4.8 Article

How properties of low molecular weight model competitors impact organic micropollutant adsorption onto activated carbon at realistically asymmetric concentrations

Journal

WATER RESEARCH
Volume 202, Issue -, Pages -

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.watres.2021.117443

Keywords

Activated carbon; Competitive adsorption; Dissolved organic matter (DOM); Model compounds; Complementary adsorption; Adsorbability

Funding

  1. German Federal Ministry for Education and Research (Bundesministerium fur Bildung und Forschung, BMBF) [02WRS1278A]
  2. National Key R&D Program of China [2018YFE0204100]
  3. National Natural Science Foundation of China [52070185]

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The study found that hydrophobicity interactions and pi-interactions increase the competitiveness of LMW DOM, with pi-interactions outweighing hydrophobic interactions. By using a bottom-up approach and model compounds, the research elucidated how DOM characteristics impact competitive adsorption.
Low molecular weight (LMW) dissolved organic matter (DOM) is the predominant competitor for adsorption sites against organic micropollutants (OMPs) in activated carbon adsorption. However, top-down approaches using highly complex mixtures of real water DOM do not allow to concisely examine the impacts of specific LMW DOM molecular properties on competitive adsorption. Therefore, we followed a bottom-up approach using fifteen model compounds (mDOM) to elucidate how important DOM characteristics, including hydrophobicity and unsaturated structures (ring, double/triple bond), impact competitiveness. Large concentration asymmetry (similar to 500 mu g DOC/mu g OMP) made mDOM compounds, which were overall less preferentially adsorbed than OMPs, become competitive against OMPs and inhibit OMP adsorption kinetics by pre-occupation of adsorption sites. Our results revealed that both hydrophobicity interactions and pi-interactions increased mDOM competitiveness, while pi-interactions outweighed hydrophobic interactions. However, pi-interactions could not be satisfactorily evaluated with a parameter such as specific ultraviolet absorbance (SUVA) due to interferences of carboxyl groups in aromatic mDOMs. Instead, mDOM adsorbability, described by mDOM adsorption capacity, proved to be a comprehensive indicator for mDOM competitiveness. To our knowledge, this is the first study that systematically clarifies the impacts of intricately interacting molecular properties on DOM adsorption and the related competition against OMP adsorption. DOM adsorbability may inspire a new fractionation, and assist the further isolation, identification and detailed characterization of LMW DOM competitors in real DOM-containing waters.

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