Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
8.3
3.9
Journals
Energies
Special Issues
Hydrothermal Carbonization for Sustainable Energy and Resource Recovery from Organic...
energies-logo
Submit to Energies Review for Energies Propose a Special Issue

Journal Menu

► Journal Menu

Journal Browser

► Journal Browser
share announcement

Hydrothermal Carbonization for Sustainable Energy and Resource Recovery from Organic Waste

A Special Issue of Energies (ISSN 1996-1073) belonging to the section "B: Energy and Environment".

Deadline for manuscript submissions: closed (31 May 2026) | Viewed by 2936

Editor

Dr. Klaudia Szkadłubowicz

E-Mail Website
Guest Editor
Department of Heat Engineering & Environment Protection, Faculty of Metals Engineering and Industrial Computer Science, AGH University of Krakow, Mickiewicza 30 Ave., 30-059 Krakow, Poland
Interests: hydrothermal carbonization; sewage sludge; organic waste; hydrochar; post-processing liquid

Special Issue Information

Dear Colleagues,

The growing global demand for sustainable energy and effective waste management has brought increasing attention to hydrothermal carbonization (HTC). This innovative thermochemical process converts diverse organic wastes into valuable solid, liquid, and gaseous products. HTC offers a sustainable pathway for converting biomass residues, sewage sludge, food waste, and other organic materials into hydrochar and nutrient-rich byproducts, thereby contributing to renewable energy production, resource recovery, and greenhouse gas reduction.

As societies move toward a circular and low-carbon economy, HTC is emerging as a key technology that bridges waste valorization with energy and material recovery. Its versatility, scalability, and ability to process wet feedstocks make it a promising solution for both urban and industrial applications. Recent developments in reactor design, process optimization, product utilization, and system integration have further expanded its role in sustainable development and environmental protection.

This Special Issue aims to present and disseminate the latest research, technological innovations, and practical applications of hydrothermal carbonization in the context of sustainable energy transition and resource efficiency. Submissions addressing experimental, theoretical, environmental, and techno-economic aspects of HTC are particularly encouraged.

Topics of interest include, but are not limited to:

  • Fundamentals and mechanisms of hydrothermal carbonization;
  • Process optimization and modeling;
  • Characterization and utilization of hydrochar;
  • Nutrient and resource recovery from HTC process liquids;
  • Integration of HTC with other renewable technologies;
  • Environmental and life cycle assessment;
  • Pilot and full-scale applications;
  • Policy and economic perspectives for HTC implementation.

Dr. Klaudia Szkadłubowicz
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 250 words) can be sent to the Editorial Office for assessment.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-anonymized peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Energies is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • hydrothermal carbonization
  • organic waste valorization
  • sustainable energy
  • circular economy
  • resource recovery
  • waste-to-energy
  • hydrochar
  • post- processing liquid
  • environmental sustainability

Benefits of Publishing in a Special Issue

  • Ease of navigation: Grouping papers by topic helps scholars navigate broad scope journals more efficiently.
  • Greater discoverability: Special Issues support the reach and impact of scientific research. Articles in Special Issues are more discoverable and cited more frequently.
  • Expansion of research network: Special Issues facilitate connections among authors, fostering scientific collaborations.
  • External promotion: Articles in Special Issues are often promoted through the journal's social media, increasing their visibility.
  • Reprint: MDPI Books provides the opportunity to republish successful Special Issues in book format, both online and in print.

Further information on MDPI's Special Issue policies can be found here.

Published Papers (5 papers)

Download All Papers
Order results
Result details
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:

Research

Jump to: Review

14 pages, 863 KB  
Article
Valorization of Bay Tree Pruning by Autohydrolysis: Chemical Characterization and Energy Potential
by Idalina Domingos, Miguel Ferreira, José Ferreira, Helder Viana, Luísa Cruz-Lopes and Bruno Esteves
Energies 2026, 19(15), 3630; https://doi.org/10.3390/en19153630 - 3 Aug 2026
Viewed by 268
Abstract
Bay laurel (Laurus nobilis L.) leaves and branches represent promising lignocellulosic residues for biorefinery and bioenergy applications. The present study evaluated the effect of autohydrolysis at different temperatures and residence times on the chemical composition, structural properties, and higher heating value (HHV) [...] Read more.
Bay laurel (Laurus nobilis L.) leaves and branches represent promising lignocellulosic residues for biorefinery and bioenergy applications. The present study evaluated the effect of autohydrolysis at different temperatures and residence times on the chemical composition, structural properties, and higher heating value (HHV) of both biomass fractions. The initial characterization revealed that leaves were richer in extractives and lignin, whereas branches contained higher amounts of α-cellulose and hemicelluloses. Autohydrolysis promoted the selective solubilization of biomass components, reaching maximum values of approximately 38% for leaves and 30% for branches. Increasing treatment severity enhanced hemicellulose removal and resulted in a relative enrichment of lignin and cellulose in the solid residues, while FTIR analysis showed that the main lignocellulosic structure was largely preserved. The solid residue after polyalcohol liquefaction presented a higher heating value, improving the heating value of the resulting solids, achieving maximum HHVs of 30.08 MJ kg−1 for leaves and 29.46 MJ kg−1 for branches at 180 °C for 30 min. Overall, the results indicate that autohydrolysis is a suitable strategy for the selective extraction of hemicellulose-rich fractions and the production of lignin-enriched solid residues. This process contributes to the sustainable valorization of bay laurel biomass within an integrated biorefinery framework. Full article
(This article belongs to the Special Issue Hydrothermal Carbonization for Sustainable Energy and Resource Recovery from Organic Waste)
►▼ Show Figures

Figure 1

18 pages, 4771 KB  
Article
Overcoming the HHV–Energy Recovery Tradeoff in Hydrothermal Carbonization of Water Hyacinth via Co-Biomass Selection and Citric Acid Catalysis
by Tassapak Wutisirirattanachai, Yudai Kohira, Mekuanint Lewoyehu, Desalew Fentie, Pranshu Bhatia, Masaaki Fujiwara, Solomon Addisu and Shinjiro Sato
Energies 2026, 19(11), 2541; https://doi.org/10.3390/en19112541 - 25 May 2026
Cited by 1 | Viewed by 490
Abstract
Hydrothermal carbonization (HTC) of wet biomass faces a fundamental tradeoff between higher heating value (HHV) and energy recovery (ER), where conditions that enhance carbon densification often reduce solid-phase energy retention. This study investigates whether co-biomass selection combined with citric acid (CA) catalysis can [...] Read more.
Hydrothermal carbonization (HTC) of wet biomass faces a fundamental tradeoff between higher heating value (HHV) and energy recovery (ER), where conditions that enhance carbon densification often reduce solid-phase energy retention. This study investigates whether co-biomass selection combined with citric acid (CA) catalysis can overcome this tradeoff in HTC of water hyacinth (WH), an invasive aquatic feedstock. WH was co-processed with wheat straw (WS), rice husk (RH), and chicken manure (CM) at 240–270 °C, with CA-assisted experiments performed at 240 °C. Individual feedstock HTC confirmed the HHV–ER tradeoff, and co-HTC without catalysis failed to resolve it. CA addition improved carbon densification but reduced ER when applied to WH alone. The WH–CM–CA system uniquely achieved a concurrent HHV of 21.3 MJ kg−1 and ER of 95.8%, with synergistic effects of 50.0% and 29.7%, respectively. FTIR and elemental analysis indicated that Maillard-type condensation between WH-derived sugars and CM-derived amino acids drove preferential solid-phase carbon retention. These findings demonstrate that resolving the HHV–ER tradeoff requires coupling CA catalysis with biochemical complementarity between carbohydrate-rich and protein-rich feedstocks. This approach provides a practical route for hydrochar production with high energy density and recovery for waste-to-energy applications, supporting circular and low-carbon valorization of invasive aquatic biomass and livestock waste streams. Full article
(This article belongs to the Special Issue Hydrothermal Carbonization for Sustainable Energy and Resource Recovery from Organic Waste)
►▼ Show Figures

Figure 1

16 pages, 1302 KB  
Article
Valorization of Sargassum via Hydrothermal Co-Liquefaction with Food Waste: Effects of Reaction Temperature and Feedstock Ratio on Biocrude Yield and Fuel Properties
by Md Mostafizur Rahman and Toufiq Reza
Energies 2026, 19(10), 2277; https://doi.org/10.3390/en19102277 - 8 May 2026
Viewed by 732
Abstract
The massive invasion of Sargassum (SG) in coastal regions has emerged as a growing environmental and economic challenge, driving interest in sustainable valorization strategies. Although hydrothermal liquefaction (HTL) has demonstrated potential for valorizing SG into biocrude, its high ash and low lipid content [...] Read more.
The massive invasion of Sargassum (SG) in coastal regions has emerged as a growing environmental and economic challenge, driving interest in sustainable valorization strategies. Although hydrothermal liquefaction (HTL) has demonstrated potential for valorizing SG into biocrude, its high ash and low lipid content limit conversion efficiency. In this context, hydrothermal co-liquefaction (CoHTL) offers a promising route by leveraging synergistic interactions with complementary feedstocks. This study investigates the effects of HTL temperature (275–350 °C) and feedstock ratio (5–15 wt% SFW) on biocrude production during the CoHTL of SG with simulated food waste (SFW). CoHTL with 5 wt% SFW at 300 °C produced the maximum biocrude yield of 45.6 ± 0.8 wt%, which was 27.6 wt% higher than that obtained from the individual HTL of SG, indicating a significant positive synergistic effect. However, this synergy decreased with increasing temperature and SFW fraction, with temperature exerting a more pronounced influence than feedstock ratio. CoHTL also produced biocrude with higher carbon and energy contents than HTL of SG, reaching up to 78.7 ± 0.3% and 37.2 ± 0.1 MJ/kg, respectively. The boiling point distribution showed a dominance of lighter volatile compounds in the 125–340 °C range, although this fraction decreased slightly after CoHTL. In addition, a slight increase in nitrogen content was observed in the CoHTL biocrude, indicating a trade-off associated with the process. Overall, CoHTL with SFW is an effective strategy for improving biocrude yield and energy recovery from SG, offering an enhanced pathway for its valorization. Full article
(This article belongs to the Special Issue Hydrothermal Carbonization for Sustainable Energy and Resource Recovery from Organic Waste)
►▼ Show Figures

Figure 1

Review

Jump to: Research

33 pages, 3203 KB  
Review
The Potential Role of the Liquid Phase Generated During Hydrothermal Carbonization in Energy Systems
by Klaudia Szkadłubowicz
Energies 2026, 19(13), 3129; https://doi.org/10.3390/en19133129 - 1 Jul 2026
Viewed by 350
Abstract
Hydrothermal carbonization (HTC) is a promising thermochemical process for valorizing wet biomass and organic waste streams, generating hydrochar, gas, and a liquid phase commonly referred to as HTC process liquid or the aqueous phase. Depending on feedstock type and process severity, hydrochar typically [...] Read more.
Hydrothermal carbonization (HTC) is a promising thermochemical process for valorizing wet biomass and organic waste streams, generating hydrochar, gas, and a liquid phase commonly referred to as HTC process liquid or the aqueous phase. Depending on feedstock type and process severity, hydrochar typically accounts for approximately 40–70 wt.% of the initial dry feedstock, the liquid phase for about 30–60 wt.% in lignocellulosic and agricultural residues, and the gas phase for about 1–10 wt.%, while highly hydrated waste streams may generate even higher liquid-phase shares. Although hydrochar has traditionally been considered the main energy product, the liquid phase may retain approximately 20–65% of the initial feedstock carbon and around 15–25% of the initial energy content. However, its high chemical oxygen demand, elevated organic carbon content, variable biodegradability, toxicity, and inhibitory compounds often lead to its classification as a wastewater stream requiring treatment. The crucial novelty of this review is its system-oriented evaluation of HTC process liquid as an energy-bearing and system-integrating stream rather than merely as a wastewater by-product or as a substrate for isolated valorization routes. Therefore, this review evaluates the role of HTC process liquid in energy systems, focusing on its formation mechanisms, chemical composition, energy potential, valorization pathways, integration strategies, and environmental implications. The reviewed evidence shows that HTC process liquid contains a complex mixture of dissolved organic compounds, including volatile fatty acids, sugars, furans, phenols, ketones, aldehydes, amino acids, ammonia, and nitrogen-containing heterocycles. These compounds may support anaerobic digestion, dark fermentation, aqueous phase reforming, electrochemical conversion, nutrient recovery, and process-water recirculation. Among these routes, anaerobic digestion is currently the most mature, although its efficiency depends strongly on HTC severity, feedstock type, inhibitor formation, and microbial adaptation. Hydrogen-oriented and electrochemical pathways offer additional opportunities but still require further validation using real HTC liquids, standardized yield reporting, and long-term stability assessment. Overall, HTC process liquid should not be regarded solely as an environmental burden, but as a chemically complex and energy-rich stream that may improve the performance of integrated HTC-based bioenergy systems. Future research should focus on standardized liquid-phase energy metrics, long-term process integration, toxicity control, and experimentally validated techno-economic and life-cycle assessments. Full article
(This article belongs to the Special Issue Hydrothermal Carbonization for Sustainable Energy and Resource Recovery from Organic Waste)
►▼ Show Figures

Figure 1

24 pages, 2125 KB  
Review
Hydrothermal Carbonization of Marine Biowaste: A Focused Review of Hydrochar Production, Characterization, and Applications
by Tatwadhika Rangin Siddhartha, Frederik Ronsse and Philippe M. Heynderickx
Energies 2026, 19(13), 3124; https://doi.org/10.3390/en19133124 - 1 Jul 2026
Viewed by 463
Abstract
Marine biowaste (fish and crustacean processing residues) is produced in tens of millions of tons annually, yet remains dramatically underutilized as a feedstock. Hydrothermal carbonization offers a technically attractive valorization route for these high-moisture, non-lignocellulosic materials, converting them to carbon-enriched hydrochar without the [...] Read more.
Marine biowaste (fish and crustacean processing residues) is produced in tens of millions of tons annually, yet remains dramatically underutilized as a feedstock. Hydrothermal carbonization offers a technically attractive valorization route for these high-moisture, non-lignocellulosic materials, converting them to carbon-enriched hydrochar without the energy-intensive pre-drying required by pyrolysis. This focused review treats marine animal waste as the primary studies and micro- and macroalgal hydrothermal carbonization as a comparative benchmark to understand how the current research is going, the impact of production parameters, potential application, and possible research gaps to explore. Crustacean waste yields substantially more hydrochar (37–69%) than fish waste (15–34%) under equivalent conditions, driven by calcium carbonate retention in the solid phase. Unactivated hydrochars have low BET surface areas (<30 m2/g) and modest adsorption capacities (~10 mg/g). Acid deashing followed by KOH activation at 700 °C unlocks nanoporous structures with BET surface areas up to 680 m2/g and oxytetracycline adsorption capacities of 61.3 mg/g. Critical research gaps include the absence of techno-economic analysis, limited life-cycle assessment, and non-standardized reporting conventions. These must be addressed before upscaling to industrial viability can be achieved. Full article
(This article belongs to the Special Issue Hydrothermal Carbonization for Sustainable Energy and Resource Recovery from Organic Waste)
►▼ Show Figures

Figure 1

Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
 
Displaying articles 1-5
Back to TopTop