Antonio Carlos Silva Costa Teixeira

Photo-Fenton degradation of wastewater containing organic compounds in solar reactors

Abstract In this work, the photo-Fenton oxidation of phenol in aqueous solutions has been investigated using Fe 2+ , H 2 O 2 and UV–visible light (sunlight). Laboratory-scale experiments were carried out using solar reactors of two different configurations: (1) a concentrating parabolic trough reactor (PTR) and (2) a non-concentrating thin-film reactor. Global solar irradiance was measured during the experiments. Additional laboratory experiments were carried out in an annular photochemical reactor using an artificial light source, at the same experimental conditions. The results indicate that the photo-Fenton process using solar irradiation is an effective treatment for industrial wastewater containing phenol. At low contaminant concentration (TOC 0 =100 ppm), more than 90% of the total organic carbon content of the initial phenol solution could be converted to inorganic carbon within about 3 h of irradiation, using artificial light or sunlight (even on cloudy days), in reactors of different geometry. At moderate or higher phenol concentrations (TOC 0 =550 or 1000 ppm), the results indicate satisfactory TOC removal (45–55%) at reasonable degradation rates. Experiments under different insolation conditions suggest a direct linear dependence of the organic carbon removal on the accumulated sunlight energy reaching the system. Solar light can be used either as a complementary or alternative source of photons to the process.

Deactivation of steam reforming catalysts by sintering: experiments and simulation

Sintering of coprecipitated Ni/Al2O3 catalysts was studied in a microreactor at 500 and 800°C under steam reforming reaction. Changes in microstructure (crystalline phases, average metal crystallite sizes and size distributions) were investigated by temperature programmed reduction (TPR), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Differences between particle size distributions determined by XRD and TEM are discussed in view of their specific limitations. Low temperature calcination of unpromoted catalysts may have a beneficial stabilizing effect upon reduction. The rate of sintering of small nickel crystallites increases as a result of the combined action of steam and high temperature, particularly for narrow initial crystallite size distributions and high initial dispersions. This behavior suggests a shift, from crystallite migration in the initial stages of heat treatment, to atomic migration in the latter stages. The lanthanum promoter seems to inhibit metal crystallite growth under reduction and reaction conditions. Predictions of a developed Monte Carlo based model are in good qualitative agreement with experimental observations.

Environmental contamination by fluoroquinolones

Over the past few decades, a high number of pharmaceuticals have been detected in surface, ground and drinking waters. This contamination comes from domestic sewage, livestock, hospitals and chemical-pharmaceutical industries. Typical examples of these pollutants are the fluoroquinolones - powerful antibiotics used in human and veterinary medicine. The presence of fluoroquinolones in the environment can pose a serious threat to the ecosystem and to human health due to their high consumption globally: in 1998, around 120 tons were produced. Even at low environmental concentrations, antibiotics stimulate bacterial resistance. The consequences of the presence of fluoroquinolones in the environment are not fully understood, but are known to be toxic to plants and aquatic organisms. Approximately 85% of the fluoroquinolones present in influents can be removed by conventional wastewater treatment plants, but the removed fraction is frequently accumulated in the sludge, which is sometimes used as fertilizer, representing an additional input route into the environment. The removal of fluoroquinolones by biological treatment is ineffective, and it is believed that only advanced oxidation technologies are able to destroy these emerging pollutants.

Use of solar energy in the treatment of water contaminated with phenol by photochemical processes

The solar driven photo-Fenton process for treating water containing phenol as a contaminant has been evaluated by means of pilot-scale experiments with a parabolic trough solar reactor (PTR). The effects of Fe(II) (0.04-1.0 mmol L-1), H2O2 (7-270 mmol L-1), initial phenol concentration (100 and 500 mg C L-1), solar radiation, and operation mode (batch and fed-batch) on the process efficiency were investigated. More than 90% of the dissolved organic carbon (DOC) was removed within 3 hours of irradiation or less, a performance equivalent to that of artificially-irradiated reactors, indicating that solar light can be used either as an effective complementary or as an alternative source of photons for the photo-Fenton degradation process. A non-linear multivariable model based on a neural network was fit to the experimental results of batch-mode experiments in order to evaluate the relative importance of the process variables considered on the DOC removal over the reaction time. This included solar radiation, which is not a controlled variable. The observed behavior of the system in batch-mode was compared with fed-batch experiments carried out under similar conditions. The main contribution of the study consists of the results from experiments under different conditions and the discussion of the system behavior. Both constitute important information for the design and scale-up of solar radiation-based photodegradation processes.

Industrial Wastewater Treatment by Photochemical Processes Based on Solar Energy

Background: The solar photo-Fenton process has enormous potential for becoming a viable alternative to conventional processes for the treatment of industrial wastewater. However the costs associated with the use of artificial irradiation have hindered many times industrial application of these processes. Method of Approach: In this work, the photo-Fenton remediation of various industrial wastewaters (containing silicones, pesticides, phenol and hydrocarbons, model, and real) in aqueous systems has been studied using Fe(II), H 2 O 2 , and UV-visible sunlight. Experiments were carried out using a concentrating parabolic trough reactor (PTR) and a nonconcentrating falling-film reactor. Results: In general, at low contaminant concentration, more than 90% of the total organic carbon content could be converted to inorganic carbon within about 2-3 h, using sunlight, in reactors of different geometry. Conclusions: Solar light can be used either as an effective complementary or alternative source of photons to the photo-Fenton degradation process of a diversity of chemical pollutants.

Photo-fenton remediation of wastewaters containing agrochemicals

The photochemical degradation of agrochemicals in aqueous solution by means of advanced oxidation processes (AOPs) was studied. The photo-Fenton process was evaluated in terms of the time evolution of dissolved organic carbon (COD) and chemical oxygen demand (DOC), their total removals, and increase in biodegradability of treated wastewater. Under the experimental conditions studied, the process showed to be superior to other AOPs, at any Fe(II) and H2O2 concentrations. The results pointed towards the use of solar irradiation and low cost commercial application.

Estimating reaction constants by ab initio molecular modeling: a study on the oxidation of phenol to catechol and hydroquinone in advanced oxidation processes

Molecular modeling is growing as a research tool in Chemical Engineering studies, as can be seen by a simple research on the latest publications in the field. Molecular investigations retrieve information on properties often accessible only by expensive and time-consuming experimental techniques, such as those involved in the study of radical-based chain reactions. In this work, different quantum chemical techniques were used to study phenol oxidation by hydroxyl radicals in Advanced Oxidation Processes used for wastewater treatment. The results obtained by applying a DFT-based model showed good agreement with experimental values available, as well as qualitative insights into the mechanism of the overall reaction chain. Solvation models were also tried, but were found to be limited for this reaction system within the considered theoretical level without further parameterization.

A Monte Carlo model for the sintering of Ni/Al2O3 catalysts

Abstract A mathematical model was developed to describe the sintering of nickel crystallites in Ni/Al 2 O 3 catalysts used for steam reforming. Atom migration and particle migration were considered along with many contributions from phenomenological models previously described in the literature. The model combines both mechanisms according to a Monte Carlo approach. Size-dependent surface and interface properties and the influence of surrounding atmosphere and temperature were accomplished. Model predictions qualitatively describe experimentally observed behavior.

Molecular-Scale Modeling of the Degradation of Phenol in Advanced Oxidation Processes Reaction Media

Abstract Modeling, in its diverse length and time scales, has been pointed as one of the most remarkable features responsible for the advances in Chemical Engineering science. The smallest physically relevant scale modeling deals with frozen individual molecules; an approach known as quantum modeling (QM): length scales of the order of Angstrons (10-10 m) and no time effects taken into account. Modeling in this scale is useful to obtain a large amount of data on properties which can be further applied into other modeling approaches or serve as parameters to process design and optimization. In this work, Density Functional and Semiempirical methods were used to study the degradation of phenol promoted by hydroxyl radicals, as those generated in Advanced Oxidation Processes media. The results are discussed and compared with experimental data collected by the group. A method is presented for modeling ChE interesting reactions and obtaining kinetic constant values.

Degradation of Phenolic Compounds in Aqueous Sucrose Solutions by Ozonation

ABSTRACT The sugar industry is concerned with color formation due to the oxidation of phenolic compounds in the presence of carbohydrates. In this study, we investigated the ozonation of a mixture of five phenolic compounds in water and aqueous sucrose solution: p-coumaric (p-COU), caffeic (CAF), syringic (SYR), and chlorogenic (CHO) acids, as well as the flavonoid quercetin (QUE). The experiments were carried out in a 3-L glass reactor with magnetic stirring and a diffuser plate at the bottom to feed the ozone-oxygen gas mixture. Initial solution concentrations of 5 mg L−1 of each acid, 15 mg L−1 of quercetin, and 40 g L−1 of sucrose were used. The degradation of phenolic compounds followed apparent first-order kinetics, with rate constants and percent removals decreasing in the presence of sucrose. In water, average consumed ozone dosages of 10.4 and 18.7 mg L−1 were necessary for 50% and 90% removals, respectively, for CHO, CAF, and p-COU; for QUE they were slightly higher (13.9 and 20.5 mg L−1, respectively). At a consumed dosage of 20.8 mg O3 L−1, more than 99% removal was obtained for CHO, CAF, and p-COU, while 96.2% was achieved for SYR. In contrast, QUE revealed to be more recalcitrant during ozonation in the absence of sucrose, with only 70% removal at the highest consumed O3 dosage. The consumed ozone dosages for 50% and 90% removals were higher for CHO, CAF, and p-COU in aqueous sucrose solution, which may impact ozone consumption during real sugarcane juice treatment. Sucrose and t-butanol were the main influential parameters that significantly affected the total amount of phenolic compounds degraded.