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There is a growing demand for water treatment systems for which the quality of feedwater in and product water out are not necessarily fixed with "tunable" technologies essential in many instances to satisfy the unique requirements of particular end-users. For example, in household applications, the optimal water hardness differs for particular end uses of the supplied product (such as water for potable purposes, water for hydration, or water for coffee or tea brewing) with the inclusion of specific minerals enhancing the suitability of the product in each case. However, conventional softening technologies are not dynamically flexible or tunable and, typically, simply remove all hardness ions from the feedwater. Membrane capacitive deionization (MCDI) can potentially fill this gap with its process flexibility and tunability achieved by fine tuning different operational parameters. In this article, we demonstrate that constant-current MCDI can be operated flexibly by increasing or decreasing the current and flow rate simultaneously to achieve the same desalination performance but different productivity whilst maintaining high water recovery. This characteristic can be used to operate MCDI in an energy-efficient manner to produce treated water more slowly at times of normal demand but more rapidly at times of peak demand. We also highlight the "tunability" of MCDI enabling the control of effluent hardness over different desired ranges by correlating the rates of hardness and conductivity removal using a power function model. Using this model, it is possible to either i) soften water to the same hardness level regardless of the fluctuation in hardness of feed waters, or ii) precisely control the effluent hardness at different levels to avoid excessive or insufficient hardness removal., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

An industrially viable catalyst for heterogeneous catalytic ozonation (HCO) in water purification requires the characteristics of good dispersion of active species on its surface, efficient electron transfer for ozone decay, and maximum active species utilization. While metal-organic frameworks (MOFs) represent an attractive platform for HCO, the metal nodes in the unmodified MOFs exhibit low catalytic activity. Herein, we present a perfluorinated Fe-MOF catalyst by substituting H atoms on the metalated ligands with F atoms (termed 4F-MIL-88B) to induce structure evolution. The Lewis acidity of 4F-MIL-88B was enhanced via the formation of Fe nodes, tailoring the electron distribution on the catalyst surface. As a result of catalyst modification, the rate constant for degradation of the target compounds examined increased by ∼700% compared with that observed for the unmodified catalyst. Experimental evidence and theoretical calculations showed that the modulated polarity and the enhanced electron transfer between the catalyst and ozone molecules contributed to the adsorption and transformation of O 3 to • OH on the catalyst surface. Overall, the results of this study highlight the significance of tailoring the metalated ligands to develop highly efficient and stable MOF catalysts for HCO and provide an in-depth mechanistic understanding of their structure-function evolution, which is expected to facilitate the applications of nanomaterial-based processes in water purification.

Packed fixed-bed reactors are traditionally used for heterogeneous catalytic ozonation. However, a high solid-to-liquid requirement, poor ozone dissolution, ineffective utilization of catalyst surface area, and production of large amounts of catalyst waste impede application of such reactors. In this study, we designed a suspension catalytic ozonation reactor and compared the performance of this reactor with that of a traditional fixed-bed catalytic ozonation reactor employing oxalic acid (OA) as the target contaminant. Our results showed that total O 3 dissolved into the suspension reactor (117-134 mg.L -1 ) was much higher compared to that measured in the fixed-bed reactor (53 mg.L -1 ) due to a higher O 3 (g) interphase mass transfer rate in the suspension reactor. In accordance with the higher O 3 (g) interphase mass transfer, we observed a much higher proportional OA removal (32 %) compared to that achieved in the fixed-bed reactor (10%) employing an Fe-oxide catalyst supported on Al 2 O 3 (Fe-oxide@Al 2 O 3 ) in both reactors. Use of a double-layered Cu-Al hydroxide (Cu-Al LDHs) catalyst in the suspension reactor further enhanced the performance with nearly 90 % OA removal observed. Given the superior performance of the suspension reactor, we investigated the impact of operating conditions (catalyst dosage, hydraulic retention time and ozone dosage) employing Cu-Al LDHs as the catalyst. We also developed a mathematical kinetic model to describe the performance of the suspension reactor and, through use of the kinetic model, showed that O 3 (g) interphase transfer rate was the rate-limiting step in OA removal. Thus, improvement in ozone gas diffuser design is required to improve the performance of the suspension reactor. Overall, the present study demonstrated that suspension reactors were more effective than fixed-bed reactors for oxidation of surface-active organic compounds such as OA due to the higher ozone interphase mass transfer rate and effective utilization of the catalyst surface area that can be achieved. As such, further research on suspension reactor design and development of catalysts suitable for use in suspension reactors should facilitate large-scale application of catalytic ozonation processes by the wastewater treatment industry., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

A long-term field trial of membrane capacitive deionization (MCDI) was conducted in a remote community in the Northern Territory of Australia, with the aim of producing safe palatable drinking water from groundwater that contains high concentrations of salt and hardness ions and other contaminants. This trial lasted for 1.5 years, which, to our knowledge, is one of the longest reported studies of pilot-scale MCDI field trials. The 8-module MCDI pilot unit reduced salt concentration to below the Australian Drinking Water Guideline value of 600 mg/L total dissolved solids (TDS) concentration with a relatively high water recovery of 71.6 ± 8.7 %. During continuous constant current operation and electrode discharging at near zero volts, a rapid performance deterioration occurred that was primarily attributed to insufficient desorption of multivalent ions from the porous carbon electrodes. Performance could be temporarily recovered using chemical cleaning and modified operating procedures however these approaches could not fundamentally resolve the issue of insufficient electrode performance regeneration. Constant current discharging of the electrodes to a negative cell cut-off voltage was hence employed to enhance the stability and overall performance of the MCDI unit during the continuous operation. An increase in selectivity of monovalent ions over divalent ions was also attained by implementing negative voltage discharging. The energy consumption of an MCDI system with a capacity of 1000 m 3 /day was projected to be 0.40∼0.53 kWh/m 3 , which is comparable to the energy consumption of electrodialysis reversal (EDR) and brackish water reverse osmosis (BWRO) systems of the same capacity. The relatively low maintenance requirements of the MCDI system rendered it the most cost-efficient water treatment technology for deployment in remote locations. The LCOW of an MCDI system with a capacity of 1000 m 3 /day was projected to be AU$1.059/m 3 and AU$1.146/m 3 under two operational modes, respectively. Further investigation of particular water-energy trade-offs amongst MCDI performance metrics is required to facilitate broader application of this promising water treatment technology., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Membrane capacitive deionization (MCDI) is a water desalination technology that involves the removal of charged ions from water under an electric field. While constant-current MCDI coupled with stopped-flow during ion discharge is expected to exhibit high water recovery and good performance stability, previous studies have typically been undertaken using NaCl solutions only with limited investigation of MCDI performance using multi-electrolyte solutions. In the present work, the desalination performance of MCDI was evaluated using feed solutions with different levels of hardness. The increase of hardness resulted in the degradation of desalination performance with the desalination time (Δt d ), total removed charge, water recovery (WR) and productivity decreasing by 20.5%, 21.8%, 3.8% and 3.2%, respectively. A more serious degradation of WR and productivity would be caused if Δt d decreases further. Analysis of the voltage profiles and effluent ion concentrations reveal that the insufficient desorption of divalent ions at constant-current discharge to 0 V was the principal reason for the degradation of performance. The Δt d and WR can be improved by discharging the cell using a lower current but the productivity decreased by 15.7% on decreasing the discharging current from 161 to 107 mA. Discharging the cell to a negative potential was shown to be a better option with the Δt d , total removed charge, WR and productivity increasing by 27.4%, 23.9%, 3.6% and 5.3%, respectively, when the cell was discharged to a minimum voltage of - 0.3 V. Use of such a method should be feasible for operation of full scale MCDI plants and would be expected to lead to better regeneration of the electrode, improved desalination performance and, potentially, a significant reduction in the need for use of clean-in-place procedures., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

The performance of membrane capacitive deionization (MCDI) desalination was investigated at bench, pilot, and field scales for the removal of uranium from groundwater. It was found that up to 98.9% of the uranium can be removed using MCDI from a groundwater source containing 50 μg/L uranium, with the majority (94.5%) being retained on the anode. Uranium was found to physiochemically adsorb to the electrode without the application of a potential by displacing chloride ions, with 16.6% uranium removal at the bench scale via this non-electrochemical process. This displacement of chloride did not occur during the MCDI adsorption phase with the adsorption of all ions remaining constant during a time series analysis on the pilot unit. For the scenarios tested on the pilot unit, the flowrate of the product water ranged from 0.15 to 0.23 m 3 /h, electrode energy consumption from 0.28 to 0.51 kW h/m 3 , and water recovery from 69 to 86%. A portion (13-53% on the pilot unit) of the uranium was found to remain on the electrodes after the brine discharge phase with conventional cleaning techniques unable to release this retained uranium. MCDI was found to be a suitable means to remove uranium from groundwater systems though with the need to manage the accumulation of uranium on the electrodes over time.

Membrane Capacitive Deionization (MCDI) is a promising electrochemical technique for water desalination. Previous studies have confirrmed the effectiveness of MCDI in removing contaminants from brackish groundwaters, especially in remote areas where electricity is scarce. However, as with other water treatment technologies, performance deterioration of the MCDI system still occurs, hindering the stability of long-term operation. Herein, a machine learning (ML) modelling framework and various ML models were developed to (i) investigate the performance deterioration due particularly to insufficient charging/discharging of the electrode caused by accumulation of ions and electrode scaling and (ii) optimise MCDI operating parameters such that the impacts of these deleterious effects on unit performance were minimized. The ML models developed in this work exhibited a prediction accuracy of cycle time with average mean absolute percentage error (MAPE) values of 16.82% and 16.09% after 30-fold cross validation for Random Forest (RF) and Multilayer Perceptron (MLP) models respectively. The pre-trained ML model predicted different declining trends of water production for two different operating conditions and provided corresponding recommendations on frequencies of chemical cleaning. A case study on the adjustment of operating parameters using the results suggested by the optimization ML model was conducted. The model validation results showed that the overall water production and water recovery of the system using the cycle-based optimized process control parameters (SCN 1) exceeds the MCDI system performance under three fixed parameter settings that were used at each stage of SCN 1 by 1.78% to 4.48% and 2.95% to 9.46%, respectively. Permutation-based and Shapley additive explanation (SHAP) coefficients were also employed for variable importance (VIMP) analysis to uncover the "black-box" nature of the ML models and to better understand the various features' contributions to overall MCDI system performance., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Boron is present in the form of boric acid (B(OH) 3 or H 3 BO 3 ) in seawater, geothermal waters, and some industrial wastewaters but is toxic at elevated concentrations to both plants and humans. Effective removal of boron from solutions at circumneutral pH by existing technologies such as reverse osmosis is constrained by high energy consumption and low removal efficiency. In this work, we present an asymmetric, membrane-containing flow-by electrosorption system for boron removal. Upon charging, the catholyte pH rapidly increases to above ∼10.7 as a result of water electrolysis and other Faradaic reactions with resultant deprotonation of boric acid to form B(OH) 4 - and subsequent removal from solution by electrosorption to the anode. Results also show that the asymmetric flow-by electrosorption system is capable of treating feed streams with high concentrations of boron and RO permeate containing multiple competing ionic species. On the basis of the experimental results obtained, a mathematical model has been developed that adequately describes the kinetics and mechanism of boron removal by the asymmetric electrosorption system. Overall, this study not only provides new insights into boron removal mechanisms by electrosorption but also opens up a new pathway to eliminate amphoteric pollutants from contaminated source waters.

The efficacy of oxidation of recalcitrant organic contaminants in municipal and industrial wastewaters by ozonation is influenced by chemical reaction kinetics and hydrodynamics within a reactor. A 3D computational fluid dynamics (CFD) model incorporating both multiphase flow and reaction kinetics describing ozone decay, hydroxyl radical ( • OH) generation, and organic oxidation was developed to simulate the performance of continuous flow ozonation reactors. Formate was selected as the target organic in this study due to its well-understood oxidation pathway. Simulation results revealed that the dissolved ozone concentration in the reactor is controlled by rates of O 3 (g) interphase transfer and ozone self-decay. Simulations of the effect of various operating conditions showed that the reaction stoichiometric constraints between formate and ozone were reached; however, complete utilization of gas phase ozone was hard to achieve due to the low ozone interphase mass transfer rate. Increasing the O 3 (g) concentration leads to an increase in the formate removal rate by ∼5% due to an enhancement in the rate of O 3 (g) interphase mass transfer. The CFD model adequately describes the mass transfer occurring in the two-phase flow system and confirms that O 3 (g) interphase mass transfer is the rate-limiting step in contaminant degradation. The model can be used to optimize the ozone reactor design for improved contaminant degradation and ozonation efficiency.

As(III) removal from groundwaters is challenging because of its neutral charge and low surface affinity under circumneutral pH conditions. In this work, we investigate the influence of Ca 2+ and Mg 2+ on the removal of As(III) by a redox active polyvinylferrocene (PVF) functionalized electrode in a modified double potential step chronoamperometry (DPSC) setup. In the absence of divalent cations, nearly 90% As(III) removal is achieved over ten continuous cycles by single-pass DPSC, even in the presence of competing anions, however the presence of divalent cations at concentrations ≥ 1.25 mM significantly inhibits As(III) removal. The divalent cations enhance arsenic removal in the first (removal) step but suppress electrode regeneration in the 2 nd step. Our results suggest that Ca 2+ /Mg 2+ either acts as a bridge between the electrode surface and As anions or the sorption of Ca 2+ /Mg 2+ increases the positive charge on the electrode surface thereby facilitating As(V) sorption. We show that effective electrode regeneration can be achieved using an NaOH wash however the overall complexity of the process increases. Overall, we conclude that the influence of divalent cations on As removal by electro-sorption processes needs to be taken into consideration for application of this technology for real groundwater treatment., (Copyright © 2021 Elsevier B.V. All rights reserved.)

The heterogeneous catalytic ozonation process is a promising treatment option for high salinity reverse osmosis concentrate (ROC) however the influence of salts on the catalyst performance is not well understood. In this work, we investigate the effect of salts on the performance of the catalytic ozonation process for treatment of synthetic ROC using a commercially available Fe-loaded Al 2 O 3 catalyst. Our results show that the presence of salts influences the rate and extent of degradation of organic compounds present in the synthetic ROC when subjected to the heterogeneous catalytic ozonation process. Scavenging of aqueous O 3 by chloride ions and/or transformation of organics (particularly humics) to more hydrophobic form as a result of charge shielding between adjacent functional groups and/or intramolecular binding by cations inhibits the bulk oxidation of organics to a measurable extent. While the scavenging of aqueous hydroxyl radicals at the salt concentrations investigated here was minimal, the accumulation of chloride ions in the electric double layer near the catalyst surface, particularly when pH< pH pzc , results in more significant scavenging of surface associated hydroxyl radicals. Overall, the presence of salts (particularly chloride ions) has a significant influence on the performance of both conventional and catalytic ozonation processes with some scope to mitigate this effect through appropriate choice of catalyst., (Copyright © 2021 Elsevier B.V. All rights reserved.)

In this study, copper aluminum layered hydroxides (Cu-Al LDHs) and copper oxide (CuO) were utilized as catalysts for heterogeneous catalytic ozonation (HCO). Target compounds oxalate and formate were used with removal by adsorption and oxidation quantified to elucidate the role of the catalyst in contaminant removal. Oxidation of oxalate mostly occurred on the catalyst surface via interaction of surface oxalate complexes with surface-located oxidants. In contrast, the oxidation of formate occurred in the bulk solution as well as on the surface of the catalyst. Measurement of O 3 decay kinetics coupled with fluorescence microscopy image analysis corresponding to 7-hydroxycoumarin formation indicates that while surface hydroxyl groups in Cu-Al LDHs facilitate slow decay of O 3 resulting in the formation of hydroxyl radicals on the surface, CuO rapidly transforms O 3 into surface-located hydroxyl radicals and/or other oxidants. Futile consumption of surface-located oxidants via interaction with the catalyst surface was minimal for Cu-Al-LDHs; however, it becomes significant in the presence of higher CuO dosages. A mechanistic kinetic model has been developed which adequately describes the experimental results obtained and can be used to optimize the process conditions for the application of HCO.

Membrane capacitive deionization (MCDI) is an emerging electric field-driven technology for brackish water desalination involving the removal of charged ions from saline source waters. While the desalination performance of MCDI under different operational modes has been widely investigated, most studies have concentrated on different charging conditions without considering discharging conditions. In this study, we investigate the effects of different discharging conditions on the desalination performance of MCDI electrode. Our study demonstrates that low-current discharge (1.0 mA/cm 2 ) can increase salt removal by 20% and decrease volumetric energy consumption by 40% by improving electrode regeneration and increasing energy recovery, respectively, while high-current discharge (3.0 mA/cm 2 ) can improve productivity by 70% at the expense of electrode regeneration and energy recovery. Whether discharging electrodes at the low current or high current is optimal depends on a trade-off between productivity and energy consumption. We also reveal that stopped flow discharge (85%) can achieve higher water recovery than continuous flow discharge (35-59%). However, stopped flow discharge caused a 20-30% decrease in concentration reduction and a 25-50% increase in molar energy consumption, possibly due to the higher ion concentration in the macropores at the end of discharging step. These results reveal that an optimal discharging operation should be obtained from achieving a balance among productivity, water recovery and energy consumption by varying discharging current and flow rate., (Copyright © 2021. Published by Elsevier Ltd.)

A novel design for a flow-electrode capacitive deionization (FCDI) system consisting of tubular electrodes in a shell and tube heat exchanger configuration is proposed. Each electrode consists of a metallic mesh current collector along the inner circumference of a tubular ion-exchange membrane. This tubular FCDI design is suitable for scale-up as it consists of easily manufactured components which can be assembled in an array. An apparatus with 4 tubular electrodes with a large effective area (202.3 cm 2 ) was constructed and shown to provide a high net salt (NaCl) removal rate (0.15 mg s -1 at 1.2 V applied voltage and ∼2000 mg L -1 influent total dissolved solids concentration). A computational fluid dynamics (CFD) model incorporating ion migration and transport mechanisms was developed to simulate the ion concentration and electrical potential profiles in the water channel. The results of CFD modelling highlighted the need to maximize regions of both high potential gradient and high hydraulic flow in order to achieve optimal salt removal. In brief, this study presents a new design approach for FCDI scale-up and provides a computational tool for optimization of this design and future innovative FCDI designs., (Copyright © 2021. Published by Elsevier Ltd.)

The contamination of water resources by nitrate is a major problem. Herein, we report a mechanically flexible 2D-MXene (Ti 3 C 2 T x ) membrane with multilayered nanofluidic channels for a selective electrochemical reduction of nitrate to nitrogen gas (N 2 ). At a low applied potential of -0.8 V (vs Ag/AgCl), the MXene electrochemical membrane was found to exhibit high selectivity for NO 3 - reduction to N 2 (82.8%) due to a relatively low desorption energy barrier for the release of adsorbed N 2 (*N 2 ) compared to that for the adsorbed NH 3 (*NH 3 ) based on density functional theory (DFT) calculations. Long-term use of the MXene membrane for treating 10 mg-NO 3 -N L -1 in water was found to have a high faradic efficiency of 72.6% for NO 3 - reduction to N 2 at a very low electrical cost of 0.28 kWh m -3 . Results of theoretical calculations and experimental results showed that defects on the MXene nanosheet surfaces played an important role in achieving high activity, primarily at the low-coordinated Ti sites. Water flowing through the MXene nanosheets facilitated the mass transfer of nitrate onto the low-coordinated Ti sites with this enhancement of particular importance under cathodic polarization of the MXene membrane. This study provides insight into the tailoring of nanoengineered materials for practical application in water treatment and environmental remediation.

Electrochemical advanced oxidation processes (EAOPs) have emerged as a promising water treatment alternative but major breakthroughs are still needed in order for EAOPs to be competitive with traditional treatment technologies in terms of energy cost. Most existing studies have been conducted at high potentials to generate the powerful hydroxyl radical oxidant (aqueous •OH). While adsorbed hydroxyl radicals (OH*) may form at a much lower energy cost, their possible utilization is limited due to the poor mass transfer of this highly reactive species on solid electrodes. In this report, we describe a novel flow anode system using 4-16 μm Magnéli phase titanium suboxide particles as the anode material which enables the generation of a high steady state •OH concentration (5.4 × 10 -12  mol m -2 ) at only 1.5 V (vs SHE) in a dilute electrolyte (5 mM KH 2 PO 4 ). The energy cost of removal per order of selected water contaminants (tetracycline and orange II in this study) using the flow anode is 1.5--6.7 Wh m -3 , which is 1 - 4 orders of magnitude lower than that of existing techniques. The anode material used demonstrates great stability with the configuration readily scaled up. The results of this study provide new insight into a high efficiency, low cost water treatment technology for organic contaminant degradation., (Copyright © 2021. Published by Elsevier Ltd.)

With the increasing severity of global water scarcity, a myriad of scientific activities is directed toward advancing brackish water desalination and wastewater remediation technologies. Flow-electrode capacitive deionization (FCDI), a newly developed electrochemically driven ion removal approach combining ion-exchange membranes and flowable particle electrodes, has been actively explored over the past seven years, driven by the possibility of energy-efficient, sustainable, and fully continuous production of high-quality fresh water, as well as flexible management of the particle electrodes and concentrate stream. Here, we provide a comprehensive overview of current advances of this interesting technology with particular attention given to FCDI principles, designs (including cell architecture and electrode and separator options), operational modes (including approaches to management of the flowable electrodes), characterizations and modeling, and environmental applications (including water desalination, resource recovery, and contaminant abatement). Furthermore, we introduce the definitions and performance metrics that should be used so that fair assessments and comparisons can be made between different systems and separation conditions. We then highlight the most pressing challenges (i.e., operation and capital cost, scale-up, and commercialization) in the full-scale application of this technology. We conclude this state-of-the-art review by considering the overall outlook of the technology and discussing areas requiring particular attention in the future.

It is critical to both effectively remove and recover phosphate (P) from wastewater given the wide-ranging environmental (i.e., preventing eutrophication and restoring water quality) and economic (i.e., overcoming P resource scarcity) benefits. More recently, considerable academic effort has been devoted towards harvesting P as vivianite, which can be used as a potential slow-release fertilizer and possible reagent for the manufacture of lithium iron phosphate (LiFePO 4 ), the precursor in fabricating Li-ion secondary batteries. In this study, we propose an innovative P recovery process, in which P is first preconcentrated via a flow-electrode capacitive deionization (FCDI) device followed by immobilization as vivianite crystals in a fluidized bed crystallization (FBC) column. The effects of different operational parameters on FCDI P preconcentration performance and energy consumption are investigated. Results show that 63% of P can be removed and concentrated in the flow-electrode chamber with a reasonable energy requirement under optimal operating conditions. The FBC system resulted in immobilization of ~80% of P as triangular or quadrangular pellets, which were verified to be high-purity vivianite crystals by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX) and extended X-ray absorption fine structure (EXAFS) spectroscopy. This study provides a pathway for efficient recovery of P as a value-added product (i.e., vivianite) from P-rich wastewaters., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021. Published by Elsevier Ltd.)

Field studies were conducted in a Croatian city supplied by two distinct groundwater sources (referred to as A and B) to investigate both the effects of changing water source on the water quality in the drinking water supply system, as well as to further understand discoloration events that occurred in city locations that switched water from source A to B. The water treatment processes at site A were found to alter organic matter (OM) characteristics, removing humic substances while enhancing protein-derived (tryptophan) content. Although the humic-like component predominated in raw waters, microbially/protein-derived components were found to increase throughout the distribution networks of both systems. Disinfection byproducts (DBPs) such as total trihalomethane (TTHM) and total haloacetic acid (THAA) were prevalent in water distribution system (WDS)-A, which correlated with elevated OM content as well as re-chlorination with hypochlorite (NaOCl). Our field study revealed that THMs were more readily formed than HAAs during ClO 2 treatment. Unsurprisingly, chlorite concentrations were generally higher than chlorate concentrations during ClO 2 treatment, whereas (secondary) NaOCl disinfection contributed to higher chlorate production. Principal component analysis indicated that variable pH values and humic-like OM could affect Mn, As and Al concentrations at the consumer's tap. Our results suggested that although Mn concentrations complied with regulations at WDS-B and were below 50 μg/L after disinfection, Mn was oxidized and formed particulate Mn oxides capable of causing discoloration events depending on prevailing network physico-chemical and hydraulic conditions. Aluminium also appears to be released during hydraulic disturbances from extensive deposits within the network. Thermodynamic calculations showed that Mn-oxidation was strongly dependent upon the ORP, and to lesser extent the pH value. Collectively, our results confirm that ensuring the provision of safe drinking waters to consumers requires an understanding of water quality across entire distribution networks in addition to any routine post-treatment monitoring., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

The recovery of phosphorus (P) from wastewaters is a worthy goal considering the potential environmental and economic benefits. Flow-electrode capacitive deionization (FCDI), which employs flowable carbon electrodes instead of the static electrodes used in conventional CDI, has been demonstrated to be a promising P recovery technology. FCDI outperforms CDI and other competitive technologies in a number of aspects including (i) large salt adsorption capacity and (ii) extremely high water recovery rate. In this study, magnetic (Fe 3 O 4 impregnated) activated carbon particles were prepared and applied as FCDI electrodes. The magnetic carbon electrodes were found to have a strong affinity towards P, facilitating the selective adsorption of P to the magnetic particles through a ligand exhange mechanism. Continuous operation of the FCDI system could be achieved with only three minutes required to separate the electrode particles from the brine stream on application of an external magnetic field. A P-rich stream was produced on regeneration of the exhausted magnetic electrodes using alkali solution. We envision that the use of magnetic carbon enhanced flow-electrodes will pave the way for efficient operation of FCDI as well as the preferential recovery of P., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In this work, we investigate selective sorption of arsenic from simulated groundwaters at pH 8 by a redox-active polyvinylferrocene (PVF)-functionalized electrode using a modified double potential step chronoamperometry (DPSC) method. Our results show that effective and sustainable As(III) removal can be achieved at 0 V once the electrode is activated via anodic polarization. During activation, ferrocene (Fc) in PVF is oxidized to the ferrocenium ion (Fc + ) with the latter facilitating As(III) sorption and subsequent oxidation as well as As(V) sorption. The high affinity of Fc + to As and weak attraction to competing anions at 0 V ensure high selectivity of As over Cl - , SO 4 2- , and NO 3 - at concentrations typical of groundwaters. Following the removal process, efficient regeneration of the electrode is achieved at -1.2 V wherein Fc + is reduced to Fc thereby facilitating As desorption from the electrode surface. Our results further show that O 2 and associated generation of hydrogen peroxide during the regeneration step drive the oxidation of Fc to Fc + , thereby maintaining the constant generation of Fc + required to achieve As(III) removal in subsequent cycles. Our results show that 91.8 ± 0.6% of As(III) could be selectively removed from simulated groundwater over 10 cycles at an ultralow energy consumption of 0.12 kWh m -3 .

Frequent occurrence of harmful algal blooms (HABs) and red tides in freshwater and seawater poses serious threats to water treatment and drives the application of membrane-based technologies in algal separation. Despite the high removal efficiency of algal cells and their metabolites (e.g. organic matter and toxins) by membranes, the generation of concentrate and waste streams presents a major challenge. In this paper, we review the scenarios under which membrane-based processes are integrated with algal separation, with particular attention given to (i) drinking water production and desalination at low algal concentrations and (ii) cyanobacteria-laden water treatment/desalination. The concentrate and waste streams from backwashing and membrane cleaning in each scenario are characterised with this information facilitating a better understanding of the transport of algal cells and metabolites in membrane processes. Current strategies and gaps in managing concentrate and waste streams are identified with guidance and perspectives for future studies discussed in an Eisenhower framework., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Flow electrode capacitive deionization (FCDI) is a promising configuration for capacitive deionization due to its capability of continuous operation and achieving a relatively large salinity reduction. Due to the complexity of the multi-phase flow involved in FCDI, modeling FCDI system performance has been a challenge with no predictive FCDI model thus far developed. In this study, we developed an equivalent film-electrode (EFE) model for FCDI in which the flow electrodes are approximated as moving film electrodes that behave in a manner similar to conveyor belts. The EFE-FCDI model is validated using results from a series of FCDI experiments and then applied to elucidate the spatial variations of the key properties of the FCDI system and to resolve the contributions of different aspects of the system to energy consumption. The impact of activated carbon loading in the flow electrode and the feed and effluent target concentrations on the overall FCDI performance are also discussed based on model simulation. In summary, the EFE-FCDI model enhances our understanding of the system-level behavior of FCDI systems and can be employed for optimizing FCDI design and operation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

In the present study, radiolabelled formate was used as a probe compound in order to gain mechanistic insight into the catalytic ozonation process using a commercially available iron oxide-impregnated activated carbon catalyst. We simultaneously analysed the adsorptive and oxidative removal of formate in order to determine the contribution of the catalyst to adsorption and oxidant generation processes respectively. Our results show that the presence of the catalyst enhanced ozone decay as well as the rate and extent of formate oxidation at pH 3.0 compared to that observed in the presence of ozone alone as a result of oxidant generation via O 3 -Fe oxide interaction. A reduction in rate and extent of formate oxidation on addition of t-butanol and Cl - (known hydroxyl radical ( • OH) scavengers under acidic conditions) provides evidence that the oxidant generated during catalytic ozonation at pH 3.0 is • OH. Moreover, the oxidation of formate during catalytic ozonation mostly occurs at the solid-liquid interface and/or in bulk solution with adsorption playing no role in the overall oxidation process with this finding supported by the exceptionally high oxidation efficiency compared to the extent of adsorption observed when no O 3 was added. While catalytic ozonation was effective in formate oxidation at pH 3.0, the presence of the catalyst did not lead to an increase in either the rate or extent of formate oxidation at pH 7.3 and 8.5 suggesting that only protonated iron oxide surface sites generate strong oxidant(s) on interaction with O 3 . Based on our understanding of the processes operating during the ozonation and catalytic ozonation processes, a mathematical model has been developed that adequately describes the experimental results obtained here. Overall, this study shows that systematic measurement of ozone decay, removal of the parent compound as well as formation of the oxidized products under well controlled conditions are required for unequivocal elucidation of the mechanism of catalytic ozonation., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

While flow-electrode capacitive deionization (FCDI), one of the most popular CDI variants, possesses a number of advantages over conventional fixed-electrode CDI (e.g., large salt adsorption capacity, high flow efficiency and convenient management of the electrodes), challenges remain in constructing and operating an FCDI system such that it can operate continuously. Here we achieve effective continuous removal of salt from a brackish feed stream using flowing carbon electrodes which are regenerated in a closed-loop manner by using our previously introduced integrated FCDI/MF strategy. The performance of the FCDI/MF system is characterized over a two week period of operation with key factors influencing the desalination performance identified. Results show that the FCDI/MF system is capable of continuously desalinating brackish water (∼2 g L -1 ) to portable levels (<0.5 g L -1 ) whilst sustaining an extraordinary water recovery rate (∼92%) and relatively low energy consumption (∼0.5 kWh m -3 ). No obvious deterioration in performance or membrane fouling was observed during the 14-day operation. While the carbon particles used in the flow electrode exhibited only a minor increase in oxygen-containing groups over the 14 days of operation, a significant reduction in particle size was observed, likely as a consequence of the high-frequency collisions and associated friction between particles that occurred in the FCDI/MF system. Further studies regarding flowable electrode optimization, cell configuration design and process modelling are needed in order to realize the scale-up and practical implementation of this emerging technology., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

An energy recovery technique using a high-current bi-directional dc-dc converter for membrane capacitive de-ionization (mCDI) of brackish waters is described and it's performance assessed in a pilot-scale prototype. The energy recovery system is shown to reduce the energy consumption of the pilot-scale mCDI unit, powered by photovoltaics and with battery storage, by between 30 and 40%. Use of a stopped flow process also enables water recovery of up to 87%. The contributions to energy consumption in the system are quantified with the insights gained from this analysis enabling the selection of an optimum voltage range for desorption termination that maximizes the daily recovered energy. The experimental results demonstrate that energy usage by the mCDI process of lower than 0.4 kWh/m 3 is achievable with almost 40% of the energy supplied by the batteries recovered., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Flow-electrode capacitive deionization (FCDI) is an attractive variant of CDI with distinct advantages over fixed electrode CDI including the capability for seawater desalination, high flow efficiency and easy management of the electrodes. Challenges exist however in increasing treatment capacity with this attempted here through use of a membrane stack configuration. By comparison of standardised metrics (in particular, average salt removal rate (ASRR), energy normalized removed salt (ENRS) and productivity), results show that that an FCDI system with two pairs of ion exchange membranes had the highest efficiency in desalting a brackish influent (1000 mg L -1 ) to potable levels (∼150 mg L -1 ) at higher ASRR and ENRS. Further increase in the number of membrane pairs resulted in a decrease in current efficiency, likely as a result of the dominance of electrodialysis. Results of this study provide proof of concept that (semi-)continuous desalination can be achieved in FCDI at high energy efficiency (13.8%-20.2%) and productivity (> 100 L m -2  h -1 ) and, importantly, provide insight into possible approaches to scaling up FCDI such that energy-efficient water desalination can be achieved., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

While flow-electrode CDI is a promising desalination technology that has major advantages when the electrodes are operated in the short-circuited closed-cycle (SCC) mode, little attention has been paid to the water recovery rate, which, in the SCC mode, is determined by the need for partial replacement of the saline electrolyte of the flow electrodes. Results of this study show that an extremely high water recovery rate of ∼95% can be achieved when desalting a 1000 mg NaCl L -1 brackish influent to a potable level of 150 mg L -1 . The improved performance with regard to the electrical cost is related, at least in part, to the alleviated concentration polarization at the membrane/electrolyte interface during electrosorption. In effect, the current efficiency decreases with an increase in the water recovery rate. This finding is ascribed to inevitable co-ion leakage since the flow electrodes reject ions with the same charge. In addition, water transport across the ion exchange membranes also influences the water recovery rate. The effect of partial replacement of the saline electrolyte during (semi-)continuous operation requires particular consideration because the associated dilution of the carbon content in the flow electrodes results in a decrease in process performance.

Flow-electrode capacitive deionization (FCDI) is an emerging electrochemically driven technology for brackish and/or sea water desalination with merits of large salt adsorption capacity, high flow efficiency, and easy electrode management. While FCDI holds promise for continuous operation, there are very few investigations with regard to the regeneration/reuse of flowable electrodes and the separation of brine from electrodes with these operation prerequisites for real nonintermittent water desalination. In this study, we propose a novel module design to achieve these critical steps involving integration of an FCDI cell and a ceramic microfiltration (MF) contactor. Our investigations reveal that the brine discharge rate is the dominant factor for stable and efficient operation of the integrated module. Results obtained show that the integrated FCDI/MF system can be used to successfully separate brackish water (of salinities 1, 2 and 5 g L -1 ) into both a potable stream (<0.5 g L -1 ) and a brine stream (concentrated by 2-20 times) in a continuous manner with extremely high water recovery rates (up to 97%) and reasonable energy consumption. Another notable characteristic of the integrated system is the high thermodynamic energy efficiency (∼30%) with such efficiencies 4-5 times larger than those of conventional capacitive deionization units and comparable to reverse osmosis and electrodialysis systems achieving similar separation efficiencies. In brief, the results of studies described here indicate that continuous and efficient operation of FCDI is a real possibility and pave the way for scale-up of this emerging technology.

Constrained by low energy efficiency and ineffectiveness in As(III) removal under circumneutral pH conditions by many exsiting technologies, As(III) removal has become an issue. In this work we present proof of concept of a modified double potential step chronoamperometry (DPSC) method of As(III) oxidation and concomitant As(V) electro-sorption from aqueous solution. Results show that in situ anodic As(III) oxidation, As(V) electro-sorption, and As(V) electro-desorption are affected by aqueous pH with high oxidation and sorption/desorption rates observed at the elevated pH. We particularly show that effective As(III) oxidation and concomitant As(V) adsorption are related to (i) the rapid oxidation of the deprotonated species compared to the protonated species and (ii) stronger electrochemical interaction between the multicharged As(V) species and the electrodes. At 1.2 V and an electric energy consumption of 0.06 kWh m -3 , the total As concentration can be reduced from 150 to 15 μg L -1 using an electrochemical cell with electrode area of 10 × 8 cm 2 and electro-sorption time of 120 min. On the basis of the experimental results, we have developed a mathematical model to describe the kinetics and mechanism of arsenic removal by the modified DPSC method with this model of use in predicting, and potentially optimizing, process performance under various conditions.

Capacitive de-ionization (CDI) systems are well-known for their low energy consumption making them suitable for applications powered by renewable energy. In this study, CDI technology is, for the first time, integrated with a suitably-scaled, stand-alone, renewable power system comprising photovoltaic panels and battery storage. Guidelines for designing and sizing such power systems are proposed including determining electrode charging current, PV panels and battery capacity. A 1 kW pilot plant was designed, constructed and operated to verify the proposed guidelines. Using the pilot plant, the total energy consumption of the system has been evaluated with different electrode charging currents and influent flow rates and the relationship between these parameters analyzed. This analysis has enabled the development of practical design guidelines for bulk water treatment with MCDI electrodes. The results of this study show that use of photovoltaic-powered MCDI water treatment, particularly when combined with energy recovery, is competitive against more mature water-treatment technologies for particular applications and at particular locations., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

While flow-electrode capacitive deionization (FCDI) is a potential alternative to brackish and/or sea water desalination, there is limited understanding of both the fate of ions following migration across the ion exchange membranes and the mechanisms responsible for ion separation. In this study, we investigate the desalting performance of an FCDI system operated over a range of conditions. Results show that although ion transport as a result of electrodialysis is inevitable in FCDI (and is principally responsible for pH excursion in the flow electrode), the use of high carbon content ensures that a high proportion of the charge and counterions are retained in the electrical double layers of the flowing carbon particles, even at high charging voltages (e.g., 2.0 V) during the deionization process. Estimation of the portions of sodium and chloride ions adsorbed in the flow electrode after migration through the membranes suggests that the ongoing capacitive adsorption exhibits asymmetric behavior with the anodic particles demonstrating better affinity for Cl - (than the cathodic particles for Na + ) during electrosorption. These findings provide an explanation for the change in electrode properties that are observed under imperfect adsorption scenarios and provide insight into aspects of the design and operation of flow electrode pairs that is critical to achieving effective desalination by FCDI., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

While flow-electrode capacitive deionization (FCDI) is an emerging desalination technology, reduction in water hardness using this technology has so far received minimal attention. In this study, treatment of influents containing both monovalent and divalent cations using FCDI was carried out with flow-electrodes operated in short-circuited closed-cycle (SCC) configuration. Divalent Ca 2+ cations were selectively removed compared to monovalent Na + with the selectivity becoming dominant when the FCDI unit was operated at lower current densities and hydraulic retention times. Results showed that SCC FCDI operation was much more energy-efficient for brackish water softening compared to operation in isolated closed-cycle (ICC) mode, particularly with implementation of energy recovery. This finding was largely ascribed to (i) charge neutralization of the flow-electrodes in SCC configuration and (ii) regeneration of the active materials to maintain pseudo "infinite" capacity during electrosorption. In addition, mixing of the flow-electrodes in SCC operation significantly inhibited pH excursion in the flow-electrode with resultant alleviation of calcium precipitation on the carbon surface.

Capacitive deionization (CDI) is considered to be one of the most promising technologies for the desalination of brackish water with low to medium salinity. In practical applications, Faradaic redox reactions occurring in CDI may have both negative and positive effects on CDI performance. In this review, we present an overview of the types and mechanisms of Faradaic reactions in CDI systems including anodic oxidation of carbon electrodes, cathodic reduction of oxygen and Faradaic ion storage and identify their apparent negative and positive effects on water desalination. A variety of strategies including development of novel electrode materials and use of alternative configurations and/or operational modes are proposed for the purpose of mitigation or elimination of the deterioration of electrodes and the formation of byproducts caused by undesired side Faradaic reactions. It is also recognized that Faradaic reactions facilitate a variety of exciting new applications including i) the incorporation of intercalation electrodes to enhance water desalination or to selectively separate certain ions through reversible Faradaic reactions and ii) the use of particular anodic oxidation and cathodic reduction reactions to realize functions such as water disinfection and contaminant removal., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Removal of sulfate from water is an environmental challenge faced by many industrial sectors as most existing options are inefficient, costly or unsustainable. The situation is further complicated by the typical coexistence of other ions. In this work, the feasibility of sulfate removal from brackish water by single-pass constant-current membrane capacitive deionization (MCDI) under reverse-current desorption was investigated. Results revealed that sulfate is preferentially removed from the aqueous solution by MCDI compared to chloride. Equivalent circuits of the MCDI system during adsorption and desorption were proposed and the dynamic variation of cell voltage and charging voltage at different adsorption currents was satisfactorily elucidated. Optimization studies were conducted with attention given to discussing the effects of four operating parameters, i.e., adsorption current, pump flow rate, ending cell voltage and desorption current, on three performance indicators (i.e., water recovery, energy consumption and sorption ratio of sulfate to chloride) on the premise of maintaining the effluent sulfate concentration below the specified threshold of 300 mg L -1 . Water recovery-energy consumption mapping and sorption ratio of sulfate to chloride-energy consumption mapping indicated that the combination of a lower adsorption current and a lower matching pump flow rate which reduced the effluent sulfate concentration to 300 mg L -1 was more favorable in practical applications. An appropriately small ending cell voltage was advantageous while a trade-off between water recovery and energy cost was required in optimizing the desorption current., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Capacitive deionization (CDI) and membrane capacitive deionization (MCDI) are the most common cell architectures in the use of CDI for water treatment. In this work, the Faradaic reactions occurring in batch-mode CDI and MCDI processes were compared by investigating the variation of H 2 O 2 and dissolved oxygen (DO) concentrations, pH, conductivity and current during charging and discharging under different charging voltages. During charging, the H 2 O 2 concentration in CDI increased rapidly and then decreased while almost no H 2 O 2 was generated in MCDI due to the inability of oxygen to penetrate the ion exchange membrane. Chemical kinetic models were developed to quantitatively describe the variation of H 2 O 2 concentration and found to present satisfactory descriptions of the experimental data. The pH drop during charging could be partially explained by Faradaic reactions with proton generation associated with oxidation of the carbon electrodes considered to be the major contributor. The electrode potentials required for the induction of Faradaic reactions were analyzed with this analysis providing robust thermodynamic explanations for the occurrence of carbon oxidation at the anode and H 2 O 2 generation at the cathode during the ion adsorption process. Finally, electrochemically-induced ageing of the carbon electrodes and the resulting performance stability were investigated. The findings in this study contribute to a better understanding of Faradaic reactions in CDI and MCDI and should be of value in optimizing CDI-based technologies for particular practical applications., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

An innovative flow electrode comprising redox-active quinones to enhance the effectiveness of water desalination using flow-electrode capacitive deionization (FCDI) is described in this study. The results show that, in addition to carbon particle contact, the presence of the aqueous hydroquinone (H 2 Q)/benzoquinone (Q) couple in a flowing suspension of carbon particles enhances charge transfer significantly as a result of reversible redox reactions of H 2 Q/Q. Ion migration through the micropores of the flow electrodes was facilitated in particular with the desalination rate significantly enhanced. The cycling behavior of the quinoid mediators in the anode flow electrode demonstrated a relatively high stability at the low pH induced, suggesting that the mediator would be suitable for long-term operation.

Charging capacitive deionization (CDI) at constant voltage (CV) produces an effluent stream in which ion concentrations vary with time. Compared to CV, charging CDI at constant current (CC) has several advantages, particularly a stable and adjustable effluent ion concentration. In this work, the feasibility of removing fluoride from brackish groundwaters by single-pass constant-current (SPCC) CDI in both zero-volt and reverse-current desorption modes was investigated and a model developed to describe the selective electrosorption of fluoride and chloride. It was found that chloride is preferentially removed from the bulk solution during charging. Both experimental and theoretical results are presented showing effects of operating parameters, including adsorption/desorption current, pump flow rate and fluoride/chloride feed concentrations, on the effluent fluoride concentration, average fluoride adsorption rate and water recovery. Effects of design parameters are also discussed using the validated model. Finally, we describe a possible CDI assembly in which, under appropriate conditions, fluoride water quality targets can be met. The model developed here adequately describes the experimental results obtained and shows how change in the selected system design and operating conditions may impact treated water quality.

Capacitive deionization (CDI) is an emerging water desalination technology in which pairs of porous electrodes are electrically charged to remove ionic species from water. In this work, the feasibility of fluoride and nitrate removal from brackish groundwaters by batch-mode CDI was investigated. Initially, the effects of flow rate, initial fluoride concentration, and initial coexisting NaCl concentration on fluoride removal were studied. The steady-state fluoride concentration declined as the initial fluoride concentration decreased while initial NaCl concentration remained constant. Due to the competitive electrosorption between fluoride and chloride for limited pore surface sites, a higher initial chloride concentration resulted in a higher equilibrium dissolved fluoride concentration. A simplified one-dimensional transport model for dual anions was developed and found to reliably describe the dynamic process of removal of both fluoride and chloride ions in CDI cells over a range of well-defined operating conditions. Based on the ability of the model to describe fluoride removal, it was extended to description of nitrate removal from brackish groundwaters and also found to perform well. Thus, the approach to description of ion removal, at least in batch studies, appears robust and should assist in optimization of design and operating conditions such that optimal removal of trace ionic species is achieved even when high background concentrations of salt are present., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Silver nanoparticles (AgNPs) were successfully synthesized and impregnated on silica using chemical reduction methods. XPS and Ag K-edge XANES analysis revealed that the impregnation of AgNPs onto silica using a chitosan + sodium borohydride (NaBH4) method results in higher silver loading and Ag(0)/Ag(I) ratio compared to that obtained using NH3 + NaBH4/glucose methods. The effects of the dosage of chitosan on silver loading, Ag(I) release, and bactericidal activities of AgNP-impregnated silica were investigated, with results showing that, at high dosages of chitosan, Ag(I) released from AgNP-impregnated silica plays an important role in disinfection, while AgNP-mediated bactericidal action dominates at low dosages of chitosan. To further decrease the manufacturing cost, partially oxidized "black rice husk ash" containing substantial residual carbon was applied as AgNP support and found to lead to a greater degree of silver impregnation and to exhibit a longer disinfection lifetime than that of lower carbon content silica supports. On the basis of these findings, it is clear that considerable scope exists for careful optimization in the design and production of AgNP-based bactericidal materials for water treatment purposes.

The majority of small, remote communities within the Northern Territory (NT) in Central Australia are reliant on groundwater as their primary supply of domestic, potable water. Saturation indices for a variety of relevant minerals were calculated using available thermodynamic speciation codes on collected groundwater data across the NT. These saturation indices were used to assess the theoretical formation of problematic mineral-scale, which manifests itself by forming stubborn coatings on domestic appliances and fixtures. The results of this research show that 63% of the measured sites within the NT have the potential to form calcium carbonate (CaCO(3)) scale, increasing to 91% in arid, central regions. The data also suggests that all groundwaters are over-saturated with respect to amorphous calcium-bridged ferric-silica polymers, based on the crystalline mineral index (Ca(3)Fe(2)Si(3)O(12)), although the quantitative impact of this scale is limited by low iron concentrations. An assessment of possible low-cost/low-technology management options was made, including; lowering the temperature of hot-water systems, diluting groundwater with rainwater and modifying the pH of the source water. Source water pH modification (generally a reduction to pH 7.0) was shown to clearly alleviate potential carbonate-based scale formation, over and above the other two options, albeit at a greater technical and capital expense. Although low-cost/low-technology treatment options are unlikely to remove severe scale-related issues, their place in small, remote communities with minor scale problems should be investigated further, owing to the social, technical and capital barriers involved with installing advanced treatment plants (e.g. reverse osmosis) in such locations., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Mesoporous anatase (TiO(2)) was modified with silver (Ag) nanoparticles using a photoreduction method. Performance of the resulting TiO(2)-Ag nanocomposites for water purification was evaluated using degradation of Rhodamine B (RhB) and disinfection of Escherichia coli (E. coli) under ultraviolet (UV) irradiation. The composites with different Ag loadings were characterized using physical adsorption of nitrogen, X-ray diffraction, X-ray photoelectron spectroscopy and UV-Visible diffuse reflectance spectroscopic techniques. The results showed that metallic Ag nanoparticles were firmly immobilized on the TiO(2) surface, which improved electron-hole separation by forming the Schottky barrier at the TiO(2)-Ag interface. Photocatalytic degradation of RhB and inactivation of E. coli effectively occurred in an analogical trend. The deposited Ag slightly decreased adsorption of target pollutants, but greatly increased adsorption of molecular oxygen with the latter enhancing production of reactive oxygen species (ROSs) with concomitant increase in contaminant photodegradation. The optimal Ag loadings for RhB degradation and E. coli disinfection were 0.25 wt% and 2.0 wt%, respectively. The composite photocatalysts were stable and could be used repeatedly under UV irradiation., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Hematite (10 mg of Fe/L) floc-humic acid assemblages have been formed at pH 4 either by first aggregating hematite particles with salt (100 mM KCl) and then adding humic acid (salt-particle-organic or SPO assemblages) or by suspending the hematite particles in humic acid solutions and then adding salt to induce aggregation (organic-particle-salt or OPS assemblages). The behavior of these assemblages upon deposition on microfiltration (MF) membranes has then been investigated. In the OPS case, the fractal dimension (dF) of the assemblages formed varied dramatically depending upon the extent of charge neutralization by added fulvic acid with dF values typical of diffusion-limited cluster aggregates at low (0.1-0.2 mg/L) humic acid concentrations and dF values typical of reaction-limited cluster aggregates either in the absence of humic acid or concentrations greater than 0.4-0.6 mg/L. In the SPO case, dF values on the order of 2.1 were initially observed and were found to decrease to around 1.8-1.9 for humic acid concentrations greater than 0.6-0.8 mg/L. OPS assemblages with low fractal dimensions were found to be highly compressible once deposited on MF membranes with significantly higher specific cake resistances than was the case for SPO assemblages at transmembrane pressures of 50 kPa and above. These results highlight the importance of both the choice of coagulant (e.g., preformed vs formed in situ) and the transmembrane pressure to which a membrane filtration process might be allowed to rise prior to removal of the fouling layer.

Addition of nanoparticulate zero-valent iron (nZVI) to oxygen-containing water results in oxidation of organic compounds. To assess the potential application of nZVI for oxidative transformation of organic contaminants, the conversion of benzoic acid (BA) to p-hydroxybenzoic acid (p-HBA) was used as a probe reaction. When nZVI was added to BA-containing water, an initial pulse of p-HBA was detected during the first 30 min, followed by the slow generation of additional p-HBA over periods of at least 24 h. The yield of p-HBA increased with increasing BA concentration, presumably due to the increasing 'ability of BA to compete with alternate oxidant sinks, such as ferrous iron. At pH 3, maximum yields of p-HBA during the initial phase of the reaction of up to 25% were observed. The initial rate of nZVI-mediated oxidation of BA exhibited a marked reduction at pH values above 3. Despite the decrease in oxidant production rate, p-HBA was observed during the initial reaction phase at pH values up to 8. Competition experiments with probe compounds expected to exhibit different affinities for the nZVI surface (phenol, aniline, o-hydroxybenzoic acid, and synthetic humic acids) indicated relative rates of reaction that were similar to those observed in competition experiments in which hydroxyl radicals were generated in solution. Examination of the oxidizing capacity of a range of Fe0 particles reveals a capacity in all cases to induce oxidative transformation of benzoic acid, but the high surface areas that can be achieved with nanosized particles renders such particles particularly effective oxidants.

The ability of a variety of nanofiltration and reverse osmosis membranes to retain the natural hormone estrone are examined here as a function of solution conditions. While size exclusion dominates retention with the tighter membranes, both size exclusion and adsorptive effects appear to be instrumental in maintaining high retention on nanofiltration membranes that otherwise exhibit relatively low ion retentions. These adsorptive effects may be driven by hydrogen bonding between estrone and the membrane. Electrostatic attraction appears to aid retention with an apparent slight decrease in retention at high NaCl concentrations. Deprotonation of estrone leads to a significant decrease in retention, most likely as a result of the effect of strong electrostatic repulsive forces decreasing the proximity of the negatively charged estrone to the negatively charged membrane surface and thus lowering the potential for adsorptive retention. This deprotonation effect is absent for tight RO membranes. The results reported here indicate that while open nanofiltration membranes may be effective in retaining estrone under some conditions, the extent of retention may be very susceptible to maintenance of adsorptive capacity at the membrane surface and depend on solution chemistry.

The degradations of phenol in air-equilibrated aqueous media were investigated using coupled sonochemistry and Fenton's reagent for a variety of operating conditions. The decomposition yields of phenol (100-500 microM) were substantially enhanced due to the addition of Fenton's reagent (FeSO4 into the solutions irradiated at 608 kHz with 30 W and with reaction temperature 25 +/- 1 degree C. The decomposition process follows a pseudo-first-order reaction kinetics with respect to phenol concentration, and the rate constant of phenol disappearance observed increases by approximately 2-3 fold when FeSO4 was between 400 and 1000 M at pH = 3.5 +/- 0.2 (controlled by phosphate buffer) as a result of Fe(II) reaction with H2O2 enabling further production of additional OH* radicals. The results obtained here also indicate that the decomposition rate of aqueous phenol using coupled ultrasound and Fenton's reagent was strongly dependant on the initial concentration of reactant, the amount of Fe(II) added as well as the pH of solution. The optimal operating conditions for 100-500 microM phenol decomposition in the air-equilibrated aqueous media were obtained when FeSO4 concentration was between 400 and 1,000 microM with pH in the range 3.5-4.2 under ultrasonic irradiation at 608 kHz, 30 W and reaction temperature 25 +/- 1 degree C.

Adsorption of the trace contaminant estrone, a natural hormone and commonly abundant in surface waters and in treated as well as untreated wastewaters, to eight commercial nanofiltration and reverse osmosis membranes was investigated under well defined conditions. Experiments were conducted in stainless steel stirred cells by spiking trace levels (100 ng x L(-1)) of estrone into five different matrices, namely MilliQ water, a bicarbonate solution, synthetic natural waters containing natural organics, and secondary effluent. Results show that estrone is adsorbed to the membranes to varying degrees with extent of adsorption influenced by the feedwater composition with different mechanisms of association controlling adsorption to different membrane types. Increase in membrane resistance is typically observed to result in decrease in extent of estrone adsorption.

This paper compares the membrane processes available for water treatment. Membranes have the advantage of currently decreasing capital cost, a relatively small footprint compared to conventional treatment, generally a reduction in chemicals usage and comparably low maintenance requirements. Three membrane processes applicable to water treatment, micro- (MF), ultra- (UF), and nanofiltration (NF), are compared in terms of intrinsic rejection, variation of rejection due to membrane fouling and increase in rejection by ferric chloride pretreatment. Twelve different membranes are compared on the basis of their membrane pore size which was calculated from their molecular weight cut-off. A pore size of < 6 nm is required to achieve substantial (> 50%) organics removal. For a fouled membrane this pore size is about 11 nm. UV rejection is higher than DOC rejection. Coagulation pretreatment allows a higher rejection of organics by MF and UF and the cut-off criterion due to initial membrane pore size is no longer valid. A water quality parameter (WQP) is introduced which describes the product water quality achieved as a function of colloid, DOC and cation rejection. The relationship between log (pore size) and WQP is linear. Estimation of membrane costs as a function of WQP suggests that open UF is superior to MF (similar cost at higher WQP) and NF is superior to tight UF. Chemical pretreatment could compensate for the difference between MF and UF. However, when considering chemicals and energy costs, it appears that a process operated at a higher energy is cheaper at a guaranteed product quality (less dependent on organic type). This argument is further supported by environmental issues of chemicals usage, as energy may be provided from renewable sources.