In a recent study published in BiomassBiomass is a complex biological organic or non-organic solid product derived from living or recently living organism and available naturally. Various types of wastes such as animal manure, waste paper, sludge and many industrial wastes are also treated as biomass because like natural biomass these More and Bioenergy, Michael A. Kruge and co-authors examined the properties and composition of five hydrochars and one reference biochar using advanced analytical methods, traditionally employed in organic geochemistry. The research explores how the conversion of diverse organic solid wastes into hydrochar using hydrothermal carbonization (HTC) could offer a sustainable solution to waste management, minimizing reliance on landfills and creating valuable, carbon-rich materials. Unlike biochar, which is produced by dry pyrolysisPyrolysis is a thermochemical process that converts waste biomass into bio-char, bio-oil, and pyro-gas. It offers significant advantages in waste valorization, turning low-value materials into economically valuable resources. Its versatility allows for tailored products based on operational conditions, presenting itself as a cost-effective and efficient More and has relatively uniform properties, hydrochar characteristics are highly dependent on the initial feedstockFeedstock refers to the raw organic material used to produce biochar. This can include a wide range of materials, such as wood chips, agricultural residues, and animal manure. More. The team’s approach was to apply methods used for fossil fuels to better understand and optimize these materials.

The hydrochars were produced at a pilot plant scale from real-world, heterogeneous wastes, including scrap wood, green waste, winery pomace, and the organic fraction of municipal solid waste (OFMSW). The waste wood hydrochar achieved the highest energy performance, with an impressive energy yield and the transformation shifts the material’s composition from that of raw biomass towards lower-rank fuels, such as peat and lignite, placing it distinctly apart from the highly carbonized oak biochar, which shows ratios consistent with high-rank coal. The hydrochars also showed a modest increase in their higher heating value, averaging 21 megajoules per kilogram, comparable to low-rank coal.

The extensive testing categorized the hydrochars into two main groups: “oily” and “woody,” based on their molecular composition. The “oily” group, comprising OFMSW and grape pomace hydrochars, was found to be rich in lipids. The OFMSW hydrochar, in particular, was characterized by a high abundance of fatty acids and esters, with oleic acid being predominant, suggesting origins from food scraps and cooking fats. The grape pomace hydrochar also contained abundant fatty acids and esters, but with linoleic acid as the primary component, a marker for grapeseed oil. These “oily” hydrochars exhibited higher H/C ratios, greater yields at lower temperatures in thermal analysis, and a dominance of aliphatic chemical bonds. Importantly, the HAWK pyrolysis indicated that OFMSW hydrochar has a significantly higher Production Index and Oil Saturation Index compared to the wood hydrochar, pointing toward a strong potential for liquid biofuel production.

In contrast, the “woody” hydrochars, derived from scrap wood and green waste, are lignocellulosic, meaning they are rich in lignin and polysaccharide components. Their molecular fingerprints were dominated by lignin pyrolysis products, specifically methoxyphenols, and the sugar pyrolysis marker, levoglucosan. These wood-based hydrochars show potential as a feedstock for obtaining valuable platform chemicals for the bio-refinery industry, such as guaiacol, a precursor for vanillin, and levoglucosan, used in the synthesis of polymers. The study also noted that processing waste wood with acidic cheese whey dramatically increased the yield of certain methoxyphenols, suggesting a catalytic effect that enhances the production of desirable chemicals.

Thermogravimetric analysis (TGA) further highlighted the difference between the material types. Furthermore, the molecular complexity of the heterogenous OFMSW hydrochar was evident in its TGA and Py-FID results, which required seven distinct thermal components to accurately model its decomposition, reflecting its diverse organic waste source. This research effectively demonstrated that the application of specialized organic geochemistry methods provides valuable, molecular-level insights crucial for understanding the composition of waste-derived hydrochar and optimizing its use as a sustainable material for both energy and chemical production. Future research is recommended to focus on quantitative analysis, particularly using TD-Py-GC-MS with internal standards, to develop predictive models for product yields.

Source: Kruge, M. A., Centeno, T. A., Amado-Fierro, Á., González-LaFuente, J. M., de, R. F., & Gallegod, J. L. R. (2026). Application of organic geochemistry to the characterization of hydrochar and biochar: Insights into composition and optimization. Biomass and Bioenergy, 207, 108706.