Removal of citrate and hypophosphite binary components using Fenton, photo-Fenton and electro-Fenton processes

Enhanced photo-Fenton degradation of contaminants in a wide pH range via synergistic interaction between 1T and 2H MoS2 and copolymer tea polyphenols/polypyrrole

In this study, we present the successful development of a unique photo-Fenton catalyst, 1T-2H MoS2@TP/PPy (MTP), achieved through the coating of a copolymer of tea polyphenol (TP) and polypyrrole (PPy) onto the surface of heterophase molybdenum disulfide (1T-2H MoS2). This innovative approach involves the integration of hydrothermal synthesis with copolymerization techniques. Our strategy utilizes nanoflower-like 1T-2H MoS2 as the foundational framework, which is then enveloped in TP and PPy copolymer. This innovative approach involves the integration of hydrothermal synthesis with copolymerization techniques. Our strategy utilizes nanoflower-like 1T-2H MoS2 as the foundational framework, which is then enveloped in TP and PPy copolymer. This distinctive architecture demonstrates exceptional catalytic performance owing to the hetero-phase entanglement of 1T-2H MoS2, which provides a diverse array of active sites. The coupled structure of TP and iron (TP-Fe2+/Fe3+) effectively overcome the limitation associated with the iron source. The incorporation of PPy not only reduces the recombination of photogenerated electron-hole pairs but also enhances the stability of 1T-2H MoS2. Remarkably, our experiments on the degradation of methylene blue (MB) and tetracycline (TC) degradation demonstrate that TP-Fe2+/Fe3+ significantly expands the pH applicability range of the MTP composite catalyst. Additionally, we examine several factors, including different catalysts, H2O2 addition, variations in light intensity, solution pH, temperature fluctuations, and the role of active species, to comprehensively understand their impact on the photo-Fenton degradation process. In conclusion, MTP composite exhibits robust catalytic stability and demonstrates a broad pH utilization range in the photo-Fenton oxidation process, highlighting its promising potential for a wide range of applications.

Activation of peroxymonosulfate by phosphite: Kinetics and mechanism for the removal of organic pollutants

In this study, phosphite (HPO₃^2-) was used as a novel activator to activate peroxymonosulfate (PMS) for acid orange 7 (AO7) removal. Under the optimized conditions, the decolorization efficiency of AO7 was 82.1% within 60 min with rate constant values (k_obs) of 0.0301 min^-1. Besides, effects of the solution pH and the co-existing inorganic anions including Cl^-, HCO₃^-, HPO₄^2- and SO₄^2- on AO7 removal were also investigated. Except for SO₄^2-, other examined co-existing inorganic anions displayed favorable effects on the removal of AO7. Furthermore, the mechanism for PMS activation by the HPO₃^2- was deeply elucidated by radical scavenger including ethanol (EtOH), tert-butanol (TBA), l-histidine and tiron, and electron spin resonance (ESR) studies. It was proposed that singlet oxygen (¹O₂) would be the dominant reactive oxygen species (ROS) in the HPO₃^2-/PMS system for contamination degradation at neutral pH condition. The findings of this study provided useful information for the application of the substances in industrial wastewaters to activate PMS for organic contaminants degradation and in particular for HPO₃^2--rich electroplating wastewater treatment.

Preparation of CeO2-doped carbon nanotubes cathode and its mechanism for advanced treatment of pig farm wastewater

The effluent from conventional treatment process (including anaerobic digestion and anoxic-oxic treatment) for pig farm wastewater was difficult to treat due to its low ratio of biochemical oxygen demand to chemical oxygen demand (BOD₅/COD_Cr) (<0.1). In the present study, electro-Fenton (EF) was used to improve the biodegradability of the mentioned effluent and the properties of self-prepared CeO₂-doped multi-wall carbon nanotubes (MWCNTs) electrodes were also studied. An excellent H₂O₂ production (165 mg L^-1) was recorded, after an 80-min electrolysis, when the mass ratio of MWCNTs, CeO₂ and pore-forming agent (NH₄HCO₃) was 6:1:1. Results of scanning electron microscopy (SEM), transmission electron microscope (TEM) and x-ray photoelectron spectroscopy (XPS) showed that addition of NH₄HCO₃ and the doping of CeO₂ could increase the superficial area of the electrode as well as the oxygen reduction reaction (ORR) electro-catalytic performance. The BOD₅/COD_Cr of the wastewater from the first stage AO process increased from 0.08 to 0.45 and COD_Cr reduced 71.5% after an 80-min electrolysis, with 0.3 mM Fe²⁺ solution. The non-biodegradable chemical pollutants from the first stage AO process were degraded by EF. The non-biodegradable pollutants identified by LC-MS/MS in the effluent from AO process including aminopyrine, oxadixyl and 3-methyl-2-quinoxalinecarboxylic acid could be degraded by EF process, with the removal rates of 81.86%, 34.39% and 7.13% in 80 min, and oxytetracycline with the removal rate of 100% in 20 min. Therefore, electro-Fenton with the new CeO₂-doped MWCNTs cathode electrode will be a promising supplement for advanced treatment of pig farm wastewater.

Phosphate removal from industrial wastewater through in-situ Fe2+ oxidation induced homogenous precipitation: Different oxidation approaches at wide-ranged pH

Phosphate removal through in-situ Fe²⁺ oxidation induced homogenous phosphate precipitation has shown its advantages in municipal wastewater treatment. Its feasibility and suitability for phosphate removal in industrial wastewater with wide-range pH variation like electro-plating wastewater were investigated in bench scale experiments using synthetic wastewater and continuous experiment using real wastewater. Bench scale experiments showed that different Fe²⁺ oxidation approaches worked well for phosphate removal at varied pH conditions. Sole dosing Fe²⁺ salt with aeration achieved sound phosphate removal at alkaline condition (pH ≥ 8). At neutral pH (6 < pH < 8), transition metallic ions catalytic oxidation is a suitable alternative. Cu²⁺ exhibited superior catalytic Fe²⁺ oxidization over Mn²⁺, Zn²⁺, and Ni²⁺. At acid pH (3.0 ＜ pH ≤ 6.0), Fenton reaction oxidation (H₂O₂ = 5 mg/L) showed its efficiency. At their corresponding optimal pH conditions and with Fe²⁺/P ratio of 1.8, dosing sole Fe²⁺ salt, Cu²⁺ catalyzed Fe²⁺ oxidation, and Fe²⁺/H₂O₂ treatments can achieve the TP discharge limit of 0.5 mg/L. In a 30-day continuous experiment using real electro-plating wastewater (pH 4.9-5.5), in both direct Fe²⁺/H₂O₂ treatment and Cu²⁺ catalyzed Fe²⁺ oxidation treatment after wastewater pH being adjusted to 7 effluent TP met China's discharge requirement 0.5 mg/L.

Ti4O7/g-C3N4 for Visible Light Photocatalytic Oxidation of Hypophosphite: Effect of Mass Ratio of Ti4O7/g-C3N4

Hypophosphite wastewater treatment is still a critical issue in metallurgical processes and the oxidation of hypophosphite to phosphate followed by the precipitation of phosphate is an important strategy for hypophosphite wastewater treatment. Herein, Ti₄O₇/g-C₃N₄ photocatalysts with various mass ratios (Ti₄O₇ (m): g-C₃N₄ (m) = 0.5, 0.2, 0.1, and 0.05) were synthesized by a hydrolysis method and the effect of the mass ratio of Ti₄O₇ (m): g-C₃N₄ (m) on Ti₄O₇/g-C₃N₄ visible light photocatalytic oxidation of hypophosphite was evaluated. The as-prepared Ti₄O₇/g-C₃N₄ were characterized and confirmed by SEM, XPS, XRD and FTIR. Moreover, the specific surface area and the distribution of pore size of Ti₄O₇/g-C₃N₄ was also analyzed. Our results showed that Ti₄O₇/g-C₃N₄ exhibited remarkably improved photocatalytic performance on hypophosphite oxidation compared with g-C₃N₄ and meanwhile 1:2-Ti₄O₇/g-C₃N₄ with a mass ratio of 0.5 showed the best photocatalytic performance with the highest oxidation rate constant (17.7-fold and 91.0-fold higher than that of pure g-C₃N₄ and Ti₄O₇, respectively). The enhanced performance of photocatalytic oxidation of hypophosphite was ascribed to the heterojunction structure of Ti₄O₇/g-C₃N₄ with broader light absorption and significantly enhanced efficiency of the charge carrier (e⁻-h⁺) generation and separation. Additionally, the generated ·OH and ·O2- radicals contributed to the hypophosphite oxidation during the photocatalytic system.

Advanced oxidation removal of hypophosphite by O3/H2O2 combined with sequential Fe(II) catalytic process

Elimination of hypophosphite (HP) was studied as an example of nickel plating effluents treatment by O₃/H₂O₂ and sequential Fe(II) catalytic oxidation process. Performance assessment performed with artificial HP solution by varying initial pH and employing various oxidation processes clearly showed that the O₃/H₂O₂─Fe(II) two-step oxidation process possessed the highest removal efficiency when operating under the same conditions. The effects of O₃ dosing, H₂O₂ concentration, Fe(II) addition and Fe(II) feeding time on the removal efficiency of HP were further evaluated in terms of apparent kinetic rate constant. Under improved conditions (initial HP concentration of 50 mg L^-1, 75 mg L^-1 O₃, 1 mL L^-1 H₂O₂, 150 mg L^-1 Fe(II) and pH 7.0), standard discharge (<0.5 mg L^-1 in China) could be achieved, and the Fe(II) feeding time was found to be the limiting factor for the evolution of apparent kinetic rate constant in the second stage. Characterization studies showed that neutralization process after oxidation treatment favored the improvement of phosphorus removal due to the formation of more metal hydroxides. Moreover, as a comparison with lab-scale Fenton approach, the O₃/H₂O₂─Fe(II) oxidation process had more competitive advantages with respect to applicable pH range, removal efficiency, sludge production as well as economic costs.

The Treatment of Aniline Wastewater by Electro-Fenton Method

To study the influences of different factors on the removal of aniline and COD and find out the optimal process parameters of electro-Fenton method, pH value, the dosage of Fe2+ and electrolytic voltage were changed in this experiment. The results show that the removal of aniline and COD could reach to 93.24% and 81.41% respectively when the pH was 3, the dosage of Fe2+ was 1g•L-1 and the electrolytic voltage was 15V. Consequently, electro-Fenton method is feasible as a treatment of aniline wastewater.

Advanced oxidation of hypophosphite and phosphite using a UV/H2O2 process

The oxidation of hypophosphite and phosphite in an aqueous solution by an ultraviolet (UV)/H2O2 process was studied in this work. The reactions were performed in a lab-scale batch photoreactor. The effect of different parameters such as H2O2 dosage, H2O2 feeding mode and the initial pH of the solution on the oxidation efficiency of the process was investigated. The results indicated that the UV/H2O2 process could effectively oxidize hypophosphite and phosphite in both synthesized and real wastewater. However, neither H2O2 nor UV alone was able to appreciably oxidize the hypophosphite or phosphite. The best way of feeding H2O2 was found to be 'continuous feeding', which maximized the reaction rate. It was also found that the process presented a wide range of applicable initial pH (5-11). When treating real rinse-wastewater, which was obtained from the electroless nickel plating industry, both hypophosphite and phosphite were completely oxidized within 60 min, and by extending by another 30 min, over 90% of the chemical oxygen demand removal was obtained. Without any additional catalyst, the UV/H2O2 process can oxidize hypophosphite and phosphite to easily removable phosphate. It is really a powerful and environmentally friendly treatment method for the wastewater containing hypophosphite and phosphite.

Design of a neutral three-dimensional electro-Fenton system with foam nickel as particle electrodes for wastewater treatment

In this work, we demonstrate a novel three-dimensional electro-Fenton system (3D-E-Fenton) for wastewater treatment with foam nickel, activated carbon fiber and Ti/RuO(2)-IrO(2) as the particle electrodes, the cathode, and the anode respectively. This 3D-E-Fenton system could exhibit much higher rhodamine B removal efficiency (99%) than the counterpart three-dimensional electrochemical system (33%) and E-Fenton system (19%) at neutral pH in 30 min. The degradation efficiency enhancement was attributed to much more hydroxyl radicals generated in the 3D-E-Fenton system because foam nickel particle electrodes could activate molecular oxygen to produce O(2)(-) via a single-electron transfer pathway to subsequently generate more H(2)O(2) and hydroxyl radicals. This is the first observation of molecular oxygen activation over the particle electrodes in the three-dimensional electrochemical system. These interesting findings could provide some new insight on the development of high efficient E-Fenton system for wastewater treatment at neutral pH.