Involvements of chloride ion in decolorization of Acid Orange 7 by activated peroxydisulfate or peroxymonosulfate oxidation

Freezing-enhanced degradation of azo dyes in the chloride-peroxymonosulfate system

In this study, we investigated the freezing-induced acceleration of dye bleaching by chloride-activated peroxymonosulfate (PMS). It has been observed that the oxidation of chloride by PMS generates a free chlorine species, such as hypochlorous acid (HOCl), under mild acidic and circumneutral pH condition. This process is the major reason for the enhanced oxidation capacity for electron-rich organic compounds (e.g., phenol) in the chloride-PMS system. However, we demonstrated that the chloride-PMS system clearly reduced the total organic carbon concentration (TOC), whereas the HOCl system did not lead to decrease in TOC. Overall, the chemical reaction is negligible in an aqueous condition if the concentrations of reagents are low, and freezing the solution accelerates the degradation of dye pollutants remarkably. Most notably, the pseudo-first order kinetic rate constant for acid orange 7 (AO7) degradation is approximately 0.252 h-1 with 0.5 mM PMS, 1 mM NaCl, initial pH 3, and a freezing temperature of -20 °C. AO7 degradation is not observed when the solution is not frozen. According to a confocal Raman-microscope analysis and an experiment that used an extremely high dose of reactants, the freeze concentration effect is the main reason for the acceleration phenomenon. Because the freezing phenomenon is spontaneous at high latitudes and at mid-latitudes in winter, and the chloride is ubiquitous elsewhere, the frozen chloride-PMS system has potential as a method for energy-free and eco-friendly technology for the degradation of organic pollutants in cold environments.

Co-Mn spinel oxides trigger peracetic acid activation for ultrafast degradation of sulfonamide antibiotics: Unveiling critical role of Mn species in boosting Co activity

Activation of peracetic acid (PAA) to generate powerful oxidizing species has become a promising advanced oxidation processes (AOPs) in wastewater treatment, yet the development of low-cost and high-performance activators is still a primary challenge. Herein, a range of Co-Mn spinel oxides (Co_3-xMn_xO₄) with varying levels of Co and Mn were successfully elaborated, in which Co_1.1Mn_1.9O₄ exhibited remarkable performance in PAA activation, outperforming most reported heterogeneous catalysts. Extensive quenching experiments and electron spin resonance (ESR) analysis indicated that acetylperoxyl radical (CH₃C(O)OO^●) was the predominated oxidizing species responsible for sulfamethoxazole (SMX) degradation. Density functional theory (DFT) calculations revealed that doping with Mn not only promoted the electron transfer and accelerated reduction of Co(III) to Co(II), but also lowered the energy barrier for PAA activation. Moreover, the prominent chemisorption and activation of PAA with Co_1.1Mn_1.9O₄ was also benefitted from the significant role of Mn in optimizing the distribution of bonding and antibonding states on Co 3d orbitals. Unexpectedly, high levels of Cl^-greatly facilitated SMX degradation due to the mass production of HOCl from the chain reactions of various radicals with Cl^-. This work provides new insights into bimetallic activation of PAA, and the knowledge obtained will further advance the application of PAA-based AOPs.

Dye mineralization under UV/H2O2 promoted by chloride ion at high concentration and the generation of chlorinated byproducts

Chloride ion (Cl^-) may promote or inhibit the oxidation of specific organic compounds treated by hydroxyl radical based advanced oxidation processes (HR-AOPs) depending on the reactivity of chlorine radicals towards the organics. However, the effects of high contents of Cl^- on the removal of total organic compounds (TOC) in high salinity organic wastewater treated by HR-AOPs were unclear. The removal and mineralization of azo dye Orange II (OrgII) by UV/H₂O₂ process with Cl^- at high contents under various pH conditions were investigated. As the pH conditions increased higher than pH 5, TOC removal rates increased slightly possibly related to the increase of O₂^- production and the reduce of futile decomposition of H₂O₂ into O₂. Cl^- at relative high concentration (1000 and 2000 mM) significantly promoted the mineralization of dyes with TOC removal increasing by 10 %-40 % under both acid and alkaline conditions. The proposed mechanism is that the reaction of Cl^- with OH would decline the decomposition of H₂O₂ into O₂ by inhibiting the reaction between OH and H₂O₂, and the generated chlorine species (Cl and Cl₂^-) could further promote the oxidation of dye molecules into intermediates and be helpful for the subsequent mineralization process. In addition, H₂O₂ and Cl^- can slowly react to give HClO and ClO^-, which may partly contribute to the decolorization and mineralization of OrgII. Meanwhile, an appropriate relative proportion between Cl₂^- and OH depending on Cl^- contents and pH conditions is important to enhance the TOC removal. However, the formation of various chlorinated byproducts especially under alkaline condition may increase the risk of environmental pollution accidents. The results demonstrate the promotion of TOC removal by UV/H₂O₂ under certain high contents of Cl^- and provide new insight into the application of HR-AOPs to the pretreatment of high salinity organic wastewater.

The efficient degradation of diclofenac by ferrate and peroxymonosulfate: performances, mechanisms, and toxicity assessment

In this study, the degradation efficiency and reaction mechanisms of diclofenac (DCF), a nonsteroidal anti-inflammatory drug, by the combination of ferrate (Fe(VI) and peroxymonosulfate (PMS) (Fe(VI)/PMS) were systematically investigated. The higher degradation efficiency of DCF in Fe(VI)/PMS system can be obtained than that in alone persulfate (PS), Fe(VI), PMS, or the Fe(VI)/PS process at pH 6.0. DCF was efficiently removed in Fe(VI)/PMS process within a wide range of pH values from 4.0 to 8.0, with higher degradation efficiency in acidic conditions. The increasing reaction temperature (10 to 30 ℃), Fe(VI) dose (6.25 to 100 µM), or PMS concentration (50 to 1000 µM) significantly enhanced the DCF degradation. The existences of HCO₃¯, Cl¯, and humic acid (HA) obviously inhibited the DCF removal. Electron paramagnetic resonance (EPR), free radical quenching, and probing experiments confirmed the existence of sulfate radicals (SO₄^•¯), hydroxyl radicals (^•OH), and Fe(V)/ Fe(IV), which are responsible for DCF degradation in Fe(VI)/PMS system. The variations of TOC removal ratio reveal that the adsorption of organics with ferric particles, formed in the reduction of Fe(VI), also were functioned in the removal process. Sixteen DCF transformation byproducts were identified by UPLC-QTOF/MS, and the toxicity variation was evaluated. Consequently, eight reaction pathways for DCF degradation were proposed. This study provides theoretical basis for the utilization of Fe(VI)/PMS process.

Non-radical dominated degradation of bisphenol S by peroxymonosulfate activation under high salinity condition: Overlooked HOCl, formation of intermediates, and toxicity assessment

Extensive studies revealed that Cl^- could inhibit the removal of targeted pollutants under low Cl^- conditions in the peroxymonosulfate (PMS) system. However, the enhanced effect of Cl^- has always been overlooked under high Cl^- conditions. Here, we find that high concentration of Cl^- played a critical role in bisphenol S (BPS) degradation by activating PMS using 16%-CoFe₂O₄@PAL (16%-CFO@PAL). The removal of BPS was sharply enhanced after introducing 0.5 and 1.0 M Cl^-, and the corresponding k_obs increased to 0.922 min^-1 and 1.103 min^-1, which was 6-fold and 7-fold higher than the control (0.144 min^-1), respectively. HOCl was demonstrated as the dominant species for removing BPS in 16%-CFO@PAL/PMS system under high Cl^- circumstances. The typical chlorinated BPS intermediates were identified, which showed higher eco-toxicity than BPS. The chlorinated byproducts along with their toxicity could be effectively eliminated after 30 min. The possible formation mechanism of chlorinated products was further revealed by theoretical calculations. Toxicity assessment experiments showed that BPS significantly affected hormone levels of zebrafish and showed toxicity on the testis and liver of zebrafish, which could be reduced using 16%-CFO@PAL/PMS system. This study attracts attention to the overlooked HOCl in PMS-based processes under high salinity conditions.

Photo-oxidative Decolorization of Brilliant Blue with AgNPs as an Activator in the Presence of K2S2O8 and NaBH4

The decolorization of brilliant blue (E133) in aqueous solution by K2S2O8 and NaBH4 with AgNPs as an activator was studied spectrophotometrically under normal laboratory conditions. Batch experiments were performed to investigate the effects of reaction time, initial dye concentration, activator concentration, solution pH, and temperature on the decolorization of E133. K2S2O8 and NaBH4 did not decolorize the dye E133 in the absence of AgNPs. The optimum dosage of AgNPs was 0.01 g/L, and 98% dye E133 degradation was observed with 3.75 mM K2S2O8 at 30 °C in ca. 60 min of reaction time. In the NaBH4/AgNPs system, only 60% dye degradation was observed for an identical reaction condition. The decolorization rate constant increases with the increase in concentrations of AgNPs, K2S2O8, NaBH4, and reaction temperature. The decolorization degree of the E133 responded linearly with K2S2O8 and NaBH4 concentrations. The existence of sulfate radicals (SO4 · -) and hydroxyl radicals (HO·) generated during the decolorization of E133 was identified by using ethanol and tertiary butyl alcohol as scavengers. Based on the E133 solution absorbance changes at 628 nm, the decolorization mechanism was proposed and discussed.

Development of polystyrene coated persulfate slow-release beads for the oxidation of targeted PAHs: Effects of sulfate and chloride ions

In this study, we synthesized polystyrene coated persulfate polyacrylonitrile beads (PC-PSPANBs) to control persulfate (PS) release for targeted PAHs' degradation in a batch reactor. Initially, the persulfate release rate (k_sr = 20.553 h^-1) from PSPANBs was fast, but coating the PSPANBs with polystyrene controlled PS release rate (k_sr= 2.841 h^-1), nearly ten times slower than without coating. When Fe(II) activated PC-PSPANBs applied for 12 h degradation of acenaphthene (ACE), 2-methlynaphthalene (2-MN) and dibenzofuran (DBF), the optimum percent removal efficiencies (% R.Es) were as ACE (82.12%) > DBF (68.57%) > 2-MN (58.80%) and the optimum degradation rate constants (k_obs) were found as ACE (11.348 h^-1) > 2-MN (3.441 h^-1) > DBF (1.101 h^-1). The effect of SO₄^2- and Cl^- on ACE degradation showed that % R.E and k_obs were enhanced with increasing anionic concentrations. The maximum % R.E was achieved for SO₄^2- (76.24%) > Cl^- (65.51%), but the highest k_obs was in case of Cl^- (1.536 h^-1) > SO₄^2- (0.510 h^-1). The effectiveness of PS release longevity was also found because net degradations of ACE and DBF after first spiking were 12 mg L^-1 and 16 mg L^-1, while after second spiking were 18 mg L^-1 and 10 mg L^-1, respectively.

Performance of UV/acetylacetone process for saline dye wastewater treatment: Kinetics and mechanism

Futility of traditional advanced oxidation processes (AOPs) in saline wastewater treatment has stimulated the quest for novel "halotolerant" chemical oxidation technology. Acetylacetone (AA) has proven to be a potent photo-activator in the degradation of dyes, but the applicability of UV/AA for saline wastewater treatment needs to be verified. In this study, degradation of crystal violet (CV) was investigated in the UV/AA system in the presence of various concentrations of exogenic Cl^- or Br^-. The results reveal that degradation, mineralization and even accumulation of adsorbable organic halides (AOX) were not significantly affected by the addition of Cl^- or Br^-. Rates of CV degradation were enhanced by elevating either AA dosage or solution acidity. An apparent kinetic rate equation was developed as r = -d[CV]/dt = k[CV]^a[AA]^b = (7.34 × 10^-4 mM^1-(a+b) min^-1) × [CV]^a=0.16 [AA]^b=0.97. In terms of results of radical quenching experiments, direct electron/energy transfer is considered as the major reaction mechanism, while either singlet oxygen or triplet state (³(AA)*) might be involved. Based on identification of degradation byproducts, a possible degradation pathway of CV in the UV/AA system is proposed.

UV/ peroxymonosulfate process for degradation of chloral hydrate: Pathway and the role of radicals

In this study, kinetics, influencing factors and potential mechanisms involved in the degradation of chloral hydrate (CH) by UV/peroxymonosulfate (PMS) process were demonstrated. The degradation rate of CH could reach 89.6% by UV₂₅₄/PMS process, significantly exceeding UV₃₀₀/PMS (0.7%), UV₃₅₀/PMS (6.3%), UV₂₅₄ direct photolysis (9.0%) and PMS alone (0.0%) processes. CH degradation in UV₂₅₄/PMS system followed pseudo first-order degradation kinetics with an apparent rate constant of 0.186 min^-1, which was suppressed by Cl^- and HCO₃^-. The optimal pH for CH degradation was around 5.0. Direct mineralization accounted for the CH degradation in UV/PMS system. Interestingly, the addition of PMS at the neutral condition before UV irradiation transferred CH into trichloroacetic acid (TCAA). The transformation efficiency of CH into TCAA at 10 min was enhanced from 2.17%-40.38% with the elevation of initial pH from 7.0-8.0. The subsequent exposure of UV lamps ceased the transformation of CH into TCAA and facilitated the direct mineralization of CH, but it did not work in the refractory TCAA degradation. Finally, it was revealed that HO predominantly participated CH degradation in UV/PMS process, while O₂^- was responsible for the transformation of CH into TCAA by addition of PMS before UV irradiation.

Oxidation of 2,4-dichlorophenol in saline water by unactivated peroxymonosulfate: Mechanism, kinetics and implication for in situ chemical oxidation

Inorganic and organic pollutants present a hazard to surface and groundwater resources. Peroxymonosulfate (PMS, HSO₅^-) has received increasing attention for in situ chemical oxidation (ISCO) capable of remediating contaminated sites. Considering that saline waters occur widely in natural environments, it is desirable to evaluate the effect of Cl^- on the PMS oxidation of organic compounds. In this study, 2,4-dichlorophenol (2,4-DCP) was used as a model pollutant. At a PMS concentration of 2.0 mM, Cl^- concentration of 50 mM, and solution pH of 7.0, 2,4-DCP was completely degraded by PMS in the presence of Cl^- (PMS/Cl^- system), while PMS alone exhibited almost no reactivity with 2,4-DCP. The degradation of 2,4-DCP was optimized at a solution pH of 8.4 and high concentrations of PMS and Cl^-. Quenching experiments and degradation pathway analyses indicated that HClO was responsible for 2,4-DCP oxidation, and HClO was mainly generated by the interaction of Cl^- with HSO₅^-, rather than SO₅^2-. Consequently, the transformation from HSO₅^- to HClO appeared under a solution pH of 10.0 and was favored in an acidic solution. Given the ambient pH and Cl^- concentrations of saline waters, a considerable amount of HClO may be produced by the interaction of PMS with Cl^- in the oxidant delivery stage of ISCO processes. Interestingly, H₂O₂ and peroxydisulfate did not exhibit reactions similar to those of PMS. This research indicated that caution must be exercised when choosing an oxidant for ISCO processes in saline waters.

CuCo2O4 supported on activated carbon as a novel heterogeneous catalyst with enhanced peroxymonosulfate activity for efficient removal of organic pollutants

CuCo₂O₄ was synthesized via a relatively simple method, and innovatively supported onto the activated carbon (AC) by calcination to obtain a novel heterogeneous catalyst (AC-CuCo₂O₄). Brilliant red 3BF (3BF) was selected as the probe compound to investigate the catalytic activity of AC-CuCo₂O₄ in the presence of peroxymonosulfate (PMS). The results showed that 98% removal rate could be achieved and the reaction rate constant (0.476 min^-1) was 5.2 times greater than that of CuCo₂O₄ alone (0.091min^-1), suggesting that the introduction of AC could greatly enhance the catalytic activity of pure CuCo₂O₄. Typically, the 3BF removal was as high as 96% after five cycles, showing the good stability of catalyst reuse. Additionally, the effects of the initial pH, catalyst dosage, PMS concentration and reaction temperature on the 3BF removal were investigated, demonstrating that AC-CuCo₂O₄ effectively remove 3BF over a wide pH range (5.0-10.0) and possessed temperature-tolerant performance. To further explore the 3BF removal mechanism, electron paramagnetic resonance technology combining with trapping agents was employed to confirm the involvement of reactive oxygen species including SO₄^•-, ^•OH, O₂^•- and ¹O₂, which distinctly differed from the reported CuCo₂O₄ for PMS activation. These findings provided an addition promising strategy in environmental remediation.

Highly efficient removal of organic pollutants via a green catalytic oxidation system based on sodium metaborate and peroxymonosulfate

The development of highly efficient and green catalytic oxidation process based on peroxymonosulfate (PMS) activation has been identified to be a significant yet challenging objective in the environmental catalysis field. A simple, environmentally benign and highly effective catalytic oxidation system was innovatively constructed by coupling NaBO₂ and PMS for the removal of Acid Red 1. The catalytic mechanism in the NaBO₂/PMS system was elucidated by electron paramagnetic resonance (EPR) combined with several radical capture reagents (ascorbic acid, methanol, tert-butyl alcohol, ethanol and _l-histidine). The experimental results indicated that singlet oxygen (¹O₂) severed as the predominant reactive oxygen species (ROS) rather than the HO or during the catalytic oxidation process, at variance with the reported radical pathway in the Co²⁺/PMS system. Inspiringly, p-benzoquinone (p-BQ) as a trapping agent in most advanced oxidation process could be turned into the positive one in the NaBO₂/PMS system, achieving a nearly 3-times enhancement in terms of the rate constant for AR1 removal. More interestingly, sodium chloride (NaCl) presented the same enhancement effect as p-benzoquinone due to generation of hypochlorous acid (HOCl) and more ¹O₂, which was completely different from the reported. This study develops a highly efficient green oxidation process and opens up a new insight in the remediation of contaminated water.

Catalytic degradation of organic pollutants in Fe(III)/peroxymonosulfate (PMS) system: performance, influencing factors, and pathway

This study demonstrated, for the first time, Fe(III)/peroximonosulphate (PMS) could be an efficient advanced oxidation process (AOP) for wastewater treatment. Bisphenol A (BPA) was chosen as a model pollutant in the present study. Fe(III)-activated PMS system proved very effective to eliminate 92.18% of BPA (20 mg/L) for 30-min reaction time at 0.50 mM PMS, 1.5 g/L Fe(III), pH 7.0. The maximum degradation of BPA occurred at neutral pH, while it was suppressed at both strongly acidic and alkaline conditions. Organic and inorganic ions can interfere with system efficiency either positively or negatively, so their interaction was thoroughly investigated. Furthermore, the presence of organic acids also affected BPA degradation rate, especially the addition of 10 mM citric acid decreased the degradation rate from 92.18 to 66.08%. Radical scavenging experiments showed that SO₄^•- was the dominant reactive species in Fe(III)/PMS system. A total of 5 BPA intermediates were found by using LC/MS. A possible degradation pathway was proposed which underwent through bridge cleavage and hydroxylation processes. Acute toxicity of the BPA degradation products was assessed using Escherichia coli growth inhibition test. These findings proved to be promising and economical to deal with wastewater using iron mineral for the elimination of organic pollutants. Graphical abstract.

Chlorine incorporation into dye degradation by-product (coumarin) in UV/peroxymonosulfate process: A negative case of end-of-pipe treatment

Recently, UV/peroxymonosulfate (PMS) seems as a panacea for the treatment of recalcitrant organic pollutants; however, the presence of high concentration of chloride in saline wastewater indeed complicates this end-of-pipe technology. Here a negative case of UV/PMS for the treatment of one of secondary degradation byproducts of dyes (coumarin, COU) is demonstrated. The removal rate of COU is reduced by addition of Cl^- (0-10 mM). Further increase in Cl^- content favors a rapid COU degradation, whereas Cl^- involvement seems to open a "Pandora's box": 1) a variety of chlorinated organic intermediates such as 4-chloroisocoumarin and 5-chloro-2-hydroxy-benzaldehyde are identified; 2) Accumulation and relative increase of absorbable organic halogen (AOX) with reaction time in the presence of high levels of chloride are observed; 3) the acute toxicity of the treated COU solution increases; 4) mineralization rate of COU decreases with the increasing [Cl^-]. The fluorescence intensity in the UV/PMS/COU system declines with the addition of Cl^-, implying the scavenging effects of chloride on hydroxyl radicals. The possible reaction pathways of COU are discussed. These findings highlight the imperativeness of minimizing auxiliary salt dosages in dyeing processes (i.e., source reduction) and developing new end-of-pipe technologies that can work in a saline environment.

A comprehensive performance evaluation of heterogeneous Bi2Fe4O9/peroxymonosulfate system for sulfamethoxazole degradation

In this study, a Bi₂Fe₄O₉ catalyst with nanoplate morphology was fabricated using a facile hydrothermal method. It was used as a catalyst to activate peroxymonosulfate (PMS) for aqueous sulfamethoxazole (SMX) removal. A comprehensive performance evaluation of the Bi₂Fe₄O₉/PMS system was conducted by investigating the effects of pH, PMS dosage, catalyst loading, SMX concentration, temperature, and halides (Cl^- and Br^-) on the degradation of SMX. The Bi₂Fe₄O₉/PMS system demonstrated a remarkable catalytic activity with >95% SMX removal within 30 min (conditions: pH 3.8, [Bi₂Fe₄O₉] = 0.1 g L^-1, [SMX]:[PMS] mol ratio =1:20). It was found that both Cl^- and Br^- can lead to the formation of PMS-induced reactive halide species (i.e. HClO, HBrO, and Br₂) which can also react with SMX forming halogenated SMX byproducts. Based on the detected degradation byproducts, the major SMX degradation pathway in the Bi₂Fe₄O₉/PMS system is proposed. The SMX degradation by Bi₂Fe₄O₉/PMS system in the wastewater secondary effluent (SE) was also investigated. The results showed that SMX degradation rate in the SE was relatively slower than in the deionized water due to (i) reactive radical scavenging by water matrix species found in SE (e.g.: dissolved organic matters (DOCs), etc.), and (ii) partial deactivation of the catalyst by DOCs. Nevertheless, the selectivity of the SO₄^•- towards SMX degradation was evidenced from the rapid SMX degradation despite the high background DOCs in the SE. At least four times the dosage of PMS is required for SMX degradation in the SE to achieve a similar SMX removal efficiency to that of the deionized water matrix.

Degradation of the Nonsteroidal Anti-Inflammatory Drug Piroxicam by Iron Activated Persulfate: The Role of Water Matrix and Ultrasound Synergy

This work examined the oxidation of Piroxicam (PIR), a representative nonsteroidal anti-inflammatory drug using iron activated persulfate. The effect of persulfate dosing was vital for the efficiency of the process. The addition of 20 mg/L sodium persulfate (SPS) eliminated 500 μg/L of PIR in less than 20 min at natural pH. PIR decomposition followed pseudo-first-order kinetics, and the observed kinetic constant increased by 2.1 times when the initial concentration of PIR decreased from 2000 to 250 μg/L. Acidic pH favored the PIR destruction, while both sulfate and hydroxyl radicals are involved in PIR destruction at natural pH. The effect of inorganic ions like bicarbonate and chlorides was almost insignificant on PIR removal. The presence of humic acid reduced PIR removal from 100% to 67% after 20 min of treatment with 2 mg/L Fe2+ and 20 mg/L SPS. The experiment that was performed with bottled water showed similar efficiency with ultrapure water, while in the case of secondary effluent, PIR removal decreased by 26% after 30 min of treatment. The Fe2+/SPS/ultrasound hybrid process showed a low degree of synergy (18.3%). The ecotoxicity of aqueous solution using the Vibrio fischeri as an indicator was reduced during the treatment, although with a different trend from the removal of PIR, possibly due to byproducts derived from the oxidation of secondary effluent and PIR.

Implementation of martite nanoparticles prepared through planetary ball milling as a heterogeneous activator of oxone for degradation of tetracycline antibiotic: Ultrasound and peroxy-enhancement

The aim of the present study was to employ martite nanoparticles synthesized through planetary ball milling instead of conventional sources of iron for the activation of Oxone in order to decompose tetracycline (TC) antibiotic in the aquatic phase. Accordingly, martite nanoparticles-activated Oxone exhibited a remarkable improvement in degrading TC molecules up to 87%. The results indicated an increased decomposition rate of TC with increasing Oxone concentration, martite nanoparticles dosage, and initial pH. In the absence of ultrasound, the decomposition rate of TC was 0.0481 min^-1 within 30 min, while the implementation of ultrasound at 320 W and addition of hydrogen peroxide at 40 mM led to increase in the decomposition rate up to 0.0770 and 0.0907 min^-1, respectively. The presence of carbonate and even persulfate ions suppressed the decomposition rate. Inversely, the addition of chloride and carbon tetrachloride enhanced the reactor performance in terms of TC degradation. Within four consecutive experimental runs, only 10.8% was dropped in the decomposition rate, indicating the appropriate reusability potential of martite nanoparticles. The results confirmed the appropriate ability of the treatment process in degrading and mineralizing the target pollutant but a longer exposure time is required for an efficient mineralization.

Peroxymonosulfate/base process in saline wastewater treatment: The fight between alkalinity and chloride ions

Both Cl^- and base can affect PMS activation to produce reactive chlorine or oxygen species, but the overall effects of chloride on this emerging PMS/base technology in saline wastewater treatment are unknown. Here effectiveness of PMS/base, PMS/Cl^- and PMS/base/Cl^- is compared with a gradient concentration of chloride and alkalinity, by probing the degradation of methylene blue (MB). Both PMS/base and PMS/Cl^- systems can rapidly degrade MB due to the generation of singlet oxygen and reactive chlorine, respectively. Interestingly, dye degradation and adsorbable organic halides (AOX) formation are inhibited in the PMS/base/Cl^- system as high concentrations of Cl^- and base co-exist. Reaction of PMS with chloride diminishes the effective concentration of PMS by base activation, whereas in return high alkalinity decreases the oxidation capacity of reactive species. Therefore, this finding may have significant technical implications for evaluating the applicability of the emerging PMS/base technology and optimizing the conditions for AOX abatement in PMS-based processes.

Oxidation of azo and anthraquinonic dyes by peroxymonosulphate activated by UV light

The photochemical degradation of two azo and two anthraquinonic dyes was performed using potassium peroxymonosulphate (Oxone®) activated by UV radiation. The fast decolourization of all dyes was observed within 6 min of UV irradiation, with corresponding dye decays higher than 80%. The kinetic rate constants of the dyes' decay were determined, along with the energetic efficiency of the photochemical treatment, taking into account the influence of a few anions commonly present in real wastewaters (i.e., chloride, nitrate, carbonate/bicarbonate and phosphate ions). Chloride and carbonate/bicarbonate ions enhanced dye degradation, whereas phosphate ions exerted an inhibitory effect, and nitrates did not have a predictable influence. The dye decolourization was not associated with efficient mineralization, as suggested by the lack of a significant total organic carbon (TOC) decrease, as well as by the low concentrations of a few detected low molecular weight by-products, including nitrate ions, formaldehyde and organic acids. High molecular weight by-products were also detected by mass spectrometry analysis. The investigated process may be proposed as a convenient pre-treatment to help dye degradation in wastewater during combined treatment methods.

Degradation of diethyl phthalate (DEP) by UV/persulfate: An experiment and simulation study of contributions by hydroxyl and sulfate radicals

Degradation of diethyl phthalate (DEP) by ultraviolet/persulfate (UV/PS) process at different reaction conditions was evaluated. DEP can be degraded effectively via this process. Both tert-butyl (TBA) and methanol (MeOH) inhibited the degradation of DEP with MeOH having a stronger impact than TBA, suggesting sulfate radical () and hydroxyl radical (HO) both existed in the reaction systems studied. The second-order rate constants of DEP reacting with and HO were calculated to be (6.4±0.3)×10⁷ M^-1s^-1 and (3.7±0.1)×10⁹ M^-1s^-1, respectively. To further access the potential degradation mechanism in this system, the pseudo-first-order rate constants (k_o) and the radical contributions were modeled using a simple steady-state kinetic model involving and HO. Generally, HO had a greater contribution to DEP degradation than . The k_o of DEP increased as PS dosages increased when PS dosages were below 1.9 mM. However, it decreased with increasing initial DEP concentrations, which might be due to the radical scavenging effect of DEP. The k_o values in acidic conditions were higher than those in alkaline solutions, which was probably caused by the increasing concentration of hydrogen phosphate (with higher scavenging effects than dihydrogen phosphate) from the phosphate buffer as pH values rose. Natural organic matter and bicarbonate dramatically suppressed the degradation of DEP by scavenging and HO. Additionally, the presence of chloride ion (Cl^-) promoted the degradation of DEP at low Cl^- concentrations (0.25-1 mM). Finally, the proposed degradation pathways were illustrated.

Synthesis of Co3O4-Bi2O3 using microwave-assisted method as the peroxymonosulfate activator for elimination of bisphenol A

In this work, Co₃O₄-Bi₂O₃ was successfully synthesized using a microwave-assisted method [Co₃O₄-Bi₂O₃(MW)] and employed as a peroxymonosulfate (PMS) activator for bisphenol A removal. A reference catalyst was prepared using the same preparation conditions but different heating mode and labeled as Co₃O₄-Bi₂O₃(CH). The series of Co₃O₄-Bi₂O₃ was characterized using XRD, SEM, and N₂ adsorption to detect their crystallinity, morphology, and surface area, among others. Results indicated that both microwave and calcination significantly affected the characteristic and catalytic activity of the catalyst. Moreover, the microwave-irradiated catalyst calcined at 300 °C showed higher catalytic activity and mineralization percentage for BPA degradation than the conventionally heated catalyst calcined at the same temperature. Microwave temperature and microwave time of the proposed microwave-assisted method were also investigated. Compared with other catalysts, the present catalyst showed considerably superior preparation time and degradation efficiency. This study broadens a new horizon for advanced oxidation process using a PMS activator.

On peroxymonosulfate-based treatment of saline wastewater: when phosphate and chloride co-exist

Both chloride and phosphate are common inorganic anions in industrial wastewater, however, their effects on peroxymonosulfate (PMS)-based oxidation systems are largely unknown. The present results show that addition of chloride (>1 mM) apparently enhanced the degradation of Acid Orange 7 (AO7) independent of the presence of phosphate (PBS) buffer. Both PBS and chloride favored the degradation of AO7, while PBS played a more important role when they co-existed. The degradation efficiency of AO7 was enhanced by increasing the concentration of PBS and chloride. A maximum of absorbable organic halides (AOX) accumulation was observed; indicating some chlorinated byproducts could be initially generated and further oxidized by increasing the reaction time. It is demonstrated that the PBS/PMS system, with a lower AOX formation at the same chloride concentration, is superior to the Co/PMS system, a typical sulfate radical-based system. The active chlorine species (HClO/Cl₂) were found to be the dominant oxidants in the presence of higher chloride concentration (>50 mM) under neutral conditions. The findings of this work may promote the further application of PMS-based oxidation processes in saline effluents treatment.

Both chloride and phosphate are common inorganic anions in industrial wastewater, however, their effects on peroxymonosulfate (PMS)-based oxidation systems are largely unknown.

Degradation of sulfolane using activated persulfate with UV and UV-Ozone

This study investigates the degradation of sulfolane in aqueous system by (NH₄)₂S₂O₈/UVC and (NH₄)₂S₂O₈/O₃/UVC. While bubbling O₃ significantly decreased the reaction time, the experimental results in both cases were consistent: firstly, the degradation of sulfolane followed pseudo-first order kinetic models, secondly, the reaction rates were affected by persulfate dosages, UV light intensity, initial pH and concentration of carbonate/bicarbonate present. Low concentration of chloride (less then 100 ppm) had no effect on the reaction rate. Application of (NH₄)₂S₂O₈/O₃/UVA for degradation of sulfolane was also investigated. It was found that for higher sulfolane degradation kinetics, higher concentrations of persulfate was required under UVA irradiation. Finally, (NH₄)₂S₂O₈/UVC was evaluated for its applicability for degradation of sulfolane in groundwater samples.

Oxidation of bisphenol A in water by heat-activated persulfate

The heat-activated persulfate oxidation of bisphenol A (BPA), a representative endocrine disrupting compound, was investigated with respect to the effect of several process variables on degradation rates. The activation temperature appears to be the single most important parameter, i.e. a temperature increase from 40 to 70 °C results in an 80-fold rate increase. Regarding initial BPA concentration, the reaction follows a pseudo-first order rate expression, where the kinetic constant decreases from 11.5 10^-2 to 3.5 10^-2 min^-1 when BPA concentration increases from 110 to 440 μg/L. Reactions in actual water matrices, such as bottled water and secondary treated wastewater, are slower than in pure water since various organic/inorganic water constituents compete with BPA for being oxidized by the reactive oxidizing species; this was confirmed with experiments in pure water spiked with humic acid or bicarbonate. Interestingly though, the presence of chloride seems to promote BPA degradation. Furthermore, degradation is favored at near-neutral pH and increased sodium persulfate (SPS) concentrations. Experiments at an increased BPA concentration of 20 mg/L were performed to identify transformation by-products (TBPs), as well as assess the mineralization and toxicity of the treated samples. Liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS) revealed the formation of eleven TBPs of BPA and plausible pathways including hydroxylation, oxidation, cleavage and oligomerization reactions are proposed. Mineralization occurs slower than BPA degradation, while the toxicity to marine bacteria Vibrio fischeri increases during the early stages of the reaction but it progressively decreases thereafter.

Excellent performance of cobalt-impregnated activated carbon in peroxymonosulfate activation for acid orange 7 oxidation

Cobalt-impregnated activated carbon (GAC/Co) was used to produce sulfate radical (SO₄^·-) from peroxymonosulfate (PMS) in aqueous solution (hereafter called PMS activation). We evaluated its effectiveness by examining the degradation of orange acid 7 (AO7). GAC/Co exhibited high activity to activate PMS to degrade AO7. The degradation efficiency of AO7 increased with increasing dosage of GAC/Co or PMS and elevated temperatures. pH 8 was most favorable for the degradation of AO7 by GAC/Co-activated PMS. The radical quenching experiments indicated that the reactions most likely took place both in the bulk solution and on the surface of GAC/Co. We found that SO₄^·- played a dominant role in AO7 degradation. Sodium chloride (NaCl) which presents in most dye wastewater had a significant impact on AO7 degradation. Low dosages (<0.4 M) of NaCl showed a slight inhibitory effect, whereas high dosages (0.8 M) increased the reaction rate. HOCl was confirmed as the main contributor for accelerating AO7 degradation with high concentration of NaCl. In a continuous-flow reaction with an empty-bed contact time of 1.35 min, AO7 was not detected in the effluent for 0 to 18.72 L of treated influent volume (156 h) and 85% removal efficiency was still observed after 40.32 L of treated volume (336 h). Finally, the azo bond and the naphthalene structure in AO7 were destroyed and the degradation pathway was proposed.

Effects of water chemistry on decolorization in three photochemical processes: Pro and cons of the UV/AA process

The poor selectivity of hydroxyl radicals is a major restriction in the practical application of the UV/H₂O₂ process for dyeing wastewater treatment. As an alternative, the target-selective UV/acetylacetone (AA) process was found highly efficient for dye decolorization. For the proper selection and application of the two photochemical processes, the effects of water matrices, including common inorganic anions (Cl^-, SO₄^2-, NO₃^-, HCO₃^-), natural organic matter, metal cations (Mg²⁺, Mn²⁺, Cu²⁺, Fe³⁺, Cr³⁺), and temperature, on the photo-degradation of an azo dye, Acid Orange 7 (AO7), were systematically investigated. The experimental results demonstrate that the UV/AA process was more sensitive to inner filter effect. NO₃^-, Cu²⁺, and Fe³⁺ were all detrimental to the UV/AA process, whereas at certain concentrations they were beneficial to the UV/H₂O₂ process. However, even with severe inhibitory effects, the decolorization efficiency of the UV/AA process was still several times higher than that of the UV/H₂O₂ process. The results are helpful for us to better understand the mechanisms behind the UV/AA process and may shed light on the application of UV-based advanced oxidation processes for wastewater treatment.

Activated carbon fiber for heterogeneous activation of persulfate: implication for the decolorization of azo dye

Activated carbon fiber (ACF) was used as a green catalyst to activate persulfate (PS) for oxidative decolorization of azo dye. ACF demonstrated a higher activity than activated carbon (AC) to activate PS to decolorize Orange G (OG). The decolorization efficiency of OG increased as ACF loading, PS dosage, and temperature increased. OG decolorization followed a pseudo first-order kinetics, and the activation energy was 40.902 kJ/mol. pH had no apparent effect on OG decolorization. Radical quenching experiments with various radical scavengers (e.g., alcohols, phenol) showed that radical-induced decolorization of OG took place on the surface of ACF, and both SO4 (·-) and HO· were responsible for OG decolorization. The impact of inorganic salts was also evaluated because they are important compositions of dye wastewater. Cl(-) and SO4 (2-) exhibited a promoting effect on OG decolorization, and the accelerating rate increased with elevating dosage of ions. Addition of Cl(-) and SO4 (2-) could increase the adsorption of OG on ACF surface, thus favorable for OG decolorization caused by the surface-bound SO4 (·-) and HO·. Conversely, HCO3 (-) and humic acid (HA) slightly inhibited OG decolorization. The azo band and naphthalene ring on OG were remarkably destructed to other intermediates and finally mineralized to CO2 and H2O.

Photodegradation of 4-tert-butylphenol in aqueous solution by UV-C, UV/H2O2 and UV/S2O8(2-) system

The photolytic degradation of 4-tert-butylphenol (4-t-BP) in aqueous solution was investigated using three kinds of systems: UV-C directly photodegradation system, UV/H2O2 and UV/S2O8(2-) system. Under experimental conditions, the degradation rate of 4-t-BP was in the order: UV/S2O8(2-) > UV/H2O2 > UV-C. The reaction kinetics of UV/S2O8(2-) system were thoroughly investigated. The increase of S2O8(2-) concentration enhanced the 4-t-BP degradation rate, which was inhibited when the concentration of S2O8(2-) exceeded 4.0 mM. The highest efficacy in 4-t-BP degradation was obtained at pH 6.5. The oxidation rate of 4-t-BP could be accelerated by increasing the reaction temperature and irradiation intensity. The highest rate constant (kobs = 8.4 × 10(-2) min(-1)) was acquired when the reaction temperature was 45 °C. The irradiation intensity was measured by irradiation distance, and the optimum irradiation distance was 10 cm. Moreover, the preliminary mechanism of 4-t-BP degradation was studied. The bond scission of the 4-t-BP molecule occurred by the oxidation of SO4(•-), which dimerized and formed two main primary products. Under the conditions of room temperature (25 °C ± 1 °C) and low concentration of K2S2O8 (0.5 mM), 35.4% of total organic carbon (TOC) was removed after 8.5-h irradiation. The results showed that UV/S2O8(2-) system was effective for the degradation of 4-t-BP.

Transformation of bromide in thermo activated persulfate oxidation processes

Sulfate radicals ( [Formula: see text] ) are applied to degrade various organic pollutants. Due to its high oxidative potential, [Formula: see text] is presumed to be able to transform bromide to reactive bromine species that can react with natural organic matter subsequently to form brominated products including brominated disinfection by-products (Br-DBPs). This research was designed to investigate the transformation of bromide in thermo activated persulfate oxidation process in the presence of humic acid (HA). Significant formation of bromoform and bromoacetic acids was verified. Their formation was attributed to the reactions of HA and reactive bromine species including Br·, [Formula: see text] HOBr(-), and free bromine resulted from the oxidation of bromide by [Formula: see text] . Yields of Br-DBPs increased monotonically at persulfate concentration of 1.0 mM and working temperature of 70 °C. However, the time-depended formation exhibited an increasing and the decreasing profile when persulfate was 5.0 mM, suggesting further degradation of organic bromine. HPLC/ICP-MS analysis demonstrated that the organic bromine was eventually transformed to bromate at this condition. Thus, a transformation scheme was proposed in which the bromine could be recycled multiple times between inorganic bromide and organic bromine before being finally transformed to bromate. This is the first study that reveals the comprehensive transformation map of bromine in [Formula: see text] based reaction systems, which should be taken into consideration when such technologies are used to eliminate contamination in real practice.

Ultrasound enhanced heterogeneous activation of peroxydisulfate by bimetallic Fe-Co/GAC catalyst for the degradation of Acid Orange 7 in water

Bimetallic Fe-Co/GAC (granular activated carbon) was prepared and used as heterogeneous catalyst in the ultrasound enhanced heterogeneous activation of peroxydisulfate (PS, S2O(2-)8) process. The effect of initial pH, PS concentration, catalyst addition and stirring rate on the decolorization of Acid Orange 7 (AO7) was investigated. The results showed that the decolorization efficiency increased with an increase in PS concentration from 0.3 to 0.5 g/L and an increase in catalyst amount from 0.5 to 0.8 g/L. But further increase in PS concentration and catalyst addition would result in an unpronounced increase in decolorization efficiency. In the range of 300 to 900 r/min, stirring rate had little effect on AO7 decolorization. The catalyst stability was evaluated by measuring decolorization efficiency for four successive cycles.

Efficient removal of endosulfan from aqueous solution by UV-C/peroxides: a comparative study

This study explored the efficiency of UV-C-based advanced oxidation processes (AOPs), i.e., UV/S2O8(2-), UV/HSO5(-), and UV/H2O2 for the degradation of endosulfan, an organochlorine insecticide and an emerging water pollutant. A significant removal, 91%, 86%, and 64%, of endosulfan, at an initial concentration of 2.45 μM and UV fluence of 480 mJ/cm(2), was achieved by UV/S2O8(2-), UV/HSO5(-), and UV/H2O2 processes, respectively, at a [peroxide]0/[endosulfan]0 molar ratio of 20. The efficiency of these processes was, however, inhibited in the presence of radical scavengers, such as alcohols (e.g., tertiary butyl alcohol and isopropyl alcohol) and natural organic matter (NOM). The inhibition was also influenced by common inorganic anions in the order of nitrite > bicarbonate > chloride > nitrate ≈ sulfate. The observed pseudo-first-order rate constant decreased while the degradation rate increased with increasing initial concentration of the target contaminant. The degradation mechanism of endosulfan by the AOPs was evaluated revealing the main by-product as endosulfan ether. Results of this study suggest that UV-C-based AOPs are potential methods for the removal of pesticides, such as endosulfan and its by-products, from contaminated water.

Chloride anion effect on the advanced oxidation processes of methidathion and dimethoate: role of Cl2(·-) radical

The reaction of phosphor-containing pesticides such as methidathion (MT) and dimethoate (DM) with dichloride radical anions (Cl(2)(·-)) was investigated. The second order rate constants (1.3 ± 0.4) × 10(8) and (1.1 ± 0.4) × 10(8) M(-1) s(-1) were determined for the reaction of Cl(2)(·-) with MT and DM, respectively. A reaction mechanism involving an initial charge transfer from the sulfide groups of the insecticides to Cl(2)(·-) is proposed and supported by the identified transient intermediates and reaction products. The formation of chlorinated byproducts was determined. The unexpected consequences of an efficient Cl(2)(·-) reactivity towards MT and DM on the degradation capacity by Advanced Oxidation Procedures applied to polluted waters containing the insecticides and Cl(-) anions is discussed.

Kinetic modeling and synergy quantification in sono and photooxidative treatment of simulated dyehouse effluent

The aim of this work was to explore the application of sulfate radical based advanced oxidation processes: photooxidation (UV/PMS/PS), sonooxidation (US/PMS/PS) and combined sono-photooxidation (US/UV/PMS/PS) for the mineralization of simulated dyehouse effluent (WW); using peroxymonosulfate (PMS) and persulfate (PS) as oxidants. Experiments were performed in a reaction vessel of a defined geometry and axially positioned source of UV-C radiation, all placed in the ultrasonic bath (35 kHz). Mathematical model of the process was developed according to the proposed degradation scheme. Decomposition of dyestuff (C.I. Reactive Violet 2, RV2 and C.I. Reactive Blue 7, RB7), surfactant (linear alkylbenzene sulfonate; hereafter: LAS) and auxiliary organic components was explored in three types of model wastewater: WW, simulated effluent excluding inorganic species (WW-IS) and model solution that consists of a specific compound (hereafter: compound model solutions). The influence of inorganic matrix (Cl(-), CO(3)(2-)/HCO(3)(-)) was studied due to the corresponding quenching affinity toward HO and SO(4)(-) radicals. The efficiency of applied processes was evaluated and the response to combined phenomena (cavitation and irradiation) was quantified as synergy index, f(Syn). Sono-photooxidative treatment (US/UV/PMS/PS) of WW resulted in a partial mineralization and partial decolourization; approximately 40% of initial TOC and 30% of initial RB7 remained after 60 min of treatment, while RV2 and LAS molecule were completely decomposed. Circumstantially, the combined process increased the mineralization efficiency by a factor of 3 (f(Syn) = 3.026).