Advanced Oxidation Processes For Wastewater Treatment Research Articles

Insights into the enhanced removal of sulfamethoxazole via peroxymonosulfate activation catalyzed by bimetallic (Co/Cu) doped graphitic carbon nitride: Reaction kinetics, mechanisms, and pathways

Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) have shown great potential for recalcitrant contaminants removal in wastewater treatment. Herein, we report the efficient activation of PMS by bimetallic oxides (cobalt and copper) co-doped graphitic carbon nitride (Co–Cu@g-C3N4) for removal of sulfamethoxazole (SMX). The morphology and chemical composition of the fresh and used Co–Cu@g-C3N4 were characterized by TEM, SEM, XRD, BET, and XPS. Nearly complete removal of SMX (50 mg/L) was observed in the presence of 50 mg/L Co–Cu@g-C3N4, 0.5 mmol/L PMS within 20 min at neutral pH with a degradation rate of 0.137 min−1. Moreover, the Co–Cu@g-C3N4 catalyst enabled more than 90 % removal of various typical pollutants within 20 min, including sulfapyridine, rhodamine B, acridine red, and malachite green, with rate constants of 0.083, 0.130, 0.096, and 0.160 min−1, respectively. Quenching experiments and electron paramagnetic resonance (EPR) analysis demonstrated that sulfate radical (SO4−) and singlet oxygen (1O2) were collectively responsible for SMX degradation. The efficient activation of PMS by Co–Cu@g-C3N4 was ascribed to the continuous conversion of Co(Ⅲ) to Co(Ⅱ) and Cu(I) to Cu(ⅠI), and the presence of oxygen vacancy (OV) on the catalyst. The Co–Cu@g-C3N4/PMS system exhibited superior durability and maintained high efficiency in real water samples. Finally, theoretical calculations of Fukui index were performed to determine the possible degradation pathways of SMX, and the ecotoxicity of the degradation products was evaluated by the ECOSAR program. This study significantly advances the understanding of the reaction between PMS and bimetallic oxides catalysts, as well facilitates the development and application of PMS-based AOPs in wastewater treatment.

Picolinic Acid-Mediated Catalysis of Mn(II) for Peracetic Acid Oxidation Processes: Formation of High-Valent Mn Species.

Metal-based advanced oxidation processes (AOPs) with peracetic acid (PAA) have been extensively studied to degrade micropollutants (MPs) in wastewater. Mn(II) is a commonly used homogeneous metal catalyst for oxidant activation, but it performs poorly with PAA. This study identifies that the biodegradable chelating ligand picolinic acid (PICA) can significantly mediate Mn(II) activation of PAA for accelerated MP degradation. Results show that, while Mn(II) alone has minimal reactivity toward PAA, the presence of PICA accelerates PAA loss by Mn(II). The PAA-Mn(II)-PICA system removes various MPs (methylene blue, bisphenol A, naproxen, sulfamethoxazole, carbamazepine, and trimethoprim) rapidly at neutral pH, achieving >60% removal within 10 min in clean and wastewater matrices. Coexistent H2O2 and acetic acid in PAA play a negligible role in rapid MP degradation. In-depth evaluation with scavengers and probe compounds (tert-butyl alcohol, methanol, methyl phenyl sulfoxide, and methyl phenyl sulfone) suggested that high-valent Mn species (Mn(V)) is a likely main reactive species leading to rapid MP degradation, whereas soluble Mn(III)-PICA and radicals (CH3C(O)O• and CH3C(O)OO•) are minor reactive species. This study broadens the mechanistic understanding of metal-based AOPs using PAA in combination with chelating agents and indicates the PAA-Mn(II)-PICA system as a novel AOP for wastewater treatment.

Enhanced production of hydroxyl radicals in plasma-treated water via a negative DC bias coupling

Hydroxyl radical (OH•) plays an important role in advanced oxidation processes (AOPs), which are employed to decompose organic pollutants in wastewater treatment. OH• is predominantly produced in AOPs for wastewater treatment via ultraviolet photolysis of hydrogen peroxide (H2O2) or ozone, which is a costly and difficult process. This paper introduces an enhanced OH• production method based on microwave-driven atmospheric pressure plasma with negatively biased water. Fluorescence analysis using terephthalic acid and 2-hydroxyterephthalic acid showed that the OH• concentration in a DC coupled plasma-treated water (PTW) can be increased by 1–2 orders of magnitude compared to the case with microwave plasma only. In addition, we found that there exists an optimal concentration of H2O2 in PTW for the ideal production of OH•. As a test case of AOPs, an Fe(III)-ethylenediaminetetraacetic acid solution containing H2O2 was treated with a DC coupled plasma for 10 min, and more than 80% decomposition was recorded.

Highly efficient activation of peracetic acid by nano-CuO for carbamazepine degradation in wastewater: The significant role of H2O2 and evidence of acetylperoxy radical contribution

Peracetic acid (PAA)-based advanced oxidation processes (AOPs) has attracted increasing attentions towards contaminant degradation in the wastewater treatment. Herein, we report the efficient activation of PAA by nano-CuO (nCuO/PAA) to degrade carbamazepine (CBZ) for the first time. Rapid degradation of CBZ was observed in the nCuO/PAA system at neutral initial pH. A new scavenging experiment with Mn2+ as a specific scavenger was developed to distinguish the dominant role of CH3C(O)OO● for CBZ degradation in the nCuO/PAA process. The oxidation of CBZ by CH3C(O)OO● was verified to proceed via the electrons transfer, and the acute and chronic toxicity of the transformation products was significantly reduced. The efficient activation of PAA by nCuO was found to be realized through continuous conversion of Cu(II) to Cu(I), which was significantly boosted by co-existing H2O2. The nCuO/PAA process was slightly affected by the water matrices, and maintained high efficiency in real water samples. The findings obtained in this study provide new insights into the catalytic formation of CH3C(O)OO● from PAA and facilitate the development and application of PAA-based AOPs in wastewater treatment.

Role of NOM in the Photolysis of Chlorine and the Formation of Reactive Species in the Solar/Chlorine System.

The solar/chlorine system has been proposed as a novel advanced oxidation process (AOP) for efficient pollutant degradation and water disinfection by producing a series of reactive species including hydroxyl radicals (HO•), chlorine radicals (Cl•), and so forth. In this study, the role of natural organic matter (NOM) in the photolysis of free available chlorine (FAC) and the formation of HO• and Cl• in the solar/chlorine system was investigated employing nitrobenzene and benzoic acid as selective chemical probes. The decay rate of FAC was significantly accelerated in the presence of NOM at pH 5.5 under simulated solar irradiation, likely due to the photoreaction between FAC and the photoexcited NOM. The decay rate of FAC increased upon increasing the electron-donating capacity of NOM, which indicated that phenolic components play a significant role in the photodegradation of FAC. This acceleration mechanism was further verified using 4-nitrophenol as a model phenolic compound. NOM promoted Cl• formation and quenched HO• in the solar/chlorine system. The proposed reaction mechanism included the reaction of excited singlet phenolic compounds in NOM with FAC, which yielded Cl•. This study provides a useful insight into future applications for using the solar/chlorine system as a novel AOP for wastewater treatment or disinfection.

Advanced Oxidation Processes for Wastewater Treatment: Facts and Future Trends

Pollution provoked by antibiotics and antibiotic-resistant bacteria must be placed as a worldwide health and ecological worry. Advanced oxidation processes (AOPs) are viewed as a greatly reasonable technique concerning water treatments for eliminating organic contaminants categorized as bio-recalcitrant and for the demobilization of pathogens, which are not touchable via traditional methods. This work discusses briefly the main recent facts and future trends in the field of applying AOPs in wastewater treatment. There is an urgent need for strengthening the studies on eliminating pollutants and microorganisms for wastewater reuse utilizing various AOPs. In-depth investigation about their reduction pathways employing AOPs is needed. Coupling AOPs with membrane processes should be kept in mind for better safety and pollutant removal.

Applications of AOPs in wastewater treatment

As Advanced Oxidation Processes (AOPs) are based on radical reactions that are very fast, non-selective and can completely oxidise substances, they have great potential for the removal of non-biodegradable pollutants from municipal and industrial wastewater. However, although there has been much progress in understanding AOPs, most work has been limited to laboratory or pilot-plant scale; there are few reports on industrial applications of AOP for wastewater treatment and hardly any disclose costs. Publication of such studies is needed if AOPs are to gain wide application as an alternative to more conventional treatment methods.