Degradation of emerging contaminant coumarin based on anodic oxidation, electro-Fenton and subcritical water oxidation processes

Optimization Strategy for Formaldehyde Removal by Carbon Cathode Electro-Fenton: Enhancement of Formaldehyde and Oxygen Co-adsorption by Rational Nitrogen Doping Types

This study investigates the effect of N-doped coal-based activated carbon cathode on formaldehyde-oxygen coadsorption. Further investigation investigates the effect of formaldehyde-oxygen coadsorption on H2O2 generation and formaldehyde removal in an electro-Fenton system. Nitrogen doping enhances formaldehyde and oxygen coadsorption by modulating competitive adsorption. Density Functional Theory (DFT) calculations confirm pyrrole nitrogen favors formaldehyde, and graphite nitrogen favors oxygen adsorption. N-doped activated carbon adsorbs 0.36 mg of formaldehyde and 0.1 mg of oxygen in 120 min and removes 82.43% of formaldehyde after electro-Fenton treatment. N-doped activated carbon enhances the synergistic adsorption of formaldehyde and oxygen. In the synergistic adsorption process, the amount of formaldehyde adsorbed is greater than the amount of oxygen adsorbed. This improves the removal efficiency of formaldehyde by electro-Fenton technology. It provides a new method for electro-Fenton removal of organic pollutants.

Tricks and tracks of prevalence, occurrences, treatment technologies, and challenges of mixtures of emerging contaminants in the environment: With special emphasis on microplastic

This paper aims to emphasize the occurrence of various emerging contaminant (EC) mixtures in natural ecosystems and highlights the primary concern arising from the unregulated release into soil and water, along with their impacts on human health. Emerging contaminant mixtures, including pharmaceuticals, personal care products, dioxins, polychlorinated biphenyls, pesticides, antibiotics, biocides, surfactants, phthalates, enteric viruses, and microplastics (MPs), are considered toxic contaminants with grave implications. MPs play a crucial role in transporting pollutants to aquatic and terrestrial ecosystems as they interact with the various components of the soil and water environments. This review summarizes that major emerging contaminants (ECs), like trimethoprim, diclofenac, sulfamethoxazole, and 17α-Ethinylestradiol, pose serious threats to public health and contribute to antimicrobial resistance. In addressing human health concerns and remediation techniques, this review critically evaluates conventional methods for removing ECs from complex matrices. The diverse physiochemical properties of surrounding environments facilitate the partitioning of ECs into sediments and other organic phases, resulting in carcinogenic, teratogenic, and estrogenic effects through active catalytic interactions and mechanisms mediated by aryl hydrocarbon receptors. The proactive toxicity of ECs mixture complexation and, in part, the yet-to-be-identified environmental mixtures of ECs represent a blind spot in current literature, necessitating conceptual frameworks for assessing the toxicity and risks with individual components and mixtures. Lastly, this review concludes with an in-depth exploration of future scopes, knowledge gaps, and challenges, emphasizing the need for a concerted effort in managing ECs and other organic pollutants.

A new strategy for improving the energy efficiency of electro-Fenton: Using N-doped activated carbon cathode with strong Fe(III) adsorption capacity to promote Fe(II) regeneration

Fe(II) regeneration plays a crucial role in the electro-Fenton process, significantly influencing the rate of ·OH formation. In this study, a method is proposed to improve Fe(II) regeneration through N-doping aimed at enhancing the adsorption capacity of the activated carbon cathode for Fe(III). N-doping not only enriched the pore structure on the surface of activated carbon, providing numerous adsorption sites, but also significantly increased the adsorption energy for Fe(III). Among the types of nitrogen introduced, pyridine-N exhibited the most substantial enhancement effect, followed by pyrrole-N, while graphite-N showed a certain degree of inhibition. Furthermore, N-doping facilitated the adsorption of all forms of Fe(III) by activated carbon. The adsorption and electrosorption rates of the NAC-900 electrode for Fe(III) were 30.33% and 42.36%, respectively. Such modification markedly enhanced the Fe3+/Fe2+ cycle within the electro-Fenton system. The NAC-900 system demonstrated an impressive phenol degradation efficiency of 93.67%, alongside the lowest electricity consumption attributed to the effective "adsorption-reduction" synergy for Fe(III) on the NAC-900 electrode. Compared to the AC cathode electro-Fenton system, the degradation efficiency of the NAC-900 cathode electro-Fenton system at pH = levels ranging from 3 to 5 exceeded 90%; thus, extending the pH applicability of the electro-Fenton process. The degradation efficiency of phenol using the NAC-900 cathode electro-Fenton system in various water matrices approached 90%, indicating robust performance in real wastewater treatment scenarios. This research elucidates the impact of cathodic Fe(III) adsorption on Fe(II) regeneration within the electro-Fenton system, and clarifies the influence of different N- doping types on the cathodic adsorption of Fe(III).

Combination of separation and degradation methods after PFAS soil washing

The current study evaluated a three-stage treatment to remediate PFAS-contaminated soil. The treatment consisted of soil washing, foam fractionation (FF), and electrochemical oxidation (EO). The possibility of replacing the third stage, i.e., EO, with an adsorption process was also assessed. The contamination in the studied soils was dominated by perfluorooctane sulfonate (PFOS), with a concentration of 760 and 19 μg kg-1 in soil I and in soil II, accounting for 97 % and 70 % of all detected per-and polyfluoroalkyl substances (PFAS). Before applying a pilot treatment of soil, soil washing was performed on a laboratory scale, to evaluate the effect of soil particle size, initial pH and a liquid-to-soil ratio (L/S) on the leachability of PFAS. A pilot washing system generated soil leachate that was subsequently treated using FF and EO (or adsorption) and then reused for soil washing. The results indicated that the leaching of PFAS occurred easier in 0.063-1 mm particles than in the soil particles having a size below 0.063 mm. Both alkaline conditions and a continual replacement of the leaching solution increased the leachability of PFAS. The analysis using one-way ANOVA showed no statistical difference in means of PFOS washed out in laboratory and pilot scales. This allowed estimating twenty washing cycles using 120 L water to reach 95 % PFOS removal in 60 kg soil. The aeration process removed 95-99 % PFOS in every washing cycle. The EO and adsorption processes achieved similar results removing up to 97 % PFOS in concentrated soil leachate. The current study demonstrated a multi-stage treatment as an effective and cost-efficient method to permanently clean up PFAS-contaminated soil.

Redundant and scattered genetic determinants for coumarin biodegradation in Pseudomonas sp. strain NyZ480

Coumarin (COU) is both a naturally derived phytotoxin and a synthetic pollutant which causes hepatotoxicity in susceptible humans. Microbes have potentials in COU biodegradation; however, its underlying genetic determinants remain unknown. Pseudomonas sp. strain NyZ480, a robust COU degrader, has been isolated and proven to grow on COU as its sole carbon source. In this study, five homologs of xenobiotic reductase A scattered throughout the chromosome of strain NyZ480 were identified, which catalyzed the conversion of COU to dihydrocoumarin (DHC) in vitro. Phylogenetic analysis indicated that these COU reductases belong to different subgroups of the old yellow enzyme family. Moreover, two hydrolases (CouB1 and CouB2) homologous to the 3,4-dihydrocoumarin hydrolase in the fluorene degradation were found to accelerate the generation of melilotic acid (MA) from DHC. CouC, a new member from the group A flavin monooxygenase, was heterologously expressed and purified, catalyzing the hydroxylation of MA to produce 3-(2,3-dihydroxyphenyl)propionate (DHPP). Gene deletion and complementation of couC indicated that couC played an essential role in the COU catabolism in strain NyZ480, considering that the genes involved in the downstream catabolism of DHPP have been characterized (Y. Xu and N. Y. Zhou, Appl Environ Microbiol 86:e02385-19, 2020) and homologous catabolic cluster exists in strain NyZ480. This study elucidated the genetic determinants for complete degradation of COU by Pseudomonas sp. strain NyZ480.IMPORTANCECoumarin (COU) is a phytochemical widely distributed in the plant kingdom and also artificially produced as an ingredient for personal care products. Hence, the environmental occurrence of COU has been reported in different places. Toxicologically, COU was proven hepatotoxic to individuals with mutations in the CYP2A6 gene and listed as a group 3 carcinogen by the International Agency for Research on Cancer and thus has raised increasing concerns. Until now, different physicochemical methods have been developed for the removal of COU, whereas their practical applications were hampered due to high cost and the risk of secondary contamination. In this study, genetic evidence and biochemical characterization of the COU degradation by Pseudomonas sp. strain NyZ480 are presented. With the gene and strain resources provided here, better managements of the hazards that humans face from COU could be achieved, and the possible microbiota-plant interaction mediated by the COU-utilizing rhizobacteria could also be investigated.

Rhodococcus Strains from the Specialized Collection of Alkanotrophs for Biodegradation of Aromatic Compounds

The ability to degrade aromatic hydrocarbons, including (i) benzene, toluene, o-xylene, naphthalene, anthracene, phenanthrene, benzo[a]anthracene, and benzo[a]pyrene; (ii) polar substituted derivatives of benzene, including phenol and aniline; (iii) N-heterocyclic compounds, including pyridine; 2-, 3-, and 4-picolines; 2- and 6-lutidine; 2- and 4-hydroxypyridines; (iv) derivatives of aromatic acids, including coumarin, of 133 Rhodococcus strains from the Regional Specialized Collection of Alkanotrophic Microorganisms was demonstrated. The minimal inhibitory concentrations of these aromatic compounds for Rhodococcus varied in a wide range from 0.2 up to 50.0 mM. o-Xylene and polycyclic aromatic hydrocarbons (PAHs) were the less-toxic and preferred aromatic growth substrates. Rhodococcus bacteria introduced into the PAH-contaminated model soil resulted in a 43% removal of PAHs at an initial concentration 1 g/kg within 213 days, which was three times higher than that in the control soil. As a result of the analysis of biodegradation genes, metabolic pathways for aromatic hydrocarbons, phenol, and nitrogen-containing aromatic compounds in Rhodococcus, proceeding through the formation of catechol as a key metabolite with its following ortho-cleavage or via the hydrogenation of aromatic rings, were verified.

Wastewater treatment by anodic oxidation in electrochemical advanced oxidation process: Advance in mechanism, direct and indirect oxidation detection methods

Electrochemical Advanced Oxidation Process (EAOP) has been applied to the degradation of refractory pollutants in wastewater due to its strong oxidation capacity, high degradation efficiency, simple operation, and mild reaction. Among electrochemical processes, anodic oxidation (AO) is the most widely used and its mechanism is mainly divided into direct oxidation and indirect oxidation. Direct oxidation means that pollutants are oxidized at the anode by direct electron transfer. Indirect oxidation refers to the generation of active species during the electrolytic reaction, which acts on pollutants. The mechanism of AO process is controlled by many factors, including electrode type, electrocatalyst material, wastewater composition, pH, applied current and voltage levels. It is very important to explore the reaction mechanism of electrochemical treatment, which determines the efficiency of the reaction, the products of the reaction, and the extent of reaction. This paper firstly reviews the current research progress on the mechanism of AO process, and summarizes in detail the different mechanisms caused by influencing factors under common AO process. Then, strategies and methods to distinguish direct oxidation and indirect oxidation mechanisms are reviewed, such as intermediate product analysis, electrochemical test analysis, active species detection, theoretical calculation, and the limitations of these methods are analyzed. Finally some suggestions are put forward for the study of the mechanism of electrochemical advanced oxidation.

Promotion of formaldehyde degradation by electro-Fenton: Controlling the distribution of ·OH and formaldehyde near cathode to increase the reaction probability

The mismatch of pollutant concentration and ·OH concentration is the key reason for the inefficient degradation of formaldehyde in the electro-Fenton system. Therefore, formaldehyde and ·OH are adsorbed near the cathode, and the high concentration reaction region is constructed to increase the reaction probability, which is called control of the reaction region. Through nitrogen doping modification of the activated carbon cathode, the adsorption capacity of the modified cathode for formaldehyde and active species, and the selectivity of the two-electron oxygen reduction reaction were deeply analyzed. The results show that the suitable nitrogen doping form of the modified cathode significantly promotes the adsorption capacity of formaldehyde and H₂O₂, which is beneficial to realizing the promotion of formaldehyde degradation by nitrogen doped cathodes in the electro-Fenton system through control of the reaction region. Graphite nitrogen and pyrrolic nitrogen improve formaldehyde adsorption by enhancing the van der Waals force (8.897 mg g^-1), and pyridinic nitrogen improve H₂O₂ adsorption (1.841 mg g^-1) by enhancing the effect of hydrogen bonding interaction. Nitrogen doping enhances Fe²⁺ regeneration, which contributes to the generation of ·OH at the cathode, and promotes formaldehyde degradation. The control of the reaction region through modification of the electro-Fenton cathode achieved formaldehyde degradation of 35.1 mg L^-1 (48.51% higher than that of the unmodified cathode), which provides a promising process for formaldehyde treatment.