In order to economically and efficiently remove dissolved organic matter (DOM) in the secondary water of wastewater treatment plants, this study adopted iron-nitrogen co-doped biochar material (Fe-N-C) as a new adsorbent and systematically analyzed the effect of this new carbon material on the secondary water DOM, as well as the adsorption performance, kinetic process, selectivity, and mechanism of action. In addition, the long-term performance and reusability of the adsorption material were thoroughly investigated through a fixed-bed adsorption device. The results show that Fe-N-C had outstanding adsorption performance for secondary water DOM. When the dosage was only 1.0 g·L-1, the removal rates of TOC, UV254, and UV280 were as high as 40.18%, 76.92%, and 78.26%, respectively, which are far higher. Regarding the adsorption effect of pure biochar and conventional activated carbon, the adsorption process conformed to the pseudo-second-order kinetics and Freundlich adsorption isotherm model, indicating that the adsorption process is a multilayer chemical adsorption involving valence electrons and the exchange of electrons. The three-dimensional fluorescence spectroscopy, molecular weight distribution, and resin analysis results, such as classification and characterization, showed that Fe-N-C had selective adsorption for different components in the secondary water DOM. The fixed bed adsorption column with Fe-N-C as the core had the maximum removal rate of secondary water TOC, UV254, and UV280 as high as 94.09%, 95.65%, and 97.18%, respectively, and had good stability. It was close to adsorption saturation when the processing capacity reached 620 times the bed volume. However, after the regeneration heat treatment, the adsorption performance was remarkably restored. These results are expected to provide reference for the further development of high-efficiency adsorption water treatment technology.
Keywords: adsorption; dissolved organic matter (DOM); fixed-bed adsorption column; hierarchical characterization; iron and nitrogen co-doped biochar; secondary water.