abstract: With the application of reverse osmosis (RO) membranes in the wastewater treatment and seawater desalination, the limitation of flux and fouling problems of RO have gained more attention from researchers. Because of the tunable structure and physicochemical properties of nanomaterials, it is a suitable material that can be used to incorporate with RO to change the membrane performances. Silver is biocidal, which has been used in a variety of consumer products. Recent studies showed that fabricating silver nanoparticles (AgNPs) on membrane surfaces can mitigate the biofouling problem on the membrane. Studies have shown that Ag released from the membrane in the form of either Ag ions or AgNP will accelerate the antimicrobial activity of the membrane. However, the silver release from the membrane will lower the silver loading on the membrane, which will eventually shorten the antimicrobial activity lifetime of the membrane. Therefore, the silver leaching amount is a crucial parameter that needs to be determined for every type of Ag composite membrane. This study is attempting to compare four different silver leaching test methods, to study the silver leaching potential of the silver impregnated membranes, conducting the advantages and disadvantages of the leaching methods. An In-situ reduction Ag loaded RO membrane was examined in this study. A custom waterjet test was established to create a high-velocity water flow to test the silver leaching from the nanocomposite membrane in a relative extreme environment. The batch leaching test was examined as the most common leaching test method for the silver composite membrane. The cross-flow filtration and dead-end test were also examined to compare the silver leaching amounts. The silver coated membrane used in this experiment has an initial silver loading of 2.0± 0.51 ug/cm2. The mass balance was conducted for all of the leaching tests. For the batch test, water jet test, and dead-end filtration, the mass balances are all within 100±25%, which is acceptable in this experiment because of the variance of the initial silver loading on the membranes. A bad silver mass balance was observed at cross-flow filtration. Both of AgNP and Ag ions leached in the solution was examined in this experiment. The concentration of total silver leaching into solutions from the four leaching tests are all below the Secondary Drinking Water Standard for silver which is 100 ppb. The cross-flow test is the most aggressive leaching method, which has more than 80% of silver leached from the membrane after 50 hours of the test. The water jet (54 ± 6.9% of silver remaining) can cause higher silver leaching than batch test (85 ± 1.2% of silver remaining) in one-hour, and it can also cause both AgNP and Ag ions leaching from the membrane, which is closer to the leaching condition in the cross-flow test. / Dissertation/Thesis / Masters Thesis Civil, Environmental and Sustainable Engineering 2017

abstract: Drinking water filtration using reverse osmosis (RO) membranes effectively removes salts and most other inorganic, organic, and microbial pollutants. RO technologies are utilized at both the municipal and residential scale. The formation of biofilms on RO membranes reduces water flux and increases energy consumption. The research conducted for this thesis involves In-Situ coating of silver, a known biocide, on the surface of RO membranes. This research was adapted from a protocol developed for coating flat sheet membranes with silver nanoparticles, and scaled up into spiral-wound membranes that are commonly used at the residential scale in point-of-use (POU) filtration systems. Performance analyses of the silver-coated spiral-wound were conducted in a mobile drinking water treatment system fitted with two POU units for comparison. Five month-long analyses were performed, including a deployment of the mobile system. In addition to flux, salt rejection, and other water quality analyses, additional membrane characterization tests were conducted on pristine and silver-coated membranes. For flat sheet membranes coated with silver, the surface charge remained negative and contact angle remained below 90. Scaling up to spiral-wound RO membrane configuration was successful, with an average silver-loading of 1.93 g-Ag/cm2. Results showed the flux of water through the membrane ranged from 8 to 13 liters/m2*hr. (LMH) operating at 25% recovery during long-term of operation. The flux was initially decreased due to the silver coating, but no statistically significant differences were observed after 14 days of operation (P < 0.05). The salt rejection was also not effected due to the silver coating (P < 0.05). While 98% of silver was released during long-term studies, the silver release from the spiral-wound membrane was consistently below the secondary MCL of 100 ppb established by the EPA, and was consistently below 5 ppb after two hours of operation. Microbial assays in the form of heterotrophic plate counts suggested there was no statistically significant difference in the prevention of biofouling formation due to the silver coating (P < 0.05). In addition to performance tests and membrane characterizations, a remote data acquisition system was configured to remotely monitor performance and water quality parameters in the mobile system. / Dissertation/Thesis / Masters Thesis Engineering 2017

L’objectif de cette thèse est de mettre en évidence le comportement à l’échelle microscopique des composés organiques au cours des procédés de traitement de mélanges complexes, en particulier les procédés membranaires. Pour cela des outils expérimentaux et de modélisation ont été mis au point. Les méthodes de caractérisation expérimentale des mélanges complexes et de l’état de surface des solides utilisés sont entre autres la construction d’isothermes d’adsorption et la mesure des tensions interfaciales par la méthode de la goutte posée. Le cas étudié ici est celui de la filtration de solutions modèles de tensioactifs par osmose inverse. Nous avons montré que le comportement des composés organiques (tensioactifs) influence la performance du procédé membranaire et les propriétés de membranes. L’outil de simulation du comportement des composés en phase liquide et à l’interface liquide-solide permettant une description à une échelle plus fine que celle atteignable expérimentalement est la DPD (Dissipative Particle Dynamics). Une première étape a permis de simuler l’agrégation des tensioactifs en solution et de retrouver les valeurs expérimentales des concentrations micellaires critiques et nombres d’agrégation de tensioactifs anioniques. L’étude de l’adsorption des tensioactifs sur une membrane d’osmose inverse a été initiée, avec pour objectif de mettre en évidence l’organisation des composés à l’échelle locale. L’apport des outils développés a été démontré et leur utilisation pourra être approfondie dans des travaux ultérieurs. / The aim of this work is a better understanding of the microscopic behavior of organic matters during the wastewater treatment of complex mixtures, especially during the membrane processes. Both experimental and simulation methods were developed in this work. Experimentally, adsorption isotherms were built to study the adsorption of organic matters on the membrane surface during the filtration. The sessile drop measurement allowed investigating the surface properties (interfacial tensions) of the membrane. After the filtration of surfactants by reverse osmosis (RO), we found that the surfactants played an important role in the performance and the surface properties of the RO membrane. The DPD (Dissipative Particle Dynamics) simulation method was used to model the behavior of anionic surfactants in solution and at the solid/liquid interface from a more detailed aspect than experiments. Firstly, the micellization of three anionic surfactants in aqueous solution was simulated and the model was validated by comparing the equilibrium properties (the critical micelle concentration and aggregation number) of micelle solutions obtained from simulation to the experimental values in literature. Then the model was extended to simulate the adsorption of surfactants on the RO membrane. The construction of a system with a membrane was initiated, and the study on the organizations of surfactants at the membrane surface opens a door to further active research.

This study investigates the desalination needs and available technologies in Sri Lanka. Lack of rainfall, pollution due to agricultural chemicals, presence of fluoride, increasing demand, exploitation of ground water and brackishness have created scarcity of fresh pure water specially in near costal and dry zones in Sri Lanka. Due to Cronic Kidney Disease (CKD) around 500 people died in dry zones annually which is suspected to cause by Arsenic and Cadmium contain in ground water due to agriculture chemicals.   The available desalination methods are Reverse Osmosis (RO), Solar distillation and conventional methods. The cost for RO is Rs.0.10 cents per liter and solar distillation Rs.2.96 per liter. Although the price shows that the RO is better but due to high initial investment as a third world country it is very difficult to afford huge initial investment without government intervention. The experimental solar desalination units only produce nearly 5liters of potable water per day and directly impacted by availability of solar radiation. The energy availability of Sri Lanka and future potable water demand predicted as 2188.3 Mn liters as maximum demand which will be in 2030, therefore by that time the government should have a proper plan to cater the demand and desalination plants need to be planned and built based on the demand of dry zones and specially agriculture areas.   The applicability of renewable energy for desalination in local arena was also simulated taking the Delf Reverse Osmosis plant for the simulation. Results show that the optimum design is combination of Solar PV and existing 100kW Diesel generator Set with Battery bank and converter.

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 diploma thesis deals with the application of membrane processes for the treatment of washing water from sand filters of pool technology to parameters suitable for its reuse, not only on a theoretical level, but also on a real example. The experimental part deals with the monitoring of relevant parameters given by Decree no. 568/2000 Sb. and other technologically significant water quality indicators. All monitored parameters in the reverse osmosis permeate reached satisfactory values and thus it was concluded that the effluent water is suitable for reuse. Instead of being discharged into the sewer, it is possible to recycle 70 to 80 % of the washed water per day thanks to the applied technology, which saves approximately 20 m3 of water per day.

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.