The clothes washing industry generates large volumes of laundry wastewater that, in principle, can be well treated by ceramic membrane filtration. However, the fouling of ceramic membranes by fibers/fragments from laundry wastewater could result in a decrease of the water permeance across the membranes. In this study, synthetic wastewater containing cotton, linen, polyester, and nylon fibers and real wastewater were characterized and prepared for the filtration experiments, which were conducted at a flux of 70 Lm−2 h−1 using an alumina (Al2O3) membrane and a silicon carbide (SiC)-coated Al2O3 membrane. Results revealed that natural fabrics, particularly cotton and linen, released higher chemical oxygen demand (COD) loads than synthetic fibers when tested at equal mass, which was further supported by microscopic and SEM imaging. The SiC-coated membrane exhibited a relatively lower reversible and irreversible fouling, attributed to its highly negatively charged surface, which repels the fibers that are negatively charged by negatively charged surfactants. The observed fouling among different fibers corresponded well with the COD levels of the synthetic laundry wastewater containing those fibers. Laser direct infrared imaging (LDIR) analysis confirmed that natural fibers dominate in real laundry wastewater. Treating hot laundry wastewater was more effective in reducing both reversible and irreversible membrane fouling than treating it at room temperature. Moreover, the filtration of hot laundry wastewater could facilitate the recovery and reuse of water, surfactants, and heat, offering a sustainable solution to reduce both water consumption and energy costs. This study underscores the importance of paying closer attention to natural fibers, as they tend to cause more severe membrane fouling compared to synthetic fibers in ceramic membrane-based water treatment systems.

Membrane modification is commonly applied in water purification and wastewater treatment to reduce fouling of membranes. However, the influence of fouling test methods on evaluating pristine and modified membranes is often overlooked. This study investigates fouling behavior of alumina and SiC-deposited alumina membranes during oil-in-water emulsion filtration under both constant flux and constant transmembrane pressure conditions. Threshold flux was first determined using flux-stepping experiments, with the 90-min SiC-deposited membrane showing the highest value at 95 L m^{− 2} h^{− 1}. In single-cycle constant flux tests, fouling trends aligned with threshold flux data. However, when backwash was included, fouling characteristics shifted and depended on the permeate flux. Enhanced hydrophilicity and surface charge improved backwash efficiency in modified membranes. Yet, extensive modification negatively affected performance due to significant permeance loss (>57 %). Under constant pressure, fouling was dominated by internal pore blocking, and backwash efficiency was solely linked to membrane permeance, regardless of surface properties. Thus, constant flux filtration with backwash best reflects operational conditions and is recommended for evaluating membrane modifications.

During the extraction of fossil fuels, a complex waste stream is produced simultaneously, also known as produced water (PW). Membrane filtration is a promising technology that can successfully enable the treatment and reuse of PW. Silicon carbide (SiC) membranes are preferred for PW treatment, due to their low (ir)reversible fouling compared to other ceramic membranes. However, full SiC membrane is expensive and thus economically less feasible. Therefore, we established a method for coating SiC on alumina (Al₂O₃) ultrafiltration membranes, based on low-pressure chemical vapor deposition at 860 °C. In the presented study the fouling resistance and behavior of these novel membranes, with various pore sizes and under different operating conditions, including flux and crossflow velocity, were evaluated. We also used Al₂O₃ membranes and SiC-coated Al₂O₃ membranes in constant flux mode to treat real oilfield PW with high salinity (142 mS/cm) and COD (22670 mg/L). Additionally, the fouling mechanisms in the SiC-coated and Al₂O₃ membranes were analyzed with the help of Focused Ion Beam-Scanning Electron Microscopy imaging. 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 alumina 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 PW for reuse purposes.

Large amounts of oily wastewater, which can be defined as produced water, are generated in oilfields. Ultrafiltration (UF) serves as an effective and economical method to purify produced water. Unfortunately, membrane fouling during produced water treatment is severe. In this paper, the effects of the ionic strength (1, 20, and 100 mM) as well as different surfactants on the membrane fouling are investigated. Four surfactants, including SDS (anionic), APG (non-ionic), CTAB (cationic) and 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 (B20) membrane showed less reversible and irreversible membrane fouling than the Al₂O₃ (B0) membrane when filtering negatively charged O/W emulsions stabilized with SDS, APG, or DDAPS. The DLVO model predicted a higher fouling 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 B20 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. By comparing both experiments and (X)DLVO modeling, this study improves the fundamental understanding of the effect of ionic strength and surfactant types on reversible and irreversible fouling of the Al₂O₃ and SiC-coated membranes fouling by O/W emulsions.

Fouling remains a critical challenge for ceramic ultrafiltration membranes, limiting their long-term performance for water treatment. Fenton-like reactions have been widely used for fouling removal due to the formation of strong radicals. Integrating these reactions into backwash offers a promising strategy for fouling control. However, it has been unclear how Fenton-like backwash is influenced by operational parameters and fouling structures. Here we reveal the key factors influencing Fenton-like backwash by systematically studying its performance under varying conditions, such as backwash pressure (0.3–1 bar), duration (18–36 min), fouling structure (caused by 1–5 mM Ca) and the long-term operation, to provide an effective and practical cleaning. CuFe₂O₄ was grown on ceramic ultrafiltration membranes due to its stability and high catalytic efficiency in activating Fenton-like reactions. We found that Fenton-like backwash achieved the highest cleaning efficacy of approximately 70 % over three cycles at a low backwash pressure of 0.3 bar, while hydraulic backwash remained ineffective under all conditions. Backwash pressure, rather than duration, was identified as the dominant factor governing the Fenton-like cleaning, due to its impact on the residence time of Fenton-like agents (H₂O₂). The presence of a high Ca concentration (3 and 5 mM) altered the fouling behaviour, and reduced the cleaning efficacy of Fenton-like backwash. This reduction was attributed to the formation of rigid alginate clusters that were resistant to Fenton-like reactions. The contribution of •OH to the enhanced Fenton-like backwash was confirmed by the quenching experiments. Furthermore, the CuFe₂O₄-coated membranes exhibited stable flux recovery (83 %–94 %) in the long-term treatment of a concentrated alginate (800 mg/L), showed low or negligible leaching in hash environments (30 mM H₂O₂, 0.1 % NaClO or 10 mM NaOH), and maintained comparable performance after 96 h aging by 30 mM H₂O₂. This study clarifies the factors governing Fenton-like backwash, and demonstrates that a robust and effective strategy for fouling removal can be achieved by coupling this cleaning method with catalytic ceramic membranes.

Recovering oil and water from palm oil mill effluent (POME) reduces environmental pollution and promotes sustainable practices. To assess the most effective recovery method, an experimental comparison was conducted between PVDF and α-Al2O3 ultrafiltration (UF) membranes at constant permeate of 20-50 LMH for PVDF and 20-70 LMH for α-Al2O3 membranes. Both membranes achieved 99.8 % chemical oxygen demand (COD) rejection, with oil concentration factor (Fo) of 186.8 % and 253.0 %, and water recovery (Rw) of 46.6 % and 60.5 %, respectively. The permeate water quality was superior to the Malaysian discharge standards, and the fat, oil, and grease (FOG) content was suitable for phase separation processes. The optimal permeate fluxes, with stable transmembrane pressures (TMP), were observed at 40 LMH (PVDF) and 60 LMH (α-Al2O3). Total resistance (Rt) values were 1.30 ×1012 m-1 (PVDF) and 1.59 ×1012 m-1 (α-Al2O3). The ratio of irreversible to total resistances (Rir/Rt) was 0.02 (PVDF) and 0.06 (α-Al2O3), indicating minimal irreversible fouling. Overall, the α-Al2O3 membrane demonstrated superior performance for oil and water recovery with more stable operation compared to the PVDF membrane. UF membrane technology emerges as an efficient technique for recovering oil and water compared to conventional methods.

The growing global water crisis necessitates advanced wastewater treatment technologies capable of addressing complex contaminants. Adsorbents and membrane technologies provide viable solutions for wastewater treatment, and their performance can be significantly enhanced through surface modification by atomic layer deposition (ALD). ALD enables nanoscale engineering of materials, offering unprecedented control over surface chemistry, pore structure, and functional properties for improved wastewater treatment efficiency. This review critically examines the advancements in ALD-modified membranes and adsorbents for industrial wastewater treatment, highlighting how ALD enhances adsorption kinetics and selectivity in adsorbents, improves hydrophilicity and antifouling behavior in polymeric membranes, and enhances chemical and mechanical stability in ceramic membranes. Despite these advantages, challenges remain in adoption of ALD in wastewater treatment. Future research should focus on optimizing ALD process parameters and exploring synergies with emerging water purification strategies. The continued development of ALD presents a promising pathway towards more efficient and sustainable wastewater treatment solutions.

Sulphate (SO42­) is a model ion due to its negative charge and multivalent nature. Its rejection behavior serves as an indicator of the separation performance for other analogous ions in modified membranes. In literature the rejection of the SO42­ by negatively charged polymeric nanofiltration (NF) membranes has been studied extensively with rejection percentages of >90 %. Silicon carbide (SiC) membranes have gained attention for wastewater treatment due to their high hydrophilicity and negative charge. However, no negatively charged ceramic ultrafiltration (UF) membranes have been tested yet for SO42­ retention. In this study, a commercial alumina (Al2O3) UF membrane was converted into a highly negatively charged tight-UF membrane by coating it with SiC. This was achieved by depositing a 5 μm SiC coating in a single-step via low-pressure chemical vapor deposition (LP-CVD). LP-CVD facilitates the preparation of a SiC at much lower temperatures (700–900 °C) compared to the sol-gel methods (ca. 2100 °C), and it does not require multiple coating cycles and sintering steps to achieve the desired selective layer thickness. Subsequently, properties and performance of the as-prepared tight-UF membrane coated with SiC were evaluated. The SiC coated membrane had a highly negative charge of −70 mV at pH of 6, and a pure water permeability (PWP) of 26 L.m−2.h−1.bar−1. The SiC coated membrane furthermore demonstrated a SO42­ rejection of 79 % despite having a large pore size of 7 nm, in comparison with the pore sizes of below 1 nm of NF membranes. These results highlight the potential of singe-step LP-CVD modification of commercial UF ceramic membranes to produce highly negatively charged SiC coated UF membranes with a high SO42­ rejection, and without a large loss of PWP normally associated with NF membranes.

Recovering oil and water from palm oil mill effluent reduces environmental pollution and promotes sustainable practices. An effective method to achieve this is ultrafiltration (UF), which uses semi-permeable membranes to separate oil, solids, and other contaminants from wastewater under pressure. To assess the most effective recovery method, an experimental comparison was conducted between PVDF and α-Al2O3 UF membranes at constant permeate of 20–50 LMH for PVDF and 20–70 LMH for α-Al2O3 membranes. Both membranes achieved 99.8% chemical oxygen demand (COD) rejection, with oil concentration factor (Fo) of 186.8% and 253.0%, and water recovery (Rw) of 46.6% and 60.5%, respectively. The permeate water quality was superior to the Malaysian discharge standards, and the fat, oil, and grease (FOG) content was suitable for phase separation processes. The optimal permeate fluxes, with stable transmembrane pressures (TMP), were observed at 40 LMH (PVDF) and 60 LMH (α-Al2O3). Total resistance (Rt) values were 1.30 × 1012 m−1 (PVDF) and 1.59 × 1012 m−1 (α-Al2O3). The ratio of irreversible to total resistances (Rir/Rt) was 0.02 (PVDF) and 0.06 (α-Al2O3), indicating minimal irreversible fouling. Overall, the α-Al2O3 membrane demonstrated superior performance in oil and water recovery with more stable operation compared to the PVDF membrane. UF membrane technology emerges as an efficient technique for recovering oil and water compared to conventional methods.

Membrane technology presents an effective solution for treating oily wastewater, a significant environmental hazard stemming from industries such as food processing, metalworking, and oil extraction. Compared to polymeric membranes, ceramic ones exhibit superior mechanical, chemical, and thermal stability, enabling more effective oil removal and easier cleaning. Despite their advantages, membrane fouling remains a challenge, impacting the efficiency of oily wastewater treatment. This review explores oily wastewater characteristics and ceramic membrane applications in treatment processes. It examines the factors influencing ceramic membrane fouling, including wastewater properties (e.g., oil concentration, pH), membrane characteristics (e.g., surface hydrophilicity, charge), and operational parameters (e.g., cross-flow velocity, permeate flux). Strategies to mitigate fouling, such as pretreatment, backpulsing/backwashing for sustained operation, and chemical cleaning for fouling removal, are discussed. By using pretreatment, membrane fouling can be reduced. Backpulsing/backwashing is effective to maintain a long-term operation. Chemical cleaning is effective in removing irreversible fouling and restoring the performance of the ceramic membranes. Moreover, membrane modification techniques that enhance performance are highlighted. Ultimately, the review identifies that effective fouling control is crucial for optimizing ceramic membrane use in oily wastewater treatment, underscoring the need for ongoing research in this area.

Ceramic nanofiltration is a potential one-step treatment for industrial waste streams. It can remove colloidal particles, oil droplets and some organic molecules. The drawback of the technology is that backwash cannot be applied to remove the accumulated cake layer from the membrane surface. At the moment only chemical cleaning with aggressive oxidizing agents like chlorine are effective to restore the permeability of the membranes after fouling. However, calcium carbonate (CaCO3) precoating has shown potential benefits in preliminary research, but have only been executed at laboratory scale, under a constant pressure and with a limited number of experimental cycles. In the presented work, the CaCO3 precoat/acid cleaning method was comprehensively studied under varying operational conditions. Dead-end filtration of a CaCO3-dispersion was used to precoat the membrane surface. Three different acids were tested to partly dissolve the precoat and remove the cake layer from the membrane surface. It was found that citric acid performed the best to recover the permeability of the membrane, probably due to the chelating properties, capturing the calcium ions, with a good removal of the cake layer during forward flush as a result. The size of precoat particles influenced the efficacy of permeability recovery. The smaller the deposited precoating particles on the membrane surface were, the better the cleaning effect was. It is expected that, when filtering real sewage water, these membranes can operate with one precoat during about 25 days with five consecutive citric acid cleaning cycles before a chlorine-based chemical treatment should thoroughly clean the membrane module.

Sodium hypochlorite (NaClO) is widely used for the chemical cleaning of fouled ultrafiltration (UF) membranes. Various studies performed on polymeric membranes demonstrate that long-term (>100 h) exposure to NaClO deteriorates the physicochemical properties of the membranes, leading to reduced performance and service life. However, the effect of NaClO cleaning on ceramic membranes, particularly the number of cleaning cycles they can undergo to alleviate irreversible fouling, remains poorly understood. Silicon carbide (SiC) membranes have garnered widespread attention for water and wastewater treatment, but their chemical stability in NaClO has not been studied. Low-pressure chemical vapor deposition (LP-CVD) provides a simple and economical route to prepare/modify ceramic membranes. As such, LP-CVD facilitates the preparation of SiC membranes: (a) in a single step; and (b) at much lower temperatures (700–900 °C) in comparison with sol-gel methods (ca. 2000 °C). In this work, SiC ultrafiltration (UF) membranes were prepared via LP-CVD at two different deposition temperatures and pressures. Subsequently, their chemical stability in NaClO was investigated over 200 h of aging. Afterward, the properties and performance of as-prepared SiC UF membranes were evaluated before and after aging to determine the optimal deposition conditions. Our results indicate that the SiC UF membrane prepared via LP-CVD at 860 °C and 100 mTorr exhibited excellent resistance to NaClO aging, while the membrane prepared at 750 °C and 600 mTorr significantly deteriorated. These findings not only highlight a novel preparation route for SiC membranes in a single step via LP-CVD, but also provide new insights about the careful selection of LP-CVD conditions for SiC membranes to ensure their long-term performance and robustness under harsh chemical cleaning conditions.

This study investigated the performance of direct hollow fiber nanofiltration (dNF40) membranes from NX Filtration BV on a pilot scale for the treatment of pre-treated IJsselmeer water from Waterwinstation Prinses Juliana (WPJ) in Andijk, as well as the direct treatment of raw IJsselmeer water. The objective was to evaluate the long-term fouling potential and the retention of ions and natural organic matter (NOM) using both WPJ pre-treated IJsselmeer water and raw IJsselmeer water. Additionally, the rejection of organic micropollutants (OMPs) under artificially elevated conditions, referred to as ‘spiked solution’, using WPJ pre-treated IJsselmeer water was investigated. Limited to no fouling was observed on the dNF40 membrane during stable operation when treating both WPJ pre-treated IJsselmeer water and raw IJsselmeer water, even under changing process conditions. NOM removal consistently exceeded 90% regardless of process conditions or water type. The retention of per- and polyfluoroalkyl substances (PFAS) was above 80%, with even higher retention observed for higher molecular weight values. Low molecular weight pharmaceuticals, all below the molecular weight cut-off (MWCO) of the dNF40 membrane (400 Da), exhibited approximately 30% retention. The dNF40 membrane showed better retention of negatively charged pharmaceuticals in the spiked solution compared to positively charged and neutral pharmaceuticals. A total cost of ownership (TCO) analysis unveiled that operational expenditures (OPEX) were three times higher than capital expenditures (CAPEX) for a 5-stage full-scale dNF40 system. Among the components, membrane replacement costs constituted the majority of OPEX (68%), followed by energy costs (31%) and chemical costs (<1%). Overall, the study showcased the suitability of the dNF40 membranes for treating IJsselmeer water, achieving effective removal of NOM and PFAS.

A large decrease in permeability is often observed during the filtration of nano-sized colloids, while fouling is widely regarded as the main explanation for this phenomenon. The osmotic pressure or concentration polarization (CP) of colloids can also contribute to the flux decline. However, the contribution of CP to flux loss cannot be determined by the traditional CP model. In this study, the effect of fouling and CP/osmotic pressure on flux was distinguished. The CP values of polyethylene glycol (PEG) and silica-colloids were determined by the osmotic pressures near the membrane surface and in the feed. The CP induced by colloids accounted for 43–95% of the flux loss in our experiments. Silica exhibited higher CP values (127–460), compared to 7–71 for PEG. This was attributed to the slower back diffusion caused by the larger colloids, as evidenced by the diffusion coefficients of 4.30 × 10⁻¹¹ m²/s for silica (10 nm) and 1.45 × 10⁻¹⁰ m²/s for PEG (2.9 nm). Although the CP was mitigated by increasing the cross-flow velocity, CP values of 31 and 250 were observed for PEG and silica at high Reynolds number of 7317, respectively. The experimentally obtained CP values were also compared with those calculated by the film diffusion model.

Worldwide, a considerable amount of oily wastewater is generated, with oil droplets from 2 to 200 nm that are difficult to separate because of their size and colloidal stability. This study presents a novel approach for effectively separating microemulsions via cubic silicon carbide (3C-SiC)-coated alumina (Al ₂O ₃) membranes fabricated based on low pressure chemical vapor deposition (LPCVD). SiC was deposited at a relatively low temperature at 860 °C on 100 nm Al ₂O ₃ membranes using two precursors: SiH ₂Cl ₂ and C ₂H ₂. With the increase in deposition time, up to 25 min, the pore size decreased from 41 nm to 33 nm, which is a smaller pore size of a SiC membrane than previously used for oil/water separation. The polycrystalline 3C-SiC-coated membranes showed improved hydrophilicity (water contact angle of 15°) and highly negatively charged surfaces (−65 mV). Microemulsion filtration experiments were carried out at a constant permeate flux (80 Lm ⁻² h ⁻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 Al ₂O ₃ 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 alumina 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. Lastly, the 62 nm SiC-coated membrane with 20 min coating time was the best choice for the filtration of the microemulsion, because of the high rejection of the oil droplets and low fouling tendency.

Ceramic nanofiltration (NF) is a promising alternative for direct surface water treatment, but is hampered for full-scale applications by fouling and a lack of eco-friendly cleaning regimes. In this work, an innovative reactive pre-coat layer, consisting of an iron oxychloride catalyst, was constructed on top of commercial ceramic NF membranes, for segregating a large-sized colloid fraction in canal water and Fenton cleaning with a hydrogen peroxide (H₂O₂) solution. The large-sized colloids (3−30 μm) were identified as dominant substances fouling the TiO₂ separation layer of the pristine membranes, leading to a fast increase in their filtration resistance, in contrast to the small-sized colloids (<0.04 μm) and natural organic matter (NOM). As a consequence, the catalyst pre-coat layer with a pore size of 0.1–0.5 μm was able to segregate the large-sized colloids from the TiO₂ separation layer during direct filtration of the raw water. Moreover, filtration under an acceptable flux of around 23 L m⁻² h⁻¹ did not cause pore clogging in the catalyst pre-coat. In addition, Fenton oxidation initiated by the catalytic pre-coat efficiently restored the filtration resistance, whereas sole H₂O₂ flush of the pristine membrane was not effective. In the meantime, the TiO₂ separation layer of the membrane exerted a high NOM rejection of approximately 90%, measured as dissolved organic carbon, while the catalyst pre-coat on the membrane remained active in Fenton cleaning, over five one-day cycles. The findings of this work may provide guidance on the structural and functional design of a catalytic pre-coat layer for a dual purpose of foulant segregation and oxidative removal, particularly in response to key fouling-causing substances, during membrane-based treatment of real water matrices.

Verwijdering van organische microverontreinigingen uit huishoudelijk afvalwater, waaronder medicijnresten, staat sterk in de belangstelling om de oppervlaktewater kwaliteit te verbeteren, de drinkwaterbronnen te beschermen en te voldoen aan toekomstige EU richtlijnen. In minder dan vijf jaar is AdOx, een technologie waarin adsorptie en oxidatie word en gecombineerd, ontwikkeld tot een veelbelovende techniek. Ten opzichte van referentietechnieken zijn de CO2-voetafdruk klein en de kosten laag. De Nederlandse richtlijn van 70% verwijdering wordt gehaald. Ondanks het gebruik van ozon resulteert AdOx niet in bromaat vorming en oxidatiebijproducten in het behandelde afvalwater. Er is nog veel ruimte voor verdere optimalisatie.

Catalytic ceramic nanofiltration (NF) is a promising technology for direct wastewater reclamation, given its high separation selectivity and reactive surfaces for oxidative removal of fouling. A better understanding of the relation between fouling types and oxidative cleaning efficacy under high organic loading conditions is of practical importance for realizing stable filtration/cleaning performance in long-term water reclamation operations. In this work, Fenton cleaning, using a hydrogen peroxide solution and an iron oxychloride catalyst pre-coat layer on top of commercially available ceramic NF membranes, was studied with respect to high organic loaded fouling, simulated by a concentrated sodium alginate solution in the presence of calcium. Adsorption (in the absence of a permeate flow) and constant-pressure filtration (with a permeate flow) experiments were performed to distinguish between permeance decreases as a result of either adsorptive or cake layer fouling. The results show that the flux evolution could be divided into an initial sharp flux decline, due to rapid adsorption of the foulants, and a subsequent gradual flux decrease, resulting from progressive cake build-up on the membrane. The two-stage flux decrease was enhanced during the constant-pressure filtration experiments, because they start at a high flux with a high fouling rate, while the flux gradually decreases as fouling proceeds. During multiple adsorption/cake filtration/Fenton cleaning cycles, the cake layer fouling was sufficiently removed by Fenton cleaning in contrast to the adsorptive fouling. However, the total permeate production during ceramic NF was not influenced by the remaining adsorptive fouling (after cleaning), since the adsorptive fouling always only occurs at the beginning of each cycle. The findings provide new insights into the criteria for evaluating and optimizing the efficacy of oxidative (Fenton) cleaning during ceramic NF in water treatment.

This work presents the first comprehensive investigation of natural organic matter (NOM) fraction removal using ceramic membranes in South Africa. The rate of removal of bulk NOM (measured as UV₂₅₄ and DOC % removal), the biodegradable dissolved organic carbon (BDOC) fraction, polarity-based fractions, and fluorescent dissolved organic carbon (FDOM) fractions was investigated from water abstracted from drinking water treatment plants (WTPs) in South Africa. Further, mechanisms of ceramic membrane fouling by waters of South Africa were studied. Ceramic membranes removed more than 80% DOC from samples from coastal WTPs, whereas for inland plants, the removal was between 60% and 75% of DOC. FDOM was removed to at least 80% regardless of the site of the plant. The BDOC removal by the ceramic membranes was above 85%. The hydrophobic fraction was the most amenable to removal by ceramic membranes regardless of the site of sample abstraction (above 60% for all sites). The freshness index (β:α) correlated strongly to UV₂₅₄ removal (R² = 0.96), thus UV₂₅₄ removal can serve as a proxy for the susceptibility to removal of such class of NOM by ceramic membranes. This investigation demonstrated that ceramic membranes could be a valuable technology if integrated into the existing WTPs. Practitioner Points: The removal of bulk parameters by ceramic membrane was greater than unit conventional processes used in all the sampled water treatment plants. The hydrophobic polarity-based fraction of NOM was the most amenable to removal by ceramic membranes regardless of the site of the WTP. Polarity-based fractions, aromaticity, and initial DOC had a combined influence on the removal of organic matter by ceramic membranes as explained by principal component three.

There is a global need for optimizing the use of water that has resulted from increased demand due to industrial development, population growth, climate change and the pollution of natural water resources. One of the solutions is to use reclaimed water in industrial applications that do not require water of potable quality, such as cooling water. However, for cooling water, (treated) wastewater’s hardness is too high, apart from having a high load of suspended solids and organic matter. Therefore, a combination of softening with ceramic micro-filtration was proposed for treating wastewater treatment effluent containing fouling agents for potential use in industrial cooling systems. The effectiveness of the softening process on model-treated wastewater with calcium hydroxide in the presence of phosphate and sodium alginate was first evaluated using jar tests. Furthermore, membrane fouling was studied when filtering the softened water. The results showed that the inhibition of calcium carbonate precipitation occurred when inorganic substances, such as phosphate and organic compounds, were present in the water. The fouling of the membranes due to sodium alginate in water was only slightly negatively affected when combined with softening and phosphate. Therefore, this combination of treatments could be potentially helpful for the post-treatment of secondary effluent for cooling systems.