Real Drinking Water Research Articles

Simple, Specific, and Ultra‐Sensitive Arsenic Detection in Real Drinking Water Samples Using an Impedimetric Green Sensor with Dimercaprol‐Doped Solid Electrolyte

AbstractArsenic monitoring is of paramount importance due to its toxicity, which poses potential public health hazards. While numerous sensitive methods exist, many are unsuitable for on‐site, rapid, real‐time measurements, and their sensor preparation is often time‐consuming and intricate. Addressing this gap necessitates the development of an easy‐to‐use, rapid, and reasonably affordable arsenic detection device featuring an eco‐friendly sensor. For on‐site arsenic monitoring, the optimal solution involves creating a sensitive impedimetric electrochemical sensor that is real‐time, fast, low‐cost, simple to design and use, and portable. This study introduces an electrochemical impedimetric sensor with a patent‐pending, solid electrolyte based on gelatin enriched with dimercaprol. The results demonstrate the detection of phenylarsine oxide in real drinking water samples, achieving a detection limit of 0.02 ng/mL within the linear range of 0.05 ng/mL to 100 ng/mL in just 40 minutes, utilizing a simple method and easily accessible, inexpensive, biodegradable chemicals. The methodology yields a sensitive sensor with biodegradable potential, exerting a negligible impact on the environment and human health.

Current Challenges in Monitoring Low Contaminant Levels of Per- and Polyfluoroalkyl Substances in Water Matrices in the Field.

The Environmental Protection Agency (EPA) of the United States recently released the first-ever federal regulation on per- and polyfluoroalkyl substances (PFASs) for drinking water. While this represents an important landmark, it also brings about compliance challenges to the stakeholders in the drinking water industry as well as concerns to the general public. In this work, we address some of the most important challenges associated with measuring low concentrations of PFASs in drinking water in the field in real drinking water matrices. First, we review the "continuous monitoring for compliance" process laid out by the EPA and some of the associated hurdles. The process requires measuring, with some frequency, low concentrations (e.g., below 2 ppt or 2 ng/L) of targeted PFASs, in the presence of many other co-contaminants and in various conditions. Currently, this task can only (and it is expected to) be accomplished using specific protocols that rely on expensive, specialized, and laboratory-scale instrumentation, which adds time and increases cost. To potentially reduce the burden, portable, high-fidelity, low-cost, real-time PFAS sensors are desirable; however, the path to commercialization of some of the most promising technologies is confronted with many challenges, as well, and they are still at infant stages. Here, we provide insights related to those challenges based on results from ab initio and machine learning studies. These challenges are mainly due to the large amount and diversity of PFAS molecules and their multifunctional behaviors that depend strongly on the conditions of the media. The impetus of this work is to present relevant and timely insights to researchers and developers to accelerate the development of suitable PFAS monitoring systems. In addition, this work attempts to provide water system stakeholders, technicians, and even regulators guidelines to improve their strategies, which could ultimately translate in better services to the public.

Electrochemical removal of antibiotics and multi-drug resistant bacteria using S-functionalized graphene sponge electrodes

In this study, we synthesized S-functionalized graphene sponge electrode and applied it for electrochemical oxidation of five commonly used antibiotics, namely sulfamethoxazole, trimethoprim, ofloxacin, roxithromycin and erythromycin, and the inactivation of a multi-drug resistant Escherichia coli (E. coli). The experiments were performed using real drinking water in a flow-through, one-pass mode. Highly polar antibiotics such as sulfamethoxazole did not adsorb onto the graphene sponge but were completely removed (i.e., ≥95% removal) at low applied current densities (14.5 A m−2). Antibiotics with high affinity for π-π interactions such as ofloxacin were completely removed already in the open circuit, and current application led to their further degradation. S-doped graphene sponge anode resulted in 4.5 log removal of a multi-drug resistant E. coli at 29 A m−2. There was no regrowth of bacteria observed during storage of the electrochemically treated samples, suggesting that the treatment severely impacted the cell viability. Further E. coli removal of 0.7 log was observed after the storage of electrochemically treated samples. The energy consumption of a continuously operated electrochemical system that achieved 4.5 log inactivation of a multi-drug resistant E. coli and 87–99% removal of antibiotics was 1.1 kWh m−3.

CRISPR/Cas9-based engineered Escherichia coli biosensor for sensitive and specific detection of Cd(II) in drinking water

Cadmium (Cd) is a ubiquitous pollutant that poses a potential threat to human health. Monitoring Cd(II) in drinking water has significant implications for preventing potential threats of Cd(II) to human. However, the weak signal output and response to nontarget interference limit the detection of Cd(II) using bacterial biosensors. In this study, to enable sensitive and specific detection of Cd(II) in water, a stable whole-cell biosensor, K12-PMP-luxCDABE-△cysI, was constructed in a dual-promoter mode by fusing the mercury promoter Pmer, regulatory gene merR(m), and luciferase gene luxCDABE into the E.coli chromosome based on CRISPR/Cas9 gene editing technology. By knocking out the cadmium-resistance-gene cysI, the sensitivity of the biosensor to Cd(II) was further enhanced. The constructed E. coli biosensor K12-PMP-luxCDABE-△cysI exhibited good nonlinear responses to 0.005–2 mg/L Cd(II). Notably, among the three constructed E. coli biosensor, it exhibited the strongest fluorescence intensity, with the limit of detection meeting the allowable limit for Cd(II) in drinking water. Simultaneously, it could specifically detect Cd(II). Nontarget metal ions, such as Zn(II), Hg(II), and Pb(II), did not affect its performance. Furthermore, it exhibited superior performance in detecting Cd(II) in real drinking water samples by avoiding background interference, and showed excellent stability with the relative standard deviation under 5%. Thus, K12-PMP-luxCDABE-△cysI holds promise as a potential tool for the detection of Cd(II) in drinking water.

Nonradical-dominated pathway toward selective catalytic ozonation of NH4+-N to N2 in drinking water over birnessite

Ammonia nitrogen (NH4+-N), which exists in the dominant form of ammonium ion (NH4+) under the pH of 6.5–8.5, is one of the regular indexes and the most important pollutants in drinking water. The selective conversion of NH4+-N into harmless substances is urgently needed and also a great challenge. Herein we propose a new NH4+-N conversion pathway based on a catalytic ozonation process with birnessite-type MnO2 (δ-MnO2) catalysts. The δ-MnO2 exhibits a superior performance for NH4+-N (1.0 mg/L) removal in adsorption (8.26 %) and oxidation (44.6 %) as well as up to 95.2 % of N2 selectivity, surpassing almost all the reported O3-based catalysts. Unlike the traditional radical oxidation, a singlet oxygen (1O2)-dominated nonradical oxidation pathway is confirmed for the efficiently selective conversion of NH4+-N to N2 through the successive dehydrogenation, leading to a 15.0-fold enhancement in NH4+-N oxidation rate compared with ozone oxidation. The Mn(III)/Mn(IV) redox sites and surface lattice oxygen in δ-MnO2 act as the active sites promoting the decomposition of O3 into •O2− and then 1O2 via electrons transfer. In application, δ-MnO2 catalytic ozonation effectively removes NH4+-N in real drinking water and presents excellent stability. This work finds a nonradical reaction mechanism in catalytic ozonation for NH4+-N selective conversion to N2, and solidly solves the problem of low-concentration NH4+-N removal from drinking water under the limited pH of 6.5–8.5 condition.

Evaluation of inactivation of bacterial indicators in real drinking water using UVC-LED

Bacterial contamination of drinking water sources is a serious problem. Here, we investigated the inactivation of bacterial indicators, namely total heterotrophic bacteria, total and fecal coliform in real drinking water using UVC-LED devices. Real drinking water samples collected every fortnight for a year from five different sampling sites showed significant prevalence of bacterial indicators. Each device was made up of 9 UVC-LED chips arranged in a line on a heat sink, covered with quartz tube, and submersible in water. A UVC-LED chip had an emission maximum, wall plug efficiency, and radiant power of around 276 nm, 0.018, and 10–12 mW, respectively. Inactivation was performed with 4 UVC-LED devices placed in series in a rectangular stainless-steel chamber with 1.2 L effective volume. With 30 LPH flow rate, and corresponding energy dosage of about 10.8 mJ/cm2, all bacterial indicators (initial load about 103 CFU/100 mL) were inactivated, as required by regulatory bodies. Notably, dark repair of bacterial indicators was not significant (<1 %) up to 24 h of storage in clean opaque (dark) vessel, whereas slight photo repair of bacterial indicators was observed (<10 %). Electrical energy (EE3) for complete inactivation and cost for water disinfection were determined to be about 1.397 kWh/m3 and ₹ 9.03 (€ 0.09 or $ 0.10), respectively. The estimated cost is affordable in developing countries. The study may be a referral to develop applications of UVC-LED irradiation for point-of-use drinking water disinfection and useful for resource-poor communities challenged with bacterial contaminated drinking water.

Photo driven homogeneous advanced oxidation coupled to adsorption process for an effective arsenic removal from drinking water

The presence of arsenic (As) in drinking water is a major concern for human health. As(III) is the most toxic water-soluble form and it is hard to remove by separation methods, including adsorption, while As(V) is less toxic and easily removable by adsorption. In this work homogenous photo driven advanced oxidation processes (HP-AOPs), namely UVC/H2O2 and UVC/NaOCl, have been investigated in the oxidation of As(III) (initial concentration of 0.1 mg/L) to As(V) and commercial available adsorbents (γ-Al2O3, Bayoxide E33, MgAl-LDHs and ZnAl-LDHs) were tested for subsequent As(V) removal. UVC/H2O2 (99% of As removal, 19 mg/L of H2O2, 2 min of treatment time) and UVC/NaOCl (99% of As removal, 5.1 mg/L of NaOCl, 2 min of treatment time) were found to be more effective than H2O2 (2% of As removal in the same condition of UVC/H2O2) and NaOCl (6% of As removal in the same condition of UVC/NaOCl), respectively and the optimum operation conditions were identified by response surface methodology (RSM) in distilled water and subsequently confirmed in real drinking water (with differences of less than 1%). UVC/NaOCl was the most suitable process being a good compromise among oxidation efficiency, oxidant dose and treatment time. The best results in terms of subsequent removal of As(V) by adsorption were obtained using ZnAl-LDH (88% in both distilled and drinking water). Accordingly, UVC/NaOCl advanced oxidation coupled to ZnAl-LDH adsorption is the best combination for an effective removal of arsenic from drinking water.

Decentralized approach toward organic pollutants removal using UV radiation in combination with H2O2-based electrochemical water technologies

The current literature lacks a comprehensive discussion on the trade-off between pollutant degradation/mineralization and treatment time costs in utilizing UV light in combination with H2O2-based electrochemical advanced oxidation processes (EAOPs). The present study sheds light on the benefits of using the photoelectro-Fenton (PEF) process with UVA or UVC for methylparaben (MetP) degradation in real drinking water. Although light boosts the photodegradation of refractory Fe(III) complexes and the photolysis of H2O2 (with UVC only), the energy-intensive nature of light-based treatments is acknowledged. To help tackle the high energy consumption issue, a novel approach was employed: partial application of UVA or UVC light after a predetermined electro-Fenton electrolysis time. The proposed treatment approach yielded satisfactory comparable results to those obtained from the application of PEF/UVA or PEF/UVC in terms of total organic carbon removal (ca. 100%), with notably lower energy consumption (ca. 50%). The study delves into the combined method's feasibility, analyzing pollutant degradation/mineralization process and overall energy consumption. The research identifies possible degradation routes based on intermediate detection and radical quenching experiments. Finally, toxicological assessments evaluate the toxicity levels of MetP and its intermediates. The findings of this study bring meaningful contributions to the fore and point to the highly promising potential of the proposed approach, in terms of sustainability and cost-effectiveness, when applied for decentralized water treatment.

Formation of disinfection by-products within the drinking water production system and distribution network of a real case study

This work presents a collaboration between the so-called Gasset Service Association (responsible for providing drinking water to 100,000 inhabitants from a surface water reservoir) and researchers from the University of Castilla-La Mancha (Spain). The main aim of this work was providing a comprehensive characterization of the formation and removal of disinfection by-products in a real drinking water treatment plant (DWTP) and water distribution network. According to the results obtained, it can be stated that bromate is formed on the pre-oxidation stage and it is not eliminated throughout the DWTP; meanwhile, total organic carbon is partially removed on the clarification process. Moreover, it demonstrates the key role of the residence time and the type of water storage throughout the distribution network (either in pipes or in tanks) due to the combined effect of, at least, four overlapped mechanisms: THMs chemical generation, air stripping, hydrolysis and biological removal. This comprehensive view of the drinking water production and distribution network represents an excellent framework for allowing the improvement in the drinking water quality for a very common water production case study: a medium-size city fed by a surface water source.

Efficient inactivation of amoeba spores and their intraspore bacteria by solar/chlorine: Kinetics and mechanisms

Amoebae are widespread in water and serve as environment vectors for pathogens, which may threaten public health. This study evaluated the inactivation of amoeba spores and their intraspore bacteria by solar/chlorine. Dictyostelium discoideum and Burkholderia agricolaris B1qs70 were selected as model amoebae and intraspore bacteria, respectively. Compared to solar irradiation and chlorine, solar/chlorine enhanced the inactivation of amoeba spores and intraspore bacteria, with 5.1 and 5.2-log reduction at 20 min, respectively. The enhancement was similar in real drinking water by solar/chlorine under natural sunlight. However, the spore inactivation decreased to 2.97-log by 20 min solar/chlorine under oxygen-free condition, indicating that ozone played a crucial role in the spore inactivation, as also confirmed by the scavenging test using tert‑butanol to scavenge the ground-state atomic oxygen (O(3P)) as a ozone precursor. Moreover, solar/chlorine induced the shape destruction and structural collapse of amoeba spores by scanning electron microscopy. As for intraspore bacteria, their inactivation was likely ascribed to endogenous reactive oxygen species. As pH increased from 5.0 to 9.0, the inactivation of amoeba spores decreased, whereas that of intraspore bacteria was similar at pH 5.0 and 6.5 during solar/chlorine treatment. This study first reports the efficient inactivation of amoeba spores and their intraspore pathogenic bacteria by solar/chlorine in drinking water.

Confined water–encapsulated activated carbon for capturing short-chain perfluoroalkyl and polyfluoroalkyl substances from drinking water

The global ecological crisis of perfluoroalkyl and polyfluoroalkyl substances (PFASs) in drinking water has gradually shifted from long-chain to short-chain PFASs; however, the widespread established PFAS adsorption technology cannot cope with the impact of such hydrophilic pollutants given the inherent defects of solid-liquid mass transfer. Herein, we describe a reagent-free and low-cost strategy to reduce the energy state of short-chain PFASs in hydrophobic nanopores by employing an in situ constructed confined water structure in activated carbon (AC). Through direct (driving force) and indirect (assisted slip) effects, the confined water introduced a dual-drive mode in the confined water-encapsulated activated carbon (CW-AC) and completely eliminated the mass transfer barrier (3.27 to 5.66 kcal/mol), which caused the CW-AC to exhibit the highest adsorption capacity for various short-chain PFASs (C-F number: 3-6) among parent AC and other adsorbents reported. Meanwhile, benefiting from the chain length- and functional group-dependent confined water-binding pattern, the affinity of the CW-AC surpassed the traditional hydrophobicity dominance and shifted toward hydrophilic short-chain PFASs that easily escaped treatment. Importantly, the ability of CW-AC functionality to directly transfer to existing adsorption devices was verified, which could treat 21,000 bed volumes of environment-related high-load (~350 ng/L short-chain PFAS each) real drinking water to below the World Health Organization's standard. Overall, our results provide a green and cost-effective in situ upgrade scheme for existing adsorption devices to address the short-chain PFAS crisis.

Electrochemical interference study of manganese and iron by multiplex method and the application for manganese analysis in drinking water

AbstractManganese is an emerging concern in drinking water, due to its potential health and aesthetic effects. Although accurate and sensitive, spectroscopic techniques for Mn2+ detection are costly and not capable of rapid detection. Electrochemical methods, such as cathodic stripping voltammetry, have been intensively explored as portable low‐cost methods for Mn2+ detection. Challenges of reliability and matrix interference are difficult to overcome with current electrochemical methods. Among the interference reagents, Fe2+ is one of the biggest challenges for Mn2+ detection. Herein, a new method based on multiplex chronoamperometry at potentials between 0.9 and 1.4 V by a multichannel potentiostat is explored for its ability for interference resistance and applicability for Mn2+ detection in real drinking water samples. Compared to conventional one‐channel electrochemical techniques, the multiplex method generates a reliable pattern that is unique to the sample components. The interference between Mn2+ and Fe2+ is investigated and the results are promising even at 100:1 Fe2+:Mn2+ concentrations. The detection limit determined for the multiplex method was 25.3 μM, and the optimum recovery rate in a real drinking water sample was 99.8%.

Chemical conditioning of drinking groundwater through Ca2+/Mg2+ ratio adjust as a treatment to reduce Ca precipitation: Batch assays and test bench experiments

Drinking groundwater sources can vary in their calcium (Ca)/magnesium (Mg) ratios, alkalinity levels, and temperatures. High levels of calcium relative to magnesium in water encourage Ca precipitation, causing pipe obstruction problems during water distribution. Ca/Mg ratio was studied in batch experiments using synthetic and real groundwater at different alkalinity levels, and temperatures to obtain an optimal condition that reduces Ca precipitation. The addition of magnesium salts to real drinking water was also investigated as a means of adjusting the Ca/Mg ratio and reducing Ca precipitation. A test bench was used to examine the effect of water velocity during its conduction on Ca precipitation, simulating an intermittent water supply. The results were analyzed and compared in terms of initial precipitation, rate of precipitation, and maximum precipitation of Ca using a modified model of Gompertz, and the precipitate was analyzed through X-ray Diffraction. The results of the present work found an optimal Ca/Mg ratio (1.1) that avoided Ca precipitation at batch conditions and during water conduction at different velocities, as well as Ca/Mg ratios that retarded or increased both the induction time and the maximum rate of Ca precipitation. Chemical conditioning by adjusting the Ca/Mg ratio is a viable option to minimize Ca precipitation in pipes.

Incorporating quartz crystal microbalance with chronoamperometry to enhance manganese detection stability in drinking water

Mn was previously considered a mere esthetic issue in drinking water; however, excessive Mn exposure has been linked to negative effects on children's neurological development. Current conventional laboratory techniques are constrained in their ability to provide real-time measurement of Mn release events, due to expensive bench-sized instrumentation and lengthy turn-around times. Herein, we developed and investigated the working principle and application of a portable and rapid electrochemical method to detect Mn2+ in drinking water. The method employs quartz crystal microbalance (QCM) integrated with chronoamperometry (CA) to measure charge transfer and weight change during Mn2+ oxidation. The deposition of MnO2 is characterized by electrochemical methods, SEM, EDS and QCM. The CA-QCM calibration curves were determined in Milli-Q water and a real drinking water sample with a detection limit of 12.9 µM in drinking water sample. Additionally, an effective cleaning procedure was developed to regenerate the sensor after use. The CA-QCM technique demonstrated higher reproducibility and interference resistance than other conventional electrochemical methods in the presence of common drinking water components, as well as an excellent recovery rate (101.7%) in a real drinking water sample.

Peroxymonosulfate activated by composite ceramic membrane for the removal of pharmaceuticals and personal care products (PPCPs) mixture: Insights of catalytic and noncatalytic oxidation

A composite manganese-based catalytic ceramic membrane (Mn-CCM) was developed by a solid-state sintering method, and its effectiveness toward activation of peroxymonosulfate (PMS) for the degradation of 11 pharmaceutical and personal care products (PPCPs) mixture was tested. The optimized Mn-CCMs/PMS system showed remarkable degradation efficiencies for PPCPs mixture with total removal >90% in ultrapure water, river water and natural organic matter (NOM) solution. The Mn-CCMs/PMS system showed the contribution of different phenomena in PPCPs removal in the order of catalytic oxidation (54.7%, Mn-CCMs/PMS) > noncatalytic oxidation (42.3%, PMS oxidation) > adsorption (3.0%, by Mn-CCMs). The singlet oxygen (1O2) was the dominant reactive oxygen specie for the degradation of PPCPs in all water matrices proved by the quenching experiments and electro-paramagnetic resonance (EPR) spectroscopy. The extraordinary stability of Mn-CCMs for the activation of PMS has been noted in terms of repeatability experiments for PPCPs degradation with fewer leaching of Mn (1.9 to 3.6 µg/L). Mineralization was achieved in the range of 28–65% for different water matrices. The toxicity of the PPCPs mixture was reduced by 85.9%. The Mn-CCMs/PMS system showed a reduction (25–100%) in precursors of different carbon- and nitrogen-based disinfection by-products. This study found the Mn-CCMs/PMS system as a feasible purification unit for removing trace concentrations of PPCPs (ng/L) in real drinking water matrices.

Superfast degradation of micropollutants in water by reactive species generated from the reaction between chlorine dioxide and sulfite

Chlorine dioxide (ClO2) is used as an oxidant or disinfectant in (waste)water treatment, whereas sulfite is a prevalent reducing agent to quench the excess ClO2. This study demonstrated that seven micropollutants with structural diversity could be rapidly degraded in the reaction between ClO2 and sulfite under environmentally relevant conditions in synthetic and real drinking water. For example, carbamazepine, which is recalcitrant to standalone ClO2 or sulfite, was degraded by 55%–80% in 10 s in the ClO2/sulfite process at 30-µM ClO2 and 30-µM sulfite concentrations within a pH range of 6.0–11.0. Results from experiments and a kinetic model supported that chlorine monoxide (ClO·) and sulfate radicals (SO4·–) were generated in the ClO2/sulfite process, while hydroxyl radical generation was insignificant. Apart from radicals, dichlorine trioxide (Cl2O3) was generated and largely contributed to micropollutant degradation, supported by experimental results using stopped-flow spectrometry and quantum chemical calculations. The impacts of pH, sulfite dosage, and water matrix components (chloride, bicarbonate, and natural organic matter) on micropollutant abatement in the ClO2/sulfite process were evaluated and discussed. When treating the real potable water, the concentrations of organic (five regulated disinfection byproducts) and inorganic byproducts (chlorite and chlorate) formed in the ClO2/sulfite process were all below the drinking water standards. This study disclosed fundamental knowledge advancements relevant to the reaction mechanisms between ClO2 and sulfite, and highlighed a novel process to abate micropollutants in water and wastewater.

Microseira wollei and Phormidium algae more than doubles DBP concentrations and calculated toxicity in drinking water

Warm weather and excess nutrients from agricultural runoff trigger harmful algal blooms, which can affect drinking water safety due to the presence of algal toxins and the formation of disinfection by-products (DBPs) during drinking water treatment. In this study, 66 priority, unregulated and regulated DBPs were quantified in chlorinated controlled laboratory reactions of harmful algae Microseira wollei (formerly known as Lyngbya wollei) and Phormidium using gas chromatography (GC)-mass spectrometry (MS). Live algae samples collected from algae-impacted lakes in South Carolina were chlorinated in both ultrapure water and real source waters containing natural organic matter. DBPs were also measured in finished water from a real drinking water plant impacted by a Microseira bloom. Results show that the presence of Microseira and Phormidium more than doubles total concentrations of DBPs formed by chlorination, with levels up to 586 μg/L formed in natural lake waters. Toxic nitrogen-containing DBPs also more than doubled in concentration, with levels up to 36.1, 3.6, and 37.9 μg/L for haloacetamides, halonitromethanes, and haloacetonitriles, respectively. In ultrapure water, DBPs also formed up to 314 μg/L when algae was chlorinated, demonstrating their ability to serve as direct precursors for these DBPs. When environmentally relevant levels of bromide and iodide were added to chlorination reactions, total DBPs increased 144, 51, and 24% for drinking water reservoir, Lake Marion and Lake Wateree Microseira respectively and 29% for Phormidium. Iodo-DBPs, bromochloroiodomethane, chloroiodoacetic acid, bromoiodoacetic acid, and diiodoacetic acid were observed in finished water from a drinking water plant impacted by Microseira, and bromochloroiodomethane and dibromoiodomethane were observed in chlorinated ultrapure water containing algae, bromide, and iodide. Notably, total calculated cytotoxicity tripled in Microseira–impacted waters and doubled for Phormidium-impacted waters. Calculated genotoxicity doubled for Microseira-impacted waters and more than doubled in Phormidium-impacted waters. Haloacetonitriles were major drivers of calculated cytotoxicity in algae-impacted waters, while haloacetic acids were major drivers of calculated genotoxicity in algae-impacted waters. These results provide the most extensive assessment of DBPs formed from chlorination of algae-impacted waters and highlight potential impacts to drinking water and human health. Results from this study are particularly applicable to drinking water treatment plants that employ pre-chlorination, which can cause the release of algal organic matter (AOM) precursors to form DBPs.

The influence of drinking water constituents on the level of microplastic release from plastic kettles

Microplastic (MP) release from household plastic products has become a global concern due to the high recorded levels of microplastic and the direct risk of human exposure. However, the most widely used MP measurement protocol, which involves the use of deionized (DI) water, fails to account for the ions and particles present in real drinking water. In this paper, the influence of typical ions (Ca2+/HCO3-, Fe3+, Cu2+) and particles (Fe2O3 particles) on MP release was systematically investigated by conducting a 100-day study using plastic kettles. Surprisingly, after 40 days, all ions resulted in a greater than 89.0% reduction in MP release while Fe2O3 particles showed no significant effect compared to the DI water control. The MP reduction efficiency ranking is Fe3+ ≈ Cu2+ > Ca2+/HCO3- > > Fe2O3 particles ≈ DI water. Physical and chemical characterization using SEM-EDX, AFM, XPS and Raman spectroscopy confirmed Ca2+/HCO3-, Cu2+ and Fe3+ ions are transformed into passivating films of CaCO3, CuO, and Fe2O3, respectively, which are barriers to MP release. In contrast, there was no film formed when the plastic was exposed to Fe2O3 particles. Studies also confirmed that films with different chemical compositions form naturally in kettles during real life due to the different ions present in local regional water supplies. All films identified in this study can substantially reduce the levels of MP release while withstanding the repeated adverse conditions associated with daily use. This study underscores the potential for regional variations in human MP exposure due to the substantial impact water constituents have on the formation of passivating film formation and the subsequent release of MPs.

Mechanistic and kinetic understanding of micropollutant degradation by the UV/NH2Cl process in simulated drinking water

The UV/monochloramine (UV/NH2Cl) process has attracted increasing attention in water treatment, in which hydroxyl radicals (HO•), reactive chlorine species (RCS) and reactive nitrogen species (RNS) are produced. This study investigated the effects of water matrices including halides, natural organic matter (NOM), alkalinity and pH, on the degradation kinetic of a variety of micropollutants and radical chemistry in the UV/NH2Cl process. The presence of chloride blunted HO• and Cl• impacts, but enhanced Cl2•- effect on micropollutants reactive toward Cl2•-. The presence of 30 μM bromide led to an 82% decrease in the specific pseudo-first-order rate constants (k') by HO• (kHO•'), and significantly diminished RCS efficacy. Reactive bromine species (RBS) were formed in the presence of bromide, while the contribution could not compensate for the decrease of HO• and RCS due to their lower reactivity toward micropollutants. Iodide rapidly transformed to HOI via reacting with NH2Cl, which resulted in a 59% decrease of kHO•' and 12% ∼ 100% decreases of k' by reactive halogen species (RHS) and RNS (kRHS+RNS') for most micropollutants. Nevertheless, k' of phenolic compounds, such as paracetamol, bisphenol A and salbutamol, increased in the presence of iodide by 78%, 360% and 130%, respectively, due to the roles of HOI and reactive iodine species (RIS). Bicarbonate decreased the contributions of HO• and RCS, but enhanced that of CO3•- for micropollutants reactive toward CO3•-. The presence of 1 mg/L NOM scavenged over half the amount of HO•, and also consumed RCS and RNS, resulting in significantly decreased removal of micropollutants. High pH value witnessed enhanced degradation for those micropollutants reactive toward RCS and RNS through deprotonation. The degradation of most micropollutants was inhibited in real drinking water and in the coexistence of halides. This study provides a better understanding of radical chemistry in the UV/NH2Cl process under a practical water treatment condition.

Geosmin and 2-methylisoborneol adsorption using different carbon materials: Isotherm, kinetic, multiple linear regression, and deep neural network modeling using a real drinking water source

High concentrations of geosmin (GSM) and 2-methylisoborneol (MIB) caused by cyanobacterial blooms are problematic issues in drinking water treatment plants on the Nak-Dong River in South Korea. The goal of this study was to identify the best-performing carbon materials to treat GSM and MIB in river water and to predict the final concentrations of GSM and MIB according to different water quality parameters using computational predictive modeling, multiple linear regression (MLR), and a deep neural network (DNN) for practical applications. Three types of powdered activated carbon (PAC) and three types of mesoporous carbon (MC) were compared in terms of their adsorption capacities using a source of drinking water from the Nak-Dong River. The highest maximum adsorption capacities were achieved when using C-PAC (1485.06 μg/g) in both distilled water and river water. C-PAC possesses a high micropore volume (0.45 cm3/g), low mesopore volume (0.11 cm3/g), and small, narrow pore size distribution, yielding optimal adsorption conditions. PACs yielded better results than MCs because dominant mesopore structures can hinder the adsorption of small molecules (0.6–0.8 nm) and allow them to pass through pores. GSM was removed more effectively than MIB because GSM is more hydrophobic and has a flatter structure. The high dissolved organic carbon concentration in the river water caused no reduction in GSM and MIB adsorption, but actually enhanced adsorption because a small portion of natural organic matter can compete with adsorption sites and provide additional adsorption sites based on the shrunk pore effect. The MLR and DNN models were used to predict the removal efficiency of C-PAC for GSM and MIB using 72 individual datasets with cross-validation for robust prediction and sensitivity analysis. MLR predicted the relationships between the input variables and GSM and MIB concentrations with an acceptable mean absolute error (MAE) of 6.43 ng/L for GSM and 5.80 ng/L for MIB. However, the DNN provided better agreement with a higher R2 value (>0.99) and lower MAE of 1.67 ng/L for GSM and 1.24 ng/L for MIB.