Dissertations / Theses on the topic 'Purification of contaminated water'

[Truncated abstract] An ethanol delivery system, consisting of silicone (poly(dimethylsiloxane)) tubing coiled and shaped as mats, was characterised and evaluated for its potential to act as a permeable reactive barrier (PRB), to promote reducing conditions and enable the enhanced bioremediation of a variety of groundwater contaminants in situ. Aqueous ethanol solutions were recirculated through the inner volume of the silicone polymer tubing in the mat, to allow permeation and delivery of ethanol by diffusion through the tubing walls to a target contamination zone. The aim of the system was to provide control over subsurface geochemistry by overcoming carbon source limitations, and as a result stimulate indigenous bacteria to remove contaminants. The physical properties of the silicone tubing were initially characterised, which included the determination of the ethanol sorption and diffusion properties of the tubing. A model for the mass of ethanol transferred via diffusion from an aqueous solution on the inner volume of a length of polymer tubing was developed to enable prediction of the ethanol delivery capacity of the silicone polymer mats. A number of large-scale laboratory column studies were then conducted to validate this ethanol mass delivery model, and to evaluate the use of silicone polymer mats to deliver ethanol and promote the biodegradation of a range of different contaminated groundwaters. The laboratory column experiments were observed to produce ethanol mass flux delivery statistically similar to that predicted by the model; however this was only with the application of an effective diffusion coefficient within the model, which was determined from the model under subsurface-simulated conditions. Ethanol delivery using the silicone tubing polymer mat system was also quantified in a pilot field-scale demonstration. The mass of ethanol delivery in the field was shown to be within the range of model-predicted ethanol delivery; however delivery was not as consistent and predictable as that observed in the column studies. Successful ethanol enhanced nitrate contamination removal (via denitrification) was observed at a field scale. For field applications, this innovative polymer mat amendment delivery system may provide targeted, predictable and cost-effective amendment delivery compared to aqueous injection methods for groundwater bioremediation, however, knowledge and quantification of the hydrogeology of the particular field site is required. Two other ethanol-driven biologically-mediated contaminant removal processes were also investigated in the laboratory-scale soil column studies, and included the assessment of the removal of dissolved metals/sulfate via sulfate reduction and metalsulfide precipitation, and the removal of trichloroethene via reductive dechlorination.

Water has always been an important and life-sustaining drink to humans and is essential for the survival of all known organisms. Though water is available in plenty, in the present day scenario availability of pure drinking water has become a rare commodity that is attributed to a number of known reasons.

Ferrihydrite in a suspension has been studied as a solution for purification of arsenic contaminated water. Many development countries, amongst them Burkina Faso, have arsenic in their groundwater and the current methods for purification are too expensive. Measurements have shown extremely high levels of arsenic in the groundwater in several places in Burkina Faso. Since the availability of surface water is limited, the groundwater is still used as drinking water.   A suspension of ferrihydrite has capacity to adsorb arsenic in water due to its chemical characteristics. Small-scale laboratory work with ferrihydrite suspensions has been performed in parallel in Uppsala, Sweden, and Ouagadougou, Burkina Faso. To purify the water with regard to the economical and practical circumstances in Burkina Faso, a column with safety filter was made out of simple materials such as plastic bottles, plastic tubes and glass wool. The contaminated water was flowing upwards through the column to prevent the filter from clogging.   In Uppsala it was discovered that a 1 L ferrihydrite suspension containing 10 g ferrihydrite can adsorb 0.7 g arsenic while it was shaken and centrifuged well. In Ouagadougou it was possible, in the setup, to clean 2 L arsenic contaminated water with the concentration of 100 µg/L. The conclusions from the experiments in this project are that ferrihydrite can adsorb arsenic in contaminated water but that the setup used needs to be further evaluated and developed

Thesis (MTech (Chemistry))--Cape Peninsula University of Technology, 2012.
Polychlorinated biphenyls (PCBs) are known harmful chemicals which require urgent remediation, monitoring and assessment in the environment. The predominant current methods used to analyze PCBs involve expertise and are cost intensive. Most of these methods are chromatographic based techniques which are difficult to sustain in Africa due to the expensive nature of the instrument, costly running expenses and skilled labour required. These limitations face Africans, who are the most affected by the presence of PCBs in their environment as a result of improper disposal and usage of these compounds.

Chromium is a common groundwater pollutant originating from industrial processes such as metal plating, leather tanning and pigment manufacturing. Permeable reactive barriers (PRBs) have proven to be viable and cost-effective systems for remediation of chromium contaminated groundwater at many sites. The purpose of this research presented in this thesis is to focus on two parameters that affect the performance of PRB on chromium removal, namely the concentration of reactive media and groundwater flux by analyzing the data obtained from laboratory column studies. Laboratory scale columns packed with different amounts of iron powder and quartz sand mixtures were fed with 20 mg/l chromium influent solution under different fluxes. When chromium treatment efficiencies of the columns were compared with respect to iron powder/quartz sand ratio, the amount of iron powder was found to be an important parameter for treatment efficiency of PRBs. The formation of H2 gas and the reddish-brown precipitates throughout the column matrix were observed, suggesting the reductive precipitation reactions. SEM-EDX analysis of the iron surface after the breakthrough illustrated chromium precipitation. In addition to chromium
calcium and significant amount of iron-oxides or -hydroxides was also detected on the iron surfaces. When the same experiments were conducted at higher fluxes, an increase was observed in the treatment efficiency in the column containing 50% iron. This suggested that the precipitates may not be accumulating at higher fluxes which, in turn, create available surface area for reduction. Extraction experiments were also performed to determine the fraction of chromium that adsorbed to ironhydroxides. The analysis showed that chromium was not removed by adsorption to oxyhydroxides and that reduction is the only removal mechanism in the laboratory experiments. The observed rate of Cr(VI) removal was calculated for each reactive mixture which ranged from 48.86 hour-1 to 3804.13 hour-1. These rate constants and complete removal efficiency values were thought to be important design parameters in the field scale permeable reactive barrier applications.

Les activités industrielles (et plus particulièrement d’exploitation minière et métallurgique) menées depuis plus d’un siècle dans les départements du Nord et du Pas-de-Calais ont laissé comme héritage une contamination des sols, des eaux et de la flore avérée en métaux lourds. Cette pollution métallique est source, à ce jour, des conséquences environnementales et sanitaires. Le présent travail ne traitera que de certains aspects environnementaux. Ainsi, dans l’objectif de remédier ces sols dégradés tout en souhaitant les valoriser au travers de l’utilisation des polluants métalliques, une approche de phytomanagement de ces sols a été mise en place. Ainsi, ont été produits sur ces derniers trois espèces végétales (Lolium perenne L, Miscanthus x giganteus et Cichorium intybus L.) dont les comportements vis à vis des éléments métalliques présents dans les sols ont été étudiés. Enrichies en éléments métalliques d’intérêt pour la synthèse organique, les biomasses issues de Lolium perenne L. et de Miscanthus x giganteus ont été utilisées pour concevoir différents catalyseurs biosourcés. Leur application en chimie organique verte pour la synthèse de molécules à haute valeur ajoutée a ensuite été évaluée. Les catalyseurs biosourcés se sont révélés particulièrement efficaces dans diverses transformations chimiques telles que l’amidification d’esters non activés ou encore la réaction de Hurtley. Ont également été valorisés les déchets de biomasses issus de la production des catalyseurs biosourcés. En effet, ces derniers ont été utilisés en tant que filtres permettant de purifier des eaux artificiellement contaminées par des polluants métalliques ou organiques. La technologie a alors été largement étendue à d’autres matériaux également considérés comme des sous-produits issus de divers processus industriels
The industrial activities (in particular mining and metallurgy) carried out for over a century in the departments of Nord and Pas-de-Calais have left behind areas considerably contaminated with heavy metals. Currently, this metallic pollution is seriously problematic regarding health and environmental aspects. It is these environments, and more particularly, these contaminated agricultural soil surfaces that constitute the starting point of this research work. With the aim of remedying these contaminated surfaces while enhancing this metallic pollution, a phytomanagement approach for these soils has been implemented. Thus, three plant species were produced on these last (Lolium perenne L., Miscanthus x giganteus and Cichorium intybus L.) and their behavior with respect to the metallic elements present in these soils was studied. So sufficiently rich in metals of interest for organic synthesis, the biomasses obtained from Lolium perenne L. and Miscanthus x giganteus were used to design various biosourced catalysts. Their application in green organic chemistry for the synthesis of molecules with high-added value was then evaluated and proved to be particularly effective in various chemical transformations such as amidification of non-activated esters or the Hurtley reaction. Finally, biomass wastes from the production of the biosourced catalysts have also been studied for potential use in a different application. Indeed, these latter have been used as a filter for purifying aqueous media contaminated with metallic or organic pollutants. The technology developed during this research thesis was then widely extended to other materials which are also considered as waste in various industrial processes

Submitted by Marcio Emanuel Paixão Santos (marcio.santos@ucsal.br) on 2018-06-21T17:02:54Z No. of bitstreams: 1 DISSERTACAOVICTORMAGALHAESDUARTE.pdf: 5911465 bytes, checksum: 6117af0ebbe7176d6a0b430080b16c8e (MD5)
Approved for entry into archive by Linda Bulhosa (linda.gomes@ucsal.br) on 2018-06-21T19:19:19Z (GMT) No. of bitstreams: 1 DISSERTACAOVICTORMAGALHAESDUARTE.pdf: 5911465 bytes, checksum: 6117af0ebbe7176d6a0b430080b16c8e (MD5)
Made available in DSpace on 2018-06-21T19:19:19Z (GMT). No. of bitstreams: 1 DISSERTACAOVICTORMAGALHAESDUARTE.pdf: 5911465 bytes, checksum: 6117af0ebbe7176d6a0b430080b16c8e (MD5) Previous issue date: 2010-03-31
A pesquisa trata da qualidade da água potável consumida na cidade do Salvador, bem como apresenta as principais conseqüências para a saúde pela ingestão dos contaminantes que possam estar presentes na água potável e as medidas preventivas mais adequadas para removê-las. As contaminações que ocorrem nas fontes advêm do aumento da atividade industrial, do desenvolvimento de compostos agrícolas sintéticos, do despejo dos esgotos doméstico e industrial no meio ambiente sem o devido tratamento. A metodologia adotada incluiu análises da água potável consumida em Salvador, avaliação da legislação brasileira, sendo demonstrado que, mesmo quando são atendidos os parâmetros contidos na mesma, não pode ser garantida que a água potável não vá trazer sérios problemas para a saúde das pessoas a curto, médio e longo prazo. Os resultados demonstram que as pessoas avaliadas não possuem conhecimentos básicos necessários sobre os riscos dos contaminantes da água e o que fazer para minimizar as suas conseqüências. Mesmo sabendo que as concentrações dos contaminantes na água mudam muito de um dia para o outro, adotamos critérios científicos modernos ao serem avaliadas as análises de água fornecida pela empresa de saneamento da cidade, dos poços de água de uma empresa do Pólo Petroquímico de Camaçari e de amostras de água mineral encaminhadas a laboratórios especializados. Varias contaminantes da água foram mencionados e avaliados segundo critérios toxicológicos usando-se valores máximos fixados nas legislações do Brasil, Estados Unidos e Comunidade Européia (Organização Mundial de Saúde). Efeitos aditivos e sinergéticos dos contaminantes da água alem do fator denominado susceptibilidade individual foram citados como condições essenciais nas avaliações dos riscos reais das concentrações e das misturas dos contaminantes presentes na água potável consumida. Foram apresentadas técnicas de tratamento que possibilitam remover as impurezas orgânicas, inorgânicas, biológicas e radioativas da água potável, permitindo que as pessoas possam minimizar ao máximo os riscos de contaminação por via hídrica, conservando a saúde em elevados níveis. Foram ainda feitas sugestões que objetivam reduzir/eliminar as contaminações dos nossos mananciais de água potável, quer seja por ações federais, estaduais e municipais e da colaboração direta dos próprios cidadãos. Diante dos aspectos científicos abordados aqui, concluímos que tanto a água mineral quanto a água da rede de distribuída municipal não são isentas de riscos para consumo humano.
The research talks about the drinking water which is consumed in Salvador city and presents the main health consequences of the contaminants that can be found in the water and the prevention measurements more suitable to remove them. Contaminations which can be found in the water sources come from the growth industrial activities, synthetic agriculture compounds, domestic sewage and waste water that run-off without a proper treatment. The methodology used included drinking water analyzes consumed in Salvador city, an evaluation of Brazilian legislation, being demonstrated that, even when the legal parameters in the laws are fulfilled, it can not warranty that drinking this water will not produce serious health problems in the people in a short, medium and long period of time. The results show that people who were evaluated do not have enough basic knowledge about the risks of water contaminants and they do not know what to do to minimize their consequences. Even knowing that the concentration of the drinking water contaminants change a lot from one day to another, it was adopted modern scientific methodology when the water analyzes from the municipal water supply company were evaluated. The same methodology was adopted in the well water samples from a company in the Petrochemical Complex in Camaçari area and from mineral water samples which were sent to specialized laboratories. Many contaminants in the water were mentioned and evaluated under toxicological standards using maximum values established in the Brazilian, United States and European legislation (World Health Organization). Additive and synergetic effects of the drinking water contaminants besides the factor named individual susceptibility were cited as essential conditions in the real risk assessment of the contaminants concentration and mixtures of them present in the drinking water in study. It was presented point of use treatment techniques that make possible to remove organic, inorganic, biological and radioactive contaminants from drinking water. Doing that, people can minimize as much as possible the contamination risks from water sources, keeping the health in high levels. Yet it was done suggestions that aim to reduce or eliminate the contaminants of our drinking water sources, by federal, state and municipal actions and direct collaboration of the citizens themselves. In front of the scientific aspects mentioned here, we concluded that as much the mineral water as the municipal water from the distribution network are not free of risks to the human consumption.

In the last decades, the scientific community has been involved in the research of new kinds of contaminants generally known as of “emerging concern” (CECs). The harmfulness of CECs, even at small concentrations as well as, property of bioaccumulation and persistence, makes them extremely dangerous for the human health. The scientific community is constantly researching about novel treatments able to achieve the removal of these contaminants. Advanced Oxidation Processes (AOPs) are considered one of the most useful treatments to achieve CECs degradation. Among the AOPs, Fenton and photo‐Fenton processes are particularly powerful, cheap and easily managed. Nevertheless, some setting requirements of Fenton processes have limited their application at industrial scale. One of the most important limits is the necessity to operate a tight control of the pH in order to avoid iron precipitation (optimum pH~2.8). Unfortunately, the optimum pH for Fenton reaction is essentially far from the normal values of the wastewater treatment plant (WWTP) effluents. Scientific community is then working on the improvement of the operating conditions of Fenton processes in order to improve the applicability in wastewater treatment. These modifications are essentially focused on the possibility to perform the treatment at circumneutral pH (Fenton and photo‐ Fenton like processes). Fenton like processes can be carried out in heterogeneous or homogeneous way according to the phase of the catalyst into the solution. In this study was firstly confirmed the suitability of Fenton based processes in recalcitrant compounds removal. Fenton, UV‐A photo‐Fenton and UV‐C photo‐Fenton were, in fact, applied for atrazine removal from secondary effluent (SE) of municipal wastewater treatment plant (MWWTP). UV‐A and UV‐C photo‐Fenton allowed remove 50% and 100% of the initial atrazine content respectively. The main objective of this thesis was then the assessment of photo‐Fenton’s suitability for recalcitrant contaminant at circumneutral pH. Thus, homogeneous photo‐Fenton like at neutral pH was applied for sulfamethoxazole (SMX) removal. In order to avoid iron precipitation, chelating agents were used to keep soluble the iron at circumneutral pH. The chelating ability of four chelating agents (ethylenediaminetetraacetic acid‐EDTA, nitrilotriacetic acid‐NTA, oxalic acid and tartaric acid) was tested. Then, once determined the optimum molar ratio L:Fe for iron chelation (1.5:1 for EDTA and NTA, 10:1 for tartaric acid and 20:1 for oxalic acid), their catalytic activity was evaluated when employed in photo‐Fenton like for SMX removal. The highest SMX percentage removal, together with the minimum chelating agents required and the better property of biodegradability and low toxicity, demonstrated the suitability of NTA for the purpose. A further study on the stability of the chelates under reaction was carried out. The operating conditions adopted for the treatment significantly influence the stability of the chelate solution. Thus, in order to proper control the parameter set up the behavior of chelates has been study under thermal, oxidative and photochemical stress. It was demonstrated as the temperature control can represent an interesting tool to extend the chelates lifetime under oxidative and photochemical stress. By adopting different H2O2 doses, a linear correlation between doses and chelate decomposition could be identified. The better suitability of UV‐A irradiation, against UV‐C and Xe lamp, to preserve the iron chelate solution was demonstrated. Moreover, the influence of the influent characteristics on the process efficiency needed to be also considered. Thus, different water matrices were used for the experiments. The efficiency of photo‐Fenton like catalyzed by Fe(III)‐NTA has been compared when applied to different aqueous matrixes (Milli‐Q water, tap water, secondary effluent wastewater and well water). It was demonstrated as the ions content, especially Ca2+ and Mg2+, significantly compromise the process of chelation. High alkalinities and organic matter, instead, mainly influenced the phase of process, when acting as radicals scavengers, reduced the amount available for SMX oxidation. Some strategies were then adopted to promote SMX removal. Between them, Mn2+ mediated photo‐Fenton like showed somehow possibility for improvement. Highest removal rate was in fact exhibited in the first minutes of reaction when adding Mn2+ to the solution in ratio molar Mn:Fe 0.5:1. The conclusive study of the thesis regarded the assessment of the Br‐ presence on the efficiency achievable in recalcitrant compounds removal when applying UV/PS/Fe2+ for removal of benzophenone‐4 (BZ4), nitrobenzene (NB), nitrobenzoic acid (NBA), atrazine (ATZ) and ampicilline (AMP). Br‐ demostrated to be a strong inhibitor in the removal of all the considered contaminants except for NB when, the removal was instead enhanced in bromide containing water.

Ozonation is nowadays a competent technology for micropollutant oxidation in wastewater effluents. The combination of ozone with hydroxyl radical formed through ozone decomposition is effective in the abatement of a number of organic compounds. However, there are still some points to be addressed for a more efficient application of ozone-based processes to wastewater treatment and reclamation. There are, for instance, several organic compounds that react very slowly with ozone. They are known as ozone-resistant micropollutants. If a high quality water is wanted to be obtained, these substances should be also removed from the effluent. In addition, modelling the abatement of micropollutants during wastewater ozonation is essential for process simulation, optimization and real-time control. To make this possible, performance characterization in terms of oxidation efficiency is required, as well as some kinetic information regarding the abatement of micropollutants. The first can be addressed by using normalizing parameters allowing the estimation, for instance, of hydroxyl radical availability as a function of the consumed ozone, or any other parameter whose measurement during the process is simple. The most accurate way of obtaining kinetic data of micropollutants oxidation is conducting individual studies on this chemicals degradation by ozone and hydroxyl radicals. Some complementary tests, in addition, may be useful to obtain valuable data regarding the mechanisms of degradation and the potential ecotoxicological effects of formed transformation products. This thesis was divided in two parts: first, individual batch ozonation studies of selected concerning micropollutants were conducted. Particularly, the pesticides methiocarb, acetamiprid and dichlorvos were selected for that work. The second part consisted of the application of single ozonation and the combination O3/H2O2 was tested in the removal of ozone-refractory micropollutants from actual wastewater effluents. The latter was done through semi-batch ozonation experiments. The objectives were, on one hand, obtaining kinetic, mechanistic and toxicological data of some priority/emerging concern chemicals. On the other, ozonation studies with real effluent samples were performed with the aim of exploring the removal of ozone-recalcitrant chemicals and potential strategies for the modelling and real-time control of this process. In addition, improvement strategies for O3/H2O2 process application were investigated. Different kinetics were observed for pesticides reaction with ozone, being acetamiprid the most recalcitrant compound. In addition, toxicity of some of the pesticides transformation products was revealed, especially in the case of methiocarb degradation. Regarding ozone-based processes application to actual wastewater effluents, the removal of model ozone-recalcitrant compounds was found difficult, concluding that ozone doses higher than the immediate ozone demand (IOD) value are required for a more effective abatement of these substances regardless of the process employed. In the case of the O3/H2O2 process application, dosing hydrogen peroxide simultaneously to ozone bubbling was found to potentially entail important energy savings related to oxidants use. The oxidation performance of ozone-based processes and thus the abatement of ozone-refractory compounds could be effectively modelled using kinetic parameters, the monitoring of water quality parameters and empirical relationships obtained for each effluent. Furthermore, side reactions of involved oxidants with effluent organic compounds was found to increase the content in small and oxidized organic compounds in all cases. In the case of effluents containing suspended solids, ozone application also caused a net increase in the dissolved organic load.
El proceso de ozonización constituye una de las tecnologías de tratamiento de aguas con mayor potencial para la eliminación de microcontaminantes de los efluentes de depuradoras municipales. Pese a ello, algunos aspectos como la eliminación de aquellos contaminantes resistentes al ataque del ozono y la modelización cinética de este proceso ofrecen aún amplias posibilidades de mejora. La formación de productos de transformación a partir de reacciones del ozono y el radical hidroxilo con la materia orgánica del efluente es otro aspecto escasamente considerado. Dados los problemas técnicos y ambientales que dichos subproductos pueden ocasionar, la investigación de este fenómeno es también de gran interés. En esta tesis se estudiaron en primer lugar los fundamentos (cinética, mecanismos de reacción y efectos toxicológicos de los productos de transformación) del proceso de degradación de tres microcontaminantes orgánicos de preocupación emergente mediante el proceso de ozonización. A continuación, éstos y otros compuestos típicamente detectados en aguas residuales urbanas se emplearon como sustancias modelo en el estudio de la aplicación del ozono en efluentes reales de depuradora de calidad variada, con el fin de evaluar la eficiencia del proceso y proponer estrategias para la modelización del mismo. En este sentido, se propuso la combinación de parámetros cinéticos y la monitorización de parámetros de calidad del agua para el control a tiempo real del proceso. Las predicciones de eliminación de contaminantes llevadas a cabo mediante esta metodología mostraron una gran concordancia con los datos experimentales, tanto para el proceso de ozonización simple como para la combinación ozono-peróxido de hidrógeno, que por otro lado exhibió una gran eficiencia en la eliminación de contaminantes resistentes al ozono cuando se aplicó con dosificación simultánea de ambos oxidantes. Finalmente, la evaluación de los cambios experimentados por la materia orgánica del efluente durante la aplicación del ozono reveló una acumulación de compuestos de bajo peso molecular en todas las aguas ensayadas, además de la solubilización de materia orgánica en suspensión en efluentes con mayor carga orgánica.

[ES] La presente Tesis Doctoral se centra en el estudio del comportamiento electroquímico de nuevos electrodos cerámicos basados en SnO2 dopado con Sb2O3. El estudio está orientado a la posterior aplicación de estos electrodos en procesos electroquímicos de oxidación avanzada. Inicialmente, se consideraron diferentes temperaturas de sinterización (entre 1050°C y 1250°C) y se observó que un aumento en la temperatura de sinterización favorecía la deposición del Sb2O3 en la superficie anódica, disminuyendo así la resistividad del electrodo. Posteriormente, se estudió el comportamiento electroquímico de estos nuevos electrodos obteniendo el potencial de descarga del oxígeno mediante la técnica de voltametría de barrido lineal. Los resultados obtenidos revelaron que el valor del potencial de descarga del oxígeno disminuye con el aumento de la temperatura de sinterización. Además, estos electrodos presentaron un comportamiento intermedio entre el ánodo de Pt y el ánodo de BDD. Este último electrodo se emplea habitualmente en los procesos electroquímicos de oxidación avanzada debido a su elevada capacidad para generar radicales hidroxilo, los cuales son capaces de oxidar los compuestos orgánicos a dióxido de carbono y agua. A continuación, se llevaron a cabo ensayos de oxidación electroquímica con estos electrodos cerámicos para seleccionar la temperatura de sinterización. Los resultados mostraron que con el electrodo cerámico sinterizado a 1250°C se alcanza una menor degradación del compuesto orgánico, mientras que los electrodos sinterizados a menores temperaturas presentan un comportamiento similar entre ellos. Por tanto, se seleccionó el electrodo cerámico sinterizado a 1200°C ya que presenta una baja resistividad y un buen comportamiento electroquímico para ser utilizado como ánodo en los procesos electroquímicos de oxidación avanzada. Seguidamente se analizó la vida útil de estos electrodos cerámicos, y se comprobó que la matriz cerámica incrementa en gran medida la estabilidad a la polarización anódica de los electrodos basados en SnO2. Posteriormente, se llevaron a cabo procesos de electro-oxidación en modo galvanostático de distintos contaminantes difíciles de eliminar por las técnicas convencionales utilizando como ánodo los nuevos electrodos cerámicos y el electrodo de BDD, para así poder comparar los resultados obtenidos. Se observó que, aunque con los electrodos cerámicos se consigue degradar el 100% de los distintos contaminantes, el electrodo de BDD es el más eficiente ya que genera mayor cantidad de especies oxidantes activas en su superficie. Para un mismo electrodo, se observó que un aumento en la densidad de corriente aplicada mejora la velocidad de degradación y mineralización de cada contaminante, mientras que la eficiencia eléctrica disminuye. Por otro lado, se estudió el efecto de la presencia de una membrana de intercambio catiónico entre ánodo y cátodo. Los resultados mostraron que el uso de la membrana beneficia la degradación y la mineralización del contaminante, ya que mejora la cinética de reacción anódica y evita la reducción de las especies oxidantes electrogeneradas. A continuación, se analizó la influencia de la concentración del Na2SO4 como electrolito soporte. En este estudio se observó que un aumento en la concentración del Na2SO4 mejora la mineralización del contaminante para el electrodo de BDD y, por el contrario, empeora para el electrodo cerámico. Esto se debe a la capacidad de cada electrodo para oxidar los sulfatos a persulfatos. Por último, se llevaron a cabo ensayos de ecotoxicidad de las muestras tratadas, y se demostró que, en presencia de membrana, a mayor densidad de corriente y con el electrodo de BDD la toxicidad de la muestra es mayor debido a la mayor presencia en disolución de iones persulfato. Por tanto, con el electrodo cerámico, además de alcanzar un elevado grado de degradación del contamina
[CAT] La present Tesi Doctoral es centra en l'estudi del comportament electroquímic de nous elèctrodes ceràmics basats en SnO2 dopat amb Sb2O3. L'estudi està orientat a la posterior aplicació d'aquests elèctrodes en processos electroquímics d'oxidació avançada. Inicialment, es van considerar diferents temperatures de sinterització (entre 1050°C i 1250°C) i es va observar que un augment en la temperatura de sinterització afavoria la deposició de Sb2O3 en la superfície anòdica, disminuint així la resistivitat de l'elèctrode. Posteriorment, es va estudiar el comportament electroquímic d'aquests nous elèctrodes obtenint el potencial de descàrrega de l'oxigen mitjançant la tècnica de voltametria de passada lineal. Els resultats obtinguts van revelar que el valor del potencial de descàrrega de l'oxigen disminueix amb l'augment de la temperatura de sinterització. A més, aquests elèctrodes ceràmics van presentar un comportament intermedi entre l'ànode de Pt y l'ànode de BDD. Aquest últim elèctrode s'utilitza habitualment en els processos electroquímics d'oxidació avançada a causa de la seua elevada capacitat per a generar radicals hidroxil, els quals són capaços d'oxidar els compostos orgànics a diòxid de carboni i aigua. A continuació, es van dur a terme assajos d'oxidació electroquímica amb aquests elèctrodes ceràmics per a seleccionar la temperatura de sinterització. Els resultats van mostrar que amb l'elèctrode ceràmic sinteritzat a 1250°C s'aconsegueix una menor degradació del compost orgànic, mentre que els elèctrodes sinteritzats a menors temperatures presenten un comportament similar entre ells. Per tant, es va seleccionar l'elèctrode ceràmic sinteritzat a 1200 °C ja que presenta una baixa resistivitat i un bon comportament electroquímic per a ser utilitzat com a ànode en els processos electroquímics d'oxidació avançada. Seguidament, es va analitzar la vida útil d'aquests elèctrodes ceràmics, i es va comprovar que la matriu ceràmica incrementa en gran mesura l'estabilitat a la polarització anòdica dels elèctrodes basats en SnO2. Posteriorment es van dur a terme processos d'electro-oxidació en mode galvanostàtic de diferents contaminants difícils d'eliminar per les tècniques convencionals utilitzant com a ànode els nous elèctrodes ceràmics i l'elèctrode de BDD, per a així poder comparar els resultats obtinguts. Es va observar que, encara que amb els elèctrodes ceràmics s'aconsegueix degradar el 100% dels diferents contaminants, l'elèctrode de BDD és el més eficient ja que genera una major quantitat d'espècies oxidants actives en la seua superfície. Per a un mateix elèctrode, es va observar que un augment en la densitat de corrent aplicada millora la velocitat de degradació i mineralització de cada contaminant, mentre que l'eficiència elèctrica disminueix. D'altra banda, es va estudiar l'efecte de la presència d'una membrana d'intercanvi catiònic entre ànode i càtode. Els resultats van mostrar que l'ús de la membrana beneficia la degradació i la mineralització del contaminant, ja que millora la cinètica de reacció anòdica i evita la reducció de les espècies oxidants electrogenerades. A continuació, es va analitzar la influència de la concentració del Na2SO4 com a electròlit suport. En aquest estudi es va observar que un augment en la concentració del Na2SO4 millora la mineralització del contaminant per a l'elèctrode de BDD i, per contra, empitjora per a l'elèctrode ceràmic. Això es deu a la capacitat de cada elèctrode per a oxidar els sulfats a persulfats. Finalment, es van dur a terme assajos d'ecotoxicitat de les mostres tractades, i es va demostrar que, en presència de membrana, a major densitat de corrent i amb l'elèctrode de BDD la toxicitat de la mostra és major a causa de la major presència en dissolució d'ions persulfat. Per tant, amb l'elèctrode ceràmic, a més d'aconseguir un elevat grau de degradació del con
[EN] The present Doctoral Thesis focuses on the study of the electrochemical behaviour of new ceramic electrodes based on SnO2 doped with Sb2O3. The study is oriented at the subsequent application of these electrodes in electrochemical advanced oxidation processes. Initially, different sintering temperatures were considered (between 1050°C and 1250°C) and it was observed that an increase in the sintering temperature favoured the deposition of Sb2O3 on the anodic surface, thus decreasing the resistivity of the electrode. Later, the electrochemical behaviour of these new electrodes was studied by means of the oxygen discharge potential using the linear sweep voltammetry technique. The results obtained revealed that the value of the oxygen discharge potential decreases with increasing the sintering temperature. Furthermore, these electrodes showed an intermediate behaviour between the Pt anode and the BDD one. This last electrode is commonly used in advanced electrochemical oxidation processes due to its high capacity to generate hydroxyl radicals, which are capable of oxidizing the organic compounds to carbon dioxide and water. Then, electrochemical oxidation tests were carried out with these ceramic electrodes to select the sintering temperature. The results showed that with the ceramic electrode sintered at 1250°C, a lower degradation and mineralization of the organic compound is achieved, while the electrodes sintered at lower temperatures showed a similar behaviour. Therefore, the ceramic electrode sintered at 1200°C was selected as it presents low resistivity good electrochemical behaviour to be used as anode in electrochemical advanced oxidation processes. Next, the service life of these ceramic electrodes was analyzed, and it was found that the ceramic matrix greatly increases the anodic polarization stability of the electrodes based on SnO2. Subsequently, electro-oxidation processes were carried out in galvanostatic mode for different contaminants that are difficult to remove by conventional techniques, using the new ceramic electrodes and the BDD electrode as anodes, in order to compare the results obtained. It was observed that ceramic electrodes can be used as anodes for electrochemical oxidation, since for high current densities it is possible to degrade a 100% of the different contaminants. However, the BDD electrode is the most efficient one since it generates more active oxidant species on its surface. For a given electrode, an increase in the current density improves the degradation and mineralization of each contaminant, while the electrical efficiency decreases. On the other hand, the effect of the presence of a cation-exchange membrane between anode and cathode was studied. The results showed that its use benefits the degradation and mineralization of the contaminants, since it improves the kinetics of the anodic reaction and avoids the reduction of the electrogenated oxidant species. Next, the influence of the concentration of Na2SO4 as supporting electrolyte was analyzed. In this study it was observed that an increase in the Na2SO4 concentration improves the mineralization of the contaminant for the BDD electrode and, on the contrary, worsens for the ceramic electrode. This is due to the ability of each electrode to oxidize sulfates to persulfates. Finally, ecotoxicity tests on the treated samples were carried out, and it was shown that, in the presence of the membrane, at higher current density and with the BDD electrode, the toxicity of the sample is greater due to the higher presence of persulfate ions. Therefore, with the ceramic electrode, in addition to achieving a high degree of contaminant degradation, the treated samples are less toxic than the samples treated with the BDD electrode.
Agradezco al Ministerio de Economía y Competitividad por la financiación recibida mediante los proyectos CTQ2015-65202-C2-1-R y RTI2018-101341-B-C21, y a la cofinanciación con los fondos FEDER, que han permitido llevar a cabo la investigación en la Universitat Politècnica de València para la realización de la presente Tesis. También agradecer a Sergio Mestre Beltrán por proporcionarnos los nuevos electrodos cerámicos en los que se ha basado este trabajo.
Mora Gómez, J. (2020). Eliminación de contaminantes orgánicos emergentes mediante procesos electroquímicos de oxidación avanzada [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/158751
TESIS

Advanced water purification methods are required to answer the growing demand for clean water throughout the world. Current methods of removing the pollutants rely on moving the pollutants from one place to another rather than breaking them down. The use of advanced oxidative processes (AOPs) presents a highly effective opportunity to achieve the full mineralisation of pollutants without the added cost of regeneration methods. Photocatalysts, such as titanium dioxide and zinc oxide, can be used as AOPs when activated by electromagnetic radiation in the form of ultraviolet and visible light. To facilitate the activation with visible light, titanium dioxide doped with rare earth elements was produced via a sol gel method. Both single doped and co-doped systems were investigated with efficiency determined by the percentage of degraded methylene blue over 48 hours under ultraviolet filtered visible light. The incorporation of rare earth ions restricted the growth of the more active anatase phase and the method produced highly agglomerated, sintered nano particles which exhibited as micron sized particles. The highest methylene blue removal rate achieved in 48 hours for a single doped system was 70% for the 1 mol% yttrium doped titanium dioxide. This was improved further on inclusion of 1 mol% praseodymium which showed an 86% removal of methylene blue over the same time period. The coating of known up-converting phosphors with the successfully developed doped titanium dioxide was investigated. Yttrium silicate doped with praseodymium and lithium, was found to be the most successful known phosphor when used with the commercially available P25 titanium dioxide. When coated with the doped titanium dioxide shell at a 2:1 ratio of phosphor to titanium dioxide, a methylene blue degradation of 94% was reached. Initial tests on the coating of titanium dioxide with the known up-converting phosphor showed that methylene blue was absorbed rather than broken down so was not developed further. An investigation into the incorporation of zinc oxide, both pure and doped with the same successful titanium dioxide system was carried out. Zinc oxide shells were coated onto doped titanium dioxide, the known up-converting phosphor and the doped titanium dioxide coated known phosphor. The crystalline form of zinc oxide was inhibited by the incorporation of rare earth ions, as with the titanium dioxide system, and from the thickness of the zinc oxide shell. The highest degradation achieved was a 91% removal rate for the ZnO-PrY:TiO2-PrY:Y2SiO5-Pr,Li core shell shell structure indicating there was no further improvement on incorporation of zinc oxide, either doped or un-doped.

Perchlorate is a stable and soluble substance that can last for decades in the environment. Studies have shown that it can reduce iodine uptake into the thyroid gland which is of concern for people with decreased iodine intake, pregnant women and small children. Perchlorate is removed from drinking water using highly selective ion exchange (IX) resins that are replaced after exhaustion and incinerated or disposed in a landfill since there are no viable methods for regenerating them. One of the major limitations in regeneration of these single use resins is achieving complete desorption of perchlorate. The sustainability of treatment processes for perchlorate contaminated water can be achieved by regenerating the exhausted resin. A study on the adsorption and desorption equilibrium, kinetics and biological regeneration of perchlorate from a trybutylamine strong base anion (SBA) exchange resin was conducted. Adsorption and desorption equilibrium could be described using the Freundlich model with estimated parameters KF = 50 (mg/g)(L/mg)1/n and n = 2.36. The calculated average perchlorate-chloride separation factor was 4700 ± 1700 and the resin capacity was 1.4 meq/mg. The kinetics of adsorption and desorption of perchlorate from the resin were found to be controlled by chemisorption since a pseudo-second order rate model fit the data the best. The results from the physical/chemical studies were then applied to model the biological regeneration of the resin using the culture NP30. Experiments conducted with the exhausted resin inside a membrane to avoid direct contact with the culture, demonstrated the biological regeneration of the resin by degradation of the desorbed perchlorate. The model was able to describe the desorption and biodegradation of perchlorate from the exhausted resin and the results were comparable to the experimental data. The model was found to be sensitive to the Freundlich adsorption intensity parameter n.

The objective of this work was to evaluate the technical feasibility of potable water production from both sea water and sodium chloride solutions via the membrane distillation process. Membrane distillation is a thermally driven process in which a hydrophobic microporous membrane separates a hot or warm saline solution from a cold desalinated one. Water, in the form of vapour, migrates from the hot solution to the cold one.
Two different hollow fibre membrane distillation modules were used to conduct experiments. Tests were performed to determine the sensitivity of permeate flux and quality to stream temperatures and flowrates, and feed concentration. The hot side temperature was found to have a greater effect on the water flux than the cold side temperature. Water flux values ranged from 0.5 to 1.6 Kg/m$ sp2$hr with salt removals of over 99.99%. A semi-empirical model, based on well established heat and mass transfer correlations, was developed and its predictions were validated with the experimental results.

Although many aspects of the semiconductor photocatalysed mineralisation of water contaminants have been studied by researchers over the past decade, there are still certain areas which need further clarification, if the technique is to be used as an alternative to the presently available methods of water purification. It was the objective of the work in this thesis to provide further understanding of some of these remaining areas. One of the greatest inducements for the introduction of the technique of semiconductor photocatalysed pollutant mineralisation, in preference to the currently available technology, would be an efficiency advantage. The work in Chapter 3, studies the effect of many reaction variables (e.g. T, pH, [TiO₂]) in order to provide rate enhancements and therefore further efficiency of the technique. In Chapter 4 the model pollutant, 4-chlorophenol, is used to illustrate the role of activation energies in semiconductor photocatalysed mineralisation reactions, an area which has been largely ignored by researchers in this field to date. In order to speed up the process of reactor designs for commercial semiconductor photocatalysis reactors, there was a need for a predictive kinetic model, to provide information on individual pollutant mineralisation rates, under certain reaction conditions. Chapter 5 outlines a kinetic model which is able to accurately model the mineralisation of various pollutants and can also be used as a predictive tool for non-standard conditions. Chapter 6 enhances this work, to provide a model capable of modelling further pollutant systems, previously unable to be modelled. The technique of semiconductor photocatalysed pollutant mineralisation, will only become a plausible alternative to the currently available technology, if it can be scaled up from the batch reactor level. The work in Chapter 7 aims to provide scale up of the batch system used in Chapter 3 from 2.5 ml to 101.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2017.
Cataloged from PDF version of thesis.
Includes bibliographical references.
The demand for clean water has been increasing for several reasons, such as rapid industrialization of developing countries, environmental pollution and climate change, and development of biofuels and the resulting irrigation growth. To meet the needs for this growing demand for clean water, desalination has become an appealing solution as saline water (brackish water, seawater and brine) are the most abundant water source for most of the world. However, desalination is energy and capital intensive compared to other water treatment processes, and oftentimes it is not economically feasible. Current desalination technologies require further engineering and development to become more sustainable in the long term. My Ph.D thesis is focused on engineering of electromembrane desalination, which is a set of electrically driven desalination technologies that utilize ion transport through ion exchange membranes. We employed microfluidic platforms and numerical modeling tools for the study, for they help reveal novel insights regarding the micro-scale details that are difficult to be discovered from the conventional large-scale systems. In this thesis, we consider three topics: i) engineering of structures that enhance mass transport in electrodialyis (ED), ii) techno-economic analysis of ion concentration polarization (ICP) desalination for high salinity brine treatment, and iii) development of electrocoagulation (EC) - ion concentration polarization (ICP) desalination hybrid that removes dissolved ions and non-ionic contaminants from water in a single device. First, we employed an electrodialysis (ED) system as a model to investigate the mass transport effects of embedded microstructures, also known as spacers, in electromembrane desalination systems. The spacer engineering is especially critical for low salinity (i.e., brackish water) desalination, where the mass transport in the solution is a dominant contributor to the electrical energy consumption in the system. Parametric studies of the spacer design revealed that small cylindrical structures effectively re-distribute the local flow velocity and enhance mass transport in the system. Furthermore, we found that relative diffusivities of cation and anion in the solution should be considered in designing the spacer and that the optimal design should maximize the mass transport while keeping the effect on the hydrodynamic resistance small. Next, we built an empirical model to estimate an electrical energy consumption of ICP desalination and utilized it to obtain the water cost and optimal operating parameters for high salinity applications. We performed cost analyses on two specific cases (i.e., partial desalination of high salinity brine to the seawater level, and brine concentration for salt production) and compared the performance with mainstream desalination technologies for each application. Lastly, we combined two electrical water treatment technologies and created an EC-ICP hybrid for total water treatment, which removes dissolved ions and non-ionic contaminants from the feed solution. We demonstrated a continuous EC-ICP operation that successfully removed salt and suspended solids. Our system is flexible in terms of the system size, and the type and concentration of contaminants it can handle, and thus it can find applications as a portable water treatment system.
by Siwon Choi.
Ph. D.

Clean water is hard to obtain in certain areas, such as remote locations and during emergency response. Our study developed a membraneless water purification system using diffusiophoresis and tested the influence of various factors (gas pressure, liquid flow rate, etc.) on the turbidity of filtered water. The main component in the separation system is a tube-in-tube-in-tube separator. The inner tube and the middle tube are made of a semipermeable material (Teflon AF-2400), which allows gas (CO2) to permeate through it, but retains liquid (water). In this strategy, the CO2 permeates through the inner tube (the end is sealed) then dissolves into the dirty water/particle suspension passing through the middle tube. It then diffuses radially to the outer tube, where a vacuum collects the CO2, forming a concentration gradient of ions through the water, which induces the migration of charged particles to concentrate at the inner wall of the middle tube. The vacuum phase in the outer tube can increase the concentration gradient of ions in the water and recycle the CO2. Finally, purified water can be collected from the center of the middle tube by a needle in the effluent. The purification system is able to take initial turbid water (243 NTU) to below the WHO drinking water standard (

Los fármacos, compuestos químicos con actividad biológica, y sus productos de transformación, metabolitos y otros derivados en las plantas de tratamiento y en el medio ambiente, con actividad farmacológica remanente, son contaminantes antropogénicos que, en muchos casos, están llegando al medioambiente a través de las aguas residuales, y son las aguas superficiales el primer y principal compartimento ambiental destino. Este es un hecho que, en la actualidad, es ya ampliamente reconocido por la comunidad científica, tras el desarrollo de métodos de análisis capaces de la determinación de estos microcontaminantes en el medio ambiente, y su posterior aplicación en estudios de presencia en diferentes matrices ambientales. Los científicos, por lo tanto, están demandando medidas de control de los mismos por parte de las autoridades. Aunque tímidos, se están dando pasos adelante en materia legislativa en la lucha contra este tipo de contaminación, lo que muestra la toma de conciencia de la importancia en el control de las fuentes de entrada de estos contaminantes emergentes, así como de su eliminación del medioambiente. Esto conlleva un aumento importante en el número de estudios y, por lo tanto, en las muestras a procesar por parte de los laboratorios medioambientales. De ahí nace la necesidad de optimizar la eficiencia y competitividad de los métodos analíticos actuales, de manera que progresen en fiabilidad y sensibilidad, aumentando al mismo tiempo su versatilidad, así como su capacidad y rendimiento. El desarrollo tecnológico en el sector es muy rápido, y en general, es la comunidad científica la que evalúa en primer término la viabilidad y bonanza de las diferentes propuestas tecnológicas. Con la presente tesis se ha pretendido dar respuesta a estas necesidades. Así se ha llevado a cabo: - El desarrollo y validación de métodos analíticos para la determinación de fármacos y sus derivados en aguas medioambientales y residuales, mostrando las ventajas y puntos débiles de cada uno de ellos. En concreto, se han usado dos fuentes de fiabilidad, que no son excluyentes y pueden ser utilizadas simultáneamente. La primera ha consistido en la introducción de la automatización en el tratamiento de muestra, llevando al mínimo la manipulación de las muestras por parte del analista. La segunda ha consistido en la introducción de surrogados y patrones internos adecuados que han puesto de manifiesto las incidencias producidas durante el proceso analítico, para que hayan podido ser corregidas. Por otro lado, se han conseguido métodos que presentan una elevada sensibilidad para la determinación de los microcontaminantes objeto de estudio presentes a bajas concentraciones en matrices complejas. Para ello se ha utilizado espectrómetros de masas de triple cuadrupolo de última generación, que trabajando en modo SRM (Selected Reaction Monitoring), han proporcionado una muy buena sensibilidad, además de una elevada selectividad, que ha allananado el camino de la fiabilidad comentada anteriormente. Además, se apostó también, por el desarrollo de métodos con la suficiente versatilidad como para que hayan podido ser aplicados sobre cualquier tipo de agua ambiental dulce continental, tanto superficial como subterránea, así como a agua residual y potable, con el fin de propiciar la intercalación de muestras de diferente naturaleza analizadas consecutivamente en una misma tanda. Finalmente, se propusieron métodos dotados de una elevada capacidad, de manera que un solo método haya sido capaz de analizar el mayor número de residuos de interés posibles, incluyendo fármacos y sus derivados, metabolitos y otros productos de transformación. Pero a la vez, se ha conseguido un aumento en el rendimiento analítico de estos métodos, es decir, se ha logrado una disminución del tiempo de análisis por muestra y un aumento del número de muestras por día. Para esto se apostó claramente por la automatización, eliminando algunas etapas en el proceso analítico, lo que, además de redundar en fiabilidad como se ha comentado anteriormente, ha proporcionado métodos analíticos más cortos y autónomos y, por lo tanto, capaces de trabajar en ausencia del analista. Otra enfoque en esta dirección fue la utilización de cromatografía rápida. - Otra parte importante de la presente tesis, ha sido la aplicación posterior de los métodos desarrollados, en estudios medioambientales de elevado interés científico por su innovación. En concreto en los siguientes: A) Estudio del impacto medioambiental a escala real, en un escenario de reutilización de agua residual para el mantenimiento del caudal ecológico de un río mediterráneo. Además, se valoró el riesgo ecotoxicológico y de estrogenicidad en las muestras del río. B) Estudio de presencia de fármacos y sus productos de transformación en las aguas superficiales de la cuenca del río Ebro. C) Estudio de la distribución tridimensional y origen de residuos farmacéuticos (fármacos y sus productos de transformación) en las aguas subterráneas bajo la ciudad de Barcelona (España). D) Determinación enantiomérica de 13 residuos farmacéuticos quirales en las aguas superficiales de la cuenca del río Guadalquivir, así como en las aguas de entrada y salida a las principales EDARs asociadas a la cuenca. Además, se discutieron las implicaciones en la toxicidad de las relaciones racémicas y no racémicas.
Pharmaceuticals are compounds with biological activity and their transformation products with remaining activity are arriving the environment through sewage waters, and superficial waters are the main receiving compartment. Some steps towards the fight this kind of contamination. This is creating an increase in the number of studies, and therefore, in the number of samples to be processed by the environmental laboratories. For this reason, the need to optimize the efficiency of current analytical methods, by improving the reliability, sensitivity, versatility, capacity and throughput, is a must. Technologic development is very fast in the sector, and the scientific community is generally the one that first assesses it. This thesis has tried to give answer to these requests. Thus, four multi-residue analytical methods for the analysis of pharmaceuticals and their transformation products in environmental and sewage waters, have been developed making use of cutting edge technology. The advantages and disadvantages of each of them have been discussed. Different online and offline pre-treatment technologies, fast and conventional liquid chromatographies and several kinds of triple quadrupoles for mass spectrometry, have been tested. Other important part of this thesis has been the application of the developed methods with high scientific studies, as follows: - Impact of the discharge of reclaimed sewage water in a Mediterranean river, and assessment of the eco-toxicological consequences. - Presence of pharmaceuticals and their transformation products in Ebro River basin, one of the main ones in the Iberian Peninsula. - Three-dimensional distribution of pharmaceuticals and their transformation products in the ground waters underlying Barcelona city (Spain). - Enantimeric determination of 13 chiral pharmaceutical residues in Guadalquivir River basin, one of the main ones in the Iberian Peninsula, and the assessment of the eco-toxicity issues related.

This study has shown that OH˙ radicals can be generated in an Fe/O2 cell from the electrode products via Fenton&rsquo
s reaction and used for water disinfection. The cell system in which the experiments were carried out was open and undivided and contained two electrodes with iron (Fe) as the anode and oxygen (O2) gas diffusion electrode. Typically, 100 ml of Na2SO4.10H2O (0.5M) solution was used as a background electrolyte. OH˙ radicals were produced in-situ in an acidic solution aqueous by oxidation of iron (II), formed by dissolving of the anode, with hydrogen peroxide (H2O2). The H2O2 was electrogenerated by reduction of oxygen using porous reticulated vitreous carbon (RVC) as a catalyst.

As traditional disinfection techniques have proved to be inefficient in coping with toxic pollutants, there is a real need to create and develop alternatives such as Advanced Oxidation Processes (AOP's). As one of the most promising AOP's developed to date, heterogeneous semiconductor UV-photocatalysis has been shown to efficiently mineralise and inactivate a wide range of organic, inorganic and biological pollutants. This technique is based on the powerful redox properties of UV-illuminated semiconductors. The photocatalyst (semiconductor), which is insoluble in water, can be used in the form of a dispersion or as a thin coated film over which the pollutant can flow and interact in the liquid as well as in the gas phase. Although many pollutants have been studied, the development of more powerful analytical tools has meant that trace levels of water pollutants such as bromate, a potential carcinogenic by-product of the ozonation process and their destruction needs to be addressed. Chapters Three, Four and Five investigate the development and use of an analytical method for monitoring trace levels of bromate (ppb level or μg.dm^-3), in studies involving the use of Granular Activated Carbon (or GAC) and platinised TiO₂ (Pt-TiO₂) UV-photocatalysis for the removal of this inorganic pollutant. In Chapter Six, a study of TiO₂ photocatalysed oxidation of urea-based pesticides is given. Chapter Seven investigates two photoreactor designs for use in flow systems with larger volumes of pollutant which is required if the system is to be commercially viable. These flow photoreactors use thin immobilised films of TiO₂ over which the pollutant can flow. Finally, using the flow photoreactor designs studied in Chapter Seven, Chapter Eight presents a study of the photocatalysed oxidation of volatile organic pollutants (or VOC's) in the gas phase.

Ion exchange is used extensively for the removal of ionised impurities found in natural waters. The final stage in the production of ultra pure water is normally a bed of mixed anion and cation exchange resins. Three areas within the operating cycle of a regenerable mixed bed - resin separation, resin mixing and anion exchange kinetics - have been investigated. Complete separation of the two resins by backwashing, prior to chemical regeneration, is necessary to prevent the subsequent release of trace impurities into the purified water. Various published models of particle segregation by backwashing were examined but none accurately described the separation of two ion exchange resins with similar bead size distributions and densities. A new model has been proposed based on variations in fluidised bed porosity combined with overlapping bulk circulation cells of particles. A graphical technique has been developed to predict resin separability and the predictions compared with practical data. The effects of variations in bead size, bead density, backwash flow rate and temperature have been calculated. The variations in bead density with ionic form and polymer/matrix type of the exchanger have been measured. Following regeneration the resins are remixed by air agitation of a resin/water slurry. A mechanism to describe the progressive stages of air mixing has been proposed, based on bubble transport and bulk circulation of resin beads. The subsequent sedimentation of the resins was also considered. Laboratory and full scale studies confirmed the predicted effects of mixing fault conditions, particularly re-separation of the mixed resins. A mass transfer equation has been developed to describe the leakage of influent ions through a column of exchange resins. In conjunction with laboratory column tests the equation has been used to investigate the influence on anion exchange of polymer/matrix type, influent anion and the presence of foulants on the resin beads. Sulphate and phosphate ions exchange more slowly than monovalent chloride and nitrate ions. On a fouled exchanger the rate of sulphate exchange deteriorates more rapidly and seriously than for chloride exchange. This has been attributed to steric hindrance of the divalent sulphate ion. A laboratory method has been developed for the routine assessment of mixed bed anion exchangers and the prediction of their performance potential in service, with particular application to condensate purification for boiler feedwater.

The world is facing a serious water crisis due to rapid population growth, industrialization and climate change. Water purification using membrane technologies provides a promising solution to address this problem. This thesis investigated the feasibility of membrane technologies in a wide range of applications covering drinking water purification and wastewater treatment. Target contaminants included fluoride, natural organic matter (NOM), emerging contaminants bisphenol A (BPA) and cimetidine, and the waterborne parasite Cryptosporidium. The first part of the thesis explored the solute-solute interactions of fluoride and humic substances (HS) in order to understand the behaviour of fluoride in natural water and during membrane filtration processes. It is shown that, at low pH and high ionic strength, fluoride ions are temporarily trapped inside the structure of HS aggregates. The second part of the thesis examined the feasibility of nanofiltration (NF) and reverse osmosis (RO) in treating challenging natural waters in Tanzania containing high fluoride and NOM concentrations, with the aim to increase the availability of drinking water sources. Fluoride retention was found to be dependent on ionic strength and recovery, which was predominantly due to a solution-diffusion mechanism. NOM retention was independent of water matrices but was governed by a size exclusion mechanism. NOM was observed to have a positive impact on fluoride removal. The third part of this work evaluated the on-site performance of a pilot-scale renewable energy powered membrane system in remote areas under varying solar conditions. While the technology is well established, the adaptation to remote areas is far from achieved. The system used in this study reliably produced high-quality drinking water despite of solar fluctuations. This area requires further work in terms of integration, technology adaptation and operation and maintenance schemes. The last part of the thesis reported the development of a series of novel photocatalytic polymers and tested their capabilities in removing wastewater contaminants. The photoactive polymers were highly capable of degrading BPA and cimetidine, as well as inactivating Cryptosporidium. These are very promising materials for simultaneous decontamination and disinfection of wastewater. The results obtained from this thesis provide new insights into solute-solute interactions, solute transport mechanisms, decentralized membrane system and novel membrane materials, which are hoped to contribute to advancements in current membrane technologies.

The removal of PCP from aqueous solution in contact with metallic iron was investigated by laboratory batch experiments. The decline in PCP concentration as well as inorganic parameters were monitored over time. Removal of up to 90% of the initial PCP was observed within 24 hours. The initial geochemical conditions of the PCP solution changed rapidly to basic and reductive conditions when in contact with metallic iron. Organic degradation by-products were not found during the removal of PCP using two distinct analytical procedures. Chloride ions analyzed in the solution after PCP removal were relatively low and showed high variability between experiments. The extraction of iron with solvents showed that a maximum of 37% PCP was sorbed. The effectiveness of iron on PCP removal appeared to be limited by the number of contacts with a fresh PCP solution. The rate constant in PCP removal appeared to be directly proportional to the iron to solution ratio. The PCP removal behaviour fitted well two sorption models (Freunlich, Langmuir). The results indicate that the process involved in the removal of PCP does not seem to be dechlorination because of the lack of by-products and low level in chloride ion, and is not completely sorption because of the lack of reversibility.

Arsenic (As) contamination is a worldwide problem, and millions of people are suffering from it. There are two major inorganic forms of As in waters: arsenate(V) and arsenite(III), and adsorption to a sorbent material may be an efficient method to handle them. In this study, we focused on As(III), the more toxic form, which predominates under reducing conditions. The As(III) removal properties of four sorbent materials: hydrotalcite, Mg−Al layered double hydroxide, amorphous aluminium hydroxide and amorphous titanium oxide, are examined from the following viewpoints: As(III) adsorption, the effects of pH, the effects of adsorbent concentration, adsorption as a function of dissolved As(III), and the effect of co-existing anions (HCO3− and PO43−). The maximum adsorption of As(III) to HT (0.1 mmol As(III)/g adsorbent), Mg-Al LDH (0.1 mmol As(III)/g adsorbent), am-Al(OH)3 (0.22 mmol As(III)/g adsorbent), and am-TiO2 (0.21 mmol As(III)/g adsorbent) occurred at pH 7.5, 7, 7, 8, respectively. At this pH, approximately 20%, 62%, 35%, and 98.3%, respectively, of the added As(III) was adsorbed. When the As(III) to sorbent ratio was increased, the adsorption was instead around 7% to am-Al(OH)3 (2.2 mmol As(III)/g adsorbent), and 46.3% to am-TiO2 (2.1 mmol As(III)/g adsorbent). These figures show that am-TiO2is the most efficient sorbent for As(III) adsorption of the four materials tested, Mg-Al LDH is second best, while HT and am-Al(OH)3 are not suitable for As(III) removal. The adsorption of As(III) to Mg-Al LDH as a function of dissolved As(III) could be adequately described by a linear equation, suggesting that As(III) adsorption to Mg-Al LDH was governed by anion exchange. As a result, the co-existing anions (HCO3- and PO43-) showed a significant influence on As(III) adsorption to Mg-Al LDH. Considering the interfering effects of co-existing anions on am-TiO2, HCO3− did not influence As(III) adsorption, while PO43- caused a slight but clear competition effect. Overall, am-TiO2 would be the best choice of these four materials in contact with As-contaminated groundwater due to its superior As(III) removal properties and the limited competition from co-existing anions on As(III) adsorption.
Alltför höga halter av arsenik (As) i vatten är ett världsomspännande problem som orsakar hälsoproblem för miljontals människor. Det finns två huvudsakliga oorganiska former av As i vatten: arsenat(V) och arsenit(III), och adsorption till ett material (s.k. ”sorbent”) kan vara eneffektiv metod för att avlägsna dem från vatten. I denna studie fokuserade vi på arsenit(III), den mer giftiga formen, vilken dominerar under reducerande förhållanden. Vi undersökte adsorptionsegenskaperna för arsenit(III) för fyra sorbentmaterial som kan vara tänkbara när det gäller arsenikrening av förorenade vatten: hydrotalkit, s.k. Mg-Al LDH (Mg-Al-skiktad dubbelhydroxid), am-Al(OH)3 (amorf aluminiumhydroxid), och am-TiO2 (amorf titandioxid). Dessa material undersöktes när det gäller följande: adsorption av arsenit(III) som funktion av pH,betydelsen av sorbentkoncentration, adsorption som funktion av löst arsenit(III) (”isoterm”), och konkurrens från samexisterande anjoner (HCO3− och PO43−). Den maximala adsorptionen av As (III) till HT (0,1 mmol As(III)/g sorbent), Mg-Al LDH (0,1 mmol As(III)/g sorbent), am-Al(OH)3 (0,22 mmol As(III)/g sorbent) och am-TiO2(0,21 mmol As(III)/g sorbent) inträffade vid pH 7,5, 7, 7, respektive 8. Vid dessa pH-värden adsorberades ungefär 20%, 62%, 35% respektive 98,3% tillsatt As(III). När kvoten mellan As(III) till sorbent ökades blev adsorptionen istället cirka 7% till am-Al(OH)3 (2,2 mmol As(III)/g sorbent) och 46,3% till am-Ti02(2,1mmol As(III)/g sorbent). Dock var adsorptionsmängden per viktsenhetsorbenthögre över hela pH-området. Dessa siffror visar att am-TiO2 är det mest effektiva av de fyra testade materialen för As(III)-adsorption, Mg-Al LDH det näst bästa, medan HT och am-Al(OH)3 är olämpliga för detta ändamål. Adsorptionen av As(III) till Mg-Al LDH som funktion av löst As(III) kunde beskrivas väl med en linjär ekvation, vilket antyder att adsorptionen av As(III) till Mg-Al LDH styrdes av anjonbyte. I konsekvens med detta hade de samexisterande anjonerna (HCO3- och PO43-) ett betydande inflytande på As(III)-adsorptionen till Mg-Al LDH. För am-TiO2 påverkade HCO3− inte As(III)-adsorptionen, medan PO43- orsakade en liten men tydlig konkurrenseffekt. Sammantaget är am-TiO2 det bästa valet av dessa fyra material i kontakt med As- kontaminerat grundvatten på grund av dess betydligt bättre förmåga att avskilja arsenit(III) och den förhållandevis blygsamma konkurrensen från andra anjoner.

The use of natural remediation methods to remove contaminants from waste water is becoming more popular. Plants have been used for several decades, yet their use for municipal waste water contaminated by heavy metals is limited to a few studies which focus on the Mercury and Chromium (Bennicelli, et.al, 2004). This study specifically attempted to determine the viability for using Lemna minor to remediate municipally generated wastewater contaminated with copper. The study used 100 ml samples of wastewater, artificially spiked with 8 mg/L of copper sulfate and seeded with approximately 100 Lemna minor fronds. Each treatment was repeated 15 times and distilled water was added daily to maintain 100 ml samples. The addition of Lemna minor statistically lowered the copper concentration of the treatment groups (55% reduction in total Cu concentration). No significant decrease was seen in the control groups. While Lemna minor has metals accumulation potential, its wide spread use is limited by the toxic effect of copper on Lemna minor at relatively low levels.

The purpose of this study was to evaluate the level of nitrate contamination in the water in Cherry Valley. It examines the theory that human effluent is the source of the nitrate and evaluates the role of politics in the nitrate issue.

A comparative study of electrolysers using different anodic materials for the electrolysis of brine (sodium chloride) for the production of sodium hypochlorite as a source of available chlorine for disinfection of rural water supplies has been undertaken. The electrolyser design used was tubular in form, having two chambers i.e. anode inside and cathode outside, separated by a tubular inorganic ceramic membrane. The anode was made of titanium rod coated with a thin layer of platinum and a further coat of metal oxide. The cathode was made of stainless steel wire. An assessment of these electrolysers was undertaken by studying the effects of some variable parameters i.e.current, voltage and sodium chloride concentration. The cobalt electrolyser has been shown to be superior as compared to the ruthenium dioxide and manganese dioxide electrolysers in terms of hypochlorite generation. Analysis of hydroxyl radicals was undertaken since there were claims that these are produced during brine electrolysis. Hydroxyl radical analysis was not successful, since sodium hypochlorite and hypochlorous acid interfere using the analytical method described in this study.

Biodiesel purification processes generate wastewater streams that require a large amount of energy when distillation is used as a treatment technology. Process simulation software was used to show that an alternative water treatment process involving ion exchange would require only 31% of the energy used by distillation. Experiments showed that multiple washing stages were required to meet the standard specification for sodium, an impurity present in crude biodiesel, when washing biodiesel made from used frying oil. A comparison was made between washing biodiesel in a cross-current washing configuration and a counter-current configuration. Both configurations met the specification for sodium within three washing stages; however, the counter-current configuration required less water, making it the more efficient process. Lastly, the removal of sodium from wastewater samples using an ion exchange resin was experimentally investigated. The results validated the use of ion exchange to reduce energy consumption in biodiesel purification.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemical Engineering, 2015.
Cataloged from PDF version of thesis.
Includes bibliographical references.
Electrospun membranes are attractive for the liquid filtration applications especially as microfiltration membranes because they are low in solidity and have open, highly interconnected porous structures. Nevertheless, liquid filtration processes are pressure driven; hence, it is crucial to understand the compressive behaviors of electrospun membranes. Compressive properties of electrospun fiber mats are reported for the first time in this thesis. Membranes of bisphenol-A polysulfone (PSU) and of poly(trimethyl hexamethylene terephthalamide) (PA6(3)T) were electrospun and annealed at a range of temperatures spanning the glass transition temperature of each polymer. The data for applied stress versus solidity of membrane were found to be welldescribed by a power law of the form [sigma]zz =kE([phi]n - [phi]no) where [sigma]-zz is the applied stress and [phi] is solidity, in accord with the analysis of Toll (Polym. Eng Sci., 2004). The values of n range from 3.2 to 6 for PSU and from 8.0 to 20 for PA 6(3)T. The lowest values in each case were exhibited by mats annealed near the glass transition temperature of the fiber material. The higher values of n are attributed to fiber slippage via a mechanism analogous to that of work hardening of metals. The values of kE can vary by an order of magnitude and were difficult to determine precisely, due to the nature of the power law and the inhomogeneity of the mats. The hydraulic permeabilities of electrospun fiber membranes are found to be functions of their compressibilities. Hydraulic permeabilities of electrospun PSU membranes experience a decrease of more than 60% in permeability between 5 and 140 kPa, due to the increase in solidity, attributed to flow-induced compression. This behavior is explained using a simple model based on Darcy's law applied to a compressible, porous medium. Happel's equation is used to model the permeability of the fiber membranes, and Toll's equation is used to model their compressibilities. The permeation model accurately estimates the changes in solidity, and hence the permeability of the electrospun membranes, over a range of pressure differentials. The permeability of commercial phase inversion membrane was higher than those of electrospun membranes at pressures greater than 8 kPa. Microfiltration of emulsions of oil (dodecane) in water using electrospun PA6(3)T membranes was demonstrated. Rejection of the emulsified dodecane decreased from (85 +/- 5) % to (4.3 +/- 0.9) % when the ratio of droplet diameter to fiber diameter (dp/df) decreased from 2.5 +/- 0.4 to 0.57 +/- 0.04, respectively. The normalized flux (relative to the pure water flux) decreased in proportion to the increase in emulsified oil concentration, and decreased with the increase in the total solidity of the membranes. The resistances from the oil were in series with the resistances of the membranes tested. The resistivity of the foulant increased with an increase in the concentration of oil. Foulant deposition models showed that the oil droplets formed a coating that enveloped the fibers. The normalized flux of electrospun membranes was approximately three times higher than that of commercial phase inversion membrane of comparable bubble point diameter, while exhibiting a similar rejection.
by Looh Tchuin (Simon) Choong.
Ph. D.

Thesis (MTech (Mechanical Engineering))--Cape Peninsula University of Technology, 2015.
Access to adequate quantities of clean drinking water has become a serious issue on the worldwide level. This is particularly true in arid and rural areas where for the majority of people water is a limited and a vulnerable resource. These water sources which are often highly contaminated are potentially the cause for several diseases (waterborne diseases) and ultimately death especially in infants. Due to poverty and sometimes to the remote conditions of their regions, the population is unable to afford adequate water purification technologies, since they are relatively expensive and energy intensive. It is therefore vital to investigate appropriate water purification technology that people can afford or construct, operate and maintain themselves. A promising technology is solar distillation for the supply of drinking water on a small-scale level. It has proved to be a unique purification method as it can purify almost any type of water by using the high solar energy potential of the affected regions. The most basic form of solar distillation is the use of a single basin single slope solar still. However the downside of this technology is that it presents a low efficiency and productivity. To try to tackle this problem, many studies have been carried out to enhance productivity, effectiveness and efficiency of single-basin solar stills. In this present study, a solar distillation unit was designed, fabricated and experimentally tested. Its performance in terms of distillate output and energy efficiency was analysed under Cape Town conditions and compared to similar stills that have been reported in the literature. The main configuration of the solar still is a double glazed single basin solar still coupled to an external condenser. The study indicated that the performance of the solar still unit can be enhanced by increasing the evaporation rate which is a combined effect of solar radiation, ambient temperature, and the system components temperature. It was concluded that the applied techniques such as the external condenser, double glazing, good insulation and low level of water are effective. The unit was found to have an efficiency ranging between 21 and 29% over the test period and a mean distillate yield of about 2.5 litres per square meter was achieved per day.