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.
Abstract The temporal evolution of dike volume can help elucidate its propagation dynamics, however, such an estimation is possible only when there are geodetic observations available along the dike ...path. Here it is shown that dike volume history during eight eruptions can be reconstructed from seismic moment release using high resolution earthquake catalogs. The critical volume needed for each dike to reach the surface is simulated and compared to the accumulated volume prior to eruption in order to infer fracture toughness, a measure of resistance to fracture. It is found that fracture toughness varies between 123–833 MPa m 1/2 , with larger values corresponding to longer dikes. Resistance to fracture dominates over viscous dissipation when the dikes propagate through unfractured heterogeneous material with large rigidity contrast, or when there is dike segmentation. These results can be utilized for real time monitoring of dike growth, forecasting eruption volume, and for constraining analog or numerical models of dike propagation.
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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 presence of resistant organic pollutants in environmental substrates requires the development and finding of novel decontamination methods. Advanced oxidation processes are among the most ...effective methods used for degradation of these pollutants through their oxidation and degradation into non-toxic and harmless, for the environment, final products. Ιn this research, a series of perovskites of ABO3-type, with La and Fe and/or Co in A and B positions respectively, LaFe1-xCoxO3 (x = 0, 0.25, 0.5, 0.75, 1), were synthesized with two different methods, a soft template method using anionic surfactant and by glycine combustion method and studied for their catalytic activity towards the degradation of phenolic compounds, a major class of environmental pollutants, through persulfate activation. The catalytic activity depended both by the B metal ion of perovskites and their ratio as well as by the synthesis method. LaCoO3 prepared with the anionic surfactant method, showed the highest catalytic activity with a rate constant of 0.024 min−1. Furthermore, the synthesis method also influenced the stability of perovskites as metal leaching studies showed that perovskites synthesized with the anionic surfactant showed greater stability. Quenching experiments were also used in order to shed light on the catalytic activation mechanism of persulfate for the degradation of phenolics. Overall, the results showed that the synthesis method can significantly affect the catalytic activity of the materials and their stability since the same materials synthesized with different methods show significantly different catalytic properties.
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•ABO3-type LaFe1-xCoxO3 series were synthesized by surfactant and glycine combustion.•Perovskites were studied for the activation of persulfates towards phenolics removal.•Catalytic activity depended both by B metal ion and by the synthesis method.•LaCoO3 prepared with anionic surfactant method showed the highest catalytic activity.•Perovskites synthesized with the anionic surfactant showed greater stability.
Organic booster biocides were recently introduced as alternatives to organotin compounds in antifouling products, after restrictions imposed on the use of tributyltin (TBT) in 1987. Replacement ...products are generally based on copper metal oxides and organic biocides. This ban has led to an increase in alternative coating products containing the above biocides. The most commonly used biocides in antifouling paints are: Irgarol 1051, diuron, Sea-nine 211, dichlofluanid, chlorothalonil, zinc pyrithione, TCMS (2,3,3,6-tetrachloro-4-methylsulfonyl) pyridine, TCMTB 2-(thiocyanomethylthio) benzothiazole, and zineb. Since 1993, several studies have demonstrated the presence of these biocides in European coastal environment as a result of their increased use. More recently, the presence of these biocides was also revealed in waters from Japan, United States, Singapore, Australia and Bermuda. This paper reviews the currently available data on the occurrence of these biocides in the aquatic environment. Some data dealing with the environmental fate, partitioning, behaviour and risk assessment of antifouling paint booster biocides are also reported in order to discuss the detected levels of contamination.
The Water Framework Directive (WFD) methodology, proposed by the Ministry of Environment and Energy of Greece (WFD-MEEG), and the Canadian Council of Ministers of Environment Water Quality Index ...(CCME-WQI) are comparatively applied to evaluate the chemical status of a major transboundary river. Water quality parameters were monitored at 11 sites along the main stream of the river and its main tributaries, and at five sites in the reservoirs, on a monthly frequency, in the period from May 2008 to May 2009. Water temperature (T), dissolved oxygen (DO), pH, and electrical conductivity (EC) were measured in-situ, while water samples were collected for the determination of total suspended solids (TSS), biochemical oxygen demand (BOD), chemical oxygen demand (COD), nitrite-, nitrate- and ammonium-nitrogen, total Kjeldahl nitrogen (TKN), ortho-phosphates (OP), total phosphorus (TP), and chlorophyll-a (Chl-a). The water samples were also analyzed for the determination of seven heavy metals (i.e., Cd, Pb, Hg, Ni, Cr, Cu, Zn) and 33 priority substances, as listed in Annex II of EU Directive 2008/105/EC. The results showed that the physicochemical parameters (i.e., T, DO, pH, EC, inorganic nitrogen, TKN, OP, TP, TSS, and Chl-a) were within the natural range. The mean concentration of the measured heavy metals did not exceed the limits set by WHO (2003, 2017) for drinking water. Regarding the priority substances, some of them (i.e., anthracene, fluoranthene, and polyaromatic hydrocarbons) were measured in various stations at higher concentrations than the Annual Average Environmental Quality Standards (AA-EQS). Based on the WFD-MEEG methodology, the river water was in the ‘good’ quality class, while according to CCME-WQI the river quality ranged from ‘marginal’ to ‘good’ category. It seems that CCME-WQI is stricter than WFD-MEEG but could be a WQI appropriate for use.
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•WFD priority and priority hazardous substances were monitored in a transboundary river.•Parameters included heavy metals, agrochemicals, PAHs, and nutrients in river and reservoirs.•The WFD-based methodology was compared to CCME-WQI to classify the water quality.•The CCME-WQI classification was more conservative than the WFD-based one.•Pesticide concentrations in the river were lower than AA-EQS and MAC-EQS values.
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•Photocatalytic degradation and mineralization kinetics of DEET were studied.•Degradation products were elucidated using HR-LC–MS and GC–MS techniques.•Hydroxy-methylcyclohexadienyl ...radicals were detected as initial DPs by EPR.•The acute toxicity of DEET and its TPs was assessed along photocatalytic treatment.
Analytical and electron paramagnetic resonance (EPR) spectroscopic methods were systematically used for the kinetic and mechanistic investigation of the photocatalytic degradation of N,N-diethyl-m-toluamide (DEET), in aqueous TiO2 suspensions under simulated solar light. The degradation of DEET followed first-order kinetics while enhanced reduction (>85%) of total organic carbon (TOC) and stoichiometric transformation of nitrogen to nitrate and ammonium ions took place after 240min of irradiation. Numerous different structures of transformation products (TPs), with at least one isomer for the majority of them, were identified with high resolution accurate mass liquid chromatography (HR-LC–MS) and gas chromatography mass spectrometry (GC–MS). Low temperature EPR spectroscopy was used to study the photoinduced radicals created during the initial events of the photocatalytic oxidation. Two kinds of aromatic ring carbon-centered radicals i.e. hydroxy-methylcyclohexadienyl radicals have been resolved at 77K. The second-transient conformation of the radicals is maximized after 5min. of irradiation and then slowly decays. On the basis of identified products and radicals, a proposed pathway of photocatalytic degradation of DEET is presented, involving mono- and polyhydroxylation and/or oxidation, dealkylation and continuously the opening of the aromatic ring. Scavenging experiments indicated the contribution of OH as the main species in the DEET oxidation while O2- contributes also to the degradation in a lesser extend after the initial steps of the reaction. Finally, toxicity studies based on luminescence of Vibrio fischeri bacteria before and after the photocatalytic treatment were also performed.
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•N,S-doped TiO2 photocatalysts have been prepared by sol–gel.•N,S-TiO2 catalysts showed low crystallite sizes and visible-light response.•Photocatalytic activity was evaluated towards ...TCPP degradation in aqueous solutions.•N-doped TiO2 was found the most photoactive catalyst under UV–vis light.•N,S-TiO2 with equimolar Ti:N,S ratio showed the higher activity under visible light.
N and N,S co-doped TiO2 catalysts were prepared by a simple sol–gel method and were characterized by various techniques such as X-ray diffraction, scanning electron microscopy, UV–vis spectroscopy, porosimetry and particle size distribution. The photocatalytic efficiency of the prepared catalysts was evaluated for the degradation of organophosphorus flame retardant TCPP in aqueous solutions at environmental relevant concentrations under UV–vis and visible light irradiation. All the prepared N and N,S doped catalysts showed lowered crystallite size and higher visible-light response compared to the undoped TiO2 catalyst. An increased surface acidity was observed for N,S co-doped catalysts as a result of surface sulfate species which play a crucial role in the photocatalytic performance. N-doped TiO2 was found to be the most photoactive catalyst for the removal of TCPP, under UV–vis irradiation. Among N,S co-doped TiO2 catalysts, the one prepared with equimolar Ti:N,S ratio showed the higher performance for the removal of TCPP under both UV–vis and visible irradiation. Its higher activity was attributed to the higher surface area, larger pore volume, well-crystallized anatase and red shift in light absorption. Under visible light irradiation the degradation kinetics of TCPP were slower than under UV–vis irradiation due probably to reduced production of hydroxyl radicals.
•The photocatalytic degradation of IPMP in aqueous solution was investigated in detail.•Eleven intermediates identified using HR-LC–MS and GC–MS techniques.•Photogenerated •OH radicals were ...principally responsible for the degradation of IPMP.•Almost total detoxification of the irradiated solution after 300min.
In recognition of the growing demand regarding the control of undesired taste and odor (T&O) problems in natural water resources, the photocatalytic degradation of 2-isopropyl-3 methoxy pyrazine (IPMP), a common metabolite of soil actinomycetes which contributes a rotten vegetable odor to water, was investigated under simulated solar irradiation. Under the studied conditions (C=10mgL−1, CTiO2=100 mg L−1 and I=600Wm−2), 95% of IPMP was removed within 20min of irradiation. The reaction intermediates were completely mineralized to CO2 and the nitrogen was predominantly released as NH4+ ions after 240min irradiation. The major transformation products of TiO2 photocatalysis of IPMP have been determined by the use of high resolution accurate liquid chromatography–orbitrap mass spectrometry as well as gas chromatography–mass spectrometry (GC–MS) techniques. Hydroxylation of the isopropyl and methoxy groups has been identified as the main reaction pathway. Scavenging experiments indicated the important role of HO•, h+ and O2•− in the photocatalytic process. Toxicity assessment revealed the efficiency of the photocatalytic treatment to achieve almost complete detoxification of the irradiated solution.
The accelerating growth of seismic unrest before eruptions has been observed at many volcanoes and utilized for eruption forecasts. However, there are still many eruptions for which no precursory ...unrest has been identified, even at well-monitored volcanoes. The recent eruptions of Shinmoe-dake, Japan, have been another negative example of this kind. Here we present seismological evidence that the eruption preparation had been ongoing at the shallow depths beneath Shinmoe-dake for several months to a year. We investigated the seismic background level (SBL) of eleven-year data recorded around the volcano, including two stations about 1 km from the eruptive crater. We searched for persistent weak signals, focusing on low-amplitude time windows recorded during quiet nighttime. Then the spectra of daily background noise were classified by clustering analysis. The SBL analysis successfully revealed very weak precursory tremors from more than several months before the eruption, and residual tremors to the end of the eruptive period. The precursory signals grew acceleratory in a similar way as is assumed in the material failure forecast method applied to eruption forecasts. However, their growth was significantly slower and longer compared to other cases reported in the literature. Such slow and quiet eruption preparations would not be captured by conventional seismological methods. We expect that long-term SBL analyses on proximal seismic data will help detect early precursors, even at seismically quiet volcanoes, and will also help towards judging the end of an eruptive period.
