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

Advanced oxidation coupled with LC-HRMS: Elucidating transformation products of linezolid, discovering in wastewaters and conducting in silico toxicity assessments

Antibiotics are prevalent in wastewater treatment plants and are subsequently released into aquatic environments, threatening aquatic organisms and compromising drinking water quality. Consequently, investigating their environmental fate and developing efficient removal processes is crucial. The degradation and fate of the antibiotic drug linezolid were investigated, focusing on the formation of transformation products (TPs). Various advanced oxidation processes, such as UV/S2O82-, UV/TiO2, Fe2+/S2O82- and UV/Fe2+/S2O82-, proved effective in eliminating linezolid within minutes. Liquid chromatography coupled to high-resolution mass spectrometry was employed to elucidate the photo-generated TPs and propose tentative transformation pathways. Overall, 28 TPs were identified, with 17 elucidated for the first time herein. The fluorophenyl and morpholine rings of the linezolid molecule were the main sites of attack, leading to two primary transformation routes: defluorination and hydroxylation. The predominant route varied with the treatment applied. In silico toxicity assessment indicated alarming toxicity for two TPs but decreased toxicity for most TPs compared to linezolid, suggesting the detoxification role of the treatments. However, concerning predictions emerged for the carcinogenicity, mutagenicity and biodegradability of linezolid and its TPs. Finally, a suspect screening analysis investigated the presence of TPs in wastewaters, revealing the occurrence of three TPs at notable levels, primarily in effluents.

Potential for nutrients reuse, carbon sequestration, and CO2 emissions reduction in the practice of domestic and industrial wastewater recycling into agricultural soils: A review

This review assesses the feasibility of reusing treated wastewater for irrigation in agricultural soils as a strategy for nutrients recycling and mitigation of CO2 emissions. Through a literature review, it was examined wastewater sources enriched with carbon and nutrients, including municipal wastewater and associated sludge, vinasse, swine wastewater, as well as wastewater from the food industry and paper and pulp production. The review also explores the dynamics of organic matter within the soil, discussing the aspects related to its potential conversion to CO2 or long-term storage. It was found that industrial wastewaters, owing to their higher organic matter and recalcitrance, exhibit greater potential for carbon storage. However, the presence of pollutants in wastewater necessitates careful consideration, particularly concerning their impact on soil quality. Toxic metals, microplastics, and organic compounds emerged as significant contaminants that could accumulate in the soil, posing risks to ecosystem health. To mitigate the environmental impacts, it was evaluated various wastewater treatment technologies and their associated carbon emissions. While advanced treatments may effectively reduce the contaminant load and mitigate soil impacts, their adoption is often associated with an increase in CO2 emissions. Membrane bioreactors, microfiltration, ultrafiltration, and up-flow anaerobic sludge blanket reactors were identified as promising technologies with lower carbon footprints. Looking ahead, future research should aim to enhance the understanding of carbon dynamics in soil and validate the environmental impacts of treated wastewater disposal. Despite remaining uncertainties, the literature indicates a positive outlook for wastewater recycling in soil, offering a viable strategy for carbon storage and mitigation of greenhouse gas emissions.

Performance improvement of triple-doped nanocomposite membrane towards hairwork dyeing effluent reclamation approaching zero liquid discharge

It is highly anticipated that efforts will be made to raise the level of industrial effluent reclamation on the background of continuously minimizing waste stream based on preconcentration tool. For this purpose, a triple-doped nanocomposite (TFN-tri) membrane through partially alternative doping spiro-structured 2,2'-dimethyl-1,1'-biphenyl-4,4'-diamine dihydrochloride and flexible 4,4'-bipiperidyl dihydrochloride and continuous incorporating of molybdenum disulfide quantum dots was successfully fabricated. With the assistance of self-synthesized biodegradable flocculant pretreatment, raw hairwork dyeing effluent (HDE) was stably recycled up to 95.1% on the premise of meeting the requirements of the relevant national standard. As a deep processing unit, TFN-tri membrane displayed accurate salt rejection of nearly 66% as expected. More impressively, it also exhibited permeability basically increased by 2.5 folds, while fouling layer thickness, running time and specific energy consumption decreased by 5 μm, 54.7% and 72.5%, respectively, than its counterpart in long-term reuse testing. These changes may mainly be due to the finely expand sub-nanopores coupled with an enhanced electrostatic exclusion and the improved fouling resistance brought about by other critical skin features in terms of smoothness and hydrophilicity optimization. In brief, this study has taken a vigorous and reliable step towards heavily polluted HDE reclamation approaching zero liquid discharge.

Olive mill wastewater treatment strategies to obtain quality water for irrigation: A review

The olive mill industry is a relevant sector in the economy of Mediterranean countries, while it involves high consumption of water and the production of effluents with high environmental impact. The efficient treatment of olive mill wastewater (OMW) is of high relevance, particularly for these countries. Climate changes are leading to increasing periods of droughts, and water recovery from polluted streams is essential to ensure the sustainability of this scarce resource. A combination of various technologies involving physical, chemical, and biological processes has been developed for OMW treatment. However, the treatments studied have limitations such as the operation costs, difficulty of industrial scale-up, and the fact that the vast majority do not lead to suitable treated water for discharge/reuse. As such, it is urgent to develop a solution capable of efficiently treating this effluent, overcoming the disadvantages of existing processes to convert OMW from a serious environmental problem into a valuable source of water and nutrients. In this review, several studies based on the OMW treatment are critically discussed, from conventional approaches such as the physical (e.g. centrifugation, filtration, and adsorption) and biological (anaerobic digestion and anaerobic co-digestion) processes, to the most recent technologies such as advanced membrane filtration, advanced oxidation processes (AOPs) and sulfate radical based AOPs (SR-AOPs). Due to the complexity of the effluent, OMW cannot be efficiently treated by a single process, requiring a sequence of technologies before reaching the required characteristics for discharge into water courses or use in crop irrigation. Reviewing the published results in this matter, it seems that the sequence of processes encompassing ozonation, anaerobic digestion, and SR-AOPs could be the ideal combination for this purpose. However, membrane technologies may be necessary in the final stage of treatment so that the effluent meets legal discharge or irrigation limits.

Preparation of Cobalt-Nitrogen Co-Doped Carbon Nanotubes for Activated Peroxymonosulfate Degradation of Carbamazepine

Cobalt-nitrogen co-doped carbon nanotubes (Co3@NCNT-800) were synthesized via a facile and economical approach to investigate the efficient degradation of organic pollutants in aqueous environments. This material demonstrated high catalytic efficiency in the degradation of carbamazepine (CBZ) in the presence of peroxymonosulfate (PMS). The experimental data revealed that at a neutral pH of 7 and an initial CBZ concentration of 20 mg/L, the application of Co3@NCNT-800 at 0.2 g/L facilitated a degradation rate of 64.7% within 60 min. Mechanistic investigations indicated that the presence of pyridinic nitrogen and cobalt species enhanced the generation of reactive oxygen species. Radical scavenging assays and electron spin resonance spectroscopy confirmed that radical and nonradical pathways contributed to CBZ degradation, with the nonradical mechanism being predominant. This research presents the development of a novel PMS catalyst, synthesized through an efficient and stable method, which provides a cost-effective solution for the remediation of organic contaminants in water.

Solar photo-Fenton and persulphate-based processes for landfill leachate treatment: A critical review

Landfilling is the most usual solid waste management strategy for solid residues disposal. However, it entails several drawbacks such as the generation of landfill leachate that seriously threaten human life and the environment due to their toxicity and carcinogenic character. Among various technologies, solar photo-Fenton and sulphate-based processes have proven to be suitable for the treatment of these polluted streams. This review critically summarises the last three decades of studies in this field. It is found that the solar homogeneous photo-Fenton process should be preferably used as a pre- and post-treatment of biological technologies and as a standalone treatment for young, medium, and mature leachates, respectively. Studies on heterogeneous solar photo-Fenton process are lacking so that this technology may be scaled-up for industrial applications. Sulphate radicals are attractive for removing both COD and ammonia. However, no study has been reported on solar sulphate activation for landfill leachate treatment. This review discusses the main advances and challenges on treating landfill leachate through solar AOPs, it compares solar photo-Fenton and solar persulphate-based treatments, indicates the future research directions and contributes for a better understanding of these technologies towards sustainable treatment of landfill leachate in sunny and not-so-sunny regions.

Recent advances in eco-friendly technology for decontamination of pulp and paper mill industrial effluent: a review

The economic development of a country directly depends upon industries. But this economic development should not be at the cost of our natural environment. A substantial amount of water is spent during paper production, creating water scarcity and generating wastewater. Therefore, the Pollution Control Board classifies this industry into red category. Water is used in different papermaking stages such as debarking, pulping or bleaching, washing, and finishing. The wastewater thus generated contains lignin and xenobiotic compounds such as resin acids, chlorinated lignin, phenols, furans, dioxins, chlorophenols, adsorbable organic halogens (AOX), extractable organic halogens (EOCs), polychlorinated biphenyls, plasticizers, and polychlorinated dibenzodioxins. Nowadays, several microorganisms are used in the detoxification of these hazardous effluents. Researchers have found that microbial degradation is the most promising treatment method to remove high biological oxygen demand (BOD) and chemical oxygen demand (COD) from wastewater. Microorganisms also remove AOX toxicity, chlorinated compounds, suspended solids, color, lignin, derivatives, etc. from the pulp and paper mill effluents. But in the current scenario, mill effluents are known to deteriorate the environment and therefore it is highly desirable to deploy advanced technologies for effluent treatment. This review summarizes the eco-friendly advanced treatment technologies for effluents generated from pulp and paper mills.

Comparative study of Fe2+/H2O2 and Fe2+/persulfate systems on the pre-treatment process of real pharmaceutical wastewater

Advanced oxidation technologies based on hydroxyl radical (•OH) and sulfate radical (SO4-•) are two common types of advanced oxidation technologies, but there are not many reports on the application of advanced oxidation methods in actual wastewater pretreatment. This article compares the pre-treatment performance of Fe2+/H2O2 and Fe2+/Persulfate systems in actual pharmaceutical wastewater, and combines EEM, GC-MS, and toxicity testing results to explore the differences in TOC, COD, and NH3-N removal rates, optimal catalyst dosage, applicable pH range, toxicity of effluent after reaction, and pollutant structure between the two systems. The results indicate that the Fe2+/H2O2 system has a higher pollutant removal rate (TOC: 71.9%, COD: 66.9%, NH3-N: 34.1%), but also requires a higher catalyst (Fe2+) concentration (6.0 g/L), and its effluent exhibits characteristic peaks of aromatic proteins. The Fe2+/Persulfate system has a wider pH range (pH ≈ 3-7) and is more advantageous in treating wastewater containing more cyclic organic compounds, but the effluent contains some sulfur-containing compounds. In addition, toxicity tests have shown that the toxicity reduction effect of the Fe2+/Persulfate system is stronger than that of the Fe2+/H2O2 system.

Sulfadiazine removal efficiency with persulfate driven by electron-rich Cu-beta zeolites

Surface electron transport and transfer of catalysts have important consequences for persulfate (PS) activation in PS system. In this paper, an electron-rich Cu-beta zeolites catalyst was synthesized utilizing a straightforward solid-state ion exchange technique to efficiently degrade sulfadiazine. The X-ray diffraction (XRD) and fourier transform infrared spectroscopy (FTIR) results revealed that Cu element substitutes Al element and enters the beta molecular sieve framework smoothly. Furthermore, the X-ray photoelectron spectroscopy (XPS) measurements demonstrated that the Cu-beta catalyst is primarily Cu0. Cu-beta zeolites catalyst can exhibit excellent catalytic activity to degrade sulfadiazine with the oxidant of PS. The optimal sulfadiazine removal performance was explored by adjusting reaction parameters, including sulfadiazine concentration, catalyst dosage, oxidant dosage, and solution pH. The sulfadiazine removal efficiency in the Cu-beta zeolites/PS system could reach 90.5% at the optimal reaction condition ([PS]0 = 0.5 g/L, [Cu-beta zeolites]0 = 1.0 g/L, pH = 7.0) with 50 mg/L of sulfadiazine. Meanwhile, The degradation efficiency was less affected by anionic interference (Cl-, SO4-, HCO3-). The surface electron transport and transfer of the Cu-beta zeolites catalyst were significant causes for the remarkable degradation performance. According to electron paramagnetic resonance (EPR) and quenching studies, the Cu-beta zeolites/PS system was mostly dominated by SO4•- in the degradation of sulfadiazine. Furthermore, two possible pathways for sulfadiazine degradation were proposed according to the analysis of intermediate products detected by the liquid chromatography-mass spectrometry (LC-MS).

Alternative treatment of olive mill wastewater by combined sulfate radical-based advanced electrocoagulation processes

The aim of this study is to investigate the performance of advanced electrocoagulation (EC) process for the treatment of olive mill wastewater. In EC process, iron plates were used as electrodes, and peroxydisulfate (PS) and peroxymonosulfate (PMS) were added as oxidants. The effects of the initial pH value, current density, oxidant dose, and electrolysis time were optimized for pollutant removal from olive mill wastewater by EC-PS and EC-PMS processes. Control experiments showed that addition of oxidants to the conventional EC process increased the pollutant removal efficiency. Classical optimization method was used to determine optimum conditions, which were initial pH 4, current density 40 mA/cm2 , oxidant dose 5 g/L, and electrolysis time 30 min for both processes. Under these conditions, EC-PS and EC-PMS processes achieved 50.5% and 48.9% chemical oxygen demand (COD), 93.8% and 89.3% total phenol, 87.7% and 83% UV254 , and 74.5% and 64.1% total suspended solid removal efficiencies. Quenching experiments were performed to determine the dominant radical species participating in the processes. It was observed that hydroxyl and sulfate radicals were involved in both processes but hydroxyl radicals were more active. Specific energy consumption was calculated as 5.90 kWh/kg COD for EC process, 4.95 kWh/kg COD for EC-PS process, and 5.20 kWh/kg COD for EC-PMS process. The organic removal/sludge ratio of EC-PS process was found to be higher with 17.5 g/L value. Although the application of EC-PS and EC-PMS processes alone is insufficient to meet the discharge limits, they have been found to be effective in olive mill wastewater treatment. PRACTITIONER POINTS: Peroxydisulfate (PS) and peroxymonosulfate (PMS)-based advanced electrocoagulation (EC) was used in olive mill wastewater treatment. 50.5% chemical oxygen demand (COD), 93.8% TP, 87.7% UV254 , and 74.5% TSS removals were achieved by EC-PS. 48.9% COD, 89.3% TP, 83% UV254 , and 64.1% TSS removals were obtained by EC-PMS. Hydroxyl and sulfate radicals were involved in both processes.

Catalytic degradation of crystal violet and methyl orange in heterogeneous Fenton-like processes

Metals-loaded (Fe3+, Cu2+ and Zn2+) activated carbons (M@AC) with different loading ratios (0.1%, 0.5%, 1%, 5% and 10%) were prepared and employed for catalytic degradation of dye model compounds (crystal violet (CV) and methyl orange (MO)) in wastewater by heterogeneous Fenton-like technique. Compared with Cu@AC and Zn@AC, 0.5% Fe3+ loaded AC (0.5Fe@AC) had better catalytic activity for dyes degradation. The effects of dyes initial concentration, catalyst dosage, pH and hydrogen peroxide (H2O2) volume on the catalytic degradation process were investigated. Cyclic performance, stability of 0.5Fe@AC and iron leaching were explored. Degradation kinetics were well fitted to the pseudo-second-order model (Langmuir-Hinshelwood). Almost complete decolorization (99.7%) of 400 mg L-1 CV was achieved after 30 min reaction under the conditions of CV volume (30 mL), catalyst dosage (0.05 g), H2O2 volume (1 mL) and pH (7.7). Decolorization of MO reached 98.2% under the same conditions. The abilities of pyrolysis char (PC) of dyeing sludge (DS) and metal loaded carbon to remove dye pollutants were compared. The intermediate products were analyzed and the possible degradation pathway was proposed. This study provided an insight into catalytic degradation of triphenylmethane- and aromatic azo-based substances, and utilization of sludge char.

Prussian blue analogues-derived zero valent iron to efficiently activate peroxymonosulfate for phenol degradation triggered via reactive oxygen species and high-valent iron-oxo complexes

It is of great significance to develop the effective technique to treat phenol-containing wastewater. Herein, Fe-based prussian blue analogues-derived zero valent iron (ZVI) was successfully synthesized by one-step calcination method. Owing to high specific surface area and rich active sites, ZVI-2 possessed excellent performance in charge transfer. Notably, in comparison with conventional ZVI and Fe2+, ZVI-2 can effectively activate peroxymonosulfate (PMS) for achieving rapid degradation of phenol, and the highest removal efficiency of phenol reached 94.9% within 24 min. More importantly, developed ZVI-2/PMS oxidation system with good stability displayed strong anti-interference capability. Interestingly, Fe0 loaded on the surface of ZVI-2 can efficiently break the O-O bond of PMS to generate reactive oxygen species (i.e., SO4•-, OH•, O2•- and 1O2). As main adsorption sites of PMS, the existence of oxygen vacancy promote the formation of high-valent transition metal complexes (namely ZVI-2≡Fe4+=O). Under the combined action of reactive oxygen species and ZVI-2≡Fe4+=O, phenol can be eventually degraded into CO2 and H2O. The possible degradation pathways of phenol were also investigated. Furthermore, proposed ZVI-2/PMS oxidation system displayed great potential for application in the field of wastewater treatment. All in all, current work provided a valuable reference for design and application of Fe-based catalysts in PS-AOPs.

Ultrasound-activated nanosonosensitizer for oxygen/sulfate dual-radical nanotherapy

An all-in-one therapy for cooperatively fighting cancer, infection and boosting wound repair is exceedingly demanded for patients with advanced superficial cancers or after surgical intervention to avoid multiple drug abuse and resultant adverse effects. Here, the ultrasound-activated nanosonosensitizer PHMP that integrated peroxymonosulfate (PMS) into the Pd-catalyzed hydrogenated mesoporous titanium dioxide (PHM) was dexterously designed for combined therapy of cancer and infected wound based on oxygen/sulfate dual-radical nanotherapy. Firstly, the PHM with single crystal structure and abundant oxygen deficiencies exhibited excellent ultrasound-excited reactive oxygen species (ROS) production for enhanced sonodynamic therapy (SDT) under the support of Pd nanozyme-mediated O2 supply. Simultaneously, the physically targeted ultrasound irradiation effectively transformed PMS loaded in the hollow cavities into distinct sulfate radical (•SO4-) with longer half-life and stronger oxidation, which remarkably enhanced the therapeutic efficacy of PHM-mediated SDT for cancer and bacteria. In addition, by embedding PHMP into the hydrogel, the enrichment of PHMP in the focal site was guaranteed, and meanwhile a moist and ventilated environment was created to speed up wound repair. The study broadens the potential of •SO4- in the therapeutic fields and contributes a simple and appealing tactic for the comprehensive treatment of cancer, infection and wound repair.

Remediation technologies for neonicotinoids in contaminated environments: Current state and future prospects

Neonicotinoids (NEOs) are synthetic insecticides with broad-spectrum insecticidal activity and outstanding efficacy. However, their extensive use and persistence in the environment have resulted in the accumulation and biomagnification of NEOs, posing significant risks to non-target organisms and humans. This review provides a summary of research history, advancements, and highlighted topics in NEOs remediation technologies and mechanisms. Various remediation approaches have been developed, including physiochemical, microbial, and phytoremediation, with microbial and physicochemical remediation being the most extensively studied. Recent advances in physiochemical remediation have led to the development of innovative adsorbents, photocatalysts, and optimized treatment processes. High-efficiency degrading strains with well-characterized metabolic pathways have been successfully isolated and cultured for microbial remediation, while many plant species have shown great potential for phytoremediation. However, significant challenges and gaps remain in this field. Future research should prioritize isolating, domesticating or engineering high efficiency, broad-spectrum microbial strains for NEO degradation, as well as developing synergistic remediation techniques to enhance removal efficiency on multiple NEOs with varying concentrations in different environmental media. Furthermore, a shift from pipe-end treatment to pollution prevention strategies is needed, including the development of green and economically efficient alternatives such as biological insecticides. Integrated remediation technologies and case-specific strategies that can be applied to practical remediation projects need to be developed, along with clarifying NEO degradation mechanisms to improve remediation efficiency. The successful implementation of these strategies will help reduce the negative impact of NEOs on the environment and human health.

Nitrilotriacetic acid-assisted Mn(II) activated periodate for rapid and long-lasting degradation of carbamazepine: The importance of Mn(IV)-oxo species

Periodate-based (PI, IO₄^-) oxidation processes for pollutant elimination have gained increased attention in recent years. This study shows that nitrilotriacetic acid (NTA) can assist trace Mn(II) in activating PI for fast and long-lasting degradation of carbamazepine (CBZ) (100% degradation in 2 min). PI can oxidize Mn(II) to permanganate(MnO₄^-, Mn(VII)) in the presence of NTA, which indicates the important role of transient manganese-oxo species. ¹⁸O isotope labeling experiments using methyl phenyl sulfoxide (PMSO) as a probe further confirmed the formation of manganese-oxo species. The chemical stoichiometric relationship (PI consumption: PMSO₂ generation) and theoretical calculation suggested that Mn(IV)-oxo-NTA species were the main reactive species. The NTA-chelated manganese facilitated direct oxygen transfer from PI to Mn(II)-NTA and prevented hydrolysis and agglomeration of transient manganese-oxo species. PI was transformed completely to stable and nontoxic iodate but not lower-valent toxic iodine species (i.e., HOI, I₂, and I^-). The degradation pathways and mechanisms of CBZ were investigated using mass spectrometry and density functional theory (DFT) calculation. This study provided a steady and highly efficient choice for the quick degradation of organic micropollutants and broadened the perspective on the evolution mechanism of manganese intermediates in the Mn(II)/NTA/PI system.

Enhanced Heterogeneous Peroxymonosulfate Activation by MOF-Derived Magnetic Carbonaceous Nanocomposite for Phenol Degradation

Degradation efficiency and catalyst stability are crucial issues in the control of organic compounds in wastewater by advanced oxidation processes (AOPs). However, it is difficult for catalysts used in AOPs to have both high catalytic activity and high stability. Combined with the excellent activity of cobalt/copper oxides and the good stability of carbon, highly dispersed cobalt-oxide and copper-oxide nanoparticles embedded in carbon-matrix composites (Co-Cu@C) were prepared for the catalytic activation of peroxymonosulfate (PMS). The catalysts exhibited a stable structure and excellent performance for complete phenol degradation (20 mg L-1) within 5 min in the Cu-Co@C-5/PMS system, as well as low metal-ion-leaching rates and great reusability. Moreover, a quenching test and an EPR analysis revealed that ·OH, O2·-, and 1O2 were generated in the Co-Cu@C/PMS system for phenol degradation. The possible mechanism for the radical and non-radical pathways in the activation of the PMS by the Co-Cu@C was proposed. The present study provides a new strategy with which to construct heterostructures for environmentally friendly and efficient PMS-activation catalysts.

La2CoO4+δ perovskite-mediated peroxymonosulfate activation for the efficient degradation of bisphenol A

Sulfate radical-based technology has been considered as an efficient technology to remove pharmaceuticals and personal care products (PPCPs) with heterogeneous metal-mediated catalysts for the activation of peroxymonosulfate (PMS). In this study, La₂CoO_4+δ perovskite with Ruddlesden-Popper type structure was synthesised by the sol-gel method, which was employed in PMS activation. Different characteriazation technologies were applied for the characterization of La₂CoO_4+δ , such as SEM-EDX, XRD, and XPS technologies. A common organic compound, bisphenol A (BPA), is used as a target contaminant, and the effect impactors were fully investigated and explained. The results showed that when the dosage of La₂CoO_4+δ was 0.5 g L^-1 and the concentration of PMS was 1.0 mM in neutral pH solution, about 91.1% degradation efficiency was achieved within 25 minutes. Quenching experiments were introduced in the system to verify the catalytic mechanism of PMS for the BPA degradation, proving the existence of superoxide, hydroxyl radicals and sulfate radicals, which are responsible for the catalytic degradation of BPA. Moreover, the reusability and stability of the catalyst were also conducted which showed good stability during the reaction. This work would improve the applications of A₂BO₄-type perovskites for activating PMS to degrade BPA.

An efficient removal approach for degradation of metformin from aqueous solutions with sulfate radicals

Metformin consumption for diabetes treatment is increasing, leading to its presence in wastewater treatment plants where conventional methods cannot remove it. Therefore, this work aims to analyze the performance of advanced oxidation processes using sulfate radicals in the degradation of metformin from water. Experiments were performed in a photoreactor provided with a low-pressure Hg lamp, using K₂S₂O₈ as oxidant and varying the initial metformin concentration (C_A0), oxidant concentration (C_ox), temperature (T), and pH in a response surface experimental design. The degradation percentages ranged from 26.1 to 87.3%, while the mineralization percentages varied between 15.1 and 64%. Analysis of variance (ANOVA) showed that the output variables were more significantly affected by C_A0, C_ox, and T. Besides, a reduction of C_A0 and an increase of C_ox up to 5000 μM maximizes the metformin degradation since the generation of radicals and their interaction with metformin molecules are favored. For the greatest degradation percentage, the first order apparent rate constant achieved was 0.084 min^-1. Furthermore, while in acidic pH, temperature benefits metformin degradation, an opposite behavior is obtained in a basic medium because of recombination and inhibition reactions. Moreover, three degradation pathways were suggested based on the six products detected by HPLC-MS: N-cyanoguanidine m/z = 85; N,N-dimethylurea m/z = 89; N,N-dimethyl-cyanamide m/z = 71 N,N-dimethyl-formamide m/z = 74; glicolonitrilo m/z = 58; and guanidine m/z = 60. Finally, it was shown that in general the toxicity of the degradation byproducts was lower than the toxicity of metformin toward Chlamydomonas reinhardtii.

One-pot synthesis of a cellulose-supported CoFe2O4 catalyst for the efficient degradation of sulfamethoxazole

Cellulose-supported cobalt ferrite (CoFe₂O₄/RC) was synthesized via a facile one-pot hydrothermal method and demonstrated to be an efficient catalyst to activate peroxymonosulfate (PMS) for the degradation of sulfamethoxazole (SMX). The characterizations of CoFe₂O₄/RC catalysts revealed that an appropriate particle size of the cellulose support could promote the dispersion of CoFe₂O₄ nanoparticles and consequently promote the catalytic activity of the resulting CoFe₂O₄/RC catalysts. The degradation of SMX reached 97.6 % within 20 min at 30 °C with the CoFe₂O₄/RC/PMS system. The mechanism of SMX degradation over CoFe₂O₄/RC-activated PMS was studied via EPR, XPS, and quenching tests. The results suggested that ¹O₂ was the dominant reactive oxygen species and was accompanied by SO₄^-, OH, and O₂^- radicals for SMX degradation. The CoFe₂O₄/RC catalyst exhibited high stability and recyclability and maintained high catalytic activity after five experimental cycles.