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With growing environmental consciousness, biomaterials (BMs) have garnered attention as sustainable materials for the adsorption of hazardous water contaminants. These BMs are engineered using surface treatments or physical alterations to enhance their adsorptive properties. The lab-scale methods generally employ a One Variable at a Time (OVAT) approach to analyze the impact of biomaterial modifications, their characteristics and other process variables such as pH, temperature, dosage, etc., on the removal of metals via adsorption. Although implementing the adsorption procedure using BMs seems simple, the conjugate effects of adsorbent properties and process attributes implicate complex nonlinear interactions. As a result, artificial neural networks (ANN) have gained traction in the quest to understand the complex metal adsorption processes on biomaterials, with applications in environmental remediation and water reuse. This review discusses recent progress using ANN frameworks for metal adsorption using modified biomaterials. Subsequently, the paper comprehensively evaluates the development of a hybrid-ANN system to estimate isothermal, kinetic and thermodynamic parameters in multicomponent adsorption systems.

The COVID-19 pandemic highlighted public awareness of airborne disease transmission in indoor settings and emphasized the need for reliable air disinfection technologies. This increased awareness will carry in the post-pandemic era along with the ever-emerging SARS-CoV variants, necessitating effective and well-defined protocols, methods, and devices for air disinfection. Ultraviolet (UV)-based air disinfection demonstrated promising results in inactivating viral bioaerosols. However, the reported data diversity on the required UVC doses has hindered determining the best UVC practices and led to confusion among the public and regulators. This article reviews available information on critical parameters influencing the efficacy of a UVC air disinfection system and, consequently, the required dose including the system's components as well as operational and environmental factors. There is a consensus in the literature that the interrelation of humidity and air temperature has a significant impact on the UVC susceptibility, which translate to changing the UVC efficacy of commercialized devices in indoor settings under varying conditions. Sampling and aerosolization techniques reported to have major influence on the result interpretation and it is recommended to use several sampling methods simultaneously to generate comparable and conclusive data. We also considered the safety concerns and the potential safe alternative of UVC, far-UVC. Finally, the gaps in each critical parameter and the future research needs of the field are represented. This paper is the first step to consolidating literature towards developing a standard validation protocol for UVC air disinfection devices which is determined as the one of the research needs.

Per- and polyfluoroalkyl substances (PFAS) are potential human carcinogens that have been ubiquitously detected in drinking water sources. Ion exchange (IX) resins offer promising potential for the treatment of water sources impacted by high natural organic matter (NOM) and PFAS concentrations. Several kinetic models such as the pseudo-first-order (PFO), pseudo-second-order (PSO) and intraparticle diffusion (ID) have been investigated to examine the PFAS uptake kinetics on IX resins. However, the kinetic parameters are strongly impacted by the sorption test conditions, especially the sorbate-to-sorbent ratio, which were highly variable in past studies, resulting in several discrepancies when comparing published data. This study examined the use of the homogenous surface diffusion model (HSDM) coupled with the equivalent background concentration (EBC) model as an approach to describe competitive uptakes of regulated long- and short-chain PFAS, NOM, and inorganic ions (such as sulphate and nitrate) with IX resins. Kinetic studies confirmed surface diffusion as the rate-limiting step in NOM-rich waters (Biot number >30), while the multicomponent equilibrium model demonstrated that the initial NOM concentration of approximately 0.35–0.95 μmol L−1 (C0 = 5 mg C per L) competed with PFAS for active exchange sites. More importantly, the HSDM (R2 > 0.98)/EBC (R2 > 0.95) models provided an adequate fit to describe PFAS removal in a recycled wastewater.

Zwitterionic per- and polyfluoroalkyl substances are increasingly detected in aquatic environments. The magnitude of their concentration and increased frequency of detection worldwide raise questions on their presence in drinking water and associated health risk. Scientific knowledge on the identification of treatment technologies to effectively capture such zwitterionic PFAS from contaminated water sources remains largely unknown. In this study, we investigated the application of anionic organic scavenger ion exchange (IX) resins (A860), nonionic IX resins (XAD 4 and XAD 7), PFAS-specific resins (A694 and A592), and Ti

Ion exchange (IX) process is increasingly used as a cost-effective treatment for the removal of natural organic matter (NOM) from drinking water. However, fundamental studies under the influence of variable NOM characteristics and inorganic anions have often been overlooked. This is important given NOM characteristics (such as charge density and molecular weight) and inorganic anions concentrations are geographically and seasonally variable. We examined the performance of a strongly basic IX resin for the simultaneous removal of NOM, inorganic ions and micropollutants (Per- and polyfluoroalkyl substances (PFAS) and algal toxins), from different surface and recycled waters. The results indicated >70% removal of NOM for ∼20,000 Bed Volumes (BV) with an uptake of NOM fractions following the order of their respective charge densities. IX pore blockage and consequent site reduction was observed in the presence of higher molecular weight NOM fractions (breakthrough ∼7,000 BV). Moreover, NOM and inorganic ions breakthrough corresponded to ∼85–90% site occupancy (in meq) in the absence of pore blocking compounds. IX also provided simultaneous removal of inorganic ions (>90%) and charged micropollutants. Complete removals of Microcystin-LR and multiple long- and short-chained PFAS were achieved at environmentally relevant concentrations with dosages of 1,000 mg/L (or 4.5 mL/L) or higher.

Cyanobacterial blooms are a growing concern around the world. A feasible approach for small treatment plants fed by sources contaminated with cyanobacteria is vacuum UV (VUV). VUV is a promising advanced oxidation process used to treat water impacted by cyanobacterial blooms, with potential applicability in small and remote communities because of its simplicity. In this work, water samples from three Canadian lakes periodically affected by cyanobacteria were used to assess the impact of natural and algal organic matter (NOM/AOM) on treatment with VUV. NOM and AOM were characterized before and after VUV treatment by size exclusion chromatography (SEC) and fluorescence emission–excitation matrix (FEEM). FEEM spectra were analyzed with the parallel factor analysis (PARAFAC) tool. As a result, we found seven principal components describing the whole dataset. Disinfection by-product (DBP) formation after VUV treatment was analyzed and trihalomethanes (THM) yield was calculated. THM yield increased by 15–20% after VUV treatment. Regarding DBP formation and NOM/AOM fractions from SEC, we found that humic substances are the most important fraction causing the increase in DBP formation with at least 3 times higher yield than the other fractions: biopolymers, building blocks, low weight molecular acids and neutrals.

This study investigates an electrochemical approach for the treatment of water polluted with per- and poly-fluoroalkyl substances (PFAS), looking at the impact of different variables, contributions from generated radicals, and degradability of different structures of PFAS. Results obtained from a central composite design (CCD) showed the importance of mass transfer, related to the stirring speed, and the amount of charge passed through the electrodes, related to the current density on decomposition rate of PFOA. The CCD informed optimized operating conditions which we then used to study the impact of solution conditions. Acidic condition, high temperature, and low initial concentration of PFOA accelerated the degradation kinetic, while DO had a negligible effect. The impact of electrolyte concentration depended on the initial concentration of PFOA. At low initial PFOA dosage (0.2 mg L

The City of White Rock, Canada has been facing challenges of elevated concentrations of arsenic and manganese in its drinking water supply. A pilot water treatment study was conducted to explore effective contaminant removal solutions for human health risk mitigation. The arsenic and manganese removal performance of four treatment processes, including ozonation-manganese greensand filtration (OSF), OSF-iron-based granular media adsorption (OSFIA), the Burgess Iron Removal Method (BIRM), and BIRM-iron-based granular media adsorption (BIA) were evaluated. The non-cancer health risks and the incremental lifetime cancer risks (ILCR) posed by arsenic in different water sources were also assessed. The results show that OSFIA treatment achieved the highest arsenic and manganese removal. An average arsenic removal rate of 68.5% (initial concentration = 9.3 μg/L) was observed using OSFIA during two months of treatment, while manganese (initial concentration = 133.9 μg/L) can be completely removed. The arsenic removal was mainly be attributed to the adsorption of iron-based granular media. The mean values of non-cancer health risks of arsenic exposure due to oral intake of treated water were identified to be lower than the critical threshold for different age groups. In addition, the probability of critical ILCR occurrence can be greatly reduced. Based on the results from the pilot study, OSFIA was selected to construct a full-scale water treatment plant. Arsenic and manganese concentrations in the effluent from the plant can be reduced to a low-to-undetectable level, achieving negligible health risks to the residents of the city.

Quantifying total organic fluorine (TOF) in water is vital in monitoring the occurrence and persistence of all fluorine-containing organic compounds in the environment, while currently most studies focus on analyzing individual fluorine-containing organic compounds. To fill the technology gap, we herein proposed to convert TOF completely into fluoride with vacuum ultraviolet (VUV) photolysis, followed by analysis of fluoride with ion chromatography. Results showed that the tailored VUV photoreactor achieved satisfying recoveries of fluorine from ten model TOF compounds not only in ultrapure water (83.9 ± 2.0% to 109.4 ± 0.8%) but also in real water samples (92.1 ± 1.0%-106.2 ± 15.7%). Unlike other ultraviolet-based processes that favor alkaline conditions, this VUV process preferred either neutral or acidic conditions to defluorinate selected compounds. While the mechanisms remain to be explored in the future, it has been evidenced that the photo-degradation and photo-defluorination rates of these TOF compounds varied significantly among compounds and operation conditions. The method obtained a method detection limit (MDL) of 0.15 μg-F/L, which is lower than the MDLs of many other TOF analytical methods, along with excellent calibration curves for concentrations ranging from 0.01 to 10.0 mg-F/L. Notably, minimizing fluoride in sample prior to photoconversion was necessary to avoid subtraction-induced errors for TOF measurement, especially when the fluoride/TOF ratio was high. The robust VUV is also green for sample pretreatment due to its unreliance of chemicals or additives.

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.

Biological ion exchange (BIEX) refers to operating ion exchange (IX) filters with infrequent regeneration to favor the microbial growth on resin surface and thereby contribute to the removal of organic matter through biodegradation. However, the extent of biodegradation on BIEX resins is still debatable due to the difficulty in discriminating between biodegradation and IX. The objective of the present study was to evaluate the performance of BIEX resins for the removal of organic micropollutants and thereby validate the occurrence of biodegradation. The removals of biodegradable micropollutants (neutral: caffeine and estradiol; negative: ibuprofen and naproxen) and nonbiodegradable micropollutants with different charges (neutral: atrazine and thiamethoxam; negative: PFOA and PFOS) were respectively monitored during batch tests with biotic and abiotic BIEX resins. Results demonstrated that biodegradation contributed to the removal of caffeine, estradiol, and ibuprofen, confirming that biodegradation occurred on the BIEX resins. Furthermore, biodegradation contributed to a lower extent to the removal of naproxen probably due to the absence of an adapted bacterial community (Biotic: 49% vs Abiotic: 38% after 24 h batch test). The removal of naproxen, PFOS, and PFOA were attributable to ion exchange with previously retained natural organic matter on BIEX resins. Nonbiodegradable and neutral micropollutants (atrazine and thiamethoxam) were minimally (6%–10%) removed during the batch tests. Overall, the present study corroborates that biomass found on BIEX resins contribute to the removal of micropollutants through biodegradation and ion exchange resins can be used as biomass support for biofiltration.

Microcystin-LR (MCLR) is the most commonly encountered toxic microcystin variant. MCLR is usually present along with common surface water constituents such as inorganic ions and natural organic matter (NOM) which compete with MCLR for active sites during ion exchange (IX) process. Consequently, development of a multicomponent competitive model is essential for practical IX applications. This is critically important given that the NOM characteristics (charge density and molecular weight distribution) and inorganic ions concentrations are spatially variable and can change seasonally. In the present study, a systematic study was carried out into the multicomponent interactions of IX resin with inorganic ions and NOM during the MCLR removal process. This involved evaluation of MCLR removal in a single component system (i.e., MCLR only), a dual component system (MCLR and one other contaminant such as NOM), and a multiple component system (MCLR with NOM and different inorganic ions present in natural waters). A comprehensive understanding of the dynamic adsorption behavior showed that the experimental data for single component systems agree well with a Freundlich isotherm. For multicomponent interactions, the Equivalent Background Concentration (EBC) model which is derived from the Ideal Adsorption Solution Theory (IAST) provided the best correlation with the experimental data in natural waters. The concentrations of competing NOM and inorganic ions estimated by the EBC model were

The City of White Rock purchased the water utility on October 30, 2015, from EPCOR Utilities Inc. The City of White Rock‘s water utility provides safe and clean drinking water to its residents. The...

Ultraviolet light-emitting diode (UV-LED) is an emerging UV source with many special features due to the nature of semiconductor devices. One such feature is wavelength diversity that does not exist in conventional mercury based UV lamps, which provides opportunities to selectively combine multiple wavelengths for potentially additional effects by UV-LEDs. In this work, the inactivation of different microorganisms in water was investigated by UV-LEDs wavelength combinations. Various wavelength combinations, including simultaneous and sequential exposures, in different UV ranges such as UVC, UVB and UVA, were examined. These combinations were applied to the inactivation of indicator bacterium E. coli and coliphage MS2 in water. The results showed the effect of UV-LEDs multiple wavelengths depends on which wavelengths (UVC, UVB and UVA) are combined and the manner that different wavelengths (simultaneous, sequential) are used. Also, different microorganisms (bacteria, virus) respond differently to wavelength combinations. Combinations of UVC/UVB always achieved additive effect on microorganisms inactivation due to the same photochemical reaction induced by UVC/UVB on DNA. Combining UVA with UVC/UVB simultaneously or applying UVA after UVC/UVB reduced the inactivation of bacterium E. coli due to DNA repair and photoreactivation effect of UVA. However, applying extended UVA exposure before UVC significantly improved E. coli inactivation. For virus MS2 inactivation, only additive effect was observed under various wavelength combinations. This study presented a comprehensive work on UV-LEDs wavelength combinations, which is of significance on the application of UV-LEDs for water disinfection.

Cyanobacterial blooms are becoming a serious challenge across the globe due to changing climate and rainfall patterns as a consequence of human activities. In the present study, the fundamental interactions involved during the removal of Microcystin-LR (MCLR), one of the most commonly occurring cyanobacterial toxins, were investigated by employing strongly basic anion exchange (IX) resins. Several factors including the stoichiometric coefficients, competitive fractions and solute affinities were determined under various concentrations of inorganic ions and natural organic matter. The results indicated that suphates were the most competitive fractions with high affinity (α (affinity coefficient) values ~ 9) followed by nitrates (α ~ 4.7) and NOM fractions (α ~ 4.5, p 0.05). The Equivalent Background Concentration Mode (EBC), that arises from the Ideal Adsorption Solution Theory (IAST), indicated a competitive fraction of ~2 μeq/L NOM, which approximates to10% of the initial NOM concentrations, indicating a small fraction of the NOM resulting in the competitive effect. Further, studies with natural surface waters indicated that the MCLR uptake could be modeled using the IAST-EBC model and the IX resin could simultaneously removal of90% of NOM, inorganic ions and MCLR at resin dosages of 3.6 meq/L or higher.

One of the factors affecting overbreak or slough of the roof and walls of underground stopes, causing unplanned dilution is blast vibration. The amount of damage caused by earth vibration can be measured in terms of peak particle velocity (PPV). In this study, in order to investigate the effects of blast vibration on the occurrence of unplanned dilution, 72 three-component records acquired upon 24 blasts were obtained at underground Venarch Manganese Mines. Once finished with data analysis, scale distance was used to propose an exponential equation for predicting PPV based on the cubic root of the charge weight per delay. Then, the effect of blast vibration on walls and roof of the stope was examined on 24 different explosions, dilution values were recorded at various scaled distances to the face, and the relationship between them was determined. Equivalent linear overbreak/slough (ELOS) was used to determine dilution, with cavity monitoring system (CMS) being used to calculate it. Then a practical diagram was presented to predict the boundary of the dilution area from the explosion. Finally, The relationship between the amount of ELOS against the PPV was presented and it was determined if the PPV was fewer than or equal to 6.73 mm / s, the dilution will not occur.

We report the electrosynthesis of Fe(VI) in a flow reactor operating in batch recirculation mode at neutral conditions using boron doped diamond (BDD) and Fe(III). The impact of several variables including current density (5–15 mA cm−2), pH (5–9), temperature (15–30 °C), and the concentration of the dissolved iron salts (3–30 mM) on the production of ferrates in the reactor were examined. In addition, the impact of a membrane in the reactor was evaluated, showing an increase on Fe(VI) generation rate and current efficiency. The rate constants for ferrate generation are affected by the initial concentration of Fe(III) and current density, and to a lesser extent by the temperature. Results show that the use of this type of reactor leads to higher current efficiency in comparison with a batch reactor, exceeding 90% for the first 25 minutes using 30 mM of Fe(III) and 10 mA cm−2. The recirculating reactor results were successfully interpreted by a simple model which considered first-order kinetics for Fe(VI) degradation.

Perfluoroalkyl substances (PFAS) are drinking water contaminants of emerging concern due to their persistence in the environment and tendency to bio-accumulate. Although anionic ion exchange (IX) resins offer a cost-effective alternative for removing PFAS from natural waters, the studies on PFAS removal by IX under the influence of variable characteristics of the organic compounds present in the natural water sources, have been overlooked. This is critically important given that the organic matter (OM) characteristics are spatially variable and can change seasonally. In the present study, a strongly basic anion exchange resin was used to remove two of the most persistent PFAS, namely per-fluorooctanoic acid (PFOA) and per-fluorooctanesulfonic acid (PFOS). Factors influencing the uptake behavior included the PFOA and PFOS concentrations, resin dosage, and background OM characteristics, more specifically the charge density and molecular weight distribution of source water OM. The equivalent background concentration (EBC) was employed to evaluate the competitive uptake between OM and PFAS. Experimental data were fitted to different mathematical and physical models to evaluate the competitive interactions. Further, IX was able to achieve complete PFAS removal with simultaneous >60% dissolved organic carbon (DOC) removal. Evidence of size exclusion and pore blockage was also observed in the presence of humics and larger molecular weight organic fractions. Results of this study indicate that IX exhibits great potential for simultaneous OM and PFAS removal for drinking and potable water reuse applications.

The increasing frequency with which cyanobacterial blooms are affecting sources of drinking water is a growing concern worldwide. Such events are usually responsible for the presence of cyanotoxins as well as taste and odor (T&O) compounds. Vacuum UV (VUV) is a promising advanced oxidation process used to treat water impacted by cyanobacterial blooms, with potential applicability in small and remote communities because of its simplicity. Here, we present the performance of a VUV process, in both a collimated beam reactor (CBR) and a pilot scale flow-through reactor, using two cyanobacterial-laden Canadian source waters with different inorganic and natural organic matter contents. First, VUV performance was assessed by comparing the removal of microcystin-LR (MC-LR), 2-methylisoborneol (MIB), and geosmin (GSM). The average kinetic rates obtained in the CBR case were 2.9 × 10−3 cm2 mJ−1 for MIB and GSM and 6.6 × 10−3 cm2 mJ−1 for MC-LR. Under bloom conditions, removals of 40–60% for T&O compounds and MC-LR were achieved in the flow-through reactor. It was observed that although MC-LR, GSM, and MIB were impacted by VUV treatment, the removals achieved may not be sufficient to completely eliminate toxicity and T&O at the tested fluences (up to 400 mJ cm−2). In addition, we observed a 20% increase in disinfection by-products (DBPs), on average. Hence, achieving high MC-LR, MIB, and GSM removals with VUV may cause the generation of more DBPs.

MXenes are a new type of two-dimensional (2D) material which are rapidly gaining traction for a range of environmental, chemical and medical applications. MXenes and MXene-composites exhibit high surface area, superlative chemical stability, thermal conductivity, hydrophilicity and are environmentally compatible. Consequently, MXenes have been successfully employed for hydrogen storage, semiconductor manufacture and lithium ion batteries. In recent years, MXenes have been utilized in numerous environmental applications for treating contaminated surface waters, ground and industrial/ municipal wastewaters and for desalination, often outperforming conventional materials in each field. MXene-composites can adsorb multiple organic and inorganic contaminants, and undergo Faradaic capacitive deionization (CDI) when utilized for electrochemical applications. This approach allows for a significant decrease in the energy demand by overcoming the concentration polarization limitation of conventional CDI electrodes, offering a solution for low-energy desalination of brackish waters. This article presents a state-of-the-art review on water treatment and desalination applications of MXenes and MXene-composites. An investigation into the kinetics and isotherms is presented, as well as the impact of water constituents and operating conditions are also discussed. The applications of MXenes for CDI, pervaporation desalination and solar thermal desalination are also examined based on the reviewed literature. The effects of the water composition and operational protocols on the regeneration efficacy and long-term usage are also highlighted.

Per- and poly-fluoroalkyl substances (PFAS) represent a large family of anthropogenic organic compounds with a wide range of industrial and commercial applications. PFAS have become a global concern due to their toxicity and bio-accumulative properties. PFAS species have been ubiquitously detected in natural waters, wastewaters, sludge, and aquatic and terrestrial species which are anionic, zwitterionic and neutral. The ion exchange (IX) process for PFAS removal is an efficient technology for the remediation of PFAS-laden surface, ground and effluent wastewaters. This approach is more effective towards eliminating emerging short-chain PFAS which are not removed by carbon-based adsorption processes. This article presents a state-of-the-art review of PFAS removal from water via IX process. The evaluation and comparison of various IX resins in terms of kinetics and isotherms is presented. Literature data indicates that IX isotherm uptake capacity for perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) can range up to 5 mmol/g on commercially available IX resins such as IRA 958 and IRA 67. The mechanism involved in the PFAS uptake process, such as diffusion, electrostatic interactions and hydrophobic effects are discussed. The effects of the eluent variability on the regeneration efficacy are also highlighted and the effect of single-use vs reuse for newly developed PFAS-specific IX resins are also examined based on the reviewed literature.

The impact of chloride ion and chlorine radical on the formation of nitrite was investigated under Vacuum-UV (VUV) photolysis of nitrate contaminating water. An increase in chloride concentration reduced nitrite formation in part due to the relatively high VUV absorption of chloride. The use of various radical scavengers, such as acetate and acetone, helped delineate the specific roles of hydroxyl radical (HO) and chlorine radical (Cl) in oxidation and VUV photolysis of nitrate, and the subsequent formation of nitrite. HO reduced nitrite formation due to its high reaction rate constant with nitrite. Nitrite formation in both chloride and dissolved organic carbon (DOC) containing solution depended primarily on their relative concentrations. Carbamazepine (CBZ) was also used to analyze the effect of Cl on both the degradation of CBZ and the formation of nitrite. Cl showed to significantly increase the degradation of CBZ, but it had little impact on the formation of nitrite. This paper, utilizing detailed experimental data combined with kinetic modeling and mechanistic analysis of VUV photolysis in the presence of chloride and nitrate, provides the necessary scientific guidance towards more effective and optimized applications of VUV technology for drinking water treatment.

Treatment technologies such as ion exchange (IX) process exhibit promising potentials for the removal of toxic per- and poly-fluoroalkyl substances (PFAS) from natural waters. In recent years, industries have started manufacturing PFAS-specific resins which are typically operated in a single use-and-dispose mode until exhaustion. However, this increases the resin demand and the consequent operational cost and environmental burden of the IX process. In this study, the performance of a PFAS-specific resin (A592) was compared with that of a regenerative organic scavenger resin (A860) which is traditionally employed for dissolved organic matter (DOM) and micorpollutant removal. Comparative studies were performed to examine the removal of multiple long- and short-chain carboxylic, sulfonic, precursor and emerging PFAS (including GenX) from synthetic and natural waters. The A592 resin exhibited faster uptake kinetics for PFAS while simultaneously removing 10–15% of DOM. The A860 resin removed ~60–70% of DOM; however, it required approximately 3-fold higher contact times for achieving the same degree of PFAS removal when compared to the PFAS-specific resin. The resin breakthrough (Ctreated (PFAS) > 70 ng/L) was observed around 125,000 ± 5000 bed volumes (BVs) for the PFAS-specific resin (via multiple loading tests), while it ranged between 15,000–27,000 BVs for the organic scavenger. Yet, a mass balance on PFAS and DOM removal indicated ~90–98% site saturation (in milli-equivalents (meqs)) on both IX resins before exhaustion. More importantly, the regenerated organic scavenger resin (A860) exhibited PFAS and DOM removal capabilities for longer operational BVs when compared to A592 operated in a single-use-mode in natural waters.

We present the first study investigating optimized regeneration strategies for anionic ion exchange (IX) resins during the removal of persistent per- and poly-fluoroalkyl substances (PFAS, including GenX) from surface and treated wastewater effluents. IX regeneration studies are of critical importance from environmental perspectives. Specifically, the knowledge is essential for water utilities who presently operate IX (for PFAS removal) in a single use-and-dispose mode. In this study, legacy PFAS such as PFOA/PFOS were tested along with other harmful short-chained PFAS (PFBA/PFBS) and other toxic perfluorinated substitutes (GenX). Studies were performed on synthetic water (spiked with Suwannee River Natural Organic Matter (SRNOM), Fulvic Acid (SRFA) and Humic Acid (SRHA)), surface water, and wastewater effluents, and the regeneration was performed in batch stirred reactors. The resin service life with and without regeneration was investigated in the presence of background organic matter. In ultra-pure waters, all PFAS (C0 ∼10 μg/L, concentrations similar to that of natural waters) were effectively removed for >100,000 Bed Volume (BV) of operation. This was reduced to ∼23,500 BV in the presence of SRNOM (C0 = 5 mg C/L), 20,500 BV in SRFA and 8500 BV in SRHA, after which the saturated resins required regeneration. More importantly, all resin breakthrough (PFAS> 70 ng/L) corresponded to > 90% resin site saturation (in meqs), an essential information for optimizing IX loading. The competitive dissolved organic matter (DOM) fractions were estimated to be approximately 5–9% of the initial DOC, as estimated by the IAST-EBC model. Finally, it was identified that IX regeneration efficiency improved with increasing brine contact time but effectiveness plateaued for brine concentrations above 10% (W/V). Nonetheless, a regeneration with 10% NaCl solution with a contact time of 2 h was found to be optimal for IX operations in synthetic and natural waters. Therefore, this study provides key knowledge essential for the scientific community and the water industry on optimizing IX operational parameters for DOM and PFAS removal and would be highly valuable for systems which presently operate IX in a use-and-dispose mode.

Biofiltration is a widely used process in drinking water treatment plants to remove natural organic matter (NOM). A novel biofiltration process using ion exchange resins as supporting media (i.e., biological ion exchange or BIEX) has been demonstrated to provide a superior performance compared to conventional biological activated carbon (BAC). In order to optimize the performance of BIEX filters, the impact of temperature and empty bed contact time (EBCT) on NOM removal was systematically studied. In the present study, bench-scale BIEX filters were set up in parallel with BAC filters and operated at different temperatures (i.e., 4 °C, 10 °C and 20 °C) and EBCTs (i.e., 7.5 min, 15 min and 30 min). Higher average dissolved organic carbon (DOC) removal was achieved in BIEX filters (73 ± 6%) than BAC filters (22 ± 9%) at the steady state with an EBCT of 30 min. Higher temperatures improved NOM removal in both BAC and BIEX filters, with the impact being greater at lower EBCTs (i.e., 7.5 min and 15 min). Higher EBCTs could also improve NOM removal, with the impact being greater at lower temperatures (i.e., 4 °C and 10 °C). DOC removal for BIEX and BAC filters can be modeled with a first-order kinetic model (R2 = 0.93–0.99). BAC had a higher temperature activity coefficient than BIEX (1.0675 vs. 1.0429), indicating that temperature has a greater impact on BAC filtration than BIEX filtration. Overall, temperature and EBCT must be considered simultaneously for biofilters to efficiently remove NOM.

In the present study, the synergistic effects of capacitive deionization (CDI) and ultraviolet (UV) based advanced oxidation process (AOP) have been investigated for the simultaneous removal of NaCl salt and humic acid (HA), by an organic contaminant approach. A specific CDI rod geometry setup was utilized to allow for direct UV irradiation on the electrodes’ surface during CDI experiments. The characteristics of the coated electrodes were examined by scanning electron microscope (SEM) and electrochemical impedance spectroscopy (EIS). The results of desalination experiments showed that the maximum salt adsorption capacity (mSAC) and salt removal efficiency were 3.96 mg/g and 52.5%, respectively under constant operating conditions (i.e., an applied voltage of 1.2 V and an initial salt concentration of 20 mM). Also, experiments involving simultaneous removal of salt and organic contaminant, demonstrated that the presence of HA in water has little impact on the desalination efficiency. After combining CDI and AOP under constant operating conditions (i.e., an applied voltage of 1.2 V, UV irradiation with a fluence rate of 6.8 mW/cm2, and initial concentrations of 20 mM of salt and 10 ppm of HA), the HA removal efficiencies in the charge and discharge reservoirs were 76.0% and 75.4%, respectively after 200 min of experimental time.

Microcystins are the most commonly occurring cyanotoxins, and have been extensively studied across the globe. In the present study, a strongly basic anion exchange resin was employed to investigate the removal of Microcystin-LR (MCLR), one of the most toxic microcystin variants. Factors influencing the uptake behavior included the MCLR and resin concentrations, resin dosage, and natural organic matter (NOM) characteristics, specifically, the charge density and molecular weight distribution of source water NOM. Equivalent background concentration (EBC) was employed to evaluate the competitive uptake between NOM and MCLR. The experimental data were compared with different mathematical and physical models and pore diffusion was determined as the rate-limiting step. The resin dose/solute concentration ratio played a key role in the MCLR uptake process and MCLR removal was attributed primarily to electrostatic attractions. Charge density and molecular weight distribution of the background NOM fractions played a major role in MCLR removal at lower resin dosages (200 mg/L ∼ 1 mL/L and below), where a competitive uptake was observed due to the limited exchange sites. Further, evidences of pore blockage and site reduction were also observed in the presence of humics and larger molecular weight organic fractions, where a four-fold reduction in the MCLR uptake was observed. Comparable results were obtained for laboratory studies on synthetic laboratory water and surface water under similar conditions. Given their excellent performance and low cost, anion exchange resins are expected to present promising potentials for applications involving the removal of removal of algal toxins and NOM from surface waters.

Ultraviolet light-emitting diode (UV-LED) is an emerging UV source and has a number of features that do not exist in conventional mercury based UV lamps. One such feature is the ability to turn the radiation on and off with a high frequency, which enables pulsed irradiation with flexible pulse patterns by UV-LEDs. In this study, the inactivation of different microorganisms by continuous and pulsed irradiation was investigated using UV-LEDs, in order to utilize this unique feature to distinguish the effect of pulsation on inactivation, and to explore the potential benefits of UV-LEDs pulsed irradiation for water disinfection. The analysis was based on the equivalent UV fluence between continuous and pulsed irradiation using two types of actinometry techniques (iodide-iodate and ferrioxalate) for UV fluence determination. The disinfection study involved the inactivation of E. coli and coliphage MS2 in laboratory water, as well as E. coli and total coliform in wastewater. The effects of pulse patterns including frequency (i.e., the number of on-off cycles per second) and duty rate (i.e., the percentage of irradiation time in each on-off cycle) on the inactivation effectiveness were also examined for these microorganisms. The results showed comparable inactivation of all the examined microorganisms by 265 nm UV-LED continuous and pulsed irradiation with various pulse patterns under equivalent UV fluence. The findings in this study were compared with those from conventional xenon lamps pulsed irradiation studies, which not only distinguished the role of pulsed UV irradiation on microorganisms inactivation, but also revealed a key feature of UV-LEDs pulsed irradiation with respect to improved thermal management, potentially affecting application of high output UV-LEDs for water disinfection.

The photochemical treatment of water using 185 nm radiation forms the basis of an advanced oxidation process (AOP) that does not require chemical addition. The 185 nm photolysis of water generates the hydroxyl radical ( OH) able to degrade trace organic contaminants. However, the strong absorbance of water ( a H 2 O ) at 185 nm imposes severe geometrical constraints on reactor design. Investigation of the reported temperature dependence of a H 2 O on treatment efficiency was conducted between 5 and 35 ° C, in model solutions using carbamazepine as a radical probe. Comparison was made with the temperature dependence of the 254 nm photolysis of hydrogen peroxide under similar conditions. It was found that the 185 nm AOP is less sensitive to temperature under the conditions tested, suggesting the absorbance of water has a negligible effect in this range. This is postulated to be due to the fundamental structure of liquid water, whereby 185 nm photons are absorbed by a small population of interstitial H 2 O monomers, with no hydrogen bonds to impede the escape of OH from the solvent cage.

Harmful algal blooms (HAB) release microtoxins that contaminate drinking water supplies and risk the health of millions annually. Crystalline ferrate(VI) is a powerful oxidant capable of removing algal microtoxins. We investigate in-situ electrochemically produced ferrate from common carbon steel as an on-demand alternative to crystalline ferrate for the removal of microcystin-LR (MC-LR) and compare the removal efficacy for both electrochemical (EC) and chemical dosing methodologies. We report that a very low dose of EC-ferrate in deionized water (0.5 mg FeO42− L−1) oxidizes MC-LR (MC-LR0 = 10 μg L−1) to below the guideline limit (1.0 μg L−1) within 10 minutes' contact time. With bicarbonate or natural organic matter (NOM), doses of 2.0–5.0 mg FeO42− L−1 are required, with lower efficacy of EC-ferrate than crystalline ferrate due to loss of EC-ferrate by water oxidation. To evaluate the EC-ferrate process to concurrently oxidize micropollutants, coagulate NOM, and disinfect drinking water, we spiked NOM-containing real water with MC-LR and Escherichia coli, finding that EC-ferrate is effective at 10.0 mg FeO42− L−1 under normal operation or 2.0 mg FeO42− L−1 if the test water has initial pH optimized. We suggest in-situ EC-ferrate may be appropriate for sporadic HAB events in small water systems as a primary or back-up technology.

This study investigated the efficiency of a strongly basic macroporous anion exchange resin for the co-removal of Microcystin-LR (MCLR) and natural organic matter (NOM) in waters affected by toxic algal blooms. Environmental factors influencing the uptake behavior included MCLR and resin concentrations, NOM and anionic species, specifically nitrate, sulphate and bicarbonate. A860 resin exhibited an excellent adsorption capacity of 3800 μg/g; more than 60% of the MCLR removal was achieved within 10 min with a resin dosage of 200 mg/L (∼1 mL/L). Further, kinetic studies revealed that the overall removal of MCLR is influenced by both external diffusion and intra-particle diffusion. Increasing NOM concentration resulted in a significant reduction of MCLR uptake, especially at lower resin dosages, where a competitive uptake between the charged NOM fractions and MCLR was observed due to limited active sites. In addition, MCLR uptake was significantly reduced in the presence of sulphate and nitrate in the water matrix. Moreover, performance of the resin proved to be stable from one regeneration cycle to another. Approximately 80% of MCLR and 50% of dissolved organic carbon (DOC) were recovered in the regenerated brine. Evidences of resin saturation and site reduction were also observed after 2000 bed volumes (BV) of operation. For all the investigated water matrices, a resin dosage of 1000 mg/L (∼4.5 mL/L) was sufficient to lower MCLR concentration from 100 μg/L to below the World Health Organization guideline of 1 μg/L, while simultaneously providing more than 80% NOM removal.

With the growing application of the ultraviolet light emitting diodes (UV-LED) for water treatment purposes, the significance of modeling their output for designing UV reactors becomes crucial. In this study, the radiation distributions of two UV-LEDs with different radiation profiles are modeled. These UV-LEDs represent the two most common radiation profiles of UV-LEDs – balloon shape and heart shape. Irradiance and fluence rate distribution were predicted and experimentally validated by measuring irradiance through an accurate radiometry setup and determining fluence rate by iodide-iodate actinometry. The consistency of the results among the actinometry, radiometry, and the model proves the reliability of the model. The model helps demonstrate the extend to which the irradiance distribution and average fluence rate are affected as a function of distance and how they are affected by the UV-LED’s radiation profile. For UV-LEDs with any radiation profiles, higher average fluence rate occurs at closer distances to the UV-LED; however, to study the microbiological inactivation kinetics, uniformity of the radiation distribution on the surface of the petri dish has to be taken into account. Using the validated model, common radiation modeling presumptions such as the point source assumption and symmetry assumption for radiation profile of UV-LEDs are evaluated.