Electrocoagulation using novel configurations electrodes for treatment of textile wastewater

Textile wastewater is considered as one of the most polluted wastewater. Conventional chemical coagulation is the most famous technique used to treat the textile effluent. However, this method produces low removal rate, long retention time and a large quantity of sludge and chemicals. The electrocoagulation (EC) technology is an active wastewater treatment used before sedimentation and filtration. It is still in the "black box" stage where process design, control, and optimization have been primarily empirical. In this research, the EC process was performed in two models for the treatment of textile wastewater. The first model is the conventional reactor with a new configuration that has static electrodes, classified in two phases. The two phases are the EC process alone, using Mp Al-Bp Al or Mp Al-Bp Fe and EC combined with electrooxidation process (EO) in the same reactor using MpTi-Bp Al or MpTi-Bp Fe. The second model is a novel reactor design with a rotating anode using aluminum electrodes. The rotating anode consists of 10 impellers supported by a shaft with 10 rings used as a cathode. The operational parameters were investigated, and the process was performed under optimal conditions. For model one, the results showed that the Mp Al-Bp Al was more effective than the Mp Al-Bp Fe and it was more efficient than chemical coagulation. The optimal combination (EC-EO) treatment was established with Mp Ti-Bp Al, and it is found to be more active than EC alone. The optimal parameters of the EC process with a novel rotating anode were 4 mA/cm2 current density, 150 rpm rotational speed, and 10 minutes reaction time. EC process with a rotating anode was more active than model one and chemical coagulation, where the removal efficiency was higher, and the operational cost were reduced significantly. The increase of impellers anode diameter led toenhance the mass transfer coefficient of ionic aluminum. This result was confirmed by computational fluid dynamic (CFD) simulation results. By solar cell supply, the EC process with rotating anode reactor using batch and continuous flow regime had almost similar removal rate. Zeta potential tests showed that reaction was chemo-adsorption, and this was validated by the X-ray diffraction (XRD) analysis. Moreover, the reaction product was environmental friendly. Hydrogen production was improved at a rotation speed of anode. The electrode passivation was reduced by increasing rotational speed of anode which led to an improved in the EC process performance and validated the reactor design. Finally, the contribution of this study is a novel EC reactor with a rotating anode which is more efficient and economic as compared to the conventional coagulation process in the textile wastewater treatment

Self sustainable cathodes for microbial fuel cells

The ultimate goal of this thesis was to investigate and produce an MFC with self-sustainable cathode so it could be implemented in real world applications. Using methods previously employed [polarisation curve experiments, power output measurements, chemical assays for determining COD in wastewater and other elements present in anolyte or catholyte, biomass assessments] and with a focus on the cathode, experiments were conducted to compare and contrast different designs, materials and nutrient input to microbial fuel cells with appropriate experimental control systems.Results from these experiments show that: Firstly, the choice of polymeric PEM membrane showed that the most effective materials in terms of power performance were cation exchange membranes. In terms of cost effectiveness the most promising was CM-I, which was the preferred separator for later experiments.Secondly, a completely biotic MFC with the algal cathode was shown to produce higher power output (7.00 mW/m2) than the abiotic control (1.52 mW/m2). At the scale of the experimental system, the reservoir of algal culture produced sufficient dissolved oxygen to serve the MFCs in light or dark conditions. To demonstrate usable power, 16 algal cathode-designed MFCs were used to power a dc pump as a practical application.It has been presented that the more power the MFC generates, the more algal biomass will be harvested in the connected photoreactor. The biomass grown was demonstrated to be a suitable carbon-energy resource for the same MFC units in a closed loop scenario, whereby the only energy into the system was light.In the open to air cathode configuration various modifications to the carbon electrode materials including Microporous Layer (MPL) and Activated Carbon (AC) showed catholyte synthesis directly on the surface of the electrode and elemental extraction such as Na, K, Mg, from wastewater in a power dependent manner. Cathode flooding has been identified as an important and beneficial factor for the first time in MFCs, and has been demonstrated as a carbon capture system through wet scrubbing of carbon dioxide from the atmosphere. The captures carbon dioxide was mineralised into carbonate and bicarbonate of soda (trona). The novel inverted, tubular MFC configuration integrates design and operational simplicity showing significantly improved performance rendering the MFC system feasible for electricity recovery from waste. The improved power (2.58 mW) from an individual MFC was increased by 5-fold compared to the control unit, and 2-fold to similar sized tubular systems reported in the literature; moreover it was able to continuously power a LED light, charge a mobile phone and run a windmill motor, which was not possible before

Waste and wastewater clean-up using microbial fuel cells

A sustainable energy portfolio should include a range of carbon-neutral and renewable energy technologies. Amongst the renewable energy technologies, MFCs can offer a solution for both sustainable energy and clean water demands. In order to take the MFC technology to commercial level, more effort has to be spent to improve the performance and treatment efficiency. The goal for this thesis was to improve anode performance and waste utilisation. To achieve this goal, the approach taken was system scale-up through multiples of relatively small sized MFC units. Two main aspects of the MFC anode, design and biofilm affecting parameters, were investigated in order to better understand and enhance the anode performance. Through a number of experiments, better performing material for each MFC component was chosen. For example, by replacing the previous electrode material with modified anode and cathode, a 2.2 and 4.9 fold increase in power output was achieved respectively. Investigations into biofilm affecting parameters such as temperature, external load and feedstock, yielded novel findings helping to understand the dynamic characteristics of MFC anode biofilms. For the final part of this thesis, these findings were used to implement the MFC technology for practical applications such as treating wastes and resource recovery as well as producing electrical energy. Two troublesome wastes, urine and uric scale showed great potential for being power sources of MFC electricity generation. Furthermore it was demonstrated that MFCs can contribute to recovery of resources such as nitrogen and phosphorus in the form of struvite. A commercial electronic appliance was run continuously, powered by a stack of 8 MFCs fed with neat human urine, which successfully demonstrated a great potential of the MFC technology for both electricity generation and waste treatment

Intensificación del proceso electroquímico para la remoción de cromo en residuos líquidos

173 páginas. Doctorado en Ingeniería de Procesos.El cromo es un metal comúnmente utilizado en la industria galvanoplástica, la cual genera aguas de enjuague que contienen concentraciones de cromo hexavalente por encima de las permisibles por la regulación ambiental. Varias alternativas de tratamiento se han propuesto para atacar este problema, de donde destacan los métodos electroquímicos. Entre estos últimos, un proceso atractivo es el que utiliza electrodos de hierro, los cuales son fuente para la generación electroquímica in situ del agente reductor, que químicamente reduce al cromo en el seno del líquido, de su estado hexavalente a trivalente. El efluente, pasa a un tanque de mezclado para propiciar la precipitación de los metales en hidróxidos metálicos, mediante el incremento del pH del medio, con la finalidad de separarlos del agua tratada. En este trabajo se presentan distintas estrategias para intensificar este proceso de tratamiento, con la finalidad de mejorar el desempeño hidrodinámico del reactor electroquímico y la etapa de precipitación. Para la evaluación del comportamiento de los procesos, tanto en el reactor electroquímico como en el de precipitación, se realizaron pruebas experimentales en reactores de mezcla completa y de jarras, las cuales se complementaron con estudios mediante la dinámica computacional de fluidos, para integrar la información del desempeño de los procesos bajo los diferentes escenarios probados. El capítulo dos detalla el estudio realizado mediante herramientas de dinámica computacional de fluidos al reactor electroquímico de anillos rotatorios, el cual ha mostrado altas eficiencias de remoción de cromo hexavalente en aguas contaminadas. Esta parte del proyecto da a conocer cuál es el enfoque de modelado más apropiado para simular la hidrodinámica que se desarrolla dentro del reactor. Se realiza la comparación de los resultados predichos por tres variantes del modelo de turbulencia κ-ε (standard, RNG y realizable) acoplado al modelo de múltiples marcos de referencia para simular la rotación del electrodo. También se evalúa el efecto de la posición de las fronteras del marco de referencia rotacional respecto a las fronteras del marco de referencia estacionario. Se demuestra que la predicción con el modelo κ−ε realizable en conjunto con la posición a 0° genera los resultados con mayor acercamiento a las mediciones experimentales de tiempo de mezclado obteniendo un 6% de error. En el capítulo tres se muestran los resultados de la incorporación de una novedad, la cual consiste en un reactor equipado con el electrodo estático de electro-deflectores agitado por dos impulsores de alabes inclinados, conocido como PBT. Los resultados de esta modificación se comparan respecto a los obtenidos con el desempeño del reactor electroquímico equipado con el electrodo dinámico de anillos rotatorios. La comparación se realiza de forma teórica para evaluar sus diferencias en cuanto a su desempeño hidrodinámico, y experimental para conocer su eficiencia frente a la reducción de cromo hexavalente. Para realizar la comparación, los reactores se operaron a la misma velocidad de agitación y al mismo número de Reynolds. Los resultados del análisis hidrodinámico muestran que el arreglo de electro-deflectores estáticos junto con el par de impulsores permite mejorar el tiempo de mezclado en 36%, incrementando la eficiencia hidráulica en 85% cuando el reactor se opera al mismo número de Reynolds. Se evidencia que la capacidad de circulación del reactor afecta directamente la tasa de reducción de cromo hexavalente, ya que los tiempos de tratamiento tienen una tendencia parecida a los tiempos de circulación axial. También se muestra que hay una reducción del consumo energético de al menos un 21% cuando el reactor es equipado con los electro-deflectores y el sistema de agitación de dos impulsores. En el capítulo cuatro se evalúan las condiciones de operación del reactor electroquímico, como son: configuración geométrica del electrodo, velocidad de agitación e intensidad de corriente. Para evaluar el cambio en la configuración del electrodo se utiliza el electrodo de anillos estáticos y electro-deflectores. Al operar el electrodo con anillos estáticos también se evalúa la necesidad de incorporar deflectores convencionales. Los sistemas de agitación del reactor están compuestos por dos impulsores PBT, de los cuales también se evalúa la separación entre ellos. Al realizar las simulaciones se consideró la interacción de la interfase líquido-gas. Los resultados revelan que por la posición de los impulsores es necesario tomar en cuenta en el modelo la interacción líquido aire para obtener una predicción más realista del patrón de flujo en la configuración de electro-deflectores. Resultado de los estudios, se obtuvo que la configuración con menor consumo energético fue la de los electro-deflectores con una separación entre impulsores igual a su diámetro pues sus características geométricas e hidrodinámicas le permiten ser más eficiente. En este sistema se exploró el efecto de la velocidad de agitación y de la intensidad de corriente. La velocidad de agitación aumenta la tasa de reducción de cromo hexavalente, hallando su límite en 300 rpm. En esta velocidad de agitación se exploró el efecto de la intensidad de corriente, de donde se encuentra una dependencia lineal del consumo energético del reactor respecto a esta variable en el rango evaluado. En el capítulo cinco se estudia la etapa de precipitación. Los estudios se realizan en un sistema de jarras agitado con dos tipos de impulsores, uno radial y otro axial. Se realiza la evaluación del efecto del pH al que se ajusta el efluente para realizar la precipitación en los valores de 4, 6, 7 y 9. Los resultados muestran que después de precipitar el agua tratada a un pH = 9.0, se obtiene un clarificado con pH neutro y se logran precipitar todas las especies. Se evalúa también el ambiente hidrodinámico de las jarras de forma experimental y numérica, determinando que el impulsor radial disipa mayor energía turbulenta respecto al impulsor axial. Por lo anterior, el impulsor axial propicia un ambiente hidrodinámico favorable para el desarrollo de los flóculos, lo que se traduce en velocidades de sedimentación mayores con respecto a las alcanzadas cuando la jarra se opera con el impulsor radial. Además, el impulsor axial consume solo el 50% de la energía que consume el impulsor radial.Chromium is a metal commonly used in the electroplating industry, which generates rinsing water containing hexavalent chromium concentrations above those allowed by environmental regulations. Several treatment alternatives have been proposed to attack this problem, among which electrochemical methods stand out. Among the latter, an attractive process is the one that uses iron electrodes, which are the source for the in situ electrochemical generation of the reducing agent, which chemically reduces the chromium in the liquid from its hexavalent to its trivalent state. The effluent is passed to a mixing tank to promote the precipitation of the metals into metal hydroxides by increasing the pH of the medium in order to separate them from the treated water. In this work, different strategies are presented to intensify this treatment process in order to improve the hydrodynamic performance of the electrochemical reactor and the precipitation stage. To assess the processes performance, in both systems, the electrochemical reactor and in the precipitation reactor, experimental tests were carried out in stirred tank reactors and jars test, which were complemented with studies using computational fluid dynamics to integrate the information on the performance of the processes under the different scenarios tested. Chapter two details the study carried out using computational fluid dynamics tools on the rotating rings electrochemical reactor, which has shown high removal efficiencies of hexavalent chromium in pollulet water. This part of the project shows the most appropriate modeling approach to simulate the hydrodynamics inside the reactor. Comparison of the results predicted by three variants of the κ-ε turbulence model (stadard, RNG and realizable) coupled to the multi-reference frame model to simulate the electrode rotation is performed. The effect of position of the rotational reference frame boundaries relative to the stationary reference frame boundaries is also evaluated. It is shown that the prediction with the κ-ε realizable model in conjunction with the position at 0° generates the results with the closest approach to the experimental mixing time measurements obtaining a 6% error. Chapter three shows the results of the incorporation of a novelty, which consists of a reactor equipped with the static electrode of electro-baffles agitated by two inclined vane impellers, known as PBT. The results of this modification are compared with those obtained with the performance of the electrochemical reactor equipped with the dynamic rotating ring electrode. The comparison is made theoretically to evaluate their differences in terms of hydrodynamic performance, and experimentally to know their efficiency against the reduction of hexavalent chromium. For the comparison, the reactors were operated at the same stirring speed and Reynolds number. The results of the hydrodynamic analysis show that the arrangement of static electro-baffles together with the pair of impellers improves the mixing time by 36%, increasing the hydraulic efficiency by 85% when the reactor is operated at the same Reynolds number. It is evident that the circulation capacity of the reactor directly affects the reduction rate of hexavalent chromium, since the treatment times have a similar trend to the axial circulation times. It is also shown that there is a reduction in energy consumption of at least 21% when the reactor is equipped with the electro-baffles and the two-impeller agitation system. In chapter four, the operating conditions of the electrochemical reactor are evaluated, such as: geometric configuration of the electrode, stirring speed and current intensity. To evaluate the change in the electrode configuration, the static ring electrode and electro-baffles are used. When operating the electrode with static rings, the need to incorporate conventional baffles is also evaluated. The reactor agitation systems are composed of two PBT impellers, of which the separation between them is also evaluated. In performing the simulations, the interaction of the liquid-gas interface was considered. The results reveal that due to the position of the impellers it is necessary to take into account the liquid-air interaction in the model to obtain a more realistic prediction of the flow pattern in the electro-baffles configuration. As a result of the studies, it was found that the configuration with the lowest energy consumption was the electro-baffles with a separation between impellers equal to their diameter, since its geometrical and hydrodynamic characteristics allow it to be more efficient. The effect of agitation speed and current intensity was explored in this system. The agitation speed increases the reduction rate of hexavalent chromium, finding its limit at 300 rpm. At this agitation speed, the effect of the current intensity was explored, from which a linear dependence of the reactor energy consumption on this variable was found in the range evaluated. In chapter five, the precipitation stage is studied. The studies are carried out in an agitated jar system with two types of impellers, one radial and the other axial. The evaluation of the effect of the pH at which the effluent is adjusted to perform precipitation at values of 4, 6, 7 and 9 is carried out. The results show that after precipitating the treated water at pH = 9.0, a clarified product with neutral pH is obtained and all species are precipitated. The hydrodynamic environment of the jars is also evaluated experimentally and numerically, determining that the radial impeller dissipates more turbulent energy than the axial impeller. Therefore, the axial impeller provides a favorable hydrodynamic environment for the development of flocs, which results in higher sedimentation velocities than those achieved when the jar is operated with the radial impeller. In addition, the axial impeller consumes only 50% of the energy consumed by the radial impeller.Investigación realizada con el apoyo del Programa Nacional de Posgrados de Calidad del Consejo Nacional de Ciencia y Tecnología (CONACYT)

Diseño del electrodo de un reactor electroquímico mediante modelamiento y simulación hidrodinámica

88 páginas. Maestría en Ingeniería de Procesos.El proceso electroquímico se ha colocado como una alternativa importante para el tratamiento de aguas residuales con concentraciones de Cr (VI) superiores a las permitidas por la legislación en materia ambiental. A diferencia de los electrodos rotatorios reportados en otros trabajos, aquí se proponen dos tipos de electrodos estáticos de un reactor electroquímico para la remoción de este metal pesado, en el cual se mantiene la mezcla completa mediante impulsores tipo pitched blade turbine (PBT). En una de las configuraciones evaluadas se utiliza un electrodo estático con anillos intercalados, que tienen la función de cátodos y ánodos, y que se distribuyen a lo largo de la altura del reactor (Caso 1). La segunda configuración, utiliza dos tubos de acero inoxidable en forma de deflector (Caso 2). El objetivo de emplear electrodos estáticos es evitar el movimiento de los electrodos y hacer un uso más eficiente de la energía aplicada en la agitación. Los sistemas fueron analizados utilizando mediciones experimentales, así como dinámica computacional de fluidos (CFD, por sus siglas en ingles), herramienta moderna que se emplea en el diseño, evaluación y optimización de tecnologías en las diversas ramas de la ingeniería. El análisis se llevó a cabo con el software ANSYS Fluent®, el cual se ha aplicado con éxito en el estudio de tanques agitados, este análisis cumple con el objetivo de identificar cuál arreglo tiene un mejor desempeño hidrodinámico, cuantificando la energía utilizada para la agitación del fluido y los tiempos requeridos para alcanzar un cierto grado de homogeneidad en la concentración dentro del reactor. La validación de los resultados obtenidos con la simulación se realizó con la medición experimental del torque y de los tiempos de mezclado con la técnica de medición de conductividad eléctrica. El análisis CFD permitió identificar que el Caso 2 promueve una mejor circulación en todo el volumen del tanque reduciendo en un 70% el tiempo de mezclado, en comparación con los electrodos rotatorios. Para las pruebas experimentales, se utilizó un reactor electroquímico con una capacidad de 19 L, se construyeron los electrodos de acero al carbón y se realizaron pruebas de remoción de Cr (VI) a una concentración inicial de 130 mg/L. La remoción del Cr(VI) siguió una cinética de orden variable. Los resultados obtenidos muestran que el tiempo de tratamiento obtenido con los arreglos propuestos se reduce en al menos 50%, con respecto a los encontrados con electrodos rotatorios. Con toda la información generada en este trabajo fue posible calcular la energía total que se requiere en cada uno de los sistemas para remover 1 g de Cr (VI), los resultados muestran que los diseños propuestos reducen en 70% el consumo energético total para el proceso electroquímico, en comparación con los electrodos rotatorios, lo que demuestra que la mejora en la eficiencia hidrodinámica dentro del reactor, impacta directamente en los costos del proceso, haciéndolo más factible para la aplicación del tratamiento electroquímico a este tipo de efluentes a nivel industrial.Consejo Nacional de Ciencia y Tecnología (México)

Impact of sulphur contamination on the performance of mixed ionic-electronic conducting membranes for oxygen separation and hydrogen production

PhD ThesisMixed ionic-electronic conducting (MIEC) membranes are a promising technology for oxygen separation but they are not commercialised yet due to sealing issue and sensitivity to impurities in feedstock. In this study, La0.6Sr0.4Co0.2Fe0.8O3- (LSCF6428) was successfully sealed for long-term operation of 963 h using a gold-glass-ceramic sealant. The membrane was then tested for air separation in presence of hydrogen sulphide for 100 h and results showed that the impurity caused a drop in oxygen flux to zero within few hours. The flux could not be fully restored after hydrogen sulphide removal and only 6 to 35% was recovered. It was proposed that hydrogen sulphide was adsorbed on the membrane in the form of sulphur and it occupied oxygen vacancies. With time, strontium segregates toward sulphur to form irreversible layer of strontium sulphate. To restore the damaged surface, the membrane was treated by 1% (mol) of hydrogen for 20 h and the recovery improved from 6 to 12%. It was discovered that the poisoning mechanism is a function of oxygen partial pressure and change of partial pressure from 0.21 to 0.01 bar resulted in 90% recovery and this can be used as a strategy to reduce the damage. The next step was to test the membrane for hydrogen production using 1% (mol) of methane and results showed that methane conversion was steady at 33% for 350 h. Methane oxidation was also carried in presence of hydrogen sulphide but it resulted in drop of conversion to 8%. However, the conversion was slowly regenerating with time and it reached a constant value of 15%. This recovery was interpreted by the reaction of methane with hydrogen sulphide or methane decomposition and the membrane acted as a catalyst for these reactions. After hydrogen sulphide removal from the feed, the conversion kept on decreasing and this was linked to the change of membrane properties and therefore the membrane could not provide the sites for methane-oxygen reaction. For better stability under hydrogen sulphide, the membrane was modified by adding a powder of LSCF6428 material over the dense membrane. This dual layer membrane was stable for air separation under hydrogen for 33 h and the flux was only reduced by 5%