DOM removal from surface water by activated carbon vs. a nanocomposite: an experimental and modeling approach to optimize treatment

Abstract

Dissolved organic matter (DOM) is commonly removed from surface water by adsorption columns packed with sand (enhanced with coagulants), high-cost activated carbons, or specifically developed adsorbents. A main challenge in removing DOM is its chemical heterogeneity, both within and among water bodies, which makes adsorbent selection, DOM removal efficiency and removal prediction complex. Our approach to address these challenges consisted of three steps: 1. developing a facile UV-based methodology to represent DOM composition using three operationally defined fractions: humic acid, fulvic acid, and a non-UV-254 nm absorbing fraction, 2) parameterizing a hydraulic-adsorption model using commercially available humic and fulvic acids, and 3) applying the parameterized model to predict DOM removal from surface waters, which we mathematically partitioned using our UV methodology. We tested DOM removal from binary solutions of HA and FA and from three surface waters varying in UV absorption properties by three adsorbents differing in surface properties – new and regenerated granular activated carbon (GAC and rGAC, respectively) and a clay–polymer nanocomposite (PD-MMT). Despite the complexity of surface water DOM, we found that DOM removal can be predicted by its specific absorption of UV at 254 nm (SUVA₂₅₄), and that SUVA₂₅₄ was positively correlated with DOM removal by PD-MMT and negatively correlated with DOM removal by rGAC and GAC. One implication is that a column can potentially be tailored with an optimal adsorbent composition, i.e., PD-MMT and GAC based on water source SUVA₂₅₄. Facile DOM characterization using UV absorption enabled us to predict DOM removal by three adsorbents from three surface waters. Finally, we estimated column capacity for UV₂₅₄ adsorbing compounds under large treatment scales and found that the capacity of PD-MMT was three times larger than that of a commercial GAC.