Release of Dissolved Organic Matter from Sludge Biochar and Its Spectral Characteristics in Different Environmental Media

The widespread use of biochar in soil remediation has heightened interest in the role of its derived dissolved organic matter (DOM) in soil nutrient dynamics. However, how pyrolysis temperature shapes the characteristics of DOM released from sludge biochar remains unclear. The study examined variations in the composition and properties of DOM extracted from sludge biochar under two different solutions—ultrapure water (UP) and artificial root exudates (ARE)—across a range of pyrolysis temperatures. Results indicate that the dissolved organic carbon (DOC) content did not differ significantly between extraction environments. In contrast, pyrolysis temperature markedly influenced both the content and composition of DOM. DOM in sludge biochar was primarily composed of humic-like (C1, C2, C3) and tyrosine-like (C4) components. Specifically, DOM from low-temperature biochar was dominated by C2, C3, and C4, whereas high-temperature biochar contained mainly C2 and C4.