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

Pharkphum Rakruam; Pumis Thuptimdang; Sumana Siripattanakul-Ratpukdi; Phanwatt Phungsai

doi:10.1016/j.scitotenv.2020.142074

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

Sci Total Environ. 2021 Feb 1:754:142074. doi: 10.1016/j.scitotenv.2020.142074. Epub 2020 Aug 29.

Authors

Pharkphum Rakruam¹, Pumis Thuptimdang², Sumana Siripattanakul-Ratpukdi³, Phanwatt Phungsai⁴

Affiliations

¹ Department of Environmental Engineering, Faculty of Engineering, Chiang Mai University, Chiang Mai 50200, Thailand; Research Program in Control of Hazardous Contaminants in Raw Water Resources for Water Scarcity Resilience, Center of Excellence on Hazardous Substance Management (HSM), Chulalongkorn University, Bangkok 10330, Thailand.
² Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand; Environmental Science Research Center (ESRC), Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
³ Department of Environmental Engineering, Faculty of Engineering and Research Center for Environmental and Hazardous Substance Management, Khon Kaen University, Khon Kaen 40002, Thailand; Center of Excellence on Hazardous Substance Management (HSM), Chulalongkorn University, Bangkok 10330, Thailand.
⁴ Department of Environmental Engineering, Faculty of Engineering and Research Center for Environmental and Hazardous Substance Management, Khon Kaen University, Khon Kaen 40002, Thailand; Center of Excellence on Hazardous Substance Management (HSM), Chulalongkorn University, Bangkok 10330, Thailand. Electronic address: phanphu@kku.ac.th.

PMID: 33254897
DOI: 10.1016/j.scitotenv.2020.142074

Abstract

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.

Keywords: Carbon fiber adsorbent; Magnetized sorbent; Molecular characterization; Orbitrap mass spectrometry; Unknown disinfection by-products; Unknown screening analysis.