In view of the global concern about the occurrence of taste and odor (T&O) compounds in waters for drinking water supply and the necessity for the development of more innovative and efficient ...technologies for water treatment and depuration, the focus of this study is to provide a state of the art overview on current knowledge for the application of advanced oxidation technologies for the treatment of T&O compounds in aquatic media. The most representative and newly emerging compounds belonging to the major groups of T&O compounds, such as geosmin, methylisoborneol, benzothiazoles, mercaptans and sulfides as well as aromatic and other miscellaneous T&O compounds, are included in the systematic overview. The current data has been compiled and extensively discussed in terms of the degree of degradation, reaction kinetics, effect of operational parameters and water quality, identity of intermediate and final products and possible transformation pathways.
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•The applications of AOPs for the treatment of T&O compounds in water are reviewed.•AOPs exhibited fast kinetics and great degrees of mineralization of T&O compounds.•The main effects of operational parameters and water constituents are discussed.•An overview of the transformation products and reaction mechanisms is provided.•Data gaps and future research needs of AOPs for T&O removal have been assessed.
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•The photocatalytic degradation and mineralization of venlafaxine was studied.•A great number of intermediates were detected by HR-LC–MS.•Ηydroxylation, oxidation, demethylation ...and/or dehydration were the main routes.•Near additive/synergistic toxicity effects between TPs were observed.
The photochemical degradation of the antidepressant drug venlafaxine (VNF) by UV/TiO2 process was investigated in the present study. Prescreening experiments were conducted to study the effects of main parameters affecting the photocatalytic process. In addition, the effects and interactions of most influenced parameters were evaluated and optimized by using a central composite design model and a response surface methodology. Results indicated that VNF was quickly removed in all the irradiation experiments and its degradation was mainly affected by the studied variables (catalyst dose, initial VNF concentration and pH), as well as their interaction effects. Parallel to kinetic studies, the transformation products (TPs) generated during the treatment was investigated using LC coupled to low and high resolution mass spectrometry. Based on identification of the main TPs, tentative transformation pathways were proposed, including hydroxylation, demethylation and dehydration as major transformation routes. Τhe potential risk of VNF and its TPs to aqueous organisms was also investigated using Microtox bioassay before and during the processes. The obtained results showed an increment in the acute toxicity in the first stages and a continuously decreasing after then to very low values reached within 240min of the photocatalytic treatment, demonstrating that UV/TiO2 can lead to the elimination of parent compound and the detoxification of the solution.
The photocatalytic degradation of dimethoate, an organophosphorous pesticide, has been investigated using TiO
2 and ZnO as catalysts. The degradation kinetics were studied under different conditions ...such as substrate and photocatalyst concentration, temperature, pH and addition of oxidants. The degradation rates proved to be strongly influenced by these parameters. Comparison between the two catalysts showed that TiO
2 is more efficient to the disappearance of dimethoate and follows first-order kinetics. DOC measurements were carried out in order to evaluate the degree of mineralization. Both catalysts were unable to mineralize dimethoate, but the addition of oxidants improved the efficiency of the processes. Measurements of phosphate, ammonium and sulphate ions gave valuable information about how this process is achieved. Toxicity measurements showed that only the addition of hydrogen peroxide in the illuminated titanium dioxide suspension was able to lead to a complete detoxification of the solution.
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•Cytarabine degradation by TiO2/SSL, TiO2/S2O82−/SSL and TiO2/H2O2/SSL processes.•The effect of operational parameters and addition of oxidants was studied.•Hydroxylation and ...oxidation were found as the main transformation routes before ring cleavage.•OH radicals were the major oxidant species based on scavenging experiments.•Microtox bioassay toxicity increased at the first stages but nearly eliminated at the end-stages.
The photochemical degradation of antineoplastic drug cytarabine (CY) by TiO2 photocatalysis under simulated solar light (SSL) radiation, TiO2/S2O82−/SSL and TiO2/H2O2/SSL processes was investigated in the present study. Experimental results indicated that CY was quickly degraded in all the studied treatments and degradation kinetics were dependent by all studied variables (i.e. catalyst dose, initial CY concentration, pH, oxidant concentration). In addition to kinetic studies, the transformation products (TPs) generated during the treatments were investigated using liquid chromatography coupled to high resolution mass spectrometry while mineralization was also followed by ion chromatography and total organic carbon measurements. Based on the identification of TPs and scavenging experiments, the major transformation routes followed were hydroxylation and subsequent oxidation, in all studied treatments. Microtox bioassay was applied before and during the TiO2 photocatalytic process, in order to investigate the potential risk of CY and its TPs to aqueous organisms. The obtained results showed an increase in the acute toxicity in the first stages and a continuously decrease afterwards, leading to very low toxicity levels within 360min of TiO2/SSL treatment. Overall results indicated that photocatalytic degradation of CY can lead to its complete elimination and detoxification of the solution.
In the present study, the coupling of adsorption capacity and photocatalytic efficiency of two different industrially produced titania catalysts was investigated and compared. The azo dye Reactive ...Red 195 was selected as a model compound. The tested catalysts, PK-10 and PK-180, exhibited different adsorption capacities due to their significant difference in their specific surface, but both have proven to be effective photocatalysts for photodegradation of the studied dye. PK-10 exhibited strong adsorption of the studied dye due to its high specific surface area, while the second studied catalyst, PK-180, demonstrated negligible adsorption of Reactive Red 195. The effect of the pH, the concentration of the catalyst and the initial concentration of the dye appear to affect the photocatalytic rate. The effect of the presence of humic acids and inorganic ions was also examined, while the contribution of various reactive species was indirectly evaluated through the addition of various scavengers. To evaluate the extent of mineralisation of the studied dye, total organic carbon (TOC) measurements during the experiment were also conducted. Besides total colour removal, evident reduction of TOC was also achieved using both catalysts.
The photocatalytic degradation of two selected insecticides (dimethoate and methyl parathion) has been studied using the photo-assisted Fenton reaction. The degradation kinetics were studied under ...different conditions such as iron's and oxidant's concentration, temperature and inorganic ions. The degradation rates proved to be strongly influenced by these parameters. The replacement of hydrogen peroxide with peroxydisulfate was also tested in a photo-Fenton-like reaction. This system achieved high degradation rates of the selected compounds. Intermediate products formed during photocatalytic treatment were identified by means of solid-phase extraction (SPE) coupled to gas chromatography–mass spectroscopy techniques (GC–MS). Eight possible by-products were identified for parathion methyl and three for dimethoate formed through mainly oxidation and dealkylation reactions. Mineralization studies showed also that the photo-Fenton and the photo-Fenton-like systems are able to achieve mineralization of the insecticides. However, complete detoxification is achieved only in the presence of the photo-Fenton reagent.
The photocatalytic oxidation of two selected organophosphorous insecticides (dichlorvos and dimethoate) has been investigated. The aim of the study was the identification of the intermediates that ...are formed during photocatalytic treatment. Intermediate products from the slurry system were identified by means of solid-phase extraction (SPE) coupled to gas chromatography–mass spectroscopy techniques (GC–MS). Nine possible by-products were identified for dimethoate and three for dichlorvos. A proposed degradation pathway for each insecticide is presented, involving mainly oxidation and dealkylation reactions. The results demonstrated that some of the transient intermediates formed (oxon derivatives, disulfide, chlorinated fragments), were more toxic compared to parent compounds whereas most of them are less toxic than the parent compounds.
In this study, the heterogeneous photocatalytic degradation of prometryn using TiO
2 as photocatalyst was investigated. The main objectives of the study were: (I) to evaluate the kinetics of the ...pesticide disappearance, (II) to compare the photocatalytic efficiency of two different types of TiO
2, (III) to examine the influence of various parameters such as initial concentration of pesticide or catalyst and presence of oxidants (H
2O
2 and K
2S
2O
8), (IV) to evaluate the degree of mineralization and (V) to assess the detoxification efficiency of the studied processes. The experiments were carried out in a 500
ml pyrex UV reactor equipped with a 125
W high-pressure mercury lamp surrounded by a pyrex filter blocking wavelengths below 290
nm. Prometryn concentration was determined using HPLC. It was found that the degradation of the pesticide follows the first order kinetics according to the Langmuir–Hinshelwood model. Parameters like the type and concentration of the catalyst affect the degradation rate. A synergistic effect was observed when an oxidant was added in the TiO
2 suspensions increasing the reaction rate of photodegradation. In order to examine the extent of pesticide mineralization, DOC measurements were carried out. After 6
h of illumination, mineralization was achieved up to almost 70%. The toxicity of the treated solution was evaluated using the Microtox test based on the luminescent bacteria
Vibrio fisheri, in order to compare the acute toxicity of prometryn and its photoproducts. The detoxification efficiency was found to be dependent on the studied system and it did not follow the rate of pesticide disappearance.
The photodegradation of three triazines, atrazine, simazine, and prometryn, in aqueous solutions and natural waters using UV radiation (λ > 290 nm) has been studied. Experimental results showed that ...the dark reactions were negligible. The rate of photodecomposition in aqueous solutions depends on the nature of the triazines and follows first-order kinetics. In the case of the use of hydrogen peroxide and UV radiation, a synergistic effect was observed. The number of photodegradation products detected, using FIA/MS and FIA/MS/MS techniques, suggests the existence of various degradation routes resulting in complex and interconnected pathways. Keywords: Photodegradation; triazines; pesticides; hydrogen peroxide; FIA/MS; FIA/MS/MS
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•Six GO-TiO2 composites were synthesized and characterized.•The GO content affects the degradation kinetics.•Photocatalytic treatment in a leachate reduces the photodegradation ...rate.•Forty-six intermediates were detected during treatment.•Different transformation routes can be followed in different matrices.•The cyclopropyl ring remains in most cases the main site of reaction.
The photocatalytic treatment of the antiviral drug abacavir has been studied using graphene oxide (GO)-titania (TiO2) nanocomposites as catalysts under simulated solar irradiation. A mild ultrasonically assisted synthetic route was followed for the preparation of the GO-TiO2 composites. Their characterization and determination of their physicochemical properties was conducted employing Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), BET analysis and X-ray Diffraction (XRD). Six different nanocomposites were tested towards their photocatalytic efficiency containing a varying amount of GO ranging from 1 % to 20 %. The degradation kinetics followed the first-order kinetic law. The synthesized composite with 2 % GO appeared to be the most effective achieving complete disappearance of the target compound within 20 min. The photocatalytic degradation of the target compound proceeded in slower rates when using a landfill leachate as a water matrix due to its increased complexity. The identification of the transformation products (TPs) revealed the formation of forty-six intermediates arising from different transformation routes. The cyclopropyl ring appears to be the main site of reaction although hydroxylation, dehydrogenation, deamination/hydroxylation and isomerization of the parent compound may be also observed. The evolution profiles of the most abundant TPs in the two matrices (ultrapure water and leachate) revealed that different transformation routes may be more favored in each matrix.
