Publications
412 results found
Liu M, Rashid S, Wang W, et al., 2024, The application of chitosan quaternary ammonium salt to replace polymeric aluminum ferric chloride for sewage sludge dewatering, Water Research, Vol: 256, Pages: 121539-121539, ISSN: 0043-1354
Liu M, Liu X, Graham NJD, et al., 2024, Uncovering the neglected role of anions in trivalent cation-based coagulation processes, Water Research, Vol: 254, ISSN: 0043-1354
Coagulation efficiency is heavily contingent upon a profound comprehension of the underlying mechanisms, facilitated by the evolution of coagulation theory. However, the role of anions, prevalent components in raw and wastewaters, has been relatively overlooked in this context. To address this gap, this study has investigated the impact of three common anions (i.e., chloride, sulfate, and phosphate) on Al-based coagulation. The results have shown that the influence of anions on coagulation depends predominantly on their ability to compete with hydroxyl groups throughout the entire coagulation process, encompassing hydrolysis, aggregation, and the growth of large flocs. Moreover, this competition is subject to the dual influence of both anion concentration and hydroxyl concentration (i.e., pH). The results have revealed the intricate interplay between anions and coagulants, their impact on floc structure, and their importance in optimizing coagulation efficiency and ensuring the production of high-quality water.
Zhao L, Lei T, Chen R, et al., 2024, Bioinspired stormwater control measure for the enhanced removal of truly dissolved polycyclic aromatic hydrocarbons and heavy metals from urban runoff, Water Research, Vol: 254, ISSN: 0043-1354
Stormwater harvesting (SWH) addresses the UN's Sustainable Development Goals (SDGs). Conventional stormwater control measures (SCMs) effectively remove particulate and colloidal contaminants from urban runoff; however, they fail to retain dissolved contaminants, particularly substances of concern like polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs), thereby hindering the SWH applicability. Here, inspired by protein folding in nature, we reported a novel biomimetic SCM for the efficient removal of dissolved PAHs and HMs from urban runoff. Lab-scale tests were conducted together with a more mechanistic investigation on how the contaminants were removed. By integrating hydrophobic organic chains with low-cost hydrophilic flocculant matrixes, our biomimetic flocculants achieved a 1.4–9.5 times removal of all detected dissolved PAHs and HMs, while enhancing the removal of a wide-spectrum of particulate and colloidal contaminants, compared to existing SCMs. Ecotoxicity, as indicated by newborn Daphnia magna as experimental organisms, was reduced from “acute toxicity” of the original runoff sample (toxic unit of ∼2.6) to “non-toxicity” (toxic unit < 0.4) of the treated water. The improved performance is attributed to the protein-folding-like features of the bioinspired flocculants providing: (i) stronger binding to PAHs (via hydrophobic association) and HMs (via coordination), and (ii) the ability of spontaneous aggregation. The bio-inspired approach in this work holds strong promise as an alternative or supplementary component in SCM systems, and is expected to contribute to sustainable water management practices in relation to SDGs.
Zhang L, Graham N, Li G, et al., 2024, Excessive Ozonation Stress Triggers Severe Membrane Biofilm Accumulation and Fouling., Environ Sci Technol, Vol: 58, Pages: 5899-5910
The established benefits of ozone on microbial pathogen inactivation, natural organic matter degradation, and inorganic/organic contaminant oxidation have favored its application in drinking water treatment. However, viable bacteria are still present after the ozonation of raw water, bringing a potential risk to membrane filtration systems in terms of biofilm accumulation and fouling. In this study, we shed light on the role of the specific ozone dose (0.5 mg-O3/mg-C) in biofilm accumulation during long-term membrane ultrafiltration. Results demonstrated that ozonation transformed the molecular structure of influent dissolved organic matter (DOM), producing fractions that were highly bioavailable at a specific ozone dose of 0.5, which was inferred to be a turning point. With the increase of the specific ozone dose, the biofilm microbial consortium was substantially shifted, demonstrating a decrease in richness and diversity. Unexpectedly, the opportunistic pathogen Legionella was stimulated and occurred in approximately 40% relative abundance at the higher specific ozone dose of 1. Accordingly, the membrane filtration system with a specific ozone dose of 0.5 presented a lower biofilm thickness, a weaker fluorescence intensity, smaller concentrations of polysaccharides and proteins, and a lower Raman activity, leading to a lower hydraulic resistance, compared to that with a specific ozone dose of 1. Our findings highlight the interaction mechanism between molecular-level DOM composition, biofilm microbial consortium, and membrane filtration performance, which provides an in-depth understanding of the impact of ozonation on biofilm accumulation.
Liu X, Yang Y, Takizawa S, et al., 2024, New insights into the concentration-dependent regulation of membrane biofouling formation via continuous nanoplastics stimulation, Water Research, Vol: 253, ISSN: 0043-1354
The release of nanoplastics (NPs) into the environment is growing due to the extensive use of plastic products. Numerous studies have confirmed the negative effects of NPs on microorganisms, which poses uncertainties concerning their impact on nanofiltration (NF) membrane biofouling. This study investigated the initial cell adhesion process, NF membrane biofouling kinetic processes and bacterial responses of Pseudomonas aeruginosa (P. aeruginosa) exposed to varied NPs concentrations (0–50 mg·L−1). Transcriptome analysis demonstrated that low concentration of NPs (0.1 mg·L−1) promoted bacterial quorum sensing, energy metabolism, exopolysaccharide biosynthesis and bacterial secretion systems. Correspondingly, the polysaccharide content increased remarkably to 2.77 times the unexposed control, which served as a protective barrier for bacteria to avoid the impact of NPs-induced stress. Suppressed homologous recombination, microbial metabolic potentials and flagellar assembly were detected in bacteria exposed to a high concentration (50 mg·L−1) of NPs, mainly due to the triggered reactive oxygen species (ROS) generation, genomic DNA damage, and decreased energy production. Overall, enhanced formation of the extracellular polymeric substances (EPS) and aggravated membrane flux decline were observed when NPs interacted with the membrane surface by cell secretions (low NPs levels) or cell lysis (high NPs levels). These findings shed light on understanding the microbial metabolism mechanism and membrane biofouling propensity with NPs stress at both the molecular and gene levels.
Liu H, Mu M, Graham NJD, et al., 2024, Alkaline-oxidized MXene composite membrane of ultra high flux and advanced rejection performance for water purification, Journal of Membrane Science, Vol: 698, ISSN: 0376-7388
MXene is a metal-carbon/nitrogen compound material with a two-dimensional layered structure. As a new form of two-dimensional material, it has great potential in the field of water purification because of its properties of high permeability and hydrophilicity. In this study, a MXene composite membrane was prepared by in-situ oxidation of titanium dioxide on the MXene surface by an alkaline oxidation method. A series of characterizations of the prepared MXene composite membrane was carried out. Scanning electron microscopy showed that with an increasing degree of oxidation, the extent of agglomeration of MXene nanosheets increased, thus generating more water channels that are conducive to the transport of water molecules, and an increasing water flux. The penetration performance, interception performance, and stability of the MXene composite membrane were tested. The effect of different concentrations of KOH on the properties of the composite membrane was investigated. It was found that the flux of the composite membrane increased with alkali concentration by 4.6–28.8 times the flux without exposure to alkali. It was found that the rejection rate of the composite membrane for pollutants (dyes, humic acid, bovine serum albumin protein) decreased only slightly with increasing alkali concentration, and was ≥94% of the pure MXene membrane rejection rate in all cases. The rejection performance of the composite membrane was related to the size and charge properties of the pollutant molecules. The results of the stability tests showed that the composite membranes had a high degree of physical and flux stability in a range of aqueous solutions.
Liu M, Graham N, Gregory J, et al., 2024, Towards a molecular-scale theory for the removal of natural organic matter by coagulation with trivalent metals, Nature Water, Vol: 2, Pages: 285-294
Xing B, Li J, Li L, et al., 2024, Promoting denitrification via high electron conversion ratio in the iron valence Cycle: Prospects for Pseudomonas sp. JM-7 application in environmental engineering, Chemical Engineering Journal, Pages: 150495-150495, ISSN: 1385-8947
Xu L, Song S, Graham NJD, et al., 2024, Simultaneous removal of NOM and sulfate in a bioelectrochemical integrated biofilter treating reclaimed water, Water Research, Vol: 252, ISSN: 0043-1354
Biofiltration is an environmentally ‘green’ technology that is compatible with the recently proposed sustainable development goals, and which has an increasingly important future in the field of water treatment. Here, we explored the impacts of bioelectrochemical integration on a bench-scale slow rate biofiltration system regarding its performance in reclaimed water treatment. Results showed that the short-term (<3 months) integration improved the removal of natural organic matter (NOM) (approximately 8.8%). After long-term (5 months and thereafter) integration, the cathodic charge transfer resistance was found to have a significant reduction from 2662 to 1350 Ω. Meanwhile, bioelectrochemical autotrophic sulfate (SO42−) reduction (over 27.6% reduction) through the syntrophic metabolism between hydrogen oxidation strains (genus Hydrogenophaga) and sulfate-reducing microbes (genera Dethiobacter, Desulfovibrio, and Desulfomicrobium) at the cathodic region was observed. More significantly, the microbial-derived chromophoric humic substances were found to act as electron shuttles at the cathodic region, which might facilitate the process of bioelectrochemical SO42− reduction. Overall, this study provided valuable insights into the potential application of bioelectrochemical-integrated biofilter for simultaneous reduction of NOM and SO42− treating reclaimed water.
Yang H, Li Y, Liu H, et al., 2024, The variation of DOM during long distance water transport by the China South to North Water Diversion Scheme and impact on drinking water treatment, Frontiers of Environmental Science & Engineering, Vol: 18, ISSN: 2095-2201
In this study, samples were taken from three locations, upstream to downstream, along the central route project of the China South to North Water Diversion (SNWD) scheme in summer and winter. These were used to reveal the variations of dissolved organic matter (DOM) during the water transfer process, and the effects of these variations on drinking water treatment and disinfection by-products formation potential (DBPs-FP). The results showed that polysaccharides accumulate in summer and reduce in winter with flow distance, which has an important effect on the overall properties of DOM, as well as on the performance of coagulation, ultrafiltration, and the formation of DBPs. Humic substances, and their hydrophilic content, also increased in summer and decreased in winter with flow distance. In contrast, the concentration of small organic substances (MW ⩽ 1000 Da) increased in both summer and winter with flow distance, which affected both nanofiltration (NF) membrane fouling and DBPs-FP. The results provide a useful case study of spatial and temporal changes in raw water DOM during long distance water transfer and their impact on the treatment and quality of drinking water from the SNWD.
Hou J, Guo S, Graham N, et al., 2024, r-HGO/MXene composite membrane with enhanced permeability and rejection performance for water treatment, Journal of Membrane Science, Vol: 691, ISSN: 0376-7388
Pure graphene oxide (GO) membranes have a tendency to swell in water and have a relatively low flux, making them impractical for water treatment applications. Herein, a novel two-dimensional (2D) composite membrane based on reduced-holey GO (r-HGO) and MXene materials was developed. As a consequence of synergistic effects arising from its unique heterogeneous structure, the r-HGO/MXene composite membrane exhibited an exemplary performance for water treatment, in terms of its permeability and pollutant rejection, and high physical stability. The preparation conditions, especially the reduction degree of GO and the proportions of r-HGO and MXene, determine the properties and performance of the composite membrane. The water flux of the r-HGO/MXene composite membrane with a r-HGO/MXene mass ratio of 1/1 achieved 121.0 L m−2 h−1·bar−1, which was 23 times higher than that of pure GO membrane (∼5.2 L m−2 h−1·bar−1). The removal rates of Coomassie brilliant blue, Methyl blue, Crystal violet, Rhodamine B, Methylene blue, were all above 90 %. Furthermore, the r-HGO/MXene composite membrane was found to be physically stable for more than a week in an aqueous environment. The results of this work show that the r-HGO/MXene composite membrane has great potential as a separation method in water treatment by overcoming some of the important limitations of other current 2D materials.
Chen C, Yang Y, Graham NJD, et al., 2024, A comprehensive evaluation of the temporal and spatial fouling characteristics of RO membranes in a full-scale seawater desalination plant, Water Resources, Vol: 249, ISSN: 0097-8078
The fouling of seawater reverse osmosis (SWRO) membranes remains a persistent challenge in desalination. Previous research has focused mainly on fouling separately; however, organic, inorganic, and biofouling can coexist and influence each other. Hence, in-depth study of the spatiotemporal changes in actual combined fouling in full-scale seawater desalination will provide more effective information for fouling investigation and control. In this study, we monitored (i) the operational performance of a full-scale desalination plant for 7 years and (ii) the development and characterization of membrane and spacer fouling at different locations of spiral-wound membrane modules sampled after 2.5-, 3.5-, and 7-year operation. The findings showed that (i) operational performance indicators declined with time (normalized flux 40 % reduction, salt rejection 2 % in 7 years), with a limited effect of the 20-day cleaning frequency, (ii) fouling accumulation in the membrane module mainly occurred at the feed side of the lead module and the microbial community in these area exhibited the highest diversity, (iii) the dominant microbial OTUs belonged mainly to Proteobacteria (43-70 %), followed by Bacteroidetes (10-11 %), (iv) Phylogenetic molecular ecological networks and Spearman correlation analysis revealed that Chloroflexi (Anaerolineae) and Planctomycetes were keystone species in maintaining the community structure and biofilm maturation and significantly impacted the foulant content on the SWRO membrane, even with low abundance, and that (v) fouling accumulation was composed of polysaccharides, soluble microbial products, marine humic acid-like substances, and inorganic Ca/Fe/Mg/Si dominate the fouling layer of both the membrane and spacer. Overall, variation partitioning analysis quantitatively describes the increasing contribution of biofouling over time. Ultimately, the organic‒inorganic-biofouling interaction (70 %) significantly contributed to th
Zhou P, Tian L, Siddique MS, et al., 2024, Divergent fate and roles of dissolved organic matter from spatially varied grassland soils in China during long-term biogeochemical processes, Environmental Science and Technology (Washington), Vol: 58, Pages: 1164-1176, ISSN: 0013-936X
Terrestrial dissolved organic matter (DOM) is critical to global carbon and nutrient cycling, climate change, and human health. However, how the spatial and compositional differences of soil DOM affect its dynamics and fate in water during the carbon cycle is largely unclear. Herein, the biodegradation of DOM from 14 spatially distributed grassland soils in China with diverse organic composition was investigated by 165 days of incubation experiments. The results showed that although the high humified fraction (high-HS) regions were featured by high humic-like fractions of 4-25 kDa molecular weight, especially the abundant condensed aromatics and tannins, they unexpectedly displayed greater DOM degradation during 45-165 days. In contrast, the unique proteinaceous and 25-100 kDa fractions enriched in the low humified fraction (low-HS) regions were drastically depleted and improved the decay of bulk DOM but only during 0-45 days. Together, DOM from the high-HS regions would cause lower CO2 outgassing to the atmosphere but higher organic loads for drinking water production in the short term than that from the low-HS regions. However, this would be reversed for the two regions during the long-term transformation processes. These findings highlight the importance of spatial and temporal variability of DOM biogeochemistry to mitigate the negative impacts of grassland soil DOM on climate, waters, and humans.
Xu L, Song S, Graham NJD, et al., 2024, Direct generation of DBPs from city dust during chlorine-based disinfection, Water Research, Vol: 248, ISSN: 0043-1354
Chlorine-based disinfectants, such as sodium hypochlorite, are extensively used in our daily lives. In particular, during the recent Covid-19 pandemic and post-pandemic period, excessive amounts of chlorine-based disinfectants were used both indoors and outdoors to interrupt virus transmission. However, the interaction between disinfectants and city dust during the disinfection process has not been sufficiently evaluated. In this study, we conducted a comprehensive investigation into the intrinsic characteristics (e.g. morphology, size, elemental composition, and organic content, etc.) of dust collected from various indoor and outdoor areas. The results showed that the organic carbon content of indoor dust reached 6.14 %, with a corresponding measured dissolved organic carbon value of 4.17 ± 0.23 mg/g (normalized to the dust weight). Concentrations of regulated DBPs, resulting from the interaction between dust and NaClO, ranged from 57.78 ± 2.72 to 102.80 ± 22.63 µg/g for THMs and from 119.18 ± 6.50 to 285.14 ± 36.95 µg/g for HAAs (normalized to the dust weight). More significantly, using non-target analysis through gas chromatography quadrupole time-of-flight mass spectrometry (GC-qTOF-MS), we identified a total of 68, 89, and 87 types of halogenated DBPs from three typical indoor and outdoor sites (R-QH, C-JS, and W-BR, respectively). These unknown DBPs included compounds with higher toxicity compared to regulated DBPs. These findings highlight that city dust is a significant source of DBP generation during chlorine-based disinfection, posing potential harm to both the ecological environment and human health.
Yang B, Rashid S, Graham N, et al., 2023, In-depth study of the removal of Mn(II) by Fe(VI) treatment and the profound influence of NOM on floc formation and properties, Water Research, Vol: 247, ISSN: 0043-1354
The presence of manganese(II) in drinking water sources poses a significant treatment difficulty for water utilities, thus necessitating the development of effective removal strategies. Treatment by Fe(VI), a combined oxidant and coagulant, has been identified as a potential green solution; however, its effectiveness is hampered by natural organic matter (NOM), and this underlying mechanism is not fully understood. Here, we investigated the inhibitory effect of three different types of NOM, representing terrestrial, aquatic, and microbial origins, on Mn(II) removal and floc growth during Fe(VI) coagulation. Results revealed that Fe(VI) coagulation effectively removes Mn(II), but NOM could inhibit its effectiveness by competing in oxidation reactions, forming NOM-Fe complexes, and altering floc aggregation. Humic acid was found to exhibit the strongest inhibition due to its unsaturated heterocyclic species that strongly bond to flocs and react with Fe(VI). For the first time, this study has presented a comprehensive elucidation of the atomic-level structure of Fe(VI) hydrolysis products by employing Extended X-ray Absorption Fine Structure Spectroscopy (EXAFS). Results demonstrated that NOM strengthened single-corner and double-corner coordination between FeO6 octahedrons that were consumed by Mn(II), resulting in an increased contribution of γ-FeOOH in the core-shell structure (γ-FeOOH shell and γ-F2O3 core), thereby inhibiting coagulation effects. Furthermore, NOM impeded the formation of stable manganite, resulting in more low-valence Mn(III) being incorporated in the form of an unstable intermediate. These findings provide a deeper understanding of the complex interplay between Fe coagulants, heavy metal pollution, and NOM in water treatment and offer insight into the limitations of Fe(VI) in practical applications.
Zhang K, Guo F, Graham N, et al., 2023, Engineering morphology and electron redistribution of a Ni/WO₃ Mott-Schottky bifunctional electrocatalyst for efficient alkaline urea splitting, ACS Applied Materials and Interfaces, Vol: 15, Pages: 50116-50125, ISSN: 1944-8244
Construction of the desired morphology and nanointerface to expose the active sites and modulate the electronic structure offers an effective approach to boosting urea splitting for energy-saving hydrogen generation. Herein, we fabricate a Ni/WO3 Mott-Schottky heterojunction electrocatalyst with a hedgehog-like structure supported on Ni foam toward alkaline urea splitting. Different Ni/WO3 morphologies, such as microspheres, hedgehog-like structures, octahedrons, and cubes, were obtained when various ratios of Ni/W feeds were used. The Mott-Schottky nanointerfaces between Ni and WO3 domains are visually confirmed by high-resolution transmission electron microscopy images, which also accelerated the charge transfer rate. Benefiting from the high electrochemically active surface area and enhanced charge transferability, the optimal Ni/WO3 electrode exhibits outstanding catalytic activity toward hydrogen generation with a low overpotential of 163 mV at 100 mA cm-2 in alkaline solution and reduced cell voltage of 1.67 V when coupled with urea oxidation reaction. Theoretical calculations reveal that the Ni sites in Ni/WO3 optimize the H adsorption energy (ΔGH*) with the |ΔGH*| value of 0.097 eV, much lower than that of Ni (0.35 eV) and WO3 (0.235 eV). This work demonstrates important guidance in designing an efficient electrocatalyst for urea splitting.
Yang B, Rashid S, Graham N, et al., 2023, The impact of small organic molecules on Fe(II) coagulation: facilitating vs. shielding mechanisms on charge transfer, Separation and Purification Technology, Vol: 323, ISSN: 0950-4214
During the Fe(II) coagulation process, organics can significantly alter the structure of formed flocs, thereby influencing their efficacy in water treatment. However, the underlying mechanisms are not fully understood. This study investigates the impact of small organic molecules (SOM) on Fe(II) coagulation using serine, cysteine, histidine, and citric acid as examples. Results demonstrate that different SOM can significantly change the coagulation behavior by forming particles with distinct nanostructures, including flake-shaped γ-FeOOH, spherical γ-FeOOH, and ferrihydrite globules. The detection of Fe2+ in solution partially explains these phenomena, as Fe2+ can catalyze lattice rearrangement through charge transfer. By controlling the oxidation rate of Fe2+, SOM can influence the structure of flocs: cysteine and serine prolong the existence time of Fe2+ and promote the formation of highly crystalline γ-FeOOH, while citric acid accelerates Fe2+ oxidation, resulting in the opposite effect. However, histidine, despite delaying the oxidation of Fe2+, inhibits the formation of crystalline minerals, leading to the presence of flocs containing spherical γ-FeOOH. Mediated electrochemical analyses indicate that this is due to the adsorption of SOM on flocs, which hinders the effective entry of Fe2+ into the solid phase and disrupts the charge transfer. This study demonstrates that SOM can affect the interaction between Fe2+ and the nanostructure of flocs in two ways: directly influencing the oxidation rate of Fe2+ and indirectly interfering with the charge transfer between flocs and free Fe2+, which highlights the critical role of Fe(II)-Fe(III) charge transfer in coagulation and provides new possibilities for analyzing more complex organics-coagulation systems.
Zhou P, Wu M, Graham N, et al., 2023, Revealing molecular level changes of dissolved organic matter in black soils during continuous leaching and their implications for drinking water treatment, ACS ES&T engineering, Vol: 3, Pages: 1592-1603, ISSN: 2690-0645
The dynamics of dissolved organic matter (DOM) transport from black soil and its potential effects on the quality, safety, and treatability of water are poorly understood. Here, sequential column leaching experiments with black soil, surface water, and synthetic rainwater were performed to explore the molecular variations in leachable organic matter and its potential influences on water treatment. The fluorescence and UV–vis spectroscopy, together with size exclusion chromatography, showed that the greater proportion of low molecular weight (MW) aliphatic DOM in initial eluates gradually changed to higher fractions of larger aromatic DOM in later eluates. Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) revealed a decrease in lignin-like molecules and increase in condensed aromatic components of the DOM upon continuous leaching. The disinfection byproduct formation potential (DBPFP) was reduced with increasing leaching volume, along with the decreasing yields of dissolved organic carbon (DOC). Furthermore, compared with that of the first leaching phase (P1), the chlorine reactivity (DBPFP normalized to DOC) of DOM at the tenth leaching phase (P10) increased by 26–53%, 51–60%, and 39–44%, for trihalomethanes, haloacetic acids, and chloral hydrates, respectively, due to increased aromatic fractions in DOM. The principal component analysis (PCA) and partial least-squares path model (PLS–PM) showed that the quantity and quality of DOM leached by surface water and synthetic rainwater were significantly different. Lastly, despite the pronounced variations in DOM properties, the black soil-derived DOM displayed high treatability, with 52–71% of DOC, 54–69% of trihalomethane (THM) precursors, 60–80% of haloacetic acid (HAA) precursors, and nearly all (∼100%) of the nitrogen-containing DBP (N-DBP), haloketone (HK), and chloral hydrate (CH) precursors being removed by a nanofiltration membrane. Our res
Xu L, Song S, Graham NJD, et al., 2023, An overlooked crystallization effect during the O3 participated coagulation improves the performance of dual-membrane process, Chemical Engineering Journal, Vol: 472, ISSN: 1385-8947
Till now, the transformation of amorphous flocs formed during the hydrolysis stage of coagulation has not been fully addressed. In this work, by using a conventional coagulant (alum), the transformation process was explored by observing the interactions between O3 and the amorphous alum flocs formed during flocculation at neutral pH. It was found that O3 promoted the transition of the in-situ formed alum flocs from tetrahedral Al (Al(O)4) to octahedral Al (Al(O)6) structures, through an accelerated dehydroxylation process, and therefore facilitated the crystallization process to form boehmite. During this process, the surface functional groups of amorphous Al flocs (triple bondAl–H2O and triple bondAl–OH) were observed to take part in the O3 catalytic oxidation with the generation of hydroxyl radicals (radical dotOH). This synergistic effect significantly favored the performance of the subsequent dual-membrane (UF-NF) process in terms of both fouling alleviation (1.78 and 1.60 times higher flux of UF and NF, respectively) and final effluent quality improvement, including the reduction in disinfection byproduct (DBP) formation potential (48.1% and 22.4% lower generation of total trihalomethanes and total haloacetic acid, respectively) and the corresponding calculated toxicity. The results obtained here provide a greater understanding of the transformation of amorphous Al flocs formed during flocculation with O3, and valuable information regarding its practical application in membrane filtration process with greater treatment performance.
Yang H, Xu L, Li Y, et al., 2023, FexO/FeNC modified activated carbon packing media for biological slow filtration to enhance the removal of dissolved organic matter in reused water, Journal of Hazardous Materials, Vol: 457, ISSN: 0304-3894
The biological slow filtration reactor (BSFR) process has been found to be moderately effective for the removal of refractory dissolved organic matter (DOM) in the treatment of reused water. In this study, bench scale experiments were conducted using a mixture of landscape water and concentrated landfill leachate as feed water, to compare a novel iron oxide (FexO)/FeNC modified activated carbon (FexO@AC) packed BSFR, with a conventional activated carbon packed BSFR (AC-BSFR), operated in parallel. The results showed that the FexO@AC packed BSFR had a refractory DOM removal rate of 90%, operated at a hydraulic retention time (HRT) of 10 h at room temperature for 30 weeks, while under the same conditions the removal by the AC-BSFR was only 70%. As a consequence, the treatment by the FexO@AC packed BSFR substantially reduced the formation potential of trihalomethanes, and to a less extent, haloacetic acids. The modification of FexO/FeNC media raised the conductivity and the oxygen reduction reaction (ORR) efficiency of the AC media to accelerate the anaerobic digestion by consuming the electrons that are generated by anaerobic digestion itself, which lead to the marked improvement in refractory DOM removal.
Siddique MS, Song Q, Xiong X, et al., 2023, Hydrolyzed polyacrylonitrile UF-membrane for surface and TAP water treatment: influence on DBPs formation and removal, Chemical Engineering Journal, Vol: 471, ISSN: 1385-8947
The integration of pre-treatment methods with low pressure-driven ultrafiltration (UF) has been found effective for reducing the formation of disinfection by-products (DBPs) in drinking water. In this study, a low dose peroxone (H2O2/O3) assisted alkaline hydrolyzed polyacrylonitrile (HPAN) UF-membrane system was explored, to determine its performance efficiency against two dissolved organic matter (DOM) sources and TAP water, specifically focusing the formation and removal of regulated DBPs. Increased hydrophilicity, enhanced incorporation of carboxyl groups, and decreased surface porosity were observed for the PAN membrane as a function of increased hydrolysis time. Filtration experiments involving humic acid (HA) and samples of real DOM sources displayed a high flux recovery (>90%) with the HPAN membrane. The initial flux for the optimized HPAN was found to be twice than that of the NF-3 membrane, irrespective of the DOM source. However, a relatively comparable removal efficiency was observed for both HPAN and NF-3 membranes in terms of organic matter and DBPs formation potential. Additionally, the H2O2/O3-HPAN system significantly reduced the aromatic and fluorescent content of the DOM by upto 70–80%, as represented by the DOC, UV254 and parallel factor analysis (PARAFAC) components. The fluorescence ratio C1/C2 showed a relatively greater reduction for soil-derived organic matter (SOM) as compared to the Olympic Lake (OL) water. Post-chlorination was found highly effective for the degradation of the humic-like DOM component (C1) than that of the fulvic and protein-like components. Moreover, the integration of H2O2/O3 with HPAN was able to remove 80% of the THMs and HAAs formation for both OL and SOM samples, together with a comparable reduction in DBP cytotoxicity. Interestingly, the HPAN membrane by reducing the TAP water DBPs upto 50%, fulfills the criteria of USEPA maximum contaminant level for drinking water.
Song Q, Yang B, Liu M, et al., 2023, Floc aging: crystallization and improving low molecular weight organic removal in re-coagulation, Water Research, Vol: 243, ISSN: 0043-1354
Iron coagulants have been used extensively in drinking water treatment. This typically produces substantial quantities of insoluble iron hydrolysis products which interact with natural and anthropogenic organic substances during the coagulation process. Previous studies have shown that the removal of low molecular weight (MW) organics is relatively poor by coagulation, which leads to their presence during disinfection, with the formation of halogenated byproducts, and in treated water supplies as potentially biodegradable material. Currently, there is little knowledge about the changes that occur in the nature of coagulant flocs as they age with time and how such changes affect interactions with organic matter, especially low MW organics. To improve this deficiency, this study has investigated the variation of aged flocs obtained from two commonly used iron salts and their impact on representative organic contaminants, natural organic matter (NOM) and tetracycline antibiotic (TC), in a real surface water. It was found that aging resulted in increasing crystallization of the flocs, which can play a beneficial role in activating persulfate oxidant to remove the representative organics. Furthermore, acidification was also found to further improve the removal of low MW natural organics and tetracycline. In addition, the results showed that the low MW fractions of NOM (<1 K Dalton) were substantially removed by the aging flocs. These results are in marked contrast to the poor removal of low MW organic substances by conventional coagulation, with or without added oxidants, and show that aged flocs have a high potential of reuse for re-coagulation and activation of oxidants to reduce low MW organics, and enhance drinking water quality.
Yang B, Graham N, Liu P, et al., 2023, Atomic-level structural differences between Fe(III) coprecipitates generated by the addition of Fe(III) coagulants and by the oxidation of Fe(II) coagulants determine their coagulation behavior in phosphate and DOM removal, Environmental Science and Technology (Washington), Vol: 57, Pages: 12489-12500, ISSN: 0013-936X
In situ Fe(III) coprecipitation from Fe2+ oxidation is a widespread phenomenon in natural environments and water treatment processes. Studies have shown the superiority of in situ Fe(III) (formed by in situ oxidation of a Fe(II) coagulant) over ex situ Fe(III) (using a Fe(III) coagulant directly) in coagulation, but the reasons remain unclear due to the uncertain nature of amorphous structures. Here, we utilized an in situ Fe(III) coagulation process, oxidizing the Fe(II) coagulant by potassium permanganate (KMnO4), to treat phosphate-containing surface water and analyzed differences between in situ and ex situ Fe(III) coagulation in phosphate removal, dissolved organic matter (DOM) removal, and floc growth. Compared to ex situ Fe(III), flocs formed by the natural oxidizing Fe2+ coagulant exhibited more effective phosphate removal. Furthermore, in situ Fe(III) formed through accelerated oxidation by KMnO4 demonstrated improved flocculation behavior and enhanced removal of specific types of DOM by forming a more stable structure while still maintaining effective phosphate removal. Fe K-edge extended X-ray absorption fine structure spectra (EXAFS) of the flocs explained their differences. A short-range ordered strengite-like structure (corner-linked PO4 tetrahedra to FeO6 octahedra) was the key to more effective phosphorus removal of in situ Fe(III) than ex situ Fe(III) and was well preserved when KMnO4 accelerated in situ Fe(III) formation. Conversely, KMnO4 significantly inhibited the edge and corner coordination between FeO6 octahedra and altered the floc-chain-forming behavior by accelerating hydrolysis, resulting in a more dispersed monomeric structure than ex situ Fe(III). This research provides an explanation for the superiority of in situ Fe(III) in phosphorus removal and highlights the importance of atomic-level structural differences between ex situ and in situ Fe(III) coprecipitates in water treatment.
Tian L, Zhou P, Graham N, et al., 2023, Long-term operation and biofouling of graphene oxide membrane in practical water treatment: insights from performance and biofilm characteristics, Journal of Membrane Science, Vol: 680, ISSN: 0376-7388
The widespread research of graphene oxide (GO) membranes has revealed the need to investigate their long-term performance and associated biofouling behavior in practical water treatment conditions. In this study, we have evaluated the long-term operation of GO membranes from the perspective of filtration performance and biofilm characteristics, based on two representative GO membranes (V-GO and P-GO, fabricated by vacuum and pressure filtration, respectively) with different surface properties and a natural surface water, using a gravity driven membrane system. The results showed that the GO membranes were capable of achieving sustainable water purification over 45 days of operation, associated with a complete rejection for biopolymers and desirable removal for fluorescent organic matters. Furthermore, the V-GO membrane with a rougher surface, reduced hydrophilicity and higher sheet-edge exposure than that of the P-GO membrane formed a highly heterogeneous and porous biofilm with high permeability, despite its greater biofilm thickness and extracellular polymeric substances (EPS) contents. In contrast, the P-GO membrane biofilm exhibited a thin but dense structure, and therefore an increased hydraulic resistance (∼1.5 times greater than V-GO membrane). The microbial community analysis revealed that bacteria related to biofilm formation was richer in V-GO biofilm. While bacteria associated with the degradation of organic matters and the aggregation of microorganisms accounted for a greater proportion in P-GO biofilm. These factors were responsible for forming a thick biofilm for V-GO, and a thin but high resistance biofilm for P-GO membrane. Our findings highlight the sustainable water purification performance of the GO membranes, and the P-GO membrane can alleviate biofilm formation but not necessarily reduce biofouling during the long-term filtration, while this was opposite in case of the V-GO membrane.
Wang J, Su Z, JD Graham N, et al., 2023, Double positively charged polyamide nanofiltration membrane with PEI/Zr4+ for Cr3+ and trimethoprim removal, Chemical Engineering Journal, Vol: 469, ISSN: 1385-8947
This paper focuses on the functionalization of double positively charged polyethylenimine (PEI)/Zr4+-polyamide (PA) nanofiltration (NF) membrane by connecting Zr4+ with positively charged PEI-PA NF membrane surface. In particular, the properties of prepared PEI/Zr4+-PA NF membrane, performance on removing aquatic contaminants (Cr3+ and trimethoprim), and its antifouling ability were evaluated in detail. In this regard, zirconium acetate was successfully adopted as the zirconium source for stable membrane surface charge control. Zr4+ loading increased the hydrophilicity of the PEI-PA NF membrane, improved permeate flux, and enhanced the removal behavior of PEI/Zr4+-PA NF membrane especially when exposed to Cr3+ and trimethoprim at high concentrations. Furthermore, effectiveness of PEI/Zr4+-PA NF membrane was not affected by high filtering degree, filtration cycle, and negatively charged macromolecules, such as bovine serum albumin (BSA). Also, antifouling ability of PEI/Zr4+-PA NF membrane could be further improved by continuously loading Zr4+.
Xing B, Graham NJD, Zhao B, et al., 2023, Goethite formed in the periplasmic space of pseudomonas sp. JM-7 during Fe cycling enhances its denitrification in water, Environmental Science and Technology (Washington), Vol: 57, Pages: 11096-11107, ISSN: 0013-936X
Denitrification-driven Fe(II) oxidation is an important microbial metabolism that connects iron and nitrogen cycling in the environment. The formation of Fe(III) minerals in the periplasmic space has a significant effect on microbial metabolism and electron transfer, but direct evidence of iron ions entering the periplasm and resulting in periplasmic mineral precipitation and electron conduction properties has yet to be conclusively determined. Here, we investigated the pathways and amounts of iron, with different valence states and morphologies, entering the periplasmic space of the denitrifier Pseudomonas sp. JM-7 (P. JM-7), and the possible effects on the electron transfer and the denitrifying ability. When consistently provided with Fe(II) ions (from siderite (FeCO3)), the dissolved Fe(II) ions entered the periplasmic space and were oxidized to Fe(III), leading to the formation of a 25 nm thick crystalline goethite crust, which functioned as a semiconductor, accelerating the transfer of electrons from the intracellular to the extracellular matrix. This consequently doubled the denitrification rate and increased the electron transport capacity by 4-30 times (0.015-0.04 μA). However, as the Fe(II) concentration further increased to above 4 mM, the Fe(II) ions tended to preferentially nucleate, oxidize, and crystallize on the outer surface of P. JM-7, leading to the formation of a densely crystallized goethite layer, which significantly slowed down the metabolism of P. JM-7. In contrast to the Fe(II) conditions, regardless of the initial concentration of Fe(III), it was challenging for Fe(III) ions to form goethite in the periplasmic space. This work has shed light on the likely effects of iron on environmental microorganisms, improved our understanding of globally significant iron and nitrogen geochemical cycles in water, and expanded our ability to study and control these important processes.
Liu M, Graham N, Xu L, et al., 2023, Bubbleless aerated-biological activated carbon as a superior process for drinking water treatment in rural areas, Water Research, Vol: 240, ISSN: 0043-1354
Drinking water supply in rural areas remains a substantial challenge due to complex natural, technical and economic conditions. To provide safe and affordable drinking water to all, as targeted in the UN Sustainable Development Goals (2030 Agenda), low-cost, efficient water treatment processes suitable for rural areas need to be developed. In this study, a bubbleless aeration BAC (termed ABAC) process is proposed and evaluated, involving the incorporation of a hollow fiber membrane (HFM) assembly within a slow-rate BAC filter, to provide dissolved oxygen (DO) throughout the BAC filter and an increased DOM removal efficiency. The results showed that after a 210-day period of operation, the ABAC increased the DOC removal by 54%, and decreased the disinfection byproduct formation potential (DBPFP) by 41%, compared to a comparable BAC filter without aeration (termed NBAC). The elevated DO (> 4 mg/L) not only reduced secreted extracellular polymer, but also modified the microbial community with a stronger degradation ability. The HFM-based aeration showed comparable performance to 3 mg/L pre-ozonation, and the DOC removal efficiency was four times greater than that of a conventional coagulation process. The proposed ABAC treatment, with its various advantages (e.g., high stability, avoidance of chemicals, ease of operation and maintenance), is well-suited to be integrated as a prefabricated device, for decentralized drinking water systems in rural areas.
Siddique MS, Lu H, Xiong X, et al., 2023, Exploring impacts of water-extractable organic matter on pre-ozonation followed by nanofiltration process: Insights from pH variations on DBPs formation, Science of the Total Environment, Vol: 876, ISSN: 0048-9697
This study investigated the influence of pH (4-10) on the treatment of water-extractable organic matter (WEOM), and the associated disinfection by-products (DBPs) formation potential (FP), during the pre-ozonation/nanofiltration treatment process. At alkaline pH (9-10), a rapid decline in water flux (> 50 %) and higher membrane rejection was observed, as a consequence of the increased electrostatic repulsion forces between the membrane surface and organic species. Parallel factor analysis (PARAFAC) modeling and size exclusion chromatography (SEC) provides detailed insights into the WEOM compositional behavior at different pH levels. Ozonation at higher pH significantly reduced the apparent molecular weight (MW) of WEOM in the 4000-7000 Da range by transforming the large MW (humic-like) substances into small hydrophilic fractions. Fluorescence components C1 (humic-like) and C2 (fulvic-like) exhibited a predominant increase/decrease in concentration for all pH conditions during pre-ozonation and nanofiltration treatment process, however, the C3 (protein-like) component was found highly associated with the reversible and irreversible membrane foulants. The ratio C1/C2 provided a strong correlation with the formation of total trihalomethanes (THMs) (R2 = 0.9277) and total haloacetic acids (HAAs) (R2 = 0.5796). The formation potential of THMs increased, and HAAs decreased, with the increase of feed water pH. Ozonation markedly reduced the formation of THMs by up to 40 % at higher pH levels, but increased the formation of brominated-HAAs by shifting the formation potential of DBPs towards brominated precursors.
Tian L, Graham NJD, Tian X, et al., 2023, Fenton induced microdefects enable fast water transfer of graphene oxide membrane for efficient water purification, Journal of Membrane Science, Vol: 675, ISSN: 0376-7388
Recent studies have highlighted the great potential of graphene oxide (GO) as the basis of advanced separation membranes for water-related environmental applications. However, pristine GO membranes usually suffer from low water permeability and inadequate stability that limit their further progress and application in practice. Here, a novel approach involving intra-defect construction, combined with cation cross-linking, was used to prepare highly permeable and stable GO membranes for water purification. The preparation was based on Fenton system to achieve enhanced regulation of the membrane structure. The in-situ generated Fe(III) and reaction products (hydroxyl radical and Fe-based nanoparticles) enabled the formation of tightly cross-linked GO nanosheets and favorable pinholes and void defects within the membrane, which stabilized the membrane structure and enhanced its permeability. The resultant membrane achieved an ultrahigh water flux (∼45 L m−2 h−1 bar−1), together with a favorable rejection of Coomassie brilliant blue dye (>91%), natural organic matter (humic acid and bovine serum albumin, >95%) and superior dye/salt selectivity. Moreover, the membrane exhibited a long-term operating stability and pressure-resistance performance. This study offers a facile and scalable method for the design of high performance GO and other two-dimensional (2D) membranes for water purification.
Wang Z, Chen R, Li Y, et al., 2023, Protein-folding-inspired approach for UF fouling mitigation using elevated membrane cleaning temperature and residual hydrophobic-modified flocculant after flocculation-sedimentation pre-treatment, Water Research, Vol: 236, Pages: 1-12, ISSN: 0043-1354
Hydrophobic-modified flocculants have demonstrated considerable promise in the removal of emerging contaminants by flocculation. However, there is a lack of information about the impacts of dosing such flocculants on the performance of subsequent treatment unit(s) in the overall water treatment process. In this work, inspired by the ubiquitous protein folding phenomenon, an innovative approach using an elevated membrane cleaning temperature as the means to induce residual hydrophobic-modified chitosan flocculant (TRC), after flocculation-sedimentation, to reduce membrane fouling in a subsequent ultrafiltration was proposed; this was evaluated in a continuous flocculation-sedimentation-ultrafiltration (FSUF) process treating samples of the Yangtze River. The hydrophobic chains of TRC had similar temperature-dependent hydrophobicity to those of natural proteins. In the 40-day operation of the FSUF system with combined dosing of alum and TRC, a moderately elevated cleaning water temperature (45 °C) of both backwash with air-bubbling and soaking with sponge-scrubbing cleaning, significantly reduced reversible and irreversible fouling resistance by 49.8%∼61.3% and 73.9%∼83.3%, respectively, compared to the system using cleaning water at 25 °C. Material flow analysis, statistical analysis, instrumental characterizations, and computational simulations, showed that the enhanced fouling mitigation originated from three factors: the reduced contaminant accumulation onto membranes, the strengthened membrane-surface-modification role of TRC, and the weakened structure of the fouling material containing TRC, at the elevated cleaning temperature. Other measures of the performance, these being water purification, membrane stability and economic aspects, also confirmed the potential and feasibility of the proposed approach. This work has provided new insights into the role of hydrophobic-modified flocculants in membrane fouling control, in addition to emerging conta
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