Sulfate Radical Technologies as Tertiary Treatment for the Removal of Emerging Contaminants from Wastewater

A review of pathogen removal from municipal wastewater using advanced oxidation processes: Agricultural application, regrowth risks, and new perspectives

Pathogen removal in wastewater offers a chance to recover water and nutrients for crop production, reducing environmental contamination and public health risks. However, the risk of pathogens regrowing in treated effluents can endanger public health if reused in agriculture, attracting stringent reuse standards. While advanced oxidation processes (AOPs) promise to reduce pathogens, eliminating regrowth potential in AOP-treated effluents requires further scrutiny. This review aimed to summarize the available evidence on understanding pathogen reduction and regrowth potential in AOP-treated effluents, following best practices for scoping reviews like the preferred reporting items for systematic reviews and meta-analysis (PRISMA). It covers recent pathogen studies under AOPs, current AOP investigations, the impact of AOP dosage and retention time on pathogen control, and challenges in reusing AOP-treated effluents for crop production. Additionally, it identifies areas needing improvement or complementary treatments for pathogen-free effluents with no regrowth potential. The review concludes by summarizing key findings and suggesting research areas for further exploration.

Unique effect of bromide ion on intensification of advanced oxidation processes for pollutants removal: A systematic review

Advanced oxidation processes (AOPs) have been developed to decompose toxic pollutants to protect the aquatic environment. AOP has been considered an alternative treatment method for wastewater treatment. Bromine is present in natural waters posing toxic effects on human health and hence, its removal from drinking water sources is necessary. Of the many techniques advanced oxidation is covered in this review. This review systematically examines literature published from 1997 to April 2024, sourced from Scopus, PubMed, Science Direct, and Web of Science databases, focusing on the efficacy of AOPs for pollutant removal from aqueous solutions containing bromide ions to investigate the impact of bromide ions on AOPs. Data and information extracted from each article eligible for inclusion in the review include the type of AOP, type of pollutants, and removal efficiency of AOP under the presence and absence of bromide ion. Of the 1784 documents screened, 90 studies met inclusion criteria, providing insights into various AOPs, including UV/chlorine, UV/PS, UV/H2O2, UV/catalyst, and visible light/catalyst processes. The observed impact of bromide ion presence on the efficacy of AOP processes, alongside the AOP method under scrutiny, is contingent upon various factors such as the nature of the target pollutant, catalyst type, and bromide ion concentration. These considerations are crucial in selecting the best method for removing specific pollutants under defined conditions. Challenges were encountered during result analysis included variations in experimental setups, disparities in pollutant types and concentrations, and inconsistencies in reporting AOP performance metrics. Addressing these parameters in research reports will enhance the coherence and utility of subsequent systematic reviews.

K2S2O8-Mediated or Azobisisobutyronitrile-Catalyzed Regioselective Aerobic Oxidative Cleavage of 1-Arylbutadienes to Cinnamaldehydes

This work reveals the regioselective oxidative cleavage of 1-arylbutadienes to cinnamaldehydes mediated by K2S2O8 or catalyzed by azobisisobutyronitrile, a very common free radical initiator, in an easy to handle, simple procedure and free of transition metals. This approach demonstrates excellent regioselectivity, mild reaction conditions, and compatibility with a broad range of functional groups (45 examples).

Photocatalytic activity of ZnO doped Nano hydroxyapatite/GO derived from waste oyster shells for removal of Methylene blue

Hydroxyapatite (HAp) stands as an inorganic compound, recognized as a non-toxic, bioactive ceramic, and its composition closely resembles that of bone material. In this study, nHAp was prepared from waste oyster shells, which are biowaste rich in calcium carbonate. nHAp with its unique catalytic property can be used as an adsorbent in various fields, including wastewater treatment. nHAp with an exceptional surface adsorbent with excellent chemical stability, enabling its catalytic function. Nano hydroxyapatite doped with Zinc oxide (ZnO) by wet chemical precipitation and made into a composite with Graphene oxide (GO) by modified hummers method followed by grinding, which was taken as 9:1 ratio (nHAp/ZnO and GO) of weight, enhances its tensile and mechanical strength. The energy band gap of nHAp photocatalyst was evaluated as 3.39 eV and that of the in nHAp/ZnO/GO photocatalyst was narrowed to 1.77 eV. The ternary nanocomposites are very efficient in generating the photogenerated electrons and holes, thereby improving the degradation potential of dye effluents to by-products such as CO2 and H2O. The nanocomposites photocatalyst were characterized by FTIR, XRD, SEM, TEM, EDS, XPS, DRS, and BET techniques. The UV-visible study shows the complete dye degradation efficiency of the prepared nanocomposites photocatalyst. In this study, the prepared nanocomposites nHAp/ZnO/GO have studied their efficiency for the removal of MB dye in a batch process by varying the dosage from 0.1 to 0.5 g, and the effects of dosage variations, pH, kinetic, scavenger study were evaluated at a time interval of 30 min. The removal of dye was found to be 99% at 150 min of 0.3 g dosage and pH = 12 is most favorable as it reached the same percentage at 90 min. The as-prepared nanocomposite nHAp/ZnO/GO fits the kinetic rate constant equation and shows a pseudo-first-order reaction model. This study indicates the suitability for dye removal due to the synergistic effect and electrostatic interaction of the synthesized ternary nanocomposite, which shows the potential, socially active, low-cost-effective, eco-friendly, and safe for photocatalytic degradation of MB from wastewater.

Piezoelectric catalytic driven advanced oxidation process using two-dimensional metal dichalcogenides for wastewater pollutants remediation

The public and society have increasingly recognized numerous grave environmental issues, including water pollution, attributed to the rapid expansion of industrialization and agriculture. Renewable energy-driven catalytic advanced oxidation processes (AOPs) represent a green, sustainable, and environmentally friendly approach to meet the demands of environmental remediation. In this context, 2D transition metal dichalcogenides (TMDCs) piezoelectric materials, with their non-centrosymmetric crystal structure, exhibit unique features. They create dipole polarization, inducing a built-in electric field that generates polarized holes and electrons and triggers redox reactions, thereby facilitating the generation of reactive oxygen species for wastewater pollutant remediation. A broad spectrum of 2D TMDCs piezoelectric materials have been explored in self-integrated Fenton-like processes and persulfate activation processes. These materials offer a more simplistic and practical method than traditional approaches. Consequently, this review highlights recent advancements in 2D TMDCs piezoelectric catalysts and their roles in wastewater pollutant remediation through piezocatalytic-driven AOPs, such as Fenton-like processes and sulfate radicals-based oxidation processes.

Mineralization of palm oil mill effluent by advanced oxidation processes: A review on current trends and the way forward

Palm oil mill effluent (POME) is regarded as deleterious to the environment, primarily owing to the substantial volume of waste it produces during palm oil extraction. In terms of contaminant composition, POME surpasses the pollutant content typically found in standard municipal sewage, therefore releasing it without treatment into water bodies would do irreparable damage to the environment. Main palm oil mills are normally located in the proximity of natural rivers in order to take advantage of the cheap and abundant water source. The same rivers are also used as a water source for many villages situated along the river banks. As such, it is imperative to degrade POME before its disposal into the water bodies for obvious reasons. The treatment methods used so far include the biological processes such as open ponding/land application, which consist of aerobic as well as anaerobic ponds, physicochemical treatment including membrane technology, adsorption and coagulation are successful for the mitigation of contaminants. As the above methods require large working area and it takes more time for contaminant degradation, and in consideration of the strict environmental policies as well as palm oil being the most sort of vegetable oil in several countries, numerous researchers have concentrated on the emerging technologies such as advanced oxidation processes (AOPs) to remediate POME. Methods such as the photocatalysis, Fenton process, sonocatalysis, sonophotocatalysis, ozonation have attained special importance for the degradation of POME because of their efficiency in complete mineralization of organic pollutants in situ. This review outlines the AOP technologies currently available for the mineralization of POME with importance given to sonophotocatalysis and ozonation as these treatment process removes the need to transfer the pollutant while possibly degrading the organic matter sufficiently to be used in other industry like fertilizer manufacturing.

Photodegradation and photocatalysis of per- and polyfluoroalkyl substances (PFAS): A review of recent progress

Per- and polyfluoroalkyl substances (PFAS) are oxidatively recalcitrant organic synthetic compounds. PFAS are an exceptional group of chemicals that have significant physical characteristics due to the presence of the most electronegative element (i.e., fluorine). PFAS persist in the environment, bioaccumulate, and have been linked to toxicological impacts. Epidemiological and toxicity studies have shown that PFAS pose environmental and health risks, requiring their complete elimination from the environment. Various separation technologies, including adsorption with activated carbon or ion exchange resin; nanofiltration; reverse osmosis; and destruction methods (e.g., sonolysis, thermally induced reduction, and photocatalytic dissociation) have been evaluated to remove PFAS from drinking water supplies. In this review, we will comprehensively summarize previous reports on the photodegradation of PFAS with a special focus on photocatalysis. Additionally, challenges associated with these approaches along with perspectives on the state-of-the-art approaches will be discussed. Finally, the photocatalytic defluorination mechanism of perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) following complete mineralization will also be examined in detail.

Persulfate promoted carbamoylation of N-arylacrylamides and N-arylcinnamamides with 4-carbamoyl-Hantzsch esters

Carbamoyl-Hantzsch esters were used as carbamoyl radical precursors for oxidative carbamoylation of N-arylacrylamides and N-arylcinnamamides in the presence of inexpensive persulfates. This protocol can be applied to a broad range of substrates with various functional groups, providing a variety of 3,3-disubstituted oxindoles and 3,4-disubstituted dihydroquinolin-2(1H)-ones in moderate to good yields via an intermolecular addition/cyclization process.

Comparison of TiO2 and ZnO for Heterogeneous Photocatalytic Activation of the Peroxydisulfate Ion in Trimethoprim Degradation

The persulfate-based advanced oxidation process is a promising method for degrading organic pollutants. Herein, TiO2 and ZnO photocatalysts were combined with the peroxydisulfate ion (PDS) to enhance the efficiency. ZnO was significantly more efficient in PDS conversion and SO4•- generation than TiO2. For ZnO, the PDS increased the transformation rate of the trimethoprim antibiotic from 1.58 × 10-7 M s-1 to 6.83 × 10-7 M s-1. However, in the case of TiO2, the moderated positive effect was manifested mainly in O2-free suspensions. The impact of dissolved O2 and trimethoprim on PDS transformation was also studied. The results reflected that the interaction of O2, PDS, and TRIM with the surface of the photocatalyst and their competition for photogenerated charges must be considered. The effect of radical scavengers confirmed that in addition to SO4•-, •OH plays an essential role even in O2-free suspensions, and the contribution of SO4•- to the transformation is much more significant for ZnO than for TiO2. The negative impact of biologically treated domestic wastewater as a matrix was manifested, most probably because of the radical scavenging capacity of Cl- and HCO3-. Nevertheless, in the case of ZnO, the positive effect of PDS successfully overcompensates that, due to the efficient SO4•- generation. Reusability tests were performed in Milli-Q water and biologically treated domestic wastewater, and only a slight decrease in the reactivity of ZnO photocatalysts was observed.

Applications of biochar in sulfate radical-based advanced oxidation processes for the removal of pharmaceuticals and personal care products

Recently, biochar (BC) has been increasingly used as a catalyst for the degradation of 'emerging pollutants' (EPs). Pharmaceuticals and personal care products (PPCPs), which come under 'EPs', can be harmful to the aquatic ecosystem despite being present in very low concentrations (ng/L-μg/L). Advanced oxidation processes (AOPs), which produce sulfate radical (SR-AOPs), show a great potential to degrade PPCPs effectively from wastewater. It is mainly due to the higher stability, long half-lives and better non-selectivity of SO₄^{• -} compared with AOPs with •OH generation. Furthermore, research focus is now given on AOPs coupled with BC-supported catalyst to enhance the degradation of PPCPs because of quicker generation of radicals (•OH, SO₄^•-) by the activation of persulfate (PS) and peroxymonosulfate (PMS). This article sheds light on the catalytic ability of BC after its physical and chemical modifications such as acid/alkali treatment and metal doping. The role of persistent free radicals (PFRs) in the BC for effective removal of PPCPs has been elaborated. Its potential applications in synthetic as well as real wastewater have also been discussed.

Near-Infrared (NIR) Silver Sulfide (Ag2S) Semiconductor Photocatalyst Film for Degradation of Methylene Blue Solution

A silver sulfide (Ag₂S) semiconductor photocatalyst film has been successfully synthesized using a solution casting method. To produce the photocatalyst films, two types of Ag₂S powder were used: a commercialized and synthesized powder. For the commercialized powder (CF/comAg₂S), the Ag₂S underwent a rarefaction process to reduce its crystallite size from 52 nm to 10 nm, followed by incorporation into microcrystalline cellulose using a solution casting method under the presence of an alkaline/urea solution. A similar process was applied to the synthesized Ag₂S powder (CF/syntAg₂S), resulting from the co-precipitation process of silver nitrate (AgNO₃) and thiourea. The prepared photocatalyst films and their photocatalytic efficiency were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and UV-visible spectroscopy (UV-Vis). The results showed that the incorporation of the Ag₂S powder into the cellulose films could reduce the peak intensity of the oxygen-containing functional group, which indicated the formation of a composite film. The study of the crystal structure confirmed that all of the as-prepared samples featured a monoclinic acanthite Ag₂S structure with space group P₂₁/C. It was found that the degradation rate of the methylene blue dye reached 100% within 2 h under sunlight exposure when using CF/comAg₂S and 98.6% for the CF/syntAg₂S photocatalyst film, and only 48.1% for the bare Ag₂S powder. For the non-exposure sunlight samples, the degradation rate of only 33-35% indicated the importance of the semiconductor near-infrared (NIR) Ag₂S photocatalyst used.

Development of activated carbon for removal of pesticides from water: case study

The work primarily concerns development of activated carbon dedicated for adsorption of pesticides from water prior directing it to the distribution system. We provide an information on research on important practical aspects related to research carried out to develop and to manufacture activated carbons. The paper concerns preliminary works on selection raw materials, a binder used for producing granulated adsorbent, activating gases, conditions of the production process, and others. The key attention in this research was paid to its target, i.e., industrial process to produce activated carbon revealing fulfilling required properties including satisfying adsorption of selected pesticides and meeting the requirements of companies dealing with a large-scale production of drinking water. Therefore, among others, the work includes considerations concerning such aspects like pore structure and specific surface area of the activated carbon, formation of granules that are the most demanded and thus preferred in an industrial practice form of activated carbons, and other aspects important from practical point of view. Using the results of our preliminary work, a batch of granular activated carbon was produced in industrial conditions. The obtained material was tested in terms of removing several pesticides at a water treatment plant operating on an industrial scale. During tests the concentration of acetochlor ESA was decreased from ca. 0.4 µg/l in raw water to below 0.1 µg/l. During 11 months of AC use specific surface area of adsorbent lowered significantly by 164 m²/g, and total pore volume declined from initial 0.56 cm³/g to 0.455 cm³/g. We discuss both a performance of the obtained activated carbon in a long-term removal of acetochlor and its derivatives from water and an effect of exploitation time on the removal efficiency. The explanations for the reduction in pesticide removal efficiency are also proposed and discussed.

Application of Fe-RGO for the removal of dyes by catalytic ozonation process

Due to continuous industrialization, the discharge of hazardous dyes has enormously disrupted the ecosystem causing environmental problems. Due to the stable recalcitrant nature of dyes, advanced catalytic ozonation processes with the latest catalyst are under investigation. Fe-RGO is an effective oxidation catalyst, and the metal loaded platform provides enhanced catalytic performance. This study aims to investigate the effectiveness of Fe-RGO/O3 process for the removal of dyes. In the current research, the application of iron-coated reduced graphene oxide (Fe-RGO) was studied as a catalyst in the heterogeneous catalytic ozonation process to remove dyes. Methylene blue (MB) was selected as a model pollutant. RGO was prepared using the improved Hummers method and was coated with iron (Fe) implying the impregnation method. The FTIR, SEM-EDX, XRD, and BET analyses of RG and Fe-RGO were performed to characterize the catalyst. The effect of various parameters such as pH (3-10), catalyst dose (0.01-0.04 g), and radical scavengers (NaHCO3, NaCl) on removal efficiency was elucidated. The result revealed an excellent catalytic efficiency of Fe-RGO in the ozonation process. At optimum conditions, 96% removal efficiency was achieved in catalytic ozonation at pH 7 with a catalyst dose of 0.02 g and ozone dose 0.5 mg/min, after 10 min. Interestingly, a slight decrease in removal efficiency was observed in the catalytic ozonation process in hydroxyl radical scavengers (NaCl and NaHCO3), which makes the proposed catalyst more applicable in real conditions. Therefore, it is concluded that Fe-RGO can be used as an excellent catalyst for the removal of dyes in real conditions where radical scavengers may be present in a significant amount.

Comparison of sunlight-AOPs for levofloxacin removal: kinetics, transformation products, and toxicity assay on Escherichia coli and Micrococcus flavus

Levofloxacin (LFX) is a widely used antibiotic medication. Persistent traces of LFX in water and wastewater may induce bacterial resistance. Photon-driven advanced oxidation processes (AOPs) can assist in attaining complete abatement of LFX for environmental protection. This work benchmarks different solar AOPs based on hydroxyl radical (OH^•) and sulphate radical (SO₄^•-) chemistry. Other oxidant precursors, as radical sources, were used to selectively control the generation of either hydroxyl radical (i.e., H₂O₂), sulphate radical (i.e., peroxydisulphate (PDS)), or a controlled mixture ratio of both OH^•/SO₄^•- (i.e., peroxymonosulphate (PMS)). The influence of pH on degradation performance was evaluated using unbuffered and buffered solutions. Simulated irradiation/PMS process exhibited a strong pH-dependence attaining partial degradation of ca. 56% at pH 5 up to complete degradation at pH 7. Despite the similitudes on the abatement of target pollutant LFX in pristine solutions, only simulated irradiation/PDS treatment achieved effective abatement of LFX in wastewater samples given the higher selectivity of SO₄^•-. Toxicity tests were conducted with Escherichia coli (LMG2092) and Micrococcus flavus (DSM1790), demonstrating successful inhibition of the antibiotic character of polluted waters, which would contribute to preventing the development of resistant bacterial strains. Finally, a degradative pathway was suggested from the by-products and intermediates identified by LC-MS. Results demonstrate that the degradation of specific functional groups (i.e., piperazine ring) is associated with the loss of antibacterial character of the molecule.

Sulfate radical based advanced oxidation processes for agro-industrial effluents treatment: A comparative review with Fenton's peroxidation

Agro-industrial wastewater management becomes a major task while environmental regulations are becoming stricter worldwide. Agro-industrial wastewaters are known by high content of organic pollutants that cause an adverse effect on the water bodies. Industries are looking for efficient, easy-to-use and affordable treatment processes. Sulfate radical based advanced oxidation processes (S-AOPs) are arising as suitable alternatives for agro-industrial effluents treatment. In this review, the major findings regarding the application of this technology for real agro-industrial wastewater depuration are discussed. Moreover, these technologies are compared as an alternative to Fenton's process, which is a widely studied advanced oxidation process and with high efficiency in the treatment of agro-industrial effluents. The studies already carried out are promising, but there is still a great lack of studies in this area and using this technique.

UV-Based Advanced Oxidation Processes of Remazol Brilliant Blue R Dye Catalyzed by Carbon Dots

UV-based advanced oxidation processes (AOPs) (UV/H₂O₂ and UV/S₂O₈^2-) with a titanium(IV)-doped carbon dot, TiP-CD, as a catalyst were developed for the decomposition of Remazol Brilliant Blue R (Reactive Blue 19), an anthraquinone textile dye (at T = 25 °C and pH = 7). The Ti-CD, with marked catalytic UV properties, was successfully synthesized by the one-pot hydrothermal procedure, using L-cysteine as carbon precursor, ethylenediamine as nitrogen source, PEG (polyethylene glycol) as a capping agent, and titanium(IV) isopropoxide (precursor of TiO₂ doping). Contrary to azo dyes (methyl orange, orange II sodium salt, and reactive black 5), which achieved complete degradation in a time interval less than 30 min in the developed AOP systems (UV/H₂O₂, UV/S₂O₈^2-, and UV/TiO₂), the RBB-R showed relatively low degradation rates and low discoloration rate constants. In the presence of the catalyzer, the reaction rate significantly increased, and the pseudo-first-order rate constants for the RBB-R discoloration were UV/3.0 mM H₂O₂/TIP-CD-0.0330 min^-1 and UV/1.02 mM S₂O₈^2-/TIP-CD-0.0345 min^-1.

Persulfate-nitrogen doped graphene mixture as an oxidant for the synthesis of 3-nitro-4-aryl-2H-chromen-2-ones from aryl alkynoate esters and nitrite

A series of 3-nitro-4-aryl-2H-chromen-2-ones in good yields have directly been obtained from aryl alkynoate esters and nitrite by employing a mixture of K₂S₂O₈-nitrogen doped graphene as an oxidant in a watery medium at room temperature. A plausible mechanism for the reaction is also reported. It reveals that the product is formed through a cascade of nitro radical addition, spirocyclization, and ester migration. When compared to known methods for the synthesis of 3-nitro-4-aryl-2H-chromen-2-ones from aryl alkynoate esters, this protocol is environmentally friendly, sustainable, practical and energy efficient and does not use a harmful nitro source. Furthermore, nitrogen doped graphene used in this approach can be easily recovered and reused at least four times without losing its activity.

Chemo-selective control of Ritter-type reaction by coordinatively unsaturated inorganic salt hydrates

We used a readily available water source, MgSO4·2H2O, to realize the control of the chemo-selectivity of the Ritter-type reaction efficiently.

Oxidative degradation of p-chlorophenol by the persulfate-doped Fe-Mn bimetallic hydroxide, the parametrical significance, and systematical optimization

Aqueous Fe(II)-catalyzed activation commonly deteriorates the oxidation performance of persulfate (PS) to the treatment of organic contaminants. In this study, a PS-doped layered bimetallic hydroxide (Fe-Mn hydroxide) was synthesized to construct a heterogeneously catalytic system to solve the issue brought by homogeneity. The molar ratio of Fe(II) to Mn(II) and the mass ratio of PS to Fe-Mn hydroxide both had a significant impact on the catalytic degradation of p-CP. Reaction temperatures engaged in the most essential role in influencing the degradation and removal of p-chlorophenol (p-CP). The optimal combination of factors for the preparation of PS-hydroxide and the treatment of p-CP was finally determined by significance analysis. The degradation process was appropriately fitted by the pseudo-first-order kinetic model. The benzene ring in p-CP was broken by PS-hydroxide during the adsorption. The surface modification of PS-hydroxide caused by the valence transition of Mn was beneficial to the adsorption and catalytic degradation of p-CP.

Mo2C/C catalyst as efficient peroxymonosulfate activator for carbamazepine degradation

Compared with generally reported Mo⁴⁺/Mo⁶⁺ redox cycle, the exposed Mo²⁺ active sites of Mo-based materials may have a superior potential to effectively activate PMS. However, Mo²⁺-involved materials as efficient catalysts in sulfate radical-based advanced oxidation processes (SR-AOPs) has rarely been researched. In this work, a spherical Mo₂C-loaded carbon material, Mo₂C/C, was prepared for the first time by hydrothermal-calcination method directly used as peroxymonosulfate (PMS) activator towards carbamazepine (CBZ) degradation. The results showed that the Mo₂C/C could effectively remove nearly 100% CBZ (5 mg·L^-1) in the presence of 0.75 mM PMS within 75 min under the optimal conditions. It was attributed to the reductive Mo²⁺, as active sites, benefits to absorb PMS on the surface to trigger electron transmission, and the defective carbon structures accelerate the activation of PMS. Consequently, the efficient Mo²⁺/Mo⁴⁺/Mo⁶⁺ electron transfer was achieved, resulting in excellent catalysis. A series of reactive species including SO₄^-, OH and ¹O₂ species participated in CBZ oxidation degradation. Derived from the superior stability and reusability of Mo₂C/C, the removal rate of CBZ still maintained above 80% even after five consecutive cycles, which is expected to be applied in the wastewater treatment including pharmaceuticals in the future.

Contemporary Techniques for Remediating Endocrine-Disrupting Compounds in Various Water Sources: Advances in Treatment Methods and Their Limitations

Over the years, the persistent occurrence of superfluous endocrine-disrupting compounds (EDCs) (sub µg L⁻¹) in water has led to serious health disorders in human and aquatic lives, as well as undermined the water quality. At present, there are no generally accepted regulatory discharge limits for the EDCs to avert their possible negative impacts. Moreover, the conventional treatment processes have reportedly failed to remove the persistent EDC pollutants, and this has led researchers to develop alternative treatment methods. Comprehensive information on the recent advances in the existing novel treatment processes and their peculiar limitations is still lacking. In this regard, the various treatment methods for the removal of EDCs are critically studied and reported in this paper. Initially, the occurrences of the EDCs and their attributed effects on humans, aquatic life, and wildlife are systematically reviewed, as well as the applied treatments. The most noticeable advances in the treatment methods include adsorption, catalytic degradation, ozonation, membrane separation, and advanced oxidation processes (AOP), as well as hybrid processes. The recent advances in the treatment technologies available for the elimination of EDCs from various water resources alongside with their associated drawbacks are discussed critically. Besides, the application of hybrid adsorption–membrane treatment using several novel nano-precursors is carefully reviewed. The operating factors influencing the EDCs’ remediations via adsorption is also briefly examined. Interestingly, research findings have indicated that some of the contemporary techniques could achieve more than 99% EDCs removal.

Advanced Oxidation Processes for Water and Wastewater Viral Disinfection. A Systematic Review

Water and wastewater virological quality is a significant public health issue. Viral agents include emerging and re-emerging pathogens characterized by extremely small size, and high environmental stability. Since the mainly used conventional disinfection methods are usually not able to achieve complete disinfection of viral and other microbial targets, in real water and wastewater matrices, effective strategies for the treatment, use and reuse of water and the development of next-generation water supply systems are required. The scope of the present systematic review was to summarize research data on the application of advanced oxidation processes (AOPs) for viral disinfection of water and wastewater. A literature survey was conducted using the electronic databases PubMed, Scopus, and Web of Science. This comprehensive research yielded 23 records which met the criteria and were included and discussed in this review. Most of the studies (14/23) used only MS2 bacteriophage as an index virus, while the remaining studies (9/23) used two or more viral targets, including phages (MS2, T4, T7, phiX174, PRD-1, S2, ϕB124-14, ϕcrAssphage) and/or Adenovirus, Aichivirus, Norovirus (I, II, IV), Polyomavirus (JC and BK), Sapovirus, Enterovirus, Coxsackievirus B3, Echovirus, and Pepper mild mottle virus. The vast majority of the studies applied a combination of two or more treatments and the most frequently used process was ultraviolet light-hydrogen peroxide (UV/H₂O₂) advanced oxidation. The review is expected to highlight the potential of the AOPs for public health protection from the waterborne viral exposure.

Removal of a reactive dye from simulated textile wastewater by environmentally friendly oxidant calcium peroxide

In the present study, calcium peroxide (CaO2) was used separately for potential application as an environmentally friendly and low-cost oxidant for the removal of a textile dye ‘Reactive Black 5’ (RB5) from simulated textile wastewater containing auxiliary chemicals of textile production. The specific morphology, elemental analysis, particle size distribution, specific surface area, identification of crystalline phases and surface functional groups of the synthesized CaO2 were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX), laser diffraction (LD), Brunaure–Emmett–Teller method (BET), X-ray diffraction (XRD) and Fourier transmission infrared (FTIR), respectively. X-ray Diffraction analysis confirmed the synthesized oxidant as CaO2 with the tetragonal crystalline structure. The signal corresponded to a bending vibration of O–Ca–O was detected in the fingerprint region of the FTIR spectroscopy. The effects of various independent parameters such as contact time, pH, initial RB5 concentration and CaO2 dosage on decolorization were investigated. The results of the study showed that pH, initial dye concentration and the CaO2 amounts have significant effects on removal of the RB5. The optimum pH was determined 7 for the removal of RB5 by CaO2. 2.0 g CaO2 was found to be sufficient for the removal of 300 mg/L RB5 with 96.93% removal efficiency. Also 82.8% chemical oxygen demand (COD) removal efficiency from simulated textile wastewater (STW) was obtained by 2.0 g CaO2. The results of the present study showed that the CaO2 can be used as an environmentally friendly and low-cost oxidant for effective removal of reactive textile dyes.

K2S2O8 activation by glucose at room temperature for the synthesis and functionalization of heterocycles in water

While persulfate activation at room temperature using glucose has primarily been focused on kinetic studies of the sulfate radical anion, the utilization of this protocol in organic synthesis is rarely demonstrated. We reinvestigated selected K₂S₂O₈-mediated known organic reactions that invariably require higher temperatures and an organic solvent. A diverse, mild functionalization and synthesis of heterocycles using the inexpensive oxidant K₂S₂O₈ in water at room temperature is reported, demonstrating the sustainability and broad scope of the method. Unlike traditional methods used for persulfate activation, the current method uses naturally abundant glucose as a K₂S₂O₈ activator, avoiding the use of higher temperature, UV light, transition metals or bases.

Copper-promoted direct amidation of isoindolinone scaffolds by sodium persulfate

Isoindolinones are ubiquitous structural motifs in natural products and pharmaceuticals. Establishing an efficient method for structural modification of isoindolinones could significantly facilitate new drug development. Herein, we describe copper-promoted direct amidation of isoindolinone scaffolds mediated by sodium persulfate. The method exhibits mild reaction conditions and high site-selectivity, and enables the structural modification of the drug indobufen ester with various amides with yields of 49 to 98%. It is also gram-scalable. Additionally, the reaction mechanism appears to involve a radical and a carbocationic pathway.

Insight into sludge dewatering by advanced oxidation using persulfate as oxidant and Fe2+ as activator: Performance, mechanism and extracellular polymers and heavy metals behaviors

This study established a Fe²⁺/persulfate oxidation system to dewater sludge in WWTPs. Dewatering performance, persulfate consumption and the variations of sludge pH, TN and TP during dewatering process were monitored. EPS and ζ-potential behaviors for ameliorating sludge dewatering was investigated. Transformation, leaching toxicity and environmental risk of heavy metals in sludge during dewatering were determined. Results demonstrated that after treated by Fe²⁺/persulfate oxidation system with 0.6 mmol/g-VS of persulfate at Fe²⁺/persulfate molar ratio 0.6, WC decreased to 53.5% and SCST increased to 4.15, which implied an excellent improvement of sludge dewatering. The fast persulfate consumption, the decrease of sludge pH and the increase of TN illustrated the positive effects of Fe²⁺ in activating persulfate and the decomposition of EPS by the activation products, SO₄^•- and ^•OH. Another product (Fe³⁺) generated during persulfate activation could decrease the content of phosphorus-containing matter (released from EPS decomposition) through the precipitation reaction with PO₄^3-. The decrease of TOC and UV-254 happened in HPO-A, HPO-N and TPI-A organic substance of EPS (mainly contained in TB-EPS fraction) indicated that the destruction of hydrophobic organic matter of EPS would stimulate the release of bound water, which was beneficial to dewater sludge. The largest protein loss in TB-EPS (from 24.5 to 10.7 mg/L) indicated that the effective decomposition of TB-EPS could significantly ameliorate sludge dewatering. The increase of ζ-potential indicated the degradation of organic matter in EPS with negative charge. To sum up, the destruction of protein-like substances in hydrophobic organic matter of TB-EPS was the main mechanism for improving sludge dewatering by Fe²⁺/persulfate oxidation system. 3D-EEM fluorescence spectroscopy analysis proved that these protein-like substances were mainly tryptophan protein and humic acid. Moreover, due to the disruption of EPS, the contents of heavy metals in sludge, and their leaching toxicity and environmental risk were reduced. Therefore, Fe²⁺/persulfate oxidation system has potential and application prospects to improve sludge dewatering and optimize sludge management in WWTPs.

Recent advances in cobalt-activated sulfate radical-based advanced oxidation processes for water remediation: A review

Sulfate radical-based advanced oxidation processes (SR-AOPs) have attracted increasing attention for the degradation of organic contaminants in water. The oxidants of SR-AOPs could be activated to generate different kinds of reactive oxygen species (ROS, e.g., hydroxyl radicals (OH), sulfate radicals (SO₄^-), singlet oxygen (¹O₂), and superoxide radicals (O₂^-)) by various catalysts. As one of the promising catalysts, cobalt-based catalysts have been extensively investigated in catalytic activity and stability during water remediation. This article mainly summarizes recent advances in preparation and applications of cobalt-based catalysts on peroxydisulfate (PDS)/peroxymonosulfate (PMS) activation since 2016. The review covers the development of homogeneous cobalt ions, cobalt oxides, supported cobalt composites, and cobalt-based mixed metal oxides for PDS/PMS activation, especially for the latest nanocomposites such as cobalt-based metal-organic frameworks and single-atom catalysts. This article also discussed the activation mechanisms and the influencing factors of different cobalt-based catalysts for activating PDS/PMS. Finally, the future perspectives on the challenges and applications of cobalt-based catalysts are presented at the end of this paper.

Degradation of petroleum hydrocarbons in soil via advanced oxidation process using peroxymonosulfate activated by nanoscale zero-valent iron

Recently, the use of nanoscale zero-valent iron (nZVI) for removal of organic contaminants from aqueous and soil system has increased. In this study, we employ nZVI to activate peroxymonosulfate (PMS) for the degradation of total petroleum hydrocarbons (TPHs) in aged diesel-contaminated soil. Upon PMS activation by nZVI, PMS produces more highly reactive oxygen species (ROS) in both aqueous solution and soil compared to other compounds (PMS/Co(II)), as determined by electron paramagnetic resonance spectroscopy. Thus, nZVI is an effective catalyst for PMS activation, leading to the efficient degradation of diesel oil in soil compared to other catalysts and oxidants. The optimal concentrations of PMS and nZVI were found to be 3 and 0.2%, respectively, showing the best degradation efficiency (61.2% in 2 h). The observed TPH degradation was retarded (up to 19.1-37% efficiency) in the presence of radical scavengers, such as tert-butyl alcohol, nitrobenzene, ethyl alcohol, and isopropyl alcohol. These results also demonstrate that ROS (hydroxyl and sulfate free radicals) are generated via PMS activation by nZVI. Moreover, more than 96% of TPH can be degraded by sequential applications of PMS/nZVI. Factors affecting TPH degradation, namely PMS/nZVI concentration, soil:solution ratio, soil pH, activators, and oxidants, are also analyzed. The results demonstrate that TPH is degraded to below the residential soil quality limit using PMS/nZVI based on the advanced oxidation process (AOP), which is therefore an effective option for chemical remediation of diesel-contaminated soils over a wide range of pH.

Supported cuprous oxide-clinoptilolite nanoparticles: Brief identification and the catalytic kinetics in the photodegradation of dichloroaniline

The supported CuO onto the ball-mill prepared clinoptilolite nanoparticles (CNPs) was prepared via an ion exchange process in Cu(II) aqueous solution followed by the calcination process. The CuO-CNP samples with various CuO loading were briefly characterized by XRD, FTIR, and DRS. pHpzc was varied in the range of 6.3 to 6.8 depending on the amount of loaded CuO in the samples. The band gap energy was estimated by applying the Kubelka-Munk equation on the DRS results that varied from 2.41 to 2.50 eV depending on the CuO loading. Based on the Scherrer equation nano-sized CuO-CNP at about 50 nm was estimated. The CuO-CNP contained 3.9% CuO showed the highest photocatalytic activity toward dichloroaniline (DCA). The effects of the experimental variables on DCA photodegradation were studied by using the Hinshelwood model. The optimal conditions for obtaining a higher rate for DCA photodegradation were the catalyst dose of 0.5 g/L, C_DCA: 5 ppm, and the initial pH: 3. HPLC analysis of the photodegraded DCA solutions for 180 and 300 min gave the degradation extents 71% and 90%, respectively.

Catalyst-Free and Transition-Metal-Free Approach to 1,2-Diketones via Aerobic Alkyne Oxidation

A catalyst-free and transition-metal-free method for the synthesis of 1,2-diketones from aerobic alkyne oxidation was reported. The oxidation of various internal alkynes, especially more challenging aryl-alkyl acetylenes, proceeded smoothly with inexpensive, easily handled, and commercially available potassium persulfate and an ambient air balloon, achieving the corresponding 1,2-diketones with up to 85% yields. Meanwhile, mechanistic studies indicated a radical process, and the two oxygen atoms in the 1,2-diketons were most likely from persulfate salts and molecular oxygen, respectively, rather than water.

Contrasting hydrogen peroxide- and persulfate-driven oxidation systems: Impact of radical scavenging on treatment efficiency and cost

For the first time, the fate of radicals generated in heterogeneous chemical oxidation treatment systems has been accounted for and used to assess treatment performance in three reaction compartments; reaction with the target compound, rhodamine B (RhB), the aqueous phase scavengers, and the solid phase scavengers. Radicals formed during the ultra-violet (UV) activation of hydrogen peroxide (H₂O₂) (UV-AHP) and persulfate (S₂O₈ ^2-) (UV-APS) include hydroxyl (•OH) and sulfate radicals (SO₄ ^•-), respectively. •OH and SO₄ ^•-, used in oxidation treatment systems to degrade a broad spectrum of environmental contaminants, may also react with non-target chemical species (scavengers) that limit treatment efficiency. UV-AHP and UV-APS treatment systems were amended with solid phase alumina to assess scavenging by solid surfaces. The overall rate of reaction and rate of radical scavenging was greater for •OH than SO₄ ^•-. Scavenging by dissolved constituents was dominated by the oxidant used (H₂O₂, S₂O₈ ^2-); and the rate of radical scavenging by alumina was greater than the rate of RhB oxidation in all cases. Treatment efficiency was lower in the UV-AHP than in the UV-APS treatment system and was attributed to greater aqueous and solid phase scavenging rates. The cost of commercially available H₂O₂ ($0.031 mol^-1) and PS ($0.24 mol^-1) was used in conjunction with the overall treatment efficiency to assess specific cost of treatment. The specific cost to treat the probe compound with UV-AHP was greater than UV-APS and was attributed to the much lower treatment efficiency with UV-AHP. The much-desired high reaction rate constants between •OH and environmental contaminants, relative to SO₄ ^•-, may come at the cost of greater combined scavenging rates, and consequently lower treatment efficiency.

Metal free decarboxylative aminoxylation of carboxylic acids using a biphasic solvent system

The smooth oxidative radical decarboxylation of carboxylic acids with TEMPO and other derivatives as radical scavengers is reported. The key to success was the use of a two-phase solvent system to avoid otherwise predominant side reactions such as the oxidation of TEMPO by persulfate and enabled the selective formation of synthetically useful alkoxyamines. The method does not require transition metals and was successfully used in a new synthetic approach for the antidepressant indatraline.

Natural clay minerals and fly ash waste as green catalysts for heterogeneous photo-Fenton reactions

This review highlights recent advances in the use of natural clay minerals and fly ash waste as efficient catalysts for the heterogeneous photo-Fenton degradation of emerging contaminants.

Photocatalytic Degradation of Polyamide 66; Evaluating the Feasibility of Photocatalysis as a Microfibre-Targeting Technology

Wastewater treatment plants (WWTPs) have been identified as main contributors to releasing microfibres into the environment, however, WWTPs do not have microfibre-targeting technologies. In this study, photocatalysis is evaluated as a potential technology to treat microfibres in WWTPs by studying the degradation of polyamide 66 (PA66) microfibres using ultraviolet (UV) and titanium dioxide (TiO2). PA66 microfibres suspended in deionised water were exposed to different combinations of UV and TiO2. The degradation of the PA66 microfibres was monitored by changes in mass, carbonyl index and morphology using microbalance, infrared spectroscopy, and scanning electron microscopy. The formation of by-products from the degradation of the fibres was evaluated by measuring the chemical oxygen demand (COD) of the treated water. The degradation efficiency was optimised under UVC with a dose of 100 mg TiO2/L. Under these conditions, the PA66 microfibres presented a 97% mass loss within 48 h. The photocatalytic conditions applied generated a relatively low level of by-products (<10 mg/L of COD). Therefore, photocatalysis with TiO2 an UVC could potentially be a feasible technology to treat microfibres in WWTPs, although more investigation is required to establish if this treatment leads to the formation of nanofibres. Further work is needed to translate the present optimised conditions to WWTPs.

Removal of benzo(a)pyrene in polluted aqueous solution and soil using persulfate activated by corn straw biochar

An activator, corn straw biochar, was produced and applied in persulfate-based oxidation to remove benzo(a)pyrene (BaP) in polluted aqueous solution and soil. Polluted aqueous solution remediation results showed that at pH 7, approximately 88.4% of BaP was removed by 10 mM of persulfate activated by 1.6 g/L of biochar, and degradation played a dominant role. Polluted soil remediation results demonstrated that the activated persulfate solution (at 9 g/L) by biochar (at 3 wt% of soil) can remove 93.2% of BaP. In remediation of BaP-polluted soil, increasing biochar dosage and persulfate concentration accelerated BaP degradation to some extent, while excessive biochar or persulfate inhibited the degradation of BaP probably due to the unnecessary SO₄^- consumption. The biochar-activated persulfate oxidation reflected a good performance in tolerating the influences of background electrolytes (such as HCO₃^-, Cl^-, and humic acid (HA)) in soil on BaP remediation. In addition, in the removal of BaP by the oxidation systems activated by biochar, persulfate was proved as a superior oxidant compared to peroxymonosulfate and H₂O₂, and the removal efficiencies of BaP were 93.2%, 86.5%, and 84.4% under the same treatment condition. To sum up, the biochar-activated persulfate oxidation would be a potential application in remediation of BaP-polluted aqueous solution and soil.

Membrane-Based Processes Used in Municipal Wastewater Treatment for Water Reuse: State-Of-The-Art and Performance Analysis

Wastewater reuse as a sustainable, reliable and energy recovery concept is a promising approach to alleviate worldwide water scarcity. However, the water reuse market needs to be developed with long-term efforts because only less than 4% of the total wastewater worldwide has been treated for water reuse at present. In addition, the reclaimed water should fulfill the criteria of health safety, appearance, environmental acceptance and economic feasibility based on their local water reuse guidelines. Moreover, municipal wastewater as an alternative water resource for non-potable or potable reuse, has been widely treated by various membrane-based treatment processes for reuse applications. By collecting lab-scale and pilot-scale reuse cases as much as possible, this review aims to provide a comprehensive summary of the membrane-based treatment processes, mainly focused on the hydraulic filtration performance, contaminants removal capacity, reuse purpose, fouling resistance potential, resource recovery and energy consumption. The advances and limitations of different membrane-based processes alone or coupled with other possible processes such as disinfection processes and advanced oxidation processes, are also highlighted. Challenges still facing membrane-based technologies for water reuse applications, including institutional barriers, financial allocation and public perception, are stated as areas in need of further research and development.

Treatability studies of naphthalene in soil, water and air with persulfate activated by iron(II)

Chemical oxidation was applied to an artificially contaminated soil with naphthalene (NAP). Evaluation of NAP distribution and mass reduction in soil, water and air phases was carried out through mass balance. Evaluation of NAP distribution and mass reduction in soil, water and air phases was carried out through mass balance. The importance of the air phase analysis was emphasized by demonstrating how NAP behaves in a sealed system over a 4 hr reaction period. Design of Experiments method was applied to the following variables: sodium persulfate concentration [SP], ferrous sulfate concentration [FeSO₄], and pH. The system operated with a prefixed solid to liquid ratio of 1:2. The following conditions resulted in optimum NAP removal [SP] = 18.37 g/L, [FeSO₄] = 4.25 g/L and pH = 3.00. At the end of the 4 hr reaction, 62% of NAP was degraded. In the soil phase, the chemical oxidation reduced the NAP concentration thus achieving levels which comply with Brazilian and USA environmental legislations. Besides the NAP partitioning view, the monitoring of each phase allowed the variabilities assessment over the process, refining the knowledge of mass reduction. Based on NAP distribution in the system, this study demonstrates the importance of evaluating the presence of semi-volatile and volatile organic compounds in the air phase during remediation, so that there is greater control of the system as to the distribution and presence of the contaminant in the environment. The results highlight the importance of treating the contaminant in all its phases at the contaminated site.

Degradation behaviors of naproxen by a hybrid TiO2 photocatalyst system with process components

A hybrid system combining microwave and a microwave discharge electrodeless lamp (MDEL) was proposed to overcome the limitations of conventional TiO₂ photocatalysts. The degradation efficiency and mechanism of naproxen were determined using a series of single processes, including conventional TiO₂ photocatalyst reactors and a hybrid system that fuses them. Although the degradation efficiency tended to increase after changing the experimental condition of a single process, the optimal conditions existed for these experimental conditions. On the other hand, remarkable synergy was observed in the fused process, whose efficiency was significantly higher than that of the unit process. In particular, the optimal degradation ability was obtained by adding hydrogen peroxide together with microwave irradiation. The seven intermediates in the proposed photocatalytic degradation pathway were generated by the demethylation and hydroxylation by hydroxyl radicals. These results are expected to provide new data on the design of high efficiency photocatalytic systems at low cost.

Activated persulfate by iron-based materials used for refractory organics degradation: a review

Recently, the advanced oxidation processes (AOPs) based on sulfate radicals (SRs) for organics degradation have become the focus of water treatment research as the oxidation ability of SRs are higher than that of hydroxyl radicals (HRs). Since the AOP-SRs can effectively mineralize organics into carbon dioxide and water under the optimized operating conditions, they are used in the degradation of refractory organics such as dyes, pesticides, pharmaceuticals, and industrial additives. SRs can be produced by activating persulfate (PS) with ultraviolet, heat, ultrasound, microwave, transition metals, and carbon. The activation of PS in iron-based transition metals is widely studied because iron is an environmentally friendly and inexpensive material. This article reviews the mechanism and application of several iron-based materials, including ferrous iron (Fe²⁺), ferric iron (Fe³⁺), zero-valent iron (Fe⁰), nano-sized zero-valent iron (nFe⁰), materials-supported nFe⁰, and iron-containing compounds for PS activation to degrade refractory organics. In addition, the current challenges and perspectives of the practical application of PS activated by iron-based systems in wastewater treatment are analyzed and prospected.

Superhydrophilic graphene oxide/electrospun cellulose nanofibre for efficient adsorption of organophosphorus pesticides from environmental samples

Superhydrophilic graphene oxide/electrospun cellulose nanofibre (GO/CNF) was synthesized, characterized and successfully used in a solid-phase membrane tip adsorption (SPMTA) as an adsorbent towards a simultaneous analysis of polar organophosphorus pesticides (OPPs) in several food and water samples. Separation, determination and quantification were achieved prior to ultra-performance liquid chromatography coupled with ultraviolet detector. The influence of several parameters such as sample pH, adsorption time, adsorbent dosage and initial concentration were investigated. SPMTA was linear in the range of 0.05 and 10 mg l^-1 under the optimum adsorption conditions (sample pH 12; 5 mg of adsorbent dosage; 15 min of adsorption time) for methyl parathion, ethoprophos, sulfotepp and chlorpyrifos with excellent correlation coefficients of 0.994-0.999. Acceptable precision (RSDs) as achieved for intraday (0.06-5.44%, n = 3) and interday (0.17-7.76%, n = 3) analyses. Low limits of detection (0.01-0.05 mg l^-1) and satisfactory consistency in adsorption (71.14-99.95%) were obtained for the spiked OPPs from Sungai Pahang, Tasik Cheras, cabbages and rice samples. The adsorption data were well followed the second-order kinetic model and fits the Freundlich adsorption model. The newly synthesized GO/CNF showed a great adsorbent potential for OPPs analysis.