Feasibility study on applying the iron-activated persulfate system as a pre-treatment process for clofibric acid selective degradation in municipal wastewater

Clofibric acid (CFA) was selected as an example of the widespread micropollutants in municipal wastewater to investigate the feasibility of the application of an iron-activated persulfate (Fe-PS) system for selective micropollutants removal prior to biological wastewater treatment. In pure CFA solution, the CFA degradation rate was accelerated with an increase in oxidant dosage and 2.15 mg·L^-1 (0.01 mM) CFA could be completed removed within 30 min with 270 mg·L^-1 (1 mM) potassium persulfate (PS) activated by 56 mg·L^-1 iron powder (Fe). Although both sulfate radicals (SO₄^∙-) and hydroxyl radicals (HO^∙) were generated in the Fe-PS system, SO₄^∙- was identified as the dominant oxidant for CFA degradation. To investigate the interference from model compounds in the municipal wastewater, CFA degradation in different concentrations of ammonia or/and glucose solutions, the synthetic municipal wastewater, and real municipal wastewater systems were investigated. A complete removal of CFA was achieved with ammonia or/and glucose interferences. Less than 3% ammonia was removed due to the formation of aminopropyl radicals. About 15% degradation of dissolved organic carbon (DOC) was mainly attributed to the oxidation of glucose by HO^∙, Indicating the excellent selective oxidation ability of the Fe-PS system targeting at CFA over glucose. Even though the alkalinity significantly hindered the oxidation of CFA in both synthetic and real municipal wastewater system, the removal efficiency of CFA was significantly higher than that of DOC. The decrease of CFA removal efficiency in municipal wastewater system comparing to the other tests was due to the slow degradation of PS in the system and further hindered the SO₄^∙- generation. Therefore, the impacts of other impurities in municipal wastewater on the oxidation activities of Fe-PS system should be further investigated. In general, this study confirmed the feasibility of using the Fe-PS system for selective degrading resistant CFA in municipal wastewater.

Sulfate radical-induced destruction of emerging contaminants using traces of cobalt ions as catalysts

Cobalt is part of vitamin B12, which is essential to maintain human health, and trace levels of cobalt ions are ubiquitous in water and soil environments. In this study, the destruction of 1,4-dioxane (1,4-D) by peroxymonosulfate (PMS) under the catalysis of trace levels of Co²⁺ was investigated under buffered conditions. The results showed that near 100% removal of 1,4-D was achieved after reaction for 6 and 10 min with 50 and 25 μg/L Co²⁺, respectively, in the presence of 5 mM phosphate ions. Mechanism studies revealed that radicals mediated the destruction of 1,4-D and sulfate radicals were the primary reactive species. The traces of Co²⁺ had the greatest reactivity for the catalysis of PMS in neutral environments (pH 7.0). However, pH 5.5 was observed to be the best condition for 1,4-D destruction, which was probably caused by the involvement of phosphate radicals. Common water components including chloride ions and bicarbonate ions were observed to have promoting and inhibiting effects, respectively, on the removal of 1,4-D. To further demonstrate the potential of Co²⁺-PMS in practical applications, we explored the simultaneous degradation of 20 antibiotics using trace levels of Co²⁺. The results showed that all the investigated antibiotics, except for lomefloxacin, could be efficiently degraded by Co²⁺-PMS with removal rates of greater than 97%. The findings from this study demonstrate the promise of using trace levels of cobalt for environmental remediation applications, even when high concentrations of phosphate ions are co-present.

Heterogeneous activation of peroxymonosulfate by hierarchically porous cobalt/iron bimetallic oxide nanosheets for degradation of phenol solutions

Bimetallic oxide nanomaterials have received much attention owing to their competing performances in heterogeneous catalysis. Herein, hierarchically porous cobalt-iron oxide nanosheets were successfully prepared using NaBH₄ as a reductant and high concentration cetyl trimethylammonium bromide (CTAB) as a surfactant. Characterization results showed that the CTAB would induce the form of a bilayer structure while NaBH₄ would promote the generation of enriched oxygen vacancies. As a result, the as-prepared Co₁Fe₁-300 exhibited high activity for activating peroxymonosulfate and achieved 100% phenol degradation within 30 min. This excellent catalytic activity can be attributed to its hierarchically porous structure, more active sites and oxygen vacancies. Co leaching test indicated that the Co₁Fe₁-300 exhibited excellent catalytic stability. Mechanistic studies suggested that two main degradation pathways were involved during phenol oxidation process, in which SO₄^•- played a significant role. This work may offer a novel strategy for the synthesis of high activity catalysts and a promising system for the remediation of environmental pollutant.

Significant acceleration of Fe2+/ peroxydisulfate oxidation towards sulfisoxazole by addition of MoS2

Activation of peroxydisulfate (PDS) by Fe²⁺ has been considered as an effective activation method to generate reactive oxygen species (ROS). However, the process is limited for the low production yield of ROS owing to the inefficient Fe³⁺/Fe²⁺ cycle. Herein, we demonstrated that Fe²⁺/PDS system in the presence of molybdenum sulfide (MoS₂) was significantly efficient for the degradation of sulfisoxazole (SIX). As a co-catalyst in the Fe²⁺/PDS system, MoS₂ could greatly enhance the Fe³⁺/Fe²⁺ cycle by the exposed Mo⁴⁺ active sites, which could also improve the PDS decomposition efficiency. As a result, the degradation efficiency of SIX in the MoS₂/Fe²⁺/PDS system could reach to as high as 97.1% within 40 min, which was in distinct comparison with the 45.5% achieved by Fe²⁺/PDS system without MoS₂. Besides, effects of various reaction conditions on SIX degradation were also evaluated during the experiments, including the dosages of MoS₂, Fe²⁺, PDS and initial solution pH and the coexisting inorganic anions. In addition, both of sulfate radicals and hydroxyl radicals were identified as the dominant active species for SIX degradation by the radical scavenging experiments and verified by electron paramagnetic resonance (EPR). This study provides a promising idea for the degradation of organic contaminants in water treatment based on Fe²⁺/PDS process.

Degradation of aqueous cefotaxime in electro-oxidation - electro-Fenton -persulfate system with Ti/CNT/SnO2-Sb-Er anode and Ni@NCNT cathode

Due to the potential threatening of antibiotics in aqueous environment, a novel electro-oxidation (EO) - electro-Fenton (EF) -persulfate (PS) system with the addition of peroxydisulfate and Fe²⁺ was installed for the degradation of cefotaxime. Ti/CNT/SnO₂-Sb-Er with an ultra-high oxygen evolution potential (2.15 V) and enhanced electrocatalytic surface area was adopted as anode. The OH production and electrode stability test demonstrated great improvement in the electrochemical performances. Ni@NCNT cathode was tested with higher H₂O₂ generation by the presence of nitrogen functionalities due to the acceleration of electron transfer of O₂ reduction. Experiment results indicated CNT and ErO₂ modification increased the molecular and TOC removal of cefotaxime. Coupling processes of EO-EF and EO-PS both resulted in shorter electrolysis time for complete cefotaxime removal, however, the mineralization ability of EO-PS process was lower than EO-EF, which might result from the immediate vanishing of PS. Thus, a further improved treatment EO-EF-PS system achieved an 81.6% TOC removal towards 50 mg L^-1 cefotaxime after 4 h electrolysis, under the optimal working condition Fe²⁺ = PS = 1 mM. The influence of current density and initial concentration on the performance of all processes was assessed. Methanol and tert-butanol were added in the system as OH and SO₄^- scavengers, which illustrating the mechanism of EO-EF-PS oxidizing process was the result of the two free radicals. Major intermediates were deduced and the degradation pathway of cefotaxime was analyzed. This research provides a potential coupling process with high antibiotic removal efficiency and effective materials for practical uses.

The application of microwaves in sulfate radical-based advanced oxidation processes for environmental remediation: A review

The generation of sulfate radicals is a key factor to limit the catalytic activities of sulfate radical-based advanced oxidation processes (SR-AOPs). Microwave irradiation is a specific method to heat solutions via thermal and nonthermal effects, and has attracted an increasing amount of attention in recent years. Herein, we focus on the application of microwaves in SR-AOPs that called SR-MAOPs in environmental remediation, including wastewater, landfill leachate, biological waste sludge and soil, etc. treatment. Various systems including homogeneous and heterogeneous SR-MAOPs were reviewed. In wastewater treatment, not only the dyes and pharmaceutical and personal care products (PPCPs) were considered, the application in actual water matrices was also summarized. In addition, the function of remediation for organic-contaminated soil, landfill leachate and biological waste sludge were assessed using SR-MAOPs. In addition to evaluating the degradation efficiency of various organic pollutants from environment, the dewaterability is another key to treat biological waste sludge. The SR-MAOPs could break up hydrogen bonds and inactivate and denature complex biological molecules via microwave effects to achieve the dewatering of microorganisms in sludge. Furthermore, the COD of the sludge increased to a high level after microwave irradiation of sludge, which means that biopolymers released from microbial cells into the solution. Then, the released COD could be well treated by the SR-MAOPs. Based on the summary, we reveal that SR-MAOPs are potential technologies for environmental remediation, especially for systems with complicated organic compounds.

Application of activated persulfate for the inactivation of fecal bacterial indicators in water

Activated persulfate, as a member of the broad group of Advanced Oxidation Processes (AOPs), has emerged as a promising method for the elimination of microorganisms in aqueous matrices. This study evaluates the disinfection efficiency of this technique with respect to the inactivation of Escherichia coli and Enterococcus faecalis in water samples, as representative Gram negative and Gram positive bacterial indicators, respectively. In this perspective, various activators were employed, namely, ferric ion, heating, ultrasound application and UVA irradiation, which exhibited different bactericidal effect, depending on the operating conditions and the structural properties of each species. The highest disinfection rates were achieved with 200 mg/L of persulfate and ferric ion or heating as activators. For instance, 6 Log reductions were recorded within only 10-15 min when 30 mg/L of iron were applied, whereas the same bacterial removal was noted upon heat-activation at 50 °C, but in longer periods (i.e. 45-60 min). Nevertheless, in all cases E. faecalis was more resistant than E. coli, which was readily inactivated in shorter treatment periods. The overall process activity was deteriorated above the limit of 200 mg/L of persulfate. Ultrasound application exhibited lower performance, as even more prolonged treatment was required (120-150 min) for the same bacterial decay with the persulfate concentration not affecting substantially the process. In an attempt to improve the ultrasound activity, it was combined together with iron but with no synergistic results, as no actual enhancement of the method was observed. Finally, UVA did not seem to serve as an activator under the applied conditions, taking into account that it resulted in negligible loss of bacterial viability. Based on the current results, activated persulfate may be used successfully for disinfection purposes; however, the appropriate establishment of process variables is mostly required, considering the various resistance levels of aquatic microorganisms under stressed conditions.

Integration of •SO4--based AOP mediated by reusable iron particles and a sulfidogenic process to degrade and detoxify Orange II

The sulfate radical (•SO₄^-)-based advanced oxidation processes (AOPs) for the degradation of refractory organic pollutants consume a large amount of persulfate activators and often generate toxic organic by-products. In this study, we proposed a novel iron-cycling process integrating •SO₄^--based AOP mediated by reusable iron particles and a sulfidogenic process to degrade and detoxify Orange II completely. The rusted waste iron particles (Fe⁰@Fe_xO_y), which contained Fe^II/Fe^III oxides (Fe_xO_y) on the shell and zero-valent iron (Fe⁰) in the core, efficiently activated persulfate to produce •SO₄^- and hydroxyl radicals (•OH) to degrade over 95% of Orange II within 120 min. Both •SO₄^- and •OH destructed Orange II through a sequence of electron transfer, electrophilic addition and hydrogen abstraction reactions to generate several organic by-products (e.g., aromatic amines and phenol), which were more toxic than the untreated Orange II. The AOP-generated organic by-products were further mineralized and detoxified in a sulfidogenic bioreactor with sewage treatment together. In a 170-d trial, the organic carbon removal efficiency was up to 90%. The inhibition of the bioreactor effluents on the growth of Chlorella pyrenoidosa became negligible, due to the complete degradation and mineralization of toxic AOP-generated by-products by aromatic-degrading bacteria (e.g., Clostridium and Dechloromonas) and other bacteria. The sulfidogenic process also well recovered the used Fe⁰@Fe_xO_y particles through the reduction of surface Fe^III back into Fe^II by hydrogen sulfide formed and iron-reducing bacteria (e.g., Sulfurospirillum and Paracoccus). The regenerated Fe⁰@Fe_xO_y particles had more reactive surface Fe^II sites and exhibited much better reactivity in activating persulfate in at least 20 reuse cycles. The findings demonstrate that the integrated process is a promising solution to the remediation of toxic and refractory organic pollutants because it reduces the chemical cost of persulfate activation and also completely detoxifies the toxic by-products.

Spatial confinement of cobalt crystals in carbon nanofibers with oxygen vacancies as a high-efficiency catalyst for organics degradation

Catalytic activation of peroxymonosulfate (PMS) to generate radicals has received considerable and increasing attention in the environmental catalysis for treatment of recalcitrant pollutants. In the current study, a series of highly porous, cobalt-loaded activated carbon nanofibers (Co/CNFs) were prepared by one-pot electrospinning followed by thermal treatment. Observations showed that the limited addition of Co (≤8%) had no obvious effect on the morphology of the resulted CNFs, but it did affect the surface area and porosity of the CNFs as well as the carbon graphitic process during the carbonization. The applicability of this confined nanoreactor used in sulfate-radical based advanced oxidation processes (SR-AOPs) was systematically investigated. The effect of pH on the radical generation and organics removal was examined. The oxygen species on the CNFs played an important role in the activation of PMS. The carbon layer encapsulated on the Co crystal surface inhibited the Co leaching during the reaction and increased the catalytic efficiency due to the enhanced interfacial charge transfer. Meanwhile, the carbon layer could synchronously function as the adsorptive active sites during the degradation of organics. Results showed that the Co/CNFs possessed the highest catalytic efficiency under neutral pH, corresponding to the sulfate radical generation. The Co leaching and XPS results showed that the Co served as the main active site in PMS activation.

Prussian Blue Analogue-derived co/fe bimetallic nanoparticles immobilized on S/N-doped carbon sheet as a magnetic heterogeneous catalyst for activating peroxymonosulfate in water

While Co is the most effective metal for activating PMS, extensive efforts are made to develop Co/Fe species (CF) (e.g., CoFe₂O₄) for imparting magnetic properties and facilitating recovery of catalysts. When carbon substrates are doped with heteroatoms (e.g., S and N) and CF is embedded within the heteroatom-doped carbon matrix, synergies can occur to boost catalytic activities. This study proposes an alternative CF-bearing carbonaceous composite, a cobalt-containing Prussian Blue Analogue (PBA) (Co₃[Fe(CN)₆]₂) is employed as a precursor for preparing CF species embedded in N-doped carbon matrix and immobilized on S/N-co-doped carbon (SNC). Specifically, PBA in-situ grows on SNC by a heat treatment of trithiocyanuric acid to form PBA@SNC, which is then carbonized into CF species@SNC (CF@SNC). By adopting Amaranth degradation as a model reaction, CF@SNC shows a higher catalytic activity (k_app = 0.230 min^-1) than CF (k_app = 0.152 min^-1) and SNC (k_app = 0.016 min^-1) for activating PMS. In comparison with Co₃O₄, CF@SNC exhibits a higher catalytic activity for PMS activation. CF@SNC renders a relatively low E_a value (53 kJ/mol) for Amaranth degradation in comparison to other reported catalysts. These comparisons demonstrate the advantageous features of CF@SNC as a magnetic and efficient catalyst for PMS activation.

Ultrasound-assisted heterogeneous peroxymonosulfate activation with Co/SBA-15 for the efficient degradation of organic contaminant in water

A potential advanced oxidation process is provided by SBA-15 supported cobalt (Co/SBA-15) activated peroxymonosulfate (PMS, HSO₅^-) in the ultrasound (US) enhanced system, named Co/SBA-15/PMS/US process, for the elimination of refractory organic contaminants (ROCs) in water. This process exhibited favorable behavior with 95.5 % C.I. Acid Orange 7 (AO7) degradation using 5 mM PMS, 0.5 g/L Co/SBA-15 catalyst, 190 W US power at initial pH of 6.0 after 90 min reaction. Co/SBA-15 particles remained satisfied catalytic activity and stability with very low level of cobalt release in 10 successive cycles. The scavenge tests and electron paramagnetic resonance (EPR) result as well as the cobalt leaching concentration revealed that the reactive radicals (SO₄^- and OH) on catalyst surface were primarily responsible for AO7 oxidation, and a rational mechanism was elucidated accordingly. The presence of chloride ions and bicarbonate could improve AO7 removal. The probable pathway of AO7 degradation was proposed based on the intermediates identified. This Co/SBA-15/PMS/US process could be well applied for the destruction of other typical ROCs (bisphenol A, clofibric acid, and rhodamine B) and the treatment of lake and river water spiked with AO7, and this study may provide an efficient PMS technique for the remediation of ROCs in water.

Simultaneous desulfurization and denitrification from flue gas by catalytic ozonation combined with NH3/(NH4)2S2O8 absorption: Mechanisms and recovery of compound fertilizer

An integrated method of simultaneous desulfurization and denitrification from flue gas by catalytic ozonation combined with NH₃/(NH₄)₂S₂O₈ absorption was developed for the first time. It consisted of two parts: (1) the catalytic ozonation of NO over FeO_x/SAPO-34 to study the effects of the various influencing factors, and (2) the absorption-oxidation of NO_x and SO₂ induced by ozone combined with a NH₃/(NH₄)₂S₂O₈ solution in a bubble column reactor. In Part 1, results showed that under the optimal condition of a molar ratio of 0.5 for O₃/NO, a residence time of 3 s, a water vapor volume fraction of 4%, a NO initial concentration of 536 mg/m³, and a SO₂ initial concentration of 343 mg/m³, the oxidation rate of NO was 55%. The characterizations of poisoned catalyst are briefly discussed. In Part 2, as the gas passed sequentially through the ozonizing reactor and the absorber (NH₃/(NH₄)₂S₂O₈ solution of 0.8% ammonia and 0.2 mol/L (NH₄)₂S₂O₈), a NO conversion rate of approximately 92.6% and SO₂ conversion rate of 100% were obtained. The pH of the NH₃/(NH₄)₂S₂O₈ solution had a significant impact on the NO conversion. According to the analysis of the composition of products under different pHs, a mechanism of desulfurization and denitrification based on NH₃/(NH₄)₂S₂O₈ solutions was proposed. The reaction product as a compound fertilizer contained up to 24.5% nitrogen.

Visible and UV photocatalysis of aqueous perfluorooctanoic acid by TiO2 and peroxymonosulfate: Process kinetics and mechanistic insights

The global occurrence and adverse environmental impacts of perfluorooctanoic acid (PFOA) have attracted wide attention. This study focused on the PFOA photodegradation by using photocatalyst TiO₂ with peroxymonosulfate (PMS) activation. Aqueous PFOA (50 mg L^-1) at the pH 3 was treated by TiO2/PMS under 300 W visible light (400-770 nm) or 32 W UV light (254 nm and 185 nm). The addition of PMS induced a significant degradation of PFOA under powerful visible light compared with sole TiO₂. Under visible light, 0.25 g L^-1 TiO₂ and 0.75 g L^-1 PMS in the solution with the initial pH 3 provided optimum condition which achieved 100% PFOA removal within 8 h. Under UV light irradiation at 254 nm and 185 nm wavelength, TiO₂/PMS presented excellent performance of almost 100% removal of PFOA within 1.5 h, attributed to the high UV absorbance by the photocatalyst. The intermediates analysis showed that PFOA was degraded from a long carbon chain PFOA to shorter chain intermediates in a stepwise manner. Furthermore, scavenger experiments indicated that SO₄^•-radicals from PMS and photogenerated holes from TiO₂ played an essential role in degrading PFOA. The presence of organic compounds in real wastewater reduced the degradation efficacy of PFOA by 18-35% in visible/TiO₂/PMS system. In general, TiO₂/PMS could be an ideal and effective photocatalysis system for the degradation of PFOA from wastewater using either visible or UV light source.

Influence of [sulfite]/[Fe(VI)] molar ratio on the active oxidants generation in Fe(VI)/sulfite process

Although several groups have made efforts to study micropollutants degradation by Fe(VI)/sulfite process, the mechanism is far from clear and warrants further investigation. Herein, the degradation kinetics and mechanism of selected micropollutants by sulfite (SO₃^2-)-activated Fe(VI) oxidation were systematically investigated. The oxidation rates of enrofloxacin (ENR) and phenol in Fe(VI)/sulfite process ranged from 0.151 s^-1 to 6.18 s^-1 at pH 6.5 and 8.0. Sulfite applied in multiple-addition mode improved the degradation efficiency of micropollutants with electron-rich moieties compared to the single-addition mode. Based on results of the quenching experiments and kinetic simulation, Fe(V) was identified as the predominant active oxidant at [SO₃^2-]/[Fe(VI)] molar ratio of 0.1 to 0.3. However, both Fe(V) and SO₄^-/OH contributed to micropollutants oxidation at [SO₃^2-]/[Fe(VI)] molar ratio ≥ 0.4 and their contributions were strongly dependent on the properties of micropollutants. The different degradation products of ENR in Fe(VI)/sulfite process at different sulfite dosages further supported the contribution of different active oxidants at different [SO₃^2-]/[Fe(VI)] molar ratios. The toxicity of the reaction products of ENR towards Vibrio qinghaiensis sp.-Q67 decreased dramatically after Fe(VI)/sulfite treatment. The results of this work may promote the application of sulfite-activated Fe(VI) oxidation in water treatment.

Synergistic activation of peroxymonosulfate and persulfate by ferrous ion and molybdenum disulfide for pollutant degradation: Theoretical and experimental studies

Activation of peroxymonosulfate (PMS) and persulfate (PS) by Fe²⁺ is widely used for oxidizing organic pollutants. However, their application is limited by the slow conversion rate of Fe³⁺ to Fe²⁺ and the accumulation of Fe³⁺. Here, we introduce commercial molybdenum disulfide (MoS₂) to promote the activation of PMS and PS by Fe²⁺, and explore the mechanism of this promotion using experimental and theoretical methods. The Fe²⁺/PMS/MoS₂ and Fe²⁺/PS/MoS₂ systems achieved faster rate of PMS and PS conversion and also higher degradation efficiency toward pollutants. About 94.7% and 87.6% of rhodamine B (RhB) could be degraded in Fe²⁺/PMS/MoS₂ (54 μM Fe²⁺, 1 mM PMS) and Fe²⁺/PS/MoS₂ (54 μM Fe²⁺, 0.25 mM PS) system, respectively. MoS₂ addition simultaneously promoted the Fe³⁺/Fe²⁺ cycle, the PMS and PS conversion, and the RhB mineralization. As a co-catalyst, MoS₂ exhibited excellent stability for eight successive cycles of use. The predominant oxidant was identified as SO₄^- in Fe²⁺/PMS/MoS₂ and Fe²⁺/PS/MoS₂ systems. Theoretical calculations and a kinetic model were employed to evaluate the catalytic performance of the systems. These novel findings indicate that the combination of a commercially available MoS₂ catalyst with a low dosage of Fe²⁺ is a promising and effective approach for efficient activation of PMS and PS to produce SO₄^- and OH.

Novel α-Fe2O3/MXene nanocomposite as heterogeneous activator of peroxymonosulfate for the degradation of salicylic acid

The development of non-cobalt-based heterogeneous catalysts with efficient catalytic activity, good stability and nontoxicity is very important for the application of peroxymonosulfate-based advanced oxidation processes (AOPs) in water treatment. In this work, with two dimensional MXene as the catalyst substrate, a novel α-Fe₂O₃/MXene (FM) nanocomposite was fabricated through a facile solvothermal method. Systematic characterization demonstrated that the MXene substrate could facilitate the size reduction and good dispersion of α-Fe₂O₃ nanoparticles. The FM nanocomposite achieved high efficiency and stability towards activating peroxymonosulfate (PMS) to produce free radicals for the degradation of salicylic acid (SA) in aqueous solution. The operating parameters, including catalyst dosage, PMS dosage, SA concentration and initial pH value, were evaluated and analysed. The co-existence of sulfate radicals (SO₄^-) and hydroxyl radicals (OH) was confirmed using electron paramagnetic resonance spectroscopy and radical scavenger tests, while SO₄^-was identified as the main reactive species in the FM/PMS catalytic system. The possible mechanisms for the electron transfer and radical generation during the process of PMS activation by the FM nanocomposite are further investigated using XPS and in situ Raman analysis. The results provide an avenue for rationally constructing and developing alternative catalysts for the treatment of organics in wastewater.

Improved photocatalysis of perfluorooctanoic acid in water and wastewater by Ga2O3/UV system assisted by peroxymonosulfate

Perfluorooctanoic acid (PFOA) has attracted considerable attention worldwide due to its widespread occurrence and environmental impacts. This research focused on the photocatalytic process for the treatment of PFOA in water and wastewater. Gallium oxide (Ga₂O₃) and peroxymonosulfate (PMS) were mixed directly in PFOA solution, which was irradiated under different light sources. The treatment system showed excellent performance that 100% PFOA was degraded within 90 min and 60 min under 254 nm and 185 nm UV irradiation, respectively. Moreover, the degradation efficacy was unaffected by initial PFOA concentration from 50 ng L^-1 to 50 mg L^-1. Acidic solution (pH 3) improved the degradation process. The quantum yield in the PMS/Ga₂O₃ system under UV light (254 nm) was estimated to be 0.009 mol E^-1. Scavengers such as tert-butanol (t-BuOH), disodium ethylenediaminetetraacetate (EDTA-Na₂) and benzoquinone (BQ) were added into PFOA solution to prove that sulfate radicals (SO₄^•-), superoxide radical (O₂^•-) and photogenerated electrons (e^-) were the main active species with strong redox ability for PFOA degradation in PMS/Ga₂O₃/UV system. Combined with the intermediates analysis, PFOA was degraded stepwise from long chain compound to shorter chain intermediates. In addition, PFOA in real wastewater exhibited similar degradation efficiency, together with 75-85% TOC removal by Ga₂O₃/PMS under 254 nm UV irradiation. Therefore, Ga₂O₃/PMS system was highly effective for PFOA photodegradation under UV irradiation, which has potential to be applied for the perfluoroalkyl substances (PFAS) treatment in water and wastewater.

Manganese oxide integrated catalytic ceramic membrane for degradation of organic pollutants using sulfate radicals

Membrane separation and advanced oxidation processes (AOPs) have been respectively demonstrated to be effective for a variety of water and/or wastewater treatments. Innovative integration of membrane with catalytic oxidation is thus expected to be more competing for more versatile applications. In this study, ceramic membranes (CMs) integrated with manganese oxide (MnO₂) were designed and fabricated via a simple one-step ball-milling method with a high temperature sintering. Functional membranes with different loadings of MnO₂ (1.67%, 3.33% and 6.67% of the total membrane mass) were then fabricated. The micro-structures and compositions of the catalytic membranes were investigated by a number of advanced characterisations. It was found that the MnO₂ nanocatalysts (10-20 nm) were distributed uniformly around the Al₂O₃ particles (500 nm) of the membrane basal material, and can provide a large amount of active sites for the peroxymonosulfate (PMS) activation which can be facilitated within the pores of the catalytic membrane. The catalytic degradation of 4-hydroxylbenzoic acid (HBA), which is induced by the sulfate radicals via PMS activation, was investigated in a cross-flow membrane unit. The degradation efficiency slightly increased with a higher MnO₂ loading. Moreover, even with the lowest loading of MnO₂ (1.67%), the effectiveness of HBA degradation was still prominent, shown by that a 98.9% HBA degradation was achieved at the permeated side within 30 min when the initial HBA concentration was 80 ppm. The stability and leaching tests revealed a good stability of the catalytic membrane even after the 6th run. Electron paramagnetic resonance (EPR) and quenching tests were used to investigate the mechanism of PMS activation and HBA degradation. Both sulfate radicals (SO₄^•-) and hydroxyl radicals (^•OH) were generated in the catalytic membrane process. Moreover, the contribution from non-radical process was also observed. This study provides a novel strategy for preparing a ceramic membrane with the function of catalytic degradation of organic pollutants, as well as outlining into future integration of separation and AOPs.

Degradation of dimethyl phthalate using persulfate activated by UV and ferrous ions: optimizing operational parameters mechanism and pathway

The present study aimed to model and optimize the dimethyl phthalate (DMP) degradation from aqueous solution using UV_C/ Na₂S₂O₈/Fe²⁺ system based on the response surface methodology (RSM). A high removal efficiency (97%) and TOC reduction (64.2%) were obtained under optimum conditions i.e. contact time = 90 min, SPS concentration = 0.601 mM/L, Fe²⁺ = 0.075 mM/L, pH = 11 and DMP concentration = 5 mg/L. Quenching experiments confirmed that sulfate radicals were predominant radical species for DMP degradation. The effect of CO₃ ^- on DMP degradation was more complicated than other aquatic background anions. The possible pathway for DMP decomposition was proposed according to HPLC and GC-MS analysis. The average oxidation state (AOS) and carbon oxidation state (COS) values as biodegradability indicators demonstrated that the UV_C/SPS/Fe²⁺ system can improve the bioavailability of DMP over the time. Finally, the performance of UV_C/SPS/Fe²⁺ system for DMP treatment in different aquatic solutions: tap water, surface runoff, treated and raw wastewater were found to be 95.7, 88.5, 80.5, and 56.4%, respectively. Graphical abstract.

Application of persulfate salts for enhancing UV disinfection in marine waters

Over the years, industrial activities that generate high salinity effluents have been intensifying; this has relevant potential for causing organic and microbiological pollution which damages both human and ocean health. The development of new regulations, such as ballast water convention, encourage the development of treatment systems that can be feasible for treating seawater effluents. Accordingly, an approach based on the UV activation of persulfate salts has been assessed. In this scenario, two different persulfate sources (S₂O₈^2- and HSO₅^-) were evaluated under UV-C irradiation for disinfection purposes. An optimization process was performed with low chemical doses (<1 mM). In order to extensively examine the applicability on seawater, different water matrices were tested as well as different microorganisms including both fecal and marine bacteria. An enhancement of UV-inactivation with the addition of persulfate salts was achieved in all cases, kinetic rate constant has been accelerated by up to 79% in seawater. It implies a UV-dose saving up to 45% to achieve 4-log reductions. Best efficiencies were obtained with [HSO₅^-] = 0.005 mM and [S₂O₈^2-] = 0.5 mM. Higher effectiveness was obtained with the use of HSO₅^- due to its low stability and interaction with chloride. Also, different responses were obtained according to the specific microorganisms by achieving faster disinfection in Gram-negative than in Gram-positive bacteria, the sensitivity observed was Vibrio spp. > E. coli > E. faecalis ≈ Marine Heterotrophic Bacteria. With an evaluation of regrowth after treatment, greater cell damage was detected with the addition of persulfate salts. The major ability of regrowth for marine bacteria encourages the use of a residual disinfectant after disinfection processes.

Photo-assisted catalytic degradation of acetaminophen using peroxymonosulfate decomposed by magnetic carbon heterojunction catalyst

Catalytic oxidative degradation of acetaminophen (ACT) was evaluated using magnetic mesoporous carbon (MNPs@C) coupled with UV light and peroxymonosulfate (PMS). The performance of hybrid system (i.e., MNPs@C/UV/PMS) was assessed as a function of some operational factors (e.g., reaction time and different concentrations of catalyst, PMS and ACT) in a batch system. MNPs@C represented a high magnetic response and was easily recovered from aqueous solution via an external magnet. A significant synergistic effect was observed among the applied techniques in MNPs@C/UV/PMS system for ACT degradation. After 40 min reaction, the removal efficiencies of 97.4 and 63.5% were obtained for ACT and TOC, respectively. Both adsorption and oxidation mechanisms were responsible simultaneously for ACT removal in MNPs@C/UV/PMS system. Under optimum conditions, the removal rates of ACT and TOC were reduced slightly to 91.7 and 49.4% after five consecutive catalyst uses, which indicates the excellent reusing potential of MNPs@C. In addition, a high stability was detected for as-prepared catalyst during recycling tests, since the quantity of leached Fe was <0.2 mg/L. Methanol and tert-butyl alcohol showed a strong quenching effect on the performance of MNPs@C/UV/PMS system, demonstrating the dominant role of SO₄^•- and HO radicals in ACT degradation process. MNPs@C in comparison with ferrous ions, as a homogeneous catalyst, showed a better performance in the activation of PMS and ACT degradation. Integration of MNPs@C, UV and PMS exhibited an excellent performance into ACT removal over 40 min reaction, which can be utilized as an effective and promising technique for the efficient decontamination of polluted waters.

Surface treatment by the Fe(III)/sulfite system for flotation separation of hazardous chlorinated plastics from the mixed waste plastics

A novel advanced oxidation process by a combination of Fe(III) and sulfite for surface treatment of waste plastic mixtures is proposed. The Fe(III)/sulfite system has been found to enhance hydrophilicity of the mixed waste plastics, including acrylonitrile butadiene styrene (ABS), polystyrene (PS) and polycarbonate (PC), while it has little effect on hazardous polyvinyl chloride (PVC), thus promoting separation of PVC from the mixed waste plastics by flotation. Radical scavenging experiments indicate that sulfate radicals are the main reactive species. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) results imply the formation of CO or CO groups on the treated plastics surface except for PVC and a plausible mechanism for oxidizing plastics with sulfate radicals is proposed. PVC with 100.00% recovery and 99.84% purity is achieved under optimum surface treatment conditions of sodium sulfite concentration 10 mM, ferric sulfate concentration 0.4 mM, pH 6.0, temperature 25 °C and treatment time 15 min. Consequently, surface treatment by the Fe(III)/sulfite system is an effective technology for separating hazardous PVC from the mixed waste plastics by flotation.

An often-overestimated adverse effect of halides in heat/persulfate-based degradation of wastewater contaminants

Halides (X^-) in the industrial wastewater are usually thought to adversely affect the degradation kinetics and mineralization rates in several SO₄^--based advanced oxidation processes. However, their unfavorable effects might be overestimated, particularly the heat/persulfate (PS) system as tested in the present study. Here the degradation of phenol, benzoic acid, coumarin and acid orange 7 (AO7) was examined with the presence of chloride or bromide in a heat/PS process. Cl^- was found to have a dual effect (inhibition followed by enhancement) on the decomposition rates of organic pollutants, whereas the effects of Br^- are insignificant within the tested concentration (0-0.2 mM). However, some chlorinated or brominated compounds were still identified in this heat/PS system. Unexpectedly, the mineralization rates of AO7, phenol, benzoic acid and coumarin were not apparently inhibited. In addition, the formation of adsorbable organic halogen (AOX) in the heat/PS system was much less than those in the peroxymonosulfate (PMS)/Cl^- or PMS/Br^- systems. According to the results of kinetic modeling, SO₄^- was the dominating radical for AO7 degradation without Cl^- or Br^-, but Cl₂^- was the main oxidant in the presence of Cl^-, SO₄^-, Br and Br₂- were responsible for the oxidation of AO7 in the presence of Br^-. The present study assumes that X₂/HOX, rather than halogen radicals, is responsible for the enhanced formation of organohalogens. These findings are meaningful to evaluate the PS-based technologies for the high-salinity wastewater and to develop useful strategies for mitigating the negative effects of halides in advanced oxidation processes (AOPs).

Sulfate radicals mediated oxidation of amoxicillin: Optimization of key parameters

The lack of selectivity of hydroxyl radical species used in Advanced Oxidation Processes (AOPs) to eliminate organic pollutants has swayed the investigation towards more selective oxidizing agents. In the current work, we investigated the oxidation of amoxicillin, the most commonly used antibiotic worldwide, by sulfate radical species generated from the activation of Persulfate (PS) and Peroxymonosulfate (PMS-Oxone^®). The optimization of this oxidation using the box-behnken experimental design was conducted. From this study, it was shown that the PS/Fe²⁺ mixture was capable of dose-dependently inducing a significant amount of degradation of the Amoxicillin compound with a higher degradation rate detected with higher amounts of PS and Fe²⁺. Sulfate radicals generated from the "Oxidant-Catalyst" mixture were shown to be the predominant oxidizing species involved in this process with the second order rate constant of Amoxicillin degradation found to be equal to 2.79 × 10⁹ M^-1. S^-1. In the optimization procedure, the box-benhken methodology allowed us to assess the impact of various factors and their interaction on COD removal efficiency (mineralization rate), which is the objective response needed to be optimized. The variables considered were PS as the oxidant, Fe²⁺ as the catalyst, and pH. It was concluded that among the various parameters tested, pH was the most influential as a decrease in pH values was shown to be positively correlated with a significant increase in COD removal rate. Hence, the highest mineralization rate of Amoxicillin (≈76.10% COD removal) was achieved with PS = 300 μM, Fe²⁺ = 250 μM, and a pH value of 3.

Magnetic cobalt-embedded carbon nitride composite derived from one-dimensional coordination polymer as an efficient catalyst for activating oxone to degrade methyltheobromine in water

As methyltheobromine (MTB) has been increasingly detected in wastewater, it would be necessary to develop more intensive and effective approaches to remove MTB. As Co species immobilized on carbonaceous materials appears as a promising catalyst, doping carbon with nitrogen has been also validated to significantly enhance catalytic activities for Oxone activation. Therefore, it is desired to develop a composite of immobilizing Co species on N-doped carbonaceous supports for activating Oxone to degrade MTB. Unfortunately, very few studies have demonstrated such composites for activating Oxone to degrade MTB as this type of composites are conventionally prepared via complex procedures. Alternatively, this study aims to develop such a composite conveniently by using a cobaltic coordination polymer (CP) as a precursor. Specifically Co²⁺ and 4,4-bipyridine (BIPY) are selected for formulating a special one-dimensional CP, which is then carbonized to convert Co to Co nanoparticles (NPs) and transform BIPY to carbon nitride (CN) matrices. Because of 1-D coordinated structure of CoBIPY, the resulting magnetic Co NPs are well-distributed and protected within CN to form a magnetic Co-embedded carbon nitride composite (MCoCN). In comparison to pristine CN and Co₃O_4, MCoCN exhibits much higher catalytic activities to activate Oxone for degrading MTB completely within 7 min. MCoCN also shows a much lower activation energy of 24.6 kJ/mol than other reported catalysts for activating Oxone to degrade MTB. The findings of this study validate that the 1-D coordination polymer of CoBIPY is a useful precursor to prepare MCoCN for effectively activating Oxone to degrade MTB.