Evolution Of Total Organic Carbon Research Articles

Towards a better understanding of flow-related processes in the vertically distributed compartments of karst aquifers by combining natural tracers and stable isotopes

Understanding infiltration pathways throughout the different compartments of karst systems (soil-epikarst-unsaturated zone-saturated zone) is vital to assess recharge processes, vulnerability to pollution, and the general hydrogeological functioning of these kind of aquifers. To gain deeper insight into the soil-water-rock hydrogeochemical processes occurring throughout the vertically hierarchized compartments of the aquifer and to evaluate the applicability of different soil natural parameters as groundwater flow tracers, the present work analyzes the spatial and temporal evolution of total organic carbon -TOC-, intrinsic fluorescence related to organic matter, nitrates, δ13CTDIC, and the values of stable isotopes of δ2H and δ18O from water molecules and at different sampling points in a geologically complex karst aquifer in south Spain (Jarastepar carbonate massif). Over two years, rain and soil water (30 and 60 cm deep) samples were collected simultaneously at an experimental plot along with groundwater from the top of the saturated zone and a base-level spring. Results show that the variation in the concentration of natural soil tracers and the signal of water stable isotopes (δ2H and δ18O) smooth throughout the different compartments of the aquifer, with rapid variations in the unsaturated zone after recharge events and delayed effects in the saturated zone. At the same time, δ13CTDIC and nitrate values rise along the subsurface flow. While the carbon isotope evidences a shorter transit time between recharge areas and the top of the saturated zone than the subsequent path toward the permanent base springs, nitrate evolution is affected by pollution sources near discharge areas, so its applicability is questionable. Finally, organic matter (TOC and intrinsic fluorescence) mineralizes (or degrades) up to 90% from the first centimeters of soil to the permanent basal springs. An exponential decreasing trend defines the relationship between TOC and δ13CTDIC caused by organic matter attenuation along the groundwater flow path, while δ13CTDIC increases because of a higher residence time of water in contact with the host rock. These results, together with previous research based on other natural tracers (chemical, isotopes, and dating tools) and dye tracing experiences, permit to link TOC and δ13CTDIC values with a range of transit times, from hours-days to years-decades. Meanwhile, the attenuation of natural intrinsic fluorescence and TOC signal evidence the filter function of the aquifer from the soil to the saturated zone. All these findings highlight the usefulness of natural fluorescence and, particularly, TOC and δ13CTDIC, as tracers of groundwater flow and hydrogeochemical processes within the different compartments of complex karst aquifers.

Application of a Combined Adsorption−Ozonation Process for Phenolic Wastewater Treatment in a Continuous Fixed-Bed Reactor

This work studied the removal of phenol from industrial effluents through catalytic ozonation in the presence of granular activated carbon in a continuous fixed-bed reactor. Phenol was chosen as model pollutant because of its environmental impact and high toxicity. Based on the evolution of total organic carbon (TOC) and phenol concentration, a kinetic model was proposed to study the effect of the operational variables on the combined adsorption–oxidation (Ad/Ox) process. The proposed three-phase model expressed the oxidation phenomena in the liquid and the adsorption and oxidation on the surface of the granular activated carbon in the form of two kinetic constants, k1 and k2 respectively. The interpretation of the constants allow to study the benefits and behaviour of the use of activated carbon during the ozonisation process under different conditions affecting adsorption, oxidation, and mass transfer. Additionally, the calculated kinetic parameters helped to explain the observed changes in treatment efficiency. The results showed that phenol would be completely removed at an effective contact time of 3.71 min, operating at an alkaline pH of 11.0 and an ozone gas concentration of 19.0 mg L−1. Under these conditions, a 97.0% decrease in the initial total organic carbon was observed.

Heterogeneous Catalytic Ozonation of Aniline-Contaminated Waters: A Three-Phase Modelling Approach Using TiO2/GAC

This work aims to study the sustainable catalytic ozonation of aniline promoted by granular active carbon (GAC) doped with TiO2. Aniline was selected as a model compound for the accelerator manufacturing industries used in the manufacture of rubber due to its environmental impact, low biodegradability, and harmful genotoxic effects on human health. Based on the evolution of total organic carbon (TOC), aniline concentration measured using high performance liquid chromatography (HPLC), pH and ozone concentration in liquid and gas phase, and catalyst loading, a three-phase reaction system has been modelled. The proposed three-phase model related the ozone transfer parameters and the pseudo-first order kinetic constants through three coefficients that involve the adsorption process, oxidation in the liquid, and the solid catalyst. The interpretation of the kinetic constants of the process allowed the predominance of the mechanism of Langmuir–Hinshelwood or modified Eley–Rideal to be elucidated. Seven intermediate aromatic reaction products, representative of the direct action of ozone and the radical pathway, were identified and quantified, as well as precursors of the appearance of turbidity, with which two possible routes of degradation of aniline being proposed.

Biodegradability of di-(2-ethylhexyl) phthalate by a newly isolated bacterium Achromobacter sp. RX

Di-(2-ethylhexyl) phthalate (DEHP) is a chemical plasticizer that has been commonly used in the manufacture of polyvinyl chloride. DEHP is one of the environmental pollution sources. In this study, a gram-negative strain RX bacterium utilizing DEHP as sole carbon source was isolated from activated sludge through screening test. This strain RX was identified as Achromobacter sp. RX based on its morphology, physiological properties and 16S rRNA gene sequence analysis. The results showed that the optimal conditions for the DEHP degradation were 30.0 °C and pH 7.0. The DEHP degradation induced by strain RX demonstrated nitrogen source dependent, while followed a decreasing degradation rate under the source of: NO3− > NH4+ > NO2−. The biodegradability of Achromobacter sp. RX was enhanced with Masson pine seed powder as a co-metabolic substrate and Tween-80 as a solubilizing agent. Meanwhile, the degrading kinetics analysis was performed in the condition of DEHP as sole carbon source. The DEHP degradation curves fitted well with the first-order kinetic model at 50–300 mg/L of DEHP, with the half-life ranging from 13.0 to 16.4 h. During the biodegradation of DEHP, mono-(2-ehtylhexyl) phthalate (MEHP) was firstly generated through de-esterification, followed by the formation of phthalic acid and benzoic acid after further de-esterification of MEHP. Benzoic acid was finally mineralized to CO2 and H2O. The decontamination of DEHP-contaminated soil by Achromobacter sp. RX was investigated using a rotating-drum bioreactor. Evolution of total organic carbon from the contaminated soil showed that 86.4%–91.7% of DEHP was mineralized at pH 7.0 and 30.0 °C within 96 h. Reusability of Achromobacter sp. RX and its lifetime were observed over six consecutive cycles. Thus, Achromobacter sp. RX possessed high DEHP biodegradability, which provided a good potential in dealing with DEHP-contaminated soil.

Degradation of imidazolium‐based ionic liquids in aqueous solution by Fenton oxidation

AbstractBACKGROUNDThe breakdown of imidazolium ionic liquids (ILs) by Fenton oxidation has been demonstrated, but using unaffordable doses of hydrogen peroxide (H2O2). The literature studies so far do not report on the evolution of total organic carbon (TOC) and ecotoxicity. Therefore, the potential application of the process for the degradation of ILs still remains an open question. This work investigates the feasibility of the Fenton process for the treatment of aqueous effluents containing imidazolium‐based ILs of different structures, represented by the length of the alkyl chain and the nature of the anion. Special attention is paid to the evolution of the ecotoxicity and the consumption of H2O2 as a critical issue for the economy of the process. The experiments were performed at 70 °C.RESULTSWith the stoichiometric H2O2 dose, the complete conversion of the starting imidazolium‐based ILs was achieved in less than 5 min, at 70°C, with 60% of TOC reduction after 4 h, except in the [C4mim][CH3CO2] case, where iron precipitation was observed, thus inhibiting its catalytic action. Low ecotoxicity effluents were obtained at the stoichiometric H2O2 dose, even in the cases of the highly ecotoxic ILs of long alkyl chain with chloride anion.CONCLUSIONFenton oxidation is shown to be a promising solution for the degradation of imidazolium‐based ILs in water, allowing deep detoxification with the stoichiometric H2O2 dose. © 2014 Society of Chemical Industry

Electrochemical oxidation of urea in aqueous solutions using a boron-doped thin-film diamond electrode

Abstract In the present paper, the electrocatalytic abatement of urea in aqueous solutions has been studied by means of cyclic voltammetry and galvanostatic electrolysis, using different anodes such as Pt, Ti–Ru oxide, boron-doped diamond (BDD) and antimony-doped tin oxide. HPLC analysis, total organic carbon (TOC) and ionic chromatography have been used to evaluate the oxidation and the mineralization of the treated aqueous solutions. The results of the cyclic voltammetries have shown that, in the case of Pt and Ti–Ru oxides a decrease in current density in the oxygen evolution region can be observed in the presence of urea, due to the blockage of the electrode active oxygen evolution sites as a consequence of the reversible adsorption of urea. Instead, a notable increase in the current density has been observed in the region of the oxygen evolution for the BDD and antimony-doped tin oxide electrodes, in the presence of urea, indicating that the oxidation of urea involves hydroxyl radicals. The bulk electrolysis tests have shown that the complete removal of urea and TOC can only be achieved using a boron-doped diamond and that Pt, the Ti–Ru oxide and antimony-doped tin oxide only permit a partial oxidation of urea. On the basis of the TOC evolution and the identification of the organic intermediates and inorganic ions released during the treatment, a total mineralization has been proposed. Finally, electrolysis has been performed in the presence of chloride ions, which act as oxidation mediator, and a comparison has been done between direct and mediated electro-oxidation.

Influence of seawater exchanges across the Bab-el-Mandeb Strait on sedimentation in the Southern Red Sea during the last 60 ka

[1] The location of core MD92-1008 close to the southern edge of the Red Sea is ideal to study the evolution of seawater exchanges with the Northern Indian Ocean through the Bab-el-Mandeb narrow strait. The present study was aimed at documenting the paleoceanographic evolution of this area over the past 60 ka using high-resolution magnetic, sedimentological, and geochemical indicators. Two modes of variability dominate the records: (i) long-term, glacial-interglacial variations and (ii) rapid, millennial scale variability (Dansgaard-Oeschger type) during the last glacial period. Changes in magnetic concentration were documented from natural and laboratory magnetizations after proper normalization. They are inversely correlated to the total organic carbon (TOC) content, pointing out the key role played by reductive dissolution of magnetite on the evolution of magnetic concentration. Based on the temporal evolution of TOC, CaCO3, and planktonic δ13C, we suggest that past changes in the organic matter content (i) were closely linked to glacio-eustatic variations which modulated long-term seawater exchanges and nutrient supplies to the Red Sea through the narrow Bab-el-Mandeb Strait and (ii) reflect millennial-scale changes in productivity driven by monsoon wind intensity which controlled the amount of nutrient-rich intermediate waters upwelled in the Gulf of Aden during the summer season and advected into the Southern Red Sea. The sea level rise following the onset of deglaciation generated a rapid flush of detrital material that was accumulated on the continental margins and on the previously emerged zones of the Bab-el-Mandeb area.

Quantitative evaluation of TOC, organic porosity and gas retention distribution in a gas shale play using petroleum system modeling: Application to the Mississippian Barnett Shale

Shale reservoirs have not benefited from advanced modeling tools to the extent of conventional resources. Thus an approach is proposed to integrate key parameters, such as total organic carbon (TOC) content, methane adsorption and organic porosity in a basin simulator. Original TOC has an impact on both gas generated volume and gas retention within source rocks. The conversion of organic matter into hydrocarbons also creates additional intraparticle kerogen porosity in which oil and gas can be stored. In this work, a method is proposed to calculate the evolution of TOC, organic porosity and gas retention capacity (free versus adsorbed) through time in shale gas by means of petroleum system modeling. Gas adsorption potential on organic material is calculated using a Langmuir model, which accounts for pressure, temperature and remaining solid TOC. Organic porosity is calculated as the result of the change of the organic matter from solid immature kerogen to less dense fluid hydrocarbons during thermal maturation.The method is tested on a 3D basin model of the Mississippian Barnett Shale in Texas (USA). The computed organic porosity varies from 0% in immature zones, to a maximum of 4% of rock volume in organic-rich and mature zones. Computed retained methane in the Lower Barnett Shale ranges between 20 and 60 scf/t (from 1 to nearly 3 kg/m3) and is mainly concentrated in mature areas of the basin. Simulated results are consistent with available Barnett Shale data. Possible effects of assumptions made in the approach and perspectives are discussed.

Adsorption and photocatalytic degradation of cysteine in presence of TiO2

Abstract Amino-acids are elemental constituents of microorganisms, e.g. bacteria, fungi, virus, mold, among others and are at the origin of the formation of odorous compounds after chlorination treatment due to the filtration of these microorganisms. Our study aims at studying the photocatalytic degradation of cysteine chosen as model of amino acid for understanding better the photocatalytic chemical pathway of microorganisms. The kinetics of adsorption in the dark and under UV light, the kinetics of photocatalytic oxidation, the effect of pH and the main initial pathways of cysteine degradation have been investigated in aerated TiO 2 Degussa P-25 aqueous suspensions illuminated at λ > 340 nm. Langmuir and Langmuir–Hinshelwood kinetics were observed respectively in the dark and under UV light. The coverage of TiO 2 surface under UV revealed a coverage of TiO 2 equivalent to that in the dark, indicating no modification of adsorption sites under irradiation. This behaviour is in agreement with a geometrical adsorption of cysteine as proved by using the molecular surface of cysteine and by taking into account the accessibility of water molecules. The effect of pH on adsorption and photocatalytic degradation showed a good correlation between dark adsorption and photocatalytic degradation. The mineralisation of organic carbon and nitrogen shows the presence of traces of organics hardly mineralisable but also the formation of similar amount of NH 4 + and NO 3 − ions from the beginning of the reaction contrarily to what was observed for other amino-acids. This behaviour is explained by the different ionisation states of cysteine. Taking into account the evolution of Total Organic Carbon, sulphate, nitrate and ammonium, an initial reaction pathway has been proposed.

Long-term durum wheat monoculture: modelling and future projection

The potential effects of future climate change on grain production of a winter durum wheat cropping system were investigated. Based on future climate change projections, derived from a statistical downscaling process applied to the HadCM3 general circulation model and referred to two IPCC scenarios (A2 and B1), the response on yield and aboveground biomass (AGB) and the variation in total organic carbon (TOC) were explored. The software used in this work is an hybrid dynamic simulation model able to simulate, under different pedoclimatic conditions, the processes involved in cropping system such as crop growth and development, water and nitrogen balance. It implements different approaches in order to ensure accurate simulation of the mainprocess related to soil-crop-atmosphere continuum.The model was calibrated using soil data, crop yield, AGB and phenology coming from a long-term experiment, located in Apulia region. The calibration was performed using data collected in the period 1978–1990; validation was carried out on the 1991–2009 data. Phenology simulation was sufficiently accurate, showing some limitation only in predicting the physiological maturity. Yields and AGBs were predicted with an acceptable accuracy during both calibration and validation. CRM resulted always close to optimum value, EF in every case scored positive value, the value of index r2 was good, although in some cases values lower than 0.6 were calculated. Slope of the linear regression equation between measured and simulated values was always close to 1, indicating an overall good performance of the model. Both future climate scenarios led to a general increase in yields but a slightly decrease in AGB values. Data showed variations in the total production and yield among the different periods due to the climate variation. TOC evolution suggests that the combination of temperature and precipitation is the main factor affecting TOC variation under future scenarios. Incorporation of crop residues had a positive effect, in the first 35 cm the amount of carbon increase with both the future scenarios.

Photocatalytic degradation of linuron in aqueous suspensions of TiO2

The photocatalytic degradation of linuron (3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea), a widely used herbicide and potential environmental contaminant, in irradiated titanium dioxide aqueous suspensions is investigated. The photocatalytic performance of two nano-sized materials prepared by a sol–gel process, and the influence on the degradation rate of some operational parameters, such as catalyst amount, pH of the medium and hydrogen peroxide concentration, are evaluated. Within the range of the explored experimental conditions, degradation of linuron in an aqueous suspension of TiO2 at mg l−1 contamination levels is described by a pseudo-first-order kinetic model, the apparent half-life time of the herbicide being about 30 min in optimal conditions. Based on the evolution of total organic carbon and the fate of inorganic species, the disappearance of linuron seems to be accompanied by its almost quantitative mineralization.

Photocatalytic degradation of a mixture of two anionic dyes: Procion Red MX-5B and Remazol Black 5 (RB5)

Abstract The photocatalytic degradation of a mixture of two anionic dyes, Remazol Black (RB5) and Red Procion MX-5B in presence of TiO 2 Degussa P-25 was investigated using wavelength higher than 290 nm. UV–vis spectroscopy was employed to monitor the amount of each dye in the mixture and to compare the degradation of both dyes individually and mixed. The adsorption equilibrium of each dye, the influence of pH and the initial concentration of dyes on the kinetics of discoloration and mineralization were performed and compared to their kinetics when they are individually degraded. Although no complex was put in evidence between these two coloring agents using spectroscopy UV–vis, an important modification of the RB5 adsorption is noted in the mixture. However, the presence of RB5 has no effect on the MX-5B adsorption. This difference of behaviour can be explained by considering the modification of pH by increasing the initial concentration of MX-5B in the mixture. Above 15 μmol/L, both anionic dyes are in competition for the same site. Even if the adsorption of RB5 is modified, the disappearance rate of both dyes individually or mixed are similar at low concentration of dyes. At high concentration their disappearance rates in the mixture decrease in agreement with the number of available site. Besides the study of the discoloration, we studied the evolution of Total Organic Carbon (TOC), the formation of NH 4 + , NO 3 − , SO 4 2− of both dyes during their individual or mixed photocatalytic degradation are compared. The results suggest that the mechanisms of degradation are modified in the mixture.

Catalytic ozonation-biological coupled processes for the treatment of industrial wastewater containing refractory chlorinated nitroaromatic compounds

A treatability study of industrial wastewater containing chlorinated nitroaromatic compounds (CNACs) by a catalytic ozonation process (COP) with a modified Mn/Co ceramic catalyst and an aerobic sequencing batch reactor (SBR) was investigated. A preliminary attempt to treat the diluted wastewater with a single SBR resulted in ineffective removal of the color, ammonia, total organic carbon (TOC) and chemical oxygen demand (COD). Next, COP was applied as a pretreatment in order to obtain a bio-compatible wastewater for SBR treatment in a second step. The effectiveness of the COP pretreatment was assessed by evaluating wastewater biodegradability enhancement (the ratio of biology oxygen demand after 5 d (BOD(5)) to COD), as well as monitoring the evolution of TOC, carbon oxidation state (COS), average oxidation state (AOS), color, and major pollutant concentrations with reaction time. In the COP, the catalyst preserved its catalytic properties even after 70 reuse cycles, exhibiting good durability and stability. The performance of SBR to treat COP effluent was also examined. At an organic loading rate of 2.0 kg COD/(m(3)xd), with hydraulic retention time (HRT)=10 h and temperature (30+/-2) degrees C, the average removal efficiencies of NH(3)-N, COD, BOD(5), TOC, and color in a coupled COP/SBR process were about 80%, 95.8%, 93.8%, 97.6% and 99.3%, respectively, with average effluent concentrations of 10 mg/L, 128 mg/L, 27.5 mg/L, 25.0 mg/L, and 20 multiples, respectively, which were all consistent with the national standards for secondary discharge of industrial wastewater into a public sewerage system (GB 8978-1996). The results indicated that the coupling of COP with a biological process was proved to be a technically and economically effective method for treating industrial wastewater containing recalcitrant CNACs.

Treatment of a mixture of three pesticides by photo- and electro-Fenton processes

In the present work, a comparative study of a mixture of three pesticides (chlortoluron, carbofuran and bentazon) has been investigated by advanced oxidation processes such as photo-Fenton and electro-Fenton. These processes are based on the in situ production of hydroxyl radical, a highly strong oxidant, which allows the degradation of organic pollutants until their mineralization into CO2 and H2O. For the photo-Fenton process, the effect of key parameters such as initial catalyst (Fe3+) concentration and hydrogen peroxide (H2O2) dosage were studied. Under optimal operating conditions, the evolution of total organic carbon (TOC) has been investigated for the two processes. Obtained results showed that more than 90% of TOC removal was obtained after only 2h of photo-Fenton treatment whereas the electro-Fenton process needed 8h of treatment. Nevertheless, the comparison of cost treatment shows that the photo-Fenton process is more expensive than electro-Fenton. The evolution of pesticide's concentration during treatment was determined by high performance liquid chromatography (HPLC). Inorganic ions released such as chloride, nitrate, sulphate and ammonium ions are identified and their kinetic evolution was measured by ion chromatographic analyses.

Oxidation of dissolved organic matter in the effluent of a sewage treatment plant using ozone combined with hydrogen peroxide (O3/H2O2)

The effluent from the secondary clarifier of an Urban Sewage Treatment Plant was oxidized by the combined and simultaneous use of ozone and hydrogen peroxide. The purpose was to increase the wastewater's reuse potential by improving water quality. The removal of dissolved organic chemicals was enhanced by adding periodic pulses of hydrogen peroxide while keeping pH above 8.0 throughout the runs. These conditions led to almost complete mineralization in less than 1 h. Under similar conditions, without the addition of hydrogen peroxide, the removal of total organic carbon (TOC) was no higher than 35%. The evolution of TOC was related to the concentration of hydroxyl radicals using a second-order kinetic model in which the exposure to hydroxyl radical was included by assuming a quasi-steady-state approximation. The concentration of hydroxyl radical was computed using the experimental data from ozone and hydrogen peroxide. The kinetic constants for the hydroxyl-mediated mineralization process were determined for wastewaters collected during a 1-year sampling campaign. The results showed that the mineralization process takes place in two periods whose rate constants were linked to the chemical oxygen demand (COD) to biochemical oxygen demand (BOD) ratio and to the chloride content of wastewaters. During the first part of the runs, the specific rate of mineralization was high, before subsequently decreasing after a period of 5–15 min by an average factor of 6.4 whose 95% confidence interval was in the 3.4–9.3 range. The moles of TOC removed per mole of ozone consumed were in the range of 9.2–17.7 mg O3/mg TOC measured at maximum ozone efficiency, which always occurred within the first 10 min.

Removal of Acid Orange 7 from water by electrochemically generated Fenton's reagent

The removal of azo dye Acid Orange 7 (AO7) from water was investigated by the electro-Fenton technology using electrogenerated hydroxyl radicals (OH) which leads to the oxidative degradation of AO7 up to its complete mineralization. H(2)O(2) and Fe (II) ions are electrogenerated in a catalytic way at the carbon-felt cathode. AO7 decay kinetics and evolution of its oxidation intermediates were monitored by high-performance liquid chromatography. The absolute rate constant of AO7 hydroxylation reaction has been determined as (1.20+/-0.17)x10(10)M(-1)s(-1). The optimal current value for the degradation of AO7 was found as 300 mA. AO7 degradation rate was found to decrease by increase in Fe(3+) concentration beyond 0.1mM. Mineralization of AO7 aqueous solutions was followed by total organic carbon (TOC) measurements and found to be 92%. Based on TOC evolution and identification of aromatic intermediates, short-chain carboxylic acids and inorganic ions released during treatment, a plausible mineralization pathway was proposed.

Removal of pharmaceuticals and kinetics of mineralization by O 3/H 2O 2 in a biotreated municipal wastewater

The ozonation of an effluent from the secondary clarifier of two Municipal Wastewater Treatment Plants was performed by using alkaline ozone and a combination of ozone and hydrogen peroxide. Alkaline ozonation achieved only a moderate degree of mineralization, essentially concentrated during the first few minutes; but the addition of hydrogen peroxide eventually led to a complete mineralization. The evolution of total organic carbon (TOC) as a measure of the extent of mineralization and the concentration of dissolved ozone were analyzed and linked in a kinetic model whose parameter represented the product of the exposure to hydroxyl radicals and the kinetic constant of indirect ozonation. This rate parameter yielded the highest values during the first part of O 3/H 2O 2 runs. The kinetic constant for the decomposition of ozone at the end of the run was also measured and computed for the non-oxidizable water matrix and yielded essentially the same values regardless of whether or not hydrogen peroxide was used. A group of 33 organic compounds, mainly pharmaceuticals and some relevant metabolites present in the wastewater effluents, were evaluated before and after the ozonation process using a liquid chromatography-hybrid triple-quadrupole linear ion trap system (LC-QqLIT-MS). The results demonstrate that the ozonation degrades these compounds with efficiencies of over 99% in most cases, even under low mineralization conditions in alkaline ozonation.

Highly efficient photodegradation of the pesticide metolcarb induced by Fe complexes

Here we show the efficient photoinduced degradation of the pesticide metolcarb, in less than 400 min, using iron(III) aquacomplexes and 365 nm light. The degradation is mainly due to the formation of hydroxyl radical. It was complete when molecular oxygen was present. The analytical study gives evidence for the primary formation of several byproducts formed from 1) the scission of the O–C bond, 2) the hydroxylation of the aromatic moiety and 3) the attack of the two methyl groups. Under prolonged irradiation and in aerated solutions, efficient mineralization was evidenced by the study of total organic carbon evolution as a function of irradiation time.

Photochemical and photocatalytic degradation of salicylic acid with hydrogen peroxide over TiO 2/SiO 2 fibres

The effect of hydrogen peroxide on the photo-oxidation of salicylic acid (SA) in aqueous solutions under UV-irradiation was investigated in both purely homogeneous and photocatalytic conditions. Results obtained show that in absence of photocatalyst and under UV-irradiation, the SA degradation rate increases with increasing the amount of hydrogen peroxide added, although for high concentrations of H 2O 2 the enhancement of the activity is progressively attenuated. In the case of the photocatalytic degradation, nanocrystallites of anatase immobilised over SiO 2 fibres were used as catalyst. In the present of TiO 2/SiO 2, the addition of hydrogen peroxide results in almost a three-fold increment of the photoactivity at low concentration (29.1 mM). In contrast, when the amount of H 2O 2 added exceeds certain limit, the rate of SA removal becomes slightly lower than those measured in absence of photocatalyst. A simple kinetic model which considers the summation of both photochemical and photocatalytic contributions is used to account for the dependence of the rate on the H 2O 2 concentration. The efficiency of the SA mineralization was also evaluated by monitoring the evolution of total organic carbon (TOC) with irradiation time. In this respect, remarkable differences are found when comparing pure photochemical degradation, which only reduce the TOC concentration in about a 3% after 300 min of irradiation, with the photocatalytic treatment, which achieve a 38% of SA mineralization in the same period.

Mineralisation of Monuron photoinduced by Fe(III) in aqueous solution

The degradation of Monuron (3-(4-chlorophenyl)-1,1-dimethylurea) photoinduced by Fe(III) in aqueous solution has been investigated. The rate of degradation depends on the concentration of Fe(OH) 2+, the most photoreactive species in terms of OH radical formation. These OH radicals are able to degrade Monuron until total mineralisation. The primordial role of the speciation of Fe(III)-hydroxy complex in aqueous solution, for the efficiency of the elimination of pollutant, was shown and explained in detail. The formation of Fe(II) in the irradiated solution was monitored and correlated with the total organic carbon evolution. Degradation photoproducts were identified and a mechanism of degradation is proposed.