The variable biodegradability and compositional complexity of natural organic matter (NOM) in surface waters pose an appreciable challenge for drinking water treatment. The study characterized NOM found in nine South African water sources for predicting treatability under regional conditions by integrating biodegradability dissolved organic carbon (BDOC) analysis, fluorescence excitation-emission matrix (EEM) spectroscopy, optical analysis, and bulk parameters, such as specific UV absorbance (SUVA), UV254 and dissolved organic carbon (DOC). Water sources that exhibited the highest BDOC potential index included Umzinto, Hazelmere, Mona, and Mtwalume (3.55, 2.21, 2.06, and 1.73, respectively). Strong Peak B, T, and M intensities were experienced by these sites, for example, Umzinto peak intensities were 0.32, 0.74, and 2.49 RU, respectively, indicative of the presence of the NOM pool largely influenced by microbial activity, likely derived from diffuse anthropogenic inflow or recent biological production. Water sources exhibiting such fluorescence profiles characteristic of a NOM pool with high biological reactivity are expected to respond well to treatment stages such as slow sand filtration, biologically active carbon (BAC), or biofiltration. The findings demonstrate the need for developing tailored treatment strategies based on site-specific NOM characteristics. Data-driven approaches helping utilities move toward adaptive water quality management have been proven.

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.

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.

Organic micropollutants such as pharmaceuticals pose significant environmental and public health risks. These contaminants not only contribute to the spread of antibiotic resistance but also disrupt aquatic ecosystems. Advanced oxidation processes are known to effectively degrade pharmaceuticals, and among these, photoelectrocatalysis (PEC) offers a promising method for removing contaminants present at trace levels (μg/L to ng/L). The focus of the presented study was to assess the influence of five quaternary ammonium compounds (QACs) on BiVO₄ photoanodes, modifying the structural properties and enhancing photoelectrocatalytic performance. The QAC-modified BiVO₄ photoanode variants were characterized using X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, UV-Vis spectroscopy, and linear sweep voltammetry. PEC degradation experiments were conducted using effluent, collected after secondary treatment, at a wastewater treatment plant, spiked with 10 selected pharmaceuticals at an initial concentration of 10 μg/L. The removal efficacy of the modified BiVO₄ photoanodes was evaluated under simulated solar irradiation. Among the tested variants, the photoanode modified with the alkyl trimethyl ammonium compound ATMAC C18 modified exhibited the most rapid degradation, with several pharmaceuticals removed within the first 15 minutes. However, dialkyl dimethyl ammonium compound DADMAC C18 modified photoanode was identified as the best-performing variant, with sulfamethoxazole emerging as the critical compound due to its longest half-life.

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.

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.

Managed Aquifer Recharge (MAR) systems have supplied drinking water to rural communities in southwestern Bangladesh since 2009. Although MAR enhances water availability, there are concerns about the potential mobilization of iron (Fe), manganese (Mn), and arsenic (As) during storage. Fourteen push-pull tests (PPTs) were performed under oxidative and reductive conditions at four MAR sites. These tests involved injecting filtered and O2-saturated pond water for oxidative conditions, and sucrose-amended anoxic stored MAR water for reductive conditions, via a well in the stored MAR water. During oxidative PPTs, repeated aeration, injection, and abstraction cycles resulted in rapid consumption of dissolved oxygen (DO) with first-order rate constants of ∼52 to 72 day^-1 across all sites. DO was mainly consumed by adsorbed and dissolved Fe, with no apparent signs of pyrite and organic matter (OM) oxidation. The consistently high rate constant across the cycles suggests that heterogeneous Fe oxidation dominates. DO oxidizes Fe(II) to form Fe-(oxyhydr)oxides, resulting in the temporary removal of dissolved Fe (∼98 %), Mn (∼70–80 %), and As (60–70 %) at sites GMF11 and JJS91 due to sorption onto newly formed Fe-(oxyhydr)oxides. At sites MGS and MF05, increased As concentrations were noted due to the desorption of As from the Fe-(oxyhydr)oxides surface during abstraction. During reductive PPTs, the sucrose degraded over time, resulting in increased bicarbonate (HCO₃) and acetate concentrations and decreased pH and (sucrose-derived) DOC in abstracted water. These conditions led to the reductive dissolution of Fe-(oxyhydr)oxides, mobilizing Fe, Mn, and As, resulting in concentration peaks up to 70 mg/L Fe, 3.5 mg/L Mn, and 120 µg/L As. At MGS and MF05, similar trends for Fe and Mn were observed, while As levels did not increase. Peak concentrations were observed after about one day at JJS91, and two days at the other sites. Regular infiltration of O2-saturated water may limit mobilization of Fe, Mn, and As, while the occurrence of reduced conditions should be prevented, as they could result in mobilization of these geogenic metals and endanger the provision of safe drinking water.

Activated carbon (AC) is widely used for organic micro-pollutants (OMPs) removal, yet adsorbability evaluation remains challenging due to molecular diversity and adsorbent heterogeneity, especially given the limitations of traditional assessment metrics such as hydrophobicity (logD). This study proposed a machine learning (ML)-driven assessment strategy by aligning the adsorbability of various AC adsorbents with a hypothetical “Standard AC” to evaluate the adsorbabilities across 56 OMPs. XGBoost, RF, and ET models achieved high prediction accuracy on the test set (R² = 0.88–0.98, RMSE = 0.17–0.38, MAE = 0.13–0.27), and were further validated against a published experimental dataset. Interpretable ML analysis identified a logD threshold of ≈ 2, at which the dominant adsorption mechanisms transitioned from hydrophobic interactions for OMPs with higher hydrophobicity to π-π interactions, hydrogen bonding, and pore-filling for those with lower hydrophobicity. Adsorbability increased with molecular weight, as flexible molecules (rotatable bond ratio > 0.012) overcame steric hindrance in micropores, enhancing pore-filling efficiency through improved accessibility. By introducing a standardized, data-driven adsorbability reference and elucidating the intrinsic interplay between molecular properties and adsorption mechanisms, this study offers a robust framework for knowledge-informed treatability evaluation and a practical benchmark to guide adsorption process design.

Monitored natural attenuation is commonly used to manage petroleum hydrocarbon-contaminated groundwater. However, it requires periodic, costly grab sampling. We propose a cost-effective, real-time groundwater monitoring proof-of-concept machine learning (ML) framework using in-situ sensors—pH, dissolved oxygen, electrical conductivity, and redox potential—to detect benzene, ethylbenzene, and xylenes (BEX). We built upon the established correlations between hydrocarbon concentrations and in-situ water quality parameters (iWQPs). Due to limited field data, we validated the framework using datasets at virtual wells within a simulated aquifer from our previously developed reactive transport model. In this application, we detected the spreading of pollution downstream of the established pollution plume. The used framework is a binary classification system that flags contamination at virtual downstream wells. We compared five ML classifiers, i.e. Logistic Regression, Random Forest, XGBoost, Multi-layer Perceptron, and Support Vector Classifier, for early warning when BEX reached or exceeded the regulatory threshold of 5 μg/L. The models were trained on virtual wells at and near the source zone and predicted contamination before BEX reached the threshold at downstream virtual wells. This reflects the spatial variability in flow and reaction dynamics that altered BEX-iWQP relationships. Scenario analyses revealed the ML models' sensitivity to aquifer properties, i.e., hydraulic conductivity, electrical conductivity, and electron acceptor availability. We also assessed the impact of sensor noise and seasonal fluctuations on iWQPs. We found that even moderate levels of noise (10–20 %) can significantly affect model accuracy, particularly when the noise was introduced into the test data. Therefore, we recommended to combine hardware stabilization with adaptive smoothing techniques. With these approaches, our proposed framework remains promising for providing early warnings of plume migration toward sensitive receptors.

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.

Powdered activated carbon (PAC) adsorption is widely applied for the removal of organic micropollutants in drinking water treatment. However, conventional single-dose PAC application requires high dosages to overcome competitive adsorption from natural organic matter (NOM). This study evaluates a multi-stage PAC dosing strategy to mitigate NOM competition and enhance the removal efficiency of representative odorous micropollutants. Experiments with NOM-rich surface water showed that multi-stage dosing increased adsorption capacity and achieved up to 48% PAC savings at an 80% micropollutant removal benchmark, compared to single-stage application. In contrast, no improvement was observed in NOM-free water. Two-stage PAC dosing considerably improved the removal of weakly adsorbing compounds such as 2-methylisoborneol (MIB) and 2-ethyl-5,5-dimethyl-1,3-dioxane (EDD), while incremental gains were observed for strongly adsorbing micropollutants (e.g., 2-butyl-5,5-dimethyl-1,3-dioxane) with three- or four-stage configurations. Mechanistic analysis indicated that early-stage PAC doses preferentially adsorbed competitive NOM components, preserving high-affinity sites for micropollutants in later stages. PACs enriched in narrow mesopores outperformed microporous PACs in the staged dosing configuration. The proposed strategy, as compared to existing designs summarized from the literature, requires minimal infrastructural modifications and offers a cost-effective, scalable approach for improving micropollutant removal under NOM-rich conditions.

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.

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.

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 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.

Introduction:
Water scarcity is a significant global challenge that frequently manifests as inadequate water supply for domestic purposes. However, domestic water insecurity can occur even in regions where water is naturally abundant. Despite Colombia’s plentiful surface water resources, rural and peri-urban communities often experience limited access to water. Existing water supply systems are frequently susceptible to poor maintenance, particularly in remote areas where much of the infrastructure remains outdated. Consequently, water is often lost through leaks or unintentional non-domestic use. Although a regulatory framework for water usage exists, it does not consistently translate into effective implementation.

Methodology:
Based on an extensive survey of approximately 1000 households in four rural and four peri-urban communities in the Valle del Cauca Department, Colombia, we identified the factors underlying inefficient water supply and use. Perceived water use at the household level, based on self-reported time spent on various use types, such as bathing, and water supplied at the system level, was estimated.

Results and discussion:
Household size, education level, age and occupation were found to be critical factors influencing end water use and water supply. This not only elucidates why water is supplied and used inefficiently in rural systems (e.g., due to non-domestic use), but also accounts for the variability of perceived water use within peri-urban systems. The water use perceived by households in the rural systems was statistically similar across the rural systems studied and was significantly lower than that in the peri-urban systems. Most rural systems exhibited very low ratios of perceived water use to water supplied, indicating that either water is lost in conveyance or that water is used for non-domestic purposes. Peri-urban users, who perceived to use more water than users in rural areas, were associated with younger and more educated households. Higher education levels were also associated with better financial capacity and technical ability to manage water systems; therefore, peri-urban systems were better managed.

Activated carbon is employed for the adsorption of organic micropollutants (OMPs) from water, typically present in concentrations ranging from ng L⁻¹ to μg L⁻¹. However, the efficacy of OMP removal is considerably deteriorated due to competitive adsorption from background dissolved organic matter (DOM), present at substantially higher concentrations in mg L⁻¹. Interpreting the characteristics of competitive DOM is crucial in predicting OMP adsorption efficiencies across diverse natural waters. Molecular weight (MW), aromaticity, and polarity influence DOM competitiveness. Although the aromaticity-related metrics, such as UV₂₅₄, of low MW DOM were proposed to correlate with DOM competitiveness, the method suffers from limitations in understanding the interplay of polarity and aromaticity in determining DOM competitiveness. Here, we elucidate the intricate influence of aromaticity and polarity in low MW DOM competition, spanning from a fraction level to a compound level, by employing direct sample injection liquid chromatography coupled with ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry. Anion exchange resin pre-treatment eliminated 93% of UV₂₅₄-active DOM, predominantly aromatic and polar DOM, and only minimally alleviated DOM competition. Molecular characterization revealed that nonpolar molecular formulas (constituting 26% PAC-adsorbable DOM) with medium aromaticity contributed more to the DOM competitiveness. Isomer-level analysis indicated that the competitiveness of highly aromatic LMW DOM compounds was strongly counterbalanced by increased polarity. Strong aromaticity-derived π-π interaction cannot facilitate the competitive adsorption of hydrophilic DOM compounds. Our results underscore the constraints of depending solely on aromaticity-based approaches as the exclusive interpretive measure for DOM competitiveness. In a broader context, this study demonstrates an effect-oriented DOM analysis, elucidating counterbalancing interactions of DOM molecular properties from fraction to compound level.

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.

Long-term consumption of groundwater containing elevated levels of arsenic (As) can have severe health consequences, including cancer. To effectively remove As, conventional treatment technologies require expensive chemical oxidants to oxidise neutral arsenite (As(III)) in groundwater to negatively charged arsenate (As(V)), which is more easily removed. Rapid sand filter beds used in conventional aeration-filtration to treat anaerobic groundwater can naturally oxidise As(III) through biological processes but require an additional step to remove the generated As(V), adding complexity and cost. This study introduces a novel approach where As(V), produced through biological As(III) oxidation in a sand filter, is effectively removed within the same filter by embedding and operating an iron electrocoagulation (FeEC) system inside the filter. Operating FeEC within the biological filter achieved higher As(III) removal (81 %) compared to operating FeEC in the filter supernatant (67 %). This performance was similar to an analogous embedded-FeEC system treating As(V)-contaminated water (85 %), confirming the benefits of incorporating FeEC in a biological bed for comparable As(III) and As(V) removal. However, operating FeEC in the sand matrix consumed more energy (14 Wh/m³) compared to FeEC operated in a water matrix (7 Wh/m³). The efficiency of As removal increased and energy requirements decreased in such embedded-FeEC systems by deep-bed infiltration of Fe(III)-precipitates, which can be controlled by adjusting flow rate and pH. This study is one of the first to demonstrate the feasibility of embedding FeEC systems in sand filters for groundwater arsenic removal. Such systems capitalise on biological As(III) oxidation in aeration-filtration, effectively eliminating As(V) within the same setup without the need for chemicals or major modifications.

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.