Molecular dissolved organic matter removal by cotton-based adsorbents and characterization using high-resolution mass spectrometry

This research investigates the characteristics of dissolved organic matter (DOM) removal by synthesized cotton-fiber adsorbents using unknown screening analysis with high resolution and accurate mass spectrometry. Molecular characteristics of DOM removed by adsorbents were investigated semiquantitatively and unknown disinfection byproduct (DBP) formation potentials were also investigated. Adsorbents were modified using ferric nitrate to increase the magnetic property. The XRD pattern showed Fe-containing crystalline structures in the modified adsorbent (M-CF). The M-CF possessed higher mesopore volume, which enhanced the dissolved organic carbon (DOC) removal efficiency to 74.50% (compared to 32.12% in the unmodified CF adsorbent). The kinetics experiment showed that both adsorbents were better fitted to pseudo-second orders than pseudo-first orders. The initial rate constant was higher in M-CF (1.40 mg/g min) than in CF (0.02 mg/g min) treatments due to the higher mesopore volume in M-CF. M-CF removed almost 700 carbon-hydrogen-oxygen based DOMs (CHO features), 300 more CHO features than CF. CF selectively adsorbed only higher-molecular-weight (MW) CHO features (more CH2 groups), while the mesopores in M-CF removed DOM with lower MW (fewer CH2 groups) that were refractory to CF. The low MW DOM removed only by M-CF mesopore exhibited more oxidized (positive carbon oxidation state, C-os) and saturated characters (negative oxygen-subtracted double bond equivalent per carbon, (DBE-O)/C). After chlorination, over 50 unknown DBPs were detected, 33 of which were commonly found in all samples. M-CF decreased unknown formation potential more than CF. However, adsorption of M-CF and CF before chlorination resulted in different remaining precursors to water chlorination and formed unique DBPs from those precursors. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

This research investigated the removal characteristics of dissolved organic matter (DOM) by synthesized cotton-fiber adsorbents, with a focus on the impact of ferric nitrate modification on the efficiency and kinetics of DOM removal. The results showed that the modified adsorbent (M-CF) had higher mesopore volume and better performance in removing both high and low molecular weight DOM components compared to the unmodified CF adsorbent. Additionally, the modified adsorbent exhibited a higher initial rate constant and reduced formation potential of unknown disinfection byproducts (DBPs) after chlorination.