Lingjun Bu

Degradation of oxcarbazepine by UV-activated persulfate oxidation: kinetics, mechanisms, and pathways.

The degradation kinetics and mechanism of the antiepileptic drug oxcarbazepine (OXC) by UV-activated persulfate oxidation were investigated in this study. Results showed that UV/persulfate (UV/PS) process appeared to be more effective in degrading OXC than UV or PS alone. The OXC degradation exhibited a pseudo-first order kinetics pattern and the degradation rate constants (kobs) were affected by initial OXC concentration, PS dosage, initial pH, and humic acid concentration to different degrees. It was found that low initial OXC concentration, high persulfate dosage, and initial pH enhanced the OXC degradation. Additionally, the presence of humic acid in the solution could greatly inhibit the degradation of OXC. Moreover, hydroxyl radical (OH•) and sulfate radical (SO4−••) were identified to be responsible for OXC degradation and SO4−• made the predominant contribution in this study. Finally, major intermediate products were identified and a preliminary degradation pathway was proposed. Results demonstrated that UV/PS system is a potential technology to control the water pollution caused by emerging contaminants such as OXC.

Removal of 2-MIB and geosmin by electrogenerated persulfate: Performance, mechanism and pathways

In this study, the degradation of 2-methylisoborneol (2-MIB) and geosmin (GSM) was evaluated by electrochemical oxidation (EO) using boron-doped diamond (BDD) electrode. Both 2-MIB and GSM could be degraded efficiently in sulfate electrolyte compared to inert nitrate or perchlorate electrolytes, implying that in-situ generated persulfate may be responsible for contaminants degradation. The observed linear relationship between 2-MIB (GSM) degradation rates and persulfate generation rates further proved that the in-situ generated persulfate enhanced 2-MIB (GSM) degradation. Moreover, a divided electrolytic cell was employed to investigate the effect of cathodic reactions on contaminants degradation and persulfate generation, and results confirmed that both anodic and cathodic reactions participated in 2-MIB (GSM) degradation. High current density and low solution pH were found to be favorable for 2-MIB and GSM degradation. The degradation intermediates were identified and the possible pathways of 2-MIB and GSM degradation were proposed. This study indicated that the EO process with BDD anode could be considered as a potential alternative for the removal of 2-MIB and GSM.

Degradation of atrazine by electrochemically activated persulfate using BDD anode: Role of radicals and influencing factors

A novel advanced oxidation process using boron-doped diamond (BDD) anode to activate persulfate (PS) with low concentration of electrolyte was systematically investigated in this study. Compared to direct electrochemical oxidation of atrazine (ATZ) using BDD anode, the addition and activation of PS significantly declined the demand for electrolytes. It was confirmed by scavenger experiments that both radical and non-radical oxidation occurred in this system. Degradation of ATZ was enhanced with the increase of current density and dosage of PS, and decrease of initial pH. However, the increase of current density can also lead to the decrease of current efficiency, then increase of energy consumption. Besides, the inhibitory effect of anions on the degradation of ATZ followed the order of HCO3->H2PO4->NO3-, while the presence of Cl- accelerated the degradation of ATZ. Furthermore, the degradation products mainly resulting from de-alkylation, de-chlorination, and hydroxylation were detected. Due to the distinctive preference to ethyl group in BDD/PS system, the formation of deethyl-atrazine was quicker than that of deisopropyl-atrazine. The study aims to provide a comprehensive understanding on the potential application of BDD/PS system in water treatment.

Enhanced degradation of Orange G by permanganate with the employment of iron anode

Iron anode was employed to enhance the degradation of Orange G (OG) by permanganate (EC/KMnO4). Continuously generated Fe2+ from iron anode facilitated the formation of fresh MnO2, which plays a role in catalyzing permanganate oxidation. The EC/KMnO4 system also showed a better performance to remove OG than Fe2+/KMnO4, indicating the importance of in situ formed fresh MnO2. Besides, the effects of applied current, KMnO4 dosage, solution pH, and natural organics were evaluated and results demonstrated that high current and oxidant dosage are favorable for OG removal. And the application of iron anode has a promoting effect on the KMnO4 oxidation over a wide pH range (5.0–9.0), while the Fe2+/KMnO4 process does not. For natural organics, its presence could inhibit OG removal due to its competitive role. And the promoting effect of OG removal by the EC/KMnO4 process in natural water was confirmed. At last, the EC/KMnO4 process showed a satisfying performance on the decolorization and mineralization of OG. This study provides a potential technology to enhance permanganate oxidation and broadens the knowledge of azo dye removal.

A comparative study of microcystin-LR degradation by electrogenerated oxidants at BDD and MMO anodes.

This study investigated the electrochemical degradation of microcystin-LR (MC-LR) using boron-doped diamond (BDD) anode and mixed metal oxides (MMO, IrO2Ta2O5/Ti) anode in different medium. In-situ electrogenerated oxidants including hydroxyl radical, active chlorine, and persulfate were confirmed in phosphate, chloride, and sulfate medium, respectively. Different from MMO anode, hydroxyl radical was observed to play a significant role in chlorine generation at BDD anode in chloride medium. Besides, BDD anode could activate sulfate electrochemically due to its high oxygen evolution potential, and MC-LR degradation rate increased with the decrease of solution pH. The effects of natural organic matters (NOM) and algal organic matters (AOM) on MC-LR degradation were evaluated and NOM presented stronger inhibition ability than AOM. Furthermore, the intermediates generated in MC-LR degradation in chloride and sulfate medium were identified by LC/MS/MS and possible degradation pathways were proposed based on the experiments results. Benzene ring and conjugated diene bonds of Adda group and double bonds of Mhda group were found to be the reactive sites of MC-LR. Overall, this study broadens the knowledge of electrochemical oxidation in removing microcystins in algae-laden water.

Electrochemical inactivation of Microcystis aeruginosa using BDD electrodes: Kinetic modeling of microcystins release and degradation

Electrochemical inactivation of cyanobacteria using boron-doped diamond (BDD) electrode were comprehensively investigated in this study. The pulse amplitude modulated (PAM) fluorometry, flow cytometry, and confocal laser scanning microscopy (CLSM) were used to characterize the photosynthetic capacity and cell integrity of Microcystis aeruginosa. Persulfate is in-situ generated and activated during the process and responsible for the inactivation of M. aeruginosa. The inactivation efficiency increases along with the increase of applied currents. Additionally, a kinetic model based on a sequence of two consecutive irreversible first-order processes was developed to simulate the release and degradation of microcystins (MCLR). The model was able to successfully predict the concentration of extracellular, intracellular and total MCLR under different applied currents and extended exposure time.

Degradation of Diuron by Electrochemically Activated Persulfate

An electrochemically activated persulfate (EC/PS) system was proposed for the degradation of herbicide diuron in this study. In the EC/PS system, the ferrous ions (Fe2+) produced from iron electrode can activate persulfate to generate sulfate radical (SO4·-) as well as hydroxyl radical (OH•). The results showed that the degradation of diuron was significantly enhanced in the EC/PS system, compared to electrocoagulation, persulfate, and Fe2+/PS process. Both of SO4·- and OH· contributed to the degradation of diuron in the EC/PS system according to the radical scavenging studies. The pseudo first-order rate constants of diuron increased with increasing the applied currents and dosages of persulfate. pH affected the degradation of diuron indirectly through the speciation of iron and resulted in higher removal efficiency in acidic condition than in alkaline condition. Chloride, carbonate, and bicarbonate in real water inhibited the degradation of diuron dramatically through consuming SO4·- and OH· and abided by the order of CO32−>HCO3−>Cl−. This study demonstrates that the EC/PS system is a novel, efficient, promising, and environmental-friendly method to treat diuron contamination.

Insight into carbamazepine degradation by UV/monochloramine: Reaction mechanism, oxidation products, and DBPs formation

UV/monochloramine (NH2Cl) process has attracted some attention for the elimination of contaminants of emerging concern as a novel advanced oxidation process. However, there is still much uncertainty on the performance and mechanisms of UV/NH2Cl process because of its complexity and generation of various species of radicals, including NH2•, HO•, Cl• and other reactive chlorine species (RCS). The mechanism and influence factors of degradation of carbamazepine (CBZ) in the UV/NH2Cl process were investigated, and a synergistic effect was observed. Degradation of CBZ under all investigated conditions followed pseudo-first order kinetics. The corresponding rate constant increased along with the dosage of NH2Cl, and was affected significantly by the presence of bicarbonate and natural organic matter. The process has little pH-dependency, while the specific contribution of RCS and HO• changed with solution pH, and RCS always act as a major contributor to the degradation of CBZ. Eleven byproducts of CBZ were identified and their respective evolution profiles were determined. The participation of UV in chloramination can reduce the formation of nitrogenous DBPs, but promote the formation of carbonaceous DBPs. Furthermore, when influent, sand filtered, and granular activated carbon filtered water was respectively used as background, degradation of CBZ was inhibited to different degree and more disinfection byproducts (DBPs) were generated, compared to deionized water. The electrical energy per order for degradation of CBZ in the UV/NH2Cl process was also calculated to obtain some preliminary cost information.