Band 11, Heft 1

Synthetic surfactants are amphipathic molecules consisting of a hydrophilic polar head moiety and a hydrophobic non-polar tail one. Alkyl benzene sulfonates are the principal type of laundry anionic surfactants, they are extensively used because of its relatively low cost, good performance, and easy-processing to a stable powder with biodegradable characteristics at low concentrations. LAS are a mixture of homologues and phenyl positional isomers, each containing an aromatic ring sulfonated at position para and attached to a C 10 -C 14 linear alkyl chain at any position except the terminal one. These surfactants are used frequently in laundry detergent formulations due to its high efficiency in detergency, wetting and dispersion processes, acting as energizers of the surface activity. LAS surfactants invade the environment mainly via discharge from sewage treatment works. In spite of the fact that the sulfonic moiety is degraded by bacterial action, the organic part, especially the ring, is firmly resistant to biological degradation. This paper reports the complete photooxidation of LAS in aqueous solution in the presence of hydrogen peroxide. Initial solutions contained 100 mg/l of surfactant LAS were oxidized at pH 3 and modifying the initial hydrogen peroxide concentration from 0 to 23.58 mM. The proposed lumped kinetic model is based on former observations and assumes the formation of intermediates lumps with different absorption behaviour. The mechanism consists in seven pseudo-first order kinetic reactions. The apparent kinetic constants are directly dependent on dosage of oxidant, and in this work, this dependence has been analysed. The model describes acceptably the evolution of the three lumps of intermediates within the operating conditions of pH and oxidant dosage analysed. Besides, changes in functional groups and aromaticity during degradation were evaluated for the samples and related to the intermediates defined in the kinetic model.

The characterization of radical oxidation was studied in phenolic compounds degradation by a H 2 O 2 / UV advanced oxidation process (AOP). The UV irradiation source was a low-pressure mercury vapour lamp that was axially centred in a tubular reaction system. The effects of hydrogen peroxide, phenol molar ratio and pH have been investigated. From bibliography regarding the generation of radicals in the H 2 O 2 /UV system, a kinetic model has been developed, making it possible to estimate the concentration of different radical species. These concentrations mark a determined oxidative level, the evolution of which will be analyzed under a series of initial conditions involving pH and the molar ratio of phenol to hydrogen peroxide.

Most of dyes are considered as non - biodegradable substances and because this, they have became in an environmental problem. Commercial dyes are used in paper and textile industries, and their by-products contaminate surface water sources. Titanium dioxide - based photocatalysis can be an alternative for treatment of dye - contaminated water streams before dumping, because this process can generate powerful oxidant species as hydroxyl free radicals (•OH). In this study, the photocatalytic decolorization of methylene blue was carried out in a compound parabolic collector (CPC) and tubular collector (TC; no reflectors) using the radiation provided by a set of six UV black-lamps. The experimental tests corresponding to a central-composite experimental design were carried out during three hours, whereas the tests for optimal conditions were carried out during 315 min. The decolorization of the dye was measured indirectly with UV- visible absorbance. The optimal region could be determined using the Response Surface Methodology, and for CPC reactor the results were 70.8% for optimal degradation at 0.44 g/L of TiO 2 and a pH of 8.41, whereas for tubular collector the optimal decolorization were 63.46% at 0.38 g/L of TiO 2 , and a pH of 6.34. For both reactors, the optimal conditions found with Response Surface methodology were experimentally validated (66.5% MB decolorization for CPC and 62.1% MB decolorization for TC). With optimal conditions found, the possibility of air sparging was also evaluated. The degradation rate of dye increased slightly with oxygen saturation, whereas it was observed a larger decolorization of dye in CPC reactor than the tubular reactor.

Global quantum yield and overall volumetric rate of photon absorption (OVRPA) were quantified for TiO 2 -based photocatalytic degradation of dichloroacetic acid (DCA) in a differential perfect-mixture reactor. A kinetic model that involves physic and radiant energy parameters is proposed for describing this reaction. The considered system behaves as an isotropic and completely-mixed slurry, and found kinetic parameters do not depend on the spatial coordinates but strictly on the effective specific-radiation phase field present in the reaction vessel. The simplified mathematical model was analytically solved for finding the generatrix function, and the parameters fitting was achieved by means of a modified Newton-Raphson’s method. Obtained values for the global quantum yield are consistent with the physic behavior of the studied system. The kinetics results have an overall associated relative-error less than 4,5%.

In this study, the performance of zinc oxide as a catalyst for photodegradation of commercial herbicide 2,4-D AMINA 4 Ⓡ (dimethylamine salt of 2,4-dichlorophenoxyacetic acid) was evaluated. The experimental was made using a flat plate reactor working in continuous mode, and ultraviolet light lamps as artificial source of radiation. By using a Response Surface Methodology (RSM), the effects on pesticide degradation of the initial pH of solution, the catalyst concentration, and the recycling flow rate were studied. The degradation was quantified by calculating total organic carbon (TOC) removal in the aqueous solution. The optimal conditions found in this study, within the studied range, were: pH 5,5, concentration of catalyst 0,35 g/L and recirculation flow rate 410 L/h. The TOC removal achieved was 38,1% after 8 hours of continuous treatment. However, the real optimal values for pH and recycling flow rate are higher than the found ones by the statistical software.

Polycrystalline tungsten-doped titanium dioxide nanopowders within a dopant concentration of 0-1 at.% were prepared by a one-step flame spray synthesis (FSS). Mixtures of titanium tetra-isopropoxide dissolved in ethanol and tungsten hexacarbonyl solubilized in tetrahydrofuran were used as precursors. The specific surface area (SSA) of the powders was between 40 and 130 m 2 /g depending on the process parameters, namely the flame combustion stoichiometry and their chemical composition. Irrespective of their composition the powders consisted of spherical particles, as visible by transmission electron microscopy (TEM). They are highly crystallized with anatase as the predominant phase, according to X-ray diffraction (XRD). The band gap energy was determined by spectrophotometric measurement and was between 3.29 eV and 3.34 eV. The photocatalytic performance of the powders was studied by the degradation of methylene blue (MB) and methyl orange (MO) in aqueous suspensions under UV-A (365 nm) as well as visible (400-500 nm) irradiation. The catalytic activity was determined as a function of the tungsten concentration, the specific surface area and the flame combustion stoichiometry. It was found that the TiO 2 -0.7 at %W particles with high SSA have the highest photoactivity for degradation of MB and MO. This can be explained by the incorporation of the tungsten into the TiO 2 crystal lattice as well as modification surface properties.

Catalytic Wet Peroxide Oxidation (CWPO) for the continuous treatment of a phenolic aqueous solution has been studied on a pilot scale process. The pilot plant has been designed by integration of a catalytic fixed bed reactor (FBR) with a continuous stirred tank reactor (CSTR). The CSTR is used as reservoir for the continuous delivering of a recirculation stream through the catalytic bed. The main part of phenol mineralization takes place by catalytic oxidation in the FBR. The mesoporous SBA-15 silica-supported iron oxide (Fe 2 O 3 /SBA- 15) agglomerated with bentonite has been selected as catalyst, according to preliminary studies for the continuous treatment of phenolic aqueous solutions in a catalytic packed-bed reactor operating in upflow (1). The efficiency of the wet peroxide oxidation treatment under different operation conditions has been evaluated in terms of phenol degradation, total organic carbon (TOC) reduction and hydrogen peroxide conversion. Among the main operation conditions, the feed and recirculation liquid flow rates, the catalyst loading and the temperature in the CSTR were studied. The increase of the residence time as the feed flow rate is reduced has shown a remarkable improvement of the process efficiency, whereas the variation of the recirculation flow through the FBR has slightly affected the overall catalytic performance. A significant enhancement of the process efficiency has been also found as the temperature of the CSTR was increased up to 80 °C. Under the most favourable operating conditions, phenol was almost totally degraded (99%) and TOC was reduced up to ca. 63% at steady-state conditions. In concern to the catalyst stability, a low dissolution of iron within the aqueous solution during the process has been proven.

The objective of this research is to assess the effect of ultrasonic irradiation (20 KHz) on the catalytic activity and catalyst particle size of different iron-containing solids (hematite/SBA-15 nanocomposite; hematite; goethite). The catalytic activities of the different catalysts were investigated in the sono-Fenton degradation of a phenolic aqueous solution in the presence of hydrogen peroxide at pH 3. The catalytic performance was monitored in terms of phenol and total organic carbon (TOC) conversions. The concentration changes of different by-products coming from incomplete mineralization of phenol were also monitored. The stability was examined by measuring iron dissolved in the reaction medium after reaction. The degradation rate in the presence of the nanocomposite material was higher than that when SBA-15 and hematite were separately suspended and also higher than that found for the bulk and unsupported iron oxides (hematite and goethite). The particle size of the catalysts suffers serious changes during the sonication which strongly depend on their nature. Unlike nanocomposite material which presents a deep catalyst particle reduction, unsupported bulk iron oxides yield an agglomeration of the particles. The considerable enhancement of the activity achieved with the nanocomposite material is due to the catalyst particles size reduction during ultrasound irradiation as well as the high dispersion of the metallic species over the mesostructured support.

The design and construction of a system consisting of a dielectric barrier cell and the electronic instrumentation intended to generate pulsed discharges at atmospheric pressure in water is showed in this paper. Also, the experimental results from the developed advanced oxidation processes (AOPs) are presented. Demineralised water with a conductivity of 5 μS/cm was used in all tests and a non-thermal plasma is produced between two concentric electrodes in a coaxial configuration by applying high voltage pulses which amplitude can be adjusted from 0 to 30 kV. The propagation of the streamers was characterized by means of the obtained waveforms of voltage and current. The concentration of the ozone generated by the discharges was monitored allowing, in this way, to carry out an analysis of the AOPs, and optic spectroscopy was used to study the discharge parameters involved in such a process.

In this research degradation of atrazine from simulated groundwater by ozonation itself and the combination of ozone and UV photocatalysis using TiO 2 have been investigated. It has been found that atrazine was degraded by photolysis alone but no reduction of TOC content has been noticed. However, with TiO 2 photocatalyst involvement the rate of degradation has increased in comparison with photolysis itself. Reduction of TOC content was observed, too. Concerning preliminary results it has been found that ozonation itself was the most efficient in the pH range from 6 to 11. Ozonation process enhancement was achieved by introducing UV irradiation into the system. The use of TiO 2 photocatalyst in the UV/O 3 process slightly improved the overall performance. For all studied processes, the kinetics of atrazine degradation was monitored.

Fenton, Fenton-Like and Photo-Fenton processes were revealed effective in the mineralization of 4-chlorophenol, 4-CP. Experiments for the Fenton photo-assisted degradation of 4-CP were planned under the Design of Experiments (DOE) scheme. Results show that for the lowest 4-CP concentration (74 mg·L -1 ) the TOC reduction rises from 65% ([H 2 O 2 ] = 200 ppm, [Fe(II)] = 10 ppm) up to close 100% ([H 2 O 2 ] = 800 ppm, [Fe(II)] = 10 ÷ 50 ppm). Complete TOC reduction was attained, probably due to the reagent excess. However, for highest 4-CP concentration (222 mg·L -1 ), TOC reduction achieved was 47% ([H 2 O 2 ] = 200 ppm, [Fe(II)] = 10 ÷ 50 ppm), for the worst case and 81% ([H 2 O 2 ] = 800 ppm, [Fe(II)] = 50 ppm) for the best. To describe this behavior, different models were fit to degradation data. These models are later compared and discussed. As recent studies notice, a second order polynomial equation (including bilinear terms) may be a questionable approach in many cases. For this reason, an alternative model, which aims at improving empirical fitting to the performance of the system, is proposed and validated.

We report the photocatalytic degradation of chlorobenzene (CB) in suspended TiO 2 aqueous solution at pH7 under UV irradiation. We measured the kinetics of CB degradation and Cl- release and calculated a pseudo-first-order rate constant in both cases. We found a higher value of the rate constant k CB than of k Cl - one, which show that the dechlorination does not take place concomitantly with the •OH attack on CB. This oxidation reaction obeyed Langmuir-Hinshelwood equation. The half life time value resulted from this equation was lower than that of the pseudo-first order rate constant at any CB initial concentration. This showed us the existence of competition between the byproducts and the pollutant for •OH radical consumption. Also, we demonstrate the positive effect of doped S-TiO 2 on CB photocatalytic degradation (powder or film) due to its enhanced absorption in UV and in addition to a new absorption band in visible.

Nanocrystalline Titania films have been deposited on glass slides by solgel solvolysis with acetic acid in the presence of surfactant template. The quantity of Titania on each slide was modified by depositing subsequent layers followed by calcination at 550 °C. Platinum was then deposited on these films by adsorption from aqueous solutions containing Na 2 PtCl 4 followed by treatment with UV radiation. This Pt/TiO 2 catalyst was employed in photocatalytic ethanol reforming and produced molecular hydrogen. Excitation was obtained with low intensity Black Light tubes. Optimization of the system has been made leading to very high active electron to incident photon quantum efficiency. It was shown that optimization can be achieved when all photocatalyst is simultaneously exposed to the exciting radiation and to the target solution without obstruction and this situation can be obtained in the form of nanostructured thin films.

This paper systematically studied the current-voltage characteristics and the spectrum characteristics of bipolar corona discharge in multi-needle electrode configuration, and determined the optimized space between electrodes. The experimental results show that the discharge current I decreases with an increase in the needle radius a or the space between electrodes d, and increases with an increase in the space between needles s. Due to the symmetry of the discharge electrode configuration, the polarity of the HV electrode has no obvious influence on the discharge. Using the method of OES for measuring N 2 emission spectrum, the spacial distribution of energetic electrons in multi-needle bipolar corona discharge has been investigated. According to the distribution of N 2 second positive band’s intensity I SPB , the outline of ionization region was drawn accurately. The relationship between I SPB and discharge current I has been obtained through the sum of I SPB . The sum of I SPB is nearly linear to I, so the distribution of I SPB is corresponding to the density distribution of energetic electrons. The effects of space between electrodes on discharge energy density have been studied. Generally, discharge energy density reduces with increase in space between needles at the same electrode s, but it has small change when s is in the range from 12 mm to 22 mm. At the same time, discharge energy density reduces with increase in space between electrodes d. The allowable discharge energy density is up to its maximum when d is about 32 mm.

Based on the former study on I-V characteristics of wire-cylinder type corona discharge, wire-plate type and wire-wire type corona discharges were studied experimentally. The field intensity E c on the ionization boundary was introduced, and V c was the corresponding electric potential. Let C=I/V(V-V c ), C-V curves could be worked out and finally a relationship that followed the experimental results was obtained, i.e. I=AV 2 (V-V c )/L[R ln(R/r 0 )] 2 . I of wire-wire bipolar discharge was greater than the sum of that of equivalent wire-plate type corona discharges. Therefore, we concluded that it was charged ions that formed current in the migration area and the recombination between positive and negative ions should be neglected; density of electrons in ionization area of bipolar discharge was twice greater than that of unipolar discharge.

A combination system of micro-pore ceramic filtration and UV radiation was built up for ballast water treatment. Two treatment methods, single micro-pore ceramic filtration and micro-pore filtration and UV radiation, were studied in the research, respectively. Chlorella removal rates and total oceanic bacteria inactivation rates were measured at different flow rates (0.6 ~ 4.7 m 3 ·h -1 ) and different initial Chlorella concentrations (0.4 × 10 4 ~1.4 × 10 4 cells·mL -1 ). In this study, Chlorella removal rate was up to 92% by the single filtration while the rate by the combination one could reach 97%. Moreover, the combination one is superior to the single one at almost all the conditions. For total oceanic bacteria, single filtration displayed no obvious inactivation ability while the combination one showed up to 99% inactivation rate.

An advanced oxidation treatment, UV/TiO 2 /Fe(III) process, was applied to an azo dye, Remazol Brilliant Blue R-A, used in textile dyestuffs in the Turkish textile industry by using a solar photocatalytic reactor. A Box-Wilson statistical experimental design was used to determine the effects of oxidant dosage and flowrate in UV/TiO 2 /Fe(III) advanced oxidation process. Degradation of color removal and organic matter concentration of the dye have been evaluated. A strong dye solution (50 mg/l) was 98% decolorized after 8 hours of irradiation, and 54% reduction of the total organic carbon (TOC) was obtained. It has been found that the degradation rates increased until optimum values of TiO 2 and Fe(III) concentrations, beyond which the reagents exerted an inhibitory effect. The degradation rate was also function of flowrate.

The treatment of industrial cork-processing water at natural pH (6.45) by ozonation alone and ozone based advanced oxidation processes (O 3 /H 2 O 2 and O 3 /UVC) in a bubble column reactor was investigated with the view of establishing optimal operating process conditions. The reaction of ozone with the organic matter in the wastewater was found to begin in the mass transfer controlled kinetic regime (fast kinetic regime), shifting to the moderate and slow kinetic regime (reaction in the bulk liquid) at later stages of the ozonation reaction. The elimination of colour from the wastewater was found to correlate with a decrease in the total amount of phenolic species. The reaction temperature was found to have little influence on the observed rates of Total Organic Carbon (TOC) removal. In the treatment of the wastewater by peroxone or by the UVC-ozone process the TOC removal rates were enhanced by the production of highly reactive hydroxyl radicals. The analysis of the observed kinetics calls for an industrial treatment process involving the peroxone process in the early stages of the oxidation reaction up to complete colour removal, followed by the O 3 /UVC process.

Proper reaction conditions have been found for the conversion of 1,2 propanediol, 1,3 butanediol and 1,4 pentanediol to the corresponding hydroxy-carbonylic compounds with good chemo- and regio-selectivity by photochemical excitation of CH 2 Cl 2 suspensions of TiO 2 . In particular, about 90% of hydroxyacetone from 1,2 propanediol and more than 75% of 4-hydroxypentanal from 1,4 pentanediol could be obtained. A remarkable conclusion is that the TiO 2 -assisted photooxidation of 1,4-pentanediol is carried out with good selectivity to 4-hydroxypentanal and low mineralization to CO 2 also under high conversion conditions. The adsorption of the diol on the semiconductor is an important parameter able to affect efficiency and selectivity of the photocatalytic process. In particular, the high polarity of the TiO 2 surface favours the preferential adsorption of the primary OH group of the diol molecule, thus favouring its subsequent oxidation.

The degradation of chlorobenzene (CB) in UV/H 2 O 2 system in aqueous solution, at pH 7, was studied. CB degradation was monitored by gas chromatography, Cl - liberation was monitored by ion chromatography at various irradiation times and a pseudo-first order kinetic in respect to both components was found. The rate constant k Cl - was lower than k CB , which suggests that chlorinated intermediates are firstly formed by the attack of •OH radicals on CB, followed by chlorine liberation. When the CB concentration was kept constant we found a linear increase in the rate constants with H 2 O 2 concentration, followed by a short interval with unmodified k I values and a decrease at higher H 2 O 2 concentration. The variation of CB concentration at constant ratio [H 2 O 2 ]/ [CB] led to the decrease in the degradation efficiency due to the competition with the intermediates, for •OH radicals consumption. Our kinetic results agreed with the literature information on the CB degradation mechanism.

The process of organic dye removal from various water solutions containing organic dyes and inorganic additives by the DC diaphragm discharge has been studied in so called “negative part” of this. The concentration of treated dye decreases almost exponentially to constant residual value. The final dye concentration reached approximately 20% of the initial value after 10 minutes of the treatment of the Direct Red 79 dye solution. The dye de-coloration was affected by the dye structure. The azo and diazo compounds have been degraded significantly faster to be compared to thiazine compounds. The degradation process requires an optimal adjustment of the initial solution conductivity. The optimum conductivity of approximately 600 μS⋅cm -1 was found when the dye solution contained either NaCl or NABr electrolytes. The type of electrolyte used for the conductivity adjustment considerably affects the process of dye de-coloration. Halogen compounds have been found to be the most proper compounds for such purpose.

In the design of UV-PCO-based air cleaners for improving IAQ, multiple compounds interference effects need to be quantified because indoor environment has multiple VOCs under low concentrations (typically at ppb and sub-ppb levels). This paper presents a systematic experimental investigation using a labscale UV-PCO reactor under individual vs. multiple VOC challenges. Tests were conducted for two aromatics (toluene and ethylbenzene) and two aldehydes (formaldehyde and acetaldehyde) as individual compound and binary mixture, and three alkanes (octane, decane and dodecane) as individual compound, binary and ternary mixtures. An annular tube reactor coated with Degussa TiO 2 /3% WO 3 (by weight) was placed in a small-scale (50 L) stainless steel chamber. The test chamber had a continuous feed flow and the system operated as a continuous stirred tank reactor. The concentration of test VOCs at chamber inlet ranged from 0.5 to 35 mg/m 3 . The overall reaction rates were measured. The mass transfer effects were quantified. The average reaction rate constants were then determined. Reversible deactivations were observed for toluene and ethylbenzene as individual VOCs and as mixture. For the individual compound tests, the bimolecular L-H rate form fit experimental data best. For the binary mixture tests, the bimolecular L-H rate model with the binary component competitive adsorption considered described the trend of experimental data well, and the rate coefficients from the PCO reaction of individual compound could apply. As for alkanes and aldehydes, the reaction rate was linearly dependent on the reactant concentration within the tested concentration range. The competition/interference effects between different compounds (except octane in one ternary mixture test) were insignificant under test conditions. Results also indicate that mass transfer resistance needs to be considered under low VOC concentration levels and high UV intensities (typical for an annular tube reactor as UV lamp is in the middle of the tube) because it is likely in the same order of magnitude as the reaction resistance.