), S (~0.3%), and ash (<9%)) is produced with respect to hydrochar obtained from individually treated wastes. Regarding biofuel characteristics, hydrochar obtained from the SM/SH mass ratio (1:3) at 240 °C complied with the requirements of the ISO/TS 17225-8:2023 (N < 2.5%; S < 0.3%; HHV > 17 MJ/kg; ash < 12%) and showed high energy content (23.2 MJ/kg) and a greater thermal stability than the hydrochar obtained from individual wastes. Hydrochar retained relatively high amounts of nutrients such as phosphorus (6.5–9.7 g/kg), potassium (2.0–3.5 g/kg), and calcium (9–20 g/kg), which supports their use as soil improvers. Moreover, all hydrochar fulfill the standards (Spanish Royal Decrees 1051/2022, 824/2024 and EU Regulation 2019/1009) for sustainable nutrition in agriculture soils in terms of heavy metals concentration. The co-HTC of swine manure and soybean hulls demonstrated a promising transformation of waste materials into biofuel and/or soil improvers.

This study aims to obtain a carbonaceous material with suitable properties to be used as a solid biofuel by recycling process water from hydrothermal carbonization (HTC) of garden and park waste (GPW). The research is focused on maximizing mass yield and energy recovery as well as facilitating the treatment of the liquid fraction throughout reusing cycles of the liquid fraction. Process water recycling moderately improved the mass performance of the hydrochar, resulting in a higher energy recovery of almost 20 percentage points compared with that achieved (less than 79%) with conventional HTC (GPW + freshwater feed). An improvement in char fuel quality was observed, showing more suitable morphological, physical, and chemical characteristics, higher reactivity and combustion temperature, and lower probability of ash sintering. Successive process water reuse cycles allowed some increase in energy yield but, at the same time, degraded the quality of hydrochar as a biofuel. Process water composition showed an increase in chemical oxygen demand and total organic carbon, which almost doubled after three successive reuse cycles. The concentration of volatile fatty acids increased around 5-fold (up to 20 g L-1), with acetic acid accounting for 85% of the total. Subsequent anaerobic digestion of the process water removed up to 75% of the COD and yielded a biogas with high methane content (225-302 N mL CH4 g(-1) CODadded). Recycling of the process water significantly improved the total energy recovery (hydrochar + methane) to 90% after a single recycling, compared to 84% achieved with conventional HTC and subsequent anaerobic treatment of the resulting process water.

Hydrothermal carbonization (HTC) of food waste produces hydrochar-a suitable biofuel-and process water (PW), which has a high organic content suitable for material and energy recovery. In this work, we study the effect of pH (4.8, 5.3, and 6.0) and organic loading rate (OLR; 2.5, 5.0, and 7.5 gCOD L- 1 d- 1) throughout the dark fermentation (DF) of PW from the HTC of food waste (180 degrees C, 1 h) in a continuous stirred tank reactor. The highest hydrogen yield (197.5 mL H2 L- 1 d- 1) was reached at pH 4.8 and OLR 5 gCOD L- 1 d- 1, associated with a prevalence of Clostridium bacteria. The highest volatile fatty acids concentration (10.2 gCOD & sdot;L- 1) was achieved at pH 4.8 and OLR 7.5 gCOD L- 1 d- 1, with a dominance of Actinobacteria phylum. The integrated system HTC-DF allowed a potential energy recovery of 11.2 MJ kg- 1.

Ionic liquids (ILs) are potential substitutes for conventional organic solvents. In the synthesis or use of ILs, wastewater discharges may occur that can introduce ILs into the aquatic system. Because of the relatively high solubility of ILs, their presence in the environment is of concern because of their low biodegradability and high ecotoxicity. However, many ILs are not readily degraded in conventional wastewater treatment plants and can accumulate in the environment. Advanced oxidation processes (AOPs) have emerged as technologies able to remove a wide range of recalcitrant pollutants. In this chapter, we evaluate the degradation of different ILs from the imidazolium and pyridinium families by AOPs, including Fenton, catalytic wet peroxide oxidation (CWPO), photo-assisted treatments, and electrochemical processes.

Hydrothermal carbonization (HTC) is a promising alternative to transform biomass waste into a solid carbonaceous material (hydrochar) and a process water with potential for material and energy recovery. In this study, two alternatives for process water treatment by conventional and acid-assisted HTC of swine manure are discussed. Process water from conventional HTC at 180 °C showed high biodegradability (55% COD removal) and methane production (∼290 mL STP CH4 g-1 CODadded) and the treatment in an upflow anaerobic sludge blanket reactor allowed obtaining a high methane production yield (1.3 L CH4 L-1 d-1) and COD removal (∼70%). The analysis of the microbiota showed a high concentration of Synergistota and Firmicutes phyla, with high degradation of organic nitrogen-containing organic compounds. Acid-assisted HTC proved to be a viable option for nutrient recovery (migration of 83% of the P to the process water), which allowed obtaining a solid salt by chemical precipitation with Mg(OH)2 (NPK of 4/4/0.4) and MgCl2 (NPK 8/17/0.5), with a negligible content of heavy metals. The characteristics of the precipitated solid complied with the requirements of European Regulation (2019)/1009 for fertilizers and amendments in agricultural soils, being a suitable alternative for the recycling of nutrients from wastes.

In this work, a novel strategy for food waste valorization was evaluated from an environmental life-cycle perspective. A system based on acid-assisted hydrothermal carbonization of food waste combined with the exploitation of hydrochar by combustion and process water through nutrient recovery stage and subsequent anaerobic digestion, was assessed and compared with stand-alone anaerobic digestion as the reference system. This combination of processes aims to recover both nutrients in a stage of struvite precipitation from process water and energy through hydrochar and biogas combustion. Both systems were modeled in Aspen Plus® to identify and quantify their most relevant input and output flows and subsequently evaluate their environmental performance through the life cycle assessment methodology. The novel combined system was found to generally involve a more favorable environmental performance than the reference stand-alone configuration, which would be closely linked to the substitution of hydrochar for fossil fuels. In addition, the impacts associated with soil application of the struvite produced in the integrated process would also be reduced compared to the use of the digestate generated in the stand-alone anaerobic digestion process. Following these results and the evolving regulatory framework for biomass waste management, mainly in the field of nutrient recovery, combined process based on acid-assisted hydrothermal treatment plus nutrient recovery stage and anaerobic digestion is concluded to be a promising circular economy concept for food waste valorization.

In this work, chicken meat and bones (C-MBM) waste is treated through a sequence of stages including hydrothermal treatment (HTT), nutrient recovery and anaerobic digestion, with the aim of evaluating their potential synergy as a circular economy approach. HTT was carried out at 170, 200 and 230 ?, under non-acidic and acidic conditions using 0.5 M HCl (HTT-A). Phosphorous from process water was recovered by chemical precipitation with the addition of a Mg salt, and the liquid effluent was anaerobically treated to degrade organic matter and produce a methane-rich biogas. Hydrochar obtained under non-acidic conditions presented poor combustion characteristics, while HTT-A yielded a bio-oil with high higher heating value (asymptotic to 38 MJ/kg), good combustibility performance and high reactivity. More than 95% phosphorous (as phosphate) and almost 100% nitrogen (being 30% as NH4-N) content in C-MBM were solubilized in the process water upon HTT-A, while these nutrients were mainly retained in the hydrochar in non-acidic reactions. Chemical precipitation of P and NH4-N from HTT-A process water allowed recovering a crystalline solid identified as struvite and a struvite-apatite mixture, with negligible heavy metals content. High methane production (250-300 mL CH4/g CODadded) and organic matter removal (up to 75%) were achieved in the anaerobic tests. HTT proves to be a suitable treatment for material and energetic valorization of C-MBM, within a circular economy framework, which allows to obtain high value-added products (hydrochar/bio-oil, biofertilizers and biogas).

This work studies the fate of nutrients (N, P, and K) during the hydrothermal treatment of anaerobically digested sewage sludge to raise their concentrations in the liquid phase and facilitate their recovery as solid minerals by chemical precipitation. The hydrothermal process has been optimized by evaluating the temperature (170-230 degrees C) and reaction time (5-60 min) in an acid-free medium or with the addition of HCl (0.1-0.5 M). In the acid-free hydrothermal reactions, nutrients were mainly concentrated in the hydrochar, which were extracted with 0.5 M HCl (10% w/v). Following this route, 6.9 g N/kg, 13.8 g P/kg, and 8.8 g K/kg contained in the feedstock were extracted from the hydrochar produced at 230 degrees C, which, considering direct nutrient solubilization to process water by acid-free hydrothermal treatments, accounts for 82, 83, and 78% N, P, and K release, respectively. In the HCl-assisted hydrothermal treatment, the release of nutrients directly into the process water was improved and depended mainly on the acid concentration used and to a lesser extent on the reaction temperature. Operating at 230 degrees C and 0.5 M HCl, the release of 98% N (more than 45% as NH4-N), 87% P (as PO4-P), and 70% K contained in the feedstock was achieved in the process water. Chemical precipitation of phosphorus and nitrogen from the process water allowed the recovery of a solid identified as crystalline struvite, with high contents in P, Mg, and NH4-N and negligible heavy-metal content. The estimated cost of digested sewage sludge treatment could reach 13.7 euros per tonne, considering the energy inputs required in the hydrothermal treatment.

Co-hydrothermal carbonization (co-HTC) is a promising strategy to improve hydrothermal carbonization (HTC) of low-quality wastes. HTC of swine manure (SM), with high N (2.9 wt%), S (0.7 wt%) and ash (22.6 wt%) contents, as well as low C (35.6 wt%) and higher heating value (HHV; 14.3 MJ kg-1), resulted in a hydrochar with unsuitable characteristics as a solid fuel. Co-HTC of SM and garden and park waste (GPW) improved hydrochar properties (C content (43 - 48 wt%) and HHV (18 - 20 MJ kg-1), and decreased N (∼2 wt%), S (<0.3 wt%) and ash (<15 wt%) content. A high GPW ratio (>50 wt%) during co-HTC resulted in a hydrochar similar to that obtained from GPW. The co-HTC increased nutrient migration to the process water, which allowed the precipitation of salt with high P (7.8 wt%) and negligible heavy metal content. Anaerobic digestion of co-HTC process water allowed high organic matter removal (up to 65%), and methane production (315 - 325 mL CH4 g-1CODadded). Gross energy recovery by HTC and anaerobic digestion was 5 - 6-fold higher than anaerobic treatment of feedstocks. Therefore, co-HTC of SM and GPW with a ratio > 50% GPW proved to be a suitable approach to valorize and manage SM and obtain value-added products (hydrochar, mineral fertilizer and methane).

Hydrothermal carbonization (HTC) is a promising alternative to transform biomass waste into a solid carbonaceous material (hydrochar) and a process water with potential for material and energy recovery. In this study, two alternatives for process water treatment by conventional and acid-assisted HTC of swine manure are discussed. Process water from conventional HTC at 180°C showed high biodegradability (55% COD removal) and methane production (~ 290 mL CH4 g-1 CODadded) and the treatment in an upflow anaerobic sludge blanket reactor allowed obtaining a high methane production yield (1.3 L CH4 d-1 L-1) and COD removal (~ 70%). The analysis of the microbiota showed a high concentration of Synergistota and Firmicutes phyla, with high degradation capacity for the degradation of nitrogenous organic compounds. Acid-assisted HTC proved to be a viable option for nutrient recovery (migration of 83% of the P to the process water), which allowed obtaining a solid salt by chemical precipitation with MgOH2 (NPK of 4/4/0.4) and MgCl2 (NPK 8/17/0.5), with a negligible content of heavy metals. The characteristics of the precipitated solid complied with the requirements of European Regulation 2019/1009 for fertilizers and amendments in agricultural soils, being a suitable alternative for the recycling of nutrients from wastes.

Root-knot nematodes (RKNs) are obligate endoparasites that feed on their host plants to complete its life cycle, representing a major threat to agriculture and economy worldwide. The development of new management strategies becomes essential as effective chemical nematicides are progressively being restricted. Hence, we analysed grape pomace-derived biochars, pyrolysed at 350 °C (BC350) and 700 °C (BC700), focusing on their potential for RKN control. The thermal treatment of grape pomace caused an increase in the concentration of carbon and plant macro- and micronutrients, which were largely present in a water-soluble form. Synchrotron radiation-based Fourier transform infrared microspectroscopy data showed a general loss of carboxylic functional groups during pyrolysis, partially contributing to the alkalinisation of both biochars, mostly in BC700. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy analysis revealed a highly porous structure filled with different crystals composed of elements such as K, Ca, Mg, P, Si or Al, which could be a suitable environment for the growth of microorganisms. Biochar-derived aqueous extracts showed phytotoxicity to tomato seedlings at high concentrations, and disappeared upon dilution, but no toxic effect was observed on the nematode’s infective stage. However, the infective and reproductive traits of a Meloidogyne javanica population in tomato were significantly reduced (i.e. egg masses and eggs per plant) in washed-biochar-treated soil in pots (0.75%; BC350W). Therefore, the large amount of grape waste generated after wine production can be transformed into a valuable product such as biochar, effective for RKNs control, thus reducing the waste management problem and contributing to a circular economy. Graphical abstract

This work studies the catalytic reduction of nitrate using N-doped activated carbon catalysts. Activated carbons were prepared by hydrothermal carbonization (220 degrees C, 80 % water, 16 h) of garden and park waste and olive stones using (NH4)2SO4 as N source, followed by chemical activation with H3PO4 at 500 degrees C (N2 atmosphere, 1 h). These were impregnated with Pd and Sn to prepare bimetallic catalysts for nitrate catalytic reduction. N-doping improved the BET surface area up to 1369 m2 g-1 and increased the N content on the catalyst surface to 3 wt%. The N-doped catalysts showed better catalytic performance than the non-doped ones, showing high stability for 100 h on stream, reaching even higher activity than a catalyst supported on a commercial activated carbon. N -doping also showed a positive effect by decreasing NH4+ selectivity. Finally, natural and drinking waters spiked with NO3- were treated in continuous flow, exhibiting the N-doped activated carbon catalysts, prepared from garden and park waste, a high tolerance to ions other than NO3- present in the water solution.

The work focuses on the study of hydrochar upgrading from hydrothermal carbonization (HTC) of swine manure by HCl-assisted HTC or washing with HCl or acetone, as a post-treatment to conventional HTC. Conventional HTC of swine manure yields a low-quality hydrochar (C content ~ 38 wt.%, higher heating value (HHV) ~ 15 MJ kg −1 , and ash content up to 32 wt.%). HCl-assisted HTC (0.5 M HCl at 230 ℃) substantially reduced the ash content up to ~10 wt.% in the hydrochar and increased the C content to 58 wt.%, reaching a HHV of 23 MJ kg −1 . However, the N and S contents remained at values similar to those of the swine manure. Washing post-treatment of conventional hydrochars with HCl or acetone significantly improved the C content and the HHV in the range 47–58 wt.% and 19–25 MJ kg −1 , respectively, as well as the ash removal with values 7-11 wt.%. Washing the hydrochar with acetone significantly reduced the N and S contents, obtaining a carbonaceous material with properties suitable for solid biofuel according to ISO/TS 17225–8, (N < 3 wt.%; S < 0.15 wt.%; HHV > 17 MJ kg −1 ; and ash < 10 wt.%). Hydrochars obtained by HCl-assisted HTC and HCl/acetone washing post-treatment yielded higher thermal stability, as well as better reactivity and low ash agglomeration indexes than compared to conventional hydrochars. Washing post-treatment with acetone proved to be the best strategy to obtain improved hydrochars from swine manure for industrial use as a solid biofuel.