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A more environmentally friendly replacement for SF6 must be found for medium voltage switchgear, as a change in European regulations will come into force soon. The mixing process of alternative binary and ternary gas mixtures is studied, which are made up of the hydrofluoroolefin HFO-1336mzz(E) (C4F6H2) and the heptafluoroisopropil trifluoromethyl ketone (C5F10O), using dry air or N2 as carrier gases. The mixture's monitoring, meaning the evolution of the concentration concerning time and position, is carried out by UV-VIS spectroscopy technology in a gas chamber that has been designed to be analogous to a medium voltage cell. The mixing process is described using a mathematical model that considers molecular diffusion, Fick’s Law, and natural convection, the effect of gravity. This work aims to configure a tool for predicting the dynamics of gas mixtures of different components, estimating the diffusivities of the mixture's components, and analyzing the behaviors derived from the use of different concentrations.

In this work, binary and ternary gas mixtures of 1,3,3,3-tetrafluoropropene, HF0234ze(E), and perfluoro-(3-methylbutan-2-one), CF3C(0)CF(CF3)2 with CO, and synthetic air, are presented as alternatives to SF6 in medium-voltage electrical equipment. They were used in four medium voltage switchgear cubicles replacing SF6 gas, and after a period of time, under permanent 30 kV AC voltage, gas mixture samples were extracted and analyzed on the same day using a validated methodology' based on gas chromatography (GC) coupled to mass spectrometry (MS) and thermal conductivity (TCD). CF4 (tetrafluoromethane), C2F6 (hexafluoroethane), C,F6 (hexafluoropropylene), C3FIF7 (1,1,1,2,2,3,3-heptafluoropropane), CHF, (difluoromethane), and the cis and trans-C3H2F4 (1,3,3,3 tetrafluoropropene) have been identified as decomposition products in these gas mixtures. In addition, a quantity of water has been observed, as well as CO in one of the cubicles. The most abundant decomposition products identified in gas mixture samples (C3HF7 and C3F6) together with water and CO content have been quantified using commercial gas mixture reference standards. The toxicity and global warming of the analyzed compounds are evaluated to determine the most adequate gas mixture among those studied as a candidate to substitute SF6. This work was supported the Basque Country Government (project Elkartek KK-2017/00090)

This work develops a kinetic model that allow to predict the water toxicity and the main degradation products concentration of aqueous solutions containing 4-chlorophenol oxidised by UV/H2O2. The kinetic model was developed grouping degradation products of similar toxicological nature: aromatics (hydroquinone, benzoquinone, 4-chlorocatechol and catechol), aliphatics (succinic, fumaric, maleic and malonic acids) and mineralised compounds (oxalic, acetic and formic acids). The degradation of each group versus time was described as a mathematical function of the rate constant of a second-order reaction involving the hydroxyl radical, the quantum yield of lump, the concentration of the hydroxyl radicals and the intensity of the emitted UV radiation. The photolytic and kinetic parameters characterising each lump were adjusted by experimental assays. The kinetic, mass balance and toxicity equations were solved using the Berkeley Madonna numerical calculation tool. Results showed that 4-chlorophenol would be completely removed during the first hour of the reaction, operating with oxidant molar ratios higher than R=200 at pH6.0 and UV=24 W. Under these conditions, a decrease in the rate of total organic carbon (TOC) removal close to 50% from the initial value was observed. The solution colour, attributed to the presence of oxidation products as p-benzoquinone and hydroquinone, were oxidised to colourless species, that resulted in a decrease in the toxicity of the solutions (9.95 TU) and the aromaticity lost. The authors are grateful to the University of the Basque Country (UPV/EHU) for their financial support of this study through the PPGA20/33 project, and C. Ferreiro's predoctoral PIF grant (PIF16/367). Document

This work proposes a mathematical model as a basis for studying the combined adsorption–ozonation process (Ad/Ox) with the complexity involved in a three-phase system. The description of this operation involves several parameters that describe the system kinetics and adsorption phenomena. This paper analyses the Ad/Ox process compared with simple ozonation, investigating the benefits of activated carbon (AC) in ozonation, primary degradation and mineralization of phenol solutions. This study focuses on Ad/Ox with granular activated carbon (GAC) and analyses how the phenol degradation kinetics depend on the amount of AC. Thus, a priority order of relevance is established for the proposed mathematical model parameters. For example, the adsorption kinetic constant may vary meaningfully within the same process. Finally, this paper studies the GAC behaviour after a given number of cycles, followed by the regeneration process. The calculated kinetic coefficients relating to the liquid and solid media explain the changes in process efficiency.

Injecting ozone by means of a venturi device causes an increase in the mass transfer coefficient with respect to gas dissolution through a microdiffuser. Moreover, it was observed that significant turbidity levels are not formed (1 NTU) when using a microdiffuser, probably due to the relatively high stirring which avoids formation of intermolecular hydrogen bonds. On the contrary, employing a venturi injector led to the production of high turbidity levels in water (up to 20 NTU). This indicates that formation of supramolecular structures causing this turbidity requires the presence of certain facilitating species which are formed through ozone decomposition mechanisms. The maximum ozone transfer takes place when operating at pH

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. The authors are grateful to the University of the Basque Country for their financial support of this study through the GIU20/56 project and C. Ferreiro’s predoctoral PIF grant (PIF16/367).

Alginate microcapsules containing cell yeasts of the species Saccharomyces cerivisae, were studied to improve the protection of cell activity during drying. Dehydration is a common operation to sta...

This work presents an efficient catalytic ozonation process for the treatment of aniline wastewater as a model pollutant. The process uses a granular activated carbon-supported titanium dioxide catalyst with environmentally-friendly and sustainable characteristics. Titanium dioxide composites were prepared by precipitation of alcoholic titanium tetrachloride solutions on two different carbon supports: Norit® GAC 1240 Plus and Norit® ROX 0.8. This method is an improvement on other composite preparation methods such as hydrothermal and impregnation by immersion techniques, which were also carried out for comparison. It characterised our composites by Brunauer–Emmett–Teller analysis, scanning electron microscopy-energy dispersive X-ray spectroscopy and Fourier-transform infrared spectroscopy to assess the influence of the carbon support. Composites synthesised via this novel precipitation method presented a 25% increase in their initial specific surface area and a 9.1% increase in titanium dioxide loading. It compared the catalytic activity of the different titanium dioxide composites on different aniline solutions, and studied the optimal pH and ozone dose. Norit® GAC 1240 Plus-supported titanium dioxide composite prepared by the precipitation method gave the highest removal yield with 80.24% mineralisation of total organic carbon in 45 min. With respect to the costs associated with the treatment, the composite achieved a removal yield of 26.8 mg ozone/mg total organic carbon.

Graphical abstract, Highlights • Ultrasound degraded the molecular structure of humic acids. • Sonochemical effects (HO•) responsible for fluorescence reduction. • No TOC and colour removal with ultrasound pre-treatment. • O3 achieved a significant reduction in TOC and almost a complete colour removal. • Ultrasound pre-treatment may reduce subsequent O3 dosage for humic acid degradation., This paper presents an intensification study of an ozonation process through an ultrasonic pre-treatment for the elimination of humic substances in water and thus, improve the quality of water treatment systems for human consumption. Humic acids were used as representative of natural organic matter in real waters which present low biodegradability and a high potential for trihalomethane formation. Ultrasonic frequency (98 kHz, 300 kHz and 1 MHz), power (10–40 W) and sonicated volume (150–400 mL) was varied to assess the efficiency of the ultrasonic pre-treatment in the subsequent ozonation process. A direct link between hydroxyl radical (HO•) formation and fluorescence reduction was observed during sonication pre-treatment, peaking at 300 kHz and maximum power density. Ultrasound, however, did not reduce total organic carbon (TOC). Injected ozone (O3) dose and reaction time were also evaluated during the ozonation treatment. With 300 kHz and 40 W ultrasonic pre-treatment and the subsequent ozonation step (7.4 mg O3/Lgas), TOC was reduced from 21 mg/L to 13.5 mg/L (36% reduction). HO• attack seems to be the main degradation mechanism during ozonation. A strong reduction in colour (85%) and SUVA254 (70%) was also measured. Moreover, changes in the chemical structure of the macromolecule were observed that led to the formation of oxidation by-products of lower molecular weight.

The water–development nexus is essential for the advancement and progress of cities in the face of problems such as climate change, water security and increasing environmental stress in the agricultural sector. Aiming for a circular economy and, at the same time, improving the resilience of water supply alternatives and achieving a goal of zero waste, this work presents a technical–economic study of a novel continuous ultrafiltration (c-UF) system with self-cleaning capacity coupled to an ozonation process, for the treatment of urban WWTP effluent. The removal efficiencies achieved were analysed both through macroscopic parameters (suspended solids, turbidity) and for the most frequently occurring contaminants of emerging concern (CECs). Consequently, an effluent suitable for irrigation was obtained, with a total recovery factor of 97.92%, a concentration of suspended solids (SS) below 1 mg L−1, 0.06 NTU turbidity and toxicity free, complying with the new European Regulation on Water Reuse (EU 2020/741). A comparative analysis of the proposed process with regard to conventional tertiary treatment revealed that the proposed process was 39.1% more economic, with a cost of 0.0325 € m−3. This alternative treatment will be of great interest because of its favourable technical–economic characteristics, being postulated as a basic process for implementation in modern water reuse plants. The authors are grateful to the University of the Basque Country (UPV/EHU) for their financial support of this study through the PPGA20/33 project, and C. Ferreiro’s predoctoral PIF grant (PIF16/367).

This work presents a case study of a wastewater treatment plant (WWTP), located in Biscay (Spain), in which the removal of high-occurrence contaminants of emerging concern (CEC) was studied. The existing biological treatment in the WWTP was complemented with a continuous ultrafiltration (c-UF) pilot plant, as a tertiary treatment. Thus, the effect on CEC removal of both treatments could be analyzed globally and after each operation. A total of 39 CEC were monitored, including pharmaceutical products, industrial additives, food additives, herbicides and personal care products. For evaluation of the efficiencies, the removal rates of the biological and of the c-UF treatments, including their variability over a day and a week in relation to the ammonium content, were examined in the influent of the WWTP. In the biological treatment, a wide range of different removal rates was obtained due to the different CEC&rsquo, s biodegradability and concentration. In UF, lower, but more constant removal rates, were achieved. In addition, the reduction of the general toxicity by the UF treatment in terms of the Microtox&reg, toxicity assay was also evaluated. After UF, all of the samples yielded values of TU50 lower than 1, confirming this result the UF effectiveness for toxicity removal.

Dehydration of the encapsulated material containing nutritional ingredients was determined to be necessary for functional foods and probiotics production. The application of a suitable drying process was required. This study proposes the development of a new dehydration process, called near fluidizing microwave drying (NFMD), to minimize the problems observed in other drying processes, such as spray drying or lyophilization. Several heating strategies, which are employed in microwave applications under fluidizing conditions, were adequately modeled to analyze the effect of the operational variables. The fitting of experimental data has enabled the determination of the mass and heat transfer coefficients: diffusivity and heat convection. The drying phases were analyzed based on the obtained values of these parameters as basis for the selection of the most favorable operational conditions. Under these conditions, the NFMD process has been employed for the dehydration of the encapsulated probiotic Bi...

This work presents an efficient method for treating industrial wastewater containing aniline and benzothiazole, which are refractory to conventional treatments. A combination of heterogeneous photocatalysis operating in a fluidised bed reactor is studied in order to increase mass transfer and reduce reaction times. This process uses a manganese dioxide catalyst supported on granular activated carbon with environmentally friendly characteristics. The manganese dioxide composite is prepared by hydrothermal synthesis on carbon Hydrodarco® 3000 with different active phase ratios. The support, the metal oxide, and the composite are characterised by performing Brunauer, Emmett, and Teller analysis, transmission electron microscopy, X-ray diffraction analysis, X-ray fluorescence analysis, UV–Vis spectroscopy by diffuse reflectance, and Fourier transform infrared spectroscopy in order to evaluate the influence of the metal oxide on the activated carbon. A composite of MnO2/GAC (3.78% in phase α-MnO2) is obtained, with a 9.4% increase in the specific surface of the initial GAC and a 12.79 nm crystal size. The effect of pH and catalyst load is studied. At a pH of 9.0 and a dose of 0.9 g L−1, a high degradation of aniline and benzothiazole is obtained, with an 81.63% TOC mineralisation in 64.8 min. The authors are grateful to the University of the Basque Country (UPV/EHU) for their financial support of this study through the GIU20/56 project and C. Ferreiro’s predoctoral PIF grant (PIF16/367).

In this work, a study of the main operating variables affecting TiO2/UV photocatalysis was carried out. The treatment of an industrial effluent containing aniline and benzothiazole from the manufacture of accelerants for vulcanization was performed in a TiO2-supported commercial photoreactor. The degradation of both contaminants was monitored by GC-MS analysis. The proposed experiments were able to properly identify the phenomenon of adsorption, as well as to improve the performance of the commercial photoreactor by adding small amounts of TiO2 in suspension. The removal performance, durability of the photocatalytic material, and energy costs were analysed. The results showed that the use of suspensions intensifies the degradation obtaining an improvement of 23.15% with respect to the use of the supported catalyst. For an aniline and benzothiazole solution, the best operating conditions were found at pH = 12.0, introducing 60.0 mg L&minus, 1 of suspended TiO2 together with the existing supported catalyst.

BACKGROUND Advanced oxidation includes a number of technologies, all of them appropriate to achieve environmental remediation. One of them is the organic compounds degradation by ozonation. The ozonation of rhodamine 6G (R6G) was investigated to study the effect of pH and subsequent predominance of the control stage, whether mass transfer from gas to liquid phase or chemical reaction, during oxidation. Several pH conditions are studied to achieve greater efficiency of the process. RESULTS A mathematical model enables analysis of the controlling stage. It was satisfactorily verified, showing that, initially, the process is controlled by the G-L mass transfer stage but, as the R6G ozonation progresses the process becomes controlled by the kinetic reaction. While 99% of the rhodamine dye is removed during the mass transfer control stage regardless of the pH value, the percentage of TOC removal is increased only during the kinetic reaction control stage. CONCLUSION The most favourable pH, given the mass transfer characteristics of this case, was found to be an intermediate value around 6.0 where a minimum value for coefficient for R6G mineralization zav of about 23 mol O3 mol−1 R6G mineralized, and near its theoretical value, was obtained. © 2016 Society of Chemical Industry

Ozonation is an efficient process for the primary degradation of most substrates but not for their mineralisation. In this work, the ozonation enhanced with the addition of H2O2 was studied for two substrates with very different oxidation resistances: the dye rhodamine 6G (R6G) and the surfactant linear alkylbenzene sulfonate (LAS). With O3 only, the primary degradation of R6G was completed in less than 10 min but its TOC removal only reached 45% in 1 h. By adding H2O2, TOC removal was increased to 70% with a molar ratio (mol H2O2/mol substrate) of 10. The analysis of pH decrease served to define the specific basicity loss (SBL). The optimum conditions for the R6G mineralisation were found to be associated with a SBL value between 1 and 10 ((min/g)/L)−1, through an adequate addition of H2O2. Moreover, in the case of LAS, the addition of H2O2 for a greater efficiency should occur after the foaming period, above all formed at acid pH. LAS degradation was also considerably improved, and the optimum for primary degradation achieved in 10 min with a TOC removal of over 65% with a molar ratio (mol H2O2/mol substrate) of 20.

Alginate microcapsules containing cell yeasts of the species Saccharomyces cerivisae, used as a reference microorganism, were studied here to improve the protection of cell activity during food processing. Here a novel drying process was proposed to optimize processing conditions. The dehydration of microcapsules by microwaves and under near fluidizing conditions (NFMD), allows performing dehydration employing lower temperatures to maintain high viability levels and a high quality end product. Thus, strategies based on the combination of different thermal gradients and processing temperatures were analysed through a series of NFMD experiments. Keywords: microwave drying, fluidization, probiotics, cell viability

Advanced oxidation processes (AOP) are able to degrade pollutants into harmless substances. To demonstrate the successful application of AOP to real, polluted effluents, ozonation has been applied for the removal of linear alkylbenzene sulfonates (LAS), a surfactant mixture commonly used in detergent formulation. LAS can be identified in a wide range of concentrations, i.e., in domestic wastewater or in the raw effluent of detergent-processing plants. The strongly tensoactive nature of LAS results in a foaming effect that eventually discourages AOP application, especially in the case of ozonation. The primary goal of this research is to analyze the LAS ozonation kinetics, considering the simultaneous effect of foam formation, by the development of a semiempirical model that is mainly based on the foaming phenomenon. Along with foaming, the proposed model also considers LAS removal by ozonation and the inverse phenomenon of LAS formation by redissolution of LAS. To the best of our knowledge, such a finding has not been previously reported. The proposed foaming model has been developed within various pH and LAS concentration values, primarily examining the initial pH value of the effluent due to its significant effect on foaming. The developed model adequately predicts the LAS concentration profiles measured in the liquid during ozonation. Moreover, this approach makes it possible to quantify the incidence of foaming and LAS redissolution during ozonation comparatively, leading to being able to propose the most desirable operating conditions for LAS removal.

This study demonstrates the importance of reaction temperature on the UV/H 2 O 2 process. Oxidation reactions have been carried out on 1 g L −1 solutions of linear alkylbenzene sulphonates (LASs) in the range from ambient to 80 °C. Use of these conditions could be justified as they often represent the thermal conditions in which some polluted effluents are discharged. At an intermediate temperature of 60 °C and using small amounts of hydrogen peroxide LAS removal is significantly improved due to a more efficient use of the oxidant. This is mainly due to the enhancement of the radical reaction rate constant, as it does the quantum yield of the LAS. The use of more severe operating conditions, temperatures of 80 °C and high amounts of peroxide is necessary if the aim is to improve biodegradability. Only in that case intensified oxidation makes possible the removal of aromatic intermediates.

The combination of H2O2 with UV radiation was applied to study the degradation of Rhodamine 6G dye (Rh-6G). The lumped kinetic model proposed in this work is a reaction-system scheme to describe the degradation of dye using lumps of intermediate compounds grouped by their chemical and colorimetric behavior. Rate constants obtained by application of the model were shown to predict the progress of dye oxidation. The effects of pH and oxidant dosage on these rate constants were also analyzed. Finally, photodecoloration was studied considering the absorption at 528 nm (the maximum absorption wavelength of the dye) as the sum of all compounds absorbing at this wavelength: Rhodamine itself and the colored intermediates produced.

This study investigates the environmental quality of water treatments by evaluating the effectiveness of advanced oxidation technologies, such as H2O2/Fe(II) and H2O2/UV, in treating phenol-contami...

The drying of sliced mushroom by microwave energy is studied for different operational conditions related to temperature control position and pressure and their effects on drying kinetics and quality. Thinly sliced mushrooms were dried in a guide cavity by applying microwave energy at 2.45 GHz. The influence on the quality of the dehydrated mushrooms was studied by two different techniques: sorption isotherms (Halsey and B.E.T. equations) and scanning electron microscopy (SEM). Drying kinetics were also analyzed through the determination of diffusivity by applying a mathematical model that takes into account changes in moisture on the product surface during the process. Thus, the results of SEM observations and quality can be linked with diffusivity values in each experiment. As a rule, the operational conditions imposed result in contrary tendencies in quality and drying kinetics. High heat levels usually lead to unfavorable quality results in the dehydrated product if not corrected with a favorable inverse temperature gradient characteristic of microwave heating. Industrial relevance The combination of drying and enzyme inactivation of mushrooms browning confers microwave drying a great interest with regard to its industrial application. The results referenced in this paper, concerning the position effect of temperature control and pressure will contribute to the continued development of microwave technology applied to food dehydration.

The characterization of radical oxidation in the degradation of phenolic compounds with H2O2/UV has been studied. A kinetic model was developed to estimate the concentration of different radical species. Radical concentration defines a determined oxidative level whose changes are analyzed for different oxidizing conditions involving pH and hydrogen peroxide dosage. This study has been developed to extend a previous radical model, only for simple phenolic solutions, to phenolic mixtures consisting of phenol and different cresols. In a mixture, the effects of composition and total amount of phenolics have a great influence on the degradation of each compound markedly modifying the behavior found in a simple solution. The application of a new extended radicalary model requires the characterization of the phenolic mixture solution through two fundamental parameters. The first one is the equivalent phenol in the mixture or phenol concentration, which gives the same oxidative level as that of the mixture case. Besides, additional information must be considered to characterize the deviation of the radical level between each compound and the mixture through the corresponding coefficient of radicalary activity. The model has been applied and verified to estimate the degradation of the different phenolics of a mixture, whatever the composition of phenolics, with good fitting to the experimental data. © 2010 American Institute of Chemical Engineers Environ Prog, 2011

Synthetic solutions of phenol, o-, m- and p-cresol were oxidised by using Fenton’s reagent. The application of substoichiometric dosage of H2O2 led to the formation of intermediate compounds, continuing later the oxidation to complete oxidation. An important objective was to analyze the effect of hydrogen peroxide dosage applied and the reaction pH together with the iron oxidation state on the degradation level. A kinetic model was derived from a reaction mechanism postulated which was used to analyze the results of the experiments. Another aim was to analyze the hydrogen peroxide consumption. Noteworthy results include an increase in oxidant consumption to intensify phenol removal. Furthermore, oxidant consumption was analyzed through the ratio H2O2 to phenol removed and the average specific rate of removal (ASRR). By analyzing these two parameters it has been possible to ascertain the most favorable strategy for an efficient application of H2O2.

A one-dimensional isothermal model is used to calculate transmembrane water profiles and current−voltage curves under different operating conditions. The mechanistic model solves the mass balance o...

This article deals with the kinetic analysis of the drying of sliced mushrooms (Agaricus bisporous) and apples (Golden Delicious), as representatives of vegetables and fruits, by the application of microwave. The drying experiments were carried out in monomode or multimode cavities, depending on the purpose of the study. In the former, the location of the temperature control is analyzed, and in the latter, the effect of pressure, air humidity, and temperature control. In the experiments, the mass loss was monitored over time and the drying kinetics described by means of a model, assuming effective diffusivity to be constant. The changes in the diffusion coefficient could be explained in terms of possible texture modifications of the product derived from the different conditions experienced during drying.

This paper describes a study of the treatment of surfactant synthetic solutions by chemical and photolytic oxidation. Synthetic solutions of linear alkylbenzene sulfonates (LAS) are treated in this work as this is a model compound commonly used in the formulation of detergents, with a great presence in urban and industrial waste-waters. The application of ultraviolet (UV) radiation combined with hydrogen peroxide to oxidize linear alkylbenzene sulfonates (LAS) is shown to be suitable as a primary oxidation step since conversions of about 50% of the original compounds are achieved in the most favorable cases. Initially, the influence of the operating variables on the degradation levels is analyzed in this work. A kinetic model that considers the contributions of both direct photolysis and radical attack is also worked out. Direct photolysis is performed to determine the quantum yield in the single photodecomposition reaction. In addition, the rate constant of the reaction between hydroxyl radicals and linear alkylbenzene sulfonates in the oxidizing system H2O2/UV is determined for different operational conditions. Finally, the contribution of each oxidation pathway is quantified, resulting in a higher contribution of the radical reaction than of photolysis in all cases.

We compared two H2O2 oxidation methods for the treatment of industrial wastewater: oxidation using Fenton's reagent [H2O2/Fe(II)] and microwave irradiation. Both methods were applied to the treatment of synthetic phenol solutions (100 mg L−1) and of an industrial effluent containing a mixture of ionic and non-ionic surfactants at high load (20 g L−1 of COD). The effects of initial pH, initial H2O2 concentration, Fenton catalyst amount and irradiation time were assessed. According to the oxidation of phenol, it has been found that the oxidation by Fenton's reagent is dependent on the pH, contrary to the microwave system, which is not influenced by this parameter. For both systems, a limiting amount of oxidant has been found; above this point the oxidation of phenol is not improved by a further addition of peroxide. The oxidation of the industrial surfactant effluent has only been successful with the Fenton's reagent. In this case, large amounts of ferrous ions are necessary for the precipitation of the ionic surfactants of the effluent, followed by the oxidation of the non-ionic constituents of the solution.

The necessary criteria for the design of a freeze-drying operation, where radiant and microwave heating are combined, are analyzed in this work. Microwave heating presents indubitable advantages fo...

The percolation leaching of heavy metals from pyrite cinder in a packed bed is considered in this work. Flow rate and physicochemical parameters have been analysed in a gravity percolation leaching system with a simultaneous dissolution reaction. The structure of the unconsolidated bed of porous cinder changes during operation as a consequence of the leaching phenomenon. The variables that influence the flow rate are: bed length, particle size distribution and leaching liquor characteristics. Head loss changes during operation are mainly explained in terms of the fine particle redistribution, migration along the bed and thickening at the bottom. Experimental values of effective void fraction are compared with values from Ergun's equation modified to be applied to a layered bed.

A study of freeze-drying (lyophilization), by immersion in an adsorbent medium (LIAM), was carried out, both at atmospheric pressure and under vacuum. The pressure and temperature effect on the drying kinetics and on the final dehydrated quality were evaluated. The kinetic analysis of both techniques has been carried out through one model that considers a uniformly retreating ice front in spherical geometry. This model calculates the pressure and temperature in the sublimation front in terms of the product moisture. Some operational strategies have been proposed which reduce the process duration without serious damage to the product. In these strategies the temperature and pressure in the fluid bed are modified.

A finite element model (FEM) with axial symmetry conditions and isoparametric elements was applied to the freeze drying of special foods in vials. The model was verified by experiments using a methyl cellulose test material. The model was used to simulate and evaluate various heating strategies in freeze drying in order to reduce drying cycles and increase process efficiency. The effect of sublimation front temperature and freeze drying periods on the process duration was analysed.

A Kinetic analysis of freeze drying by immersion in an adsorbent fluidised bed process has been carried out in this paper. The process is described based on a uniformly retreating ice front model in spherical geometry. The model needs to know both temperature and pressure driving forces, correlated as a function of water content.The influence exerted by operational conditions on the heat and mass coefficients has been studied. Transport coefficients are correlated as a function of the operating conditions to obtain equations that can be used for predicting purposes in fluid bed freeze drying. Kinetic aspects are related to quality indicators determined through shrinkage of product to select the most adequate operating conditions.

A kinetic analysis of freeze drying by immersion in an adsorbent fluidized bed process has been carried out and will be discussed in this paper. The process is described based on a uniformly retreating ice front model in spherical geometry. The model needs to know both temperature and pressure driving forces, correlated as a function of water content. The influence exerted by operational conditions on the heat and mass coefficients has been studied. Transport coefficients are correlated as a function of the operating conditions to obtain equations that can be used for predicting purposes in fluid bed freeze drying. Kinetic aspects are related to quality indicators determined through shrinkage of product to select the most adequate operating conditions.

The inhibitory effect of Ni upon a biological system of activated sludge has been analyzed in two semicontinuous sequential reactors feeding synthetic wastewater. One of the reactors was used as control while in the other given amounts of NiSO4 were added to the influent to achieve a concentration of 30 ppm Ni(II). An analysis of the characteristic biokinetic parameters has been made and the correspondence with the operating conditions stated. A series of O2 uptake tests were proposed and the results analyzed together with the specific rate of substrate removal (U) in order to explain the toxic influence of Ni(II). An accumulation of undigested substrate on the floes seems to explain certain aspects derived of the presence of Ni. The sludge residence time (SRT), within a certain range, can be used as a control operating variable to mitigate the inhibitory effect of Ni, since a somewhat contrary effect upon the settling characteristics of the sludge must be also considered.