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Dissolved organic matter(DOM)is an important element of natural aquatic systems. Due to differences in their hydrophobic/hydrophilic properties and various functional groups, chemical appearances of DOM fractions also vary. In this study, seven natural waters, extending from Xiaheyan to Toudaoguai along the Ning-Meng section of the Yellow river, were sampled in April 2015. Four DOM fractions were obtained by pumping through XAD-4 and XAD-8 resins, i.e., hydrophobic acid (HOA), hydrophobic base (HOB), weak hydrophobic acid (WHOA), and hydrophilic matter (HYI). Based on detection by three-dimensional excitation-emission matrix fluorescence (EEM) and correlation analysis, relationships with five metal ions (Pb, Zn, Cu, Cr, As) were analyzed. Results show that DOC gradually increased along an upstream to downstream continuum in the Ning-Meng section. HYI (small molecular proteins) was the main DOM fraction present, followed by HOA, suggesting enhanced microbial-sourced impact from industrial sewage discharges. The significant peaks of humic-like (A, C) and protein-like compounds (T 1 ) in the EEM chart further highlight the effect of endogenous pollution caused by wastewater. Furthermore, SPSS fitting results indicate that DOM is correlated with all five metal ions, especially with Cu. In terms of the four DOM fractions, HYI showed the strongest correlation with Cu, illustrating the significant relationship between HYI and Cu during the migration and transformation process. Moreover, the fluorescence intensity of protein-like compounds decreased with increasing Cu concentration, possibly due to fluorescence quenching caused by complexation between Cu and proteins in HYI.

Electrochemical oxidation by boron-doped diamond (BDD) electrode is an effective method of degrading refractory organics. Compared with TOC detection, the amount of gas escape can more effectively and intuitively reflect the mineralization and the removal extent. In this study, indole is chosen as a typical pollutant and the detection of its removal rate was compared at current densities of 10, 20, and 30 mA·cm -2 . Meanwhile, the degradation mechanism was analyzed based on the changes in the carbon and nitrogen forms and conservation status. As a result, BDD electrodes displayed a higher removal efficiency to indole, which can completely be removed after 8 h, 5 h, and 4 h with current densities of 10, 20 and 30 mA·cm -2 , respectively. Changes in TOC removal and CO 2 generation were both increased with increasing the current densities, suggesting that the mineralization extent was in accordance with current densities. Furthermore, the escaped CO 2 , combined with TOC and TIC constituted a conservative carbon system. The byproduct isatin was stable and accumulated at 4-5 h, as TOC, TON, and CO 2 generation was unchanged at this stage. Finally, the XPS analysis suggested the adsorption by-products such as isatin and benzoquinone on the BDD surface, which can further be removed by increasing the electrolysis time. This study demonstrated the mineralization process of indole based on the escaped gas detection and the changes in the carbon and nitrogen forms, which will increase the understanding of the electrolysis process.

Electrochemical systems were built to investigate the degradation of benzotriazole (BTA) on boron-doped diamond (BUU) and PbO2 anodes and give an insight into the mineralization ability of two electrodes in terms of the amount and activity of hydroxyl radicals. Results of bulk electrolysis showed that both BDD and PbO2 displayed perfect BTA degradation performance after 12 hours' electrolysis, with the removal percentages of 99. 48% and 98. 36%, respectively, while the mineralization ability of BDD was much stronger than that of PbO2, with the efficiency of 87. 69% for BDD and 35. 96% for PbO2. Less hydroxyl radical and hydrogen production in BDD system suggested the less amount of active sites on BDD surface, thus further verified that the generated hydroxyl radical amount was not the primary factor determining the mineralization ability of anodes. However, BDD displayed larger binding energy of adsorbed oxygen and thinner adsorption layer than those of PbO2, indicating that the BDD electrode surface was of greater catalytic activity, thus the generated hydroxyl radicals were more free, which was the key to its better mineralization ability.