Factors affecting UV/persulfate treatment of phenacetin and its disinfection byproduct formation potential

Effects of solid phase extraction conditions on molecular composition of unknown disinfection byproducts in chlorinated municipal wastewater based on FT-ICR-MS analysis

Disinfection byproducts (DBPs) have been extensively investigated during the chlorination of water and wastewater. Although over 700 DBPs have been identified, more than 50% of the total organic halogen remains unknown. Solid phase extraction (SPE) has been emerged as a popular pretreatment approach for enrichment and desalting of unknown DBPs prior to the mass spectrometry analysis. However, the effects of SPE conditions on unknown DBPs in real wastewater have not yet been reported. Herein, three factors (acid types, pH values, and sorbent types) influencing the composition of DBPs in chlorinated municipal wastewater were systematically investigated by Fourier transform ion cyclotron resonance mass spectrometry and statistical analysis. The results indicated that the number of DBPs in different SPE conditions ranged from 280 to 706, and the majority ones were Br-DBPs and CHOX compounds. Compared with H2SO4, more common DBPs were found when using HCl and HCOOH to adjust the pH values of samples. The unique DBPs extracted at pH 1.0 and 2.0 generally owned higher modified aromaticity index (AImod) value and C number than at pH 3.0. The effect of acid types on the extracted DBPs was pH dependent, and the total number of extracted DBPs increased with the increasing of pH value. In terms of sorbent types, the unique DBPs in C18 sorbent possessed low O/C ratios (O/C < 0.6), whereas the unique ones in HLB sorbent owned high O/C ratios (O/C > 0.6). Compared with C18 and HLB sorbents, the unique DBPs extracted in PPL sorbent were characterized by relatively high AImod and DBE values. Based on mass difference analysis, 1496 precursors-DBPs pairs were identified in all extracted samples, with the highest number of bromine substitution reaction. Overall, the effects of SPE conditions on the composition of unknown DBPs should not be overlooked, and the amount and diversity of DBPs may be underestimated under a single SPE condition. This study provides new methodological references for the accurate identification of unknown DBPs with different characteristics in real wastewater.

Efficient elimination of phenazone by an electro-assisted Fe3+-EDDS/PS process at neutral pH: Kinetics, mechanistic insights and toxicity evaluation

The feasibility of the degradation of phenazone (PNZ), a common anti-inflammatory drug used for reducing pain and fever, in water at neutral pH by an electrochemically assisted Fe³⁺-ethylenediamine disuccinate-activated persulfate process (EC/Fe³⁺-EDDS/PS) was investigated. The efficient removal of PNZ at neutral pH condition was mainly attributed to the continuous activation of PS via electrochemically driven regenerated Fe²⁺ from a Fe³⁺-EDDS complex at the cathode. The influence of several critical parameters, including current density, Fe³⁺ concentration, EDDS to Fe³⁺ molar ratio, and PS dosage, on PNZ degradation was evaluated and optimized. Both hydroxyl radicals (•OH) and sulfate radicals (SO₄^●-) were considered major reactive species responsible for PNZ degradation. To understand the mechanistic model of action at the molecular level, the thermodynamic and kinetic behaviors of the reactions between PNZ with •OH and SO₄^●- were theoretically calculated using a density functional theory (DFT) method. The results revealed that radical adduct formation (RAF) is the most favorable pathway for the •OH-driven oxidation of PNZ, while single electron transfer (SET) appears to be the dominant pathway for the reaction of SO₄^●- with PNZ. In total, thirteen oxidation intermediates were identified, and hydroxylation, pyrazole ring opening, dephenylization, and demethylation were speculated to be the major degradation pathways. Furthermore, predicted toxicity to aquatic organisms indicated that PNZ degradation resulted in products that were less harmful. However, the developmental toxicity of PNZ and its intermediate products should be further investigated in the environment. The findings of this work demonstrate the viability of effectively removing organic contaminants in water at near-neutral pH by using EDDS chelation combined with electrochemistry in a Fe³⁺/persulfate system.

Remediation of environmentally persistent organic pollutants (POPs) by persulfates oxidation system (PS): A review

Over the past few years, persistent organic pollutants (POPs) exhibiting high ecotoxicity have been widely detected in the environment. Persulfate-oxidation hybrid system is one of the most widely used novel advanced oxidation techniques and is based on the persulfate generation of SO₄^-∙ and ∙OH from persulfate to degrade POPs. The overarching aim of this work is to provide a critical review of the variety of methods of peroxide activation (e.g., light activated persulfate, heat-activated persulfate, ultrasound-activated persulfate, electrochemically-activated persulfate, base-activated persulfate, transition metal activated persulfate, as well as Carbon based material activated persulfate). Specifically, through this article we make an attempt to provide the important characteristics and uses of main activated PS methods, as well as the prevailing mechanisms of activated PS to degrade organic pollutants in water. Finally, the advantages and disadvantages of each activation method are analyzed. This work clearly illustrates the benefits of different persulfate activation technologies, and explores persulfate activation in terms of Sustainable Development Goals, technical feasibility, toxicity assessment, and economics to facilitate the large-scale application of persulfate technologies. It also discusses how to choose the most suitable activation method to degrade different types of POPs, filling the research gap in this area and providing better guidance for future research and engineering applications of persulfates.

Impact of water matrices on oxidation effects and mechanisms of pharmaceuticals by ultraviolet-based advanced oxidation technologies: A review

The binding between water components (dissolved organic matters, anions and cations) and pharmaceuticals influences the migration and transformation of pollutants. Herein, the impact of water matrices on drug degradation, as well as the electrical energy demands during UV, UV/catalysts, UV/O₃, UV/H₂O₂-based, UV/persulfate and UV/chlorine processes were systemically evaluated. The enhancement effects of water constituents are due to the powerful reactive species formation, the recombination reduction of electrons and holes of catalyst and the catalyst regeneration; the inhibition results from the light attenuation, quenching effects of the excited states of target pollutants and reactive species, the stable complexations generation and the catalyst deactivation. The transformation pathways of the same pollutant in various AOPs have high similarities. At the same time, each oxidant also can act as a special nucleophile or electrophile, depending on the functional groups of the target compound. The electrical energy per order (EEO) of drugs degradation may follow the order of EEO_UV > EEO_UV/catalyst > EEO_UV/H2O2 > EEO_UV/PS > EEO_UV/chlorine or EEO_UV/O3. Meanwhile, it is crucial to balance the cost-benefit assessment and toxic by-products formation, and the comparison of the contaminant degradation pathways and productions in the presence of different water matrices is still lacking.

A comprehensive review on persulfate activation treatment of wastewater

With increasingly serious environmental pollution and the production of various wastewater, water pollutants have posed a serious threat to human health and the ecological environment. The advanced oxidation process (AOP), represented by the persulfate (PS) oxidation process, has attracted increasing attention because of its economic, practical, safety and stability characteristics, opening up new ideas in the fields of wastewater treatment and environmental protection. However, PS does not easily react with organic pollutants and usually needs to be activated to produce oxidizing active substances such as sulfate radicals (SO₄^-) and hydroxyl radicals (OH) to degrade them. This paper summarizes the research progress of PS activation methods in the field of wastewater treatment, such as physical activation (e.g., thermal, ultrasonic, hydrodynamic cavitation, electromagnetic radiation activation and discharge plasma), chemical activation (e.g., alkaline, electrochemistry and catalyst) and the combination of the different methods, putting forward the advantages, disadvantages and influencing factors of various activation methods, discussing the possible activation mechanisms, and pointing out future development directions.

Degradation of dyes by UV/Persulfate and comparison with other UV-based advanced oxidation processes: Kinetics and role of radicals

This study investigated the degradation of methylene blue (MeB), methyl orange (MeO), and rhodamin B (RhB) by the UV/Persulfate (UV/PS) process. The dye degradation in the investigated UV-based Advanced Oxidation Processes (UV/AOPs) followed the first-order kinetic model. The second-order rate constant of the dyes with •OH, SO₄^•-, and CO₃^•- were calculated and found to be: k_•OH,MeB = 5.6 × 10⁹ M^-1 s^-1, [Formula: see text]  = 3.3 × 10⁹ M^-1 s^-1, [Formula: see text]  = 6.9 × 10⁷ M^-1 s^-1; k_•OH,MeO = 3.2 × 10⁹ M^-1 s^-1, [Formula: see text]  = 13 × 10⁹ M^-1 s^-1, [Formula: see text]  = 4.4 × 10⁶ M^-1 s^-1; k_•OH,RhB = 14.8 × 10⁹ M^-1 s^-1, [Formula: see text]  = 5 × 10⁹ M^-1 s^-1, [Formula: see text]  = 1 × 10⁷ M^-1 s^-1. The steady-state concentrations of •OH and SO₄^•- (including other reactive species) were determined using both chemical probes and modeling methods (Kintecus® V6.8). In the UV/PS, the dye degradation depends on the pH of the solution with the order: k_dye (at pH of 7) > k_dye (in acidic conditions) > k_dye (in alkaline conditions). The presence of water matrices had different impacts on dye degradation: 1) The HCO₃^- and Cl^- promoted the degradation efficiency of one dye, but also inhibited the degradation of other dyes; 2) Humic acid (HA) inhibited dye degradation as it scavenged both •OH and SO₄^•-. The degradation of the dyes by UV/PS was also compared with the UV/Chlorine (UV/HOCl) and UV/H₂O₂ and it was established that: 1) In UV/PS and UV/HOCl, SO₄^•- and RCS contributed to dye degradation more than •OH, while •OH played a major role in dye degradation by UV/H₂O₂; 2) The calculated toxicity in UV/PS was the lowest probably due to the low toxicity of by-products; 3) For MeO and RhB, the UV/PS process is more beneficial for the total organic carbon (TOC) removal compared to that of the UV/HOCl and UV/H₂O₂ processes; 4) The UV/PS showed lower cost than the UV/HOCl and UV/H₂O₂ systems for MeO, and RhB degradation but higher cost for MeB removal.

Application of sulfate radicals-based advanced oxidation technology in degradation of trace organic contaminants (TrOCs): Recent advances and prospects

The large amount of trace organic contaminants (TrOCs) in wastewater has caused serious impacts on human health. In the past few years, Sulfate radical (SO₄^•-) based advanced oxidation processes (SR-AOPs) are widely recognized for their high removal rates of recalcitrant TrOCs from water. Peroxymonosulfate (PMS) and persulfate (PS) are stable and non-toxic strong oxidizing oxidants and can act as excellent SO₄^•- precursors. Compared with hydroxyl radicals(·OH)-based methods, SR-AOPs have a series of advantages, such as long half-life and wide pH range, the oxidation capacity of SO₄^•- approaches or even exceeds that of ·OH under suitable conditions. In this review, we present the progress of activating PS/PMS to remove TrOCs by different methods. These methods include activation by transition metal, ultrasound, UV, etc. Possible activation mechanisms and influencing factors such as pH during the activation are discussed. Finally, future activation studies of PS/PMS are summarized and prospected. This review summarizes previous experiences and presents the current status of SR-AOPs application for TrOCs removal. Misconceptions in research are avoided and a research basis for the removal of TrOCs is provided.

MoS2-assisted Fe2+/peroxymonosulfate oxidation for the abatement of phenacetin: efficiency, mechanisms and toxicity evaluation

In this study, molybdenum disulfide (MoS₂) was chosen as a co-catalyst to enhance the removal efficiency of phenacetin (PNT) in water by a ferrous ion-activated peroxymonosulfate (Fe²⁺/PMS) process. Operating parameters, such as the initial solution pH and chemical dose on PNT degradation efficiency were investigated and optimized. Under an initial pH of 3, an Fe²⁺ dose of 25 μM, a PMS dose of 125 μM and a MoS₂ dose of 0.1 g L⁻¹, the degradation efficiency of PNT reached 94.3%, within 15 min. The presence of common water constituents including Cl⁻, HCO₃⁻, SO₄²⁻ and natural organic matter (NOM) will inhibit degradation of PNT in the MoS₂/Fe²⁺/PMS system. Radical quenching tests combined with electron paramagnetic resonance (EPR) results indicated that in addition to free radical species (˙OH, SO₄˙⁻ and O₂˙⁻), nonradical reactive species (¹O₂) were also crucial for PNT degradation. The variations in the composition and crystalline structure of the MoS₂ before and after the reaction were characterized by XPS and XRD. Further, the degradation pathways of PNT were proposed according to the combined results of LC/TOF/MS and DFT calculations, and primarily included hydroxylation of the aromatic ring, cleavage of the C–N bond of the acetyl-amino group, and cleavage of the C–O bond of the ethoxy group. Finally, toxicity assessment of PNT and its products was predicted using the ECOSAR program.

Performance, mechanisms and toxicity evaluation of PNT degradation by the MoS₂/Fe²⁺/PMS system were investigated.