Effects of chlorine dose on the composition and characteristics of chlorinated disinfection byproducts in reclaimed water

Characterizing the precursors of byproducts formed by chlorine and chlorine dioxide disinfection using unknown screening analysis with Orbitrap mass spectrometry

Chlorine (Cl2) and chlorine dioxide (ClO2) are commonly used to disinfect water but unfavorable interactions with dissolved organic matter (DOM) result in the formation of disinfection byproducts (DBPs). This study investigated the formation of organic DBPs arising from Cl2 and ClO2 disinfections under different contact times in two surface waters in Thailand and Suwannee River natural organic matter with/without bromide using unknown screening analysis with Orbitrap mass spectrometry. Many CHOCl-DBPs and CHOBr-DBPs intermediates were rapidly formed during the initial period of contact (5-30 min). Subsequently, the number of DBPs either decreased or increased (60-1440 min) due to the ongoing formation and decomposition of intermediate DBPs reacting with disinfectants. Over one hundred newly formed chlorinated DBPs were produced by Cl2 and ClO2 disinfections (CHOCl Cl2-DBPs and CHOCl ClO2-DBP, respectively). At least 40 % of the chlorinated DBPs were commonly found in the presence of both disinfectants, probably due to HOCl impurity formed by ClO2. In addition, CHO features with high degree of unsaturation ([DBE-O]/C) and moderate degree of carbon oxidation state (Cos) were found to be statistically correlated with several CHOCl-DBP and CHOBr-DBP features in Cl2 and ClO2 disinfections, and are therefore considered as putative precursors. Furthermore, the putative CHOBr-DBP precursors showed a more highly oxidized character than the putative CHOCl-DBP precursors. By tracking precursors from reactions using mass difference analysis, Cl2 preferentially reacts with saturated precursors via electrophilic substitution reaction, where the Cl2 addition reaction occurs more favorably in the presence of unsaturated precursors.

Fluorescence spectrometric analysis for diagnosing compositional variations in effluent organic matter by chlorination and ozonation

Analyzing the reactivity of organic matter to oxidants such as chlorination and ozonation is crucial for evaluating the effectiveness of water treatment systems and their potential impacts on environmental safety and human health. This study explored the changes in organic substances, specifically bovine serum albumin (BSA), humic acid sodium salt (HA), and effluent organic matter (EfOM) from a wastewater treatment facility during chlorination and ozonation. Four spectrometric techniques were employed: ultraviolet absorbance at 254 nm (UVA254), fluorescent excitation-emission matrix (EEM), synchronous fluorescence two-dimensional correlation spectroscopy (SF-2DCOS), and EEM-parallel factor integrated 2DCOS (EEM-PARAFAC-2DCOS). The findings revealed that ozone possesses superior oxidizing properties compared to chlorine, as evidenced by UVA254 and EEM analyses, resulting in more diverse structural modifications in EfOM. SF-2DCOS and EEM-PARAFAC-2DCOS provided comprehensive details on the direction and sequence of these changes, with EEM-PARAFAC-2DCOS delivering clear and intuitive insights. Protein-like and fulvic-like substances were susceptible to chlorination and ozonation, exhibiting different reaction sequences with each oxidant. Furthermore, variations in protein-like and humic-like components in actual EfOM samples may not align precisely with those in model substances, emphasizing the importance of considering specific organic matter variations in real EfOM samples compared to model substances. This research offered a deeper understanding of the reactivity and transformation of organic matter in wastewater treatment processes through simple and rapid spectroscopic methods, potentially improving the management and mitigation of undesired byproducts.

Changes in chemical characteristics and toxicity of fluoxetine and humic acid during chlorination

The coexistence of emerging pollutants and dissolved organic matter in wastewater complicates the transformation and generation of disinfection byproducts (DBPs) during chlorination treatment, which is essential for effective water quality evaluation and chlorination optimization. This study used fluoxetine (FLX) and humic acid (HA) as representative substances to analyze changes in their chemical characteristics and zebrafish embryonic developmental toxicity under different chlorination conditions. The analysis of the fluorescence characteristics and Fourier transform ion cyclotron resonance mass spectrometry indicated that chlorination treatment increased the aromatic compound content of the HA solution. FLX addition further increased the presence of aromatic ring structures and oxidized molecules, resulting in the formation of numerous Cl-DBPs with highly unsaturated and phenolic structures. Moreover, different responses in zebrafish embryo development and behavior were found with FLX, HA, and FLX + HA exposures. Cardiotoxicity was linked to changes in the concentration of cTn-I protein and expression of various genes. Prolonged chlorination conditions showed higher toxicities. Correlation analysis found a weak relation between chemical indicators and toxicity data, indicating that both analysis methods need to be considered when analyzing the impact of the chlorination. Further, a combination of chemical analyses and toxicity tests revealed that the FLX + HA solution with chlorination conditions of 3 mg/L for 30 min had lower chemical and toxic effects in this experiment. This study provides valuable scientific insights for the safe discharge of chlorinated water containing FLX and dissolved organic matter, as well as guidance for optimizing chlorination parameters in wastewater treatment.

Characterization of Disinfection By-Products Originating from Residual Chlorine-Based Disinfectants in Drinking Water Sources

In this study, samples from the Yangtze River, Han River, and Liangzi Lake in Wuhan City were utilized to characterize the formation of disinfection by-products (DBPs) from chlorine-based disinfection residues in drinking water sources. The results indicated that the main DBPs in drinking water sources were trichloromethane (TCM) and trichloroacetic acid (TCAA). The generation of DBPs was significantly positively correlated with oxidative substances, aromatic compounds, pH, and ammonia nitrogen (NH3-N) content in the water. The concentration of TCAA increased from 0 to 2.45 ± 0.31 mg/L when the reaction time increased to 72 h. As the NaClO concentration increased from 5 mg/L to 15 mg/L, the concentrations of TCAA, TBM, and DCAN increased from 2.03 ± 0.04 mg/L, 0 mg/L, and 0 mg/L to 2.49 ± 0.34 mg/L, 0.21 ± 0.07 mg/L, and 0.10 ± 0.04 mg/L before decreasing to 1.75 ± 0.19 mg/L, 0.17 ± 0.07 mg/L, and 0.04 ± 0.05 mg/L, respectively. The orthogonal experimental results showed that Br-, NH3-N, and pH all had significant influences on the TCM generation, whereas temperature affected the formation of TCAA in the Han River. This work reveals the factors influencing the generation of DBPs from chlorine-based disinfection residues, offering a prevention and control method for DBPs in drinking water sources from a theoretical perspective.

Graphitic Carbon Nitride Enters the Scene: A Promising Versatile Tool for Biomedical Applications

Graphitic carbon nitride (g-C3N4), since the pioneering work on visible-light photocatalytic water splitting in 2009, has emerged as a highly promising advanced material for environmental and energetic applications, including photocatalytic degradation of pollutants, photocatalytic hydrogen generation, and carbon dioxide reduction. Due to its distinctive two-dimensional structure, excellent chemical stability, and distinctive optical and electrical properties, g-C3N4 has garnered a considerable amount of interest in the field of biomedicine in recent years. This review focuses on the fundamental properties of g-C3N4, highlighting the synthesis and modification strategies associated with the interfacial structures of g-C3N4-based materials, including heterojunction, band gap engineering, doping, and nanocomposite hybridization. Furthermore, the biomedical applications of these materials in various domains, including biosensors, antimicrobial applications, and photocatalytic degradation of medical pollutants, are also described with the objective of spotlighting the unique advantages of g-C3N4. A summary of the challenges faced and future prospects for the advancement of g-C3N4-based materials is presented, and it is hoped that this review will inspire readers to seek further new applications for this material in biomedical and other fields.

The synergistic effect of oxidant-peroxide coupling systems for water and wastewater treatments

With the growing complexity and severity of water pollution, it has become increasingly challenging to effectively remove contaminants or inactivate microorganisms just by traditional chemical oxidants such as O3, chlorine, Fe(VI) and Mn(VII). Up till now, numerous studies have indicated that these oxidants in combination with peroxides (i.e., hydrogen peroxide (H2O2), peroxymonosulfate (PMS), peracetic acid (PAA) and periodate (PI)) exhibited excellent synergistic oxidation. This paper provided a comprehensive review on the combination of aforementioned oxidant-peroxide applied in water and wastewater treatments. From one aspect, the paper thoroughly elucidated the synergy mechanism of each oxidant-peroxide combination in turn. Among these combinations, H2O2 or PMS generally performed as the activator of four traditional oxidants above to accelerate reactive species generation and therein various reaction mechanisms, including electron transfer, O atom abstraction and oxo ligand substitution, were involved. In addition, although neither PAA nor PI was able to directly activate Fe(VI) and Mn(VII), they could act as the stabilizer of intermediate reactive iron/manganese species to improve the latter utilization efficiency. From another aspect, this paper summarized the influence of water quality parameters, such as pH, inorganic ions and natural organic matter (NOM), on the oxidation performance of most combined systems. Finally, this paper highlighted knowledge gaps and identified areas that require further research.

Phytotoxicity of trihalomethanes and trichloroacetic acid on Vigna radiata and Allium cepa plant models

Disinfection by-products (DBPs) are a concern due to their presence in chlorinated wastewater, sewage treatment plant discharge, and surface water, and their potential for environmental toxicity. Despite some attention to their ecotoxicity, little is known about the phytotoxicity of DBPs. This study aimed to evaluate the individual and combined phytotoxicity of four trihalomethanes (THMs: trichloromethane (TCM), bromodichloromethane (BDCM), dibromochloromethane (DBCM), and tribromomethane (TBM) and their mixture (THM4)), and trichloroacetic acid (TCAA) using genotoxic and cytotoxic assays. The analysis included seed germination tests using Vigna radiata and root growth tests, mitosis studies, oxidative stress response, chromosomal aberrations (CA), and DNA laddering using Allium cepa. The results showed a progressive increase in root growth inhibition for both plant species as the concentration of DBPs increased. High concentrations of mixtures of four THMs resulted in significant (p < 0.05) antagonistic interactions. The effective concentration (EC50) value for V. radiata was 5655, 3145, 2690, 1465, 3570, and 725 mg/L for TCM, BDCM, DBCM, TBM, THM4, and TCAA, respectively. For A. cepa, the EC50 for the same contaminants was 700, 400, 350, 250, 450, and 105 mg/L, respectively. DBP cytotoxicity was observed through CAs, including C-metaphase, unseparated anaphase, lagging chromosome, sticky metaphase, and bridging. Mitotic depression (MD) increased with dose, reaching up to 54.4% for TCAA (50-500 mg/L). The electrophoresis assay showed DNA fragmentation and shearing, suggesting genotoxicity for some DBPs. The order of phytotoxicity for the tested DBPs was TCAA > TBM > DBCM > BDCM > THM4 > TCM. These findings underscore the need for further research on the phytotoxicity of DBPs, especially given their common use in agricultural practices such as irrigation and the use of sludge as manure.

The occurrence, ecological risk, and control of disinfection by-products from intensified wastewater disinfection during the COVID-19 pandemic

Increased disinfection of wastewater to preserve its microbiological quality during the coronavirus infectious disease-2019 (COVID-19) pandemic have inevitably led to increased production of toxic disinfection by-products (DBPs). However, there is limited information on such DBPs (i.e., trihalomethanes, haloacetic acids, nitrosamines, and haloacetonitriles). This review focused on the upsurge of chlorine-based disinfectants (such as chlorine, chloramine and chlorine dioxide) in wastewater treatment plants (WWTPs) in the global response to COVID-19. The formation and distribution of DBPs in wastewater were then analyzed to understand the impacts of these large-scale usage of disinfectants in WWTPs. In addition, potential ecological risks associated with DBPs derived from wastewater disinfection and its receiving water bodies were summarized. Finally, various approaches for mitigating DBP levels in wastewater and suggestions for further research into the environmental risks of increased wastewater disinfection were provided. Overall, this study presented a comprehensive overview of the formation, distribution, potential ecological risks, and mitigating approaches of DBPs derived from wastewater disinfection that will facilitate appropriate wastewater disinfection techniques selection, potential ecological risk assessment, and removal approaches and regulations consideration.

Reduction of byproduct formation and cytotoxicity to mammalian cells during post-chlorination by the combined pretreatment of ferrate(VI) and biochar

Ferrate [Fe(VI)] can efficiently degrade various pollutants in wastewater. Biochar application can reduce resource use and waste emission. This study investigated the performance of Fe(VI)/biochar pretreatment to reduce disinfection byproducts (DBPs) and cytotoxicity to mammalian cells of wastewater during post-chlorination. Fe(VI)/biochar was more effective at inhibiting the cytotoxicity formation than Fe(VI) alone, reducing the cytotoxicity from 12.7 to 7.6 mg-phenol/L. The concentrations of total organic chlorine and total organic bromine decreased from 277 to 130 μg/L and from 51 to 39 μg/L, compared to the samples without pretreatment. Orbitrap ultra-high resolution mass spectrometry revealed that the number of molecules of DBPs decreased substantially from 517 to 229 by Fe(VI)/biochar, with the greatest reduction for phenols and highly unsaturated aliphatic compounds. In combination with the substantial reduction of 1Cl-DBPs and 2Cl-DBPs, 1Br-DBPs and 2Br-DBPs were also reduced. Fluorescence excitation-emission matrix coupled with parallel factor analysis suggested that fulvic acid-like substances and aromatic amino acid was obviously reduce likely due to the enhanced oxidation of Fe(IV)/Fe(V) produced by Fe(VI)/biochar and adsorption of biochar. Furthermore, the DBPs generated by electrophilic addition and electrophilic substitution of precursors were reduced. This study shows that Fe(VI)/biochar pretreatment can effectively reduce cytotoxicity formation during post-chlorination by transforming DBPs and their precursors.

Impact of invertebrates on water quality safety and their sheltering effect on bacteria in water supply systems

Invertebrates in drinking water not only affect human health, but also provide migration and shelter for pathogenic microorganisms. Their residues and metabolites also produce DBPs (disinfection by-products), which have adverse effects on the health of residents. In this study, the contributions of the rotifers and nematodes to the BDOC (biodegradable dissolved organic carbon), BRP (bacterial regrowth potential) and DBPs in drinking water were explored, and the sheltering effects of chlorine-resistant invertebrates on indigenous bacteria and pathogenic bacteria were studied, and the health and safety risk of invertebrates in drinking water was also assessed. The contributions of rotifer BAPs (biomass-associated products), UAPs (utilization-associated products) of rotifer, and nematode BAPs to the BRP were 46, 1240, and 24 CFU/mL. Nematodes were found to have a sheltering effect on indigenous bacteria and pathogenic bacteria, allowing them to resist chlorine disinfection and UV (ultraviolet) disinfection. When subjected to a UV dose of 40 mJ/cm², the inactivation rates of indigenous bacteria and three pathogenic bacteria decreased by 85% and 39-50% when bacteria were sheltered by the living nematodes; while decreased by 66% and 15-41% when they were sheltered by nematode residue. The safety risk posed by invertebrates in the drinking water was mainly due to their ability to promote bacterial regeneration and carry bacteria. This study aims to provide a theoretical basis and technical support for the risk control of invertebrates' pollution, and provides references for ensuring the safety of drinking water and formulating standards for the levels of invertebrates in drinking water.

Degradation and dechlorination of trichloroacetic acid induced by an in situ 222 nm KrCl* excimer radiation

Since the coronavirus disease 2019 (COVID-19) pandemic epidemic, the excessive usage of chlorinated disinfectants raised the substantial risks of disinfection by-products (DBPs) exposure. While several technologies may remove the typical carcinogenic DBPs, trichloroacetic acid (TCAA), their application for continuous treatment is limited due to their complexity and expensive or hazardous inputs. In this study, degradation and dechlorination of TCAA induced by an in situ 222 nm KrCl* excimer radiation as well as role of oxygen in the reaction pathway were investigated. Quantum chemical calculation methods were used to help predict the reaction mechanism. Experimental results showed that UV irradiance increased with increasing input power and decreased when the input power exceeded 60 W. Decomposition and dechlorination were simultaneously achieved, where around 78% of TCAA (0.62 mM) can be eliminated and 78% dechlorination within 200 min. Dissolved oxygen showed little effect on the TCAA degradation but greatly boosted the dechlorination as it can additionally generate hydroxyl radical (•OH) in the reaction process. Computational results showed that under 222 nm irradiation, TCAA was excited from S₀ to S₁ state and then decayed by internal crossing process to T₁ state, and a reaction without potential energy barrier followed, resulting in the breaking of C-Cl bond and finally returning to S₀ state. Subsequent C-Cl bond cleavage occurred by a barrierless •OH insertion and HCl elimination (27.9 kcal/mol). Finally, the •OH attacked (14.6 kcal/mol) the intermediate byproducts, leading to complete dechlorination and decomposition. The KrCl* excimer radiation has obvious advantages in terms of energy efficiency compared to other competitive methods. These results provide insight into the mechanisms of TCAA dechlorination and decomposition under KrCl* excimer radiation, as well as important information for guiding research toward direct and indirect photolysis of halogenated DBPs.

Novel method in emerging environmental contaminants detection: Fiber optic sensors based on microfluidic chips

Recently, human industrial practices and certain activities have caused the widespread spread of emerging contaminants throughout the environmental matrix, even in trace amounts, which constitute a serious threat to human health and environmental ecology, and have therefore attracted the attention of research scholars. Different traditional techniques are used to monitor water pollutants, However, they still have some disadvantages such as high costs, ecological problems and treatment times, and require technicians and researchers to operate them effectively. There is therefore an urgent need to develop simple, inexpensive and highly sensitive methods to sense and detect these toxic environmental contaminants. Optical fiber microfluidic coupled sensors offer different advantages over other detection technologies, allowing manipulation of light through controlled microfluidics, precise detection results and good stability, and have therefore become a logical device for screening and identifying environmental contaminants. This paper reviews the application of fiber optic microfluidic sensors in emerging environmental contaminant detection, focusing on the characteristics of different emerging contaminant types, different types of fiber optic microfluidic sensors, methodological principles of detection, and specific emerging contaminant detection applications. The optical detection methods in fiber optic microfluidic chips and their respective advantages and disadvantages are analyzed in the discussion. The applications of fiber optic biochemical sensors in microfluidic chips, especially for the detection of emerging contaminants in the aqueous environment, such as personal care products, endocrine disruptors, and perfluorinated compounds, are reviewed. Finally, the prospects of fiber optic microfluidic coupled sensors in environmental detection and related fields are foreseen.

Molecular transformation of dissolved organic matter and the formation of disinfection byproducts in full-scale surface water treatment processes

Dissolved organic matters (DOM) have important effects on the performance of surface water treatment processes and may convert into disinfection by-products (DBPs) during disinfection. In this work, the transformation of DOM and the chlorinated DBPs (Cl-DBPs) formation in two different full-scale surface water treatment processes (process 1: prechlorination-coagulation-precipitation-filtration; process 2: coagulation-precipitation-post-disinfection-filtration) were comparatively investigated at molecular scale. The results showed that coagulation preferentially removed unsaturated (H/C < 1.0 and DBE > 17) and oxidized (O/C > 0.5) compounds containing more carboxyl groups. Therefore, prechlorination produced more Cl-DBPs with H/C < 1.0 and O/C > 0.5 than post-disinfection. However, the algal in the influent produced many reduced molecules (O/C < 0.5) without prechlorination, and these compounds were more reactive with disinfectants. Sand filtration was ineffective in DOM removal, while microorganisms in the filter produced high molecular weight (MW) substances that were involved in the Cl-DBPs formation, causing the generation of higher MW Cl-DBPs under post-disinfection. Furthermore, the CHO molecules with high O atom number and the CHON molecules containing one N atom were the main Cl-DBPs precursors in both surface water treatment processes. In consideration of the putative Cl-DBPs precursors and their reaction pathways, the precursors with higher unsaturation degree and aromaticity were prone to produce Cl-DBPs through addition reactions, while that with higher saturation degree tended to form Cl-DBPs through substitution reactions. These findings are useful to optimize the treatment processes to ensure the safety of water quality.