<p>Renewable energy adoption is critical when considering future energy grids and how they impact the environment, economy and society. While fossil fuels have traditionally been employed to generate the electricity used across every facet of the global economy, renewables are becoming increasingly more attractive as a substitute. Fossil fuels have historically outperformed their clean energy counterparts in terms of levelized cost. However, over the last few decades renewables have become extremely cost competitive and are starting to outpace their opposition as advancements in technology continue. As the cost gap between “brown” and “green” energy sources decreases, energy grid mixes will adopt more sustainably responsible generation, positively impacting the planet.</p> <p>In the following thesis, two studies are presented which demonstrate new innovations for decreasing the cost of offshore wind energy and how renewables and desalination can be integrated along the US-Mexico border. The first study describes an itemized breakdown of how substituting the mechanical transmission with hydraulics can lower the life-time cost of an offshore wind turbine. The second analysis details a complex wind and solar powered clean water production and distribution network to combat ongoing water scarcity along the US-Mexico border. Both concepts push the boundaries of scientific innovation and its application for solving social and economic issues. </p>

The ability to economically desalinate seawater in arid regions of the world has become a vital advancement to overcome the problem on freshwater availability, quality, and reliability. In contrast with the major capital and operational costs for desalination plants represented by conventional open ocean intakes, subsurface intakes allow the extraction of high quality feed water at minimum costs and reduced environmental impact. A seabed filter is a subsurface intake that consists of a submerged slow sand filter, with benefits of organic matter removal and pathogens, and low operational cost. A site investigation was carried out through the southern coast of the Red Sea in Saudi Arabia, from King Abdullah University of Science and Technology down to 370 kilometers south of Jeddah. A site adjacent to the Shoaiba desalination plant was selected to assess the viability of constructing a seabed filter. Grain sieve size analysis, porosity and hydraulic conductivity permeameter measurements were performed on the collected sediment samples. Based on these results, it was concluded that the characteristics at the Shoaiba site allow for the construction of a seabed filtration system. A seabed filter design is proposed for the 150,000 m3/d Shoaiba III expansion project, a large-scale Reverse Osmosis desalination plant. A filter design with a filtration rate of 7 m/d through an area of 6,000 m2 is proposed to meet the demand of one of the ten desalination trains operating at the plant. The filter would be located 90 meters offshore where hydraulic conductivity of the sediment is high, and mud percentage is minimal. The thin native marine sediment layer is insufficient to provide enough water filtration, and consequently the proposed solution involves excavating the limestone rock and filling it with different layers of non-native sand and gravel of increasing grain size. An initial assessment of the area around Shoaiba showed similar sedimentological conditions that could lead into the application of comparable seabed filter design concepts to supply the entire feed water requirement of the plant. Considerations for the construction of a seabed filter should include technical feasibility and life cycle assessment, i.e. capital costs, operating costs and environmental impacts.

Freshwater scarcity and clean energy shortage are two grand challenges to global sustainable development. The inextricably interconnected water-energy nexus is being increasingly felt globally owing to the massive water used for electricity generation and huge amount of energy consumed in water desalination. This dissertation investigated the utilization of the waste heat of the solar cell to produce fresh water. This is achieved by constructing a multistage membrane distillation device (MSMD) at the backside of the solar cell to efficiently utilize its heat and it is capable of recycling the latent heat of the vapor condensation in each distillation stage. The first generation photovoltaic-membrane distillation (PV-MD) device exhibits a clean water production rate of 1.64 kg/m2 h with the solar cell temperature of 58 oC in a 3-stage device under one-sun radiation. However, some concentrated seawater can be produced from the PV-MD owing to its cross-flow design. To this end, an evaporative crystallizer is designed beneath the PV-MD, which can reuse the low-grade latent heat of vapor condensation in the last stage of the MSMD to evaporate the produced concentrated seawater, realizing zero liquid discharge. In addition, a theoretical model was also established to enhance the clean water production rate and reduce the solar cell temperature, which guides us to select a hydrophobic membrane with a thickness of 0.1 mm and porosity of 0.86 to fabricate the second generation photovoltaic-membrane distillation-evaporative crystallizer (PV-MD-EC) device. We experimentally demonstrate that a 5-stage PV-MD-EC device can desalinate seawater at a rate of ~2.45 kg m-2 h-1 with a lower solar cell temperature of ~48oC. The electricity generation efficiency of the solar cell is also enhanced by ~8% owing to its reduced temperature. A trade-off exists between the clean water production performance and material cost of the MSMD because a higher energy efficiency is at the expense of more stages applied. A low-cost and highly flexible 8-stage paper-based MSMD (P-MSMD) is further designed and fabricated and it showed a clean water production rate of 3.61 kg/m2 h for seawater desalination. This work sheds light on the design and fabrication of a composite system capable of achieving the simultaneous production of electricity and clean water with solar energy as an only energy source. Owing to their low barrier of entry, the devices reported in this dissertation are well suited to provide off-grid electricity and freshwater in a decentralized manner for point of consumption locations especially off-grid communities and communities with small- to medium-sized population even with challenging economic conditions.

Water samples were taken at the KAUST RO plant, the WDRC pilot plant and three other full-scale desalination installations in Saudi Arabia. The water was characterized using selected microbiological parameters, being conventional (heterotopic place count (HPC), total coliforms, Escherichia coli) and more novel and sensitive methods (adenosine tri-phosphate (ATP, a measure for bacterial activity), as well as total and intact bacterial cell concentrations (TDC using flow cytometry) and supporting parameters (pH, conductivity, residual chlorine and temperature). Selective samples were used to quantify the bacterial growth potential (“food for the bacteria”), applying a flow cytometer based easily Assimilable Organic Carbon (AOC) assay. Hypothesized was that no or very low bacterial numbers would occur after RO filtration in the plants due to the high rejection properties of the RO membranes and the produced water exceptionally low mineral and nutrient content. Key findings are that the (i) RO permeate contains bacterial cell concentrations exceeding 1.0 × 103 cells/mL. The highest percentage of cells are intact and active, based on the ATP and total cell counts (ii) advanced microbial parameters ATP and TDC enabled to detect and quantify bacteria numbers and activity while the less sensitive conventional plate counts based techniques did not, (iii) flow cytometer-based growth potential measurements indicate the presence of 8 µg AOC/L in the RO permeate. A typical last step in drinking water production is chlorination, effectively inactivating all the bacterial cells. The origin of the bacterial cells and the biodegradable nutrients enabling the bacterial growth in the RO permeate is not clear. There is a clear need to assess the origin of the nutrients and bacteria found in the RO produced water. It is not expected to be passing the RO membrane.

Nanofiltration and seawater reverse osmosis desalination are still considered energy-intensive processes. Seawater desalination can be 25 times more energy-intensive compared to conventional water treatment processes. Biofouling is a significant problem in achieving sustainable desalination, as it increases the energy demands and the overall water cost. Limiting the biodegradable substrate concentration in the feed water is proposed as a suitable approach to control biofouling in desalination membranes. Until now, nutrient manipulation studies have not fully elucidated to which extent this technique affects biofilm morphology and if the manipulated biofilms are easier to control and remove with a chemical-free approach. The main objective of this Ph.D. study is to provide a comprehensive assessment of the effect of nutrient manipulation on the physical properties of the developed biofilm to decrease the impact of biofouling on system performance and enhance the cleanability of biofilms in membrane systems. The aspects of the study included biofilm development and related system performance under varying feed water biodegradable carbon and phosphorous concentrations and the impact of permeation. The results of this study indicate that lowering the assimilable organic carbon and phosphorus concentration in the feed water controls biofilm formation and prolongs membrane system performance. A strategy of enhancing the hydraulic cleanability of biofilms in RO systems could involve avoiding the increase of the phosphorus concentration by eliminating the use of phosphonate-based antiscalants. The higher detachment for biofilms grown at a lower phosphorus concentration was explained by more soluble polymers in the EPS, resulting in a lower biofilm cohesive and adhesive strength. We demonstrated that the phosphorus concentration in the feed water affected the microbial and EPS composition. A homogenous bacterial community composition was found over the biofilm height. Permeation played a role in shaping biofilm localization, and therefore, the observed impact on the system performance parameters. This Ph.D. dissertation represents an exciting advance towards greener desalination by controlling and enhancing the cleanability of biofilms through feed water nutrient manipulation.

The global demand for potable water has increase the use of chemicals to clean or prevent undesirable biofouling in reverse osmosis membranes. Biofouling is the growth and accumulation of biomass that generates an unacceptable performance decline. To date, a thoroughly efficient and green method to remove, prevent or treat biofouling in water treatment systems has not been developed. The studies carried out during my Ph.D. aim to develop greener and more efficient biofuling prevention/cleaning methods. The first two studies introduce a polyelectrolyte coating with the atypical characteristic of being removed and reapplied under operating conditions. After the biofilm develops on the coating, both biomass and coating can be removed with brine. The application of the coating can be done in-situ without hindering membrane performance. Using this procedure, both biofilm and coating could be simultaneously removed, leaving a clean surface. The biofouled coated membrane had two-fold higher permeate flux recovery compare to the non-coated. The sacrificial polyelectrolyte coating offers a greener solution for biofouling treatment in membrane systems. As an alternative to harsh chemicals, natural deep eutectic solvents (NADES) are presented as an alternative for biofilm treatment. Our results indicate that the NADES could solubilize up to ≈70% of the main components of the biofilm. The biofilm is weakened by the biomolecule’s solubilization, which could enhance biofilm removal. NADES have a great potential to be used for biofilm and avoid the currently used solvents. The last chapter is focused on understanding the structural characteristics and stability of NADES composed of betaine, urea, and water. The NADES composition and the water content is of significant relevance for its stability and supramolecular structure. Our experimental and computational results show that water is of crucial importance to the NADES supramolecular structure and stability. Understanding the NADES characteristics leads to finding better applications and giving insights into the interaction that these solvents have with other molecules, such as biopolymers or proteins. Even though there is still further research to be done, the studies presented on this thesis are a step forward towards finding and understanding greener solutions for biofilm treatment in water treatment systems.

Reverse osmosis (RO) and nanofiltration (NF) membrane systems are high-pressure membrane filtration processes that can produce high quality drinking water. Biofouling, biofilm formation that exceeds a certain threshold, is a major problem in spiral wound RO and NF membrane systems resulting in a decline in membrane performance, produced water quality, and quantity. In practice, detection of biofouling is typically done indirectly through measurements of performance decline. Existing direct biofouling detection methods are mainly destructive, such as membrane autopsies, where biofilm samples can be contaminated, damaged and resulting in biofilm structural changes. The objective of this study was to test whether transparent luminescent planar oxygen sensing optodes, in combination with a simple imaging system, can be used for in-situ, non-destructive biofouling characterization. Aspects of the study were early detection of biofouling, biofilm spatial patterning in spacer filled channels, and the effect of feed cross-flow velocity, and feed flow temperature. Oxygen sensing optode imaging was found suitable for studying biofilm processes and gave detailed spatial and quantitative biofilm development information enabling better understanding of the biofouling development process. The outcome of this study attests the importance of in-situ, non-destructive imaging in acquiring detailed knowledge on biofilm development in membrane systems contributing to the development of effective biofouling control strategies.

High-quality drinking water can be produced with membrane-based filtration processes like reverse osmosis and nanofiltration. One of the major problems in these membrane systems is biofouling that reduces the membrane performance, increasing operational costs. Current biofouling control strategies such as pre-treatment, membrane modification, and chemical cleaning are not sufficient in all cases. Feed spacers are thin (0.8 mm), complex geometry meshes that separate membranes in a module. The main objective of this research was to evaluate whether feed spacer modification is a suitable strategy to control biofouling. Membrane fouling simulator studies with six feed spacers showed differences in biofouled spacer performance, concluding that (i) spacer geometry influences biofouling impact and (ii) biofouling studies are essential for evaluation of spacer biofouling impact. Computed tomography (CT) was found as a suitable technique to obtain three-dimensional (3D) measurements of spacers, enabling more representative mathematical modeling of hydraulic behavior of spacers in membrane systems. A strategy for developing, characterizing, and testing of spacers by numerical modeling, 3D printing of spacers and experimental membrane fouling simulator studies was developed. The combination of modeling and experimental testing of 3D printed spacers is a promising strategy to develop advanced spacers aiming to reduce the impact of biofilm formation on membrane performance and to improve the cleanability of spiral-wound membrane systems.

Philosophiae Doctor - PhD / The disposal of brine effluent from inland wastewater desalination plants is a growing global problem with adverse economic and environmental implications because of the substantial cost associated with its disposal and the potential for polluting groundwater resources. Currently, the best and most economical option for brine disposal from inland desalination plants is the use of evaporation ponds, which concentrate the liquid until getting a solid waste that can be valued or directly managed by an authorized company. The effectiveness of these ponds is therefore dependent on the evaporation rate, which has previously been improved by the addition of dyes such as methylene blue. However, the addition of chemical dyes to the evaporation ponds poses a threat to the environment, wildlife, and humans.

The goal of this study was to evaluate the feasibility of using advanced coagulation with Fe(VI) in coagulation-flocculation-sedimentation/ flotation systems for the pretreatment of SWRO desalination plants during algal bloom events. Algal organic matter (AOM) material extracted from marine diatom species (Chaetoceros affinis) was added to Red Sea water to mimic algal bloom conditions. Low dosage of Fe(VI) (<1 mg Fe/L) was very effective at improving feed water quality containing AOM (algal bloom conditions). Based on results from both a bench-scale DAF unit and Jar testing unit, 0.75 mg Fe/L of Fe (VI) proved to be effective at improving the raw water quality which is comparable to the performance of 1 and 3 mg Fe/L of Fe (III). The removal efficiency for both testing units with the use of Fe(VI) was up to 100% for algae , 99.99% for ATP, 99% for biopolymers and 70 % for DOC. The improvement in Fe(VI) performance is related to the simultaneous action of Fe(VI) as oxidant, disinfectant and coagulant. The performance of Fe(VI) coagulant was also evaluated with the use of coagulant aids (clays). The overall turbidity, DOC, biopolymers and algal cells removal was improved via using Fe(VI) and clays at very low dose. Generally, it was found that for the same pretreatment performance achieved, a much lower Fe(VI) dose was required compared to Fe (III), which make it important to study of cost effectiveness for using Fe(VI) instead of Fe(III) and estimate cost savings during algal bloom conditions. A detailed cost comparative study was conducted for Fe(III) vs. Fe(VI) coagulation process based on the removal efficiency. The use of Fe(VI) reduced the total pretreatment cost by 77% and sludge disposal cost by > 88% compared to the use of Fe(III) in the pretreatment process. The use of Fe(VI) reduces the operational and maintenance cost in SWRO desalination plant by 7% and the production cost by 4%. This study proved that the use of Fe(VI) during high turgidity and algal bloom conditions helped providing high raw water quality to the RO process with lower chemicals and operations cost as well as low chlorine and iron residuals.