Production Temperature Effects on the Structure of Hydrochar-Derived Dissolved Organic Matter and Associated Toxicity

Hydrochar
is a carbonaceous material derived from hydrothermal liquefaction,
and it carries good potential as a new material for environmental
applications. However, little is known about the dissolved organic
matter (DOM) associated with hydrochar and the consequences of its
release. The relationship between the production temperature and the
characteristics of DOM released from hydrochar as well as the associated
biotoxicity was investigated using a suite of advanced molecular and
spectroscopic tools. With the increase in production temperature,
the resulted hydrochar-based DOM contained a higher content of phenols
and organic acids but less sugars and furans. Meanwhile, the molecular
structure of DOM shifted to lower molecular weight with higher organic
contents containing <6 O atoms per compound, aromatics, and N-containing
substances. While low-temperature hydrochar-derived DOM showed minimal
biotoxicity, increase in production temperature to 330 °C led
to a great rise in toxicity. This might be attributed to the increased
contents of phenols, organic acids, and organics containing <6
O atoms and 1 N atom per compound. These results suggest that hydrochar-derived
DOM have more negative impacts on the environment than the organics
associated with biochar production. Such understanding highlights
the importance of controlling the hydrochar production process.