Degradation of organic compounds in paper and testile industrial wastewaters by advanced axidation processes

Les activitats de recerca destinades a la solució dels problemes de contaminació de les aigües estan patint un fort increment en els darrers anys. Entre les indústries més contaminants, cal esmentar la tèxtil i la paperera, i més concretament, els efluents provinents d´etapes deblanqueig. Quan els tractaments biològics convencionals d'aquests efluents contaminants no són efectius, la utilització de tecnologies emergents, tals com els processos d´oxidació avançada (AOP´s), basats en la formació in situ de radicals hidroxil, es mostra adient. Amb l´objectiu de provar la viabilitat de tractar efluents contaminants amb el radical hidroxil, vàrem triar l´ozonització i la fotocatàlisi per abordar efluents de blanqueig de pastes papereres generats en el laboratori. Aquesta prova mostrà que la fotocatàlisi pot reduir eficientment el contingut de carrega orgànica tot seguint una equació cinètica de Langmuir-Hinshelwood. A més, la combinació simultània de fotocatàlisi i ozonització produí un efecte sinèrgic que millorava el rendiment respecte al cas d´aplicar ambdós AOP´s de manera seqüencial.Tot i assumint que el radical hidroxil era l´oxidant adequat, planificàrem un extens estudi, fent servir aigües residuals industrials i distints AOP´s. La disminució del TOC i el cost en el tractament varen ésser els paràmetres contrastats en els distints estudis, amb l´objectiu de descobrir els principals avantatges i inconvenients de cada procés. El procés d´ozonització requeria disminuir el seu cost. La presència d´ions ferro en el procés ozó/UVA va aconseguir la reducció d´un 90% de TOC conjuntament amb una disminució del 15% en el cost. L´ús seqüencial de tractaments genera millors resultats (addició de ferro amb o sense llum, seguit per una etapa d´ozonització). Conclusions similars es varen obtenir en treballar amb una matriu sintètica de 2,4-diclorfenol (compost trobat usualment en els efluents de blanqueix de pasta de paper).Referent a la fotocatàlisi, s´ha posat de manifest la necessitat d´utilitzar una font de llum potent i/o la millora de l´eficiència de la llum incident en el catalitzador de TiO2. En aquest sentit vàrem provar dues vies: (a) la utilització d´un nou muntatge experimental amb una font de llum de 125 W. Determinacions d´AOX, toxicitat aguda, fenols i de GC-MS ens van portar a concloure que els compostos orgànics de clor eren eliminats eficientment en l´aigua residual. (b) la utilització de guies d'ones recobertes de TiO2. Solució que permet augmentar l´eficiència amb la que el catalitzador aprofita la llum incident per tal de millorar el disseny de reactors fotocatalitics.L´últim procés provat, el reactiu Fenton, en presència de llum solar o artificial, es va aplicar a la degradació d´efluents de blanqueig tèxtils o paperers. La degradació del contingut de càrrega orgànica d'aquests effluents s´assolia preferentment a pH = 3. El primer estudi es realitzà sobre un efluent de blanqueig de pastes de paper. La funció aproximada del sistema, estimada a partir del disseny experimental, mostrà que concentracions inicials inadequades de reactiu Fenton afectaven negativament al procés, a causa de reaccions competitives entre aquest i altres espècies oxidatives. Així mateix, la temperatura augmentà clarament les velocitats de la reacció, inclús sense presència de radiació. La millora en la disminució del TOC és particularment significativa quan les proporcions de reactiu Fenton són inadequades (en passar de 25 ºC a 40 ºC es pot aconseguir una reducció en el cost de l´ordre del 80%). Per altre banda, la llum solar aconsegueix reduir fins un 70 % el cost total d'un tractament de dues hores de durada. L'anàlisi de GC-MS constata l´eliminació dels compostos clorfenòlics. Un segon estudi sobre un efluent tèxtil corroborà la gran importància de la temperatura i de la presència de llum solar. En resum, tots els AOP´s provats mostren, sota condicions experimentals adequades, la capacitat de degradació del contingut orgànic present en efluents de blanqueig procedents d´indústries papereres i tèxtils.There is an ever increasing amount of research activities especially devoted to the solution of water pollution problems.The pulp and textile industries are considered to be some of the largest polluters of all industries. The biggest problem with those industries consists in the polluted effluents discharged during the bleaching process because conventional biological treatments are not effective in treating these toxic pollutants. In these cases, the emerging technologies called Advanced Oxidation Processes (AOPs) represent an attempt to mineralize the contaminants by the in situ formation of hydroxyl radicals.In order to determine the effectiveness of treating effluents with the hydroxyl radical we chose the photocatalytic and ozonation processes to treat bleaching pulp effluents generated in the laboratory. Our results demonstrated that the photocatalytic process could efficiently reduce the organic content in accordance with the Langmuir-Hinshelwood kinetic equation. Moreover, simultaneously combining photocatalysis and ozonation provided a synergistic effect that was superior in performance to that of applying the photocatalysis and ozonation processes sequentially.Our tests with laboratory bleaching pulp effluents assumed that the hydroxyl radical was the proper oxidant to be use. An extensive study was undertaken using industrial wastewaters and different AOPs. TOC decay and treatment costs were the operative variables compared in the study in order to discover the benefits and shortcomings of each process.It is imperative that the ozonation process decreases the treatment costs. The addition of iron ions to bleaching mill wastewater undergoing ozone/UVA treatment resulted in high rates of TOC removal (90%) and in a significant cost reduction (15%). Additionally, sequential processing (stirred iron, with or without light irradiation, followed by an ozonation stage) led to even better results. Similar results were obtained on the synthetic sample of 2,4-dichlorophenol (a compound typically found in paper pulp bleaching effluents) investigated. We noticed that the photocatalytic process requires either a powerful light source or an improvement of the light utilization efficiency of the TiO2 catalyst, or maybe both, to be most effective. We tested two strategies: (a) A new experimental setup that used a high power light (125 W) to accelerate the reaction rate. AOX, acute toxicity, phenol and a GC-MS analysis led us to conclude that the chlorine organic compounds were efficiently eliminated from the treated wastewater. (b) The second approach consisted in using titanium dioxide (TiO2)-coated waveguides. This approach increases the light utilization efficiency of the TiO2 catalyst with the aim of improve the reactor's design.The last process that was tested involved the addition of Fenton reagent to the bleaching pulp and textile effluents in conjunction with either artificial or solar light The degradation of the organic contents was successfully performed at pH = 3.The first study was performed on bleaching pulp effluent. The approximate function of the system, as assessed by the experimental design, showed that initial non-optimum concentrations of the Fenton reagent were detrimental to the process because of competitive reactions of the Fenton reagent with oxidative species. On the other hand, temperature markedly increased the reaction rates, even without light irradiation. The improvement in TOC removal was particularly significant when the reagent ratios were not optimal. A decrease in cost around 80% is possible by just increasing the temperature from 25ºC to 40ºC. Moreover, solar light reduced the total cost of a two hour treatment by up to 70 % and efficiently removed the chlorophenolic compounds as shown by GC-MS analysis.The second study performed on textile wastewater corroborates the importance of the temperature parameter and the utility of solar energy. In summary, all AOPs tested displayed the capability to degrade the organic components of bleaching Kraft mill and textile mill effluents under suitable experimental conditions.Postprint (published version

Degradation of organic compounds in paper and testile industrial wastewaters by advanced axidation processes

Les activitats de recerca destinades a la solució dels problemes de contaminació de les aigües estan patint un fort increment en els darrers anys. Entre les indústries més contaminants, cal esmentar la tèxtil i la paperera, i més concretament, els efluents provinents d´etapes deblanqueig. Quan els tractaments biològics convencionals d'aquests efluents contaminants no són efectius, la utilització de tecnologies emergents, tals com els processos d´oxidació avançada (AOP´s), basats en la formació in situ de radicals hidroxil, es mostra adient. Amb l´objectiu de provar la viabilitat de tractar efluents contaminants amb el radical hidroxil, vàrem triar l´ozonització i la fotocatàlisi per abordar efluents de blanqueig de pastes papereres generats en el laboratori. Aquesta prova mostrà que la fotocatàlisi pot reduir eficientment el contingut de carrega orgànica tot seguint una equació cinètica de Langmuir-Hinshelwood. A més, la combinació simultània de fotocatàlisi i ozonització produí un efecte sinèrgic que millorava el rendiment respecte al cas d´aplicar ambdós AOP´s de manera seqüencial.Tot i assumint que el radical hidroxil era l´oxidant adequat, planificàrem un extens estudi, fent servir aigües residuals industrials i distints AOP´s. La disminució del TOC i el cost en el tractament varen ésser els paràmetres contrastats en els distints estudis, amb l´objectiu de descobrir els principals avantatges i inconvenients de cada procés. El procés d´ozonització requeria disminuir el seu cost. La presència d´ions ferro en el procés ozó/UVA va aconseguir la reducció d´un 90% de TOC conjuntament amb una disminució del 15% en el cost. L´ús seqüencial de tractaments genera millors resultats (addició de ferro amb o sense llum, seguit per una etapa d´ozonització). Conclusions similars es varen obtenir en treballar amb una matriu sintètica de 2,4-diclorfenol (compost trobat usualment en els efluents de blanqueix de pasta de paper).Referent a la fotocatàlisi, s´ha posat de manifest la necessitat d´utilitzar una font de llum potent i/o la millora de l´eficiència de la llum incident en el catalitzador de TiO2. En aquest sentit vàrem provar dues vies: (a) la utilització d´un nou muntatge experimental amb una font de llum de 125 W. Determinacions d´AOX, toxicitat aguda, fenols i de GC-MS ens van portar a concloure que els compostos orgànics de clor eren eliminats eficientment en l´aigua residual. (b) la utilització de guies d'ones recobertes de TiO2. Solució que permet augmentar l´eficiència amb la que el catalitzador aprofita la llum incident per tal de millorar el disseny de reactors fotocatalitics.L´últim procés provat, el reactiu Fenton, en presència de llum solar o artificial, es va aplicar a la degradació d´efluents de blanqueig tèxtils o paperers. La degradació del contingut de càrrega orgànica d'aquests effluents s´assolia preferentment a pH = 3. El primer estudi es realitzà sobre un efluent de blanqueig de pastes de paper. La funció aproximada del sistema, estimada a partir del disseny experimental, mostrà que concentracions inicials inadequades de reactiu Fenton afectaven negativament al procés, a causa de reaccions competitives entre aquest i altres espècies oxidatives. Així mateix, la temperatura augmentà clarament les velocitats de la reacció, inclús sense presència de radiació. La millora en la disminució del TOC és particularment significativa quan les proporcions de reactiu Fenton són inadequades (en passar de 25 ºC a 40 ºC es pot aconseguir una reducció en el cost de l´ordre del 80%). Per altre banda, la llum solar aconsegueix reduir fins un 70 % el cost total d'un tractament de dues hores de durada. L'anàlisi de GC-MS constata l´eliminació dels compostos clorfenòlics. Un segon estudi sobre un efluent tèxtil corroborà la gran importància de la temperatura i de la presència de llum solar. En resum, tots els AOP´s provats mostren, sota condicions experimentals adequades, la capacitat de degradació del contingut orgànic present en efluents de blanqueig procedents d´indústries papereres i tèxtils.There is an ever increasing amount of research activities especially devoted to the solution of water pollution problems.The pulp and textile industries are considered to be some of the largest polluters of all industries. The biggest problem with those industries consists in the polluted effluents discharged during the bleaching process because conventional biological treatments are not effective in treating these toxic pollutants. In these cases, the emerging technologies called Advanced Oxidation Processes (AOPs) represent an attempt to mineralize the contaminants by the in situ formation of hydroxyl radicals.In order to determine the effectiveness of treating effluents with the hydroxyl radical we chose the photocatalytic and ozonation processes to treat bleaching pulp effluents generated in the laboratory. Our results demonstrated that the photocatalytic process could efficiently reduce the organic content in accordance with the Langmuir-Hinshelwood kinetic equation. Moreover, simultaneously combining photocatalysis and ozonation provided a synergistic effect that was superior in performance to that of applying the photocatalysis and ozonation processes sequentially.Our tests with laboratory bleaching pulp effluents assumed that the hydroxyl radical was the proper oxidant to be use. An extensive study was undertaken using industrial wastewaters and different AOPs. TOC decay and treatment costs were the operative variables compared in the study in order to discover the benefits and shortcomings of each process.It is imperative that the ozonation process decreases the treatment costs. The addition of iron ions to bleaching mill wastewater undergoing ozone/UVA treatment resulted in high rates of TOC removal (90%) and in a significant cost reduction (15%). Additionally, sequential processing (stirred iron, with or without light irradiation, followed by an ozonation stage) led to even better results. Similar results were obtained on the synthetic sample of 2,4-dichlorophenol (a compound typically found in paper pulp bleaching effluents) investigated. We noticed that the photocatalytic process requires either a powerful light source or an improvement of the light utilization efficiency of the TiO2 catalyst, or maybe both, to be most effective. We tested two strategies: (a) A new experimental setup that used a high power light (125 W) to accelerate the reaction rate. AOX, acute toxicity, phenol and a GC-MS analysis led us to conclude that the chlorine organic compounds were efficiently eliminated from the treated wastewater. (b) The second approach consisted in using titanium dioxide (TiO2)-coated waveguides. This approach increases the light utilization efficiency of the TiO2 catalyst with the aim of improve the reactor's design.The last process that was tested involved the addition of Fenton reagent to the bleaching pulp and textile effluents in conjunction with either artificial or solar light The degradation of the organic contents was successfully performed at pH = 3.The first study was performed on bleaching pulp effluent. The approximate function of the system, as assessed by the experimental design, showed that initial non-optimum concentrations of the Fenton reagent were detrimental to the process because of competitive reactions of the Fenton reagent with oxidative species. On the other hand, temperature markedly increased the reaction rates, even without light irradiation. The improvement in TOC removal was particularly significant when the reagent ratios were not optimal. A decrease in cost around 80% is possible by just increasing the temperature from 25ºC to 40ºC. Moreover, solar light reduced the total cost of a two hour treatment by up to 70 % and efficiently removed the chlorophenolic compounds as shown by GC-MS analysis.The second study performed on textile wastewater corroborates the importance of the temperature parameter and the utility of solar energy. In summary, all AOPs tested displayed the capability to degrade the organic components of bleaching Kraft mill and textile mill effluents under suitable experimental conditions

Professionals educats per un desenvolupament humà i sostenible

Donat un problema d’enginyeria, la sostenibilitat no n’és una finalitat, és una restricció que cal que satisfaci la solució d’aquest problema. Altrament, la solució sempre seria no fer res, tornar a les cavernes. És per això que la sostenibilitat no és ni pot ser mai una assignatura sinó una competència transversal que han d’adquirir totes les persones que es formen en les diferents disciplines de per a la solució de problemes.Peer Reviewe

Degradation and mineralization of Bisphenol A by the photo fenton process

Bisphenol A (BPA; 2,2-bis (4-hydroxyphenyl) propane) is an industrial organic chemical basically used in the plastics industry as a monomer for producing epoxy resins and polycarbonates [1,2]. It is also a well-known endocrine disruptor agent that contaminates surface waters even at low concentration [3]. Unfortunately, BPA cannot be entirely removed from water solutions by conventional treatments. Additionally, in some cases, such treatments can lead to a series of by-products with higher endocrine disrupting effect [4]. Advanced Oxidation Processes (AOPs), among them the Fenton and photo-Fenton processes, are efficient methods for BPA photodegradation [1]. However, they are energy-intensive processes and their cost is ought to be improved by reducing the reaction time as well as the consumption of reagents. In this work, the Fenton and the photo-Fenton degradation of BPA (0,5 L, 30 mg L-1) was addressed. The process efficiency was evaluated under different H2O2 and Fe(II) initial concentrations (2,37-6,41 mM H2O2 and 1,42·10-2-3,92·10-2 mM iron salt), while other variables were fixed (pH=3, 25ºC, UV light source). The treatment performance was assessed for a series of assays from a factorial design and was quantified in terms of the decay rate of total organic carbon (TOC) and the total conversion attained, according to a pseudo first order kinetics [5-6]. The performance of the mineralization may be characterized by determining the two parameters of the model, ¿max (or [TOC]8) and k, which can be obtained by fitting the model to the experimental data under the least squares criterion. The results were plot k in front to identify different clusters and the conditions which produces higher mineralization ratesPostprint (published version

Modelling of the photo-Fenton process with flexible hydrogen peroxide dosage: Sensitivity analysis and experimental validation

The supply of hydrogen peroxide (H2O2) controlling the amount of highly oxidant hydroxyl radicals is the most critical operational issue for the photo-Fenton process. Accordingly, this study addresses the development of a model for photo-Fenton processes including a flexible H2O2 supply given as a function of time. The model is aimed at its future exploitation in treatment optimization and the determination of the optimal profile for H2O2 supply. The work has adopted a photo Fenton model previously reported that includes the inlet flow (fed-batch) and describes the system dynamics under a flexible dosage. Thus, model global sensitivity analysis (GSA) and parameter estimation were performed using Simulink® to examine the behavior of the model under flexible H2O2 dosage. GSA was carried out using partial rank correlation methods and the Latin hypercube sampling to assess to which extent variations of the model parameters affect each measured response (H2O2, total organic carbon, TOC, and dissolved oxygen, O2 –the experimentally available information). Hence, the model is discussed in regard of its hypothesis and chances for reducing its complexity. This resulted in the rejection of two reactions of the initial model. Next, a set of 12 kinetic, stoichiometric and operative parameters was estimated through the fitting of H2O2, TOC, and O2 profiles. Discussion on model fitting includes computational issues, the role of initial values for the estimation process, the goodness of fit criteria, and the sampling method. The model was fit to experimental data with assorted H2O2 supply profiles and validated, and Root Mean Square Error (RMSE) below 0.009 mM, 0.42 mM, and 0.127 mM were obtained for TOC, H2O2 and O2, respectively. Therefore, this work contributes a practical model aimed at providing model-based optimization for the H2O2 dosage profile of the photo-Fenton process.Peer ReviewedPostprint (published version

Entorn web per a la gestió i aprenentatge dels procediments de seguretat i medi ambient en els laboratoris d’enginyeria química

La seguretat, la prevenció i les actituds tècnicament responsables, incloent les aspectes ètics [1], són qüestions de gran importància tècnica i social. No obstant, això no s’explicita en els continguts de les assignatures de laboratori. El laboratori acostuma a ser un lloc preparat per a verificar els continguts físicoquímics de les assignatures de teoria. Els aspectes de seguretat es limiten a procurar que ningú faci o es faci mal. Difícilment es concep el laboratori com un escenari on assajar les relacions de responsabilitat col·lectiva que s'establiran entre els futurs enginyers. Així doncs, fa falta fer-ho implementant els corresponents rols entre l'alumnat i usant les eines que aplica la indústria: protocols i sistemes de gestió de la informació i la implantació de normes de millora continua en seguretat i medi ambient.Peer Reviewe

Bisphenol A degradation and mineralization by the Fenton and the Photo-Fenton process

The performance of the Fenton and photo-Fenton processes for the degradation and mineralization of Bisphenol A was investigat-ed. A parameterized kinetic model was suitably fitted to the exper-imental data in order to determine two performance parameters related to the global equilibrium conversion and kinetic rate of the process. Further analysis allowed selecting those process condi-tions (iron and hydrogen peroxide load) that maximize the process performance. The Fenton process clearly proved to more efficient-ly degrade Bisphenol A under irradiation. The highest conversion rates were achieved with only the stoichiometric hydrogen perox-ide load and the appropriate iron load (i.e. total Bisphenol A elimination and 90 % TOC decay).Postprint (published version

Systematic optimization approach for the efficient management of the photo-Fenton treatment process

The photo-Fenton process is a photochemical process that has proved to be highly efficient in degrading new potentially harmful contaminants. Despite of this, scarce attention has been paid to the development of systematic procedures and optimisation strategies to efficiently operate such a process. The present work aims at investigating the effectiveness of a model-based approach in carrying out the dynamic optimisation of the recipe of a photo-Fenton process, performed in fed-batch mode (reactant dosage). This work has addressed and solved multiple optimisation problems, searching for the optimal hydrogen peroxide (H2O2) dosage profile, and Pareto frontiers have been built accordingly in order to point out the interaction between three main process efficiency parameters, such as processing time, total amount of H2O2 used, and Total Organic Carbon (TOC) removal. Such a study allows mapping the best operating conditions and provides a decision-making oriented overview of the process. An economic study has also been carried out with the aim of finding out the optimal H2O2 dosage profile that guarantees the minimum operating cost under a varying set of operational and environmental constraints, such as TOC removal. This work has adopted and properly adapted the model by Cabrera Reina et al. (2012) in order to describe the evolution of the system under a flexible reactant dosage. Cabrera Reina et al. (2012) proposed a semi-empirical kinetic model to track paracetamol degradation using the photo-Fenton process and experimentally validated this model for a pollutant load range between 4 and 25¿mmol L-1 of TOC (e.g. industrial wastewaters). Dynamic optimisation has been addressed applying a direct simultaneous optimisation method using this extended model. Results have been presented and discussed in regard of optimal H2O2 dosage under both economic and environmental constraints. The model-based optimisation approach has allowed a fast practical recipe adjustment with reduced experimental work.Peer ReviewedPreprin

Towards an efficient generalization of the online dosage of hydrogen peroxide in photo-fenton process to treat industrial wastewater

This work addresses the dosage of H2O2 in photo-Fenton processes and the monitoring of Dissolved oxygen (DO) that can be used to drive the dosage of H2O2. The objective of this work is to show that a smarter monitoring of a process variable such as DO (for which on-line measurement can be inexpensively obtained) enables the proposal and implementation of efficient dosage strategies. The work explores the application of a recent proposed strategy consisting of: (i) initial H2O2 addition, (ii) continuous H2O2 addition until a DO set up is reached, and (iii) automatic H2O2 addition by an on-off control system based on DO slope monitoring, and applies it to the treatment of different individual contaminants and their mixtures (paracetamol and sulfamethazine). The assays performed following this dosage strategy showed improved values of TOC removed per H2O2 consumed. For the case of sulfamethazine, this improvement increased up to 25–35% with respect to the efficiency obtained without dosage. Furthermore, a deeper analysis of the results allowed detecting and assessing the opportunity to redesign the dosage scheme and reduce its complexity and the number of control parameters. The promising results obtained are discussed in regard of future research into further increasing the simplicity and robustness of this generalized control strategy that improves the applicability of the photo-Fenton process by reducing its operating costs and increasing automationPeer ReviewedPostprint (published version

Removal of Paracetamol Using Effective Advanced Oxidation Processes

Fenton, photo-Fenton, and photo-induced oxidation, were investigated and compared for the treatment of 0.26 mmol L-1 of paracetamol (PCT) in a deionised water matrix, during a reaction span of 120.0 min. Low and high Fenton reagent loads were studied. Particularly, the initial concentration of Fe2+ was varied between 0.09 and 0.18 mmol L-1 while the initial concentration of H2O2 was varied between 2.78 and 11.12 mmol L-1. The quantitative performance of these treatments was evaluated by: (i) measuring PCT concentration; (ii) measuring and modelling TOC conversion, as a means characterizing sample mineralization; and (iii) measuring cytotoxicity to assess the safe application of each treatment. In all cases, organic matter mineralization was always partial, but PCT concentration fell below the detection limit within 2.5 and 20.0 min. The adopted semi-empirical model revealed that photo induced oxidation is the only treatment attaining total organic matter mineralization (¿MAX= 100% in 200.0 min) at the expense of the lowest kinetic constant (k = 0.007 min-1). Conversely, photo-Fenton treatment using high Fenton reagent loads gave a compromise solution (¿MAX= 73% and k = 0.032 min-1). Finally, cytotoxicity assays proved the safe application of photo-induced oxidation and of photo-Fenton treatments using high concentrations of Fenton reagents.Peer ReviewedPostprint (published version