Electrodialysis (ED) is a membrane-based process in which ions are transported under the influence of an externally applied electrical potential. Ion-exchange membranes (IEMs) are key components in ED processes. There are two types of IEMs: (1) cation-exchange membranes (CEMs), which contain fixed, negatively charged groups, and (2) anion-exchange membranes (AEMs), which contain fixed, positively charged groups. ED processes have been widely applied for water desalination. This thesis investigates the application of ED in the treatment of drainage water of greenhouses. A key objective in sustainable greenhouse horticulture is the recirculation of drainage water, thereby minimizing the water volume used, which would otherwise be disposed into the environment.[1] The drainage water of greenhouses contains both K+ and Na+. Whereas K+ is a valuable nutrient, Na+ is detrimental for plant growth. Because of its toxicity, the Na+ level should be controlled below the crop-specific threshold.[2-4] Because Na+ is not taken up by plants, it accumulates and the excess needs to be removed. The main challenge here is to selectively separate and remove Na+ without removing K+ and other key nutrients like Ca2+ and Mg2+. Na+ and K+ are two competitive cations ion separations as they have the same valence (+1), quite similar crystal and hydrated radii and a rather similar transport behavior (i.e. electrophoretic mobility), causing that separation by charge, size, and/or mobility is challenging. This thesis focusses on the development and characterization of a membrane-based process for the selective removal of Na+.... ... Read more

Magnesium ion batteries (MIB) have attracted much attention from battery researchers around the globe. Magnesium is divalent in nature and offer a higher theoretical capacity than that of lithium. However, the magnesium research is still in the niche stage and the search continues for better electrolyte systems and for high voltage cathode materials. Currently, extensive research is being done in employing organic materials for battery cathode materials. Organic materials are made from naturally occurring compounds and are easy to dispose since they have no metals. Perylene diimide is an organic material gaining importance as cathode material in metal ion batteries.

The goal of the project is to determine the voltage window of perylene in lithium and magnesium battery systems. Cyclic Voltammetry (CV) is employed to measure the electrochemical activity of the cell. The output of the CV is a scan of the current versus the voltage. During the operation of the cell, duck shaped peaks are observed which correspond to the reduction/oxidation activity of the cathode and the anode respectively. The current corresponding to the peaks is used to determine the cathodic and anodic current of the cell. Once the voltage and the current are known, the area under the peaks is calculated to determine the
charge/discharge capacity of the cell.

Since no prior research was done on magnesium, the most common cathode material (inorganic), chevrel phase molybdenum sulphide is synthesized and tested. Research with the perylene as cathode material is started with lithium because lithium is being studied extensively in the research group. Tests with both the monomer and the polymer has been conducted against lithium and magnesium battery systems. The lithium cell employing perylene is optimized as much as possible and is shown to be electrochemically active. The lithium cell shows a redox voltage of 2.5V vs Li/Li+. In the magnesium system, perylene is active as small peaks are observed at 1.5V and 1.7V vs Mg/Mg2+. However, the cell fails to operate after the first charge. This is most likely due to the electrolyte forming a passive film on the surface of the anode. It is recommended to disassemble the magnesium cell after the first discharge cycle to observe the magnesiation on the cathode and the passive film formation on the anode.
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For all pressure driven membranes, one of the main problems which hinders the membrane practical application is the permeate flux reduction due to the solute accumulation on the membrane surface. The most popular explanation for the flux decline supported by Bhattachajee &Bhattacharya (1993), contains two mechanisms: concentration polarization(CP) and fouling. The influence of CP is noteworthy in ceramic nanofiltration system. On the one hand, CP can influence the performance of membrane separation by decreasing the retention of the molecules. On the other hand, CP could have a desirable effect which can be used for membrane surface modification. In the past three or four decades, several different models have been used to verify the existence of CP or cake-enhanced CP(CECP) effect and try to quantify it. However, all these methods or models have their own limitations. Therefore, it is essential to build a new model or adjust the constants in the empirical model according to the practical situation. The flux decline behaviour of a ceramic nanofiltration membrane in the presence of polyethylene glycols (PEGs) and silica was investigated to examine the control factor in flux decline and calculate the CP factor in the filtration. The control factor in flux decline for PEGs is CP, while for silica, both CP and fouling are important. Based on the reversibility of CP and fouling, the Gel-polarization model together with the corresponded filtration method generated the modified Gel-polarization model which is suitable for calculating the fouling resistance and the osmotic pressure on the membrane. Sherwood formula is appropriate for calculating CP factor with calibrated constants. The flux decline behaviour, as well as the CECP model developed in this work, was used to investigate the possible CP&CECP during ceramic nanofiltration for phosphate retention. CECP model based on Sherwood relation can be used to investigate the influence of the fouling layer on CP with measured permeate flux, fouling mass, and an assumed/measured porosity of the fouling layer. Based on the CECP model analysis, lower crossflow velocity and cake layer porosity, larger permeate flux and fouling mass can produce a higher CECP factor. The change of permeability in phosphate retention can be used to calculate CP factors, however, the adsorption and electroviscous effect had influence on the accuracy of the results. CECP factor is not able to be measured by the change of permeability since the unstable fouling layer can influence the discovery of permeability decrease. The presence of calcium has a serious negative impact on phosphate retention probably due to the lower electrostatic repulsion of phosphate. ... Read more

In today’s industry ammonia is produced on a large scale, and is used in the production of fertilisers, cleaning products and much more. Eventually the ammonia enters our wastewater, either directly or through urine. This is then removed with conventional nitrifying-denitrifying treatment or with Anammox. That process consumes energy and does not recover the ammonia.
Therefore, the goal of the ‘From Pollutant to Power’ project, of which this thesis is a part, is to achieve a paradigm shift for ammonia to become an energy resource instead of a wastewater pollutant. The objective of the project is to recover ammonia and use it in a solid oxide fuel cell (SOFC) to produce energy. To do this, a vapour with at least a mass percentage of ammonia (m%NH3) of 5% is needed. The energy produced with the SOFC can then be used to cover the energy need for the extraction of ammonia. The SOFC can produce 4.2MJ·kg-N-1 of thermal energy and 8.4 MJ·kg-N-1 of electrical energy.
This study examines the use of vacuum membrane stripping (VMS) to strip ammonia from wastewater. The research objective is to go from using VMS to recover ammonia from synthetic wastewater to strip ammonia from real wastewater, in order to produce ammonia fuel for a SOFC. To accomplish this, some knowledge gaps need to be filled. First, methods need to be found that concentrate the permeate more than previously possible with the VMS to reach the desired m%NH3 in the permeate. Therefore, the effect of the cross-flow of the feed side was investigated and how to concentrate the permeate vapour with the help of condensation. Next, the effect of contaminants on the VMS process was examined by looking at the effect of salts in the wastewater and testing with real industrial ammonia-rich wastewater from amide production, which contains some organics. The final issue to consider was whether this process would be feasible in terms of energy; therefore, an energy balance was made.
Multiple experimental tests were conducted with VMS to investigate the knowledge gaps mentioned above. The selected test conditions were a minimum pH of 10 to exclude CO2 gas transfer, and to ensure the total ammonia nitrogen (TAN) in the water was in the form of ammonia and not ammonium. For the experiments, feed solutions of ammonium hydroxide and ammonium bicarbonate were selected with a concentration of 1.5, 12 and 20 gTAN·L-1 with a temperature of 35°C. For the cross-flow experiments, the initial test was carried out with the Reynolds numbers 200, 300, 400, 500 and 600. From this initial test it was concluded that a Reynolds number of 200 is laminar and 500 is turbulent, and those values were used in the rest of the experiments. For the experiments with condensation, a condensation tube with cooling water of 5-10°C, 15-20°C and 25-30°C was added to the setup. Next, the composition of the industrial wastewater was investigated. In the end, the results from the different experiments were used to make an energy balance.
The results of the experiments with VMS show that turbulent flow is preferred above laminar flow, due to the increased ammonia flux and the ammonia selectivity of the membrane, which both provide a higher concentration of ammonia and more permeate. Salt (high ionic strength) will lower the ammonia flux through the membrane and the selectivity of the membrane. The condensation experiment was successful and adding a subsequent condensation step will concentrate the ammonia in the permeate vapour. Moreover, this condensation step will make it possible to recover some of the energy lost in the VMS. The experiment with the real wastewater was however not successful. The membrane fouled badly due to the organics in the water, where organics acted as surfactants and decreased the hydrophobicity of the membranes. The energy balance shows that the system would be energetically beneficial in terms of electrical energy with a concentration above 12 gTAN·L-1 in the solution for both ammonium hydroxide and ammonium bicarbonate, and that a concentration around 100 gTAN·L-1 from ammonium hydroxide is needed to make it energy efficient in terms of thermal energy.
More investigation is needed to be able to use real wastewater in a VMS module. For the wastewater tested in this study, stripping with VMS is not an alternative. This does not mean that other wastewater cannot be used in the VMS, therefore, other industrial wastewaters, reject water and urine should be investigated. Another possibility could be to review other stripping methods for wastewaters with relatively high contents of organics.
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Electrochemical sensing is considered as one of the most powerful analytical detection techniques. Electrochemical methods have fast response time, high sensitivity and selectivity, and can be performed at low cost. Their inherent ease of miniaturization have made them so popular in recent years. Hence, electrochemical sensors have diverse applications including pathological, clinical, and environmental analyses. Miniaturization of analytical devices plays an important role in the sensor development studies. Miniaturized electrochemical sensors open up opportunities toward faster, more sensitive, more user friendly (ease to use) and portable systems compared to the traditional cumbersome bulky electrochemical cells. Thanks to the recent advances in nano/micro fabrication techniques, scaling down the electrode size to micro and even nano dimensions and developing “lab on a chip” technology is achievable and is considered as a hot topic in electrochemistry. Traditional electrochemical cells are composed of three electrodes: a working electrode, a reference electrode and a counter electrode. However, in this thesis the main focus is on the dual- electrode systems, where two closely spaced working electrodes are placed next to each other. Hence the events at each electrode can be affected by the other one. These two electrodes can be biased independently and the current of each can be detected separately. Biasing one of the electrodes in an oxidizing potential (according to a desired redox active analyte) and the other in a reducing potential, results in a repeated successive oxidation and reduction of analyte species on the two electrode surfaces. Accordingly, the current at each electrode is amplified which leads to a higher sensitivity. Reducing the gap size between the electrodes can further enhance the sensitivity and amplification factor (the ratio between the limiting current in dual electrode mode and the current in a single electrode mode) of the device. ... Read more

The cellular environment is characterized by confinement and macro-molecular crowding: both concepts that have been studied separately. To understand kinetics of enzymatic reactions, there is a need to understand how the diffusional encounters of enzyme and substrate proceed in an environment
that is confined and crowded simultaneously. The project carried out in this thesis is the first step towards achieving the ultimate goal of studying biochemical reactions in native cellular environment - Understanding diffusion in confinement. Despite multiple investigations of diffusion of analytes in confinement, there exists a research gap. There is inconsistency in the interpretation of the results and in the dependence of diffusion properties of analytes of different sizes in channels of different dimensions. Hence, to bridge the research gap, the main goal of this thesis project was to find the diffusion coefficient of 100 nm polystyrene beads in microchannel (200 µm wide and 4.5 µm high) and nanochannel (5 or 10 µm wide and 300 nm high). The Brownian motion of particles was observed using Confocal Laser Scanning Microscope. A preliminary study first confirmed the reliability and optimization of the particle tracking method of finding diffusion coefficient. Diffusion coefficient of the particles determined experimentally in microchannel (bulk system) was in agreement with the theoretical estimate and statistically significant. Experiments in the nanochannel revealed a reduction in the particle diffusion coefficient of about ∼52% compared to bulk, due to interactions with the confining depth
(300 nm) of nanochannel. An interesting behaviour was also exhibited by particles diffusing close to the side wall along the width of nanochannels, which was not confining (5 or 10 µm). The diffusion coefficient in such a case reduced by around ∼90% relative to bulk. The reduction in both cases can be mainly attributed to hydrodynamic interactions. The experimental investigations of diffusion coefficient carried out in this study were in agreement with long standing theoretical predictions. However, the research gap could not be fully expelled.
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Hydrogen, if produced from clean and abundant sources, has the potential for solving the concerns on energy supply security, climate change and local air pollution. Photoelectrochemical (PEC) water-splitting is a promising technology under development for the production of hydrogen from water by using sunlight. This design project aims to investigate the practical implementation of this innovative technology by developing aninitial conceptual design of a modular PEC water-splitting device that could be on the market by 2020.
An analysis of the state-of-the-art of the so-called artificial leaf technology was used to identify the main design challenges: (a) the need of finding efficient, durable, low-cost, earth-abundant semiconductors and catalysts, (b) the separation of the evolved gases in a reliable way to ensure the safety of the device, (c) the optimization of the components size and relative positioning to minimize internal losses and enhance light absorption, and (d) the optimum operating conditions.
To facilitate the design process of a device that could overcome the identified challenges, a step-wise methodology was applied. In each level, various design alternatives were investigated and evaluated according to technical, economical, safety and sustainability criteria. A device consisting of one photoelectrode and a counter metal electrode facing each other was selected, since this configuration offers low Ohmic losses.
Moreover, the photoelectrode is illuminated from the back to minimize the light losses. Low cost and earthabundant materials were selected for the main components: (i) multifunction a-Silicon for the photoelectrode, (ii) Nickel Molybdenum protection layer for the photoelectrode and (iii) Nickel counter electrode. For these materials to be stable and efficient, the device should operate under alkaline conditions. Moreover, to ensure the separation of the gases, an anion exchange membrane is placed in between the electrodes. Nevertheless, the design offer flexibility to implement material developments.
The economic feasibility of a hydrogen production plant utilising the designed device has been investigated, leading to potential hydrogen cost below 6 $/kg. This device could be manufactured with commercially available components and manufacturing process, with an estimated cost of ~70 $/m2. Moreover, a sustainability life cycle assessment (LCA) showed the potential environmental benefits of this technology,
with an energy payback time lower than 2 years, and savings of 2.5 ton CO2 eq. emissions per m2 of device during its full lifetime (15 years). It was concluded that the developed conceptual design could succeed in the market, providing a safe and environmental friendly process for hydrogen production.
Nevertheless, some practical issues were identified that need to be resolved before this PEC technology is marketable, and therefore it is recommended that laboratory research focuses on the further development of (a) protection layers to improve the stability of the semiconductor photoelectrodes and (b) anion exchange membranes to minimize the gas crossover and ensure the safety of the device. With respect to engineering development of the device it is recommended to initiate a detailed design project that focuses on the optimization of the operating conditions and the flow management to minimize the internal losses and the gas crossover. ... Read more