Unraveling the photochemical behavior of dissolved organic matter derived from hydrothermal carbonization process water: Insights from molecular transformation and photoactive species

Hydrothermal carbonization process water (HTPW) has been utilized as a substitute for chemical fertilizers in agricultural applications. However, the input of HTPW into paddy water, particularly the significant proportion of dissolved organic matter (DOM) in HTPW (DOM-HTPW), directly engages in photochemical transformations, a phenomenon often overlooked. This study observed a consistent decrease in humification (SUVA 280 , 7.7–53.9%) and aromaticity (SUVA 254 , 6.1–40.0%) of DOM-HTPW after irradiation. The primary active photobleaching components of DOM-HTPW varied depending on the feedstock, such as protein for chicken manure DOM-HTPW and lignin for rice straw DOM-HTPW. The photochemical activity of DOM-HTPW was augmented by its lower molecular weight and higher hydrophilic composition, particularly evident in chicken manure DOM-HTPW, which exhibited higher generation rates for 1 O 2 (35.1–37.1%), 3 DOM* (32.8–43.9%), and O 2 •− (28.6–48.8%) as measured by molecular probes. DOM-HTPW effectively facilitated the phototransformation of tetracycline, with the contribution of O 2 •− being more significant than 3 DOM* and 1 O 2 . These findings shed new light on the understanding the photochemical processes of DOM-HTPW as exogenous DOM and the interconnected fate of contaminants in aquatic environments.