Modelación del proceso de biofiltro percolador para el tratamiento de emisiones en aire de Compuestos Orgánicos Volátiles de elevada solubilidad en agua

La contaminación del aire producida por las emisiones a la atmosfera de compuestos orgánicos volátiles (COV) es una de las causas más importantes asociadas al deterioro de la calidad ambiental. Una de las fuentes principales de emisión de COV son las industrias que utilizan disolventes. En este sentido, las industrias deben hacer un esfuerzo por adaptar sus procesos productivos para minimizar el impacto ambiental. Sin embargo, las propiedades de los disolventes los convierten en indispensables en algunas aplicaciones por lo que el tratamiento de las emisiones derivadas de su uso se convierte en una necesidad. El uso de biofiltros percoladores para la depuración de COV de elevada solubilidad en agua es una tecnología sostenible, habiéndose demostrado que es una alternativa viable técnica y económicamente, tal y como avalan las investigaciones realizadas en las últimas décadas. Sin embargo, el desarrollo de la investigación sobre esta tecnología requiere dar un paso más para lograr consolidarla en el entorno industrial. Este trabajo de tesis doctoral tiene como objetivo principal el de desarrollar una herramienta matemática que incluya los principales mecanismos involucrados en la depuración de aire contaminado con COV de elevada solubilidad en agua mediante el proceso de biofiltro percolador en condiciones de operación típicas de la industria. Los COV de elevada solubilidad en agua están presentes de manera habitual en las emisiones gaseosas procedentes de la industria entre otras, de impresión flexográfica. Pese a que son compuestos con una biodegradabilidad relativamente elevada, la depuración de este tipo de COV suele verse limitada por la disponibilidad de oxígeno en el interior de la biopelícula, lo que favorece la acumulación de contaminante en el interior del sistema. En este sentido, una parte importante de la tesis doctoral ha consistido en profundizar en los mecanismos de transferencia de materia de contaminante y de oxígeno mediante la determinación de los coeficientes de transferencia de materia para ambos compuestos. La herramienta matemática desarrollada en la presente tesis doctoral tiene como finalidad simular y predecir la respuesta transitoria de los biofiltros percoladores sometidos a condiciones de carga variable y riego intermitente. El modelo matemático ha sido aplicado tanto a biofiltros percoladores utilizados en el laboratorio, en condiciones controladas de operación, como a biofiltros percoladores situados en instalaciones industriales, en los que se suele observar patrones de emisión más amortiguados. En la primera etapa de este trabajo se llevó a cabo el estudio experimental a escala de laboratorio de eliminación de emisiones en aire que contenían isopropanol, elegido éste como contaminante modelo. Para ello se utilizaron dos biofiltros percoladores empaquetados con diferente material de relleno: uno desordenado y otro estructurado. Durante este estudio se sometieron a los reactores a condiciones discontinuas de alimentación y de riego intermitente, y se evaluó la respuesta del biofiltro percolador a cambios en la concentración de alimentación de contaminante y de caudal de gas. Los resultados indicaron que el uso de patrones de riego intermitente provocaba una emisión fugitiva de contaminante en la corriente gaseosa de salida del biofiltro percolador que coincidía con el momento del riego. Para evaluar este efecto se aplicaron diferentes condiciones de riego al sistema, concluyendo que el patrón de riego podía utilizarse como estrategia para aumentar el rendimiento del reactor. Así mismo se sometió al reactor a un periodo de 7 semanas sin alimentación de COV. La capacidad de recuperación de los biofiltros percoladores puso de manifiesto la robustez del sistema. La siguiente fase de la tesis se centró en el estudio de la transferencia de materia en los biofiltros percoladores. Para ello se determinaron los coeficientes de transferencia de materia de isopropanol y de oxígeno para diferentes velocidades superficiales de líquido y de gas y para varios materiales de relleno. Los datos obtenidos en este estudio permitieron desarrollar correlaciones empíricas para caracterizar la relación entre los coeficientes de transferencia de materia y las velocidades superficiales de gas y de líquido aplicadas en el biofiltro percolador. Así mismo, se evaluó un material de relleno de uso industrial en términos de transferencia de oxígeno con el objetivo de compararlo con los materiales de relleno empleados en el laboratorio, demostrándose que, en las velocidades de aplicación de los biofiltros percoladores industriales, la transferencia de oxígeno para este material era similar a la obtenida con los materiales utilizados en el laboratorio. En la última parte del presente estudio se desarrolló un modelo matemático para la predicción de la respuesta transitoria de los biofiltros percoladores en condiciones de estado no estacionario de carga y de riego intermitente. El desarrollo del modelo se basó en balances de materia de isopropanol y de oxígeno en la fase gas, en la fase líquida y en la biopelícula. El modelo matemático se desarrolló asumiendo condiciones cíclicas de periodos con riego y de periodos sin riego, ya que ésta es la forma habitual de operación a nivel industrial. Durante los periodos con riego se consideró una fase líquida móvil, mientras que durante los periodos sin riego se consideró una fase líquida estancada. La calibración y validación del modelo matemático se realizó con datos de biofiltros percoladores utilizados a escala de laboratorio y a escala industrial. Las principales hipótesis del modelo estuvieron relacionadas con la resistencia a la transferencia de materia tanto durante el riego (fase líquida móvil) como durante el no riego (fase líquida estancada). La calibración del modelo se llevó a cabo con datos de experimentos realizados a escala de laboratorio en biofiltros percoladores sometidos a riego discontinuo y carga de contaminante intermitente. Considerando despreciable la resistencia a la transferencia de materia producida por la fase líquida estancada durante los periodos sin riego, el modelo fue capaz de reproducir el rendimiento global del sistema así como el patrón de emisiones ocasionado por el riego discontinuo. Además, permitió identificar que la relación entre la concentración de carbono orgánico en el tanque de recirculación y la emisión fugitiva observada durante los periodos con riego estaba asociada al incremento de la resistencia a la transferencia de materia entre la fase gas y la fase líquida móvil con respecto a las determinaciones realizadas en condiciones abióticas. Este fenómeno se asoció al cambio de las propiedades físicas que ocasiona la presencia de biopelícula. La aplicación del modelo para la predicción de las emisiones de salida de un biofiltro percolador instalado en una industria de impresión flexográfica demostró la utilidad práctica del modelo. La aplicación del modelo para la simulación de esta corriente se basó en las hipótesis de la existencia de una resistencia a la transferencia de materia de la fase gas a la fase líquida móvil durante el riego y una resistencia adicional con respecto al biofiltro percolador de laboratorio a la transferencia de materia desde la fase gas a la fase líquida estancada durante los periodos sin riego. Se utilizó un mayor espesor de biopelícula que en los biofiltros percoladores empleados en el laboratorio ya que se identificó que ésta actuaba cíclicamente como fuente/sumidero asociado a los periodos diarios de fabricación/no fabricación. El elevado espesor de la biopelícula provocó que durante los periodos de alimentación de COV al sistema, la parte no degradada del contaminante se acumulara en la biopelícula, produciéndose su desorción en los periodos en los que circulaba aire limpio por el reactor. Todo ello demostró la capacidad del modelo para reproducir los fenómenos complejos involucrados en la respuesta dinámica de los biofiltros percoladores que tratan compuestos orgánicos volátiles de elevada solubilidad en agua. El modelo matemático se integró en una herramienta informática mediante una GUI (Graphical User Inteface) desarrollada con MATLAB®. A fin de facilitar la comunicación con el usuario final, se generaron dos interfaces: una interfaz para introducir los datos para realizar las simulaciones y una interfaz de resultados. La herramienta desarrollada permite introducir de una manera sencilla patrones de concentraciones y caudales de gas variables, así como el uso de patrones de riego intermitente. Al terminar la simulación, la herramienta ofrece una pantalla de resultados con la información más relevante para evaluar el funcionamiento de los biofiltros percoladores: gráficas de patrón de emisión de la concentración de contaminante en la fase gas a la entrada y a la salida del reactor y de la variación temporal de la concentración de carbono disuelto en el tanque de recirculación, así como datos promedio de concentración de contaminante en las emisiones gaseosas a la entrada y a la salida del bioreactor, de carga volumétrica y de capacidad de eliminación.Air pollution produced by the emission to the atmosphere of volatile organic compounds (VOCs) is one of the most important causes associated with deterioration of air quality. One of the main sources of VOC emissions are companies that use solvents. In this regard, they should make an effort to adapt their production processes in order to minimise environmental impact. However, the properties of solvents make them essential in certain applications, so the treatment of derivative emissions becomes a necessity. Use of biotrickling filters for the removal of highly water soluble VOCs is a sustainable technology, having been proven to be technologically and economically a viable alternative, as supported by research in the last few decades. However, research development on this technology requires one further step to achieve consolidation in the industrial environment. The main objective of this dissertation is to develop a mathematical tool that includes the principal mechanisms involved in the removal of VOCs of high solubility in water from air emissions by the biotrickling filtration process in typical industry operating conditions. VOCs of high solubility in water are usually present in gaseous emissions from the flexographic printing industry, among others. Despite being compounds with a relatively high biodegradability, biological removal of such compounds is often limited by oxygen availability within biofilm, which leads to pollutant accumulation within the system. In this regard, an important part of the thesis was focused on the study of the mechanisms of mass transfer of pollutants and oxygen by means of the determination of the mass transfer coefficients for both compounds. The mathematical tool developed here aims to simulate and predict the transient response of the biotrickling filters under variable loading conditions and intermittent spraying. The mathematical model has been applied to biotrickling filters used in the laboratory, under controlled operating conditions, as well as to biotrickling filters located in industrial facilities, in which more buffered emission patterns are observed. The first stage of this work comprises the removal of isopropanol in air emissions at the laboratory scale, selected as a model pollutant. For this purpose, two biotrickling filters filled with different packing materials were used: a random one and a structured one. The reactors were operated under discontinuous loading conditions and intermittent spraying. The response of the biotrickling filter to variations in the inlet concentration of pollutant, as well as in the gas flow, was evaluated. The results showed that intermittent spraying caused a fugitive pollutant emission in the outlet gaseous stream of the biotrickling during spraying. To evaluate this effect, different spraying conditions were tested, concluding that the spray pattern could be used as a strategy to increase the reactor performance. Likewise, a starvation period of seven weeks was applied to both reactors. The resilience of the biotrickling filters showed the robustness of the system. The next stage was focused on the study of mass transfer in biotrickling filters. For this purpose, the mass transfer coefficients of oxygen and of isopropanol were determined. Different superficial gas and liquid velocities as well as different packing materials were tested. Results allowed empirical correlations to be established, which characterised the relationship between the mass transfer coefficients and superficial velocities of liquid and of gas applied to the biotrickling filters. Likewise, a packing material for industrial use was evaluated in terms of oxygen mass transfer, in order to compare it to the packing materials applied in the laboratory. At typical industrial operating conditions, oxygen mass transfer for the industrial material was found to be similar to those obtained for the laboratory packing materials. In the final stage, a mathematical model was developed in order to predict the transient response of the biotrickling filters under non-steady conditions of pollutant loading and of intermittent spray. The model development was based on the mass balances of isopropanol and of oxygen in the gas phase, in the liquid phase and in the biofilm. The mathematical model was built assuming cyclic conditions of spraying/non-spraying periods, the common industrial operational protocol. During spraying periods, a mobile liquid phase was considered, while during non-spraying periods, a stagnant liquid phase was considered. The calibration and validation of the mathematical model was performed using data from biotrickling filters operated at laboratory and industrial scales. The main hypotheses of the model were related to mass transfer resistance during spraying (mobile liquid phase) and mass transfer resistance during non-spraying (stagnant liquid phase). Model calibration was carried out with laboratory biotrickling filters operated under discontinuous spraying and intermittent pollutant loading. By assuming negligible mass transfer resistance for the stagnant liquid phase during non-spraying, the model was able to reproduce the average system performance and the emission pattern occasioned by the discontinuous spraying. In addition, the relationship between VOC concentration in the recirculation tank and the fugitive emission observed during spraying periods was related to higher mass transfer resistance between the gas and the mobile liquid phase during spraying than that obtained during abiotic determinations. This phenomenon was associated with variations in the physical properties caused by the presence of biofilm. The model application for predicting outlet emissions of a biotrickling filter installed in the flexographic printing industrial facility demonstrated its practical usefulness. Model application for simulating this industrial air flow was based on the hypotheses of mass transfer resistance for the mobile liquid phase during spraying and an additional mass transfer resistance from the stagnant liquid phase during non-spraying with respect to laboratory experiments. It was identified that the biofilm acted as a source/sink associated with daily periods of manufacturing/ non-manufacturing. Thus, a greater thickness of biofilm than in the laboratory biotrickling filters was fixed. The thick biofilm caused the accumulation of the non-degraded pollutant during periods with VOCs feeding to the system. The stored pollutant in the biofilm led to desorption during periods when clean air circulated through the reactor. The model capability to reproduce the complex phenomena involved in the dynamic response of the biotrickling filters treating volatile organic compounds with high water solubility was demonstrated. The mathematical model was integrated into an informatics tool using a GUI (Graphical User Interface) developed with MATLAB®. In order to facilitate communication with the end user, two interfaces were generated: an interface to enter data for simulations, and a results interface. The developed tool allows for the introduction of variable patterns of concentration and gas flows in a simple way, and also the use of intermittent spraying patterns. When the simulation ends, the tool offers a results screen with the most relevant information to evaluate the performance of the biotrickling filters: graphic information regarding the pattern of the gaseous emissions at the inlet and at the outlet of the reactor, as well as graphic information regarding the variation of dissolved organic carbon in the recirculation tank. Average data regarding the concentration in the gaseous emission at the inlet and at the outlet of the bioreactor, and the inlet load and the elimination capacity, are also provided

Enhanced styrene removal in a two-phase partitioning bioreactor operated as a biotrickling filter: Towards full-scale applications

Styrene vapor abatement was investigated in a two-phase partitioning bioreactor operated as a biotrickling filter (TPPB-BTF). The removal performance of the TPPB-BTF was simultaneously compared with a conventional BTF, which served as a control. Industrial-grade silicone oil was used as the non-aqueous phase in the TPPB-BTF due to its high affinity for styrene. Both bioreactors were operated at styrene inlet concentrations ranging from 55 to 323 mg C m−3 and empty bed residence times (EBRT) of 15-30 s, corresponding to pollutant loading rates of 13-77 g C m−3 h−1. Both bioreactors exhibited styrene removal efficiencies (REs) higher than 90% at an EBRT of 30 s. Nevertheless, the TPPB-BTF showed a superior removal performance than that recorded in the control BTF at EBRTs shorter than 30 s. REs of 89%, 84% and 57% were recorded in the TPPB-BTF at EBRT of 15 s and loading rates of 13, 22 and 77 g C m−3 h−1, respectively, while the control BTF supported removal efficiencies of 64%, 42% and 18-42% under the same experimental conditions. The resilience and robustness of the TPPB-BTF over styrene shock loadings and transient inlet concentration was also confirmed, the TPPB-BTF being able to recover a stable RE of 89% one day after such operation disturbances. The potential of the TPPB-BTF towards full scale applications was also critically discussed based on the experimental determination of silicone oil loses through aqueous phase renewal, which accounted for 0.4% of the initial volume of oil added to the TPPB-BTF after 87 days of operation

Modelling mass transfer properties in a biotrickling filter for the removal of isopropanol

A study was carried out to model mass transfer properties in biotrickling filters, treating isopropanol as the target pollutant. This study was extended to the mass transfer of oxygen related to the fact that the treatment of hydrophilic compounds by biotrickling filtration is often limited by oxygen. A simple method for each compound was developed based on their physical properties. The influence of temperature on the Henry"s law constant of isopropanol was determined. An increase of 1.8 per 10ºC for the dimensionless Henry"s law constant was obtained. The determination of the overall mass transfer coefficients of isopropanol (KGa) was carried out, obtaining values between 500 and 1800 h-1 for gas velocities of 100 and 300 m h-1. No significant influences were observed for either the liquid velocity or packing material. Also, the determination of overall mass transfer coefficients of oxygen (KLa) were carried out, obtaining values between 20 and 200 h-1 depending on the packing material for liquid velocities between 2 and 33 m h-1. Structured packing materials exhibited greater mass transfer coefficients, while for random packing materials, the mass transfer coefficients clearly benefited from the high specific surface area. Mathematical correlations found in the literature were compared with the empirical data, showing that neither was capable of reproducing the mass transfer coefficients obtained empirically. Thus, empirical relationships between the mass transfer coefficients and the gas and liquid velocities are proposed to characterise the syste

Biotrickling filter modeling for styrene abatement. Part 2: Simulating a two-phase partitioning bioreactor

Peer ReviewedPostprint (author's final draft

Study of Mass Oxygen Transfer in a Biotrickling Filter for Air Pollution Control

Biotrickling filtration is a potential and cost effective alternative for the treatment of volatile organic compound (VOC) emissions in air, so it is necessary to deepen into the key aspects of design and operation for the optimization of this technology. One of these factors is the oxygen mass transfer of the process. This study would facilitate the selection of the packing material and the mathematical modelling and simulation of bioreactors. Four plastic packing materials with a different specific surface area have been evaluated in terms of oxygen mass transfer. For the tested range of superficial liquid velocities, data show a relationship between the kLa and the superficial liquid velocity in all packing materials used, except for the biggest plastic rings. No significant differences in mass transfer coefficients at low liquid velocities were observed, however dependency between oxygen transfer and specific surface area increased considerably for high liquid velocities. No significant influences of the superficial air velocity were observed

Evolution of bacterial community in isopropanol-degrading biotrickling filters by fluorescence in situ hybridization (FISH)

In this study, the bacterial population of two biotrickling filters (BFTs) treating isopropanol by using fluorescence in situ hybridization (FISH) is analyzed. The experimental system consists in two identical laboratoryscale BFTs named as BFT1 and BFT2. The two bioreactors were operated in parallel during an experimental period of one year working under intermittent feeding conditions Operating conditions and maintenance were identical in both BFT

Aspen Plus process-simulation model: Producing biogas from VOC emissions in an anaerobic bioscrubber

A process-simulation model for a novel process consisted of an anaerobic bioscrubber was developed in Aspen Plus®. A novel approach was performed to implement the anaerobic reactor in the simulation, enabling it to be connected to the scrubber. The model was calibrated and validated using data from an industrial prototype that converted air emissions polluted with volatile organic compounds with an average daily concentration of 1129 mgC Nm−3 into bioenergy for more than one year. The scrubber, which showed a removal efficiency within 83-93%, was successfully predicted with an average absolute relative error of 5.2 ± 0.08% using an average height-to-theoretical-plate value of 1.05 ± 0.08 m and 1.37 ± 0.11 m for each of the two commercial packing materials used, respectively. The anaerobic reactor, which treated up to 24 kg of chemical oxygen demand m−3 d−1 with efficiencies of about 93%, was accurately simulated, both in effluent-stream characteristics and in the biogas stream. For example, the average absolute error between the experimental biogas production and the model values was 19.6 ± 18.9%. The model proved its capability as a predictive tool and an aid in design, resulting in savings of time and money for practitioners. In addition, the approach proposed can be expanded to other bioprocesses that include unit operations

Evolution of Bacterial Community in a Full-scale Biotrickling Filter by Fluorescence in Situ Hybridization (FISH)

The performance of a full-scale biotrickling system for the treatment of exhaust gases from two different paint sources at a furniture facility, was investigated applying Fluorescense in situ hybridization (FISH). This technique allowed the detection of major bacteria groups and, therefore, helped in understanding complex microbial communities. The results indicated that Alphaproteobacteria, Betaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria were more predominant than Firmicutes and Actiniobacterias. In addition, a variation in the composition of the bacterial community throughout the time of operation and with the paint source was observed. Betaproteobacteria showed similar relative abundance in all analyzed days. However, Gammaproteobacteria, relevant group in the degradation of VOCs, fluctuated with operational changes and the relative abundance of Alphaproteobacteria decreased when the composition of pollutants of the emission source was changed

Optimization of alkali pretreatment to enhance rice straw conversion to butanol

The use of rice straw (RS) was enhanced to produce biobutanol as biofuel, for which the NaOH pretreatment was optimized by considering the butanol-biomass ratio that quantify the mass balance efficiency of the three sequential stages of the process: pretreatment, enzymatic hydrolysis and fermentation by Clostridium beijerinckii. The optimum point (solid loading of 5% w/v with 0.75% w/v NaOH at 134 °C for 20 min) of the best cost-wise option yielded an enhanced biomass use of 77.6 g kg RS−1. A maximum butanol titer of 10.1 g L−1 was reached after 72 h of fermentation with the complete uptake of glucose and nearly complete uptake of xylose. The NaOH concentration was the most influential parameter. The appropriate dosage to maximize fermentable sugars instead of the mass balance efficiency of the three stages underestimated the biomass use by 13%, showing the importance of correctly selecting the variable response during optimization

Comprehensive clone screening and evaluation of fed-batch strategies in a microbioreactor and lab scale stirred tank bioreactor system : application on Pichia pastoris producing Rhizopus oryzae lipase

Background: In Pichia pastoris bioprocess engineering, classic approaches for clone selection and bioprocess optimization at small/micro scale using the promoter of the alcohol oxidase 1 gene (PAOX1), induced by methanol, present low reproducibility leading to high time and resource consumption. - Results: An automated microfermentation platform (RoboLector) was successfully tested to overcome the chronic problems of clone selection and optimization of fed-batch strategies. Different clones from Mut+P. pastoris phenotype strains expressing heterologous Rhizopus oryzae lipase (ROL), including a subset also overexpressing the transcription factor HAC1, were tested to select the most promising clones. The RoboLector showed high performance for the selection and optimization of cultivation media with minimal cost and time. Syn6 medium was better than conventional YNB medium in terms of production of heterologous protein. The RoboLector microbioreactor was also tested for different fed-batch strategies with three clones producing different lipase levels. Two mixed substrates fed-batch strategies were evaluated. The first strategy was the enzymatic release of glucose from a soluble glucose polymer by a glucosidase, and methanol addition every 24 hours. The second strategy used glycerol as co-substrate jointly with methanol at two different feeding rates. The implementation of these simple fed-batch strategies increased the levels of lipolytic activity 80-fold compared to classical batch strategies used in clone selection. Thus, these strategies minimize the risk of errors in the clone selection and increase the detection level of the desired product. Finally, the performance of two fed-batch strategies was compared for lipase production between the RoboLector microbioreactor and 5 liter stirred tank bioreactor for three selected clones. In both scales, the same clone ranking was achieved. - Conclusion: The RoboLector showed excellent performance in clone selection of P. pastoris Mut+ phenotype. The use of fed-batch strategies using mixed substrate feeds resulted in increased biomass and lipolytic activity. The automated processing of fed-batch strategies by the RoboLector considerably facilitates the operation of fermentation processes, while reducing error-prone clone selection by increasing product titers.The scale-up from microbioreactor to lab scale stirred tank bioreactor showed an excellent correlation, validating the use of microbioreactor as a powerful tool for evaluating fed-batch operational strategies