Strategies for the removal of halides from drinking water sources, and their applicability in disinfection by-product minimisation: a critical review

Bromine contamination and risk management in terrestrial and aquatic ecosystems

Bromine (Br) is widely distributed through the lithosphere and hydrosphere, and its chemistry in the environment is affected by natural processes and anthropogenic activities. While the chemistry of Br in the atmosphere has been comprehensively explored, there has never been an overview of the chemistry of Br in soil and aquatic systems. This review synthesizes current knowledge on the sources, geochemistry, health and environmental threats, remediation approaches, and regulatory guidelines pertaining to Br pollution in terrestrial and aquatic environments. Volcanic eruptions, geothermal streams, and seawater are the major natural sources of Br. In soils and sediments, Br undergoes natural cycling between organic and inorganic forms, with bromination reactions occurring both abiotically and through microbial activity. For organisms, Br is a non-essential element; it is passively taken up by plant roots in the form of the Br- anion. Elevated Br- levels can limit plant growth on coastal soils of arid and semi-arid environments. Br is used in the chemical industry to manufacture pesticides, flame retardants, pharmaceuticals, and other products. Anthropogenic sources of organobromine contaminants in the environment are primarily wastewater treatment, fumigants, and flame retardants. When aqueous Br- reacts with oxidants in water treatment plants, it can generate brominated disinfection by-products (DBPs), and exposure to DBPs is linked to adverse human health effects including increased cancer risk. Br- can be removed from aquatic systems using adsorbents, and amelioration of soils containing excess Br- can be achieved by leaching, adding various amendments, or phytoremediation. Developing cost-effective methods for Br- removal from wastewater would help address the problem of toxic brominated DBPs. Other anthropogenic organobromines, such as polybrominated diphenyl ether (PBDE) flame retardants, are persistent, toxic, and bioaccumulative, posing a challenge in environmental remediation. Future research directives for managing Br pollution sustainably in various environmental settings are suggested here.

Peracetic acid as an alternative disinfectant for micropollutants degradation and disinfection byproducts control in outdoor swimming pools

Peracetic acid (PAA) has garnered significant interest as a novel alternative to chlorine-based disinfectants for water treatment due to its broad-spectrum antimicrobial activity and its ability of reactive species generation when exposed to UV light. However, limited studies have investigated micropollutant degradation in the presence of PAA under solar irradiation. This is the first study to comprehensively investigate the photodegradation of caffeine (CAF) and 4-methylbenzylidene camphor (4-MBC) and the removal of disinfection byproducts (DBPs) in the presence of PAA under simulated solar light. The study revealed that the photodegradation of CAF and 4-MBC was significantly enhanced in the presence of PAA, following pseudo-first-order kinetics (R2 > 0.98) with reaction rates (kobs) of 0.220 and 0.111 h-1, respectively. In addition, substantial reduction of 21 DBPs, including trihalomethanes, haloacetic acids and haloacetonitriles, and no DBPs formation were observed in the presence of PAA and simulated solar irradiation. The proportion of coexisting H2O2 in the PAA solution considerably influenced target compounds degradation. CAF and 4-MBC were degraded faster under acidic conditions than under alkaline conditions. Hydroxyl radicals (·OH) dominated the degradation of CAF at different pH values, while direct photolysis and other reactive species played a major role in the degradation of 4-MBC.

A novel benzothiazolin-based fluorescent probe for hypobromous acid and its application in environment and biosystems

Studies have shown that hypobromous acid (HOBr) produced during chlorination disinfection of tap water can react with some organic matter in water to form toxic brominated disinfection byproducts (Br-DBPs) and HOBr also plays an important role during the process of micro pollutants degradation. Hence, real-time monitoring of HOBr in water environment plays a significant role in controlling the generation of Br-DBPs and degradation of micro pollutants. Herein, a novel highly specific fluorescent probe (PBE-HOBr) for accurate detection of HOBr was constructed based on the HOBr-induced oxidation elimination of benzothiazoline moiety employing the photo-induced electron transfer (PET) mechanism. PBE-HOBr has high sensitivity and linear response to HOBr with a low detection limit of 119 nM. PBE-HOBr not only has the ability to detect endogenous and exogenous HOBr in cells and zebrafish, but also has been used to monitor the formation of HOBr in water treatment. In addition, benzothiazoline group was demonstrated for the first time to be able to be used as a new recognition receptor for developing highly specific fluorescent probes for HOBr.

Enhancing the Mechanical Properties of Poly(vinyl alcohol) Fibers by Lithium Iodide Addition

The effect of lithium iodide (LiI) on the mechanical strength, properties, and molecular orientation of poly(vinyl alcohol) (PVA) fibers spun by wet spinning and then heat-stretched was studied. The stretchability of LiI-PVA fibers was improved, and the rupture during stretching was suppressed compared to PVA fibers. In addition, the tensile strength and elastic modulus of the thermally stretched fibers have been significantly improved. It was also found that the addition of LiI improves the molecular orientation of PVA. This was achieved because LiI reduced the hydrogen bonds between the molecular chains of PVA, resulting in reduced crystallinity. Most of the LiI in the fiber could be removed by a coagulation bath and washing during the spinning process. This means that LiI is eventually removed, and the heat-treatment strengthens the hydrogen bonds, resulting in excellent mechanical strength.

Recent Advances in the Removal of Radioactive Iodine and Iodide from the Environment

Iodine (I2) in the form of iodide ions (I-) is an essential chemical element in the human body. Iodine is a nonmetal that belongs to the VIIA group (halogens) in the periodic table. Over the last couple of centuries, the exponential growth of human society triggered by industrialization coincided with the use of iodine in a wide variety of applications, including chemical and biological processes. However, through these processes, the excess amount of iodine eventually ends up contaminating soil, underground water, and freshwater sources, which results in adverse effects. It enters the food chain and interferes with biological processes with serious physiological consequences in all living organisms, including humans. Existing removal techniques utilize different materials such as metal-organic frameworks, layered double hydroxides, ion-exchange resins, silver, polymers, bismuth, carbon, soil, MXenes, and magnetic-based materials. From our literature survey, it was clear that absorption techniques are the most frequently experimented with. In this Review, we have summarized current advancements in the removal of iodine and iodide from human-made contaminated aqueous waste.

Removal of iodide anions in water by silver nanoparticles supported on polystyrene anion exchanger

The removal of iodide (I^-) from source waters is an effective strategy to minimize the formation of iodinated disinfection by-products (DBPs), which are more toxic than their brominated and chlorinated analogues. In this work, a nanocomposite Ag-D201 was synthesized by multiple in situ reduction of Ag-complex in D201 polymer matrix, to achieve highly efficient removal of iodide from water. Scanning electron microscope /energy dispersive spectrometer characterization showed that uniform cubic silver nanoparticles (AgNPs) evenly dispersed in the D201 pores. The equilibrium isotherms data for iodide adsorption onto Ag-D201 was well fitted with Langmuir isotherm with the adsorption capacity of 533 mg/g at neutral pH. The adsorption capacity of Ag-D201 increased with the decrease of pH in acidic aqueous solution, and reached the maximum value of 802 mg/g at pH 2. This was attributed to the oxidization of I^-, by dissolved oxygen under the catalysis of AgNPs, to I₂ which was finally adsorbed as AgI₃. However, the aqueous solutions at pH 7 - 11 could hardly affect the iodide adsorption. The adsorption of I^- was barely affected by real water matrixes such as competitive anions (SO₄^2-, NO₃^-, HCO₃^-, Cl^-) and natural organic matter, of which interference of NOM was offset by the presence of Ca²⁺. The proposed synergistic mechanism for the excellent performance of iodide adsorption by the absorbent was ascribed to the Donnan membrane effect caused by the D201 resin, the chemisorption of I^- by AgNPs, and the catalytic effect of AgNPs.

Comparing risk of disinfection byproducts in drinking water under variable scenarios of seawater intrusion

The higher levels of halides in seawater increase bromide and iodide in the coastal aquifers, leading to higher concentrations of halogenated disinfection byproducts (DBPs). The populations in the coastal areas are susceptible to increased concentrations of DBPs while many DBPs are cyto- and genotoxic to mammalian cells, and are possible/probable human carcinogens. The implications of seawater intrusion on the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs), and the risks were analyzed by adding 0.0-2.0 % seawater (SW) (by volume) and chlorine to groundwater. Bromide and iodide concentrations in groundwater (0.0 %SW) were observed as 42.5 and non-detected (ND) μg/L respectively. With 2.0 %SW, these were spiked up to 1100 and 2.1 μg/L respectively. The most common THMs (THM4), iodinated THMs (I-THMs) and HAAs were 30.4, 0.13 and 27.9 μg/L for 0.0 % SW respectively. With 2.0 %SW, these values were 106.3, 1.6 and 72.9 μg/L, respectively. At 0.0 %SW, averages of chronic daily intakes (CDI) for THM4, HAAs and I-THMs were 2.61 × 10^-4, 2.26 × 10^-4 and 7.69 × 10^-7 mg/kg/day respectively, which were increased to 9.97 × 10^-4, 4.70 × 10^-4 and 9.47 × 10^-6 mg/kg/day, respectively for 2.0 %SW. For 0.0 %SW, overall cancer risks from few DBPs was 3.09 × 10^-5 (6.46 × 10^-6 - 7.23 × 10^-5) while at 1.0 % and 2.0 %SW, risks were 4.88 × 10^-5 (1.26 × 10^-5-1.08 × 10^-4) and 4.11 × 10^-5 (1.21 × 10^-5-9.28 × 10^-5) respectively. The reduction of risks for 2.0 %SW was due to the increase of bromoform (TBM), and decrease in bromodichloromethane (BDCM) and dibromochloromethane (DBCM) at 2.0 %SW. The disability-adjusted life years (DALY) loss showed an increasing trend from 0.0 %SW (DALY: 77.30) to 1.0 %SW (DALY: 122.0) while an increase to 2.0 %SW showed a decrease in DALY (DALY: 102.8). Future study on toxicity of other regulated and emerging DBPs is warranted to better predict cancer risks.

Increasing bromide removal by graphene-silver nanocomposites: Nanoparticulate silver enhances bromide selectivity through direct surface interactions

Bromide forms toxic brominated disinfection by-products during disinfection. Current bromide removal technologies are often non-specific and costly due to naturally occurring competing anions. A silver-impregnated graphene oxide (GO) nanocomposite is reported here that reduced the amount of Ag needed for Br^- removal by increasing its selectivity towards Br^-. GO was impregnated with ionic (GO-Ag⁺) or nanoparticulate Ag (GO-nAg) and compared against Ag⁺ or unsupported nAg to identify molecular level interactions. In nanopure water, Ag⁺ and nAg had the highest Br^- removal (∼0.89 mol Br^-/mol Ag⁺) followed by GO-nAg at 0.77 mol Br^-/mol Ag⁺. However, under anionic competition, the Ag⁺ removal was reduced to 0.10 mol Br^-/mol Ag⁺ while all nAg forms retained good Br^- removal. To understand the removal mechanism, anoxic experiments were performed to prevent nAg dissolution, which resulted in higher Br^- removal for all nAg forms compared to oxic conditions. This suggests that reaction of Br^- with the nAg surface is more selective than with Ag⁺. Finally, jar tests showed that anchoring nAg on GO enhances Ag removal during coagulation/flocculation/sedimentation compared to unsupported nAg or Ag⁺. Thus, our results identify strategies that can be used to design selective and silver-efficient adsorbents for Br^- removal in water treatment.

Tandem Efficient Bromine Removal and Silver Recovery by Resorcinol-Formaldehyde Resin Nanoparticles

Halogen wastewater greatly threatens the health of human beings and aquatic organisms due to its severe toxicity, corrosiveness, and volatility. Efficient bromine removal is therefore urgently required, while existing Br₂-capture materials often face challenges from limited water stability and possible halogen leaking. We report a facile and efficient aqueous Br₂ removal method using submicron resorcinol-formaldehyde (RF) resin nanoparticles (NPs). The abundant aromatic groups dominate the Br₂ removal by substitution reactions. An excellent Br₂ conversion capacity of 7441 mg g_RF^-1 was achieved by RF NPs that outperform state-of-the-art materials by ∼2-fold, along with advantages including good water stability, low cost, and easy fabrication. Two recycling-coupled (electrochemical or H₂O₂-involved) Br₂ removal routes further reveal the feasibility of in-depth halogen removal by RF NPs. The brominated resin can be downstream upcycled for silver recovery, realizing the harvesting of precious metal, reducing of heavy-metal pollution, and resource utilization of brominated resin.

Fabrication of Polyaniline/Graphene Oxide Nanosheet@ Tea Waste Granules Adsorbent for Groundwater Purification

The reuse and separation of nanomaterials from an aquatic solution is always challenging and may cause nanotoxicity if not separated completely. Nanomaterial immobilization on the surface of a macro-size material could be an effective approach to developing an efficient composite for groundwater purification. Herein, polyaniline and graphene oxide nanosheet immobilized granular tea waste (PANI/GO@GTW) has been synthesized to remove the anionic and cationic contaminants from groundwater. The synthesized materials were characterized by SEM, XRD, XPS, and FTIR spectroscopies. The optimization of experimental conditions was tested for bromide (Br−) removal from synthetic water. The results revealed that Br− adsorption behavior onto the synthesized materials was as follows: PANI/GO < PANI/GTW < PANI < PANI/GO@GTW. The optimum removal of Br− ions was observed at pH 3 with 90 min of saturation time. Br− adsorption onto PANI/GO@GTW followed the pseudo-first-order kinetic and Langmuir isotherm model, and electrostatic interaction was involved in the adsorption process. The optimum adsorption of Br− onto PANI/GO@GTW was found to be 26.80 m/g. The application of PANI/GO@GTW on real groundwater treatment demonstrated the effective removal of anion pollutants such as F−, Cl−, Br−, NO3−, and PO43−. This study revealed that PANI/GO@GTW successfully reduced Br− concentrations in synthetic and real groundwater and can be used for large-scale applications.

Iodide Removal by Resorcinol-Formaldehyde Carbon Aerogels

The adsorption technique is widely used in water purification, and its efficiency can be significantly improved by target-specific adsorbent design. Research on iodine and its ion removal from water has attracted a great deal of interest due to increased concentrations in the environment and acute toxic effects, e.g., in human thyroid cells. In this work, the iodide removal performance of two high-surface-area resorcinol-formaldehyde-based carbon aerogels was studied under acidic conditions. The BET surface area was 790 m²/g (RF_ac) and 375 m²/g (RMF-GO), with a corresponding micropore ratio of 36 and 26%, respectively. Both aerogels showed outstanding adsorption capacity, exceeding the reported performance of other carbons and Ag-doped materials. Owing to its basic nature, the RMF-GO carbon aerogel showed higher I^- capacity, up to 97 mg/g, than the acidic RF_ac, which reached a capacity of 82 mg/g. The surface chemistry of the aerogels also played a distinct role in the removal. In terms of kinetics, RF_ac removed 60% of the iodide ions and RMF-GO 30% within 8 h. The removal kinetics was of the first order, with a half-life of 1.94 and 1.70 h, respectively.

Upcycling Bread Waste into a Ag-Doped Carbon Material Applied to the Detection of Halogenated Compounds in Waters

Bread waste is a major part of food wastage which could be upcycled to produce functional materials, following the principles of the circular bioeconomy. This work shows that bread waste can be recycled and valorized to produce a composite conductive material with excellent properties for chemical sensor applications. Here, dry bread is impregnated with an aqueous solution of a silver precursor and pyrolyzed to produce a porous carbon matrix containing Ag nanoparticles with diameters ranging from 20 to 40 nm. These particles perform as catalytic redox centers for the electrochemical detection of halide ions (Cl^-, Br^-, and I^-) and organohalide target molecules such as sucralose and trichloroacetic acid. A thorough analytical characterization is carried out to show the potential application of the developed material for the manufacturing of electrochemical sensor approaches. The material preparation is sustainable, low-cost, simple, and upscalable. These are ideal features for the large-scale manufacturing by screen-printing technologies of single-use electrochemical sensors for the rapid analysis of halogenated organic pollutants in waters.

Tradeoff between micropollutant abatement and bromate formation during ozonation of concentrates from nanofiltration and reverse osmosis processes

Water treatment with nanofiltration (NF) or reverse osmosis (RO) membranes results in a purified permeate and a retentate, where solutes are concentrated and have to be properly managed and discharged. To date, little is known on how the selection of a semi-permeable dense membrane impacts the dissolved organic matter in the concentrate and what the consequences are for micropollutant (MP) abatement and bromate formation during concentrate treatment with ozone. Laboratory ozonation experiments were performed with standardized concentrates produced by three membranes (two NFs and one low-pressure reverse osmosis (LPRO) membrane) from three water sources (two river waters and one lake water). The concentrates were standardized by adjustment of pH and concentrations of dissolved organic carbon, total inorganic carbon, selected micropollutants (MP) with a low to high ozone reactivity and bromide to exclude factors which are known to impact ozonation. NF membranes had a lower retention of bromide and MPs than the LPRO membrane, and if the permeate quality of the NF membrane meets the requirements, the selection of this membrane type is beneficial due to the lower bromate formation risks upon concentrate ozonation. The bromate formation was typically higher in standardized concentrates of LPRO than of NF membranes, but the tradeoff between MP abatement and bromate formation upon ozonation of the standardized concentrates was not affected by the membrane type. Furthermore, there was no difference for the different source waters. Overall, ozonation of concentrates is only feasible for abatement of MPs with a high to moderate ozone reactivity with limited bromate formation. Differences in the DOM composition between NF and LPRO membrane concentrates are less relevant than retention of MPs and bromide by the membrane and the required ozone dose to meet a treatment target.

Removal of halides from drinking water: technological achievements in the past ten years and research needs

Disinfection is an essential process for drinking water supplies resulting in the formation of unintended disinfection by-products (DBPs), many of which are potentially toxic and are known as the possible or probable human carcinogens. As of now, 100⁺ DBPs were characterized while about 600⁺ others can be formed in the supply water. To protect the human health, many regulatory agencies have set the guideline values for several DBPs. Removal of halide ions and natural organic matter prior to disinfection is an important step to reduce DBPs, and the associated exposure and risks. To date, many publications have reported various methods for halide removal from drinking water. The most review about halide removal technologies, associated challenges, and future research needs was published in 2012. Since then, a number of studies have been published on different methods of halide removal techniques. This paper aims to review the state of research on halide removal techniques focusing on the development during the past 10 years (2012-2021). The techniques were clustered into six major groups: adsorption, ion exchange, coagulation, advanced oxidation, membrane separation, and combined techniques. The progress on these groups of technologies, their advantages, and limitations were examined, and the future research directions to produce the safe drinking water were identified.

Evaluation of disinfection byproducts for their ability to affect mitochondrial function

In the race to deliver clean water to communities through potable water reuse, disinfection and water quality assessment are and will continue to be fundamental factors. There are over 700 disinfection byproducts (DBPs) in water; evaluating each compound is practically impossible and very time consuming. A bioanalytical approach could be an answer to this challenge. In this work, the response of four major classes of DBPs toward mitochondrial membrane potential (ΔΨm) and cytoplasmic adenosine triphosphate (C-ATP) was investigated with human carcinoma (HepG2) cells. Within 90 min of cell exposure, only the haloacetic acid (HAA) mixture caused a cytotoxic response as measured by C-ATP. All four groups (haloacetonitriles (HANs), trihalomethanes (THMs), nitrosamines (NOAs), and HAAs) responded well to ΔΨm, R² > 0.70. Based on the half-maximum concentration that evoked a 50% response in ΔΨm, the response gradient was HANs >> HAAs ∼ THM > NOAs. The inhibition of the ΔΨm by HANs is driven by dibromoacetonitrile (DBAN), while dichloroacetonitrile (DCAN) did not cause a significant change in the ΔΨm at less than 2000 µM. A mixture of HANs exhibited an antagonistic behavior on the ΔΨm compared to individual compounds. If water samples are concentrated to increase HAN concentrations, especially DBAN, then ΔΨm could be used as a biomonitoring tool for DBP toxicity.

Formation of regulated and unregulated disinfection byproducts during chlorination and chloramination: Roles of dissolved organic matter type, bromide, and iodide

Algal blooms and wastewater effluents can introduce algal organic matter (AOM) and effluent organic matter (EfOM) into surface waters, respectively. In this study, the impact of bromide and iodide on the formation of halogenated disinfection byproducts (DBPs) during chlorination and chloramination from various types of dissolved organic matter (DOM, e.g., natural organic matter (NOM), AOM, and EfOM) were investigated based on the data collected from literature. In general, higher formation of trihalomethanes (THMs) and haloacetic acids (HAAs) was observed in NOM than AOM and EfOM, indicating high reactivities of phenolic moieties with both chlorine and monochloramine. The formation of haloacetaldehydes (HALs), haloacetonitriles (HANs) and haloacetamides (HAMs) was much lower than THMs and HAAs. Increasing initial bromide concentrations increased the formation of THMs, HAAs, HANs, and HAMs, but not HALs. Bromine substitution factor (BSF) values of DBPs formed in chlorination decreased as specific ultraviolet absorbance (SUVA) increased. AOM favored the formation of iodinated THMs (I-THMs) during chloramination using preformed chloramines and chlorination-chloramination processes. Increasing prechlorination time can reduce the I-THM concentrations because of the conversion of iodide to iodate, but this increased the formation of chlorinated and brominated DBPs. In an analogous way, iodine substitution factor (ISF) values of I-THMs formed in chloramination decreased as SUVA values of DOM increased. Compared to chlorination, the formation of noniodinated DBPs is low in chloramination.

Effects of seawater intrusion on the formation of disinfection byproducts in drinking water

Seawater contains high levels of halides, which can increase the concentrations of bromide and iodide ions in coastal groundwater and surface water sources. Intrusion of seawater alters the chemistry of fresh water leading to the formation of additional brominated and iodinated disinfection byproducts (DBPs), many of which are cyto- and genotoxic to the mammalian cells, and have cancer risks to humans. In this study, effects of seawater intrusion on the formation of trihalomethanes (THMs), and haloacetic acids (HAAs) were investigated by spiking groundwater using 0.0-2.0% seawater (by volume) and liquid chlorine as disinfectant. The concentrations of bromide and iodide ions in groundwater (0.0% seawater) were 42.5 and non-detected (ND) μg/L respectively, which were increased up to 1100 and 2.1 μg/L respectively, following mixing with 2.0% seawater. The regulated THMs (THM4) were increased from 30.4 to 106.3 μg/L while iodinated THMs (I-THMs) were increased from 0.13 to 1.6 μg/L respectively due possibly to molecular substitution and additional pathways of THMs formation. Bromoform was increased from 0.5 to 94.3 μg/L while iodoform was increased from ND to 1.02 μg/L. HAAs were increased from 27.9 to 72.9 μg/L where tribromoacetic acid was increased from 2.0 to 43.7 μg/L. In 0.0% seawater, bromine incorporation factor (BIF) for THM4 and HAAs were 0.077 and 0.050 respectively, which were increased to 0.942 and 0.38 at 2% seawater respectively. For dihalogenated HAAs (X2AA) and trihalogenated HAAs (X3AA), BIF in 0.0% seawater were 0.098 and 0.14 respectively, which were increased to 0.863 and 0.924 for 2.0% seawater respectively. Mixing of 2.0 seawater increased the toxicity of THM4, HAAs and I-THMs by 4.2, 5.9 and 201.8 folds, respectively indicating the importance of reducing seawater intrusion into the freshwater sources. Further, alteration of water sources and/or adaptation of advanced treatment can assist in lowering the risks.

Iodide sources in the aquatic environment and its fate during oxidative water treatment - A critical review

Iodine is a naturally-occurring halogen in natural waters generally present in concentrations between 0.5 and 100 µg L^-1. During oxidative drinking water treatment, iodine-containing disinfection by-products (I-DBPs) can be formed. The formation of I-DBPs was mostly associated to taste and odor issues in the produced tap water but has become a potential health problem more recently due to the generally more toxic character of I-DBPs compared to their chlorinated and brominated analogues. This paper is a systematic and critical review on the reactivity of iodide and on the most common intermediate reactive iodine species HOI. The first step of oxidation of I^- to HOI is rapid for most oxidants (apparent second-order rate constant, k_app > 10³ M^-1s^-1 at pH 7). The reactivity of hypoiodous acid with inorganic and organic compounds appears to be intermediate between chlorine and bromine. The life times of HOI during oxidative treatment determines the extent of the formation of I-DBPs. Based on this assessment, chloramine, chlorine dioxide and permanganate are of the highest concern when treating iodide-containing waters. The conditions for the formation of iodo-organic compounds are also critically reviewed. From an evaluation of I-DBPs in more than 650 drinking waters, it can be concluded that one third show low levels of I-THMs (<1 µg L^-1), and 18% exhibit concentrations > 10 µg L^-1. The most frequently detected I-THM is CHCl₂I followed by CHBrClI. More polar I-DBPs, iodoacetic acid in particular, have been reviewed as well. Finally, the transformation of iodide to iodate, a safe iodine-derived end-product, has been proposed to mitigate the formation of I-DBPs in drinking water processes. For this purpose a pre-oxidation step with either ozone or ferrate(VI) to completely oxidize iodide to iodate is an efficient process. Activated carbon has also been shown to be efficient in reducing I-DBPs during drinking water oxidation.

Removal of chloride from water and wastewater: Removal mechanisms and recent trends

Increased chloride concentration can cause salinization, which has become a serious and widespread environmental problem nowadays. This review aims at providing comprehensive and state-of-the-art knowledge and insights of technologies for chloride removal. Mechanisms for chloride removal mainly include chemical precipitation, adsorption, oxidation and membrane separation. In chemical precipitation, chloride removal by forming CuCl, AgCl, BiOCl and Friedel's salt. Adsorbents used in chloride removal mainly include ion exchangers, bimetal oxides and carbon-based electrodes. Oxidation for chloride removal contains ozone-based, electrochemical and sulfate radical-based oxidation. Membrane separation for chloride removal consists of diffusion dialysis, nanofiltration, reverse osmosis and electrodialysis. In this review, we specifically proposed the factors that affect chloride removal process and the corresponding strategies for improving removal efficiency. In the last section, the remaining challenges of method explorations and material developments were stated to provide guidelines for future development of chloride removal technologies.

Investigation of bromide removal and bromate minimization of membrane capacitive deionization for drinking water treatment

The ubiquitous bromide (Br^-) poses a challenge to current drinking water treatment schemes due to the formation of brominated disinfection by-products, especially bromate (BrO₃^-). A cost-effective and energy-efficient technology to remove Br^- before disinfection is highly desired. In this work, the application of membrane capacitive deionization (MCDI) for the removal of Br^- and BrO₃^- minimization for drinking water treatment was systematically investigated. Results showed that the removal of Br^- by MCDI followed the pseudo-second-order kinetics, in which kinetics was faster at lower Br^- concentration. Additionally, Br^- displayed a preferential electrosorption over Cl^- in MCDI despite the relatively smaller amounts. Due to high removal performance of Br^-, 99.49% of BrO₃^- minimization can be achieved. Moreover, the presence of humic acid (HA) had a negative effect on the removal of Br^- and BrO₃^- minimization. However, Br^- could be more preferentially removed than Cl^- in the presence of HA due to the weak interaction with HA. Finally, by treating an actual surface water sample, it was found that the removal rate of Br^- was 91.80%, and 83.97% of BrO₃^- minimization can be achieved. BrO₃^- concentration of effluent meets the control standard. Overall, these results prove the feasibility of MCDI for practical drinking water treatment.

Multifunctional β-Cyclodextrin Polymer for Simultaneous Removal of Natural Organic Matter and Organic Micropollutants and Detrimental Microorganisms from Water

Natural organic matter (NOM), organic micropollutants (OMPs), and detrimental microorganisms are three major pollutants that affect water quality. To remove these pollutants, a quaternary ammonium-functionalized β-cyclodextrin polymer (β-CDP) is successfully synthesized in the aqueous phase. The N₂ and CO₂ adsorption/desorption analysis showed that the polymer mainly contains ultra-micropores (<1 nm), with a Langmuir surface area of 89 m² g^-1. Two kinds of NOM, humic acid and fulvic acid, and five OMPs, 2-naphthol (2-NO), 3-phenylphenol (3-PH), 2,4,6-trichlorophenol (2,4,6-TCP), bisphenol A (BPA), and bisphenol S (BPS), were selected as model pollutants to study the performance of β-CDP and three kinds of commercial adsorbents, including granular activated carbon, DARCO-AC, and two resins, XAD-4 and D-201, were used for comparison. The polymer shows ultrarapid adsorption kinetics for the removal of these pollutants, with pseudo-second-order rate constants two to three orders of magnitude higher than that of the commercial activated carbon and resins. Due to the different adsorption sites of NOM and OMPs, β-CDP can simultaneously remove these pollutants without competitive adsorption. The maximum adsorption capacity of β-CDP for HA, FA, 2-NO, 3-PH, 2,4,6-TCP, BPA, and BPS based on the Langmuir model is 40, 166, 74, 101, 108, 103, and 117 mg g^-1, respectively. After use, the polymer can be easily regenerated at room temperature. In addition, β-CDP also showed excellent bactericidal properties due to the quaternary ammonium groups. At a concentration of 15 g L^-1, β-CDP can remove 98% of the tested Escherichia coli. Moreover, the synthesis of β-CDP is simple, green, and easy to industrialize. All of these findings indicate that β-CDP, as an ideal multifunctional material, presents potential for practical applications for water treatment and disinfection.

Investigation of the effective factors on the mutagen X formation in drinking water by response surface methodology

Mutagen 3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone (MX) is known as a potent factor in inducing DNA damage and increasing cancer risk. MX is a chlorination disinfection byproduct that comes from the reaction of humic acids and chlorine in drinking water. The purpose of this study was to evaluate the effects of significant factors (including pH, reaction time, chlorine and the concentration of organic materials (TOC)) and their interactions on the MX formation rate in chlorinated drinking water using Box-Behnken Design (BBD) and response surface method (RSM). For this purpose, the simulation of water chlorination disinfection process was carried out in a laboratory scale. A quadratic model was chosen to determine the mathematical relations between the response and the effective factors. All linear parameters, as well as second-degree components except chlorine, were statistically significant. Also, the interactions of contact time with TOC, free chlorine residual with TOC, and chlorine with pH were also statistically significant. Statistical results showed that the pH had a great effect on the potential of MX formation, and then the factors of TOC, chlorine and contact time were effective, respectively. The percentage of contribution (PC) of each component in the formation of MX. The highest significant percentage of contribution (48.36%) was allocated to the pH. Under the optimum conditions (contact time of 48.38 min, chlorine concentration of 0.79 mg/L, TOC concentration of 0.53 mg/L, and pH of 7.98), minimum value of MX was equal to 28.6.

Ozone-UV net-zero water wash station for remote emergency response healthcare units: Design, operation, and results

Because disease pandemics can accelerate rapidly in areas with limited clean-water access, a portable greywater reuse system may be useful to provide wash water at emergency health care units. In this study, a novel fed-batch (hybrid continuous-batch flow) net-zero water (NZW), or nearly closed-loop, reuse system comprising screening, 5 μm filter, and ozone-UV advanced oxidation was designed, constructed, and tested for performance with simulated and actual human showers. Water quality was tested for compliance with US drinking water standards, total organic carbon < 0.5 mg/L, and pathogen inactivation including 12 log₁₀ virus, 10 log₁₀ protozoa, and 9 log₁₀ bacteria as has been recommended for direct potable reuse. Energy, operation, and maintenance requirements were also evaluated, along with the system's capacity to handle shock events such as unintentional contamination with urine. Design goals were achieved without the addition of GAC point-of-use filter, except compliance with bromate and nitrate drinking water standards, which were met only for temporary use of up to three years per person. A capacity of 32 showers/day at 1920 W continuous power is projected, without generation of potentially-infectious concentrate. To avoid the further increase in system weight and energy demand needed to address urine input, future integrated urine diversion and collection, and system drain-and-fill following detection of urine in recycled water by electrical conductivity, are suggested for the field unit. Field testing is recommended. Further research should focus on potential need for bromate/nitrate mitigation, and longer-term study of microbiological inactivation.

Comparing three Australian natural organic matter isolates to the Suwannee river standard: Reactivity, disinfection by-product yield, and removal by drinking water treatments

Water treatments that provide efficient removal of organic and inorganic disinfection by-product (DBP) precursors across variable natural organic matter (NOM) sources are desirable. Treatments that effectively remove inorganic DBP precursors such as bromide, which significantly shift the speciation of DBP formation towards more toxic DBPs, are of particular interest and have been less investigated. This study characterised NOM isolated from three major drinking water sources in Southeast Queensland (SEQ), Australia, and compared it to the International Humic Substances Society (IHSS) Suwannee River NOM isolate (SR) in terms of DBP precursor removal treatments and DBP formation. Each NOM isolate was used to make synthetic water samples with otherwise identical water quality parameters, that were treated with enhanced coagulation (EC) or EC followed by; anion exchange (MIEX® resin), powdered activated carbon (PAC), granular activated carbon (GAC) or silver impregnated activated carbon (SIAC), to investigate the removal of DBP precursors (bromide and DOC), minimisation of DBPs, as well as the change in specific chlorine demand. EC/SIAC treatment was the most effective method of DBP control studied, due to the efficient simultaneous NOM and bromide adsorption of the SIAC (99 ± 1% bromide removal regardless of NOM source). This treatment also resulted in >92% removal of each of the measured DBPs across all NOM sources, with the exception of DBAN and 1,1-DCP, which achieved >80% removal across all NOM sources. Increases in tribromomethane (TBM) and dibromoacetonitrile (DBAN) formation were observed after all other treatment/NOM-isolate combinations, due to increased Br:DOC ratio after treatment, whereas chlorinated DBPs were generally well-controlled by all treatment/NOM-isolate combinations. Differences in reactivity of the individual NOM isolates were found to be related to both the origin of the isolate and the treatment employed, however, bromide removal capacity for each treatment was independent of NOM source.

Overlooked Role of Sulfur-Centered Radicals During Bromate Reduction by Sulfite

In this work, the kinetics and mechanisms of the reductive removal of BrO₃^- by sulfite in air atmosphere were determined. BrO₃^- could be effectively reduced by sulfite at pH_ini 3.0-6.0, and the reduction rate of BrO₃^- increased with decreasing pH. The coexisting organic contaminants with electron-rich moieties could be degraded, accompanied with BrO₃^- reduction by sulfite. The reaction stoichiometries of -Δ[sulfite]/Δ[bromate] were determined to be 3.33 and 15.63 in the absence and presence of O₂, respectively. Many lines of evidence verified that the main reactions in the BrO₃^-/sulfite system in air atmosphere included the reduction of BrO₃^- to HOBr and its further reduction to Br^-, as well as the oxidation of H₂SO₃ by BrO₃^- to form SO₃^·- and its further transformation to SO₄^·-. Moreover, SO₄^·- rather than HOBr was determined to be the major active oxidant in the BrO₃^-/sulfite system. SO₃^·- played a key role in the over-stoichiometric sulfite consumption because of its rapid reaction with dissolved oxygen. However, the formed SO₃^·- was further oxidized by BrO₃^- in the N₂ atmosphere. BrO₃^- reduction by sulfite is an alternative for controlling BrO₃^- in water treatment because it was effective in real water at pH_ini ≤ 6.0.

Does Granular Activated Carbon with Chlorination Produce Safer Drinking Water? From Disinfection Byproducts and Total Organic Halogen to Calculated Toxicity

Granular activated carbon (GAC) adsorption is well-established for controlling regulated disinfection byproducts (DBPs), but its effectiveness for unregulated DBPs and DBP-associated toxicity is unclear. In this study, GAC treatment was evaluated at three full-scale chlorination drinking water treatment plants over different GAC service lives for controlling 61 unregulated DBPs, 9 regulated DBPs, and speciated total organic halogen (total organic chlorine, bromine, and iodine). The plants represented a range of impacts, including algal, agricultural, and industrial wastewater. This study represents the most extensive full-scale study of its kind and seeks to address the question of whether GAC can make drinking water safer from a DBP perspective. Overall, GAC was effective for removing DBP precursors and reducing DBP formation and total organic halogen, even after >22 000 bed volumes of treated water. GAC also effectively removed preformed DBPs at plants using prechlorination, including highly toxic iodoacetic acids and haloacetonitriles. However, 7 DBPs (mostly brominated and nitrogenous) increased in formation after GAC treatment. In one plant, an increase in tribromonitromethane had significant impacts on calculated cytotoxicity, which only had 7-17% reduction following GAC. While these DBPs are highly toxic, the total calculated cytotoxicity and genotoxicity for the GAC treated waters for the other two plants was reduced 32-83% (across young-middle-old GAC). Overall, calculated toxicity was reduced post-GAC, with preoxidation allowing further reductions.

Coal-Fired Power Plant Wet Flue Gas Desulfurization Bromide Discharges to U.S. Watersheds and Their Contributions to Drinking Water Sources

Wet flue gas desulfurization (FGD) wastewater discharges from coal-fired power plants may increase bromide concentrations at downstream drinking water intakes, leading to increased formation of toxic disinfection byproducts (DBPs). Despite this, bromide was not regulated in FGD wastewater in the 2015 Effluent Limitations Guidelines and Standards for the Steam Electric Power Generating Point Source Category (ELGs). Case-by-case management was recommended instead, depending on downstream drinking water effects. The present work seeks to identify U.S. regions where power plant discharges could affect drinking water. Bromide loads were evaluated for all coal-fired power plants operating wet FGD, and flow paths were used to identify downstream surface water sources. A population-concentration metric was used to evaluate the effect of wet FGD on downstream drinking water and the vulnerability of drinking water to upstream discharges. On a hydrologic region level, results indicate the Ohio, South Atlantic Gulf, and Missouri Regions are the most likely to see effects of power plant bromide discharges on populations served by surface water. Increased refined coal use, which may be treated with bromide, contributes to uncertainty in potential bromide effects on drinking water. Measurement of bromide concentrations in wet FGD discharges would reduce this uncertainty, and control of bromide discharges may be needed in some watersheds.

Solid–liquid extraction of iodide and bromide from aqueous media by a new water-insoluble phenoxycalix[4]pyrrole-epichlorohydrin polymer

A phenoxycalix[4]pyrrole-epichlorohydrin based extractant was easily synthesized for the first time and used for iodide and bromide extraction from aqueous media.

Unregulated disinfection By-products in drinking water in Quebec: A meta analysis

Disinfection by-products (DBPs) are formed primarily by the reaction of natural organic matter and disinfectants. DBPs that are not regulated are referred to as unregulated DBPs (U-DBPs) and they are in majority in total DBPs. U-DBPs can be more toxic than regulated DBPs. U-DBPs such as haloacetonitriles (HANs), haloacetonitriles (HKs) and halonitromethanes (HNMs) are widely present in drinking water supplies in different regions of the world. This study investigated the occurrence of U-DBPs and their variability in drinking water in the Province of Quebec (Canada), using the water quality database of 40 municipal water systems generated by our research group. The concentrations of HANs, HKs, and their compounds, including chloropicrin (CPK), were highly variable in different water systems in Quebec. The concentration range of these U-DBPs is in line with drinking water concentration ranges in different regions of the world. Factors such as system size, water source, season, pH, total organic carbon content, free residual chlorine and disinfectant types cause significant variations in the concentrations of HANs, HKs and their constituent compounds, including CPK, in drinking water in Quebec. This information is valuable for decision making concerning source water selection, water distribution planning, water treatment plant design including disinfection, and overall drinking water quality management related to U-DBPs. Moreover, U-DBPs and regulated DBPs are strongly correlated, although the degree of correlation can vary with water source, system size and season, indicating that regulated DBPs can be used as surrogates of U-DBPs.

Removal of precursors and disinfection by-products (DBPs) by membrane filtration from water; a review

Disinfection by-products (DBPs) have heterogeneous structures which are suspected carcinogens as a result of reactions between NOMs (Natural Organic Matter) and oxidants/disinfectants such as chlorine. Because of variability in DBPs characteristics, eliminate completely from drinking water by single technique is impossible. The current article reviews removal of the precursors and DBPs by different membrane filtration methods such as Microfiltration (MF), Ultrafiltration (UF), Nanofiltration (NF) and Reverse Osmosis (RO) techniques. Also, we provide an overview of existing and potentially Membrane filtration techniques, highlight their strengths and drawbacks. MF membranes are a suitable alternative to remove suspended solids and colloidal materials. However, NOMs fractions are effectively removed by negatively charged UF membrane. RO can remove both organic and inorganic DBPs and precursors simultaneously. NF can be used to remove compounds from macromolecular size to multivalent ions.

One-step synthesis of Ag2O@Mg(OH)2 nanocomposite as an efficient scavenger for iodine and uranium

Ag₂O nanoparticles anchored on the Mg(OH)₂ nanoplates (Ag₂O@Mg(OH)₂) were successfully prepared by a facile one-step method, which combined the Mg(OH)₂ formation with Ag₂O deposition. The synthesized products were characterized by a wide range of techniques including powder X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and nitrogen physisorption analysis. It was found that Ag₂O nanoparticles anchored on the Mg(OH)₂ nanoplates show good dispersion and less aggregation relative to the single Ag₂O nanoaggregates. In addition, iodide (I^-) removal by the Ag₂O@Mg(OH)₂ nanocomposite was studied systematically. Batch experiments reveal that the nanocomposite exhibits extremely high I^- removal rate (<10min), and I^- removal capacity is barely affected by the concurrent anions, such as Cl^-, SO₄^2-, CO₃^2- and NO₃^-. Furthermore, I^- and UO₂²⁺ could be simultaneously removed by the nanocomposite with high efficiency. Due to the simple synthetic procedure, the excellent removal performances for iodine and uranium, and the easy separation from water, the Ag₂O@Mg(OH)₂ nanocomposite has real potential for application in radioactive wastewater treatment, especially during episodic environmental crisis.

Ozone regeneration of granular activated carbon for trihalomethane control

Spatial and temporal variations of trihalomethanes (THMs) in distribution systems have challenged water treatment facilities to comply with disinfection byproduct rules. In this study, granular activated carbon (GAC) and modified GAC (i.e., Ag-GAC and TiO₂-GAC) were used to treat chlorinated tap water containing CHCl₃ (15-21μg/L), CHBrCl₂ (13-16μg/L), CHBr₂Cl (13-14μg/L), and CHBr₃ (3μg/L). Following breakthrough of dissolved organic carbon (DOC), GAC were regenerated using conventional and novel methods. GAC regeneration efficiency was assessed by measuring adsorptive (DOC, UV absorbance at 254nm, and THMs) and physical (surface area and pore volume) properties. Thermal regeneration resulted in a brief period of additional DOC adsorption (bed volume, BV, ∼6000), while ozone regeneration was ineffective regardless of the GAC type. THM adsorption was restored by either method (e.g., BV for ≥80% breakthrough, CHBr₃ ∼44,000>CHBr₂Cl ∼35,000>CHBrCl₂ ∼31,000>CHCl₃ ∼7000). Cellular and attached adenosine triphosphate measurements illustrated the antimicrobial effects of Ag-GAC, which may have allowed for the extended THM adsorption compared to the other GAC types. The results illustrate that ozone regeneration may be a viable in-situ alternative for the adsorption of THMs during localized treatment in drinking water distribution systems.

Halide removal from aqueous solution by novel silver-polymeric materials

The objective of this study was to analyze the behavior of a new material, silver-doped polymeric cloth (Ag-cloth), in the removal of bromide and iodide from waters. Silver is immobilized on the cloth, guaranteeing selective adsorption of the halide ions as retained silver halides that therefore do not pass into the solution. Results indicate that Ag⁰ reacts with H₂O₂ in the first phases of the process, yielding Ag⁺ and superoxide radical; however, as the process advances, this radical favors Ag⁺ reduction. Increases in the concentration of H₂O₂ augment the capacity of the Ag-cloth to remove halides from the medium up to a maximum concentration (55μM), above which the removal capacity remains constant (Xm≅1.3-1.8mg halide/g Ag-cloth). Thus, when there is excess H₂O₂ in the medium, secondary competitive reactions that take place in the process guarantee a constant Ag⁺ concentration, which defines the maximum adsorption capacity of Ag-cloth, reducing its ability to remove halides. Ag-cloth has a higher capacity to remove iodide than bromide, and the presence of organic matter or chloride reduces its capacity to remove iodide or bromide from water. The results obtained shown that the capacity of Ag⁰ with H₂O₂ significantly varies as a function of the medium pH from 1mg Br^-/g Ag-cloth at very low pH to 1.6mg/g Ag-cloth at pH9.

Climatic, Geographic and Operational Determinants of Trihalomethanes (THMs) in Drinking Water Systems

Trihalomethanes (THMs) are conditionally carcinogenic compounds formed during chlorine disinfection in water treatment processes around the world. THMs occur especially when source waters are subject to marine influences, high and-or regular precipitation, and elevated levels of organic matter. THMs formation is then rooted in geographic, operational and climatic factors, the relative importance of which can only be derived from large datasets and may change in the future. Ninety three full-scale Scottish water treatment plants (WTPs) were assessed from Jan 2011 to Jan 2013 to identify factors that promote THMs formation. Correlation analysis showed that ambient temperature was the primary THMs formation predictor in potable water (r² = 0.66, p < 0.05) and water distribution systems (r² = 0.43, p = 0.04), while dissolved organic carbon (r² = 0.55, p < 0.001) and chloride (indicating marine influence; r² = 0.41, p < 0.001) also affected THMs formation. GIS mapping of median THMs levels indicated brominated THMs were most prevalent in coastal areas and on islands. This real-world dataset confirms both geographic and climatic factors are key to THMs formation. If ambient temperatures increase, THMs control will become more challenging, substantiating concerns about the impact of global warming on water quality.

Effect of capacitive deionization on disinfection by-product precursors

Formation of brominated disinfection by-products (DBPs) from bromide and natural organic matter upon chlorination imposes health risks to drinking water users. In this study, capacitive deionization (CDI) was evaluated as a potential process for DBP precursor removal. Synthetic humic acid and bromide containing saline water was used as model water prior to CDI treatment. Batch experiments were conducted at cell voltages of 0.6-, 0.9-, and 1.2V to study the influence of CDI on the ratio of bromide and dissolved organic carbon, bromine substitution factor, and DBP formation potential (FP). Results showed beneficial aspects of CDI on reducing the levels of these parameters. A maximum DBPFP removal from 1510 to 1160μg/L was observed at the cell voltage of 0.6V. For the removed DBPFP, electro-adsorption played a greater role than physical adsorption. However, it is also noted that there could be electrochemical oxidations that led to reduction of humic content and formation of new dichloroacetic acid precursors at high cell voltages. Because of the potential of CDI on reducing health risks from the formation of less brominated DBPs upon subsequent chlorination, it can be considered as a potential technology for DBP control in drinking water treatment.

Current and Potential Future Bromide Loads from Coal-Fired Power Plants in the Allegheny River Basin and Their Effects on Downstream Concentrations

The presence of bromide in rivers does not affect ecosystems or present a human health risk; however, elevated concentrations of bromide in drinking water sources can lead to difficulty meeting drinking water disinfection byproduct (DBP) regulations. Recent attention has focused on oil and gas wastewater and coal-fired power plant wet flue gas desulfurization (FGD) wastewater bromide discharges. Bromide can be added to coal to enhance mercury removal, and increased use of bromide at some power plants is expected. Evaluation of potential increases in bromide concentrations from bromide addition for mercury control is lacking. The present work utilizes bromide monitoring data in the Allegheny River and a mass-balance approach to elucidate bromide contributions from anthropogenic and natural sources under current and future scenarios. For the Allegheny River, the current bromide is associated approximately 49% with oil- and gas-produced water discharges and 33% with coal-fired power plants operating wet FGD, with 18% derived from natural sources during mean flow conditions in August. Median wet FGD bromide loads could increase 3-fold from 610 to 1900 kg/day if all plants implement bromide addition for mercury control. Median bromide concentrations in the lower Allegheny River in August would rise to 410, 200, and 180 μg/L under low-, mean-, and high-flow conditions, respectively, for the bromide-addition scenario.

Effects of chlorinated drinking water on the xenobiotic metabolism in Cyprinus carpio treated with samples from two Italian municipal networks

Drinking water (DW) disinfection represents a milestone of the past century, thanks to its efficacy in the reduction of risks of epidemic forms by water micro-organisms. Nevertheless, such process generates disinfection by-products (DBPs), some of which are genotoxic both in animals and in humans and carcinogenic in animals. At present, chlorination is one of the most employed strategies but the toxicological effects of several classes of DBPs are unknown. In this investigation, a multidisciplinary approach foreseeing the chemical analysis of chlorinated DW samples and the study of its effects on mixed function oxidases (MFOs) belonging to the superfamily of cytochrome P450-linked monooxygenases of Cyprinus carpio hepatopancreas, was employed. The experimental samples derived from aquifers of two Italian towns (plant 1, river water and plant 2, spring water) were obtained immediately after the disinfection (A) and along the network (R1). Animals treated with plant 1 DW-processed fractions showed a general CYP-associated MFO induction. By contrast, in plant 2, a complex modulation pattern was achieved, with a general up-regulation for the point A and a marked MFO inactivation in the R1 group, particularly for the testosterone metabolism. Together, the toxicity and co-carcinogenicity (i.e. unremitting over-generation of free radicals and increased bioactivation capability) of DW linked to the recorded metabolic manipulation, suggests that a prolonged exposure to chlorine-derived disinfectants may produce adverse health effects.

Comparing a silver-impregnated activated carbon with an unmodified activated carbon for disinfection by-product minimisation and precursor removal

During disinfection, bromide, iodide and natural organic matter (NOM) in source waters can lead to the formation of brominated and/or iodinated disinfection by-products (DBPs), which are often more toxic than their chlorinated analogues. The objective of this study was to compare the efficiency of a silver-impregnated activated carbon (SIAC) with the equivalent unimpregnated granular activated carbon (GAC) for the removal of bromide, iodide and NOM from a matrix of synthetic waters with variable NOM, halide, and alkalinity concentrations, and to investigate the impact on DBP formation. An enhanced coagulation (EC) pre-treatment was employed prior to sample exposure to either carbon adsorbent. Excellent halide removals were observed by the SIAC treatment across the sample matrix, with iodide concentrations consistently reduced to below the method reporting limit (<2 μg/L) from as high as 25 μg/L, and 95±4% removal of bromide achieved. Bromide removal by unimpregnated GAC was poor, however iodide removal was comparable to that achieved by SIAC. The combination of EC with SIAC treatment removed 77±8% of the dissolved organic carbon (DOC) present, across the sample matrix, which was similar to removals by EC/GAC (67±14%). Combined EC/SIAC treatment reduced both total trihalomethanes (tTHMs) and total dihaloacetonitriles (tDHANs) formation by 97±3%, while also achieving a greater than 74% removal of two chloropropanones and a 92±8% decrease in chloral hydrate (CH), compared to untreated samples, regardless of the sample's starting water quality (bromide, alkalinity and NOM concentration). Combined EC/GAC treatment led to similar DBP removals to EC/SIAC for the fully chlorinated DBPs, however, brominated DBPs were less efficiently removed, or experienced concentration increases.