The increase in the disposal of refractory organics demands for newer technologies for the complete mineralization of these wastewaters. Advanced oxidation processes (AOPs) constitute a promising technology for the treatment of such wastewaters and this study presents a general review on such processes developed to decolorize and/or degrade organic pollutants. Fundamentals and main applications of typical methods such as Fenton, electro-Fenton, photo-Fenton, sono-Fenton, sono-photo-Fenton, sono-electro-Fenton and photo-electro-Fenton are discussed. This review also highlights the application of nano-zero valent iron in treating refractory compounds.

A review on Fenton and improvements to the Fenton process for wastewater treatment

Understanding the chemistry of hydrogen peroxide (H2O2) decomposition and hydroxyl radical (•OH) transformation on the surface molecular level is a great challenge for the application of heterogeneous Fenton system in the fields of chemistry, environmental, and life science. We report in this study a conceptual oxygen vacancy associated surface Fenton system without any metal ions leaching, exhibiting unprecedented surface chemistry based on the oxygen vacancy of electron-donor nature for heterolytic H2O2 dissociation. By controlling the delicate surface structure of catalyst, this novel Fenton system allows the facile tuning of •OH existing form for targeted catalytic reactions with controlled reactivity and selectivity. On the model catalyst of BiOCl, the generated •OH tend to diffuse away from the (001) surface for the selective oxidation of dissolved pollutants in solution, but prefer to stay on the (010) surface, reacting with strongly adsorbed pollutants with high priority. These findings will exten...

Oxygen Vacancy Associated Surface Fenton Chemistry: Surface Structure Dependent Hydroxyl Radicals Generation and Substrate Dependent Reactivity

Effective decomposition of antibiotic sulfadiazine (SD) in a Fe0-catalyzed sonochemical Fenton like system (Sono-FL) was demonstrated. By using the response surface methodology (RSM), an optimized experimental condition of pH 7.00, 0.94 mM Fe0, 1.90 mM persulfate (PS) and 20 W ultrasound (US) power was concluded, which could reach the predicted SD degradation efficiency of 90%. Afterwards, effects of wastewater matrix (five inorganic anions and two chelating agents) on the SD degradation were investigated in the system, respectively. It was found that the SD degradation could be inhibited by SO42−, NO3−, HCO3−/CO32− and H2PO4− to different extents. Cl− would lead to an enhancement with a low dosage (5 mM), but an inhibition with a high dosage (100 mM). Unexpectedly, chlorinated organic intermediates were also found as SD decomposed. Appropriate dosages of oxalic acid (OxA) or EDTA could benefit the SD degradation in the Sono-FL system, while excessive chelating agents would play as competitive pollutants. It was summarized that inorganic anions would mainly react with SO4 − and/or OH to form sub-radicals of less oxidative potential. OxA and EDTA would not only participate in complexing dissolution of Fe0 but also provide additional oxidants such as H2O2 and [FeIVO]2+, through the electron transfer reactions caused by the iron-ligands species.

Decomposition of sulfadiazine in a sonochemical Fe0-catalyzed persulfate system: Parameters optimizing and interferences of wastewater matrix

Effects of chelating agents on the catalytic degradation of bisphenol A (BPA) was studied in the presence of BiFeO3 nanoparticles as a heterogeneous catalyst and H2O2 as a green oxidant. The oxidizing ability of H2O2 in the presence of nano-BiFeO3 alone was not so strong to degrade BPA at neutral pH values, due to the limited catalytic ability of nano-BiFeO3. Once the surface of nano-BiFeO3 was in situ modified by adding proper organic ligands, the BPA degradation was much accelerated in the pH range of 5–9. The enhancing effect of the ligand was observed to have an order of blank < tartaric acid < formic acid < glycine < nitrilotriacetic acid < ethylenediaminetetraacetic acid (EDTA). The addition of 0.25 mmol L–1 EDTA in the H2O2–BiFeO3 system at pH 5.0 and 30 °C increased the BPA removal from 20.4% to 91.2% with reaction time of 120 min. The enhancing effect of the ligand was found to be indifferent of the possible dissolution of iron from nano-BiFeO3, but correlated well with the accelerated •OH format...

Ligand-Induced Drastic Enhancement of Catalytic Activity of Nano-BiFeO3 for Oxidative Degradation of Bisphenol A

In this study, the effects of an inorganic ligand tetrapolyphosphate on the molecular oxygen activation and the subsequent aerobic atrazine degradation by Fe@Fe2O3 core-shell nanowires were investigated systematically at a circumneutral to alkaline pH range (pH 6.0-9.0). We interestingly found that the addition of tetrapolyphosphate could enhance the aerobic atrazine degradation rate 955 times, which was even 10 times that of the traditional organic ligand ethylenediamine tetraacetate. This tetrapolyphosphate induced dramatic aerobic atrazine degradation enhancement could be attributed to two factors. One was that the presence of tetrapolyphosphate strongly suppressed hydrogen evolution from the reduction of proton by Fe@Fe2O3 core-shell nanowires through proton confinement, leaving over more electrons for the reduction of Fe(III) to Fe(II) and the subsequent molecular oxygen activation. The other was that the complexation of tetrapolyphosphate with ferrous ions not only guaranteed enough soluble Fe(II) for Fenton reaction, but also provided another route to produce more •OH in the solution via the single-electron molecular oxygen reduction pathway. We employed gas chromatography-mass spectrometry and liquid chromatography-mass spectrometry to identify the atrazine degradation intermediates and proposed a possible aerobic atrazine degradation pathway. This study not only sheds light on the promotion effects of ligands on the molecular oxygen activation by nanoscale zerovalent iron, but also offers a facile and green iron-based method for the oxidative atrazine removal.

Dramatically Enhanced Aerobic Atrazine Degradation with Fe@Fe2O3 Core–Shell Nanowires by Tetrapolyphosphate

Elimination of phenol and aromatic compounds by zero valent iron and EDTA at low temperature and atmospheric pressure

Degradation of model olive mill contaminants of OMW catalysed by zero-valent iron enhanced with a chelant

Abstract The impedance spectroscopy technique has been used to study the microstructure of the binder resulting from the alkaline activation of SiMn slag. Two alkaline activators were used: waterglass and NaOH. Three different concentrations were analysed for both activators: 3.0, 3.5 and 4.0% Na 2 O for NaOH; and 4.0, 4.5 and 5.0% Na 2 O for waterglass with a constant SiO 2 /Na 2 O ratio of 1.0. The time evolution of the microstructure has been followed up using the non-destructive technique of impedance spectroscopy. This technique has been proved to be effective describing the microstructural changes in alkali activated pastes, and also can help predicting the mechanical behavior of mortars. The use of the resistivity itself seems to be deficient, but the analysis of the electrical parameters calculated from the impedance spectra measured gives a complete idea of the evolution in the material. 

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Use of Impedance Spectroscopy for the Characterization of the Microstructure of Alkali Activated SiMn Slag: Influence of Activator and Time Evolution

One of the main challenges of binder manufacturing industry is the reduction of its environmental impact. In this context, the key is the obtention of materials whose fabrication uses lower amount of natural resources and energy consumption. One of the the main strategies to achieve that goal is the incorporation of alkali activation processes to waste material or by-products. In this work, a SiMn slag has been alkali activated to prepare light mortars in which partial substitution of the aggregates by expanded polystyrene has been applied. An aggregate replacement up to 45% by volume has been used. In addition, also the SiMn has been used as aggregate in order to explore its valorization through that application. The following properties have been evaluated: fresh mortar workability, compressive strength, drying and autogenous shrinkage, water absorption by capillarity, apparent density and thermal conductivity. The intended application for this type of material would be as light cladding with improved isolation properties. Results have shown that the replacement up to 45% of natural aggregate by expanded polystyrene produces a decrease of the compressive strength up to 70%, a reduction of the density of 32%, an increase of the water absorption of 75% and a decrease of the thermal conductivity up to 87%. 

Irama Sanchez

Papers

Elimination of phenol and aromatic compounds by zero valent iron and EDTA at low temperature and atmospheric pressure

Degradation of model olive mill contaminants of OMW catalysed by zero-valent iron enhanced with a chelant

Use of Impedance Spectroscopy for the Characterization of the Microstructure of Alkali Activated SiMn Slag: Influence of Activator and Time Evolution

Characterization of light mortars with alkali activated SiMn slag and recycled expanded polystyrene