Revealing Molecular Level Changes of Dissolved Organic Matter in Black Soils during Continuous Leaching and Their Implications for Drinking Water Treatment

The dynamics of dissolved organic matter (DOM) transport from black soil and its potential effects on the quality, safety, and treatability of water are poorly understood. Here, sequential column leaching experiments with black soil, surface water, and synthetic rainwater were performed to explore the molecular variations in leachable organic matter and its potential influences on water treatment. The fluorescence and UV–vis spectroscopy, together with size exclusion chromatography, showed that the greater proportion of low molecular weight (MW) aliphatic DOM in initial eluates gradually changed to higher fractions of larger aromatic DOM in later eluates. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed a decrease in lignin-like molecules and increase in condensed aromatic components of the DOM upon continuous leaching. The disinfection byproduct formation potential (DBPFP) was reduced with increasing leaching volume, along with the decreasing yields of dissolved organic carbon (DOC). Furthermore, compared with that of the first leaching phase (P1), the chlorine reactivity (DBPFP normalized to DOC) of DOM at the tenth leaching phase (P10) increased by 26–53%, 51–60%, and 39–44%, for trihalomethanes, haloacetic acids, and chloral hydrates, respectively, due to increased aromatic fractions in DOM. The principal component analysis (PCA) and partial least-squares path model (PLS–PM) showed that the quantity and quality of DOM leached by surface water and synthetic rainwater were significantly different. Lastly, despite the pronounced variations in DOM properties, the black soil-derived DOM displayed high treatability, with 52–71% of DOC, 54–69% of trihalomethane (THM) precursors, 60–80% of haloacetic acid (HAA) precursors, and nearly all (∼100%) of the nitrogen-containing DBP (N-DBP), haloketone (HK), and chloral hydrate (CH) precursors being removed by a nanofiltration membrane. Our results will contribute to the understanding of soil DOM mitigation and potential impacts on drinking water production.