Photo-Fenton process at natural conditions of pH, iron, ions, and humic acids for degradation of diuron and amoxicillin

Photochemical demethylation of methylmercury (MeHg) in aquatic systems: A review of MeHg species, mechanisms, and influencing factors

Photodemethylation is the major pathway of methylmercury (MeHg) demethylation in surface water before uptake by the food chain, whose mechanisms and influence factors are still not completely understood. Here, we review the current knowledge on photodemethylation of MeHg and divide MeHg photolysis into three pathways: (1) direct photodemethylation, (2) free radical attack, and (3) intramolecular electron or energy transfer. In aquatic environments, dissolved organic matter is involved into all above pathways, and due to its complex compositions, properties and concentrations, DOM poses multiple functions during the PD of MeHg. DOM-MeHg complex (mainly by sulfur-containing molecules) might weaken the C-Hg bond and enhance PD through both direct and indirect pathways. In special, synergistic effects of both strong binding sites and chromophoric moieties in DOM might lead to intramolecular electron or energy transfer. Moreover, DOM might play a role of radical scavenger; while triplet state DOM, which is generated by chromophoric DOM under light, might become a source of free radicals. Apart from DOMs, transition metals, halides, NO3-, NO2-, and carbonates also act as radical initialaters or scavengers, and significantly pose effects on radical demethylation, which is generally mediated by hydroxyl radicals and singlet oxygen. Environmental factors such as pH, light wavelength, light intensity, dissolved oxygen, salinity, and suspended particles also affect the PD of MeHg. This study assessed previously published works on three major mechanisms, with the goal of providing general estimates for photodemethylation under various environment factors according to know effects, and highlighting the current uncertainties for future research directions.

Efficient removal of antibiotics from water resources is a public health priority: a critical assessment of the efficacy of some remediation strategies for antibiotics in water

This review discusses the fundamental principles and mechanism of antibiotic removal from water of some commonly applied treatment techniques including chlorination, ozonation, UV-irradiation, Fenton processes, photocatalysis, electrochemical-oxidation, plasma, biochar, anaerobicdigestion, activated carbon and nanomaterials. Some experimental shortfalls identified by researchers such as certain characteristics of degradation agent applied and the strategies explored to override the identified limitations are briefly discussed. Depending on interactions of a range of factors including the type of antibiotic compound, operational parameters applied such as pH, temperature and treatment time, among other factors, all reviewed techniques can eliminate or reduce the levels of antibiotic compounds in water to varying extents. Some of the reviewed techniques such as anaerobic digestion generally require longer treatment times (up to 360, 193 and 170 days, according to some studies), while others such as photocatalysis achieved degradation within short contact time (within a minimum of 30, but up to 60, 240, 300 and 1880 minutes, in some cases). For some treatment techniques such as ozonation and Fenton, it is apparent that subjecting compounds to longer treatment times may improve elimination efficiency, whereas for some other techniques such as nanotechnology, application of longer treatment time generally meant comparatively minimal elimination efficiency. Based on the findings of experimental studies summarized, it is apparent that operational parameters such as pH and treatment time, while critical, do not exert sole or primary influence on the elimination percentage(s) achieved. Elimination efficiency achieved rather seems to be due more to the force of a combination of several factors.

High efficiency three-dimensional electrochemical treatment of amoxicillin wastewater using Mn-Co/GAC particle electrodes and optimization of operating condition

In this work, Mn-Co/GAC particle electrode was prepared by loading Mn and Co as catalysts on granular activated carbon (GAC) and used in a three-dimensional (3D) electrochemical system for mineralization of amoxicillin wastewater. Observation results by SEM, EDS and XRD confirmed that Mn and Co catalysts were successfully loaded onto GAC. The electrochemical properties were measured using an electrochemical workstation. Mn-Co/GAC had a much higher oxygen evolution potential (1.46V) than GAC (1.1V), which demonstrated that it could effectively reduce the oxygen evolution side reaction. In addition, Mn-Co/GAC had an electrochemically active surface area 1.34 times that of GAC and a much smaller mass transfer resistance than GAC, which could provide favorable conditions for the degradation of pollutants. The investigation of the influences of single operating parameters on total organic carbon (TOC) removal rate and electrical energy consumption (EEC) indicated that current density and treatment time had the greatest effect. In order to maximize TOC removal rate and minimize EEC, optimization of operating parameters was also carried out using response surface method in combination with central composite design. The optimal operating parameters were determined as current density of 5.68 mA/cm², electrolyte concentration of 0.127M, particle electrode dosage of 31.14g and treatment time of 120min. Under this optimum operating condition, TOC removal rate of 85.24% and amoxicillin removal rate of 100% could be achieved with a low EEC of 0.073 kWh/g TOC. In addition, TOC removal rate and EEC were significantly improved compared to the use of bare GAC as particle electrode under the same operating conditions, demonstrating the excellent electrocatalytic ability of the new particle electrode Mn-Co/GAC. A possible mechanism of enhanced amoxicillin and TOC removal was also recommended. In summary, the 3D electrochemical method using Mn-Co/GAC particle electrodes is a suitable choice for amoxicillin wastewater treatment.

Constructing an Acidic Microenvironment by MoS2 in Heterogeneous Fenton Reaction for Pollutant Control

Although Fenton or Fenton-like reactions have been widely used in the environment, biology, life science, and other fields, the sharp decrease in their activity under macroneutral conditions is still a large problem. This study reports a MoS₂ cocatalytic heterogeneous Fenton (CoFe₂ O₄ /MoS₂ ) system capable of sustainably degrading organic pollutants, such as phenol, in a macroneutral buffer solution. An acidic microenvironment in the slipping plane of CoFe₂ O₄ is successfully constructed by chemically bonding with MoS₂ . This microenvironment is not affected by the surrounding pH, which ensures the stable circulation of Fe³⁺ /Fe²⁺ on the surface of CoFe₂ O₄ /MoS₂ under neutral or even alkaline conditions. Additionally, CoFe₂ O₄ /MoS₂ always exposes "fresh" active sites for the decomposition of H₂ O₂ and the generation of ¹ O₂ , effectively inhibiting the production of iron sludge and enhancing the remediation of organic pollutants, even in actual wastewater. This work not only experimentally verifies the existence of an acidic microenvironment on the surface of heterogeneous catalysts for the first time, but also eliminates the pH limitation of the Fenton reaction for pollutant remediation, thereby expanding the applicability of Fenton technology.

Experimental and computational study of hydrolysis and photolysis of antibiotic ceftriaxone: Degradation kinetics, pathways, and toxicity

In this work, we have experimentally and computationally investigated the process of hydrolysis and photolysis of cephalosporin antibiotics with ceftriaxone (CEF) as a model compound. The CEF hydrolysis was investigated in ultrapure and natural water, at 25 ± 1 °C and 4 ± 1 °C in the dark. It was found that CEF after 100 and 900 days at 25 ± 1°C and 4 ± 1 °C, respectively practically completely removed from ultrapure water. The CEF hydrolysis in natural water was five and three times slower at 25 ± 1 °C and 4 ± 1 °C, respectively than in ultrapure water. Further, the efficiency of direct photolysis (solar/UVA-B) and solar/H₂O₂ treatment of CEF was investigated. Under UVA-B radiation 95.6% of CEF was removed after 60 min, while for the same time of solar radiation degradation was practically not observed (only 3.2%). Also, the effects of different concentrations of H₂O₂ (0-150 mM) in the presence/absence of solar radiation were studied. The most efficient solar/H₂O₂ treatment was in the presence of 90 mM H₂O₂, whereby 66.8% of CEF was removed after 60 min (41.8% by indirect photolysis, 21.8% by H₂O₂-oxidation, and 3.2% by direct photolysis). Radial distribution functions (RDF) provided information about the distribution of water around the CEF molecule. Aside from the RDF, investigation of intramolecular noncovalent interactions and calculations of bond dissociation energies for hydrogen abstraction enabled understanding of degradation mechanism of CEF. In order to investigate sensitivity of CEF towards the radical attacks, the concept of Fukui functions was used. The structures of intermediates and degradation pathways were suggested by UHPLC-LTQ OrbiTrap MS and density functional theory calculations. Toxicity assessments showed that intermediates formed during hydrolysis exerted only mild cell growth effects in selected cell lines.

Developments in the intensification of photo-Fenton and ozonation-based processes for the removal of contaminants of emerging concern in Ibero-American countries

Contaminants of emerging concern (CECs), such as pharmaceuticals, personal care products, pesticides, synthetic and natural hormones and industrial chemicals, are frequently released into the environment because of the inability of conventional processes in municipal wastewater treatment plants to remove them. Some examples of alternative options to remove such pollutants are photo-Fenton and ozone-based processes, which are two techniques widely studied in Ibero-American countries. In fact, this region has been responsible for delivering frequently publications and conferences on advanced oxidation processes. This work is a critical review of recent developments in the intensification of the two aforementioned advanced oxidation techniques for CECs elimination in the Ibero-American region. Specifically for the photo-Fenton process (pF), this study analyses strategies such as iron-complexation with artificial substances (e.g., oxalic acid and ethylenediamine-N,N'-disuccinic acid) and natural compounds (such as humic-like substances, orange juice or polyphenols) and hybrid processes with ultrasound. Meanwhile, for ozonation, the enhancement of CECs degradation by adding hydrogen peroxide (i.e., peroxone), ultraviolet or solar light, and combining (i.e., photolytic ozonation) with catalysts (i.e., catalytic ozonation) was reviewed. Special attention was paid to how efficient these techniques are for removing contaminants from water matrices, and any potentialities and weak points of the intensified processes.

Elimination of representative fluoroquinolones, penicillins, and cephalosporins by solar photo-Fenton: degradation routes, primary transformations, degradation improvement by citric acid addition, and antimicrobial activity evolution

This work studies the degradation of seven representative antibiotics (ciprofloxacin, norfloxacin, levofloxacin, oxacillin, cloxacillin, cefalexin, and cefadroxil) by solar photo-Fenton process. The removal of antibiotics by the individual components (i.e., light, H₂O₂, or Fe (II)) and the complete photochemical system (light/H₂O₂/Fe (II)) was initially evaluated. Then, the effect of citric acid addition to the photo-Fenton system was assessed. In the third place, the primary transformation products for two illustrative cases (ciprofloxacin and oxacillin treated by photo-Fenton) were determined. Also, photo-Fenton in the presence of citric acid was applied to remove antibiotics from a simulated hospital wastewater. It was found that the solar light component induced degradation of ciprofloxacin, norfloxacin, and levofloxacin, but the rest of the considered antibiotics were not reduced by photolysis. In turn, the photo-Fenton system showed a degrading action on all the tested antibiotics. The addition of citric acid to the system significantly increased the removal of antibiotics. Initial degradation products indicated that hydroxyl radical attacked moieties of antibiotics responsible for their antimicrobial activity. Finally, the treatment of hospital wastewater evidenced the high potentiality of photo-Fenton process for degrading antibiotics in aqueous matrices containing elevated concentrations of citric acid.