Publications
414 results found
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
Zhang K, Duan Y, Graham N, et al., 2023, Unveiling the synergy of polymorph heterointerface and sulfur vacancy in NiS/Ni3S2 electrocatalyst to promote alkaline hydrogen evolution reaction, Applied Catalysis B: Environmental, Vol: 323, ISSN: 0926-3373
Efficient transition metal sulfide electrocatalysts for alkaline hydrogen evolution reaction (HER) are desired but restricted by their sluggish kinetics. Herein, we report a hydrothermal sulfurization-acid assisted etching strategy for the controllable fabrication of Mo doped NiS/Ni3S2 polymorph heterostructure with rich sulfur vacancies (Mo-NiS/Ni3S2-rich Sv). Direct spectroscopic evidence, together with theoretical analysis, demonstrate that the S centers on the Ni3S2 side of the nickel sulfide polymorphs are identified as the H2-evolving sites, while the Ni sites on the Mo-NiS side are beneficial for cleaving the HO-H bond. Importantly, in situ Raman spectroscopy further reveals that the presence of rich Sv can expedite the evolution of H* to molecular H2, promoting the HER kinetics. As expected, the optimal Mo-NiS/Ni3S2-rich Sv electrocatalyst exhibits the outstanding HER activity and excellent durability in alkaline solution. Understanding the synergy of polymorph heterostructure and element defect is crucial for the rational design of high-performance HER electrocatalysts.
Liu M, Graham NJD, Xu L, et al., 2023, Bubbleless air shapes biofilms and facilitates natural organic matter transformation in biological activated carbon., Environmental Science and Technology (Washington), Vol: 57, Pages: 4543-4555, ISSN: 0013-936X
The biodegradation in the middle and downstream of slow-rate biological activated carbon (BAC) is limited by insufficient dissolved oxygen (DO) concentrations. In this study, a bubbleless aerated BAC (termed ABAC) process was developed by installing a hollow fiber membrane (HFM) module within a BAC filter to continuously provide aeration throughout the BAC system. The BAC filter without an HFM was termed NBAC. The laboratory-scale ABAC and NBAC systems operated continuously for 426 days using secondary sewage effluent as an influent. The DO concentrations for NBAC and ABAC were 0.78 ± 0.27 and 4.31 ± 0.44 mg/L, respectively, with the latter providing the ABAC with greater electron acceptors for biodegradation and a microbial community with better biodegradation and metabolism capacity. The biofilms in ABAC secreted 47.3% less EPS and exhibited greater electron transfer capacity than those in NBAC, resulting in enhanced contaminant degradation efficiency and long-term stability. The extra organic matter removed by ABAC included refractory substances with a low elemental ratio of oxygen to carbon (O/C) and a high elemental ratio of hydrogen to carbon (H/C). The proposed ABAC filter provides a valuable, practical example of how to modify the BAC technology to shape the microbial community, and its activity, by optimizing the ambient atmosphere.
Wang J, Graham N, Sun K, et al., 2023, Ultra-low concentrations of detection for fluoride and trivalent chromium ions by multiple biomimetic nanochannels in a PET membrane, Journal of Cleaner Production, Vol: 389, ISSN: 0959-6526
The development of a detection method for fluoride and chromium (III) ions using a PET membrane with multiple biomimetic nanochannels is descibed. An asymmetric chemical etching technique was used to create conical nanochannels with a PET (polyethylene terephthalate) nuclear track membrane. SEM images showed that the pore diameter of the tip and base sides of the nanochannel were ∼40 nm and ∼180 nm, respectively. The compounds (4-aminophenyl) boronic acid (APBA) and 5-amino-2-nitrobenzoic acid (ANBA), with a specific recognition for F− and Cr3+ respectively, were modified by a conventional method with EDC and NHS. The current-voltage (I–V) curves of the modified PET membranes in response to the target ions at different concentrations were measured with a picoammeter. Excellent linear relationships between the current value of the I–V curve at −2 V and the concentration of Cr3+ and F− were established to obtain standard detection curves for Cr3+ and F−. From these relationships unknown concentrations of Cr3+ and F− can be quantitatively detected, and the results showed that the detection limits of Cr3+ and F− were as low as 4.10 nM and 0.46 nM, respectively. The performance of the novel method was compared to conventional ICP-MS analysis by the determination of Cr3+ in tap water and samples of the Jing Mi diversion canal, and good agreement was found between the two methods. The accuracy and reliability of the method has demonstrated its potential applicability to a wide range of other ionic contaminants.
Zhang K, Duan Y, Graham N, et al., 2023, Efficient electrochemical generation of active chlorine to mediate urea and ammonia oxidation in a hierarchically porous-Ru/RuO2-based flow reactor, Journal of Hazardous Materials, Vol: 444, ISSN: 0304-3894
The electrochemical chlorination of urea to CO2 and N2 end-products, via active-chlorine-mediated oxidation under nearly neutral conditions, is an effective treatment for medium-concentrated urea-containing wastewater. Herein, we design a novel flow reactor integrated with three-dimensional hierarchically porous Ru/RuO2 architectures anchored on a Ti mesh. The hierarchically macroporous electrode can create sufficient exposure of catalytically active sites and facilitate the microscopic mass transport and diffusion inside the active layer, thereby contributing to the increased removal efficiency of urea-N and ammonia-N. The combined results of electrochemical measurements, UV–visible spectrometry and in situ Raman spectrometry, show that the OCl- species produced by chlorine evolution reaction (CER) are the main active constituents for removing urea-N. Theoretical calculations reveal thLTWAat the Ru/RuO2 possesses a moderate Cl binding strength, lower theoretical overpotentials of CER and a higher conductivity, compared with pure RuO2. On this basis, we assemble a circular flow reactor with the hierarchically porous electrodes in a two-electrode system to obtain an enhanced microfluidic process, which during 9 days of uninterrupted operation, at a high electrolysis current of 500 mA, achieve a total nitrogen removal of 92.6% and an energy consumption of 7.94 kWh kg−1 N, demonstrating the promising application of the novel process.
Li Y, Wang Y, Jin J, et al., 2023, Enhanced removal of trace pesticides and alleviation of membrane fouling using hydrophobic-modified inorganic-organic hybrid flocculants in the flocculation-sedimentation-ultrafiltration process for surface water treatment, Water Research, Vol: 229, ISSN: 0043-1354
Pesticide concentrations in surface water occasionally exceed regulated values due to seasonal events (rainy season in high intensity agricultural areas) or intermittent discharges (leakage, spillage, or other emergency events). The need to remove pesticide compounds in these situations poses a challenge for drinking water treatment plants (DWTPs). In this work, the performance of dosing hydrophobic-modified inorganic-organic hybrid flocculants (HOC-M; lower acute toxicity than corresponding metal salt coagulants; acceptable economic costs when M=Al or Fe; prepared in large-scale quantities), for the removal of four different pesticides (each initial concentration: 0.25 μg/L) from Yangtze River water, and in mitigating membrane fouling, by an integrated flocculation-sedimentation-ultrafiltration (FSUF) process, was evaluated over a period of 40 days; the FSUF is well-established in many DWTPs. The mechanisms underlying the treatment were unveiled by employing a combination of instrumental characterizations, chemical computations, material flow analyses, and statistical analyses. Efficient pesticide removal (80.3%∼94.3%) and membrane fouling reduction (26.6%∼37.3% and 28.3%∼57.6% for reversible and irreversible membrane resistance, respectively) in the FSUF process were achieved by dosing HOC-M, whereas conventional inorganic coagulants were substantially inferior for pesticide removal (< 50%) and displayed more severe fouling development. Hydrophobic association between the pesticides and the hydrophobic organic chain of HOC-M played a predominant role in the improvement in pesticide removal; coexisting particulate/colloid inorganic minerals and natural organic matter with HOC-M adsorbed on the surface, acting as floc building materials, provided sites for the indirect combination of pesticides into flocs. The observed fouling alleviation from dosing HOC-M was ascribed to both the pre-removal of fouling-causing materials in the flocculation-sedimen
Zhang K, Guo F, Graham N, et al., 2023, Engineering of 3D graphene hydrogel-supported MnO<sub>2</sub>-FeOOH nanoparticles with synergistic effect of oxidation and adsorption toward highly efficient removal of arsenic, ENVIRONMENTAL POLLUTION, Vol: 317, ISSN: 0269-7491
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- Citations: 3
Tian L, Zhou P, Su Z, et al., 2023, Insights into the properties of surface waters and their associated nanofiltration membrane fouling: the importance of biopolymers and high molecular weight humics, Chemical Engineering Journal, Vol: 451, ISSN: 1385-8947
Nanofiltration (NF) membrane fouling by surface waters is still an unclear and unpredictable topic due to the heterogeneity and variability of natural organic matter (NOM) in waters. The objective of this study was to identify the key water quality parameter/s responsible for NF membrane fouling. Six representative surface waters were systematically investigated in terms of the water quality characteristics and their fouling potential on a polyamide NF membrane. The results showed that these waters exhibited significant discrepancies in DOC, Ca2+, composition, and chemical characteristics of NOM. Removal performance and membrane fouling analysis indicated a preferential rejection of hydrophobic over hydrophilic NOM, and the hydrophobicity of NOM was positively correlated with reversible fouling. The biopolymer content exhibited a strong positive correlation to the total membrane fouling and irreversible fouling, indicating that it could be used as a surrogate of NF fouling behaviors by surface waters. Ca2+ and humic substances contents could not explain the membrane fouling due to their insignificant correlation with membrane fouling. However, the proportion of high molecular weight component in humic substances (%-HMW) exhibited a negative correlation with the total membrane fouling and irreversible fouling, suggesting that the HMW component has a positive effect on NF membrane fouling prevention. A reasonable explanation is that the HMW component is preferentially deposited on the membrane surface, forming a ‘controlling layer’ that prevents low MW organics from entering and blocking the membrane pores.
Wang L, Song S, Xu L, et al., 2022, Beneficial role of pre- and post-ozonation in a low rate biofiltration-ultrafiltration process treating reclaimed water, Water Research, Vol: 226, ISSN: 0043-1354
Previous studies have shown that the combination of biological and ozone oxidation processes can achieve a greater performance in treating natural surface water than each process individually. In this work, we designed and tested an ozonation–gravity-driven up-flow slow rate (0.01 m/h) biofiltration–ozonation (O3–GUSB–O3) process for the pre-treatment of reclaimed water prior to ultrafiltration (UF), with the aim of producing high quality drinking water and a significantly reduced degree of UF fouling. Results showed that O3 coupled with GUSB can effectively remove aromatic compounds (∼ 84.8%), dissolved organic carbon (DOC, ∼ 83.4%), and biopolymers in surface water. In addition, post-ozonation greatly contributed to the reduction of the UF membrane fouling (∼ 6 times greater flux). With regard to the disinfection by-product formation potential (DBPFP) of the final treated water, both trihalomethane formation potential (THMFP) and haloacetic acid formation potential (HAAFP) were greatly reduced (86.4% and 84.8% for THMs and HAAs, respectively). The relationship between DBPFP and various spectral indexes revealed that aromatic compounds and amino acids were more likely to generate DBPs during the disinfection stage. Among these, humic substances were more likely to generate THMs, while low molecular weight carboxylate and carbonyl organic compounds were associated with the generation of HAAs. Moreover, the dosage of O3 during the post-ozonation stage was found to influence directly the generation of DBPs. Overall, this study has conducted a detailed evaluation of a novel multi-ozone biofilter UF process for treating surface water, and the results provide a valuable basis for subsequent studies at larger scale to demonstrate the potential of the treatment process for practical applications.
Su Z, Liu T, Men Y, et al., 2022, Understanding point-of-use tap water quality: From instrument measurement to intelligent analysis using sample filtration, WATER RESEARCH, Vol: 225, ISSN: 0043-1354
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- Citations: 2
Li W, Siddique MS, Liu M, et al., 2022, The migration and microbiological degradation of dissolved organic matter in riparian soils., Water Res, Vol: 224
Riparian zones are important natural means of water purification, by decreasing the aqueous concentration of terrestrial organic matter (OM) through adsorption and microbial degradation of the organic matter within the aquatic ecosystem. Limited studies have been reported so far concerning the migration of dissolved organic matter (DOM) in the horizontal and vertical planes of riparian zones. In this study, the migration of DOM in riparian zones, from forest soil to wetland soil, and with soil depth, were explored, based on a case study reservoir. Results showed that riparian wetlands can absorb the OM from the forest soils and adjacent reservoir, and act as a major OM sink through microbial action. Methylomirabilota and GAL15 bacteria increased with soil depth for the two soil systems, and the wetland soil system also contained microbial sulfates, nitrates and carbonates. These microorganisms successfully utilize the Fe3+, SO4-, and CO3- as electron acceptors in the wetland system, resulting in enhanced OM removal. Although the variation of soil DOM in the vertical direction was the same for both forest and wetland soils, the Chemical structure of the DOM was found to be significantly different. Furthermore, the soil was found to be the main source of DOM in the forest ecosystem, with lignin as the main ingredient. The lignin structure was gradually oxidized and decomposed, with an increase in carboxyl groups, as the lignin diffused down into the soil and the adjacent reservoir. PLS-PM analysis showed that the soil physicochemical properties were the main factors affecting DOM transformation. However, microbial metabolism was still the goes deeper affecting factor. This study will contribute to the analysis that migration and transform of soil organic matter in riparian zone.
Sun Y, Zhang Q, Clark JH, et al., 2022, Tailoring wood waste biochar as a reusable microwave absorbent for pollutant removal: Structure-property-performance relationship and iron-carbon interaction, Bioresource Technology, Vol: 362, ISSN: 0960-8524
This study innovated the concept in designing an efficient and reusable microwave (MW) absorbent through concurrent exploitation of carbon graphitization, oxygen functionalization, and carbothermal iron reduction underpinned by an endothermic co-pyrolysis of wood waste and low-dosage iron. A powerful MW assimilation was accomplished from nanoscale amorphous magnetic particles as well as graphitized microporous carbon-iron skeleton in the biochar composites. Relative to a weak magnetic loss derived from the iron phase, the graphitic carbon architecture with abundant surface functionalities (i.e., CO and CO) exhibited a strong dielectric loss, which was thus prioritized as major active sites during MW reuse. The MW-absorbing biochar demonstrated a fast, robust, and durable removal of a refractory herbicide (2,4-dichlorophenoxy acetic acid) under mild MW irradiation with zero chemical input, low electricity consumption, and negligible Fe dissolution. Overall, this study will foster carbon-neutral industrial wastewater treatment and wood waste valorization.
Ritson JP, Kennedy-Blundell O, Croft J, et al., 2022, High frequency UV-Vis sensors estimate error in riverine dissolved organic carbon load estimates from grab sampling, Environmental Monitoring and Assessment, Vol: 194, Pages: 1-12, ISSN: 0167-6369
High frequency ultraviolet – visible (UV-VIS) sensors offer a way of improving dissolved organic carbon (DOC) load estimates in rivers as they can be calibrated to DOC concentration. This is an improvement on periodic grab sampling, or the use of pumped sampling systems which store samples in-field before collection. We hypothesised that the move to high frequency measurements would increase the load estimate based on grab sampling due to systemic under-sampling of high flows. To test our hypotheses, we calibrated two sensors in contrasting catchments (Exe and Bow Brook, UK) against weekly grab sampled DOC measurements and then created an hourly time series of DOC for the two sites. Taking this measurement as a ‘true’ value of DOC load, we simulated 1,000 grab sampling campaigns at weekly, fortnightly and monthly frequencyto understand the likely distribution of load and error estimates. We also performed an analysis of daily grab samples collected using a pumped storage sampling system with weekly collection. Our results show that: a) grab sampling systemically underestimates DOC loads and gives positively skewed distributions of results, b) this under-estimation and positive skew decreases with increasing sampling frequency, c) commonly used estimates of error in the load value are also systemically lowered by the oversampling of low, stable flows due to their dependence on the variance in the flow-weighted mean concentration, and d) that pumped storage systems may lead to under-estimation of DOC and over estimation of specific ultra50 violet absorbance (SUVA), a proxy for aromaticity, due to biodegradation during storage.
Hassard F, Elemo T, Chipps M, et al., 2022, Underwater Remote Skimming of Slow Sand Filters for Sustainable Water Production, ACS ES and T Water, Vol: 2, Pages: 1471-1474
Slow sand filters (SSF) are a simple water treatment technology providing an important alternative to conventional drinking water treatment. SSF are extensive in terms of carbon cost and chemical use but require a large land area and are complex to operate, as periodic cleaning is required to prevent filter clogging. Therefore, redundant SSF beds are required to enable water production to occur during long cleaning downtimes. Underwater skimming (UWS) is a cleaning innovation where the foulant layer (containing sand and particles) is removed using a skimmer consisting of a shrouded blade mounted on a vehicle platform. Sand, particles, and biofilm are skimmed prior to ex situ washing of the recovered sand. In this Viewpoint, we posit that the introduction of an in situ underwater skimmer operated remotely can substantially help to offset the aforementioned challenge of downtime, with its associated loss of production, enabling the technology to operate more efficiently and remain a pertinent and advantageous process option within modern water treatment facilities or possibly resource constrained settings. Otherwise, this resilient biotechnological process could be replaced by chemical and energy-intensive processes which increase the entropy of water treatment more than SSF. The anticipated benefits and challenges of UWS of SSF are discussed.
Zhang L, Graham N, Li G, et al., 2022, Divergent accumulation of membrane biofouling by slight elevation of nitrogen and phosphorus in drinking water treatment: Performances and mechanisms, WATER RESEARCH, Vol: 222, ISSN: 0043-1354
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- Citations: 4
Liu M, Graham N, Wang W, et al., 2022, Spatial assessment of tap-water safety in China, Nature Sustainability, Vol: 5, Pages: 689-698
The quality of drinking-water supplies is of fundamental importance to public health and sustainable development. Here, we provide a spatial assessment of the tap-water quality across mainland China. We examine natural and anthropogenic origins of low quality as well as its association with public health risks. By quantifying key indicators, including total organic carbon, ionic conductivity and disinfection by-products (DBPs), we find that precipitation is a crucial factor driving the change of organic matter content and ionic conductivity of tap-water, especially for arid and semi-arid regions. Although the concentration of DBPs is closely related to the organic matter content, the occurrence of highly toxic DBPs is more subject to anthropogenic factors such as economic development and pollution emission. We show that nanofiltration is an effective point-of-use treatment to reduce the adverse effects of DBPs. The present results highlight the potential health hazards associated with low-quality drinking water, suggesting that countries and regions experiencing rapid socioeconomical development might face high levels of DBP toxicity and should consider adoption of sustainability solutions.
Zhang L, Xu L, Graham N, et al., 2022, Unraveling Membrane Fouling Induced by Chlorinated Water Versus Surface Water: Biofouling Properties and Microbiological Investigation, ENGINEERING, Vol: 15, Pages: 154-164, ISSN: 2095-8099
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- Citations: 5
Liu X, Graham N, Yu W, et al., 2022, Preparation and evaluation of a high performance Ti<sub>3</sub>C<sub>2</sub>T<sub>x</sub>-MXene membrane for drinking water treatment, JOURNAL OF MEMBRANE SCIENCE, Vol: 654, ISSN: 0376-7388
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- Citations: 8
Li W, Siddique MS, Graham N, et al., 2022, Influence of Temperature on Biofilm Formation Mechanisms Using a Gravity-Driven Membrane (GDM) System: Insights from Microbial Community Structures and Metabolomics., Environ Sci Technol, Vol: 56, Pages: 8908-8919
A biofilm has a significant effect on water treatment processes. Currently, there is a lack of knowledge about the effect of temperature on the biofilm structure in water treatment processes. In this study, a gravity-driven membrane ultrafiltration system was operated with river feedwater at two temperatures ("low", 4 °C; "high", 25 °C) to explore the biofilm structure and transformation mechanism. The results showed that the difference in dissolved oxygen concentration might be one of the main factors regulating the structural components of the biofilm. A denser biofilm formation and reduced flux were observed at the lower temperature. The linoleic acid metabolism was significantly inhibited at low temperature, resulting in enhanced pyrimidine metabolism by Na+ accumulation. In addition, the biofilm at low temperature had a higher proportion of the metabolites of lipids and lipid-like molecules (11.25%), organic acids and derivatives (10.83%), nucleosides, nucleotides, and analogues (7.083%), and organoheterocyclic compounds (6.66%). These small molecules secrete more polysaccharides having C═O and O═C-O functional groups, which intensified the resistance of the biofilm. Furthermore, the upregulation pathway of pyrimidine metabolism also increased the risk of urea accumulation at low temperature. Limnohabitans, Deinococcus, Diaphorobacter, Flavobacterium, and Pseudomonas were identified as the principal microorganisms involved in this metabolic transformation.
Song Q, Graham N, Tang Y, et al., 2022, The role of medium molecular weight organics on reducing disinfection by-products and fouling prevention in nanofiltration., Water Res, Vol: 215
Nanofiltration (NF) is utilized in water treatment for controlling disinfection by-products formation potential (DBPFP) and disinfection by-products (DBPs). Attention regarding NF-based technology has been paid on membrane fouling of NF and the rejection efficiency of contaminants by NF membranes. Natural organic matter (NOM) presenting in surface waters is one main removal target in drinking water treatment by NF-based technology, and is thereby a contributor to the membrane fouling of NF. In application, pretreatments of other membrane filtration (e.g., microfiltration (MF) and ultrafiltration (UF)) has been taken prior to NF, resulting in the separation of NOM of specific molecular weight. Meanwhile, it is well known that NOM is composed of organic compounds of different molecular weights. However, the effect of NOM of specific molecular weight has been seldom investigated from the aspects of membrane fouling and the resulting DBPFP after membrane filtration. By using combinations of MF and UF (molecular weight cut-off of 100K or 20K) as pretreatment prior to NF, the NOM of various molecular weight on DBPFP and DBPs in the NF-treated water were investigated. The experiments were conducted with two real-world surface water samples and one tap water sample. It was found that medium molecular weight NOM, defined as NOM that passed UF100K but did not pass UF20K in this study, reduced fouling of the NF membrane. This is supported by the excitation and emission matrix (EEM) fluorescence spectra, size exclusion chromatography (SEC) and flux analysis. In addition, the medium molecular weight NOM also reduced the DBPFP in the NF treated water and eventually the DBPs by participating in forming a protective layer on the NF surface, blocking the transfer of small molecular weight NOM into the NF filtrate, thereby reducing the DBPFP of the NF filtrate since small molecular weight NOM was the major contributor to DBPFP in this study.
Wan Z, Xu Z, Sun Y, et al., 2022, Stoichiometric carbocatalysis via epoxide-like C-S-O configuration on sulfur-doped biochar for environmental remediation, Journal of Hazardous Materials, Vol: 428, ISSN: 0304-3894
Heteroatom doping is a promising technique to enhance biochar for effective environmental remediation. However, development of electroactive heteroatom-doped biochars, e.g., sulfur-doped biochar, has been hindered due to complex nature of non-stoichiometric biomass-derived carbon and changeable electrochemical state of dopants. Herein, we produced a series of wood waste-derived biochars with customized levels of minerals and redox-active moieties, aiming to unravel the crucial factors for sulfur doping. Calcium (Ca) in biochar was found to preferentially coordinate with sulfur to form inactive inorganic sulfur minerals (i.e., CaSO4 and CaS) with inferior catalytic reactivity. After diminishing the inherent Ca minerals beforehand, we could introduce surface phenoxyl-type radicals (C-O•) and vacancy defects on the biochar to develop an electrophilic C-S-O bonding configuration, which guaranteed a high affinity towards peroxymonosulfate (PMS, 2.08 mM g-1, 30 min) and efficient removal of bisphenol A (BPA, 91.1%, 30 min). Scavenging experiments and in-situ Raman analyses indicated that the epoxide-like C-S-O structure induced nucleophilic addition of PMS to generate surface-bound singlet oxygen (1O2, major) and hydroxyl radicals (•OH, minor) through a preservative and stoichiometric interfacial reaction. Overall, the proposed approach overcomes the major hurdles in science-informed fabrication of sulfur-doped biochar and advances its development for environmental remediation.
Wang Z, Li Y, Hu M, et al., 2022, Influence of DOM characteristics on the flocculation removal of trace pharmaceuticals in surface water by the successive dosing of alum and moderately hydrophobic chitosan, Water Resources, Vol: 213, ISSN: 0097-8078
Hydrophobically-modified chitosan (HC) has emerged as a promising flocculant for trace pharmaceutical removal from surface water. However, the variation in the characteristics of dissolved organic matter (DOM) in different water sources influences the efficacy of HC in removing pharmaceutical compounds. In this work, the flocculation performance of sequentially dosing alum and HC (alum+HC) for the treatment of five water types (three synthetic waters, and samples of two real waters collected from the Yangtze River and the Thames River), having different DOM and five representative pharmaceuticals (initial concentration: 100 ng/L), was assessed by bench-scale jar tests. The DOM characteristics were correlated quantitatively with the removal efficiencies (REs) of the pharmaceuticals. Density functional theory computations were performed to illuminate the interfacial interactions in the flocculation. Alum+HC exhibited a remarkably higher RE of all five pharmaceuticals (maximum RE: 73%-95%) from all waters compared to a conventional coagulant or flocculant (alum or polyacrylamide, respectively). In contrast to using HC alone, alum+HC also achieved a higher RE of pharmaceuticals with nearly half the HC dosage, thereby enhancing the cost-effectiveness of the alum+HC dosing system. Among the different key DOM characteristics, the surface charge and molecular weight of DOM had no evident correlation with RE(pharmaceutical), but the hydrophobic/hydrophilic nature and functional group composition of organic carbon of DOM were strongly correlated: Strongly hydrophobic fractions, with C-C & C=C functional groups (binding pharmaceuticals via hydrophobic association), were beneficial, while hydrophilic fractions with C-OH groups were less effective, for pharmaceutical removal. This work showed the enhanced performance of the alum+HC dosing combination in the removal of different pharmaceutical compounds from different waters, and filled the knowledge gap regarding the pe
Mora AS, McBeath ST, Cid CA, et al., 2022, Diamond electrode facilitated electrosynthesis of water and wastewater treatment oxidants, Current Opinion in Electrochemistry, Vol: 32, Pages: 1-7, ISSN: 2451-9103
While diamond electrodes have been commonly used to generate •OH to treat a variety of persistent water and wastewater micropollutants, mass transfer limitations and the non-selective, short-lived nature of the •OH restrict the degradation to the solution at, or near, the electrode surface. However, diamond electrodes can generate oxidizing species that facilitate micropollutant degradation in the bulk water solution. These include persulfate, sulfate radicals, peroxodiphosphate, ferrate, permanganate, reactive chlorine species, hydrogen peroxide, and ozone, which have been reported during electrochemical treatment of water with diamond electrodes. Although still restricted to specialized applications, recent studies, summarized in this review, have proven the electrogeneration of these additional oxidant species to be effective. They have shown the adaptability and potential of diamond electrode-based water treatment to mitigate the presence of micropollutants in water.
Li X, Graham NJD, Deng W, et al., 2022, Structural variation of precipitates formed by Fe(II) oxidation and impact on the retention of phosphate., Environmental Science and Technology (Washington), Vol: 56, ISSN: 0013-936X
The oxidation-precipitation process of Fe(II) is ubiquitous in the environment and critically affects the fate of contaminants and nutrients in natural systems where Fe(II) is present. Here, we explored the effect of H2O2 concentration on the structure of precipitates formed by Fe(II) oxidation and compared the precipitates to those formed by Fe(III) hydrolysis. Additionally, the phosphate retention under different H2O2 concentrations was evaluated. XRD, TEM, PDA, XPS, and UV-visible absorbance spectroscopy were used to characterize the structure of the formed precipitates; UV-visible absorbance spectroscopy was also used to determine the residual phosphate and Fe(II) in solution. It was found that the predominant precipitates in Fe(II) solution changed from planar-shaped crystalline lepidocrocite (γ-FeOOH) to poor short-range order (poorly crystalline) spherical-shaped hydrous ferric oxide (HFO) with increasing H2O2 concentrations. Although the HFO precipitates formed from Fe(II) resembled those formed from Fe(III) hydrolysis, the former was larger and had clearer lattice fringes. During the formation of γ-FeOOH, both Fe(II)-Fe(III) complexes and ligand-to-metal charge transfer processes were observed, and it was found that Fe(II) was present in the planar-shaped precipitates. Fe(II) might be present in the interior of precipitates as Fe(OH)2, which could serve as a nucleus for the epitaxial growth of γ-FeOOH. In addition, the extent of phosphate retention increased with the H2O2 concentration, indicating the increased reactivity of formed precipitates with H2O2 concentration. More phosphate was retained via coprecipitation with Fe than adsorption on the preformed Fe precipitates due to the incorporation of phosphate within the structure of the formed Fe hydroxyphosphate via coprecipitation.
Tian L, Graham N, Liu T, et al., 2022, Dual-site supported graphene oxide membrane with enhanced permeability and selectivity, JOURNAL OF MEMBRANE SCIENCE, Vol: 646, ISSN: 0376-7388
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- Citations: 6
Xiong X, Siddique MS, Graham NJD, et al., 2022, Towards microplastics contribution for membrane biofouling and disinfection by-products precursors: The effect on microbes., Journal of Hazardous Materials, Vol: 426, Pages: 1-12, ISSN: 0304-3894
Public awareness of plastic pollution and its impact on the ecosystem has increased rapidly. The microplastics in raw waters and their removal during drinking water treatment is receiving growing attention, but the impact on the efficiency of ultrafiltration has not been examined previously, especially in regard to the formation potential of disinfection by-products (DBPs-FP) in effluent water. In this study, two bench-scale continuous-flow ultrafiltration systems, with and without microplastics, were operated to examine the effect of microplastics on ultrafiltration. Results showed that the microplastics not only increased microbial growth, but also affected the microbial community (e.g. families Xanthobacteraceae, Sphingomonadaceae, Leptolyngbyaceae), which can promote the production of extracellular polymeric substances and nitrogen fixation, causing rapid membrane fouling. The formation potential of THM (TCM and BDCM) and N-DBP (TCNM) species in UF permeate increased with the presence of microplastics, due to changes in water quality. Statistical analysis indicated that tyrosine-like components (C3), ammonium (NH4+-N) and tryptophan-like component (C1) can be used as indicators of the DBPs-FP. This study provides new insights into the relationship between microplastics, membrane biofouling and DBPs-FP, and the potential adverse impact of microplastics on drinking water treatment.
Xing B, Zhao B, Liu M, et al., 2022, The influence of crystal structure and formation path of precursor on phosphate adsorption during oxidation-hydrolysis phase transition of siderite, Chemical Engineering Journal, Vol: 431, ISSN: 1385-8947
Fe(III)-(hydr)oxides can be formed by the oxidation-hydrolysis of Fe(II) minerals, its initial state is usually amorphous, which can form dense flocs quickly with a high specific surface area, resulting in widely used in the field of water treatment. However, the rate and path of oxidation-hydrolysis lead to the difference in the crystal structure of the precursor, which are directly determined by the crystallinity and adsorption activity of the final oxidized hydrolysate. Therefore, this study investigated the phase transition of siderite under different oxidation-hydrolysis paths. The results suggested KMnO4 could first oxidize the surface layer Fe(II) of siderite; and then Mn(II), hidden in the crystal lattice of siderite, was continuously exposed to the surface of siderite; after that, Mn(II) was oxidized by KMnO4 to form MnO2, which acts as an ion channel to allow internal Fe(II) of siderite further hydrolysis to form crystalline Fe(OH)2 and then further oxidation to form crystalline two-line ferrihydrite (δ-Keggin). Although Fe(OH)2 as transient precursor will disappear with the continuation of oxidation, its presence will greatly reduce the nucleation barrier of two-line ferrihydrite. These mineral phase transitions resulted in the low concentration of KMnO4 (0.03 mmol/L) could substantially enhance the ability of siderite to remove phosphate, with the maximum adsorption capacity (13.04 mg/g, Langmuir). However, H2O2 could only oxidize Fe(II) on the surface of siderite to form amorphous Fe(OH)3, while Mn(II) in the siderite lattice could not be oxidized. The surface coverage of amorphous Fe(OH)3 and exposed Mn(II) formed a dense passive film, resulting in the termination of the oxidation and showed a low adsorption activity (3.28 mg/g).
Liu M, Siddique MS, Graham NJD, et al., 2022, Removal of small-molecular-weight organic matter by coagulation, adsorption, and oxidation: molecular transformation and disinfection byproduct formation potential, ACS ES&T engineering, Vol: 2, ISSN: 2690-0645
The removal of small-molecular-weight organic matter (SMW-OM) is important for enhancing final water quality and increasing the performance of unit processes. However, the fate of SMW-OM during drinking water treatments has received a few concerns. In this study, the performances of three common processes (coagulation, adsorption, and ozonation) on treating SMW-OM were comprehensively studied at a molecular scale. For molecules only containing C, H, and O elements, coagulation favored the removal of unsaturated structures (low H/C) with oxygen-containing groups (high O/C). While for N-containing molecules, those with higher H/C were better removed. Adsorption preferentially removed reduced molecules (low O/C) and can remove molecules with a very low mass (20% removal rate for molecules with a mass of 300–350 Da). Therefore, it showed the best performance on decreasing the disinfection byproduct formation potential (DBPFP). Ozonation had a limited mineralization effect on organic contents. In addition, it transformed haloacetic acid (HAA) precursors to trihalomethane (THM) precursors by degrading aromatic structures to aliphatic compounds (e.g., aldehydes and ketones), and thus resulted in an increase in the THM formation potential. This study focused on the fate of SMW-OM in drinking water treatment and their DBPFP, illustrated its transformation process, and can provide guidance for enhanced drinking water treatment in practical applications.
Zhang L, Graham N, Kimura K, et al., 2022, Targeting membrane fouling with low dose oxidant in drinking water treatment: Beneficial effect and biological mechanism, Water Research, Vol: 209, Pages: 1-12, ISSN: 0043-1354
Membrane fouling is the principal factor that currently limits the performance of gravity-driven membrane(GDM) filtration systems in drinking water treatment. In this study, the benefits of applying a low dose(approximately 0.1 mg⋅L− 1) of environmentally benign oxidants, both H2O2 and KMnO4, as a pretreatment toGDM filtration system has been evaluated in terms of reduced membrane fouling and treated water quality.While both oxidants improved permeate flux, the effect of KMnO4 was greater than H2O2. Both oxidants reducedthe size of influent organic substances and those of large molecular weight (>20 kDa), such as biopolymers,disappeared. The thickness of the fouling layers was substantially reduced after oxidation, and the KMnO4 systemhad a markedly different physical structure of fouling layer, with an apparent sub-layer of δ-MnO2 nanosheetsbelow a fouling sub-layer. The formation of the δ-MnO2 nanosheets sub-layer appeared to protect the underlyingmembrane pores from contamination by influent organics. Oxidation pretreatment reduced the presence ofproteins and polysaccharides in the fouling layers and significantly altered the bacterial community structures (p< 0.01) and decreased biodiversity. The microbial species that secreted amounts of extracellular polymericsubstances (EPS), such as Xanthobacter, were not eliminated in the H2O2 fouling layer, while for the KMnO4system, the manganese oxidizing bacteria (MOB; e.g., Pseudoxanthomonas) and metal-resistant genus Acidovorax, dominated the community.
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