Insights into the molecular transformation in the dissolved organic compounds of agro-waste-hydrochars by microbial-aging using electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry.

Hydrochars-based dissolved organic matters (DOM) are easily available to organisms and thus have important influence on the biota once applying hydrochars as environment amendment. Thus, positive modifications on molecular composition of DOM is indispensable before hydrochars application. In this study, the impacts of microbial-aging by anaerobic fermentation on DOM of agro-waste-hydrochars was systematically assessed. Results revealed that microbial-aging caused lower DOM release but higher DOM molecular diversity. Moreover, microbial-aging resulted in the production of more biodegradable compounds, including lipids and proteins, and reduced the aromaticity of DOM. The highly oxygenated molecules (O/C > 0.6) were shifted into lower-order ones in the hydrochars-based DOM, suggesting the transformation of hydrophilic compounds into hydrophobic ones. Additionally, microbial-aging promoted the degradation of phenols by 99.0-98.9%, phenolic acids 37.8-73.5%, and polycyclic aromatic hydrocarbons by 83.4-90.4% in hydrochar-based DOM. Overall, this study demonstrates that microbial-aging changes the molecular characteristics of hydrochars-based DOM in a positive manner.