Ceramic nanofiltration (NF) membranes are emerging as a reliable solution for advanced wastewater treatment, owing to their robustness, high chemical and thermal resistance, and high fouling resistance compared to the polymeric alternatives. These membranes, typically composed of metal oxides such as titania (TiO₂) and alumina (Al₂O₃), therefore offer advantages in rejecting organic compounds, oil, and colloidal particles..... ... Read more

Membranes are widely recognized as promising technologies for addressing the growing demand for freshwater driven by rapid population growth and industrialization. Ceramic membranes, in particular, offer advantages such as high mechanical strength, chemical resistance, and long lifespan compared to polymeric membranes. However, permeability loss during filtration is one of the challenges. The specific contributions of concentration polarization (CP) and fouling to this decline remain insufficiently understood. Fouling is a major obstacle in ceramic membrane operation, and the removal of organic micropollutants (OMPs)—increasingly detected in different water bodies—poses an additional challenge due to the relatively large pore sizes of ceramic membranes, being mostly in the range of microfiltration and ultrafiltration (UF). To address these challenges, various modification strategies have been developed to improve membrane performance in water treatment. One promising approach is to modify ceramic membranes with catalysts, enabling them to perform both separation and catalytic functions. However, currently, developed catalytic ceramic membranes often suffer from severe flux decline after deposition, especially when coated with a dense or thick coating. In addition, catalytic membranes coupled with advanced oxidation processes (AOPs) have typically been achieved by large dosages of oxidating agenting during filtration. The excessive loading of catalysts and the overdosage of chemicals not only increase operational costs but also limit the practical application of catalytic ceramic membranes.
This thesis aims to enhance the performance of ceramic membranes for water treatment, focusing on the challenges of both fouling and OMPs’ removal. First a method was proposed to determine the main reason for flux decline, suggesting that both CP and fouling had impact on flux decline. Then catalytic ceramic ultrafiltration membranes, modified with CuFe2O4 and palladium, were employed to be coupled with H2O2 and peroxymonosulfate (PMS) based AOPs, respectively. The catalytic ceramic membranes not only exhibited a high flux after coating but were also effective in fouling removal and OMPs degradation.
High flux loss in membrane filtration can result from both CP and fouling, and a high CP level may further exacerbate fouling. However, the traditional CP model is unable to qualify their individual contributions. To better understand flux decline, a practical strategy was developed to distinguish the effects of CP and fouling by measuring pure water flux before and after the filtration of nano-sized colloids by ceramic nanofiltration (NF) membrane. The results indicated that colloidal CP could account for 43% to 95% of the total flux decline, with the remainder attributed to fouling. The CP values, calculated by a modified model, showed that the colloidal CP was in the range of 7-460, which is considerably higher than the CP (typically 1-2) caused by ions in spiral-wound reverse osmosis or NF. The highest CP level, i.e., 460, was observed for larger silica colloids, likely due to their slower diffusion. Although an increased crossflow was found to mitigate CP, high CP levels, i.e., values of around 250, were still observed.
To address membrane fouling, CuFe2O4-coated ceramic UF membranes were fabricated. The catalytic membranes with a minor flux loss after coating were then combined with Fenton-like backwash to enhance fouling removal. A low cleaning efficacy (1%–14%) was found in conventional hydraulic backwash. In contrast, due to the strong radicals induced by H2O2-based AOPs, the cleaning efficacy for removing alginate fouling from the catalytic membranes was improved to approximately 70% over multiple cycles. The backwash pressure or flux, rather than duration, was found to govern the AOP-enhanced cleaning performance. This is attributed to the increased residence time of H2O2 at low backwash pressure or flux. The presence of calcium (Ca) can form the rigid alginate-Ca clusters, not only negatively influencing the flux but also limiting the transport of radicals to the internal structure to break down the fouling. Besides, the fragments of alginate can reattach to the membrane surface by binding with excess Ca, thus reducing Fenton-like backwash efficacy. During seven-cycle filtration of concentrated alginate feedwater, the catalytic membranes restored 83%-94% flux after Fenton-like backwash. The leaching of catalysts gradually ceased over time, with negligible leaching in NaClO or NaOH.
Building upon this success, the catalytic ceramic membranes were further explored with a low loading of catalyst. Therefore, atomic layer deposition (ALD) was used to achieve a precise and low loading of Pd, ensuring minimal impact on membrane flux. The catalytic membranes modified with 30 ALD cycles were coupled with PMS for in-situ AOP degradation of OMPs during filtration. The coupled system achieved nearly 100% OMP removal at flux below 100 L/(m2·h) and maintained a high degradation efficacy (76% to 96%) even at a higher flux of 200 L/(m2·h). The OMPs’ degradation was enhanced by Pd deposited within the membrane pores, improving degradation kinetics by up to three orders of magnitude due to nanoconfinement effects, compared to the effect of Pd deposited on the membrane surface. The contribution of different reactive species (RS) to OMPs degradation was found to depend on the compound. Although ions and natural organic matter had minimal impact, harsh feedwater conditions, such as high salinity of brine water and pH at 2.5 or 11, reduced the degradation of certain OMPs, likely due to inhibited PMS activation.
Although the AOPs-enhanced removal of fouling and OMPs have widely been studied, little is known about the effect of fouling on OMPs’ degradation. Therefore, Pd-deposited ceramic ultrafiltration membranes with PMS were used to treat feedwater containing alginate and OMPs. The results showed that the Pd-coated membranes effectively mitigated fouling and achieved a high degradation efficacy of OMPs, even under severe cake fouling or pore blocking. Fouling was found to influence permeability and changed fouling mechanisms (cake fouling and pore blocking) depending on the PMS concentration, flux, foulant type, and Ca concentration, but its effect on OMP degradation was minimal. This is attributed to the synergy between membrane separation of foulants and nanoconfinement, which prevents the deactivation of catalytic sites and enriches RS and OMPs within the membrane pores. Although the governed RS for OMPs degradation almost remained consistent under fouling and non-fouling conditions, fouling altered their relative contributions to OMP degradation. However, different fouling is likely to alter the dominant oxidation pathway during OMP degradation. ... Read more

Stringent industrial wastewater discharge regulations and rising energy costs demand industries to shift to sustainable water treatment technologies. The conventional physical-chemical wastewater treatment processes struggle to separate inorganic ions and emulsions. While polymeric membranes have limited mechanical, thermal and chemical stability. Ceramic membranes, and in particular silicon carbide (SiC) membranes, have emerged as promising alternatives due to their mechanical strength, thermal resilience, resistance to fouling, low isoelectric point, and super hydrophilicity. However, fabricating both SiC membrane supports and the selective layers require sintering temperatures of ca. 2100°C, with consequent high energy consumption. Additionally, preparing a SiC selective layer requires multiple coating and sintering cycles, which hinder precise pore size control and economic feasibility. To address these limitations, this thesis explores low-pressure chemical vapor deposition (LPCVD) as a route to coat commercially available alumina (Al2O3) supports by SiC at moderate temperatures to replace full SiC membranes... ... Read more

Rapid industrialization and urbanization over the past two decades have made water scarcity and water pollution the most serious and persistent challenges for people around the world. Membrane technologies have emerged as crucial solutions to tackle the global water shortage crisis, especially for the re-use of industrial effluents. Inorganic ceramic membranes are gaining increasing attention in industry due to their high mechanical and chemical stability, hydrophilicity, water permeability, antifouling abilities. Silicon carbide (SiC) membranes have shown the lowest fouling compared with other ceramic membranes. Therefore, recently, new methods have been developed to fabricate SiC membrane at a low temperature of 860 ^oC, using low pressure chemical vapor deposition (LPCVD). This thesis focuses on the fabrication and application of SiC-coated membranes, detailing their preparation via LPCVD and their performance in treating nano-sized oil-in-water (O/W) emulsions, real produced water, and laundry wastewater.

First of all, a novel approach is presented for effectively separating microemulsions via SiC (3C-SiC)-coated alumina (Al₂O₃) membranes, fabricated based on LPCVD. With the increase in deposition time, up to 25 min, the pore size of the membranes decreased from 41 nm (without deposition) to 33 nm (deposition time of 25 min). The polycrystalline 3C-SiC-coated membranes also showed an improved hydrophilicity (water contact angle of 15º) and highly negatively charged surfaces (-65 mV). Oil-in-water (O/W) microemulsions filtration experiments were carried out at a constant permeate flux (80 Lm^-2h^-1) for six cycles with varying deposition time, pH, surfactant types, and pore sizes. The fouling of the SiC-coated membrane was, compared to the Al₂O₃ membrane, effectively mitigated due to the enhanced electrostatic repulsion and hydrophilicity. Surfactant adsorption mainly occurred when the surface charge of the microemulsion and the membranes were opposite. Therefore, the surface charge of the Al₂O₃ membrane changed from positive to negative when soaked in negatively charged microemulsions, whereas SiC-coated membranes remained negatively charged regardless of surfactant type. The membrane fouling was alleviated when the membrane and oil droplets had the same charge.

Subsequently, the effects of the ionic strength (1, 20, and 100 mM) as well as different surfactants in O/W emulsions on the membrane fouling were studied. Four surfactants, including sodium dodecyl sulfate (SDS, anionic), alkyl polyglycoside (APG, non-ionic), cetyltrimethylammonium bromide (CTAB, cationic) and N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS, zwitterionic), were selected for this study. The Derjaguin-Landau-Verwey-Overbeek (DLVO) and extended DLVO (XDLVO) models were used to quantify interactions between the membrane-oil droplet and deposited oil layer-oil droplet surfaces and to compare these interactions with the fouling experiments. The (X)DLVO interaction energies of the membrane-oil droplet exhibited a strong agreement with the fouling tendencies at 1 mM salinity. The SiC-deposited membrane showed less (ir)reversible membrane fouling than the Al₂O₃ membrane when filtering O/W emulsions stabilized with SDS, APG, or DDAPS. The DLVO model predicted a higher tendency at higher salinity levels during the filtration of SDS, APG, or DDAPS-stabilized O/W emulsions and a decreased fouling tendency for CTAB-stabilized emulsion with the SiC-deposited membrane. However, at higher salinity levels, the XDLVO energy barrier was affected by both the repulsive electrostatic double layer (EL) interaction and attractive Lewis acid-base (AB) interaction. For the Al₂O₃ membrane, the XDLVO model obscured EL and Lifshitz-van der Waals (LW) interactions since the AB component was dominant, confirmed by the diminished XDLVO energy barrier, whereas for the SiC-deposited membrane, the EL interaction prevailed since the energy barrier value was positive.

Then real oilfield produced water with high salinity (142 mS/cm) and COD (22670 mg/L) was successfully treated by SiC-coated Al₂O₃ membranes in constant flux mode. The major findings were that pore blockage served as the initial (irreversible) fouling mechanism and that the (reversible) cake layer, a mixture of organic and inorganic components, dominated the rest of the filtration cycle, where the SiC-coated membrane performed better than the original Al₂O₃ membrane. In addition, it was found that the application of the SiC coating, and the selection of the appropriate pore size (62 nm) and crossflow velocity (0.8 m/s) increased the fouling mitigation, potentially advancing the utilization of ultrafiltration in treating saline produced water for reuse purposes.

Finally, synthetic wastewater containing cotton, linen, polyester, and nylon fibres and real laundry wastewater were characterized and prepared for filtration experiments, which were conducted at a flux of 70 Lm^-2h^-1 using an Al₂O₃ membrane and a SiC-coated membrane. Results revealed that natural textiles, particularly cotton and linen, released higher COD loads than synthetic fibers when tested at equal mass, in the trend of, cotton>linen>polyester>nylon, which was further supported by microscopic and SEM images. Both the Al₂O₃ membrane and the SiC-coated membrane showed a high fiber rejection (100 %), whereas the SiC-coated membrane showed lower reversible and irreversible fouling than the Al₂O₃ membrane, due to highly negatively charged surface. The fouling order of the fibers were in line with the COD concentration of the synthetic laundry wastewater containing these fibers. Finally, treatment of hot real laundry wastewater by the ceramic membranes not only mitigated membrane reversible and irreversible fouling, but also enabled the simultaneous recovery and reuse of water, surfactants, and thermal energy, offering a sustainable strategy to reduce both water consumption and energy costs.

... Read more

Organic micropollutants (OMPs) originate from organic chemicals such as drugs and pesticides that are widely used in human activities. OMPs are difficult to remove by conventional water treatment techniques, and hence continue to accumulate in natural water bodies. More effective methods need to be investigated for the removal of OMPs in drinking water treatment because of their toxicity and carcinogenicity, which may pose potential risks to human health. Previous studies have suggested that the use of activated peroxymonosulfate (PMS) catalyzed by Palladium (Pd) immobilized in ultrafiltration (UF) membranes can effectively degrade 1,4-dioxane and p-nitrophenol, while its removal efficiency for other OMPs, limiting factors and reaction mechanism still require for more research. In this study, PMS-Pd/UF system was established by coating Pd on the surface and 20 nm pores of the ultrafiltration membrane. The effectiveness of PMS-Pd/UF in the removal of OMPs from ultrapure water under various flux, pH, PMS dosages and ions presence was examined, as well as the performance in other water matrices including simulated brackish water, simulated brine water and river water. The results showed that PMS-Pd/UF achieved more than 95% of OMPs removal in 1 and 12-hour filtration tests at a flux of 30 LMH, while removal efficiency decreased with the increased flux due to the reduced contact time. The pH tests indicated that the system was more efficient under a neutral pH environment. The presence of 1 mM of various ions (Cl⁻, HCO3⁻, SO₄²⁻, and ClO⁻) had limited effects on the degradation of OMPs. However, the removal of OMPs was inhibited when OMPs coexisted with NOM in river water and, in combination with high salt concentrations simulated brine water (e.g., with 250mM of total anions). From specific scavenger dosing experiments, it was concluded that SO₄^•–, ^•OH, and O₂^•– were the main reactive species induced from Pd/UF-activated PMS for the removal of OMPs. ... Read more

Driven by the increasing demand for waste reduction and green energy production, an integrated system which combines an anaerobic membrane bioreactor (AnMBR) and a solid oxide fuel cell (SOFC) was proposed in this research project for blackwater treatment and energy production. The potentials of using an AnMBR for wastewater treatment and biogas production, and the feasibilities of producing energy from biogas with a SOFC have been investigated by many researchers. Although, combining the two equipment might raise new challenges and opportunities. The AnMBR pH has direct impacts on the biogas composition, which would subsequently affect the SOFC operational strategy. Therefore, this research project focused on the influence of the AnMBR pH on the SOFC operational strategy, which would provide insights for connecting AnMBR and SOFC. The AnMBR pH was controlled around 8 initially, and then reduced to 7. The composition of the biogas produced under each pH condition was analyzed before the biogas was conditioned for the SOFC operation. Biochar adsorption and CO2 addition were applied for biogas conditioning. pH 8 was favorable for biochar adsorption, whereas pH 7 was favorable for CO2 addition. The aim of biochar adsorption was to ensure that the H2S concentration remaining in the biogas after adsorption was less than 0.5 ppm, so that sulfur poisoning could be avoided at the anode of SOFC. A biochar column (BC) was attached to the AnMBR for the adsorption of sulfur compounds in the biogas. The BC was packed with biochar made of cow manure. The adsorption capacity of the biochar was measured to determine the amount of biochar required in the BC. After biochar adsorption, the ratio between CH4 and CO2 was balanced by adding CO2 to the biogas, to reduce the risk of carbon deposition at the anode of SOFC. The exhaust gas discharged by the SOFC could also be recycled as an alternative to CO2 addition. The performance of the SOFC system using the conditioned biogas as the fuel was assessed based on electric power output and fuel utilization efficiency. Based on the results of biogas production, conditioning, and utilization, the influence of the AnMBR pH on the SOFC operational strategy was analyzed. Furthermore, the potentials and the limitations of connecting AnMBR and SOFC were discussed. ... Read more

Aromatic compounds have always been of concern regarding their toxicity to living organisms, including microorganisms. With more anthropogenic activities (e.g. coal gasification), the need for feasible treatment of industrial effluents is highly prioritised. With the anaerobic degradation process being a competitive solution, these compounds’ toxic impact on the biomass is still of concern. These implications influence the stability of the degradation process; thus, there was a search for mechanisms to make the anaerobic degradation process more resilient. One potential mechanism is enhancing syntrophic collaboration between different species and its corresponding electron transfer. Syntrophic collaboration in an anaerobic environment can be conducted using intermediates (e.g. hydrogen) or direct electron transfer. Direct interspecies electron transfer (DIET) is reported to be more energy efficient and more thermodynamically favoured over other mechanisms that include mediators (hydrogen/ formic acid). Conductive and semi-conductive materials have been investigated to simulate this direct interspecies electron transfer mechanism (DIET), with various materials being researched, such as iron oxides, zero-valent metals, and even carbon-based materials.
This study investigated the impact of magnetite addition (as a DIET-stimulator) on p-cresol degradation, methane production and sludge characteristics, with a further interest in membrane fouling mitigation. This investigation was conducted with continuous flow reactors and batch reactors. The continuous configuration was based on an anaerobic membrane bioreactor (AnMBR) fed with a synthetic-coal gasification-like solution of phenol and p-cresol to investigate mainly the conversion rate of p-cresol and monitor the influence on the methane production, sludge characteristics, and membrane fouling. At the same time, batch experiments were conducted to investigate the acetoclastic methanogenic pathway and p-cresol degradation as a sole carbon source. The continuous experiment lasted for 143 days but was divided into two separate phases with two different magnetite dosages, starting with 40 mmol/L in phase (I), then replacing the sludge with acclimatised one (from the control) with the addition of the second dosage (20 mmol/L) in phase (II).
A Magnetite dosage of 40 mmol/L showed signs of biomass-suppressed conversion capacity compared to the control, by which the reactor conversion rate deteriorated by reaching 212 mgCOD/ gVSS/d (under a feed of 900 mgPh/L & 900 mgPcr/L). Phase (I) showed no significant differences in the methane production rate between control and magnetite reactors. On the other hand, the batch experiments fed with 1 gCOD/L acetate showed that the magnetite reactor had a lower acetoclastic methane production rate than the control. It was suggested that the 40 mmol/L magnetite dosage was suppressing the acetoclastic methanogens, which was further contributing to the lower conversion capacity observed in the AnMBR by the end of the phase. With the same methane being produced in control and magnetite reactors, it was also possible that either hydrogenotrophic methanogenesis or the DIET pathways were enhanced; however the absence of intermediates (e.g. VFAs) and the similarity of the COD balance supported the possibility of the latter one. During phase (II), the conversion rate of both reactors (control and magnetite) reached 74 mgPcr/ gVSS/d, approaching the highest conversion rates reported in the literature. While the acetoclastic methanogens showed no significant difference in the batch experiment, the magnetite-AnMBR’s methane production rate was 10%-28% higher. Furthermore, the methane yield with magnetite supplementation showed an average enhancement of 15%. In addition, the batch experiment also showed that this magnetite dosage reduced the p-cresol conversion rate by 87% compared to the control.
Both magnetite dosages (20 mmol/L & 40 mmol/L) showed a reduction in the protein and carbohydrate content of the soluble microbial products (SMP) and the extracellular polymeric substances (EPS). Magnetite had adversely impacted the loosely-bounded EPS (regarding protein and carbohydrates), whereas it was shown to be significant compared to the control. The EPS-LB showed an inverse relation with the particle size distribution (PSD), verifying that the higher increase in the particle size could be correlated with the EPS-LB reduction by the magnetite. On the other hand, the fouling rate of the membranes showed an insignificant difference between both reactors. This was suggested to be related to the incomplete formation of a mature cake layer under the influence of low operational flux. However, with the reduction of the SMP/EPS, it was suggested that the formed cake layer would be more porous and permeable. This would mean that the cake-fouling and its corresponding resistance would be expected to be lower. As the cake layer acts as a protective barrier for the membrane, its reduction would lead to a higher risk of irreversible pore-blocking by fine particles from the magnetite and the sludge. ... Read more

Membrane technology is widely used as an effective water treatment or pretreatment technology, especially in the filtration of oil-in-water (O/W) emulsions. Ceramic membranes have shown excellent performance in this regard. However, due to the complex composition of real wastewater, laboratory studies are limited to the filtration of simulated O/W emulsions, and there is little research on the favorable conditions for filtering real wastewater. Additionally, since actual devices operate as constant flux units, previous studies have been conducted under constant pressure conditions, thus further understanding of the effect of membrane pore size on constant flow membrane filtration is required to better understand the situation in real plant applications. ... Read more

Water scarcity is a serious issue on many smaller islands, with population growth and the predicted impacts of climate change as driving factors. Bonaire is a small island located in the Caribbean Sea that has rural areas without grid connections to electricity and water. Agriculture, both livestock and hobby crop farming, in the Punta Blanku region used to rely on groundwater pumped from wells. Groundwater usage had to be discontinued due to salt intrusion causing the water to become brackish. Water for a large chicken farm that supplies almost all eggs for Bonaire now has water delivered by truck, but it is not reliable due to transportation issues and costs. Reverse osmosis (RO) is recommended as a reliable way to provide water to the Punta Blanku region. Water production can be powered by renewable energy and be more economically feasible with windmill power as the electrical energy source for the RO system. Surface seawater and brackish groundwater samples were tested to determine the best water source for the RO system. Total dissolved solids and electrical conductivity values determine the total power pumping need for the RO system. Using sample results and IMSDesigns, a reverse osmosis model designed by Hydranautics, it was determined that brackish water reverse osmosis (BWRO) was preferred over seawater reverse osmosis (SWRO). With Bonaire wind speeds, FreshWaterMill can easily power 200 cubic meters permeate production per day with BWRO. Additionally, less fouling is expected for BRWO than SWRO due to prefiltration by soil. ... Read more

Constant flux MF/UF filtration is preferred in real-world applications because it
provides more consistent permeate flow rates than fixed transmembrane pressure studies. Particularly, little is understood about the fouling of ceramic membranes in constant flux filtration modes by nano-sized O/W emulsions. In this study, the effects of emulsion chemistry containing pH, different surfactants, as well as salinity on the alumina and SiC deposited ceramic UF membranes with various physicochemical surface properties in the constant flux mode were compared.
... Read more

Ceramic ultrafiltration is a promising technology for water reclamation, but issues with membrane fouling and the removal of organic micro-pollutants have limited its development. Recent research has shown that catalysis-based ultrafiltration has the potential to address these problems. In this study, catalysis-modified (CuFe2O4 and Pd) ultrafiltration was investigated for fouling mitigation and organic micro-pollutant removal.

The membranes were successfully synthesized and it was found that using Fenton oxidation (a combination of CuFe2O4 membrane with H2O2 backwash) had a 93.9% higher cleaning efficiency than applying demi-water. Besides, it was found that the backwash flux and backwash time were crucial in determining the cleaning efficiency of Fenton oxidation, with a smaller backwash flux or longer backwash time resulting in better permeability recovery.

However, the application of Fenton oxidation was also found to be limited by the instability of the CuFe2O4 catalyst in acidic environment, and the problem of catalyst leaching led to a decrease in cleaning efficiency. Additionally, it was discovered that using PMS oxidation was more effective for OMPs removal compared to Fenton oxidation, with a removal efficiency of up to
90%. Overall, this work demonstrated the potential of catalyst-coated ultrafiltration for water treatment and highlighted the benefits of combining membrane filtration with advanced oxidation processes.


... Read more

Large amounts of oily wastewater which included oil-in-water (O/W) emulsions, also known as produced water (PW), were produced in tandem with the enhanced oil recovery (EOR). Ultrafiltration (UF) was an effective and economic method to separate micron-sized O/W emulsions, while the membrane fouling limited its development. Understanding the fouling phenomena was essential to enhance the efficiency of membrane filtration for oil-water separation, hence this paper investigated the influence of different salinity (1 mM, 20 mM and 100 mM) and types of surfactants on the fouling of the alumina (Al2O3) membrane and the silicon carbide (SiC) deposited membrane filtrating 500 mg/L O/W emulsions with mean droplet sizes of approximately 4 ~ 7 μm, and the UF with the constant flux of 80 LMH and the crossflow velocity of 0.59 m/s was conducted. Sodium dodecyl sulfate (SDS, anionic), alkyl polyglycoside (APG, nonionic), and cetyltrimethylammonium bromide (CTAB, cationic) were chosen in this study due to the frequent use in EOR, and the N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS, zwitterionic) was selected because of its low tendency to foul at high salt concentrations.
Derjaguin-Landau-Verwey-Overbeek (DLVO) and the extended DLVO (XDLVO) models were used to quantify the membrane-oil droplet and deposited oil layer-oil droplet surface interaction. The results showed that the SiC-deposited membrane had less membrane fouling and irreversible fouling resistance compared with the Al2O3 membrane when filtrating O/W emulsions stabilized with SDS, APG or DDAPS. The DLVO model estimated emulsion fouling propensity to rise with increasing salinity when dealing with SDS, APG or DDAPS-stabilized O/W emulsions, while CTAB-stabilized emulsion fouling propensity for the SiC-deposited membrane would decrease with the higher salinity.
... Read more

With the development of industry, there is an increasing focus on environmental issues, while organic micro-pollutants (OMPs) have garnered significant attention as emerging contaminants in water. Due to the low concentration and small size, OMPs pose a challenge to retain in traditional low-pressure membrane filtration systems. Prior researches found that membrane coupled advance oxidation processes (AOPs) could effectively degrade OMPs. However, membrane fouling caused by natural organic matter still remains an issue. In this study, the feasibility of simultaneous OMPs removal and fouling mitigation was validated in such a membrane coupled AOPs system, where the peroxymonosulfate (PMS) worked as the oxidants and palladium was immobilized on the ceramic ultrafiltration membrane surface to activate the PMS. In a continuous four-cycle experiment, the Pd-coated membrane maintained over 60% removal for 4 OMPs and improved the hydraulic clean efficiency significantly. Furthermore, the factors related to experimental conditions were also explored. The research
found that OMP removal rates were reduced by fouling due to the competitive effect of PMS. Take Trimethoprim as an example, its kinetics constant decreased from 22.491 to 0.916 s−1. PMS dosage also played an important role in both fouling alleviation and OMP removal. The improved performances were observed with increasing PMS dosage. ... Read more

Water scarcity, population growth, and climate change are causing a shortage of water resources globally. Industries are turning to the reclamation and reuse of wastewater, including oily wastewater, which is a major byproduct of oil and gas extraction. The small droplet size of oil-in-water emulsions, however, makes them difficult to remove using traditional methods like coagulation and flocculation, gravitational settling, dissolved air flotation, hydrocyclone, and adsorption.
Membrane separation has emerged as one of the most promising techniques to deal with oil-in-water emulsions due to its high removal efficiency and small footprint. The main challenge for the wider adoption of membrane technology for oily wastewater treatment is membrane fouling. Membrane fouling is a pervasive problem in water purification membranes. It could cause serious negative effects, such as a decline in water production, higher operational pressure and associated higher energy consumption.
Ceramic membranes, particularly SiC membranes, are a promising method for removing small oil droplets from water. They are physically and chemically stable and have high fouling resistance to oil droplets. SiC membranes have better permeability and lower fouling tendency compared to other ceramic membranes. However, their high cost limits their widespread application in the market.
In this research, extensive literature reviews were first performed (Chapters 2 and 3) and then we proposed a new method, low-pressure chemical vapor deposition (LPCVD), to prepare SiC-deposited ceramic membranes for oily wastewater treatment. With LPCVD, a layer of SiC was deposited on alumina supports at a lower temperature (750 ˚C), compared to 2000 ˚C for commercial SiC preparations. Due to the low water contact angle (< 5˚) and negatively charged surface, these SiC-deposited alumina ceramic membranes are expected to be more fouling resistant to oil emulsions than the pristine alumina membranes. The performance of deposited membranes is influenced not only by the coated SiC layer but also by the filtration modes used for evaluation. As a result, we respectively used constant pressure and constant flux filtration to assess the fouling of ceramic membranes with and without SiC deposition. Additionally, the emulsion chemistry, such as surfactant concentration, pH, salinity, and Ca2+, plays a crucial role in the interactions between oil droplets and the membrane surface, which can cause membrane fouling. Understanding these mechanisms can be a crucial step towards the feasibility of using LPCVD to prepare SiC membranes for treating oily wastewater with lower fouling.
First, novel SiC-deposited ceramic membranes were developed by LPCVD at a relatively low temperature (750 ˚C) (Chapter 4). Different deposition times varying from 0 to 150 min were used to tune membrane pore size. The pure water permeance of the membranes only decreased from 350 L m-2 h-1 bar-1 to 157 L m-2 h-1 bar-1 when the deposition time was increased from 0 to 120 min. Correspondingly, the membrane pore size was narrowed down from 71 to 47 nm. Increasing the deposition time from 120 to 150 min mainly resulted in the formation of a thin, dense layer on top of the support instead of in the pores. Notably, the SiC layer rendered the pristine membrane surface more hydrophilic and negatively charged, effectively reducing membrane fouling during oil emulsion filtration.
Next, the fouling of SiC-deposited ceramic membranes and the pristine alumina membrane was respectively compared at constant pressure and constant flux filtration conditions (Chapter 5). The threshold flux of the membranes was first determined by flux-stepping experiments. Afterwards, membrane filtration was respectively conducted at below and above the threshold flux. In single cycle constant flux filtration experiment, the fouling tendency of the membranes was consistent with the results of threshold flux experiments. However, the inclusion of backwash in constant flux experiments led to a change in the fouling tendency, which was also dependent on the permeate flux. The improved surface hydrophilicity and charge made backwash more efficient for the modified membranes while extensive modification has a negative effect on membrane fouling resistance due to the huge loss in membrane permeance. In contrast, constant transmembrane pressure experiments showed that the order of membrane fouling was only related to membrane permeance, and no effect of surface properties was observed. Therefore, constant flux filtration experiments with backwash are recommended to be applied to evaluate the performance of the membranes with and without modification.
Finally, the impact of emulsion chemistry and operational parameters on the fouling of alumina membranes with and without a SiC deposition was systematically studied under constant flux filtration mode with backwash (Chapter 6). The results showed that the SiC-deposited membrane had a lower reversible and irreversible fouling when permeate flux was below 110 Lm-2h-1. In addition, a higher permeance recovery after physical and chemical cleaning was observed, as compared to the alumina membranes. The fouling of both membranes was decreased with the increase of sodium dodecyl sulphate (SDS) concentration in the feed, but to a higher extent in the alumina membranes. Increasing the pH of the emulsion could reduce the fouling of both membranes due to the enhanced electrostatic repulsion between oil droplets and membrane surface. Under high salinity conditions (100 mM NaCl), the screening of surface charge resulted in only a small difference in irreversible fouling between the alumina and SiC-deposited membranes. The presence of Ca2+ in the emulsion led to high irreversible fouling of both membranes, because of the compression of diffusion double layer and the interactions between Ca2+ and SDS. The low fouling tendency and/or high cleaning efficiency of the SiC-deposited membranes indicated their potential for oily wastewater treatment.
Overall, this dissertation shows that the fouling of SiC-deposited ceramic membranes is lower than that of the pristine alumina membranes towards oil-in-water emulsion treatment. Although there are still limitations, these SiC-deposited membranes show the potential for further development.
... Read more

NEOM is planning to build a desalination plant for the production of drinking water. The main disadvantage of desalination is the production of brine. Improper disposing of brine into the environment can have negative repercussions, and brine management can be complex due to its inherent characteristics. Brine treatment can be energy-intensive, and usually, the goal is to t avoid producing any further waste that could be discharged into the environment.
In this study, it was proposed to utilize desalination brine as a raw material for the production of 3D printable concrete. The project was conducted in collaboration with the Materials & Environment Department at TU Delft, which was responsible for all the technical experiments related to the utilization of desalination brine for the production of 3D printable concrete. The concrete experiments served as the starting point establishing the requirements for the brine.... ... Read more

Trials of surface modifications using low pressure chemical vapor deposition (LPCVD) has successfully decreased the high temperature needed for the fabrication of SiC membrane from 2000°C to below 900 °C. With this great success on the reduction of the energy con-sumption, however, further studies on the chemical stability and the fouling features of this kind of membrane were necessary. In this research, experiments were done on the SiC-Al2O3 UF membrane fabricated by LPCVD to study its chemical stability in a NaClO solution and its fouling features when filtrating sodium alginate and surface water under constant flux cross-flow mode. The backwash efficiency and the fouling resistance were analysed as well to further elucidate the fouling composition.
According to the results, the SiC-Al2O3 membrane coated under higher temperature (860°C) remained stable in the NaClO solution for 200 h, (1% for 100 h and then 5% for 100 h) while the membrane coated under lower temperature (750°C) showed a water permeability increase during chlorine treatment, indicating the dissolution of the SiC layer. The high temperature coated membrane (860°C) had a better antifouling ability than low temperature coated mem-brane (750°C) and the pristine membrane especially when filtrating the pure sodium alginate (SA) solution without Ca2+ under normal flux (170 LMH) or the surface water under lower flux (65 LMH). Cake filtration was observed in the fouling curves when the critical flux was not exceeded. The addition of Ca2+ into the pure SA solution resulted in the decrease of elec-trical repulsion and the increase of bridging between foulants and membrane surface. These led to the severe fouling of the high temperature coated membrane. The low temperature coated membrane had better antifouling ability than high temperature coated membrane and the pristine membrane when 2 mmol/L of Ca2+ was added. However, the backwash (back-wash flux of around 340 LMH for normal flux condition and around 195 LMH for lower flux condition) was not efficient for all the membranes and should be improved in the future ex-periments.
... Read more

Water scarcity and uneven distribution of water resources pose a significant challenge globally. Searching for alternative water resources could alleviate this issue. Municipal sewage reclamation with ceramic NF membrane has gained momentum nowadays. However, the inevitable fouling, especially organic fouling during membrane filtration, is the major limitation of the application. To mitigate the fouling issues and protect the membrane from frequent sodium hypochlorite cleaning, a reaction-based CaCO3 pre-coating method, which could prevent the direct contact of foulant and ceramic NF surface was developed. Acid cleaning was applied to initiate the reaction between CaCO3, which was attached with foulants (sodium alginate) and acid. Lastly, forward flush was implemented to remove the loosened CaCO3 and sodium alginate layers.

The effectiveness of hydrochloric acid cleaning, formic acid cleaning and citric acid cleaning was studied in this paper. Citric acid was found to be the most effective way of cleaning because of the highest permeability recovery rate obtained and the lowest consumption rate of the pre-coating layer. This could be ascribed to the carboxyl groups chelation with calcium ions and the ‘peeled’ chelates adsorbed with more foulants were flushed away. Formic acid was less efficient showing moderate efficiency. Besides, HCl cleaning restored the lowest extent of membrane permeability. Additionally, experiments of increasing the pre-coated CaCO3 amount (7655 mg/m2) to apply for more filtration/acid cleaning cycles were executed. The effectiveness increases in the order of HCl, formic acid and citric acid. The pre-coated membrane cleaned with citric acid could last for the whole six cycles, while the membrane cleaned with HCl only worked in the first three cycles. Lastly, the effect of bubbles generated during the reaction was explored using CaHPO4 as a pre-coating layer. However, the hypothesized positive impact of bubbles was not verified.
... Read more

In this study simultaneous and continuous inline dosing of PAC and coagulant in UF was investigated. Surface water was directly treated with PAC-UF and performance of the system was assessed by looking at membrane fouling and organic micropollutants removal. Combining adsorption and membrane processes in one technique, hybrid membrane processes, enhances performance of OMP removal by membrane processes. Powdered activated carbon (PAC) combined with coagulation and ultrafiltration (UF) is a possible treatment technique for surface water.
Permeability in UF-membranes remains steady, when dosing coagulant. Only a small increase in irreversible fouling of 0.2-0.7*109 m-1h-1 is visible. However, absence of coagulant dosing causes irreversible fouling to increase to 8.7*1010 m-1h-1 and can not be easily reversed with a chemically enhanced backwash (CEB). Inline dosing of PAC alone causes an irreversible fouling of 11.4*1010 m-1h-1 and highest increase in reversible fouling of 11.7*1010 m-1h-1. Addition of coagulant (1.2 mg/l) lowers reversible fouling compared to no dosing, on the other hand addition of PAC to coagulant shows no clear increase or decrease in reversible fouling. Coagulation has a negative effect on capillary blocking, an increase of 4-8% compared to no coagulant or adsorbent. PAC and no dosing did not influence pore blocking.
Highest removal of low to good adsorbable OMP was 10-63% for continuous and simultaneous dosing of 12 mg PAC/l and 1.2 mg FeCl3/l. Increasing filtration time (30 to 60 min) showed highest removal efficiency of 75% of Sotalol and 5-Methyl-1H-Benzotriazole, both good adsorbable OMP. Removal of PFAS varies between a few percent and 37%. Continuous dosing of coagulant (1.2 mg/l) with PAC (10 mg/l) has a negative impact on OMP adsorption including PFAS. With a higher PAC dose (15 mg/l) removal efficiency was not affected.
Addition of coagulant with PAC-UF showed to be effective to prevent irreversible fouling, with direct surface water treatment. However, coagulation is responsible for blocking of capillaries even resulting in a small decrease of permeability. Removal of OMP including PFAS was much lower compared to other PAC-UF systems and therefore PAC-UF with simultaneous and continuous inline dosing of PAC is not a good set-up. Adjustments in set-up should be made in order to make this configuration work. Possible improvements are increase of filtration time between backwash and dosing sequence of PAC and coagulant. ... Read more

Brine producing industries progressively become the centre of attentionas they carry greater environmental consequences. Despite the extensiveliterature that can be found on desalination, limited information is availableabout the practical comparison of the technologies with regards to the brineconcentration performance and associated energy consumption. This thesis studyaims to contribute to bridging this knowledge gap by comparing reverse osmosis(RO), electrodialysis (ED) and vacuum membrane distillation (VMD). RO wasstudied by simulations using WAVE software, while ED and VMD were studied byperforming lab-scale experiments. Feed NaCl concentrationsbetween 20 and 80 g/L were considered in this study. The achievedconcentration factor (CF) for RO was greatly influenced by the feedconcentration. It was found that applying higher netdriving pressures resulted in higher recoveries, but recoveries are limited by feed concentration. In the VMDstudy, the correlation between operating temperatures and permeate flux wasfound to be positive. A decrease in permeate flux wasobserved with increasing solute content, which is related to the vapourpressure lowering phenomena. It was found that the effect of operatingtemperature on permeate flux is greater than the effect of the feedconcentration. Condensation contributed to the highest energy consumption(81%), followed by the vacuum pump (18.9%). Efficient heating andcooling pumps result in a significant energy consumption decrease. In the ED study it was found that applying different current density (CD) did not influence the CF, so it ismore advantageous to apply lower CD to achieve the same desalination from anenergy saving point of view. Furthermore, the CF decreased with increasing feedconcentration and thistrend intensifies with larger volume ratios. The effectof absolute water transport became more significant at higher feedconcentrations and resulted in overall dilution of the concentrate stream. Thedistribution of mass transport was similar for different volume ratios, meaningthat higher CF can be achieved by larger volume ratios. Higher energy consumptionwas related to higher feed concentration and higher volume ratios resulted in higherenergy consumption due to smaller concentrate volume.RO, VMD and ED proved to be suitabletechnologies for concentrating different NaCl solutions. RO and ED showed verysimilar concentration performance and energy consumption. The concentration limit for RO was 118g/L, while for ED it was 140 g/L. RO was able to achieve higher CF with lowerenergy consumption at concentrations < 60 g/L, compared to ED. EDoutperforms RO at concentrations > 60 g/L. Theenergy consumption of ED and RO can be reduced by applying a multi-stageconfiguration. The VMD results showed that the energy consumptionto achieve a similar CF as RO and ED, increased by a factor of 61. VMD is moreadvantageous at higher feed concentrations and even more so with waste heat. VMD and RO are suitable for cases that require high qualitypermeate whereas ED is not. The technologies could also be applied togetherto minimize waste production, whilst prioritizing concentration. ... Read more

Ultrafiltration (UF) is an efficient and effective method of filtrating oil-in-water (O/W) emulsions. However, the favorable conditions of filtrating nano-sized O/W emulsions have not been investigated. This study investigated the influence of four different parameters including membrane pore size, cross flow velocity, pH and salinity on membrane fouling as well as oil rejection. Alumina UF membranes were employed to filtrate nano-sized O/W emulsions. O/W emulsions were synthesized using soybean oil and stabilized by surfactants. The filtration experiments were conducted under constant flux for multi cycles. The results showed that 200nm was recommended to filtrate nano-sized O/W emulsions (average droplet size -100nm) based on the high oil rejection (95% ~ 99%) and low irreversible fouling resistance. Besides, alumina membranes were proved to be more effective in fouling mitigation at low salinity, high pH, and high cross flow velocities. ... Read more