The radical and non-radical oxidation mechanism of electrochemically activated persulfate process on different cathodes in divided and undivided cell.

Electrochemically activated persulfate (PS) employing stainless steel (SS), carbon felt (CF) and carbon black modified CF (CB-CF) as the cathode, in the divided and undivided cell, respectively, for degradation of atrazine (ATZ) was first investigated using novel B, Co-doped TiO2 nanotubes (B, Co-TNT) anode. In undivided cell, ATZ degradation was followed the order of CF

Kinetic and mechanism study of UV/pre-magnetized-Fe0/oxalate for removing sulfamethazine.

In this study, UV irradiated photochemical reactions of oxalate (Ox) with premagnetized-Fe0 (pre- Fe0) as the catalyst was used to degrade sulfamethazine (SMT). Magnetic field promoted the release of iron ion from Fe0 thus enhanced SMT and Ox removal in UV/pre- Fe0/Ox process. X-ray photoelectron spectroscopy demonstrated that the presence of UV and Ox promoted the transformation of Fe3+ to Fe2+ on Fe0, which enhanced the surface bound •OH (•OHsurf) generation. Ox inhibited the formation of iron (hydro)xides and enhanced the hydroxylation of Fe0 surface. •OHsurf was mainly responsible for SMT removal (44%), while UV direct photolysis and •OH in the solution both caused around 28% SMT removal. The process with Ox exhibited much higher efficiency in SMT degradation than that added with H3PO4, citric acid and ethylenediaminetetraacetic acid, which greatly expanded the chelate-modified Fenton processes and their treatment efficiency.

A flow-through electro-Fenton process using modified activated carbon fiber cathode for orange II removal.

This study investigated the removal of Orange II by an electro-Fenton process using a novel recirculation flow-through reactor. The hydrogen peroxide was generated in-situ on the activated carbon fiber (ACF) modified with carbon black and polytetrafluoroethylene (PTFE). The modified ACF cathode was characterized by scanning electron microscopy (SEM) and nitrogen adsorption-desorption study. In light of the production of H2O2 and removal of Orange II, the optimum weight percentage of PTFE in the mixture of carbon black and PTFE was 75%. The effects of some important operating parameters such as current and flow rate were investigated. The best Orange II removal reached 96.7% with mineralization efficiency of 55.4% at 120 min under the current of 100 mA, initial pH 3, Fe2+ 0.3 mM and the flow rate of 7 mL min-1. The cathode exhibited good regeneration ability and stability. OH was proved to be the main oxidizing species in this flow-through electro-Fenton system. This work demonstrated that such electro-Fenton process using modified ACF cathode was promising for the degradation of organic pollutants.

EDTA, oxalate, and phosphate ions enhanced reactive oxygen species generation and sulfamethazine removal by zero-valent iron.

The activation rate of oxygen by zero-valent iron (Fe°) was very low. In this study, ethylenediaminetetraacetic acid (EDTA), oxalate (Ox), and phosphate ions (Na2HPO4) were used to enhance the oxygen activation by Fe° for sulfamethazine (SMT) removal. The addition of these ligands could significantly enhance the SMT degradation. SMT removal was improved from 10.5 % in the Fe° system (360 min) to 70.3 %, 85.2 % and 77.8 % in the Fe°/EDTA (60 min), Fe°/Ox (180 min) and Fe°/phosphate (360 min) systems, respectively. Scanning electron microscopy with energy dispersive X-ray (SEM-EDX), Fourier transform infrared reflection (FTIR), contact angle and X-ray photoelectron spectra (XPS) of Fe° in different systems were recorded. The presence of chelating agents hydroxylated Fe°, inhibited the iron oxide formation on the Fe° surface and promoted iron ion release from the solid. Moreover, the agents improved the recovery of surface Fe2+ which could subsequently enhance the activation of O2 to produce more H2O2 and reactive oxygen radicals for SMT removal. OH radical produced mainly through H2O2 decomposition was primarily responsible for removing SMT in all three systems. The Fe° system added with chelating agents is a new and promising approach for treating wastewaters containing ligands.

Pre-magnetized Fe0 as heterogeneous electro-Fenton catalyst for the degradation of p-nitrophenol at neutral pH.

Pre-magnetized Fe0 (Pre-Fe0) was for the first time applied as heterogeneous catalyst to enhance the oxidation efficiency of electro-Fenton (EF) for the degradation of p-nitrophenol (PNP). The parameters including current, initial pH and pre-Fe0 dosage of Pre-Fe0/EF process were optimized and compared with other two processes (conventional Fe0/EF and electro-oxidation) to confirm its advantage. The rate constants of PNP removal were 1.40-3.82 folds of those by Fe0/EF process under various experimental conditions. The application of pre-Fe0 as catalyst could extend the working pH range from 3.0 to neutral conditions for PNP removal and reduce the Fe0 dosage from 2 to 0.5 mM corresponding to Fe0/EF, avoiding the second pollution of iron sludge. The superiority of Pre-Fe0/EF process was also verified to improve the degradation and mineralization of other phenols and antibiotics. Furthermore, a possible pathway of PNP degradation was revealed by the identification of intermediates and organic acids, and the possible mechanism of pre-Fe0 efficiently enhanced the EF efficiency was proposed. This work demonstrated that such a novel heterogeneous EF process using pre-Fe0 catalyst was clean and promising for the degradation of refractory organic pollutants.

Enhanced removal of antibiotics from secondary wastewater effluents by novel UV/pre-magnetized Fe0/H2O2 process.

Antibiotics have been frequently detected in the aquatic environment and are of emerging concern due to their adverse effect and potential of inducing antibiotic resistance. In this study, we developed an UV/pre-magnetized Fe0/H2O2 process (UV/pre-Fe0/H2O2) valid for neutral pH conditions, which could remove sulfamethazine (SMT) completely within only 30 min and enhance 1.8 times of SMT removal. Meanwhile, this process demonstrated outstanding mineralization capability with the TOC removal of 92.1%, while for UV/H2O2 and UV/Fe0/H2O2 system it was 53.9% and 72.1%, respectively. Better synergetic effect between UV irradiation and pre-Fe0/H2O2 system was observed, and the value of synergetic factor was 6.3 in the presence of both ions and humic acid, which was much higher than that in deionized water (4.4), humic acid (5.5) and ions (1.5). Moreover, the process could efficiently remove various antibiotics (800 µg L-1 oxytetracycline (OTC); 800 µg L-1 tetracycline (TC); 400 µg L-1 sulfadiazine (SD) and 400 µg L-1 SMT) in the secondary wastewater effluent. After optimization of Fe0 and H2O2 dosage, these antibiotics could be removed within 10 min (kapp (103) = 288.6 min-1) with a very low treatment cost of 0.1 USD m-3, and the EE/O value was only 1.22 kWh m-3. Compared with O3, UV/Fe2+/PDS, VUV/UV/Fe2+ and other US-based processes, the degradation rates by this process could enhance as high as 22.3 folds while the treatment cost or EE/O value could reduce greatly. Therefore, UV/pre-Fe0/H2O2 process is promising and cost-effective for the treatment of antibiotics in secondary wastewater effluents.