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The key role of trivalent manganese (Mn(III)) species in promoting sulfate radical-based advanced oxidation processes (SR-AOPs) has recently attracted increasing attention. This review provides a comprehensive summary of Mn(III) (oxyhydr)oxide-based catalysts used to activate peroxymonosulfate (PMS) and peroxydisulfate (PDS) in water. The crystal structures of different Mn(III) (oxyhydr)oxides (such as α-Mn2O3, γ-MnOOH, and Mn3O4) are first introduced. Then the impact of the catalyst structure and composition on the activation mechanisms are discussed, as well as the effects of solution pH and inorganic ions. In the Mn(III) (oxyhydr)oxide activated SR-AOPs systems, the activation mechanisms of PMS and PDS are different. For example, both radical (such as sulfate and hydroxyl radical) and non-radical (singlet oxygen) were generated by Mn(III) (oxyhydr)oxide activated PMS. In comparison, the activation of PDS by α-Mn2O3 and γ-MnOOH preferred to form the singlet oxygen and catalyst surface activated complex to remove the organic pollutants. Finally, research gaps are discussed to suggest future directions in context of applying radical-based advanced oxidation in wastewater treatment processes. [ABSTRACT FROM AUTHOR]

In the present work we investigate the activation efficiency of H 2 O 2 and S 2 O 8 2− using UVA and UVB radiation. Bisphenol-A (BPA) is used as model pollutants to estimate the oxidative process efficiency in simulated and real sewage treatment plant waters. Particular attention is paid to the BPA removal efficiency and to the radical mechanism involvement considering the effect of typical inorganic water constituents (carbonates and chloride ions) and organic matter. Despite a detrimental effect observed when carbonate ions are in solution using both hydrogen peroxide and persulafate, the presence of high chloride ions concentration was found to improve BPA removal using S 2 O 8 2− as radical precursor. This enhancement, investigated combining chemical kinetic model approach and laser flash photolysis experiments, is attributed to the formation of hydroxyl radical and chlorine radical species from sulfate radical. Different transformation products are identified by means of GC–MS and HPLC-MS analyses. Moreover, experiments using sewage treatment plant water (STPW) spiked with BPA are performed in order to assess the efficiency of oxidative processes in a simulated treatment systems activated using UVA + UVB radiations. [ABSTRACT FROM AUTHOR]

• The effect of HA coating on MPs was studied in photo-Fenton-like process. • Humic acid coating enhances the H 2 O 2 and S 2 O 8 2− activation for BPA degradation. • Reactive species were identified (OH and SO 4 –) through scavenging experiments. • The recycling and reuse of MP/HA show no loss of activity. • The efficiency of MP/HA was tested in real wastewater sample. Magnetic particles (MPs) coated with humic acid (HA) prepared under anoxic atmosphere were tested as heterogeneous photo-Fenton catalyst for the activation of hydrogen peroxide (H 2 O 2) and persulfate (S 2 O 8 2−) using Bisphenol A (BPA) as a model pollutant. The role of HA coating, pH value and H 2 O 2 /S 2 O 8 2− concentration were investigated. A positive contribution of HA coating on H 2 O 2 and S 2 O 8 2− activation was found. The highest BPA degradation rates were achieved at acidic conditions (pH 3) with both H 2 O 2 and S 2 O 8 2−, however persulfate showed a significant efficiency even at pH 6, interesting feature in the light of decreasing the wastewater treatment costs. By the addition of selective quenching agents, OH and SO 4 – were identified as the main reactive species involved in the BPA abatement. An important contribution of the S 2 O 8 2− photolysis on the overall BPA transformation was highlighted. The reuse of the catalyst was investigated and similar efficiency using H 2 O 2 and S 2 O 8 2− activation was observed until the third catalytic cycle. Experiments carried out using real wastewater samples, showed a good, even if less efficient compared to pure water, BPA removal. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • SO 5 − plays a significant role in aniline oxidation in the Fe(III)-S(IV) system. • SO 5 − oxidizes aniline through direct and indirect pathways. • Aniline oxidation can be effectively enhanced via sequential S(IV) replenishing. • S(IV) replenishing accelerates both the oxysulfur radicals cycle and Fe(III)/Fe(II) cycle. Abstract In this paper, the efficiency of Fe(III)-S(IV) system used for advanced oxidation processes (AOPs) has been investigated using aniline as a pollutant model compound in water. The chemical kinetics, influencing factors, and mechanism of aniline oxidation are examined with an emphasis on the contribution of the different oxysulfur radicals (mainly SO 4 − and SO 5 −). Our results show a significant enhancement in the efficiency of aniline oxidation observed at pH 4.0 with 1.0 mM S(IV) and 0.1 mM Fe(III) concentrations. Moreover, the degradation efficiency drastically decreases to 10% in the absence of oxygen indicating the significant role of oxygen in this type of process. Through competition kinetic experiments and radical scavenger experiments, it is shown that SO 5 − is responsible for about 60% of the aniline oxidation in the Fe(III)-S(IV) system under the typical conditions investigated in this work. For the first time we have determined the second order rate constant between SO 5 − and aniline (5.8 ± 0.6 × 106 M−1 s−1 (at pH 3.0) and SO 4 − and aniline 7.7 ± 0.5 × 109 M−1 s−1 (at pH 3.0)). Sequential experiments with successive additions of sulfite drastically improve the oxidation efficiency. These findings may provide a precise understanding of the overall mechanism and may have promising implications in developing a new cost-effective technology for the treatment of organic compounds-containing water. Furthermore, the results of this work help to understand the relevance and mechanism of organic contaminants oxidation by SO 5 −, which has not been given much attention in conventional SR-AOPs using peroxymonosulfate. [ABSTRACT FROM AUTHOR]

The crucial role of manganese(III) species in the oxidative and catalytic reactivity of manganese oxides have been widely reported. However, the direct activation of radical precursors by Mn(III) oxides is still a matter of discussion. In this work, the ability of Mn(III)-bearing oxide (Mn 2 O 3) for activation of peroxydisulfate (PS) and peroxymonosulfate (PMS) was evaluated and compared using caffeine (CAF) as a model pollutant. Complete CAF removal was achieved with 5 mM of PS or PMS after 8 h of reaction time, whereas 48% of mineralization was obtained after 70 h of reaction when PMS was used as oxidant. Electron paramagnetic resonance spin trapping (EPR) and radical scavenging experiments showed that the sulfate radical (SO 4 •–) was the dominant radical in the Mn 2 O 3 /PMS system. In comparison, a non-radical mechanism such as Mn 2 O 3 surface-activated PS promoted the removal of CAF in the system of Mn 2 O 3 /PS. Liquid chromatography coupled to mass spectrometry analyses enabled the detection of main degradation products and the proposition of the CAF degradation pathways. Investigations in the real sewage treatment plant water showed that the decrease of CAF removal observed in wastewater as compared to pure water can be alleviated by increasing the Mn 2 O 3 dosage. These findings highlight the great ability of Mn-species in PS or PMS activation in different water matrices, which have important implications for the development of novel wastewater treatment technologies. [Display omitted] • Mn 2 O 3 with PS and PMS systems are able to degrade and mineralize caffeine in water. • The CAF degradation mechanism via radical and non-radical pathways is elucidated. • Mn 2 O 3 /PMS system is found to be more efficient for caffeine degradation in STPW. • Mn(III)-based AOPs can be considered as promising and efficient water treatments. [ABSTRACT FROM AUTHOR]

In the present work, the degradation of three estrogens (17β-estradiol (E2), estrone (E1) and 17α-ethinylestradiol (EE2)) was investigated under photoactivation of hydrogen peroxide and persulfate. Lab-scale irradiation experiments showed that both UVA and UVB radiations are able to photoactivate the oxidant precursors, although UVB is more efficient to generate radicals and therefore to degrade the targets. The efficiency of both oxidant precursors was investigated showing higher efficiency in the system with persulfate. The pseudo-first order degradation rate constants and the second order rate constants between the hydroxyl or the sulfate radicals and estrogens were measured. In order to evaluate the process efficiency in real treatment conditions, the degradation of the estrogens spiked into sewage treatment plant effluent was studied. Measurements of second order rate constants between the radical and the effluent organic matter by laser flash photolysis allowed to understand the involved quenching mechanisms. A Yeast Estrogen Screen (YES) assay was used to follow the decrease in estrogenic activity during the estrogen degradation. This assay permitted to ensure that the studied processes are not only able to degrade the estrogens but also to remove their estrogenic activity. ga1 • H 2 O 2 and S 2 O 8 2- are activated by UVA and UVB radiations generating highly reactive radicals. • Wastewater effluent composition inhibits E1, E2 and EE2 photo-induced degradation. • Species containing organic carbon are the main radical quenchers in wastewater effluent. • Estrogenic activity decline was shown to follow E1, E2 and EE2 concentration decrease. [ABSTRACT FROM AUTHOR]