abstract: This dissertation investigates the mechanisms that lead to fouling, as well as how an understanding of how these mechanisms can be leveraged to mitigate fouling. To limit fouling on feed spacers, various coatings were applied. The results showed silver-coated biocidal spacers outperformed other spacers by all measures. The control polypropylene spacers performed in-line with, or better than, the other coatings. Polypropylene’s relative anti-adhesiveness is due to its surface free energy (SFE; 30.0 +/- 2.8 mN/m), which, according to previously generated models, is near the ideal SFE for resisting adhesion of bacteria and organics (~25 mN/m). Previous research has indicated that electrochemical surfaces can be used to remove biofilms. To better elucidate the conditions and kinetics of biofilm removal, optical coherence tomography microscopy was used to visualize the biofouling and subsequent cleaning of the surface. The 50.0 mA cm-2 and 87.5 mA cm-2 current densities proved most effective in removing the biofilm. The 50.0 mA cm-2 condition offers the best balance between performance and energy use for anodic operation. To test the potential to incorporate electrochemical coatings into infrastructure, membranes were coated with carbon nanotubes (CNTs), rendering the membranes electrochemically active. These membranes were biofouled and subsequently cleaned via electrochemical reactions. P. aeruginosa was given 72h to develop a biofilm on the CNT-coated membranes in a synthetic medium simulating desalination brines. Cathodic reactions, which generate H2 gas, produce vigorous bubbling at a current density of 12.5 mA cm-2 and higher, leading to a rapid and complete displacement of the biofilm from the CNT-functionalized membrane surface. In comparison, anodic reactions were unable to disperse the biofilms from the surface at similar current densities. The scaling behavior of a nanophotonics-enabled solar membrane distillation (NESMD) system was investigated. The results showed the NESMD system to be resistant to scaling. The system operated without any decline in flux up to concentrations 6x higher than the initial salt concentration (8,439 mg/L), whereas in traditional membrane distillation (MD), flux essentially stopped at a salt concentration factor of 2x. Microscope and analytical analyses showed more fouling on the membranes from the MD system. / Dissertation/Thesis / Doctoral Dissertation Civil, Environmental and Sustainable Engineering 2019

An adsorbent suitable for adsorption desalination cycles is essentially characterized by a hydrophilic and porous structure with high surface area where water molecules are adsorbed via hydrogen bonding mechanism. Silica gel type A++ possesses the highest surface area and exhibits the highest equilibrium uptake from all the silica gels available in the market, therefore being suitable for water desalination cycles; where adsorbent’s adsorption characteristics and water vapor uptake capacity are key parameters in the compactness of the system; translated as feasibility of water desalination through adsorption technologies. The adsorption characteristics of water vapor onto silica gel type A++ over a temperature range of 30 oC to 60 oC are investigated in this research. This is done using water vapor adsorption analyzer utilizing a constant volume and variable pressure method, namely the Hydrosorb-1000 instrument by Quantachrome. The experimental uptake data is studied using numerous isotherm models, i. e. the Langmuir, Tóth, generalized Dubinin-Astakhov (D-A), Dubinin-Astakhov based on pore size distribution (PSD) and Dubinin-Serpinski (D-Se) isotherm for the whole pressure range, and for a pressure range below 10 kPa, proper for desalination cycles; isotherms type V of the International Union of Pure and Applied Chemistry (IUPAC) classification were exhibited. It is observed that the D-A based on PSD and the D-Se isotherm models describe the best fitting of the experimental uptake data for desalination cycles within a regression error of 2% and 6% respectively. All isotherm models, except the D-A based on PSD, have failed to describe the obtained experimental uptake data; an empirical isotherm model is proposed by observing the behavior of Tóth and D-A isotherm models. The new empirical model describes the water adsorption onto silica gel type A++ within a regression error of 3%. This will aid to describe the advantages of silica gel type A++ for the design of adsorption desalination processes where reducing capital cost and footprint area are highly important parameters to take into account.

Seawater desalination plays an important role when fighting the freshwater scarcity that many places around the world are currently facing. The increasing need for desalinated water is followed by a high energy demand. It is therefore essential that an expansion of desalination capacity is accompanied by a parallel use of renewable energy sources in this process. This thesis presents a techno-economic study on a reverse osmosis (RO) desalination plant, with a nominal power consumption of 15 MW, that is powered by a concentrated solar power (CSP) plant combined with a photovoltaic (PV) power plant, in Kuwait. The main aim of this thesis was to find which system designs would give the lowest global warming potential and levelized cost of the desalinated water. In addition, it has been investigated how electricity price and emission allowance cost could make a solar power plant competitive to the grid. For this purpose, some components in the whole system were simulated using System Advisor Model and Engineering Equation Solver. With the results obtained from the simulations, a dynamic model of the whole system was developed in MATLAB, Simulink where simulations were done for a typical meteorological year in Shagaya, Kuwait. Both on-grid and off-grid systems were considered.   In the on-grid case, the lowest cost of water was obtained with only PV (ca 0.65 USD/m3) and this could reduce carbon emissions by 30 % compared to only using the grid. Combining CSP and PV could reduce the carbon emissions by 85 % but with a 35 % increase in water cost. It was found that an electricity price of 0.1 USD/kWh or an emission allowance cost of 70 USD/tCO2-eq would make a CSP + PV plant competitive to the grid. These results indicate that the choice of which system is best for powering an on-grid RO plant depends on how the environmental and economic factors are prioritised. In the case of the off-grid system, both the lowest cost of water (ca 0.9 USD/m3) and the highest capacity factor were obtained with a CSP + PV plant with 16 h of storage, a solar multiple of 3 and a PV capacity of 28 MW.

Judicious modeling of an energy system can help provide insights as to how elements of the energy system might be configured in the longer term. The current and future electricity and water desalination systems of each GCC country were represented using a full-cost based optimization tool called MESSAGE and the following scenarios were examined: 1. The business as usual scenario (BAU): current energy system is extended into the future without any changes. The energy system structure and characteristics are kept the same. The fuel prices are also kept at the current subsidized levels. 2 - The netback-pricing scenario: all fuel costs are increased to the international market price. The freed amount of fuel is assumed to be available for export to the international market. Moreover, this scenario examines different carbon tax options of 0, 20,30 ,40 and 50 dollars per kilo tons of CO2 emissions. 3 - The Nuclear hub scenario: examines the idea of a “nuclear hub” state for the GCC region that can have all the “know-how” and logistics to provide sufficient nuclear energy for the GCC through the Interconnection Grid “GCCIG”. Results shows that fossil fuels will continue to play an important role in a least cost future for the region. This is due, in no small part, to the cheap natural gas resources in the GCC. Despite the high renewable energy technologies potential, their penetration – given the study assumptions - proved to be important, but limited in the GCC. On the other hand, nuclear energy shows clear economic potential.

The island of Malta is highly reliant on fossil fuels for its power (99%), and due to climate mitigation policies implemented by EU the Maltese government is required to have 10% of its power generation from renewables by 2020. To achieve these energy goals, the Maltese government has expressed interest in investing on a Hexicon platform to produce 9% of the Maltese energy demand. The Hexicon platform is a floating structure capable of carrying a wide range of renewable energy generators. The Hexicon platform proposed for Malta is meant to have a rated capacity of 54MW distributed by vertical and horizontal wind energy converters. Nevertheless, due to the irregular nature of wind the Hexicon platform would still use diesel generators on-board as backup power; this inherently defeats the purpose of the Maltese investment, and therefore a Hydrogen backup system was proposed and investigated for its technical and economic viability. A literature study was carried out on renewable hydrogen system in order to familiarise with the type of markets and the best way to apply the technology to the scenario at hand. Four markets were established, small-scale, transportation, stand-alone power systems, and large buffering systems; the large buffering system is the most appropriate for the study, and taking this type of system into account, the most appropriate hydrogen generation and utilisation system were then identified. It was established that the system is composed of three parts, electrolyser, storage tanks and fuel cells stacks. However, an additional water purification system is necessary; this is due to the fact that the Hexicon platform will be located offshore, and salt water is not appropriate for the electrolyser. A literature study was then performed to identify the most appropriate equipment for each stage of the process; it was established that a Reverse Osmosis (RO) system will be used to purify the water, an alkaline electrolyser will be used to generate the Hydrogen, the Hydrogen will then be stored in pressure vessels (at 30bar), thus also requiring compressors, and the recovery of energy will be performed by a proton exchange membrane (PEM) fuel cell (FC) stack. A study was carried out to establish the models to use for each equipment, and based on the hourly demand for Malta, as well as the hourly winds, a first estimate of the size of each equipment was established. The system model was developed in the HOMER software, which unfortunately did not model the desalination plant. The Hexicon (in the design considered in this study) is not able to provide Malta with 9% of the energy demand; this was mainly due to the low wind conditions. In addition to this, it was understood from the literature study that a hydrogen system backup system, i.e. a buffering system, would not be applicable to the scenario initially proposed in this thesis due to the low renewable energy penetration, and also due to the fact that the Hexicon would be connected to the grid, rendering such a system defunct. A micro-grid scenario was assumed and developed. This scenario tried to assess how low the demand would need to be in order to make a hydrogen project feasible. Different percentages were tried and the only one that met the constraints was one with 1.1% of the Maltese demand. The system would consist of a 3MW Fuel Cell, a 4.5MW electrolyser, and hydrogen storage for 10.5tonnes. The NPC of this system would be approx. 130 Million €, with an initial investment of approx. 71 Million €, LCOE of 0.257€.kWh-1, and a Hydrogen cost of approx. 20€.kg-1. While other economic indicators show viability, for example, a short payback time of 3.5 years based on the revenue from the excess electricity, the cost of hydrogen suggests that it is too expensive.

Microbial fuel cell (MFC) has become one of the energy-sustainable technologies for wastewater treatment purpose in the recent years. It combines wastewater treatment and electricity generation together so as to achieve energy balance. By inoculating microorganism in the anode chamber and filling catholyte in the cathode chamber, and also with the help of a proton exchange membrane (PEM) between them, the MFC can transfer protons and produce power. Microbial desalination cells (MDC) are based on MFC’s structure and can fulfill desalination function by the addition of a middle chamber and anion exchange membrane (AEM). This study focuses on ammonium removal and electricity generation in MDC system. Mainly two types of liquid were tested, a solution of Hjorthorn Salt and filtrated supernatant. The experiments were performed at Hammarby Sjöstad research station and laboratory of Land and Water Resources department, Stockholm. It consists of a preparation stage, a MFC stage and a MDC stage. Until the end of MFC stage, biofilm in the anode chamber had been formed and matured. After that, solutions of different initial concentrations (1.5, 2.5, 5, 15 g/L) of Hjorthorn Salt and also filtrated supernatant have been tested. Ammonium removal degree can be obtained by measuring the initial concentration and cycle end concentration, while electricity generation ability can be calculated by voltage data which was continuously recorded by a multimeter. Results showed that this MDC system is suitable for ammonium removal in both of Hjorthorn Salt solutions and supernatant. The removal degrees in Hjorthorn Salt solution at desalination chamber were 53.1%, 52.7%, 60.34%, and 27.25% corresponding to initial NH4+ concentration of 340.7, 376, 376 and 2220 mg/L. The ammonium removal degrees in the supernatant were up to 53.4% and 43.7% under 21 and 71 hours operation, respectively. In power production aspect, MDC produced maximum voltage when potassium permanganate was used in the cathode chamber (217 mV). The power density in solutions of Hjorthorn Salt was relative low (46.73 - 86.61 mW/m3), but in the supernatant it showed a good performance, up to 227.7 and 190.8 mW/m3.

The drinking water plant in this case study is a combined groundwater and reverse osmosisplant in the Stockholm archipelago. The reverse osmosis purification step was added to theplant in 1995. This technique is relatively new in Sweden and there are possibilities for it tobecome a good complement to conventional drinking water treatment. The plant has used thistechnique for over 10 years with good results. It is therefore of great interest to evaluate anddocument it for the possibility to implement this technique in areas not connected toconventional drinking water production.Reverse osmosis separates the incoming water to a clean permeate and concentrate ofremoved particles, larger molecules and ions. This technique has a high purification degree. Itcan remove dissolved particles and microorganisms without disinfection. However, it isrelatively expensive due to a high electricity consumption compared to conventional drinkingwater treatment. The high electricity consumption in this kind of system depends on aphenomenon called membrane fouling caused by the constituents in the raw water, graduallybecoming enriched on the membrane surface.The aim of this thesis was to evaluate and document a drinking water plant in the Stockholmarchipelago from a social, economical, technical and environmental perspective. A socialsurvey in the form of a questionnaire was conducted to reveal opinions about the water qualityprovided by the plant. The economical evaluation was done to estimate the cost of drinkingwater production and find the water cost in Kr/m3. The technical part involved documentationof the plant layout and evaluation of its performance. To assess the performance historicalchemical and microbial analyses were evaluated. A mass balance was attempted to drawconclusions for the overall system. The environmental part of the plant assessment, includedan estimate of the electricity and chemicals use in the plant.The results revealed that from an overall perspective the water quality from the plant issatisfactory with some concerns about metal taste and turbidity that sometimes occur. Thepotential presence of dangerous algal toxins in the water was also a concern. The totalproduction cost in Kr/m3 is higher than expected and higher than sales price. In technicalterms, the plant has functioned well. However, there is a need to monitor more parameters inthe plant including; more flow parameters, concentrations of added chemicals and more waterquality parameters. Electricity consumption has been higher than expected. Control(throttling) valves in the brine reject are relatively large energy consumers and arecommendation is to investigate potential savings by changing them for pressure exchangevalves. / www.ima.kth.se

The development of sustainable and practical technologies is essential for the continuation of civilization. Two problems that are particularly imperative for society to resolve are 1) water insecurity and 2) antimicrobial resistance. Water insecurity may be alleviated with desalination technologies, however, desalination is prone to a membrane fouling that hinders its practicality for low-resource contexts. The two primary types of membrane fouling are scaling -- mineral precipitation and deposition upon the membrane -- and biofouling -- microbial colonization of the polymeric filtration membrane. The treatment of biofouling with antibiotics is intertwined with the antimicrobial resistance (AMR) crisis, where AMR infections are projected to exceed cancer in annual deaths by the mid-21st century. The AMR crisis may be mitigated through photodynamic inactivation (PDI), which uses reactive oxygen species (ROSs) to non-selectively oxidize and kill pathogens sufficiently fast to avoid adaptive mechanisms that result in AMR. The innumerable possible combinations of control and experimental variables in studies of membrane fouling and PDI are unlikely to be completely explored experimentally, where resource limitations restrain experimentation. This Thesis, therefore, developed models and Python application programming interfaces (APIs) that can 1) explore continuums of parameter values and 2) predict the efficacy of desalination or PDI systems. These open-source Python modules may expedite the development of practical technologies that resolve water insecurity and stymie antibiotic resistant epidemics, thereby improving the likelihood of a long-lived civilization far into the future. / Graduate / 2023-04-05

This dissertation introduces desalination processes in general and multistage flash (MSF) and reverse osmosis (RO) in particular. It presents the fundamental and practical aspects of neural networks and provides an overview of their structures, topology, strengths, and limitations. This study includes the neural network applications to prediction problems of large-scale commercial MSF and RO desalination plants in conjunction with statistical techniques to identify the major independent variables to optimize the process performance. In contrast to several recent studies, this work utilizes actual operating data (not simulated) from a large-scale commercial MSF desalination plant (48 million gallonsper day capacity, MGPD) and RO plant (15 MGPD) located in Kuwait and the Kingdom of Saudi Arabia, respectively. We apply Neural Works Professional II/Plus (NeuralWare, 1993) and SAS (SAS Institute Inc., 1996) software to accomplish this task. This dissertation demonstrates how to apply modular and equation-solving approaches for steady-state and dynamic simulations of large-scale commercial MSF desalination plants using ASPEN PLUS (Advanced System for Process Engineering PLUS) and SPEEDUP (Simulation Program for Evaluation and Evolutionary Design of Unsteady Processes) marketed by Aspen Technology, Cambridge, MA. This work illustrates the development of an optimal operating envelope for achieving a stable operation of a commercial MSF desalination plant using the SPEEDUP model. We then discuss model linearization around nominal operating conditions and arrive at pairing schemes for manipulated and controlled variables by interaction analysis. Finally, this dissertation describes our experience in applying a commercial software, DynaPLUS, for combined steady-state and dynamic simulations of a commercial MSF desalination plant. This dissertation is unique and significant in that it reports the first comprehensive study of predictive modeling, simulation, and optimization of large-scale commercial desalination plants. It is the first detailed and comparative study of commercial desalination plants using both artificial intelligence and computer-aided design techniques. The resulting models are able to reproduce accurately the actual operating data and to predict the optimal operating conditions of commercial desalination plants. / Ph. D.

Membrane-based filtration technologies have seen rapid inclusion in a variety of industrial processes, especially production of drinking water by desalination. Biological fouling of membranes is a challenge that leads to increased costs from efficiency reductions, membrane damage, and ultimately, membrane replacement over time. Such costs can be mitigated by monitoring and optimizing cleaning processes for better prognosis. A fluorescence-based sensor for early biofouling detection capable of measuring extracellular enzyme activity was developed. The selected fluorogen and fluorogen-substrate were characterized and down selected by in vitro screening for compatibility in seawater and profiled over relevant Red Sea desalination parameters (pH and temperature). ATP measurements are currently regarded as start-of-the-art when assessing biomass accumulation in membrane-based filtration systems Therefore, the fluorescence sensor response was measured for a range of bacterial concentrations and validated using an ATP assay. We demonstrate the efficacy of the proposed approach for the quantitative assessment of bacteria activity in seawater rapidly and sensitively. Following in vitro testing, the method was employed in a lab-scale seawater reverse osmosis (SWRO) system for suitability in monitoring biofouling formation. The sensor successfully measured bacterial biomass accumulation rapidly and non-invasively using exogenously applied fluorogen-substrates. The sensor response was corroborated with real-time in situ non-destructive imaging of the membrane surface. This approach demonstrates the practicality of prototyping an early-detection biofouling sensor in membrane based processes using extracellular enzyme activity as a measure of bacterial abundance.