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

Phosphate-modified m-Bi2O4 enhances the absorption and photocatalytic activities of sulfonamide: Mechanism, reactive species, and reactive sites

Widespread usage of the sulfonamide class of antibiotics is causing increasing ecotoxicological concern, as they have the capacity to alter ambient ecosystems. Photocatalytic technology is an attractive yet challenging strategy for the degradation of antibiotics. For this work, the phosphate modification of m-Bi₂O₄ (Bi₂O₄-P) was prepared via a one-step hydrothermal process involving sodium bismuthate and sodium phosphate, which was employed for the degradation of sulfamethazine (SMZ) under visible light irradiation. The 0.5% Bi₂O₄-P exhibited excellent photocatalytic performance, which was 1.9 times that of pure m-Bi₂O₄. The photocatalytic degradation kinetics and mechanism of SMZ was investigated at different pH, whereupon it was revealed that m-Bi₂O₄-P exhibited improved SMZ adsorption and photocatalytic activities in contrast to pure m-Bi₂O₄. Compared with other four sulfonamide antibiotics, structures that contained additional methyl on the pyrimidine could be more easily attacked by phosphate modified m-Bi₂O₄. Reactive species (RS) scavenging experiments revealed that h⁺ was primarily responsible for the degradation of SMZ. Further studies of RS by ESR technology, and the results of photoelectrochemical properties showed phosphate-modified m-Bi₂O₄ could make greater use of photogenerated carriers, thereby producing additional RS. Based on the HRAM LC-MS/MS and the Frontier Molecular Orbital Theory, the degradation pathways of SMZ were proposed.

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.

Kinetic study of the degradation of rhodamine B using a flow-through UV/electro-Fenton process with the presence of ethylenediaminetetraacetic acid

An UV enhanced electro-Fenton (EF) process was conducted in a flow-through system to remove rhodamine B (RhB) in the presence of ethylenediamine tetraacetate (EDTA). The process was denoted as UV/EDTA/EF where EDTA formed complexes with iron ions, thus keeping them soluble at high pH values. The process was very efficient as it could initiate the fast reduction of Fe^III to Fe^II and thus the decomposition of H₂O₂. The influence of Fe dose, the ratio of EDTA:Fe, aeration rate, flow rate, current, initial RhB concentration and pH on the RhB removal in the UV/EDTA/EF process was investigated. The best RhB removal was obtained as 89.9% at [Fe]₀ = [EDTA]₀ = 0.2 mM, current = 50 mA, aeration rate = 20 mL min^-1, flow rate = 7 mL min^-1, pH = 7 and [Na₂SO₄]₀ = 0.05 M. The degradation of EDTA during the process was also studied. Radical scavenging experiments indicated that OH was the dominant radical for RhB removal. While, the photolysis of Fe^IIIEDTA was mainly responsible for EDTA degradation. RhB and EDTA removal in different systems was compared. The stability test proved that in the presence of EDTA, the UV/EF process could remove RhB with high efficiency in the first two runs. While, the efficiency dropped remarkably after EDTA's complete depletion. The mechanisms of the UV/EDTA/EF process were proposed. UV/EDTA/EF conducted in the flow-through system was able to efficiently remove RhB as well as EDTA in a wide pH range and proposed as a promising approach for wastewater treatment.

Degradation of antibiotics by advanced oxidation processes: An overview

Antibiotics are becoming emerging contaminants due to their extensive production and consumption, which have caused hazards to the ecological environment and human health. Various techniques have been studied to remove antibiotics from water and wastewater, including biological, physical and chemical methods. Among them, advanced oxidation processes (AOPs) have received increasing attention due to their fast reaction rate and strong oxidation capability, which are effective for the degradation of antibiotics in aquatic environments. In this review paper, a variety of AOPs, such as Fenton or Fenton-like reaction, ozonation or catalytic ozonation, photocatalytic oxidation, electrochemical oxidation, and ionizing radiation were briefly introduced, including their principles, characteristics, main influencing factors and applications. The current applications of AOPs for the degradation of antibiotics in water and wastewater were analyzed and summarized, the concluding remarks were given and their future perspectives and challenges were discussed.

Application of polymeric ferric sulfate combined with cross-frequency magnetic field in the printing and dyeing wastewater treatment

Polymeric ferric sulfate (PFS) was pretreated with a self-made alternating frequency magnetic field for coagulation printing and dyeing (PD) wastewater treatment. The effects of PFS dosage, magnetization intensity, frequency, and time on the removal of chemical oxygen demand (COD), color and turbidity of PD wastewater were investigated. The results indicated that the magnetized PFS significantly improved the removal efficiency in wastewater treatment. When the initial COD, color and turbidity of printing and dyeing wastewater was 464 mg/L, 180 degrees, and 54.8 NTU respectively, the maximum removal rate of COD, color and turbidity was 87.9%, 80.1%, and 95.2% respectively, under the condition of cross frequency magnetic field magnetization PFS. Moreover, the PFS treatment combined with cross-frequency magnetic field could greatly reduce the pollution of iron ions released from iron-based coagulant during wastewater treatment. Characterization of magnetized PFS flocculant by fourier transform infrared spectroscopy, ultraviolet and visible spectrophotometry, and scanning electron microscopy suggested that magnetic crystal with larger size can be formed on the surface of PFS particles.

Influence of light and Fe(III) ions on tetracycline degradation

Tetracycline (TC) is an antibiotic produced on the largest scale in the world and used for the treatment of both humans and animals. Its removal from the circulation chain between the natural environment and animals is still a serious problem. Fe(III) ions can be used to break this chain. Fe(III) ions appear in water in spite of irradiation of Fe(III)-Cit complex and oxidation by oxygen present in water. Fe(III)-Cit was a reservoir of Fe(III) ions from which they were continuously released. Therefore, in this paper we studied an interaction between tetracycline (TC) and Fe(III) ions under fluorescent light at 20 °C and 30 °C in the water environment. This interaction leads to TC + Fe(III) coordinating complex formation. Changes caused by this process were monitored within 1860 min by measuring absorption and fluorescence spectra. The absorption spectra showed a charge-transfer stacking band(s) of oxidized and non-oxidized form of TC above 400 nm; in turn the fluorescence spectra revealed decay of initial bands and formation of the new ones. The initial, main fluorescence band at 16,660 cm^-1 associated with the intramolecular proton transfer has gradually disappeared after Fe(III) ions binding to oxygen atoms in the BCD system rings of a TC molecule. Gaussian decomposition of all fluorescence spectra allowed extracting new bands, their evolution in time and calculating the rate of the first reaction step. Temperature rise of 10 °C caused more than a ten-fold increase in the first-order reaction rate.