Imperial College London

ProfessorNigelGraham

Faculty of EngineeringDepartment of Civil and Environmental Engineering

Professor
 
 
 
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Contact

 

+44 (0)20 7594 6121n.graham Website

 
 
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Assistant

 

Miss Judith Barritt +44 (0)20 7594 5967

 
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Location

 

308Skempton BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

309 results found

Sun Y, Yu IKM, Tsang DCW, Fan J, Clark JH, Luo G, Zhang S, Khan E, Graham NJDet al., 2020, Tailored design of graphitic biochar for high-efficiency and chemical-free microwave-assisted removal of refractory organic contaminants, Chemical Engineering Journal, Vol: 398, Pages: 1-10, ISSN: 1385-8947

Energy-saving, chemical-free, and high-efficiency microwave (MW)-assisted water treatment can be greatly facilitated via tailored design of an economical, sustainable, and ‘green’ carbonaceous catalyst. In this study, various biochars (BC) were pyrolyzed from two lignocellulosic waste biomasses, oak (O) and apple tree (A), at a high temperature (900 °C) and under different gases (N2 and CO2). The holistic characterization by advanced spectroscopic techniques demonstrated that CO2 pyrolysis of feedstock with more lignin (i.e., oak), produced biochar with increased aromaticity and degree of carbonization. CO2 modification created a hierarchical porous structure, improved surface hydrophilicity, polarity, and acidity, and provided higher densities of near-surface functionalities of the biochar. Without MW irradiation, ABC-900C (1 g L−1) provided the highest adsorption (52.6%, 1 min) of 2,4-dichlorophenoxy acetic acid (2,4-D) ascribed to large specific surface area, high micropore content, appropriate pore size, and abundant active groups. OBC-900C (1 g L−1) enabled significantly increased 2,4-D removal (81.6%, 1 min) under MW irradiation (90 °C) in contrast with an oil bath (55.7%, 90 °C, 1 min) and room temperature (33.9%, 1 min) conditions, due to its highest graphitization degree and medium-developed microporous structure. The MW-induced thermal effect formed “hot spots” on the biochar surface as evidenced by elevated temperature of the bulk solution and lowered energy consumption of the MW reactor in the presence of OBC-900C, compared to those of the other biochars. The scavenging tests suggested that the generation of highly oxidative hydroxyl (•OH), anionic superoxide (O2•−), and singlet oxygen (1O2) radicals contributed to the removal of 2,4-D. This study has demonstrated that biochar with customized structure and high organic adsorption capacity can act as an effective MW absorber suitable for rapi

Journal article

Li X, Graham NJD, Deng W, Liu M, Liu T, Yu Wet al., 2020, The formation of planar crystalline flocs of γ-FeOOH in Fe(II) coagulation and the influence of humic acid, Water Research, Vol: 185, ISSN: 0043-1354

Although Fe(II) salts have been widely used as coagulants in water treatment for many years, the underlying mechanisms of their performance remain unclear. Here, we present a detailed study of the coagulation behavior of Fe(II) salts and crystallization of flocs, and investigate the effect of humic acid (HA) under different DO concentrations and pH conditions. The behavior of Fe(II) and Fe(III) coagulants was found to be markedly different with the flocs from Fe(II) consisting of planar-like crystalline γ-FeOOH in contrast to the small amorphous spherical-like flocs from Fe(III) dosing. The effect of HA on Fe(II) coagulation was different under different DO concentrations and pH, where by the growth of γ-FeOOH was inhibited by the presence of HA, but independent of DO concentration and pH. It was found that Fe(II) was present within the internal structure of γ-FeOOH, and a plausible formation mechanism is proposed. Firstly, planar nanoparticles of Fe(OH)2 were formed via Fe(II) ion hydrolysis which then servedas the nucleus for subsequent crystal growth. With oxidation, Fe(II) on the surface of nanoparticles transformed to Fe(III). Finally, the formation of γ-FeOOH in Fe(II) coagulation was accompanied by a change in solution colour to yellow.

Journal article

Yang Z, Zhang Y, Wang X, Tian Z, Yang W, Graham NJDet al., 2020, Efficient adsorption of four phenolic compounds using a robust nanocomposite fabricated by confining 2D porous organic polymers in 3D anion exchangers, Chemical Engineering Journal, Vol: 396, Pages: 1-11, ISSN: 1385-8947

A novel 2D/3D hybrid nanocomposite adsorbent (TCBD/D318) was synthesized by confining a 2D porous organic polymer (POP, TCBD) in pores of commercial 3D anionic exchanger beads (D318) using a facile repetitive deposition method, and evaluated for the removal of four phenolic contaminants (phenol, 1-naphthol, 4-nitrophenol and 4-chlorophenol) from water. The immobilization of TCBD in D318 conferred on the adsorbent a robust water stability, a rapid solid-liquid separation (in 10 s after dispersion in water), and an enhanced anti-self-aggregation property. The effects of pH, contaminant type, coexisting inorganic anions and natural organic matter (NOM) on adsorption performance were studied. TCBD/D318 exhibited high adsorption capacities (Qe) for all four phenolic contaminants, and these were only slightly influenced by pH and the presence of coexisting inorganic anions and NOM, due to the combined effects of multi-binding-interactions and hierarchical pore-structures. Another equally important merit of the TCBD/D318 was its remarkably improved utilization efficiency (atom economy) of functional groups. The adsorption mechanisms were investigated by a combination of physico-chemical model fitting, instrumental analysis and chemical computation. These displayed a hierarchical-pore-structure-induced multi-step diffusion adsorption involving multi-binding-interactions, principally electrostatic attraction, π-π interaction, and H-bonding; the contaminants were more inclined to be bound onto TC units of TCBD in the nanocomposite. Regeneration tests involving 10 adsorption-desorption cycles showed that TCBD/D318 maintained a high Qe, confirming its effective reusability. The results have demonstrated the outstanding potential of TCBD/D318 for the removal of phenolic compounds from water, and more generally the possibilities of using POP-based 2D/3D hybrid nanocomposites in wider environmental applications.

Journal article

McBeath ST, Wilkinson DP, Graham NJD, 2020, Advanced electrochemical oxidation for the simultaneous removal of manganese and generation of permanganate oxidant, Environmental Science: Water Research & Technology, Vol: 6, Pages: 2405-2415, ISSN: 2053-1400

Emerging electrochemical systems, such as advanced electro-oxidation, provide a potentially powerful alternative to conventional oxidation processes which can often be unsuitable for small, remote and decentralised system applications. The one electro-oxidation process, which may be well suited for these applications, is the use of high oxygen overpotential boron-doped diamond (BDD) electrodes, as a pre-oxidation step for the removal of various raw water contaminants. While BDD electro-oxidation has been studied extensively for the abatement of organic micropollutants, its application as a pre-oxidation technology for the removal of soluble manganese (Mn2+) in source waters for drinking water supply, has not been reported to-date. In this study, we summarise the results of tests using a bench-scale electro-oxidation system and synthetic Mn2+ solutions in order to consider the simultaneous removal of manganese and the generation of permanganate. The results showed that total manganese was reduced by 9.1, 38.7 and 57.4% at current densities of 10, 40 and 80 mA cm−2, respectively, with an initial Mn2+ concentration of 39 μM. Increased Mn removal at higher current density was attributed to increased generation of, and reaction with, hydroxyl radicals, indicated by a direct proportional relationship between pseudo-first order reaction rate constants for methanol (˙OH radical scavenger) and current density. A mathematical model was developed to describe Mn removal under mass transport limitations, and was found to correlate well with experimental data. Finally, a completely novel synthesis pathway for the generation of permanganate species (Mn7+) is presented, whereby concentrations up to 0.9 μM were synthesised from Mn2+ in circumneutral conditions.

Journal article

McBeath ST, Wilkinson DP, Graham NJD, 2020, Exploiting water contaminants: In-situ electrochemical generation of ferrates using ambient raw water iron (Fe2+), Journal of Environmental Chemical Engineering, Vol: 8, Pages: 1-9, ISSN: 2213-3437

Many complexities arise when applying conventional water treatment processes to small and remote systems. A significant challenge is the difficulty and impracticality of supplying chemicals needed for oxidation processes. A burgeoning, yet currently under-utilised, type of treatment are electrochemical technologies, which are receiving considerable research attention and innovation at present. In particular, through the advancement of high oxygen overpotential electrodes, the ability to synthesise highly oxidative chemical species under circumneutral pH conditions has become possible. In this study, the generation of highly oxidative iron-based species, specifically ferrate (Fe6+), has been explored utilising a boron-doped diamond (BDD) electrode and low concentrations of Fe2+ typically found in raw water, thereby eliminating the chemical supply chain required for conventional oxidation processes. Electrochemical ferrate generation experiments were performed in a batch-recycle configuration and were found to be mass transfer limited, whereby the rate-limiting step was the diffusion of Fe2+ to the electrode surface. This was evidenced by very little variation in ferrate generation at the three current densities tested, specifically 3.1 ± 0.2, 2.6 ± 0.2 and 3.3 ± 0.2 μM were generated at 10, 40 and 80 mA/cm2, respectively. Measured Fe6+ concentrations correlated well with those predicted by a mathematical process model, which assumed a completely mass transport limited process. While cyclic voltammetry confirmed ferrate generation by direct oxidation at the BDD surface, the contribution of hydroxyl radicals was indicated by the presence and absence of methanol, an radical dotOH scavenger, with ferrate generation decreased by greater than 50 % with methanol, compared to non-scavenged experiments. The results provide one of the first quantitative studies regarding the oxidation mechanisms of ferrate generation by electro-oxidation, and the first

Journal article

Larasati A, Fowler GD, Graham NJD, 2020, Chemical regeneration of granular activated carbon: preliminary evaluation of alternative regenerant solutions, Environmental Science: Water Research & Technology, Vol: 6, Pages: 2043-2056, ISSN: 2053-1400

Granular activated carbon (GAC) is used in drinking water treatment plants worldwide to remove micro-pollutants such as pesticides. Early breakthrough of problematic micro-pollutants leads to frequent and costly thermal regeneration off-site. A potential alternative approach is to chemically regenerate GAC on-site (possibly in situ) with an appropriate solution capable of desorbing organic contaminants, having a range of physico-chemical properties. In this study, four types of regenerant solution were evaluated in batch tests for their ability to desorb five target contaminants. The solutions were: high purity water, sodium hydroxide, ethanol, and a mixture of sodium hydroxide and ethanol. The contaminants included: phenol and nitrobenzene, as representative aromatic compounds; clopyralid and metaldehyde, as poorly-adsorbed pesticides; and isoproturon, a well-adsorbed pesticide. Among the properties of the contaminants, their hydrophobicity and aqueous solubility had the most significant influence on the desorption efficiency. NaOH/CH3CH2OH was found to be more effective than individual solutions in desorbing the target contaminants, indicating an ability to desorb both hydrophobic and hydrophilic compounds. The NaOH/CH3CH2OH regenerant solution yielded desorption efficiencies in the range of approximately 40–90%, with the efficiency dependent on the contaminant. A thermodynamic study provided valuable fundamental information regarding the adsorption and desorption mechanisms, and the existence of two binding sites involving a weak physisorption and a stronger chemisorption-like interaction between the contaminants and the GAC.

Journal article

Xu L, Graham NJD, Wei C, Zhang L, Yu Wet al., 2020, Abatement of the membrane biofouling: performance of an in-situ integrated bioelectrochemical-ultrafiltration system, Water Research, Vol: 179, ISSN: 0043-1354

The practical applications of membrane-based water treatment techniques are constrained by the problem of membrane fouling. Various studies have revealed that interactions between extracellular polymeric substances (EPS) and the membrane surface determine the extent of irreversible fouling. Herein, we describe a novel bioelectrochemical system (BES) integrated with an ultrafiltration (UF) membrane in order to provide an enhanced antifouling property. It was found that the integrated BES membrane system had a superior performance compared to a conventional (control) UF system, as manifested by a much lower development of transmembrane pressure. The BES significantly reduced microbial viability in the membrane tank and the imposed electrode potential contributed to the degradation of biopolymers, which favored the alleviation of membrane fouling. Notably, the electron transfer between the acclimated microorganisms and the conductive membrane in the BES integrated system exhibited an increasing trend with the operation time, indicating a gradual increase in microbial electrical activity. Correspondingly, the accumulation of extracellular polymeric substances (EPS) on the membrane surface of the BES integrated system showed a substantial decrease compared to the control system, which could be attributed to a series of synergistic effects induced by the BES integration. The differences in the microbial diversity between the control and the BES integrated system revealed the microbial selectivity of the poised potential. Specifically, microbial strains with relatively high EPS production, like the genus of Zoogloea and Methyloversatilis, were reduced significantly in the BES integrated system, while the expression of the electroactive bacteria was promoted, which facilitated extracellular electron transfer (EET) and therefore the bioelectrochemical reactions. Overall, this study has presented a feasible and promising new approach for membrane fouling mitigation during the

Journal article

Wang J, Yu W, Graham NJD, Jiang Let al., 2020, Evaluation of a novel polyamide-polyethylenimine nanofiltration membrane for wastewater treatment: Removal of Cu2+ ions, Chemical Engineering Journal, Vol: 392, Pages: 1-14, ISSN: 1385-8947

This paper describes a novel approach for enhancing membrane technology for the removal of heavy metal cations in contaminated waters. A simple method of forming a positively charged polyamide (PA) nanofiltration (NF) membrane has been developed by attaching a layer of hyperbranched polyethylenimine (PEI) to the PA surface, involving the linking of PEI amino groups to the PA surface carboxyl groups. The nature of the PEI modified PA membrane, in terms of surface morphology, zeta potential and hydrophobicity was found to depend on the PEI molecular weight (MW), and the PEI concentration and membrane exposure time during preparation. In turn, the nature of the modified membrane determined its performance in terms of hydraulic flux and metal ion rejection. In tests using a model solution of 5 mg/L Cu2+ and a 70,000 MW PEI membrane the Cu rejection was >90%, with only a modest reduction in flux compared to blank water. The Cu2+ rejection was found to be a combination of electrostatic repulsion and adsorption, with the relative proportions depending on the nature of the PEI modified PA membrane. In addition, the Cu2+ rejection and membrane flux were found to be sustainable over repeated filtration cycles, and the rejection was not adversely affected by the presence of humic acid in solution (5 mg/L).

Journal article

He M, Wan Z, Tsang DCW, Sun Y, Khan E, Hou D, Graham NJDet al., 2020, Performance indicators for a holistic evaluation of catalyst-based degradation-A case study of selected pharmaceuticals and personal care products (PPCPs)., Journal of Hazardous Materials, Vol: 402, Pages: 123460-123460, ISSN: 0304-3894

Considerable efforts have been made to develop effective and sustainable catalysts, e.g., carbon-/biochar-based catalyst, for the decontamination of organic pollutants in water/wastewater. Most of the published studies evaluated the catalytic performance mainly upon degradation efficiency of parent compounds; however, comprehensive and field-relevant performance assessment is still in need. This review critically analysed the performance indicators for carbon-/biochar-based catalytic degradation from the perspectives of: (1) degradation of parent compounds, i.e., concentrations, kinetics, reactive oxidative species (ROS) analysis, and residual oxidant concentration; (2) formation of intermediates and by-products, i.e., intermediates analysis, evolution of inorganic ions, and total organic carbon (TOC); and (3) impact assessment of treated samples, i.e., toxicity evolution, disinfection effect, and biodegradability test. Five most frequently detected pharmaceuticals and personal care products (PPCPs) (sulfamethoxazole, carbamazepine, ibuprofen, diclofenac, and acetaminophen) were selected as a case study to articulate the performance indicators for a holistic evaluation of carbon-/biochar-based catalytic degradation. This review also encourages the development of alternative performance indicators to facilitate the rational design of catalysts in future studies.

Journal article

McBeath ST, Wilkinson DP, Graham NJD, 2020, Analytical quantification of aqueous permanganate: Direct and indirect spectrophotometric determination for water treatment processes, Chemosphere, Vol: 251, Pages: 1-7, ISSN: 0045-6535

Three spectrophotometric methods have been developed and compared for the quantification of low concentrations (0.03–63 μM) of aqueous permanganate in neutral pH conditions. Although permanganate is a widely used oxidant in drinking water and wastewater treatment, no widely accepted method of quantification has been reported to date. While one method presented does not require the need for any reagent chemicals (direct spectrophotometric analysis), it yielded a relatively low molar absorption coefficient of 3340 M−1 cm−1 at 525 nm and a level of detection (LOD) and quantification (LOQ) of 0.45 and 1.51 μM, respectively. Some instability of permanganate species during direct quantification was found to occur over 60 min, with a total decrease of 0.002 (arbitrary units) of absorbance, equivalent to a decrease in concentration of 0.6 μM. Beyond 60 min, no further degradation was observed. Indirect spectrophotometric analyses using 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and sodium iodide (NaI) provided a significantly more sensitive method for permanganate quantification, yielding molar absorption coefficients of 140,030 and 61,130 M−1 cm−1, respectively. The LOD and LOQ were determined to be 0.01 and 0.03 μM for the ABTS method and 0.02 and 0.08 μM for the NaI method, respectively. Although conservative and accurate limits of quantification for both the ABTS and NaI methods are presented, which should be sufficient of most practical applications, lower limits may be possible with further refinement of the methods.

Journal article

Yang Z, Hou T, Ma J, Yuan B, Tian Z, Yang W, Graham NJDet al., 2020, Role of moderately hydrophobic chitosan flocculants in the removal of trace antibiotics from water and membrane fouling control, Water Research, Vol: 177, Pages: 1-10, ISSN: 0043-1354

In this paper we describe the preparation and testing of a new class of chitosan-based flocculants for the treatment of surface waters containing antibiotic compounds. Three forms of moderately hydrophobic chitosan flocculants (MHCs) were prepared by chemically grafting hydrophobic branches with different lengths onto hydrophilic chitosan and these were evaluated by jar tests and a bench-scale continuous flow ultrafiltration (UF) membrane process with coagulation/sedimentation pre-treatment. Tests were conducted using both synthetic and real surface water in which norfloxacin and tylosin were added as representative antibiotics at an initial concentration of 0.1 μg/L. In jar tests, the MHCs achieved similar high removal efficiencies (REs) of turbidity and UV254 absorbance, but much higher REs of the two antibiotics (71.7–84.7% and 68.7–76.6% for synthetic and river waters, respectively), compared to several commercial flocculants; the superior performance was attributed to an enhanced hydrophobic interaction and H-bonding between the flocculants and antibiotics. The presence of suspended kaolin particles and humic acid enhanced the antibiotic removal, speculated to be through MHC bridging of the kaolin/humic acid and antibiotic molecules. In the continuous flow tests involving flocculation/sedimentation-UF for 40 days, an optimal MHC achieved a much greater performance than polyaluminium chloride in terms of the overall removal of antibiotics (RE (norfloxacin) of ∼90% and RE (tylosin) of ∼80%) and a greatly reduced rate of membrane fouling; the latter resulting from a more porous and looser structure of cake layer, caused by a surface-modification-like effect of residual MHC on the hydrophobic PVDF membrane. The results of this study have shown that MHCs offer a significant advance over the use of existing flocculants for the treatment of surface water.

Journal article

Wang Y, Hou T, Yang Z, Zhao L, Wu W, Yang W, Graham NJDet al., 2020, Nitrogen-free cationic starch flocculants: flocculation performance, antibacterial ability, and UF membrane fouling control, ACS Applied Bio Materials, Vol: 3, Pages: 2910-2919, ISSN: 2576-6422

In light of growing concerns about the formation of nitrogen-based disinfection byproducts (N-DBP) and the possible contribution from the use of quaternary-ammonium-containing flocculants, there is growing interest in the alternative use of quaternary phosphonium salts, which have been reported to have a lower DBP formation potential, stronger cationic properties, lower cytotoxicity, and greater stability. In this study, the performance of N-free quaternary-phosphonium-modified starch flocculants (S-BTP), synthesized through a facile one-step method using commercially available raw materials, in the treatment of bacteria-laden waters (E. coli as the model bacteria) was assessed in both jar tests and a bench-scale continuous-flow flocculation–sedimentation–ultrafiltration process. In jar tests, the effects of the cationic degree of substitution (DS) and dosage of the flocculant, solution pH, and presence of model contaminants on treatment performance were studied. One particular flocculant (S-BTP3), with a DS of 19.3%, displayed high removal efficiencies of E. coli, turbidity, and UV254 from water, comparable with those of ammonium-based analogues and conventional alum, via a combination of charge attraction, polymer bridging, and antibacterial effects. S-BTP3 also possessed better bactericidal properties (99.4% of E. coli killed) than alum (41.4% killed) and did not cause the release of intracellular substances into the treated water. In the continuous-flow flocculation–sedimentation–UF tests, S-BTP3 was superior to alum in the flocculation and antibacterial performance, and in mitigating UF membrane fouling. The results have clearly demonstrated the multiple benefits of the use of N-free cationic starch flocculants in water treatment as an alternative to conventional chemicals.

Journal article

Su Z, Liu T, Li X, Graham NJD, Yu Wet al., 2020, Tracking metal ion-induced organic membrane fouling in nanofiltration by adopting spectroscopic methods: observations and predictions, Science of the Total Environment, Vol: 708, ISSN: 0048-9697

Natural organic matter (NOM) with the size approaching to membrane pore size is commonly considered as the crucial component leading to severe pore blocking and superfluous energy consumption. Aquatic metal ions coexisting with this NOM constituent (target NOM) exert a significant influence on membrane filtration performance; however, little work elucidated their interactions and the impacts on nanofiltration (NF). Therefore, we systematically investigated this issue by titrating three environmentally-relevant metal ions (Al3+, Fe3+ and Cu2+) into the target NOM sample obtained by pre-filtering using NF membrane. Fast spectrophotometric techniques were employed to observe the interactive performance. Results suggested that all metal ions at their critical concentrations caused severe flux decline; Cu2+ at a very low concentration of 5 μM, Al3+ and Fe3+ at 20 μM. NF performance recovered when the concentrations were beyond their critical values, and was improved at excessive concentration when flocs formed. Relationship between spectroscopic characteristics and NF performance was particularly addressed. UV–vis spectrum can be expected to be useful and predictive in membrane fouling control when Al3+ or Fe3+ presented. However, fluorescence fingerprint was not likely that effective since fluorescence intensity continuously reduced with the increasing metal ion concentration, attributed to their quenching effect on NOM fluorophores.

Journal article

Yang H, Wu X, Su L, Ma Y, Graham NJD, Yu Wet al., 2020, The Fe–N–C oxidase-like nanozyme used for catalytic oxidation of NOM in surface water, Water Research, Vol: 171, Pages: 1-13, ISSN: 0043-1354

The removal of natural organic matter (NOM), particularly humic substances (HS) from surface waters during drinking water treatment is necessary to avoid various water quality problems in supply, such as the formation of disinfection by-products. As an alternative to conventional processes (e.g. coagulation), and in the light of the rapidly increasing applications of nanozyme in bio-catalysis, a novel Fe–N–C oxidase-like nanozyme (FeNZ) has been prepared and used to catalyze the oxidative degradation of NOM during simple aeration. Using humic acid (HA) as a model NOM it was found that the HA removal (as TOC) was increased by a factor of 6 with a low dose (10 mg/L) of FeNZ compared to an aerated solution without FeNZ. A variety of analytical methods was used to investigate the oxygen reduction reaction, including cyclic voltammetry, electron spin resonance, and density functional theory (DFT) simulation. Based on these studies, a catalytic oxidation mechanism described as “adsorption-activation-oxidation” was proposed. The enhanced NOM removal performance of FeNZ catalytic oxidation was confirmed with samples of natural surface water in terms of organic mineralization and conversion of hydrophobic to hydrophilic components. The results show great potential for the use of oxidase-like nano catalytic materials in the field of water treatment.

Journal article

Yu W, Liu M, Graham NJD, 2019, Combining magnetic ion exchange media and microsand before coagulation as pretreatment for submerged ultrafiltration: biopolymers and small molecular weight organic matter, ACS Sustainable Chemistry & Engineering, Vol: 7, Pages: 18566-18573, ISSN: 2168-0485

In order to reduce the fouling of ultrafiltration (UF) systems caused by influent organic matter and microbial activities in the membrane tank, a novel pretreatment process has been evaluated involving the combination of magnetic ion exchange media (MIEX), microsand, and alum coagulation. Using a continuous flow bench-scale UF membrane apparatus and synthetic water, the influence of MIEX and microsand with alum pretreatment on membrane fouling was studied in comparison to a conventional pretreatment by alum alone. It was found that the continuous addition of low doses of MIEX and microsand substantially reduced (∼50%) membrane fouling for nearly 60 days of operation, both in terms of reversible and irreversible fouling. MIEX adsorption increased the removal of dissolved organic matter, particularly hydrophobic and proteinaceous substances, and some fractions of humic-type substances, while the addition of microsand increased the density of flocs, and thus improved the removal of flocs and microorganisms (with flocs) in the membrane tank. As a consequence, the UF membrane with the MIEX/microsand pretreatment had a much reduced cake layer and accumulated material within membrane pores; in particular, the cake layer had much less protein-type and polysaccharide-type substances.

Journal article

Liu T, Tian L, Graham N, Yang B, Yu W, Sun Ket al., 2019, Regulating the interlayer spacing of graphene oxide membranes and enhancing their stability by use of PACl, Environmental Science and Technology (Washington), Vol: 53, Pages: 11949-11959, ISSN: 0013-936X

Graphene oxide (GO) is an ideal membrane material for water treatment due to its outstanding physicochemical properties and unique lamellar structure. However, the separation performance and practical application of GO membranes are mainly affected by the interlayer spacing and stability in aqueous solutions. Here, we report a novel and facile approach to fabricating GO membranes with adjustable interlayer spacing and high stability in aqueous solutions through cross-linking with polyaluminum chloride (PACl). With this approach, the lamellar spacing can be adjusted by changing the OH/Al ratios (B values) of the PACl, and the GO nanosheets can be tightly bonded by the strong electrostatic effect that PACl provides between them. The average interlayer spacing of the GO layer could be varied approximately in the range of 0.80-1.09 nm. The PACl-GO membranes demonstrated excellent stability in water and inorganic/organic solutions when the concentration of PACl was 0.1, 1, and 10 mM, remaining unchanged for at least 2 weeks. Moreover, the PACl-GO membranes featured exceptional sieving capabilities for model and natural organic substrates, while it was also observed that increasing the interlayer spacing of the PACl-GO membranes increased both the membrane flux and the separation performance of organic matter.

Journal article

McBeath ST, Wilkinson DP, Graham NJD, 2019, Application of boron-doped diamond electrodes for the anodic oxidation of pesticide micropollutants in a water treatment process: a critical review, Environmental Science: Water Research & Technology, Vol: 5, Pages: 2090-2107, ISSN: 2053-1400

Boron-doped diamond (BDD) electrodes have the greatest known oxygen overpotential range; a characteristic that has allowed the material to be well suited for electro-oxidation processes in aqueous media. When operating in a potential range of water decomposition, strongly oxidising hydroxyl radicals are formed while oxygen evolution is minimised. The majority of research studies undertaken to-date have focused on the application of BDDs for the remediation of wastewater contaminants, however there is an increasing need for a suitable technology to address recalcitrant micropollutants in a drinking water context. Pesticide micropollutants are widely detected in surface- and ground-waters and are of increasing concern. In this paper, the treatment of pesticides by BDD electro-oxidation is reviewed. Their degradation and mineralisation, as well as the effect of operating conditions, formation of intermediate by-products, reaction pathways and kinetics are summarized. In general, BDD electro-oxidation was found to be effective for the degradation of pesticides with the degradation performance proportional to the electrolytic current, due principally to the increased generation of ˙OH radicals. Most contaminants followed pseudo first-order reaction kinetics under mass transport limitations. Generally, the same aromatic and aliphatic by-products were formed through similar oxidation pathways. Finally, research gaps and potential future research topics are discussed.

Journal article

Ritson JP, Graham NJD, 2019, Water extractable organic matter (WEOM) as an indicator of granular activated carbon (GAC) bed life and water quality outcomes in drinking water treatment, Environmental Science: Water Research & Technology, Vol: 5, Pages: 1593-1598, ISSN: 2053-1400

Granular activated carbon (GAC) is often used in drinking water treatment to remove dissolved organic carbon (DOC), taste and odour compounds, and organic micro-pollutants. As these chemicals are adsorbed onto the GAC surface, the area available for further adsorption decreases, meaning that the removal of target compounds decreases over time. Ascertaining the correct point to regenerate the GAC is a critical parameter in terms of both water quality performance and operational expenditure for the water company. Using a test case of a UK water treatment works with five GAC beds of varying age we show that current practices of using time-in-use are ineffective for optimal removal of DOC and disinfection by-product precursors. Our data show that assessment of the water extractable organic matter (WEOM) adsorbed onto the GAC can give an accurate indicator of both DOC removal (adjusted R2 = 0.985, p = 0.001, n = 5) and reduction in trihalomethane formation (adjusted R2 = 0.970, p = 0.001, n = 5). These results suggest that simple methods using equipment commonly available at treatment works could be adopted for rapid assessment of remaining GAC bed life.

Journal article

Liu T, Zhou H, Graham N, Yu W, Sun Ket al., 2019, 2D kaolin ultrafiltration membrane with ultrahigh flux for water purification, Water Research, Vol: 156, Pages: 425-433, ISSN: 0043-1354

Membrane separation technology is an important option for the treatment of contaminated surface waters but the relatively high cost of materials and membrane fabrication represent a significant obstacle to the wider use of membrane processes. In this study, we describe the development and testing of a new kind of membrane made from two-dimensional (2D) kaolin nanosheets. The fabrication involved a layer-by-layer stacking of the nanosheets with a cationic polyacrylamide cross-linking agent, assembled on a cellulose acetate supporting layer. The kaolin membrane exhibited an ultrahigh flux (∼4000 L.m-2.h-1.bar-1) which was almost ten times greater than that of a commercial polyether sulfone (PES) ultrafiltration (UF) membrane. The membrane was tested using a range of influent water types, including samples of a lake water, river water and three natural organic matter solutions. The results showed that the kaolin membrane was stable and behaved as an UF membrane, in terms of its pore size distribution (peak distribution at 20-35 nm) and comparable treatment performance to the PES UF membrane. The kaolin membrane showed a substantially reduced rate of fouling, compared to PES membrane, despite a much greater flux, which was partly attributed to its highly hydrophilic nature. The advantages of lower cost, much higher flux and lower fouling propensity make the 2D-kaolin membrane a potentially important development in UF membrane technology for drinking water treatment, and possibly other applications.

Journal article

Ritson JP, Croft JK, Clark JM, Brazier RE, Templeton MR, Smith D, Graham Net al., 2019, Sources of dissolved organic carbon (DOC) in a mixed land use catchment (Exe, UK), Science of the Total Environment, Vol: 666, Pages: 165-175, ISSN: 0048-9697

Many catchment management schemes in the UK have focussed on peatland restoration to improve ecosystem services such as carbon sequestration, water quality and biodiversity. The effect of these schemes on dissolved organic carbon (DOC) flux is critical in understanding peatland carbon budgets as well as the implications for drinking water treatment. In many catchments, however, peatland areas are not the only source of DOC, meaning that their significance at the full catchment scale is unclear. In this paper we have evaluated the importance of different land uses as sources of DOC by combining three datasets obtained from the Exe catchment, UK. The first dataset comprises a weekly monitoring record at three sites for six years, the second, a monthly monitoring record of 25 sites in the same catchment for one year, and the third, an assessment of DOC export from litter and soil carbon stocks. Our results suggest that DOC concentration significantly increased from the peaty headwaters to the mixed land-use areas (ANOVA F = 12.52, p < 0.001, df = 2), leading to higher flux estimates at the downstream sites. We present evidence for three possible explanations: firstly, that poor sampling of high flows may lead to underestimation of DOC flux, second, that there are significant sources of DOC besides the peatland headwaters, and finally, that biological- and photo-degradation decreases the influence of upstream DOC sources. Our results provide evidence both for the targeting of catchment management in peatland areas as well as the need to consider DOC from agricultural and forested areas of the catchment.

Journal article

Sun Y, Cho DW, Graham NJD, Hou D, Yip ACK, Khan E, Song H, Li Y, Tsang DCW, Graham N, Sun Y, Cho D-W, Hou D, Yip A, Khan E, Song H, Li Y, Tsang Det al., 2019, Degradation of antibiotics by modified vacuum-UV based processes: Mechanistic consequences of H2O2 and K2S2O8 in the presence of halide ions, Science of the Total Environment, Vol: 664, Pages: 312-321, ISSN: 0048-9697

In this work, the degradation of cefalexin, norfloxacin, and ofloxacin was examined via various advanced oxidation processes (AOPs). Direct photolysis by ultraviolet (UV) and vacuum ultra violet (VUV) was less effective for the degradation of fluoroquinolone antibiotics such as norfloxacin and ofloxacin than that of cefalexin. Both hydrogen peroxide (H2O2) and potassium persulfate (K2S2O8) assisted UV/VUV process remarkably enhanced fluoroquinolone degradation. The addition of K2S2O8 was superior to H2O2 under VUV irradiation, with the best removal efficiency of norfloxacin and ofloxacin being almost 100% within 3 min in the presence of VUV/K2S2O8. The ofloxacin degradation rate was accelerated as concentrations of H2O2 and K2S2O8 was increased to 3 mM, but the degradation rate was slightly decreased with excess H2O2 (>3 mM). The performance of modified VUV processes (i.e., VUV/H2O2 and VUV/K2S2O8) was inhibited at highly alkaline condition (pH 11). The co-existence of halides (Cl− and Br−) enhanced antibiotics degradation via the modified VUV processes, but the reaction was almost unaffected in the presence of single halides. This study demonstrated that modified VUV processes (especially VUV/K2S2O8) are efficient for eliminating fluoroquinolone antibiotics from water, which can be considered as a clean and green method for the treatment of antibiotics-containing industrial wastewater.

Journal article

Sun Y, Yu IKM, Tsang DCW, Cao X, Lin D, Wang L, Graham NJD, Alessi DS, Komarek M, Ok YS, Feng Y, Li X-Det al., 2019, Multifunctional iron-biochar composites for the removal of potentially toxic elements, inherent cations, and hetero-chloride from hydraulic fracturing wastewater, Environment International, Vol: 124, Pages: 521-532, ISSN: 0160-4120

This paper evaluates a novel sorbent for the removal of potentially toxic elements, inherent cations, and hetero-chloride from hydraulic fracturing wastewater (FWW). A series of iron-biochar (Fe-BC) composites with different Fe/BC impregnation mass ratios (0.5:1, 1:1, and 2:1) were prepared by mixing forestry wood waste-derived BC powder with an aqueous FeCl3 solution and subsequently pyrolyzing them at 1000 °C in a N2-purged tubular furnace. The porosity, surface morphology, crystalline structure, and interfacial chemical behavior of the Fe-BC composites were characterized, revealing that Fe chelated with CO bonds as COFe moieties on the BC surface, which were subsequently reduced to a CC bond and nanoscale zerovalent Fe (nZVI) during pyrolysis. The performance of the Fe-BC composites was evaluated for simultaneous removal of potentially toxic elements (Cu(II), Cr(VI), Zn(II), and As(V)), inherent cations (K, Na, Ca, Mg, Ba, and Sr), hetero-chloride (1,1,2-trichlorethane (1,1,2-TCA)), and total organic carbon (TOC) from high-salinity (233 g L−1 total dissolved solids (TDS)) model FWW. By elucidating the removal mechanisms of different contaminants, we demonstrated that Fe-BC (1:1) had an optimal reducing/charge-transfer reactivity owing to the homogenous distribution of nZVI with the highest Fe0/Fe2+ ratio. A lower Fe content in Fe-BC (0.5:1) resulted in a rapid exhaustion of Fe0, while a higher Fe content in Fe-BC (2:1) caused severe aggregation and oxidization of Fe0, contributing to its complexation/(co-)precipitation with Fe2+/Fe3+. All of the synthesized Fe-BC composites exhibited a high removal capacity for inherent cations (3.2–7.2 g g−1) in FWW through bridging with the CO bonds and cation-π interactions. Overall, this study illustrated the potential efficacy and mechanistic roles of Fe-BC composites for (pre-)treatment of high-salinity and complex FWW.

Journal article

Graham N, Yu W, Liu T, 2019, Prevention of UF membrane fouling in drinking water treatment by addition of H2O2 during membrane backwashing, Water Research, Vol: 149, Pages: 394-405, ISSN: 0043-1354

Although conventional coagulation pre-treatment can mitigate the fouling of ultrafiltration (UF) membrane when treating raw waters, it is insufficient to restrict the development of irreversible fouling and reversible fouling to a low level. In this paper we demonstrate that the intermittent addition of H2O2 into the membrane tank during backwash events (after coagulation pre-treatment) successfully prevented the development of any significant membrane fouling. Laboratory-scale tests were undertaken using two membrane systems operated in parallel over 60 days, one serving as a reference coagulation-ultrafiltration (CUF) process, and the other receiving the H2O2 (CUF-H2O2), with a decreasing dose in three successive phases: 10, 5 and 2 mg/L. The results showed that the addition of H2O2 (via a separate dosing tube) during a 1 min backwash process (at 30 min intervals) reduced the growth of bacteria in the membrane tank, and the associated concentrations of soluble microbial products (SMP, including protein and polysaccharide). This resulted in a much reduced cake layer, which contained significantly less high MW organic matter (>50%), such as EPS, thereby improving the interaction between particles in the cake layer and/or particles and the membrane surface. There was also less organic matter, of all MW fractions, adsorbed in the membrane pores of the CUF-H2O2 system. The addition of H2O2 in the membrane tank appeared to alter the nature of the organic matter with a conversion of hydrophobic to hydrophilic fractions, which induced less organics adsorption within the hydrophobic PVDF membrane pores, and a reduced bonding ability for particles. There was no physico-chemical evidence of any deterioration of the membrane from exposure to H2O2, which indicates the feasibility of applying this novel method of fouling control for full-scale UF based water treatment processes.

Journal article

Semitsoglou-Tsiapou S, Templeton MR, Graham NJD, Mandal S, Hernandez Leal L, Kruithof JCet al., 2018, Potential formation of mutagenicity by low pressure-UV/H2O2 during the treatment of nitrate-rich source waters, Environmental Science: Water Research and Technology, Vol: 4, Pages: 1252-1261, ISSN: 2053-1400

Mutagenicity formation by low pressure (LP)-UV/H2O2 treatment of nitrate-rich water containing natural organic matter (NOM) was investigated. Laboratory-grade water samples spiked with either Pony Lake NOM or Suwannee River NOM (4 mg L−1 in both cases) and nitrate (50 mg L−1) were irradiated with UV fluences of 0, 1500 and 2000 mJ cm−2 and a H2O2 dose of 15 mg L−1 and tested for mutagenicity with the Ames II assay. LP-UV photolysis of nitrate in the presence of Pony Lake NOM caused a significant increase in the Ames II assay response and low concentrations of nitrite (0.08–0.09 mg NO2− L−1) and nitrophenols (0.014–0.046 μg L−1) were detected. Suwannee River NOM produced the same nitrite levels but no significant responses in the Ames II assay were observed. Additionally, samples collected from a drinking water treatment plant in the UK using LP-UV/H2O2 treatment were analysed with the Ames II assay. LC-OCD fractionation and SUVA measurements were performed to observe any changes in the properties of NOM. Significant differences in the mutagenicity response were observed between the treatment steps as well as between the two sampling periods. However, with respect to standard thresholds, none of the samples were found to be mutagenic towards the Salmonella typhimurium strain TA98 used.

Journal article

Yu W, Liu T, Crawshaw J, Liu T, Graham NJDet al., 2018, Ultrafiltration and nanofiltration membrane fouling by natural organic matter: Mechanisms and mitigation by pre-ozonation and pH, Water Research, Vol: 139, Pages: 353-362, ISSN: 0043-1354

The fouling of ultrafiltration (UF) and nanofiltration (NF) membranes during the treatment of surface waters continues to be of concern and the particular role of natural organic matter (NOM) requires further investigation. In this study the effect of pH and surface charge on membrane fouling during the treatment of samples of a representative surface water (Hyde Park recreational lake) were evaluated, together with the impact of pre-ozonation. While biopolymers in the surface water could be removed by the UF membrane, smaller molecular weight (MW) fractions of NOM were poorly removed, confirming the importance of membrane pore size. For NF membranes the removal of smaller MW fractions (800 Da–10 kDa) was less than expected from their pore size; however, nearly all of the hydrophobic, humic-type substances could be removed by the hydrophilic NF membranes for all MW distributions (greater than 90%). The results indicated the importance of the charge and hydrophilic nature of the NOM. Thus, the hydrophilic NF membrane could remove the hydrophobic organic matter, but not the hydrophilic substances. Increasing charge effects (more negative zeta potentials) with increasing solution pH were found to enhance organics removal and reduce fouling (flux decline), most likely through greater membrane surface repulsion. Pre-ozonation of the surface water increased the hydrophilic fraction and anionic charge of NOM and altered their size distributions. This resulted in a decreased fouling (less flux decline) for the UF and smaller pore NF, but a slight increase in fouling for the larger pore NF. The differences in the NF behavior are believed to relate to the relative sizes of ozonated organic fractions and the NF pores; a similar size of ozonated organic fractions and the NF pores causes significant membrane fouling.

Journal article

Bell MC, Ritson JP, Verhoef A, Brazier RE, Templeton MR, Graham NJD, Freeman C, Clark JMet al., 2018, Sensitivity of peatland litter decomposition to changes in temperature and rainfall, Geoderma, Vol: 331, Pages: 29-37, ISSN: 0016-7061

Changes to climate are projected over the next 50 years for many peatland areas. As decomposition of peat-forming vegetation is likely to be intrinsically linked to these changes in climate, a clear understanding of climate-peat dynamics is required. There is concern that increased temperature and decreased precipitation could increase the rate of decomposition and put the carbon sink status of many peatlands at risk, yet few studies have examined the impact of both climatic factors together. To better understand the sensitivity of peatland decomposition to changes in both temperature and precipitation and their interaction, we conducted a short-term laboratory experiment in which plant litters and peat soil were incubated, in isolation, in a factorial design. Treatments simulated baseline and projected climate averages derived from the latest UK climate change projections (UKCP09) for Exmoor, a climatically marginal peatland in SW England. Regular carbon dioxide flux measurements were made throughout the simulation, as well as total mass loss and total dissolved organic carbon (DOC) leached. The largest effect on carbon loss in this multifactor experiment was from substrate, with Sphagnum/peat releasing significantly less C in total during the experiment than dwarf shrubs/graminoids. Climate effects were substrate specific, with the drier rainfall treatment increasing the DOC leaching from Calluna, but decreasing it from Sphagnum. Partitioning between CO2 and DOC was also affected by climate, but only for the peat and Sphagnum samples, where the future climate scenarios (warmer and drier) resulted in a greater proportion of C lost in gaseous form. These results suggest that indirect effects of climate through changes in species composition in peatlands could ultimately turn out to be more important for litter decomposition than direct effects of climate change from increased temperatures and decreased rainfall.

Journal article

Liu T, Zhou H, Graham N, Lian Y, Yu W, Sun Ket al., 2018, The antifouling performance of an ultrafiltration membrane with pre-deposited carbon nanofiber layers for water treatment, Journal of Membrane Science, Vol: 557, Pages: 87-95, ISSN: 0376-7388

In order to improve the performance of the ultrafiltration (UF) membrane process in drinking water treatment, in terms of permeate flux and natural organic matter (NOM) removal, a new form of carbon nanofiber (CNF) layer derived from bacterial cellulose (BC) was prepared and applied as a pre-deposited coating on the UF membrane surface. Using bench-scale, dead-end filtration tests, both CNF and CNF modified by ethanol treatment (M-CNF), were evaluated for the treatment of two model NOM solutions, namely bovine serum albumin (BSA) and sodium alginate (SA). The results showed that both types of coating were effective in mitigating membrane fouling (lower flux decline), with the mitigation increasing with the coating quantity, and also enhanced the removal of BSA and SA. In particular, the M-CNF layer at the greater loading (24 g/m2) was able to reduce membrane fouling to a very substantial degree and achieve > 90% removal of BSA and SA. Characterization of the CNF and M-CNF layers showed significant differences in their morphological and structural properties which may explain the observed differences in their ability to reduce membrane fouling; protection of the UF membrane by the carbon nanofiber layers may be attributed to both physical separation and surface adsorption of the NOM biopolymers.

Journal article

Armand H, Stoianov I, Graham N, 2018, Impact of network sectorisation on water quality management, Journal of Hydroinformatics, Vol: 20, Pages: 424-439, ISSN: 1464-7141

The sectorisation of water supply networks includes the permanent closure of valves in order to achieve a cost-effective leakage management and simplify pressure control. The impact of networks sectorisation, also known as District Metered Areas (DMAs), on water quality and discolouration has not been extensively studied and it remains unknown. In addition, hydraulic variables used in the literature for assessing the likelihood of potential discolouration are limited and inconclusive. This paper investigates a methodology to evaluate the impact of networks sectorisation (DMAs) on water quality and the likelihood of discolouration incidents. The methodology utilises a set of surrogate hydraulic variables and an analysis of the hydraulic condition in pipes with historic discolouration complaints. The proposed methodology has been applied to a large-scale water supply network, with and without sectors, in order to assess the potential impact of DMAs on water quality. The results demonstrate that the sectorisation of water supply networks (DMAs) could compromise the overall water quality and increase the likelihood of discolouration incidents. The results of this study and the proposed surrogate hydraulic variables facilitate the formulation of optimisation problems for the re-design and control of water supply networks with sectorised topologies.

Journal article

Lei C, Sun Y, Khan E, Chen SS, Tsang DCW, Graham NJD, Ok YS, Yang X, Lin D, Feng Y, Li X-Det al., 2017, Removal of chlorinated organic solvents from hydraulic fracturing wastewater by bare and entrapped nanoscale zero-valent iron., Chemosphere, Vol: 196, Pages: 9-17, ISSN: 0045-6535

With the increasing application of hydraulic fracturing, it is urgent to develop an effective and economically feasible method to treat the large volumes of fracturing wastewater. In this study, bare and entrapped nanoscale zero-valent iron (nZVI) were introduced for the removal of carbon tetrachloride (CT) and 1,1,2-trichloroethane (TCA) in model high-salinity fracturing wastewater. With increasing ionic strength (I) from Day-1 (I = 0.35 M) to Day-90 (I = 4.10 M) wastewaters, bare nZVI presented significantly lower removal efficiency of CT (from 53.5% to 38.7%) and 1,1,2-TCA (from 71.1% to 21.7%) and underwent more serious Fe dissolution from 1.31 ± 1.19% in Day-1 to 5.79 ± 0.32% in Day-90 wastewater. Particle aggregation induced by high ionic strength was primarily responsible for the lowered performance of nZVI due to less available reactive sites on nZVI surface. The immobilization of nZVI in alginate with/without polyvinyl alcohol provided resistance to particle aggregation and contributed to the superior performance of entrapped nZVI in Day-90 wastewater for 1,1,2-TCA removal (62.6-72.3%), which also mitigated Fe dissolution (4.00-4.69%). Both adsorption (by polymer matrix) and reduction (by immobilized nZVI) were involved in the 1,1,2-TCA removal by entrapped nZVI. However, after 1-month immersion in synthetic fracturing wastewater, a marked drop in the reactivity of entrapped nZVI for 1,1,2-TCA removal from Day-90 wastewater was observed with significant release of Na and total organic carbon. In summary, bare nZVI was sensitive to the nature of the fracturing wastewater, while the use of environmentally benign entrapped nZVI was more promising for wastewater treatment.

Journal article

Liu T, Yang B, Graham N, Lian Y, Yu W, Sun Ket al., 2017, Mitigation of NOM fouling of ultrafiltration membranes by pre-deposited heated aluminum oxide particles with different crystallinity, Journal of Membrane Science, Vol: 544, Pages: 359-367, ISSN: 0376-7388

A major cause of ultrafiltration (UF) membrane fouling in surface water treatment is natural organic matter (NOM). Some studies have reported that heated aluminum oxide particles (HAOPs), prepared by boiling a suspension containing precipitates of the common coagulant alum, can remove substantial amounts of NOM and reduce fouling when they were pre-deposited on UF membranes. However, the influence of the size and structure of the HAOPs in mitigating NOM membrane fouling has not been fully explored so far. This work has investigated the change in microstructure of the HAOPs during the heating process and the subsequent effect on the performance of the membrane process, and especially on the mitigation of fouling. As the heating time increased, the structure of the HAOPs transformed gradually from an amorphous nature to a semi-crystal, and then to a microcrystalline phase. It was found that this micro-crystallization process played a key role in affecting the structural properties of the nano-scale particles and the membrane filtration performance. During the crystalline transition, a change of particle size distribution occurred and the average particle size was found to decrease gradually owing to a dehydration reaction. The smaller particle size of the HAOPs provides a denser pre-filtration layer for NOM separation, and their more rigid structure reduces layer compression and hydraulic resistance during operation. Optimization of the pre-heating condition and surface loading can effectively enhance the performance of the HAOPs layer in reducing NOM fouling in the UF membrane system.

Journal article

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