Publications
412 results found
Siddique MS, Xiong X, Yang H, et al., 2022, Dynamic variations in DOM and DBPs formation potential during surface water treatment by ozonation-nanofiltration: Using spectroscopic indices approach, Chemical Engineering Journal, Vol: 427, ISSN: 1385-8947
The combination of ozone and nanofiltration (NF) in drinking water treatment represents a potentially effective method of separating dissolved organic matter (DOM), and thereby reducing the potential formation of disinfection by-products (DBPs). This study has evaluated UV-absorbance and fluorescence-based optical descriptors, such as absorbance slope index (ASI), humification index (HIX), and the sum of fulvic-like and humic-like components (C1 + C2), etc., to track the variation of DOM constituents and DBP formation potential during the treatment of surface water samples by ozonation and nanofiltration (NF90 and NF270). Pre-ozonation markedly reduced the DOM molecular weight (MW) in the range of 5000–9000 Da by transforming the DOM into carboxylate-rich hydrophilic fractions, thereby mitigating the fouling of NF membranes. Among all the PARAFAC components, the humic-like component (C2) showed a predominant behavior against pre-ozonation and nanofiltration experiments. However, amino acid or microbial protein-like component (C3) was particularly associated with irreversible fouling of both membranes, compared to reversible fouling. C1 + C2 was found to be strongly correlated with both ASI and HIX, suggesting that C1 + C2 can be a useful surrogate for the humic-like content of the DOM. Principal DBPs detected after the chlorination were chloroform, bromodichloromethane and dichloroacetic acid, and DBP formation potential reduced with increased ozonation. A strong correlation between these DBPs and spectroscopic indices indicated that the humic content was an important factor in the formation of DBPs. In contrast, increasing ozonation not only shifted the DBP formation potential towards brominated precursors, but also resulted in increased brominated species of haloacetic acids. However, both NF membranes achieved approximately 90% removal of DBP precursors, for all of the detected DBPs, which was attributed to size exclusion and electrostatic interaction effec
Zhang L, Graham N, Derlon N, et al., 2021, Biofouling by ultra-low pressure filtration of surface water: The paramount role of initial available biopolymers, JOURNAL OF MEMBRANE SCIENCE, Vol: 640, ISSN: 0376-7388
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- Citations: 6
McBeath ST, Mora AS, Zeidabadi FA, et al., 2021, Progress and prospect of anodic oxidation for the remediation of perfluoroalkyl and polyfluoroalkyl substances in water and wastewater using diamond electrodes, Current Opinion in Electrochemistry, Vol: 30, Pages: 1-10, ISSN: 2451-9103
Although diamond electrodes are widely used in the field of electroanalysis and sensing, their application in the field of environmental engineering has yet to be fully realized. Many research studies have considered their potential application in water and wastewater treatment, where the in-situ electrochemical process can avoid the need for chemical additives by facilitating the oxidation of pollutants on the electrode surface or mediated by electrochemically synthesized oxidants in solution. Diamond-based electro-oxidation can effectively treat a number of organic micropollutants and is now being evaluated for the abatement of perfluoroalkyl and polyfluoroalkyl substances, which pose health concerns and are ubiquitous recalcitrant environmental contaminants. To move implementation of diamond-based electro-oxidation forward, the integration of modifications and codopants to yield more advanced electrode materials needs to be further developed and understood. The progress and current strategies associated with diamond electrode modifications for perfluoroalkyl and polyfluoroalkyl substances abatement as well as future considerations are discussed.
Liu H, Graham N, Liu T, et al., 2021, A new process combination with high water flux and superior treatment performance for stevia sugar liquor, CHEMICAL ENGINEERING JOURNAL, Vol: 421, ISSN: 1385-8947
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- Citations: 1
Hu M, Zhao L, Yu N, et al., 2021, Application of ultra-low concentrations of moderately-hydrophobic chitosan for ultrafiltration membrane fouling mitigation, Journal of Membrane Science, Vol: 635, ISSN: 0376-7388
Membrane fouling is a major obstacle for ultrafiltration (UF) in water treatment. Here, a strategy for fouling mitigation, by applying an ultra-low concentration of moderately-hydrophobic chitosan (MHC) and using a mildly elevated backwash temperature was proposed. The effects of MHC type, concentration, and backwash temperature were investigated in continuous-flow tests using PVDF hollow fiber membranes and model raw water. Compared to the process without MHC, or with the addition of chitosan or conventional coagulant polyaluminum chloride, the MHC-based UF system under optimal conditions (MHC: 0.01 mg/L; backwash water temperature: 40 °C) demonstrated its superiority with reduction of ~55% reversible fouling (RR) and ~80% irreversible fouling (IRR), as well as improved effluent quality. A mechanistic study by experimental analyses and theoretical computations revealed that the improved performance of the MHC-based UF process was attributed to the following: (1) MHC inhibited contaminant accumulation on the membrane through a hydrophilization surface-modification effect on the PVDF; (2) increased backwash temperature promoted fouling release (by destabilizing the cake layer structure) and enhanced the surface-modification effect. The additional cost of MHC dosing and backwash water heating was estimated at ~0.126 Chinese Yuan per ton of produced water, and the environmental risk of applying MHC was lower than that of conventional water treatment chemicals. In summary, the MHC-based process has the potential to be a feasible and cost-effective approach for UF fouling control.
Zhang K, Liu C, Graham N, et al., 2021, Modulation of dual centers on cobalt-molybdenum oxides featuring synergistic effect of intermediate activation and radical mediator for electrocatalytic urea splitting, NANO ENERGY, Vol: 87, ISSN: 2211-2855
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- Citations: 40
Larasati A, Fowler GD, Graham NJD, 2021, Extending granular activated carbon (GAC) bed life: A column study of in-situ chemical regeneration of pesticide loaded activated carbon for water treatment., Chemosphere, Vol: 286, Pages: 1-10, ISSN: 0045-6535
In-situ chemical regeneration of granular activated carbon (GAC) may represent an advantageous alternative to conventional off-site thermal regeneration in water treatment applications. The performance of chemical regeneration of carbon exhausted by metaldehyde and isoproturon was investigated using rapid small-scale column tests, performed using a sequence of pesticide adsorption and chemical regeneration cycles with a novel alkaline-organic regenerant solution. A fresh regenerant solution was able to achieve 82% and 45% regeneration of carbon exhausted by metaldehyde and isoproturon, respectively. After the first regeneration, the performance declined slightly to 79%, and to 36% after the fourth regeneration. A comparison using a thermally regenerated (operational) carbon suggested that chemical regeneration was more beneficial for carbon exhausted by metaldehyde. The regenerant solution has a potential to be re-used multiple times, thereby minimizing the amount of waste chemicals generated. A series of carbon characterization tests showed that chemical regeneration did not alter the surface area, pore size distribution and surface chemistry of the carbon. As part of the evaluation, the adsorption thermodynamics of virgin and chemically regenerated carbons were determined using isothermal titration calorimetry to evaluate the adsorption behaviour of the pesticides on the carbon samples. The relatively high regeneration efficiency achieved by chemical regeneration, and minimal deleterious effect to the physico-chemical properties of the carbon, demonstrated the beneficial potential of this process as an alternative to conventional thermal regeneration of GAC.
McBeath ST, Graham NJD, 2021, Degradation of perfluorooctane sulfonate via in situ electro-generated ferrate and permanganate oxidants in NOM-rich source waters, Environmental Science: Water Research & Technology, Vol: 7, Pages: 1778-13, ISSN: 2053-1400
A novel process involving the in situ electrochemical generation of ferrate and permanganate oxidants, in circumneutral conditions, from low concentration aqueous iron (Fe2+) and manganese (Mn2+), is investigated for the treatment of the ubiquitous and highly recalcitrant micro-pollutant, perfluorooctane sulfonate (PFOS). The present study investigated the efficacy of both electro-oxidation (EO), and the simultaneous EO and ferrate/permanganate generation and oxidation, of PFOS as a potential drinking water treatment technology. While permanganate was shown to have little effect on PFOS removal, significantly increased degradation was observed when EO was coupled with ferrate generation and oxidation, significantly exceeding that of solely EO. From an initial concentration of 0.80 μM, final PFOS concentrations of 0.53 (±0.004), 0.43 (±0.01) and 0.27 (±0.01) μM were yielded during 10, 40 and 80 mA cm−2 electrolysis and an initial Fe2+ = 179 μM. In general, PFOS degradation rates increased with both increasing current density and initial Fe2+ concentration. Degradation was observed to follow mixed zero- and pseudo-first-order reaction kinetics for both the EO and simultaneous EO and ferrate oxidation. Finally, PFOS oxidation was not inhibited by the presence of low and high molecular weight organic scavenger species, and high concentrations of natural organic matter (NOM) improved PFOS removal due to hydrophobic interaction. Reduced ferrate species were also observed to increase NOM removal after electrolysis, by iron coagulant formation and subsequent flocculation.
Larasati A, Fowler GD, Graham NJD, 2021, Insights into chemical regeneration of activated carbon for water treatment, Journal of Environmental Chemical Engineering, Vol: 9, ISSN: 2213-3437
Granular activated carbon (GAC) adsorption has found wide application as a treatment process for the removal of natural organic matter, small organic compounds (e.g. pesticides), inorganic compounds (e.g. heavy metals), taste and odour compounds in water over many years. During GAC operation, contaminants are adsorbed and the carbon becomes progressively saturated over time, requiring periodic regeneration of the media to restore its capacity. Chemical regeneration has been identified as an effective alternative to off-site thermal regeneration, which is the most commonly practiced carbon regeneration technique for carbon exhausted by organic contaminants. Off-site thermal regeneration poses significant disadvantages as it is a time-consuming process and represents a significant operational cost (e.g. reduced productivity) and environmental (energy/CO2) burden to water utilities. Chemical regeneration can be performed on-site, either in situ or off-line, by exposing the spent (exhausted) GAC to a selected chemical, or a combination of chemicals, to remove the adsorbed contaminants. Prior research on chemical regeneration has been limited in extent, but has considered both organic and inorganic solutions. Despite a significant number of studies, a suitable regenerant solution for desorbing a wide range of aqueous contaminants in drinking water treatment has not been identified to-date. In this paper, we provide a critical review of the performance of alternative regenerant solutions for the chemical regeneration of GAC loaded with different organic contaminants.
Liu T, Graham N, Yu W, 2021, Evaluation of a novel composite chitosan-graphene oxide membrane for NOM removal during water treatment, JOURNAL OF ENVIRONMENTAL CHEMICAL ENGINEERING, Vol: 9, ISSN: 2213-2929
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- Citations: 14
Li W, Liu M, Siddique MS, et al., 2021, Contribution of bacterial extracellular polymeric substances (EPS) in surface water purification, Environmental Pollution, Vol: 280, ISSN: 0269-7491
Naturally present aquatic microorganisms play an important role in water purification systems, such as the self-purification of surface waters. In this study, two water sources representing polluted surface water (Olympic Green; OG) and unpolluted surface water (Jingmi river; JM), were used to explore the self-purification of surface water by bacteria under different environmental conditions. The dominant bacterial community of OG and JM waters (both are Firmicutes and Proteobacteria) were isolated, cultured, and then used to carry out flocculation tests. Results showed that the flocculation ability of the dominant bacteria and extracellular polymeric substances (EPS) obtained from OG isolation was significantly greater than that from JM. Further examination illustrated that the main components of EPS were polysaccharides, which played an important role in improving the flocculation ability of bacteria. EPS from dominant cultural bacteria strains (OG1 and JM3) isolated from the two different sources lacked hydrophilic groups (e.g. COOH) and had a networked structure which are the main reasons to enhance the flocculation ability. The bacterial diversity and redundancy analysis (RDA) results also showed that microbial community composition is determined by water quality (SS, TOC, and NH4+), and different Bacteroidetes, Actinobacteria and Proteobacteria community structures can improve the water body's ability to remove environmental pollutants (such as SS, humic acid and fulvic acid). These findings provide new information showing how bacterial communities change with environmental factors while maintaining the purity of surface water.
Su Z, Liu T, Li X, et al., 2021, Beneficial impacts of natural biopolymers during surface water purification by membrane nanofiltration, Water Research, Vol: 201, Pages: 1-10, ISSN: 0043-1354
Membrane filtration in various forms has become an increasingly used treatment method worldwide for the supply of safe drinking water. The fouling of membranes is commonly considered to be the major operational limitation to its wider application since it leads to frequent backwashing and a shortening of membrane life, and increased production costs. The components of natural organic matter (NOM) in surface waters have been reported previously to be important foulants of nanofiltration (NF) membranes, however, the potential beneficial effect of particular components of these ‘foulants’ has not been investigated or demonstrated to date. In this study, we have considered the roles of different organic materials including autochthonous NOM (e.g., biopolymers) and allochthonous NOM (e.g., humic substances) on the fouling of NF membranes by bench-scale tests with samples of two representative source waters (UK) taken in two different seasons (autumn and winter). Microfiltration (MF) and ultrafiltration (UF) were employed to generate two permeates, between which the presence of biopolymers (30 kDa – 90 kDa) is the major difference. We developed sequential filtration (MF/UF-NF) to investigate biopolymers’ behaviours in NF process. The results showed that the accumulation of biopolymers on NF membranes can mitigate fouling by providing a protective layer in which medium-low molecular weight (MW) materials (e.g. humic substances) are separated by adsorption and/or size exclusion. The protective layers assisted by biopolymers were seen to be thicker under scanning electron microscope (SEM) observation and characterized by higher roughness (i.e. three-dimensional, spacial structure) and greater adsorptive capacity. Moreover, improvement on NF membrane fouling mitigation could be more significant in autumn, comparing to that in winter. The findings in this study were found to be repeatable in similar tests with samples of comparable raw waters in China
McBeath ST, Graham NJD, 2021, Simultaneous electrochemical oxidation and ferrate generation for the treatment of atrazine: A novel process for water treatment applications, Journal of Hazardous Materials, Vol: 411, Pages: 1-9, ISSN: 0304-3894
A novel process involving the simultaneous electrochemical-oxidation (EO) and electrosynthesis of ferrate has been investigated for the treatment of the commonly detected and recalcitrant pesticide, atrazine. The present study considered the electrosynthesis of ferrate, in neutral pH, using low concentration iron (Fe2+) representative of raw water levels and its subsequent effect on atrazine degradation. Ferrate synthesis was unaffected by current density (10–80 mA cm−2), indicating mass transport limitations. Synthesis was affected by the initial iron concentration, whereby 0.051, 0.108 and 0.332 mg L−1 was generated with an Fe2+ concentration of 0.5, 1.0 and 3.0 mg L−1, respectively. When operating under simultaneous EO and ferrate oxidation, atrazine degradation exceeded that of a solely EO process. From an initial concentration of 2.00 mg L−1, atrazine was degraded to 1.34, 1.05 and 0.51 mg L−1 during 10, 40 and 80 mA cm−2, characterised by pseudo-first-order kinetics. Degradation with electrochemically-generated ferrate could be described by second-order kinetics, and yielded a degradation rate constant of 23.5 M−1 s−1. The effect of natural organic matter (NOM) on atrazine degradation was also investigated. Ferrate was observed to be mostly scavenged by resorcinol, a representative NOM compound, having a second-order reaction rate constant of 9.71 × 102 M−1 s−1.
Zhang X, Graham N, Xu L, et al., 2021, The Influence of Small Organic Molecules on Coagulation from the Perspective of Hydrolysis Competition and Crystallization., Environ Sci Technol, Vol: 55, Pages: 7456-7465
Most coagulation studies focus on pollutant removal or floc separation efficiency. However, to understand the mechanism of coagulation, it is necessary to explore the behavior of coagulation in terms of the interactions among the functional groups on the surface of the metal hydrolysis precipitates during the hydrolysis process. In this study, for the first time, aluminum sulfate (alum) was used to investigate such interactions over the whole process sequence of hydrolysis, coagulation, and crystallization with, and without (as a control), the presence of specific low molecular weight (LMW) (molecular weight < 1000 Da) organic compounds with different chemical bonds. It was observed that primary nanoparticles (NPs) of around 10 nm size were produced during the hydrolysis of alum. The presence of organic compounds was found to influence the coagulation performance by affecting the metal hydrolysis and the properties of the nanoparticles. At pH 7, ethylenediaminetetraacetic acid disodium salt (EDTA) delayed the time when the particles start to aggregate but increased the maximum size of the flocs, while citric acid caused the crystallization of amorphous hydrates and inhibited the coagulation performance. In contrast, glucose, benzoic acid (BEN), and tris(hydroxymethyl)aminomethane (THMAM) had no significant effect on the coagulation performance. Therefore, LMW organics can bond to the hydrolysis products of metal ions through key functional groups, such as carboxyl groups, and then affect the coagulation process. The experimental results show that the presence of LMW organics can change the surface properties and degree of crystallization of the primary NPs, thereby affecting the performance of coagulation.
McBeath ST, English JT, Wilkinson DP, et al., 2021, Circumneutral electrosynthesis of ferrate oxidant: an emerging technology for small, remote and decentralised water treatment applications, Current Opinion in Electrochemistry, Vol: 27, Pages: 1-7, ISSN: 2451-9103
Although sophisticated water treatment technologies exist, the transportation, storage, and safe handling of chemical supplies can present major challenges for small and remote communities, putting the security of their access to potable water at risk. In-situ electrochemical methods can remove the need for chemical additives by generating reactive species on demand from the constituents of raw waters. This paper is a concise review of current literature concerning the advancement of in-situ technologies for the electrosynthesis of ferrate, which is a high-valent, strongly oxidising and environmentally benign species of iron. Synthesis mechanisms and operational parameters influencing generation in circumneutral conditions are discussed, as well as the viability of strategies to address the challenges presented by standards for drinking water and materials for constructing electrodes.
Yang Z, Zhao L, Hu M, et al., 2021, Hydrophobic-modified metal-hydroxide nanoflocculants enable one-step removal of multi-contaminants for drinking water production, iScience, Vol: 24, Pages: 1-13, ISSN: 2589-0042
Flocculation is a mainstream technology for the provision of safe drinking water but is limited due to the ineffectiveness of conventional flocculants in removing trace low-molecular-weight emerging contaminants. We described a synthesis strategy for the development of high-performance nanoflocculants (hydrophobic-organic-chain-modified metal hydroxides [HOC-M]), imitating surfactant-assembling nano-micelles, by integration of long hydrophobic chains with traditional inorganic metal (Fe/Al/Ti)-based flocculants. The core-shell nanostructure was highly stable in acidic stock solution and transformed to meso-scale coagulation nuclei in real surface water. In both jar and continuous-flow tests, HOC-M was superior over conventional flocculants in removing many contaminants (turbidity, UV254, and DOC: >95%; TP and NO3-N: >90%; trace pharmaceuticals [initial concentration: 100 ng/L]: >80%), producing flocs with better structural and dewatering properties, and lowering the environmental risk of metal leaching. The rationally designed nanoflocculants have large application potential, as a solution to increasing public concern about micro-pollutants and increasing water quality requirements.
Yang H, Graham NJD, Wang W, et al., 2021, Evaluating and improving the reliability of the UV-persulfate method for the determination of TOC/DOC in surface waters, Water Research, Vol: 196, Pages: 1-12, ISSN: 0043-1354
The UV-persulfate oxidation method is widely used for determining the total organic carbon concentration of aqueous samples (denoted for convenience as UVP-TOC). However, for some surface water samples, the measurement of TOC by this method can be unreliable, deviating significantly from the true carbon content. In this study, the performance of the UVP-TOC method has been investigated by comparing the results from the analysis of a variety of aqueous samples that included two kinds of surface water samples and related surface water model substances: bovine serum albumin (BSA), sodium alginate (SA), humic acid (HA), tannic acid (TA), benzoic acid (BA) and citric acid (CA), with those from a high-temperature combustion method (elemental analysis); the latter providing the true carbon content value. By comparing the above data, it was found that the UVP-TOC method significantly underestimated the TOC value of the surface water samples, and it was also found that the model components BSA (protein) and HA (humic substances, HS) had a substantial influence on the TOC underestimation, while the SA (polysaccharide), TA (complex organic molecule) and CA/BA (small molecules) had little effect. The results showed that the agglomeration within and between BSA and HA molecules was an important reason for the inaccurate UVP-TOC values of BSA and HA. A further limitation was that for BSA, surfactants (e.g. sodium dodecylbenzene sulfonate, SDBS) and other surfactant-like substances, foam was formed during the CO2 removal purging process by N2 that seriously interfered with the determination of TOC. The study provides new information and insight into the causes of inaccuracies in the UVP-TOC analysis of surface waters and possible approaches to improve the accuracy.
Xu L, Zhou Z, Graham NJD, et al., 2021, Enhancing ultrafiltration performance by gravity-driven up-flow slow biofilter pre-treatment to remove natural organic matters and biopolymer foulants, Water Research, Vol: 195, Pages: 1-12, ISSN: 0043-1354
Membrane fouling by influent biopolymers, and the formation of surface biofilms, are major obstacles to the practical application of membrane technologies. Identifying reliable and sustainable pre-treatment methods for membrane filtration remains a considerable challenge and is the subject of continuing research study worldwide. Herein, the performance of a bench-scale gravity-driven up-flow slow biofilter (GUSB) as the pre-treatment for ultrafiltration to reduce membrane fouling is presented. Dissolved organic carbon (DOC) was shown efficiently removed by the GUSB (around 80%) when treating a natural water influent. More significantly, biopolymers, with molecular weight (MW) between 20 kDa and 100 kDa, were effectively removed (62.8% reduction) and this led to a lower rate of transmembrane pressure (TMP) development by the UF membrane. Microbial diversity analysis further unraveled the function of GUSB in shaping microbes to degrade biopolymers, contributing to lower accumulation and different distribution pattern of SMP on the membrane surface. Moreover, the biofilm formed on the membrane surface after the pre-treatment of GUSB was observed to have a relative porous structure compared to the control system, which can also affect the fouling development. Long-term operation of GUSB further revealed its robust performance in reducing both natural organic matters and UF fouling propensity. This study overall has demonstrated the potential advantages of applying a GUSB to enhance UF process performance by reducing biofouling and improving effluent quality.
McBeath ST, Graham NJD, 2021, In-situ electrochemical generation of permanganate for the treatment of atrazine, Separation and Purification Technology, Vol: 260, Pages: 1-9, ISSN: 1383-5866
A novel process involving the simultaneous electrochemical oxidation and electrosynthesis of permanganate oxidant has been explored for the treatment of the triazine organic herbicide, atrazine. The electrochemical synthesis of permanganate in neutral pH conditions using low concentration manganese (Mn2+), analogous to levels found in some raw groundwater sources, and their subsequent effect on atrazine degradation were studied in bench-scale experiments. Permanganate synthesis was found to be largely unaffected by the operating current density (10, 40 and 80 mA cm−2) during electrolysis, indicating as mass transport controlled process. Under the same operating conditions, hydroxyl radical mediated oxidation was observed to degrade atrazine from an initial concentration of 9.27 µM (2 mg L−1), to 6.22, 4.88 and 2.36 µM after 120 min of electrolysis for 10, 40 and 80 mA cm−2 conditions. When 55 µM (3.0 mg L−1) Mn2+ was added to the water matrix, atrazine degradation increased, yielding final concentrations of 5.80, 3.66 and 2.17 µM, respectively. Atrazine degradation was found to be accurately described by pseudo-first-order reaction kinetics, with and without the enhanced oxidation by permanganate generation, as the concentration of hydroxyl radicals remained constant and comparatively high throughout electrolysis. Finally, the yielded second-order reaction rate constants of electrochemically generated permanganate, and dosed potassium permanganate, with atrazine were 9.79 and 8.35 M−1 s−1, respectively, whereby the latter degradation mechanism was kinetically limited and the former was under mass transfer control due to an extremely low permanganate-atrazine ratio. Finally, four primary oxidation by-products were observed to form in the reactions, including deethylatrazine, deisopropylatrazine and deethyldeisopropylatrazine.
Su Z, Yu W, Liu T, et al., 2021, Discovery of welcome biopolymers in surface water: improvements in drinking water production., Environmental Science and Technology (Washington), Vol: 55, Pages: 2076-2086, ISSN: 0013-936X
The presence of biopolymers in surface waters and their significance for potable water supply have received little attention previously owing to their low concentrations. In this paper, we present the results of an extensive study that has investigated the role and benefits of biopolymers during the purification of surface water with reference to their specific biological and physico-chemical properties. Using samples collected from two representative surface waters in China and the United Kingdom, macromolecular biopolymers were separated and concentrated for subsequent investigation of their role in coagulation, metal ion adsorption, and membrane separation. Our results show that biopolymers significantly improve the antifouling capability of membrane nanofiltration, in combination with the enhanced conventional coagulation performance and additional security against several unhealthy metal pollutants (e.g., Fe, Al, and Cr). We believe this is the first study that reveals the versatile benefits and the fate of natural biopolymers in surface water purification processes.
Xu L, Yu W, Graham N, et al., 2021, Revisiting the bioelectrochemical system based biosensor for organic sensing and the prospect on constructed wetland-microbial fuel cell, Chemosphere, Vol: 264, ISSN: 0045-6535
Bioelectrochemical system (BES) based biosensors for organic sensing has long been investigated. However, there is no uniform criterion to evaluate directly the performance of the BES based biosensors due to their different scale. Here, for the first time, we show that the normalized maximum detection range (NMDR) and normalized sensing time (NST) can potentially be used as the two criteria in BES based biosensors for organic sensing. Thereafter, the recently emerged, relatively larger scale BES (i.e. constructed wetland-microbial fuel cell, CW-MFC) was specifically examined in this study. The biocathode formation and the influence of anodic material on sensor performance were systematically evaluated. The system with metal-based anode was found to produce a more stable and quicker response (low NST) than that with carbon-based anode. Significantly, the continuous loading mode was found to greatly reduce the NMDR compared to the batch mode, and the hydraulic residence time (HRT) is the critical factor determining the NMDR. Furthermore, it was found that the electrical signals generated from the CW-MFC system were insignificantly influenced by some specific chemical disturbances, such as Cu2+ and herbicide. Therefore, normalized toxicity (NT) is suggested to be considered in BES based biosensor. However, for chemicals with higher reduction potentials (NO3- in this work), the system presented a high response, enabling its potential for monitoring NO3- in effluents or groundwater. This study can hopefully contribute to further development of the sustainable BES based biosensors in CW.
He M, Wan Z, Tsang DCW, et al., 2021, Performance indicators for a holistic evaluation of catalyst-based degradation-A case study of selected pharmaceuticals and personal care products (PPCPs)., Journal of Hazardous Materials, Vol: 402, Pages: 1-16, ISSN: 0304-3894
Considerable efforts have been made to develop effective and sustainable catalysts, e.g., carbon-/biochar-based catalyst, for the decontamination of organic pollutants in water/wastewater. Most of the published studies evaluated the catalytic performance mainly upon degradation efficiency of parent compounds; however, comprehensive and field-relevant performance assessment is still in need. This review critically analysed the performance indicators for carbon-/biochar-based catalytic degradation from the perspectives of: (1) degradation of parent compounds, i.e., concentrations, kinetics, reactive oxidative species (ROS) analysis, and residual oxidant concentration; (2) formation of intermediates and by-products, i.e., intermediates analysis, evolution of inorganic ions, and total organic carbon (TOC); and (3) impact assessment of treated samples, i.e., toxicity evolution, disinfection effect, and biodegradability test. Five most frequently detected pharmaceuticals and personal care products (PPCPs) (sulfamethoxazole, carbamazepine, ibuprofen, diclofenac, and acetaminophen) were selected as a case study to articulate the performance indicators for a holistic evaluation of carbon-/biochar-based catalytic degradation. This review also encourages the development of alternative performance indicators to facilitate the rational design of catalysts in future studies.
Liu X, Graham N, Liu T, et al., 2021, A comparison of the coagulation performance of PAFC and FeSO<sub>4</sub> for the treatment of leach liquor from Stevia processing, SEPARATION AND PURIFICATION TECHNOLOGY, Vol: 255, ISSN: 1383-5866
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- Citations: 9
Xing B, Graham N, Yu W, 2020, Transformation of siderite to goethite by humic acid in the natural environment, Communications Chemistry, Vol: 3
Humic acid (HA) is particularly important in iron-bearing mineral transformations and erosion at the water-mineral boundary zone of the Earth. In this study, three stages of the possible pathway by which HA causes mineral transformation from siderite to goethite are identified. Firstly, a Fe(II)-HA complex is formed by chelation, which accelerates the dissolution and oxidation of Fe(II) from the surface of siderite. As the Fe(II)-HA complex retains Fe atoms in close proximity of each other, ferrihydrite is formed by the agglomeration and crystallization. Finally, the ferrihydrite structurally rearranges upon attachment to the surface of goethite crystals and merges with its structure. The influence of low concentrations of HA (0–2 mg/L) on phosphate adsorption is found to be beneficial by the inducing of new mineral phases. We believe that these results provide a greater understanding of the impact of HA in the biogeochemical cycle of phosphate, mineral transformation.
Sun Y, Yu IKM, Tsang DCW, et al., 2020, Tailored design of graphitic biochar for high-efficiency and chemical-free microwave-assisted removal of refractory organic contaminants, Chemical Engineering Journal, Vol: 398, Pages: 1-10, ISSN: 1385-8947
Energy-saving, chemical-free, and high-efficiency microwave (MW)-assisted water treatment can be greatly facilitated via tailored design of an economical, sustainable, and ‘green’ carbonaceous catalyst. In this study, various biochars (BC) were pyrolyzed from two lignocellulosic waste biomasses, oak (O) and apple tree (A), at a high temperature (900 °C) and under different gases (N2 and CO2). The holistic characterization by advanced spectroscopic techniques demonstrated that CO2 pyrolysis of feedstock with more lignin (i.e., oak), produced biochar with increased aromaticity and degree of carbonization. CO2 modification created a hierarchical porous structure, improved surface hydrophilicity, polarity, and acidity, and provided higher densities of near-surface functionalities of the biochar. Without MW irradiation, ABC-900C (1 g L−1) provided the highest adsorption (52.6%, 1 min) of 2,4-dichlorophenoxy acetic acid (2,4-D) ascribed to large specific surface area, high micropore content, appropriate pore size, and abundant active groups. OBC-900C (1 g L−1) enabled significantly increased 2,4-D removal (81.6%, 1 min) under MW irradiation (90 °C) in contrast with an oil bath (55.7%, 90 °C, 1 min) and room temperature (33.9%, 1 min) conditions, due to its highest graphitization degree and medium-developed microporous structure. The MW-induced thermal effect formed “hot spots” on the biochar surface as evidenced by elevated temperature of the bulk solution and lowered energy consumption of the MW reactor in the presence of OBC-900C, compared to those of the other biochars. The scavenging tests suggested that the generation of highly oxidative hydroxyl (•OH), anionic superoxide (O2•−), and singlet oxygen (1O2) radicals contributed to the removal of 2,4-D. This study has demonstrated that biochar with customized structure and high organic adsorption capacity can act as an effective MW absorber suitable for rapi
Li X, Graham NJD, Deng W, et al., 2020, The formation of planar crystalline flocs of γ-FeOOH in Fe(II) coagulation and the influence of humic acid, Water Research, Vol: 185, ISSN: 0043-1354
Although Fe(II) salts have been widely used as coagulants in water treatment for many years, the underlying mechanisms of their performance remain unclear. Here, we present a detailed study of the coagulation behavior of Fe(II) salts and crystallization of flocs, and investigate the effect of humic acid (HA) under different DO concentrations and pH conditions. The behavior of Fe(II) and Fe(III) coagulants was found to be markedly different with the flocs from Fe(II) consisting of planar-like crystalline γ-FeOOH in contrast to the small amorphous spherical-like flocs from Fe(III) dosing. The effect of HA on Fe(II) coagulation was different under different DO concentrations and pH, where by the growth of γ-FeOOH was inhibited by the presence of HA, but independent of DO concentration and pH. It was found that Fe(II) was present within the internal structure of γ-FeOOH, and a plausible formation mechanism is proposed. Firstly, planar nanoparticles of Fe(OH)2 were formed via Fe(II) ion hydrolysis which then servedas the nucleus for subsequent crystal growth. With oxidation, Fe(II) on the surface of nanoparticles transformed to Fe(III). Finally, the formation of γ-FeOOH in Fe(II) coagulation was accompanied by a change in solution colour to yellow.
Yang Z, Zhang Y, Wang X, et al., 2020, Efficient adsorption of four phenolic compounds using a robust nanocomposite fabricated by confining 2D porous organic polymers in 3D anion exchangers, Chemical Engineering Journal, Vol: 396, Pages: 1-11, ISSN: 1385-8947
A novel 2D/3D hybrid nanocomposite adsorbent (TCBD/D318) was synthesized by confining a 2D porous organic polymer (POP, TCBD) in pores of commercial 3D anionic exchanger beads (D318) using a facile repetitive deposition method, and evaluated for the removal of four phenolic contaminants (phenol, 1-naphthol, 4-nitrophenol and 4-chlorophenol) from water. The immobilization of TCBD in D318 conferred on the adsorbent a robust water stability, a rapid solid-liquid separation (in 10 s after dispersion in water), and an enhanced anti-self-aggregation property. The effects of pH, contaminant type, coexisting inorganic anions and natural organic matter (NOM) on adsorption performance were studied. TCBD/D318 exhibited high adsorption capacities (Qe) for all four phenolic contaminants, and these were only slightly influenced by pH and the presence of coexisting inorganic anions and NOM, due to the combined effects of multi-binding-interactions and hierarchical pore-structures. Another equally important merit of the TCBD/D318 was its remarkably improved utilization efficiency (atom economy) of functional groups. The adsorption mechanisms were investigated by a combination of physico-chemical model fitting, instrumental analysis and chemical computation. These displayed a hierarchical-pore-structure-induced multi-step diffusion adsorption involving multi-binding-interactions, principally electrostatic attraction, π-π interaction, and H-bonding; the contaminants were more inclined to be bound onto TC units of TCBD in the nanocomposite. Regeneration tests involving 10 adsorption-desorption cycles showed that TCBD/D318 maintained a high Qe, confirming its effective reusability. The results have demonstrated the outstanding potential of TCBD/D318 for the removal of phenolic compounds from water, and more generally the possibilities of using POP-based 2D/3D hybrid nanocomposites in wider environmental applications.
McBeath ST, Wilkinson DP, Graham NJD, 2020, Advanced electrochemical oxidation for the simultaneous removal of manganese and generation of permanganate oxidant, Environmental Science: Water Research & Technology, Vol: 6, Pages: 2405-2415, ISSN: 2053-1400
Emerging electrochemical systems, such as advanced electro-oxidation, provide a potentially powerful alternative to conventional oxidation processes which can often be unsuitable for small, remote and decentralised system applications. The one electro-oxidation process, which may be well suited for these applications, is the use of high oxygen overpotential boron-doped diamond (BDD) electrodes, as a pre-oxidation step for the removal of various raw water contaminants. While BDD electro-oxidation has been studied extensively for the abatement of organic micropollutants, its application as a pre-oxidation technology for the removal of soluble manganese (Mn2+) in source waters for drinking water supply, has not been reported to-date. In this study, we summarise the results of tests using a bench-scale electro-oxidation system and synthetic Mn2+ solutions in order to consider the simultaneous removal of manganese and the generation of permanganate. The results showed that total manganese was reduced by 9.1, 38.7 and 57.4% at current densities of 10, 40 and 80 mA cm−2, respectively, with an initial Mn2+ concentration of 39 μM. Increased Mn removal at higher current density was attributed to increased generation of, and reaction with, hydroxyl radicals, indicated by a direct proportional relationship between pseudo-first order reaction rate constants for methanol (˙OH radical scavenger) and current density. A mathematical model was developed to describe Mn removal under mass transport limitations, and was found to correlate well with experimental data. Finally, a completely novel synthesis pathway for the generation of permanganate species (Mn7+) is presented, whereby concentrations up to 0.9 μM were synthesised from Mn2+ in circumneutral conditions.
Xing B, Ouyang M, Graham N, et al., 2020, Enhancement of phosphate adsorption during mineral transformation of natural siderite induced by humic acid: Mechanism and application, Chemical Engineering Journal, Vol: 393, ISSN: 1385-8947
The interfacial interactions between siderite, humic acid (HA), and phosphate, is critical to understand the transport of HA and phosphate in the environment. In this study, the influence of HA on the adsorption of phosphate by siderite not only includes competitive adsorption, but also includes indirectly facilitated adsorption. It was attributed to that humic acid as a representative natural organic matter possesses abundant carboxylic groups, which facilitate chelation between minerals and HA, and then the phosphate adsorption performance is affected. The experimental results concluded that three stages of the transformation from siderite to goethite under the action of HA can be divided. Firstly, chelation can be formed between HA and the ferrous ions from siderite, and it is favorable for the oxidation of Fe(II) by the O2 in water to form amorphous ferrihydrite; and then the ferrihydrite nano-particles were attached to the surface of goethite crystals; finally, the goethite crystal structure was formed by the structural rearrangement of ferrihydrite nano-particles. Meanwhile, the surface complex species of phosphate was formed on precipitate. It is revealed that the diprotonated bidentate binuclear complex is the main phosphate species when the HA concentration was 0.5 mg/L; as the HA concentration rose to 10 mg/L, the main phosphate species change to diprotonated monodentate mononuclear complex, which is attributed to the competitive adsorption of humic acid. We believe that these results are beneficial to guide the impact of HA for the biogeochemical cycling of phosphate, iron-bearing mineral transformation, as well as environmental remediation.
McBeath ST, Wilkinson DP, Graham NJD, 2020, Exploiting water contaminants: In-situ electrochemical generation of ferrates using ambient raw water iron (Fe2+), Journal of Environmental Chemical Engineering, Vol: 8, Pages: 1-9, ISSN: 2213-3437
Many complexities arise when applying conventional water treatment processes to small and remote systems. A significant challenge is the difficulty and impracticality of supplying chemicals needed for oxidation processes. A burgeoning, yet currently under-utilised, type of treatment are electrochemical technologies, which are receiving considerable research attention and innovation at present. In particular, through the advancement of high oxygen overpotential electrodes, the ability to synthesise highly oxidative chemical species under circumneutral pH conditions has become possible. In this study, the generation of highly oxidative iron-based species, specifically ferrate (Fe6+), has been explored utilising a boron-doped diamond (BDD) electrode and low concentrations of Fe2+ typically found in raw water, thereby eliminating the chemical supply chain required for conventional oxidation processes. Electrochemical ferrate generation experiments were performed in a batch-recycle configuration and were found to be mass transfer limited, whereby the rate-limiting step was the diffusion of Fe2+ to the electrode surface. This was evidenced by very little variation in ferrate generation at the three current densities tested, specifically 3.1 ± 0.2, 2.6 ± 0.2 and 3.3 ± 0.2 μM were generated at 10, 40 and 80 mA/cm2, respectively. Measured Fe6+ concentrations correlated well with those predicted by a mathematical process model, which assumed a completely mass transport limited process. While cyclic voltammetry confirmed ferrate generation by direct oxidation at the BDD surface, the contribution of hydroxyl radicals was indicated by the presence and absence of methanol, an radical dotOH scavenger, with ferrate generation decreased by greater than 50 % with methanol, compared to non-scavenged experiments. The results provide one of the first quantitative studies regarding the oxidation mechanisms of ferrate generation by electro-oxidation, and the first
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