Natural Organic Matter Removal Research Articles

Life Cycle Assessment of Immobilised and Slurry Photocatalytic Systems for Removal of Natural Organic Matter in Water

This study investigates the environmental impacts caused by the scaling up of the photocatalytic purification of drinking water using ultraviolet light-emitting diode technology. The life cycle assessment methodology was utilised to estimate the environmental impacts of two different reactor setups commonly used in lab-scale studies: an immobilised and a suspended TiO2 catalytic system. The functional unit adopted was the treatment of 1 L of water with an initial 7.8 mg/L concentration of natural organic matter, achieving a final 1 mg/L concentration. The use of a suspended photocatalyst was found to have an environmental footprint that was 87% lower than that of the immobilised one. From the sensitivity analysis, the environmental hotspots of the treatment process were the electricity usage and immobilised catalyst production. Therefore, alternative scenarios investigating the use of a renewable electricity mix and recyclable materials were explored to enhance the environmental performance of the photocatalytic treatment process. Using a renewable electricity mix, a decrease of 55% and 15% for the suspended and immobilised catalyst, respectively, was observed. Additionally, the process of recycling the glass used to support the immobilised catalyst achieved a maximum reduction of 22% in the environmental impact from the original scenario, with 100 glass reuses appearing to provide diminishing returns on the environmental impact savings.

Characterizing Macroporous Ion Exchange Membrane Adsorbers for Natural Organic Matter (NOM) Removal—Adsorption and Regeneration Behavior

Addressing the characterization of Natural Organic Matter (NOM) removal by functionalized membranes in water treatment, this study evaluates the effectiveness of two commercial ion-exchange membrane adsorbers: Sartobind® Q (with quaternary amines) and D (with tertiary amines). Using Suwannee River NOM (SRNOM) as a surrogate, Langmuir adsorption isotherms revealed maximum capacities (Qmax) of 2966 ± 153 mg C/m2 and 2888 ± 112 mg C/m2, respectively. Variations in flux from 50 to 500 LMH had a minimal impact on breakthrough times, proving low diffusion limitations. The macroporous (3–5 µm) functionalized cellulose-based membranes exhibited high permeabilities of 10800 L/(h m2 bar). Q maintained positive zeta potential vs. pH, while D’s zeta potential decreased above pH 7 due to amine deprotonation and turning negative above an isoelectric point of 9.1. Regeneration with 0.01 M NaOH achieved over 95% DOC regeneration for Sartobind® D, characterizing reversibility through a pH-swing. Cyclic adsorption showed that Q maintained its capacity with over 99% DOC regeneration, while D required acidic conditioning after the first regeneration cycle to mitigate capacity reduction and re-deprotonate the adsorber. These results have demonstrated the potential suitability of adsorber membranes, designed originally for biotechnological purposes, for the possible removal of disinfection byproduct precursors in drinking water treatment.

Peracetic acid-induced nanoengineering of Fe-based metallic glass ribbon in application of efficient drinking water treatment

This study presents a novel approach utilizing Fe-Si-B metallic glass-based advanced oxidation processes (AOPs) with peracetic acid (PAA) exposure to mitigate disinfection by-products (DBPs) formation in drinking water treatment. Under optimal conditions, it achieved a 98.21% removal of natural organic matter (NOM) and an 80.64% reduction in DBPs formation. The efficacy is attributed to the galvanic cell effect induced by nanoflower structures on the ribbon surface, produced via PAA exposure, thereby enhancing degradation efficiency. High-valent iron Fe(IV) was identified as the primary reactive species, showing robust cycling efficiency under near-neutral conditions. Continuous flow experiments and toxicity assessments using luminescent bacteria further validated the method, demonstrating minimal metal leaching (<0.146 mg/L) and reduced biotoxicity with a 37.68% inhibition rate decrease in 24 h. These findings underscore the promising potential of PAA-integrated Fe-based amorphous alloys for comprehensive water disinfection and purification.

Quartz Crystal Microbalance as a Holistic Detector for Quantifying Complex Organic Matrices during Liquid Chromatography: 2. Compound-Specific Isotope Analysis.

In carbon-compound-specific isotope analysis (carbon CSIA) of environmental micropollutants, purification of samples is often required to guarantee accurate measurements of a target compound. A companion paper has brought forward an innovative approach to couple a quartz crystal microbalance (QCM) with high-performance liquid chromatography (HPLC) for the online quantification of matrices during a gradient HPLC purification. This work investigates the benefit for isotope analysis of polar micropollutants typically present in environmental samples. Here, we studied the impact of the natural organic matter (NOM) on the isotopic integrity of model analytes and the suitability of the NOM-to-analyte ratio as a proxy for the sample purity. We further investigated limitations and enhancement of HPLC purification using QCM on C18 and C8 phases for single and multiple targets. Strong isotopic shifts of up to 3.3% toward the isotopic signature of NOM were observed for samples with an NOM-to-analyte ratio ≥10. Thanks to QCM, optimization of matrix removal of up to 99.8% of NOM was possible for late-eluting compounds. The efficiency of HPLC purification deteriorated when aiming for simultaneous purification of two or three compounds, leading to up to 2.5% less NOM removal. Our results suggest that one optimized HPLC purification can be achieved through systematic screening of 3 to 5 different gradients, thereby leading to a shift of the boundaries of accurate carbon CSIA by up to 2 orders of magnitude toward lower micropollutant concentrations.

Unveiling the role of cake layer in coagulation-ultrafiltration on membrane fouling and emerging application as dynamic membrane before ultrafiltration

Cake layer is considered to play a crucial role in membrane fouling during the coagulation-ultrafiltration process. However, the contribution of the cake layer on membrane fouling and probable natural organic matter (NOM) removal in this process is unclear, leading to a limited understanding of cake layer and potential secondary utilization. Here, ultrafiltration (UF) membrane fouling contribution, NOM removal, and dynamic membrane application of the cake layer were investigated. Results showed reversible fouling was dominated by cake layer, whereas irreversible fouling was determined by both cake layer and residual NOM in coagulation effluent. Compared with direct UF, the cake layer improved approximately by 15 % of HA removal with molecular weight (MW) of 2000–4000 Da. By optimizing membrane material, HA removal and membrane fouling alleviation were synchronously achieved by cake layer deposition-UF. According to mechanisms analysis, HA removal was attributed to the adsorption or interception of HA with larger MW by the cake layer. Zeta potential and fractal dimension of flocs, and contact angle of the cake layer were closely related to HA removal by cake layer, whereas reversible and irreversible fouling were positively correlated with cake layer thickness and floc fractal dimension respectively. Compared with other dynamic membranes, the cake layer had the best economic performance, which provided application potential on NOM removal in micro-polluted surface water.

Synthesis and evaluation of a novel cross-linked biochar/ferric chloride hybrid material for integrated coagulation and adsorption of turbidity and humic acid from synthetic wastewater: Implications for sludge valorisation

The deep removal of organic pollutants is challenging for coagulation technology in drinking water and wastewater treatment plants to satisfy the rising water standards. Iron (III) chloride (FeCl3) is a popular inorganic coagulant; although it has good performance in removing the turbidity (TB) in water at an alkaline medium, it cannot remove dissolved pollutants and natural organic matter such as humic acid water solution. Additionally, its hygroscopic nature complicates determining the optimal dosage for effective coagulation. Biochar (BC), a popular adsorbent with abundant functional groups, porous structure, and relatively high surface area, can adsorb adsorbates from water matrices. Therefore, combining BC with FeCl3 presents a potential solution to address the challenges associated with iron chloride. Consequently, this study focused on preparing and characterizing a novel biochar/ferric chloride-based coagulant (BC–FeCl3) for efficient removal of turbidity (TB) and natural organic matter, specifically humic acid (HA), from synthetic wastewater. The potential solution for the disposal of produced sludge was achieved by its recovering and recycling, then used in adsorption of HA from aqueous solution. The novel coagulant presented high TB and HA removal within 10 min of settling period at pH solution of 7.5. Furthermore, the recovered sludge presented a good performance in the adsorption of HA from aqueous solution. Adsorption isotherm and kinetics studies revealed that the Pseudo-second-order model best described kinetic adsorption, while the Freundlich model dominated the adsorption isotherm.

Operation and performance analysis of direct hollow fiber nanofiltration: A pilot study at IJsselmeer

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.

Simultaneous Removal of Pesticides Mixture and Natural Organic Matter from Surface Waters by Nitric and Chlorosulfonic Acid Functionalized Powdered Activated Carbon

AbstractBACKGROUNDSeveral studies have addressed the adsorption of pesticides such as alachlor, acetochlor, metolachlor, and fenthion from water and wastewater, yet the interaction of these compounds with natural organic matter (NOM) complicates their effective removal due to competitive adsorption effects. This study aims to fill this gap by exploring the efficacy of nitric acid and chlorosulfonic acid‐modified activated carbons in removing both pesticides and NOM under realistic environmental conditions.RESULTSModifications using nitric acid and chlorosulfonic acid significantly improved the pesticide removal capabilities of Norit SX F Cat (AC1) adsorbents. While both the original and chlorosulfonic acid‐modified adsorbents showed comparable efficacy in pesticide removal, nitric acid‐modified AC Puriss (AC2) adsorbents were less effective. Remarkably, a 100 mg/L dose of both original and modified powdered activated carbons (PACs) removed over 98% of all four pesticides from water samples. Additionally, a lower 25 mg/L dose effectively achieved similar removal rates, demonstrating their utility as feasible options for water treatment.CONCLUSIONModifying powdered activated carbons with nitric acid and chlorosulfonic acid has been proven to enhance their structural and adsorptive properties significantly. These modifications led to improved pesticide removal efficiencies, particularly with the chlorosulfonic acid‐modified PACs, which demonstrated superior performance in adsorption tests. The study also highlighted the competitive adsorption posed by low‐molecular‐weight organic substances in water, which compete with pesticides for active adsorption sites.This article is protected by copyright. All rights reserved.

Towards a molecular-scale theory for the removal of natural organic matter by coagulation with trivalent metals

Towards a molecular-scale theory for the removal of natural organic matter by coagulation with trivalent metals

Electro-sorption and -desorption characteristics of electrically conductive polyacrylonitrile membranes to remove aqueous natural organic matter in dead-end ultrafiltration system

Electrically conductive (EC) membranes have emerged as an innovative approach in removing natural organic matter (NOM) by electro-sorption (e-sorption) when external anodic potential (AP) is applied. In this study, the EC membranes were established by a forming a porous nanolayer of Pt nanoparticles via magnetron sputtering on both sides of virgin and chemically modified PAN ultrafiltration (UF) membranes. The modified PAN membranes were functionalized with ethylenediamine (PAN-EDA) and sodium hydroxide (PAN-NaOH). The virgin PAN membrane material contains nitrile group and demonstrated a negative zeta potential in the analyzed pH range. The PAN-EDA membrane owned amidine and amine groups, whereas PAN-NaOH membrane possessed carboxyl and amide groups in the membrane matrix. The PAN-NaOH and PAN-EDA membranes exhibited isoelectric points at 3.7 and 7.8, respectively. Electrical field-assisted UF experiments were conducted with Suwannee River NOM in dead-end mode and NOM removal was monitored using different methods of NOM characterization (e.g., SEC, DOC and UV254 absorbance). The results revealed that the non-electrically conductive (NEC) and EC virgin PAN membranes exhibited almost no intrinsic adsorption (at 0 V external potential) and e-sorption of NOM at 2.5 V AP respectively. However, NEC PAN-NaOH and PAN-EDA membranes showed DOC intrinsic sorption loadings of 17 mg·m−2 and 258 mg·m−2 at permeate flux 100 L·m−2·h−1 and pH 7 respectively. In comparison, the DOC e-sorption loadings of the EC PAN-NaOH and EC PAN-EDA membranes at 2.5 V AP were 197 mg·m−2 and 525 mg·m−2 under same test conditions respectively. The NOM e-desorption characteristics of the EC modified PAN membranes were also investigated to regenerate membranes for a sustainable filtration process. The results indicated that the EC PAN-NaOH and PAN-EDA membranes can be regenerated by reversing the electrical polarity almost completely. In conclusions, the outcomes of this work confirm that the presence of the derivatives of amines (e.g., amines, amidine and amide groups) and carboxyl group are necessary in the membrane matrix to induce e-sorption and -desorption characteristics.

The new concept of MIEX® resin dose categories. swelling effect, reactor steady-state balance, and nom removal process control

The use of powdered adsorbents for water purification has many advantages and one major drawback – lack of regeneration due to difficulty in separating powdered particles. This weakness is attempted to be broken by powdered magnetic adsorbents, in particular magnetic ion exchange resins, used to remove natural organic matter (NOM) from water. In this water treatment process, NOM removal is controlled by the adsorbent content in the reactor (adsorbent dose) and the degree of its saturation. The control over the dose and saturation is done by mutual relations between the regenerated resin stream directed to the reactor and the saturated resin stream received from the reactor. An obstacle in balancing these streams is a variable volume of the adsorbent resulting from its varied swelling, depending on the features of the solution and saturation of the adsorbent. For this reason, it was proposed to distinguish new resin dose and content categories adequate to these changes, the use of which allows full control of both streams. Thus, the reactor feed stream was associated with relative fresh resin content (RRC) and relative fresh resin dose (RRD), which indicate the volume occupied by the regenerated adsorbent in the solution of water during purification. However, the stream received from the reactor was associated with saturated resin content (SRC) and saturated resin dose (SRD), which indicate the volume occupied by saturated adsorbent in the solution of water under treatment. In turn, these two categories of contents/doses are related to the swelling degree (hSR). Another role was assigned to the third dose category, which is absolute fresh resin dose (ARD), referring to the volume occupied by the regenerated adsorbent in the solution of demineralized water. Thanks to two key features with reference properties (demineralized water, regenerated adsorbent), ARD allows one to transfer laboratory results to practice and to compare the results of various research. The resin loss factor described by the ηLS indicator was also included in this structure.

Reclamation of impacted urban phreatic water through nanofiltration technology: Insight on natural organic matter removal by fluorescence spectroscopy

Nanofiltration (NF) is a promising technology called to play a relevant role in water reclamation, which lies in the core of circular economy in the water sector. The aim of this study was to assess two aromatic polyamide-based NF membranes (the looser NF270 and the tighter NF90 ones) for the treatment of urban impacted phreatic water. The focus was centred on the removal of dissolved inorganic and organic solutes and on the differences observed between solutes. Membrane ions rejection was modelled by the Solution-Electro-Diffusion Film Model (SEDFM). DOC was tracked by Fluorescence Excitation-Emission Matrices (FEEM) coupled to Parallel Factor Analysis (PARAFAC) to get insight into the character of DOC rejected by or permeated through the membranes. Results showed that the NF90 membrane systematically achieved upper values in the rejection of ions than the looser NF270 one. Variations between ions could be interpreted by the mechanisms ruling their rejection, i.e. Donnan and dielectric exclusion phenomena. Experimental rejections were also satisfactorily fit by the SEDFM, indicating that that the presence of DOC in the phreatic water did affect modelling of ions transport through the membranes. DOC was rejected at very high percentages (>90%) by both membranes, but FEEM-PARAFAC analysis revealed that humic- and tryptophan- like components were more rejected (>90% for both membranes) than tyrosine-like compounds (45% for NF270 and 57% for NF90). The finding is of relevance from a point of view of disinfection practices, as it has been observed that humic-like substances are strongly correlated with DBPs formation.

Revealing the membrane fouling behavior and interfacial interaction mechanism in a combined visible light photocatalysis-ultrafiltration system for advanced purification of NOM

A novel visible photocatalysis nanomaterials Bi2O3/rGO/TiO2 (BRGT) was combined with polyethersulfone membrane (PES) and ceramic membrane (CM), respectively, to investigate the natural organic matter (NOM) removal performance, membrane fouling behavior and interfacial interactions. The results showed that NOM removal mainly by superoxide radical-dominated photocatalysis followed by membrane rejection enhancing the removal of fluorescent humic and proteins. Compared with PES, CM could more effectively retain the low molecular weight acidic intermediates and transitional or/and hydrophilic organic fractionations generated by photocatalysis. The mixture of NOM with BRGT (without photocatalysis) reduced the reversible fouling of the PES, causing an increase in the interfacial energy barrier of the fouling layer, while the opposite phenomenon was observed for CM. The photocatalysis time affected the membrane fouling, with short photocatalysis times (5 min) causing an increase in irreversible fouling. Extending the photocatalysis time, the interfacial interaction of the PES dominated by Lewis acid-base repulsive interaction gradually increased. And the gradual decreased of interfacial interaction of CM dominated by Lewis acid-base and Lifshitz-van der Waals attractive interactions reduced the possibility of reversible and irreversible fouling, respectively. This study provided a deeper mechanistic understanding for the application of a novel photocatalyst in combination with ultrafiltration.

Enhancing nanofiltration membrane selectivity between mineral salts and organic pollutants by sulfonic acid functionalization for drinking water treatment

Efficient removal of natural organic matter (NOM) and organic micropollutants (OMPs) while preserving essential mineral salts is a critical goal of high-quality drinking water production, which has not been satisfyingly achieved by available nanofiltration (NF) membranes. In this study, a facile modification strategy was developed to enhance membrane salt/organics selectivity, purposely utilizing the advantages of sulfonic acid groups including high hydrophilicity, strong acidity and low complexation propensity for divalent cations. The post-treatment using a heated alkaline solution of taurine endowed the membrane with reduced active layer thickness, properly enlarged pore size and more favorable surface characteristics inheriting from grafted sulfonic acid groups. Compared to the control one, the optimal modified membrane exhibited a more than doubled water permeance and significantly reduced rejections of Ca2+ and Mg2+, while maintaining a high removal capacity for OMPs. The membrane superiority in the rejection selectivity between mineral salts and NOM was further demonstrated for natural surface water treatment, which outperformed a variety of commercial NF membranes. Improved dual resistance to Ca2+-involved organic fouling and scaling was also achieved by the sulfonic acid functionalized membrane with a higher passage of Ca2+. This study provides insights on the fit-for-purpose enhancement of membrane performance for more efficient water treatment.

Research on the operational efficiency and mechanism of integrated photocatalytic/coagulation system for the removal of natural organic matter (NOM)

Natural organic matter (NOM) widely exists in natural water bodies and threat drinking water safety. This study aims to construct an integrated photocatalytic/coagulation system and explore its treatment efficiency for NOM in source water. Morphological characteristics of the floc complex were studied based on the machine vision detection system. In addition, structural change characteristics of the floc complex in the integrated photocatalytic/coagulation system were revealed from microscopic perspective to clarify the mechanism of its effect in source water treatment process. And recycling and recycling method of photocatalyst was optimized. The results showed that the integrated photocatalytic/coagulation system can effectively reduce generation of DBPs at concentration level of μg·L−1, and the formed petal-like BiFeO3-core floc complex can achieve rapid sedimentation and had excellent recycling performance. The construction of integrated photocatalytic/coagulation system in this study is expected to provide a theoretical basis for achieving low consumption and high efficiency improvement of source water quality.

Tri-protonated ferrate: A novel electro-synthesised pre-oxidant/coagulant for NOM and DBP precursors removal in drinking water production

The generation of tri-protonated form of ferrate (H3FeVIO4+) in acidic media offers unique opportunities for drinking water treatment. Compared to the more conventional deprotonated ferrate form (FeVIO42−), H3FeVIO4+ is an extremely strong oxidant rendering it both an effective pre-oxidant and coagulant for water treatment applications. In this work, the treatment performance of H3FeVIO4+ at removing natural organic matter (NOM) and disinfection by-product (DBP) precursors was evaluated and compared against FeVIO42− and the most commonly-used iron-based coagulant: ferric chloride (FeCl3) when treating the water from two drinking water reservoirs in Australia. Results demonstrate that FeVIO42− and H3FeVIO4+ react with organic matter in intrinsically different ways, influencing the removal of dissolved organic carbon (DOC) and the formation potentials of carbonaceous-DBPs upon subsequent disinfection with chlorine or chloramine. H3FeVIO4+ dosing achieved the highest DOC removal observed: 77 % for water from site A and 60 % for water from B, both significantly superior to FeVIO42− (water A: 22 % and water B:18 %) and FeCl3 (water A: 40 % and water B: 41 %) dosing. Moreover, H3FeVIO4+ pre-oxidation of water A and subsequent chlorination reduced trihalomethanes (THMs), iodo-trihalomethanes (I-THMs), haloketones (HKs) and chloral hydrate (CH) precursors by 81 %, 92 %, 53 % and 61 %, respectively, whereas for water B the THMs, I-THMs, HKs and CH precursors were reduced by 60 %, 52 %, 20 % and 58 %, respectively, heavily outperforming the performance of FeVIO42− and FeCl3 in the removal of all measured DBPs. Finally, the formation of bromate was not observed when either ferrate(VI) forms were applied, thus rendering H3FeVIO4+ an interesting alternative pre-oxidant/coagulant, even for high bromide-containing waters (such as water B: 240 μg L−1).

MnFe2O4 composited polyvinylidene fluoride catalytic ultrafiltration membrane via peroxymonosulfate activation for humic acid treatment: Exploration of synergistic mechanisms

Membrane separation has become the most promising technology in the field of wastewater purification, but there will inevitably be membrane fouling. Catalytic polymer membranes combining membrane filtration and advanced oxidation technologies (AOPs) offered an alternative for mitigating membrane fouling. This work successfully synthesized a MnFe2O4 catalytic polyvinylidene fluoride (MnFe2O4-PVDF) ultrafiltration membrane and systematically investigated the performance of peroxymonosulfate (PMS)/MnFe2O4 membrane oxidation filtration system for removing humic acid (HA). The results showed that the PVDF@MnFe2O4/PMS synergistic system oxidized HA into small molecules and further repelled them to the membrane surface by size exclusion to form a filter cake layer. The PVDF@MnFe2O4/PMS system exhibited the lowest irreversible fouling (0.414 × 1010m−1) and the highest HA removal efficiency (83.4 %) compared with PVDF single filtration. After hydrodynamic cleaning, PVDF@MnFe2O4 can achieve 73.2 % water flux recovery. The membrane fouling mitigation mechanisms were investigated by the Extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory and the combined pore blockage-cake filtration model. Quenching experiment and density functional theory calculation (DFT) revealed the HA degradation as a result of the synergistic action of free radicals (SO4⋅-, ⋅OH) and non-free radicals(1O2) in PVDF@MnFe2O4/PMS system. Additionally, we evaluated the effectiveness of the system in the removal of natural organic matter (NOM) from surface water. The results suggested that the PVDF@MnFe2O4/PMS system could validly remove the main fluorescent matters from surface water. In conclusion, this work provides a promising route for solving the membrane fouling caused by NOM in water.

Development of Tannic Acid Coated Polyvinylidene Fluoride Membrane for Filtration of River Water Containing High Natural Organic Matter

River water can be used as a source of drinking water. However, it is vital to consider the existence of natural organic matter (NOM) and its possible influence on water quality (low turbidity, high color). The level of NOM in river water significantly impacts the ecosystem’s health and the water’s quality, and needs to be removed. A membrane-based approach is attractive for treating NOM successfully, but is still hindered by the membrane fouling problem. This study aims to develop polyvinylidene fluoride (PVDF)-based membranes customized for NOM removal from river water. The anti-fouling property was imposed by a coating of tannic acid (TA) and Fe3+ on the pre-prepared PVDF membrane. The results show that the TA–Fe coatings were effective, as demonstrated by the FTIR spectra, SEM, and EDS data. The coatings made the membrane more hydrophilic, with smaller pore size and lower clean water permeability. Such properties offer enhanced NOM rejections (up to 100%) and remarkably higher fouling recovery (up to 23%), desirable for maintaining a long-term filtration performance.

Tuning nanofiltration membrane performance: OH–MoS2 nanosheet engineering and divalent cation influence on fouling and organic removal

Natural organic matter (NOM) present in surface water causes severe organic fouling of nanofiltration (NF) membranes employed for the production of potable water. Calcium (Ca2+) and magnesium (Mg2+) are alkaline earth metals present in natural surface water and severely exacerbate organic fouling owing to their ability to cause charge neutralization, complexation, and bridging of NOM and the membrane surface. Hence, it is of practical significance to engineer membranes with properties suitable for addressing organic fouling in the presence of these cations. This study employed OH-functionalized molybdenum disulphide (OH–MoS2) nanosheets as nanofillers via the interfacial polymerization reaction to engineer NF membranes for enhanced removal of NOM and fouling mitigation performance. At an optimized concentration of 0.010 wt.% of OH–MoS2 nanosheet, the membrane was endowed with higher hydrophilicity, negative charge and rougher membrane morphology which enhanced the pure water permeance by 46.33% from 11.2 to 16.39 L m−2 h−1 bar−1 while bridging the trade-off between permeance and salt selectivity. The fouling performance was evaluated using humic acid (HA) and sodium alginate (SA), which represent the hydrophobic and hydrophilic components of NOM in the presence of 0, 0.5, and 1 mM Ca2+ and Mg2+, respectively, and the performance was benchmarked with control and commercial membranes. The modified membrane exhibited normalized fluxes of 95.09% and 93.26% for HA and SA, respectively, at the end of the 6 h filtration experiments, compared to the control membrane at 89.71% and 74.25%, respectively. This study also revealed that Ca2+ has a more detrimental effect than Mg2+ on organic fouling and NOM removal. The engineered membrane outperformed the commercial and the pristine membranes during fouling tests in the presence of 1 mM Ca2+ and Mg2+ in the feed solution. In summary, this study has shown that incorporating OH–MoS2 nanosheets into membranes is a promising strategy for producing potable water from alternative water sources with high salt and NOM contents.

Trihalomethane Levels in Municipal Drinking Water of Madrid (Spain) and Health Risk Assessment for Oral Exposure

AbstractTrihalomethanes (THMs) are generated in the drinking water treatment plant, due to the reaction of the halogenated disinfection compounds with the natural organic matter (NOM). They are related to health problems both from the point of view of cancer development and other important diseases. This study aimed to assess the quality of tap water in Madrid in terms of prevention and control of THMs risks in the supply water treated by Canal de Isabel II (CYII) in a total of 108 samples throughout 2015 to 2020, to distinguish the problems of the different 21 districts or types of buildings, the seasonality and to estimate the risk of exposure to THMs from tap water in the population of Madrid. The variables considered include year, seasonality, district of Madrid and sampling point. The concentrations of THMs detected in all samples were within the current legal limit (100 µg/l). Chloroform was the compound with the highest contribution to the sum of THMs. A decreasing trend in THMs concentrations was observed over the years of the study related to the removal of NOM and the use of chloramines. THM levels were higher in the central area than in the peripheral districts and the lowest concentrations were detected in summer. Regarding risk assessment, the results of the non-carcinogenic risk indicate that there is no potential risk from tap water consumption for the adult population. For the carcinogenic risk, only water samples with THM concentrations between 50 and 75 µg/l could constitute a risk for high consumers.