Gustavo Imoberdorf

Degradation of natural organic matter in surface water using vacuum-UV irradiation

The use of vacuum-UV (VUV) radiation to degrade natural organic matter (NOM) and the main variables affecting the efficiency of this process were investigated using an annular photoreactor. After 180 min of irradiation with VUV, the total organic carbon (TOC) decreased from 4.95 ppm to 0.3 ppm. Also, decadic absorption coefficients of the water at 185 nm and 254 nm decreased from 3.2 cm(-1) to 2.85 cm(-1), and 0.225 cm(-1) to 0 cm(-1), respectively. The reactor operation was kinetically controlled for Reynolds numbers greater than 600, changes of pH between 5 and 9 had little effect, and increases in alkalinity decreased the process efficacy. Additionally, H(2)O(2)/VUV and VUV processes were compared to H(2)O(2)/UV and UV processes, where the formers showed greater effectiveness with complete mineralization of NOM as opposed to partial oxidation with H(2)O(2)/UV, and no mineralization with UV alone. Modeling and analysis of the photon flux and absorption in the reactor showed that 99% of the 185 nm radiation was absorbed by the water in the reactor. In comparison, only 48% of the 254 nm radiation was absorbed by the water. The overall quantum efficiency of the mineralization for VUV was 0.10 for 50% TOC reduction.

Novel Collimated Beam Setup to Study the Kinetics of VUV-Induced Reactions

Vacuum UV (VUV) process is an incipient advanced oxidation process, which can be used for water treatment. This process relies on the formation of hydroxyl radicals through the VUV‐induced photolysis of water. In particular, the use of ozone‐generating mercury vapor lamps, which emit 10% of the radiation at 185 nm and 90% at 254 nm, is showing very promising results for the degradation of micropollutants. The kinetics of VUV process has been studied in batch‐ and flow‐through reactors, but the effect of 254 and 185 nm photons cannot be isolated, mass transfer resistances can take place and the interpretation of the results is complex. In this technical note, a new VUV collimated beam to conduct kinetic tests is presented, which offers several advantages: (1) it allows the irradiation of samples with 185, 254 nm photons, or both, (2) the concentration of reagents is uniform in the reaction volume and (3) it allows to change the fluence rate by changing the distance between the lamp and the photoreactor. Details of the geometry are presented, as well as an analysis of the collimation and uniformity of the radiation of the new VUV‐collimated beam setup.

Experimental study of the degradation of 2,4-D induced by vacuum-UV radiation

Vacuum-UV (VUV) photoinduced degradation of the herbicide 2,4-D was studied. A flow-through VUV photoreactor was used (i) in batch mode to study the kinetics of degradation and (ii) in continuous mode under steady state to analyze the potential utilization of this process in commercial applications. In both cases, the reactants were recycled to minimize diffusive resistances. Experimental results from the batch studies showed that the initial degradation rate of 2,4-D in ultrapure water was independent of the initial concentration of the herbicide. However, a reduction in the reaction rate was obtained over the course of the treatment, largely due to the formation of 2,4-D partial oxidation by-products which compete with 2,4-D molecules for HO (scavenging effect). Increases in water alkalinity reduced 2,4-D degradation rate as a consequence of the scavenging of HO by carbonates and bicarbonates. The degradation of 2,4-D in raw surface waters was also investigated. A noticeable reduction in the degradation rate was observed because of the presence of NOM and alkalinity, both being known HO scavengers. Additionally, the presence of inorganic species/ions that absorb VUV may also have contributed to the reduction of the overall degradation rate. High conversions were obtained in the continuous system. At a residence time of 25 seconds, conversions of 97% and 65% were achieved for inlet herbicide concentrations of 1 and 10 mg L(-1), respectively. Under these conditions, the received dose of 185 nm radiation was 44.8 mJ cm(-2).

Effects of inorganics on the degradation of micropollutants with vacuum UV (VUV) advanced oxidation

ABSTRACT This research focused on the effects of inorganic water constituents on the efficiency of vacuum UV (VUV) for the degradation of micropollutants in surface water supplies. Atrazine was used as a model miropollutant, and bicarbonate, sulphate, and nitrate were used as the most common inorganic constituents in the water matrix. First, the absorbance of radiation at 254 and 185 nm was measured in the presence of different ions. At 254 nm, only nitrate showed a measurable absorption coefficient of = 3.51 M cm, and all other ions showed a molar absorption coefficient below the detection limit. However, at 185 nm, all the ions showed high absorption coefficients, with nitrate giving the highest absorption coefficient of = 5568 M cm. Second, the hydroxyl radical (HO) scavenging effects of the same inorganic ions were evaluated; nitrate and bicarbonate showed a negative effect during the UV/H2O2 and VUV advanced oxidation processes. Sulfate was photolyzed with 185 nm UV to form HO, and for this reason, it assisted the degradation of the target micropollutant, as demonstrated by increases in the degradation rate constant. An additional component of this work involved developing a method for measuring the quantum yield of atrazine at 185 nm. This made it possible to distinguish the contribution of OH radical attach from that of direct photolysis towards the degradation of atrazine.

Novel composite photocatalyst made of TiO2 nanoparticles

A novel photocatalyst based on TiO(2) nanoparticles was developed for application in fluidised bed photocatalytic reactors for water treatment. The mechanically robust photocatalyst consists of composite spheres made of TiO(2) nanoparticles and TiO(2) commercial powder. X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area analysis (BET) were used to characterise the catalyst. The photocatalytic activity was evaluated using model pesticide micro-pollutant. A complete model comprised of radiation, kinetic, and reactor bed models was also developed, allowing for detailed analysis of the photoreactor.

Micropollutants Removal from Surface Water Using a Pilot Vacuum-UV Advanced Oxidation Process

AbstractOrganic micropollutants (OMPs) are becoming more common in drinking water supplies worldwide. Vacuum-UV (VUV) radiation is an incipient chemical-free oxidation process that offers a potenti...

Synthesis, Characterization, and Comparison of Sol–Gel TiO2 Immobilized Photocatalysts

Abstract This study was focused on the synthesis of titania-based photocatalytic coatings with high photocatalytic activity, attrition resistance, and stability. Five different photocatalytic coatings were synthesized using the sol–gel technique. Three coatings were prepared using aqueous sols of TiO2 nanoparticles with different amounts of titanium tetraisopropoxide and different quantities and types of acids. The other two photocatalysts were composite sol–gel coatings which were prepared by incorporating commercial Degussa P25 into the TiO2 synthesized through sol–gel technique. The physical and optical properties of the immobilized photocatalysts were characterized with UV–vis spectroscopy, X-ray diffraction, scanning electron microscopy, and light scattering. The photocatalytic activity of each coating was determined using a lab-scale differential photoreactor by measuring the degradation rate of a model micropollutant, the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D). The conversions of 2,4-D obtained with the TiO2 coatings without Degussa P25 were in the order of 7–23%, whereas the two composite coatings provided conversions in the range of 66–69%. In addition, one of the composite coatings showed a more homogeneous morphology and less cracking, and for this reason, it was more durable and showed lower attrition.