Characterization of biochars and dissolved organic matter phases obtained upon hydrothermal carbonization of Elodea nuttallii

• Invasive Elodea nuttallii plants were subjected to hydrothermal carbonization.
• Biochars contain extraordinarily high fraction of inorganic elements.
• Process water is a good substrate for biogas production.
• Phenols, carboxylic acids and N-functionalized proved abundant breakdown products.

The invasive aquatic plant Elodea nuttallii was subjected to hydrothermal carbonization at 200 °C and 240 °C to produce biochar. About 58% w/w of the organic carbon of the pristine plant was translocated into the solid biochar irrespectively of the operating temperature. The process water rich in dissolved organic matter proved a good substrate for biogas production. The E. nuttallii plants showed a high capability of incorporating metals into the biomass. This large inorganic fraction which was mainly transferred into the biochar (except sodium and potassium) may hamper the prospective application of biochar as soil amendment. The high ash content in biochar (∼40% w/w) along with its relatively low content of organic carbon (∼36% w/w) is associated with low higher heating values. Fatty acids were completely hydrolyzed from lipids due to hydrothermal treatment. Low molecular-weight carboxylic acids (acetic and lactic acid), phenols and phenolic acids turned out major organic breakdown products.