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) transportfrom blacksoil and its potential effects on the quality, safety, and treatabilityof water are poorly understood. Here, sequential column leaching experimentswith black soil, surface water, and synthetic rainwater were performedto explore the molecular variations in leachable organic matter andits potential influences on water treatment. The fluorescence andUV-vis spectroscopy, together with size exclusion chromatography,showed that the greater proportion of low molecular weight (MW) aliphaticDOM in initial eluates gradually changed to higher fractions of largeraromatic DOM in later eluates. Fourier transform ion cyclotron resonancemass spectrometry (FT-ICR MS) revealed a decrease in lignin-like moleculesand increase in condensed aromatic components of the DOM upon continuousleaching. The disinfection byproduct formation potential (DBPFP) wasreduced with increasing leaching volume, along with the decreasingyields of dissolved organic carbon (DOC). Furthermore, compared withthat of the first leaching phase (P1), the chlorine reactivity (DBPFPnormalized to DOC) of DOM at the tenth leaching phase (P10) increasedby 26-53%, 51-60%, and 39-44%, for trihalomethanes,haloacetic acids, and chloral hydrates, respectively, due to increasedaromatic fractions in DOM. The principal component analysis (PCA)and partial least-squares path model (PLS-PM) showed that thequantity and quality of DOM leached by surface water and syntheticrainwater were significantly different. Lastly, despite the pronouncedvariations in DOM properties, the black soil-derived DOM displayedhigh treatability, with 52-71% of DOC, 54-69% of trihalomethane(THM) precursors, 60-80% of haloacetic acid (HAA) precursors,and nearly all (& SIM;100%) of the nitrogen-containing DBP (N-DBP),haloketone (HK), and chloral hydrate (CH) precursors being removedby a nanofiltration membrane. Our results will contribute to the understandingof soil DOM mitigation and potential impacts on drinking water production.