Disinfection byproduct formation during drinking water treatment and distribution: A review of unintended effects of engineering agents and materials

Comprehensive comparison of water quality risk and microbial ecology between new and old cast iron pipe distribution systems

The effects of cast iron pipe corrosion on water quality risk and microbial ecology in drinking water distribution systems (DWDSs) were investigated. It was found that trihalomethane (THMs) concentration and antibiotic resistance genes (ARGs) increased sharply in the old DWDSs. Under the same residual chlorine concentration conditions, the adenosine triphosphate concentration in the effluent of old DWDSs (Eff-old) was significantly higher than that in the effluent of new DWDSs. Moreover, stronger bioflocculation ability and weaker hydrophobicity coexisted in the extracellular polymeric substances of Eff-old, meanwhile, iron particles could be well inserted into the structure of the biofilms to enhance the mechanical strength and stability of the biofilms, hence enhancing the formation of THMs. Old DWDSs significantly influenced the microbial community of bulk water and triggered stronger microbial antioxidant systems response, resulting in higher ARGs abundance. Corroded cast iron pipes induced a unique interaction system of biofilms, chlorine, and corrosion products. Therefore, as the age of cast iron pipes increases, the fluctuation of water quality and microbial ecology should be paid more attention to maintain the safety of tap water.

Unexpected weakened formation of disinfection byproducts and enhanced production of halates by cupric oxide during chlorination of peptide-bound aspartic acid

Under the condition that the residual chlorine is guaranteed, the biofilm still thrives in drinking water distribution systems through secreting a large number of extracellular polymeric substances (EPS), in which protein components are the primary precursor of disinfection byproducts (DBPs), mostly in the form of combined amino acids. The aim of this study is to investigate the action of CuO on the formation of halates (XO3-, ClO3- and BrO3-) and DBPs (trihalomethanes, THMs; haloacetonitriles, HANs) with aspartic acid tetrapeptide (TAsp) as protein surrogate. The presence of CuO promoted the self-decay rather than TAsp-induced decay of oxidants, resulting in an increase in XO3- yield and a decrease in DBPs yield. It was CuO-induced weaker production of cyanoacetic acid and 3-oxopropanoic acid that induced the decreased yields of HANs and THMs, respectively. The FTIR and Raman spectra indicate a weak complexation between CuO and TAsp. Given this, the CuO-HOX/OX- complexes were inferred to be reactive to HOX/OX- but less reactive to TAsp. The study helps to better understand the formation of XO3- and DBPs during the chlorination of EPS, and propose precise control strategies when biofilm boosts in water pipes.

Effects of Fe(III) on the formation and toxicity alteration of halonitromethanes, dichloroacetonitrile, and dichloroacetamide from polyethyleneimine during UV/chlorine disinfection

Trace iron ions (Fe(III)) are commonly found in water and wastewater, where free chlorine is very likely to coexist with Fe(III) affecting the disinfectant's stability and N-DBPs' fate during UV/chlorine disinfection, and yet current understanding of these mechanisms is limited. This study investigates the effects of Fe(III) on the formation and toxicity alteration of halonitromethanes (HNMs), dichloroacetonitrile (DCAN), and dichloroacetamide (DCAcAm) from polyethyleneimine (PEI) during UV/chlorine disinfection. Results reveal that the maxima concentrations of HNMs, DCAN, and DCAcAm during UV/chlorine disinfection with additional Fe(III) were 1.39, 1.38, and 1.29 times higher than those without additional Fe(III), instead of being similar to those of Fe(III) inhibited the formation of HNMs, DCAN and DCAcAm during chlorination disinfection. Meanwhile, higher Fe(III) concentration, acidic pH, and higher chlorine dose were more favorable for forming HNMs, DCAN, and DCAcAm during UV/chlorine disinfection, which were highly dependent on the involvement of HO· and Cl·. Fe(III) in the aquatic environment partially hydrolyzed to the photoactive Fe(III)‑hydroxyl complexes Fe(OH)2+ and [Fe(H2O)6]3+, which undergone UV photoactivation and coupling reactions with HOCl to achieve effective Fe(III)/Fe(II) interconversion, a process that facilitated the sustainable production of HO·. Extensive product analysis and comparison verified that the HO· production enhanced by the Fe(III)/Fe(II) internal cycle played a primary role in increasing HNMs, DCAN, and DCAcAm productions during UV/chlorine disinfection. Note that the incorporation of Fe(III) increased the cytotoxicity and genotoxicity of HNMs, DCAN, and DCAcAm formed during UV/chlorine disinfection, and yet Fe(III) did not have a significant effect on the acute toxicity of water samples before, during, and after UV/chlorine disinfection. The new findings broaden the knowledge of Fe(III) affecting HNMs, DCAN, and DCAcAm formation and toxicity alteration during UV/chlorine disinfection.

Novel sunlight-induced monochloramine activation system for efficient microcontaminant abatement

As an eco-friendly and sustainable energy, solar energy has great application potential in water treatment. Herein, simulated sunlight was for the first time utilized to activate monochloramine for the degradation of environmental organic microcontaminants. Various microcontaminants could be efficiently degraded in the simulated sunlight/monochloramine system. The average innate quantum yield of monochloramine over the wavelength range of simulated sunlight was determined to be 0.068 mol/Einstein. With the determined quantum yield, a kinetic model was established. Based on the good agreement between the simulated and measured photolysis and radical contributions to the degradation of ibuprofen and carbamazepine, the major mechanism of monochloramine activation by simulated sunlight was proposed. Chlorine radical (Cl∙) and hydroxyl radical (HO∙) were major radicals responsible for microcontaminant degradation in the system. Moreover, the model facilitated a deep investigation into the effects of different reaction conditions (pH, monochloramine concentration, and water matrix components) on the degradation of ibuprofen and carbamazepine, as well as the roles of the involved radicals. The differences between simulated and measured degradation data of each microcontaminant under all conditions were less than 10 %, indicating the strong reliability of the model. The model could also make good prediction for microcontaminant degradation in the natural sunlight/monochloramine system. Furthermore, the formation of disinfection byproducts (DBPs) was evaluated at different oxidation time in simulated sunlight/monochloramine with and without post-chloramination treatment. In real waters, organic components showed more pronounced suppression on microcontaminant degradation efficiency than inorganic ions. This study provided a systematic investigation into the novel sunlight-induced monochloramine activation system for efficient microcontaminant degradation, and demonstrated the potential of the system in practical applications.

Complex impact of metals on the fate of disinfection by-products in drinking water pipelines: A systematic review

Metals in the drinking water distribution system (DWDS) play an important role on the fate of disinfection by-products (DBPs). They can increase the formation of DBPs through several mechanisms, such as enhancing the proportion of reactive halogen species (RHS), catalysing the reaction between natural organic matter (NOM) and RHS through complexation, or by increasing the conversion of NOM into DBP precursors. This review comprehensively summarizes these complex processes, focusing on the most important metals (copper, iron, manganese) in DWDS and their impact on various DBPs. It organizes the dispersed 'metals-DBPs' experimental results into an easily accessible content structure and presents their underlying common or unique mechanisms. Furthermore, the practically valuable application directions of these research findings were analysed, including the toxicity changes of DBPs in DWDS under the influence of metals and the potential enhancement of generalization in DBP model research by the introduction of metals. Overall, this review revealed that the metal environment within DWDS is a crucial factor influencing DBP levels in tap water.

N-nitrosamines in electroplating and printing/dyeing industrial wastewater treatment plants: Removal efficiency, environmental emission, and the influence on drinking water

The discharge of industrial wastewater containing high concentrations of N-nitrosamines to the aquatic environment can impair downstream source waters and pose potential risks to human health. However, the transport and fate of N-nitrosamines in typical industrial wastewater treatment plants (IWWTPs) and the influence of these effluents on source water and drinking water are still unclear. This study investigated nine N-nitrosamines in four full-scale electroplating (E-) and printing/dyeing (PD-) IWWTPs, two drinking water treatment plants (DWTPs) in the lower reaches of these IWWTPs, and the corresponding tap water in South China. The total concentrations of N-nitrosamines (∑NAs) were 382-10,600, 480-1920, 494-789, and 27.9-427 ng/L in influents, effluents, source water, and tap water, respectively. The compositions of N-nitrosamine species in different influents varied a lot, while N-nitrosodi-n-butylamine (NDBA) and N-nitrosodimethylamine (NDMA) dominated in most of the effluents, source water, and tap water. More than 70 % N-nitrosamines were removed by wastewater treatment processes used in E-IWWTPs such as ferric-carbon micro-electrolysis (Fe/C-ME), while only about 50 % of N-nitrosamines were removed in PD-IWWTPs due to the use of chlorine reagent or other inefficient conventional processes such as flocculation by cationic amine-based polymers or bio-contact oxidation. Therefore, the mass fluxes of N-nitrosamines discharged from these industrial wastewaters to the environment in the selected two industrial towns were up to 14,700 mg/day. The results based on correlation and principal component analysis significantly demonstrated correlations between E-and PD-effluents and source water and tap water, suggesting that these effluents can serve as sources of N-nitrosamines to local drinking water systems. This study suggests that N-nitrosamines are prevalent in typical IWWTPs, which may infect drinking water systems. The findings of this study provide a basis data for the scientific evaluation of environmental processes of N-nitrosamines.

PFAS promotes disinfection byproduct formation through triggering particle-bound organic matter release in drinking water pipes

Loose deposit particles in drinking water distribution system commonly exist as mixtures of metal oxides, organic materials, bacteria, and extracellular secretions. In addition to their turbidity-causing effects, the hazards of such particles in drinking water are rarely recognized. In this study, we found that trace per- and polyfluoroalkyl substances (PFASs) could dramatically promote the formation of disinfection byproducts (DBPs) by triggering the release of particle-bound organic matter. Carboxylic PFASs have a greater ability to increase chloroacetic acid than sulfonic PFASs, and PFASs with longer chains have a greater ability to increase trichloromethane release than shorter-chain PFASs. Characterization by organic carbon and organic nitrogen detectors and Fourier transform ion cyclotron resonance mass spectrometry revealed that the released organic matter was mainly composed of proteins, carbohydrates, lignin, and condensed aromatic structures, which are the main precursors for the formation of DBPs, particularly highly toxic aromatic DBPs. After the release of organic matter, the particles exhibit a decrease in surface functional groups, an increase in surface roughness, and a decrease in particle size. The findings provide new insights into the risks of loose deposits and PFASs in drinking water, not only on PFASs per se but also on its effect of increasing toxic DBPs.

A critical review of advances in tumor metabolism abnormalities induced by nitrosamine disinfection by-products in drinking water

Intensified sanitation practices amid the recent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak might result in the increased release of chloramine disinfectants into surface water, significantly promoting the formation of nitrosamine disinfection by-products (DBPs) in drinking water. Unfortunately, these nitrosamine DBPs exhibit significant genotoxic, carcinogenic, and mutagenic properties, whereas chlorinating disinfectants remain in global practice. The current review provides valuable insights into the occurrence, identification, contamination status, exposure limits, and toxicity of the new unregulated disinfection by-products (nitrosamine DBPs) in drinking water. As a result, concentrations of nitrosamine DBPs far exceed allowable limits in drinking water, and prolonged exposure has the potential to cause metabolic disorders, a critical step in tumor initiation and progression. Importantly, based on recent research, we have concluded the role of nitrosamines DBPs in different metabolic pathways. Remarkably, nitrosamine DBPs can induce chronic inflammation and initiate tumors by activating sphingolipid and polyunsaturated fatty acid metabolism. Regarding amino acid and nucleotide metabolism, nitrosamine DBPs can inhibit tryptophan metabolism and de novo nucleotide synthesis. Moreover, inhibition of de novo nucleotide synthesis fails to repair DNA damage induced by nitrosamines. Additionally, the accumulation of lactate induced by nitrosamine DBPs may act as a pivotal signaling molecule in communication within the tumor microenvironment. However, with the advancement of tumor metabolomics, understanding the role of nitrosamine DBPs in causing cancer by inducing metabolic abnormalities significantly lags behind, and specific mechanisms of toxic effects are not clearly defined. Urgently, further studies exploring this promising area are needed.

Impact of changes in biofilm composition response following chlorine and chloramine disinfection on nitrogenous disinfection byproduct formation and toxicity risk in drinking water distribution systems

In practical drinking water treatment, chlorine and chloramine disinfection exhibit different mechanisms that affect biofilm growth. This study focused on the influence of biofilm composition changes, especially extracellular polymeric substance (EPS) fractions, on the potential formation and toxicity of nitrogenous disinfection by-products (N-DBP). Significant differences in microbial diversity and community structure were observed between the chlorine and chloramine treatments. Notably, the biofilms from the chloramine-treated group had higher microbial dominance and greater accumulation of organic precursors, as evidenced by the semi-quantitative confocal laser-scanning microscopy assay of more concentrated microbial aggregates and polysaccharide proteins in the samples. Additionally, the chloramine-treated group compared with chlorine had a higher EPS matrix content, with a 13.5 % increase in protein. Furthermore, the protein distribution within the biofilm differed; in the chlorine group, proteins were concentrated in the central region, whereas in the chloramine group, proteins were primarily located at the water-biofilm interface. Notably, functional prediction analyses of protein fractions in biofilms revealed specific functional regulation patterns and increased metabolism-related abundance of proteins in the chlorine-treated group. This increase was particularly pronounced for proteins such as dehydrogenases, reductases, transcription factors, and acyl-CoA dehydrogenases. By combining the Fukui function and density functional calculations to further analyse the effect of biofilm component changes on N-DBP production under chlorine/chloramine and by assessing the toxicity risk potential of N-DBP, it was determined that chloramine disinfection is detrimental to biofilm control and the accumulation of protein precursors has a higher formation potential of N-DBPs and toxicity risk, increasing the health risk of drinking water.

Adsorption, boiling or membrane filtration for disinfection by-product removal: How to make our drinking water safer?

Disinfection by-products (DBPs) generated in drinking water have become a global concern due to their potential harm to human health. Nevertheless, there are few studies about different point-of-use water treatments in household drinking water. The study aims to compare the effectiveness of three point-of-use water treatments: adsorption, boiling, and membrane filtration. The experimental results showed that the initial average concentration of volatile DBPs and non-volatile DBPs for tap water were 63.71 μg/L and 6.33 μg/L. The removal efficiency of DBPs for adsorption which were 75.6 % (the filter volumes from 0 L to 20 L) and 45.4 % (the filter volumes from 20 L to 50 L) during the service life of the filter element (50 L). Boiling had a high removal efficiency for volatile DBPs like trihalomethanes (THMs), haloacetaldehydes (HALs), haloacetonitriles (HANs), and haloketones (HKs) (90.5 %, 100 %, 100 %, and 100 %, respectively). However, boiling had a low removal efficiency which was 15 % in removing non-volatile DBPs like haloacetic acids (HAAs). Membrane filtration had a middle removal efficiency for THMs, HAAs, HALs, HKs, and HANs (45.3 %, 75.2 %, 46.5 %, 47.6 %, and 100 %, respectively). Through analysis of the correlation between dissolved organic matter (DOM) removal efficacy and DBP removal efficiency, it was found that the strongest correlation was observed between UV254 and DBP removal efficiency. Boiling showed a lower estimated cytotoxicity of DBPs compared to adsorption and membrane filtration. Cancer risk assessment of DBPs was below the specified risk range for three point-of-use water treatments. This study provides a reference for choosing point-of-use water treatments in household drinking water.

Aging of polystyrene microplastics by UV/Sodium percarbonate oxidation: Organic release, mechanism, and disinfection by-product formation

The occurrence and transformation of microplastics (MPs) in environment has attracted considerable attention. However, the release characteristics of MP-derived dissolved organic matter (MP-DOM) under oxidation conditions and the effect of DOM on subsequent chlorination disinfection by-product (DBP) still lacks relevant information. This study focused on the conversion of polystyrene microplastics (PSMPs) in the advanced oxidation of ultraviolet-activated sodium percarbonate (UV/SPC-AOP) and the release characteristics of MP-DOM. The DBP formation potential of MP-DOM was also investigated. As a result, UV/SPC significantly enhanced the aging and fragmentation of PSMPs. Under UV irradiation, the fluorescence peak intensity and position of humus-like and protein-like components of MP-DOM were correlated with SPC concentration. The aging MP suspension was analyzed by gas chromatography-mass spectrometry (GC-MS), and various alkyl-cleavage and oxidation products were identified. Quenching experiments and electron paramagnetic resonance (EPR) detection confirmed that carbonate and hydroxyl radicals jointly dominated the conversion of PSMPs. The formation of DBP was related to the components of MP-DOM. Overall, these results help to understand the aging behavior of MPs in AOP. Moreover, MP-DOM released by MPs after AOP oxidation may be a precursor of DBPs, which deserved more attention.

Oxidation of amine-based pharmaceuticals with unactivated peroxymonosulfate: Kinetics, mechanisms, and elimination efficiency of NDMA formation

Amine-based pharmaceuticals are a significant class of N-nitrosodimethylamine (NDMA) precursors. This study investigated the use of unactivated peroxymonosulfate (PMS) to control amine-based pharmaceuticals and their NDMA formation potential. Kinetic analysis and product identification revealed that sumatriptan and doxylamine primarily underwent reactions at their tertiary amine group, while ranitidine and nizatidine had both tertiary amine and thioether group as reaction sites. The NDMA formation from sumatriptan and doxylamine during post-chloramination was significantly reduced with the abatement of the parent contaminants, while the formation of NDMA remained high even if full abatement of ranitidine and nizatidine was achieved. Product formation kinetics and reference standard tests revealed the great contribution of transformation products to NDMA formation. Ranitidine could be oxidized to sulfoxide-type product ranitidine-SO and N-oxide type product ranitidine-NO. Ranitidine-SO exhibited a high NDMA yield comparable to that of ranitidine (>90%), while ranitidine-NO showed a low NDMA yield (2%). With further oxidation of ranitidine-SO at the tertiary amine group, NDMA formation was reduced by more than 90%. The underlying mechanism for the importance of the tertiary amine group in NDMA formation was demonstrated by quantum chemical calculation. These findings underscore the potential of PMS pre-oxidation on NDMA control.

Chemical-free vacuum ultraviolet irradiation as ultrafiltration membrane pretreatment technique: Performance, mechanisms and DBPs formation

Membrane fouling induced by natural organic matter (NOM) has seriously affected the further extensive application of ultrafiltration (UF). Herein, a simple, green and robust vacuum ultraviolet (VUV) technology was adopted as pretreatment before UF and ultraviolet (UV) technology was used for comparison. The results showed that control effect of VUV pretreatment on membrane fouling was better than that of UV pretreatment, as evidenced by the increase of normalized flux from 0.27 to 0.38 and 0.73 after 30 min UV or VUV pretreatment, respectively. This is related to the fact that VUV pretreatment exhibited stronger NOM degradation ability than UV pretreatment owing to the formation of HO•. The steady-state concentration of HO• was calculated as 3.04 × 10-13 M and the cumulative exposure of HO• reached 5.52 × 10-10 M s after 30 min of VUV irradiation. And the second-order rate constant between NOM and HO• was determined as 1.36 × 104 L mg-1 s-1. Furthermore, fluorescence EEM could be applied to predict membrane fouling induced by humic-enriched water. Standard blocking and cake filtration were major fouling mechanisms. Moreover, extension of UV pretreatment time increased the disinfection by-products (DBPs) formation, the DBPs concentration was enhanced from 322.36 to 1187.80 μg/L after 210 min pretreatment. However, VUV pretreatment for 150 min reduced DBPs content to 282.57 μg/L, and DBPs content continued to decrease with the extension of pretreatment time, revealing that VUV pretreatment achieved effective control of DBPs. The variation trend of cytotoxicity and health risk of DBPs was similar to that of DBPs concentration. In summary, VUV pretreatment exhibited excellent effect on membrane fouling alleviation, NOM degradation and DBPs control under a certain pretreatment time.

Synergistic effects of trace sulfadiazine and corrosion scales on disinfection by-product formation in bulk water of cast iron pipe

The effects of trace sulfadiazine (SDZ) and cast-iron corrosion scales on the disinfection by-product (DBP) formation in drinking water distribution systems (DWDSs) were investigated. The results show that under the synergistic effect of trace SDZ (10 μg/L) and magnetite (Fe3O4), higher DBP concentration occurred in the bulk water with the transmission and distribution of the drinking water. Microbial metabolism-related substances, one of the important DBP precursors, increased under the SDZ/Fe3O4 condition. It was found that Fe3O4 induced a faster microbial extracellular electron transport (EET) pathway, resulting in a higher microbial regrowth activity. On the other hand, the rate of chlorine consumption was quite high, and the enhanced microbial EET based on Fe3O4 eliminated the need for microorganisms to secrete excessive extracellular polymeric substances (EPS). More importantly, EPS could be continuously secreted due to the higher microbial activity. Finally, high reactivity between EPS and chlorine disinfectant resulted in the continuous formation of DBPs, higher chlorine consumption, and lower EPS content. Therefore, more attention should be paid to the trace antibiotics polluted water sources and cast-iron corrosion scale composition in the future. This study reveals the synergistic effects of trace antibiotics and corrosion scales on the DBP formation in DWDSs, which has important theoretical significance for the DBP control of tap water.

Associations between urinary biomarkers of exposure to disinfection byproducts and semen parameters: A repeated measures analysis

Toxicological studies have demonstrated that disinfection byproducts (DBPs), particularly haloacetic acids, cause testicular toxicity. However, evidence from human studies is sparse and inconclusive. This study included 1230 reproductive-aged men from the Tongji Reproductive and Environmental (TREE) cohort to investigate the associations between repeated measures of DBP exposures and semen parameters. Urinary dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) as biomarkers of DBP exposures and semen parameters in up to three samples from each man were assessed. The linear mixed effect models were applied to explore the associations between urinary biomarkers of DBP exposures and semen parameters. We found inverse associations of urinary DCAA with sperm count, progressive motility, and total motility (e.g., -14.86%; 95% CI: -19.33%, -10.15% in sperm total motility for the highest vs. lowest quartiles; all P for trends < 0.05). Moreover, urinary TCAA modeled as a continuous variable was negatively associated with sperm progressive motility and total motility, while the inverse associations across increasing urinary TCAA quartiles were seen among leaner men (BMI < 25 kg/m2). Exposure to DBPs reflected by urinary DCAA and TCAA was inversely associated with sperm motility and such effects were more evident among leaner men.

Preparation and Characterization of Polyethersulfone/Activated Carbon Composite Membranes for Water Filtration

Ultrafiltration membrane technology holds promise for wastewater treatment, but its widespread application is hindered by fouling and flux reduction issues. One effective strategy for enhancing ultrafiltration membranes involves incorporating activated carbon powder. In this study, composite polyethersulfone (PES) ultrafiltration membranes were fabricated to include activated carbon powder concentrations between 0 and 1.5 wt.%, with carbon size fixed at 200 mesh. The ultrafiltration membranes were evaluated in terms of membrane morphology, hydrophilicity, pure water flux, equilibrium water content, porosity, average pore size, protein separation, and E-coli bacteria removal. It was found that the addition of activated carbon to PES membranes resulted in improvements in some key properties. By incorporating activated carbon powder, the hydrophilicity of PES membranes was enhanced, lowering the contact angle from 60° to 47.3° for composite membranes (1.0 wt.% of activated carbon) compared to the pristine PES membrane. Water flux tests showed that the 1.0 wt.% composite membrane yielded the highest flux, with an improvement of nearly double the initial value at 2 bar, without compromising bovine serum albumin rejection or bacterial removal capabilities. This study also found that the inclusion of activated carbon had a minor impact on the membrane's porosity and equilibrium water content. Overall, these insights will be beneficial in determining the optimal concentration of activated carbon powder for PES ultrafiltration membranes.

Performance evaluation of artificial intelligence with particle swarm optimization (PSO) to predict treatment water plant DBPs (haloacetic acids)

The prevention of water-borne diseases requires the disinfection of water consumed. Disinfection by-products, however, are an increasing concern, and they require advanced knowledge of water treatment plants before their release for human consumption. In this study, multivariate non-linear regression (MNR) and adaptive neuro-fuzzy inference system (ANFIS: Grid partition - GP and Sub-clustering - SC) integrated with particle swarm optimization (PSO) were proposed for the prediction of haloacetic acids (HAAs) in actual distribution systems. PSO-ANFIS-GP and PSO-ANFIS-SC were trained and verified for a total of 64 sets of data with eight parameters (pH, Temperature, UVA254, DOC, Br-; NH4+-N; NO2--N, residual free chlorine). With MNR, R2 is 0.5184 Collapse

Key Words

• Grid partition
• Haloacetic acids
• Multivariate non-linear regression
• Particle swarm optimization
• Sub-clustering

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MESH Headings

• Humans
• Artificial Intelligence
• Water Purification
• Neural Networks, Computer
• Fuzzy Logic
• Disinfection

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Grants Collapse

Affiliation(s)

Anthony I Okoji Department of Chemical Engineering, Covenant University, Ota, Ogun state, Nigeria.
Comfort N Okoji Department of Biology and Forensic, Admiralty University, Ibusa, Delta state, Nigeria
Olorunfemi S Awarun Department of Microbiology, Landmark University, Omu-Aran, Kwara state, Nigeria

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Fluorescence spectroscopy in the detection and management of disinfection by-product precursors in drinking water treatment processes: A review

Monitoring and prevention of the formation of disinfection by-products (DBPs) is paramount in drinking water treatment plants (DWTP) to ensure human health safety. This review provides an overview of how fluorescence techniques are developed to predict DBP formation and to evaluate the reduction of fluorescence components and DBPs following individual DWTP processes. Evidence has shown that common DBPs, nitrogenous DBPs and specific emerging DBPs exhibit positive linear relationships with terrestrial, anthropogenic, tryptophan-like, and eutrophic humic-like fluorescence. Due to the interrelationships of both regulated and emerging DBP types with fluorescence components, the limitations arise when attempting to predict emerging DBPs solely through linear relationships. Monitoring the reduction of DBP precursors after each treatment process can be achieved by studying the relationship between fluorescence components and DBPs. During the coagulation process, highest reduction rates are observed for terrestrial humic-like fluorescence. Advanced treatments such as granular, powdered, silver-impregnated activated carbon, magnetic ion exchange resins, and reverse osmosis, have revealed a significant reduction of fluorescent DBP precursors, ranging from 53% to 100%. During chlorination, the reduction rate follows the order: terrestrial humic-like > microbial humic-like > protein/tryptophan-like fluorescence. This review provides insights into the reduction of fluorescence signatures following individual DWTP processes, which offers information regarding DBP formation. These insights could assist in optimizing the treatment process to more effectively manage DBP formation. For the identification of emerging DBP generation, the utilization of advanced models is imperative to precisely predict emerging DBPs and to more accurately trace DBP precursors within DWTPs.

Niche Differentiation of Biofilm Microorganisms in a Full-scale Municipal Drinking Water Distribution System in China and Their Implication for Biofilm Control

Biofilms on the inner surface of a drinking water distribution system (DWDS) affect water quality and stability. Understanding the niche differentiation of biofilm microbial communities is necessary for the efficient control of DWDS biofilms. However, biofilm studies are difficult to conduct in the actual DWDS because of inaccessibility to the pipes buried underground. Taking the opportunity of infrastructure construction and relevant pipeline replacement in China, biofilms in a DWDS (a water main and its branch pipes) were collected in situ, followed by analysis on the abundances and community structures of bacterial and archaeal using quantitative PCR and high-throughput sequencing, respectively. Results showed that archaea were detected only in the biofilms of the water main, with a range of 9.4×103~1.1×105 copies/cm2. By contrast, bacteria were detected in the biofilms of branch pipes and the distal part of the water main, with a range of 8.8×103~9.6×106 copies/cm2. Among the biofilm samples, the archaeal community in the central part of the water main showed the highest richness and diversity. Nitrosopumilus was found to be predominant (86.22%) in the biofilms of the proximal part of the water main. However, Methanobrevibacter (87.15%) predominated in the distal part of the water main. The bacterial community of the water main and branch pipes was primarily composed of Firmicutes and Proteobacteria at the phylum level, respectively. Regardless of archaea or bacteria, only few operational taxonomic units (OTUs) (<0.5% of total OTUs) were shared by all the biofilms, indicating the niche differentiation of biofilm microorganisms. Moreover, the high Mn content in the biofilms of the distal sampling location (D3) in the water main was linked to the predominance of Bacillus. Functional gene prediction revealed that the proportion of infectious disease-related genes was 0.44-0.67% in the tested biofilms. Furthermore, functional genes related to the resistance of the bacterial community to disinfections and antibiotics were detected in all the samples, that is, glutathione metabolism-relating genes (0.14-0.65%) and beta-lactam resistance gene (0.01-0.05%). The results of this study indicate the ubiquity of archaea and bacteria in the biofilms of water main and branch pipes, respectively, and pipe diameters could be a major influencing factor on bacterial community structure. In the water main, the key finding was the predominant existence of archaea, particularly Nitrosopumilus and methanogen. Hence, their routine monitoring and probable influences on water quality in pipelines with large diameter should be given more attention. Besides, since Mn-related Bacillus and suspected pathogenic Enterococcus were detected in the biofilm, supplementation of disinfectant may be a feasible strategy for inhibiting their growth and ensuring water quality. In addition, the monitoring on their abundance variation could help to determine the frequency and methods of pipeline maintenance.

Porous pillararene-based polymer as adsorbent and solid disinfectant for water treatment

Pillararene polymers have been widely used as excellent adsorbents for water treatment, but pillararene polymers with ultra-high specific surface area and versatility are still rarely reported. Herein, a quaternary ammonium salt modified pillar [5] arene polymer, QPBP [5], with specific surface area of 1844 m2 g-1 was successfully synthesized. Since QPBP [5] has abundant different adsorption sites, it exhibits excellent performance for the simultaneously removal of organic pollutants with different charges from water. The selected three model pollutants, Rhodamine B (RhB, positively charged), Sulfamethazine (SMT, electrically neutral) and Fulvic acid (FA, negatively charged), could be rapidly and efficiently removed from water by QPBP [5] within 10 min, which are much faster than them by most of the reported adsorbents. RhB and SMT are mainly adsorbed through hydrophobic interactions with the QPBP [5] surface, while FA is mainly removed through ion exchange. In addition, QPBP [5] also showed excellent reusability and adsorption performance for the environmentally relevant concentration of pollutants. Furthermore, the quaternary ammonium groups on QPBP [5] makes it a solid disinfectant with excellent antibacterial properties. In conclusion, QPBP [5] is a promising multifunctional adsorbent for the treatment of complex pollutants in water.

Iron particles lower than 10 μm in drinking water dominate particle catalysis effect on disinfection byproduct formation

Iron particles could catalyze disinfection by-product (DBP) formation in drinking water distribution systems (DWDS), but the catalytic effects of iron particles considering size effects have not been focused. Here, we first found that fine particles (lower than 10 μm) dominated the particle catalysis effect of the iron particles on the formation of DBPs containing multiple Cl atoms (DBP-3Cl), especially those with aromatic structure and containing multiple N atoms (DBP-3N). The loose deposit particles were filtered through 50 μm (F50), 10 μm (F10) and 1 μm (F10) membranes, and their turbidity values were 231.6, 53.4 and 1.1 NTU, respectively. In mass ratio, F50, F10 and F1 accounted for 84 %, 15 % and 1 % of unfiltered samples. Notably, the lower mass F10 generated more DBP-3Cl and DBP-3N than F50. Metal crystals and natural organic matters showed little difference among different sizes. The high catalytic activity of particles in F10 due to size effect was proved to be the essential mechanism. F1 contained few particles to affect DBP formation. In toxicity evaluation, the toxicity of F10 was even higher than F50. Therefore, fine particles with sizes lower than 10 μm may play a dominate role in the catalytic effect on DBP transformation in DWDS.

Comparative study of UV/chlorine and VUV/chlorine as ultrafiltration membrane pretreatment techniques: Performance, mechanisms and DBPs formation

Membrane fouling, primarily resulting from natural organic matter (NOM) widely existing in water sources, has always been a chief hindrance for the prevalent application of ultrafiltration (UF). Thus, vacuum ultraviolet (VUV)/chlorine process was proposed as a strategy for UF membrane fouling control and ultraviolet (UV)/chlorine process was used for comparison. VUV/chlorine process exhibited more excellent performance on NOM removal than UV/chlorine process. [HO•]ss and [Cl•]ss were calculated as 1.26 × 10-13 and 3.06 × 10-14 M, respectively, and ClO• might not exist under the conditions of 0.08 mM chlorine and 30 min VUV irradiation. [HO•]ss, [Cl•]ss and [ClO•]ss were not available and the formation of reactive radicals was unsustainable in UV/chlorine system. Moreover, VUV/chlorine pretreatment also showed better performance on the reversible and irreversible membrane fouling control than UV/chlorine pretreatment. The dominated fouling mechanism in the final stage of filtration was cake filtration. Additionally, the amount of detected disinfection by-products (DBPs) in VUV/chlorine system was significantly lower than that in UV/chlorine system. During subsequent chlorination disinfection, the yield of DBPs with VUV/chorine pretreatment was higher than that with UV/chlorine pretreatment. VUV/chlorine pretreatment could effectively control DBPs formation when the pretreatment time was extended to 120 min. In summary, VUV/chlorine system presented a most excellent performance on membrane fouling control, NOM degradation and DBPs control.

Disinfection by-product precursors introduced by sandstorm events: Composition, formation characteristics and potential risks

Sandstorms, a natural meteorological event, occur repeatedly during the dry season and can accumulate large amounts of natural/anthropogenic pollutants during the deposition process, potentially introducing disinfection by-product (DBP) precursors into surface waters. In this study, the characteristics of sandstorm-derived dissolved organic matter (DOM) and its DBP formation potential were elucidated. Overall, sandstorm-derived DOM mainly consisted of low-molecular-weight, low-aromaticity, high-nitrogen organic matter, with a dissolved organic carbon (DOC) release yield of 14.4 mg-DOC/g. The halogenated DBP formation potential (calculated as total organic halogen) of sandstorm-derived DOM was comparable to that of surface water, while the normalized DBP-associated toxicity was 1.96 times higher. Similar to DOM introduced by other depositional pathways, sandstorm-derived DOM also had higher yields of highly cytotoxic DBPs (haloacetaldehydes [HALs], haloacetonitriles [HANs] and halonitromethanes [HNMs]). The average atmospheric deposition flux for DOM during the sandstorm event (50.4 ± 2.1 kg km-2 day-1) was 6.95 times higher than that of dry deposition, indicating a higher probability of contaminant input. Simultaneously, the estimation revealed that the sandstorm will increase the formation potential of toxicity forcing agents, such as HALs, HANs and HNMs, in surface water by 3.87%, 2.39% and 9.04%, respectively. Considering the high frequency of sandstorm events and the sorption of other organic pollutants by sand and dust, the impact of sandstorms on surface water quality should be of concern.

Removal of disinfection byproducts through integrated adsorption and reductive degradation in a membrane-less electrochemical system

Proper control/removal of disinfection byproducts (DBPs) is important to drinking water safety and human health. In this study, a membrane-less electrochemical system was developed and investigated to remove DPBs through integrated adsorption and reduction by granular activated carbon (GAC)-based cathode. Representative DPBs including trihalomethanes and haloacetonitriles at drinking water concentrations were used for removal experiments. The proposed system achieved >70% removal of most DBPs in a batch mode. The comparison with control tests under either open circuit or hydrolysis demonstrated the advantages of electrochemical treatment, which not only realized higher DPBs removal but also extended GAC cathode lifetime. Such advantages were further demonstrated with continuous treatment. High dechlorination and debromination efficiencies were obtained in both batch (82.2 and 94.3%) and continuous (79.3 and 87.6%) reactors. DBPs removal was mainly contributed by the electrochemical reduction and adsorption by the GAC-based cathode, while anode showed little oxidizing effect on DBPs and halide ions. Dehalogenated products of chloroform and dichloroacetonitrile were identified with toxicity reduction. The energy consumption of the continuously operated system was estimated to be 0.28 to 0.16 kWh m-3. The proposed system has potential applications for wastewater reuse or further purification of drinking water.

The Behavior of Polymeric Pipes in Drinking Water Distribution System-Comparison with Other Pipe Materials

The inner walls of the drinking water distribution system (DWDS) are expected to be clean to ensure a safe quality of drinking water. Complex physical, chemical, and biological processes take place when water comes into contact with the pipe surface. This paper describes the impact of leaching different compounds from the water supply pipes into drinking water and subsequent risks. Among these compounds, there are heavy metals. It is necessary to prevent these metals from getting into the DWDS. Those compounds are susceptible to impacting the quality of the water delivered to the population either by leaching dangerous chemicals into water or by enhancing the development of microorganism growth on the pipe surface. The corrosion process of different pipe materials, scale formation mechanisms, and the impact of bacteria formed in corrosion layers are discussed. Water treatment processes and the pipe materials also affect the water composition. Pipe materials act differently in the flowing and stagnation conditions. Moreover, they age differently (e.g., metal-based pipes are subjected to corrosion while polymer-based pipes have a decreased mechanical resistance) and are susceptible to enhanced bacterial film formation. Water distribution pipes are a dynamic environment, therefore, the models that are used must consider the changes that occur over time. Mathematical modeling of the leaching process is complex and includes the description of corrosion development over time, correlated with a model for the biofilm formation and the disinfectants-corrosion products and disinfectants-biofilm interactions. The models used for these processes range from simple longitudinal dispersion models to Monte Carlo simulations and 3D modeling. This review helps to clarify what are the possible sources of compounds responsible for drinking water quality degradation. Additionally, it gives guidance on the measures that are needed to maintain stable and safe drinking water quality.

Enhanced disinfection byproducts formation by fine iron particles intercepted in household point-of-use facilities

To cope with the demand for good-quality potable water, household point-of-use (POU) facilities such as polypropylene cotton filters (PCFs) are widely used. However, the behaviors of new and used PCFs under discoloration are unclear. In this study, we found that new PCF did not effectively intercept particles under discoloration within the initial 5 d of inflow. In addition, the particles, especially the fine ones, accumulated in the long-used PCF exacerbated the risks of disinfection byproducts (DBPs) and microbes. The concentrations of trihalomethanes (THMs) and haloacetonitriles (HANs) in the effluent run through the PCF all increased over time; interestingly, all sharply increased after 5 d in accordance with the decrease in effluent iron particles. During this stage, maximum increases rate of 117.89% in THMs and 75.12% in HANs were observed. For haloacetic acids (HAAs), it served as the dominant contaminants, with concentrations approximately 10-fold greater than those of THMs and HANs. The increase showed that used PCFs could exacerbate the risks in DBPs exposure. Adenosine triphosphate (ATP) also showed a similar trend, with a maximum increase from 0.0033 to 0.0055 nmol/mL. Thus, PCFs can act only as pretreatment units and should be replaced after yellow water events. This study offers important guidance for PCF usage in drinking water purification, especially under discoloration.

NaHCO3 addition enhances water permeance and Ca/haloacetic acids selectivity of nanofiltration membranes for drinking water treatment

The existence of disinfection by-products such as haloacetic acids (HAAs) in drinking water severely threatens water safety and public health. Nanofiltration (NF) is a promising strategy to remove HAAs for clean water production. However, NF often possesses overhigh rejection of essential minerals such as calcium. Herein, we developed highly selective NF membranes with tailored surface charge and pore size for efficient rejection of HAAs and high passage of minerals. The NF membranes were fabricated through interfacial polymerization (IP) with NaHCO3 as an additive. The NaHCO3-tailored NF membranes exhibited high water permeance up to ∼24.0 L m - 2 h - 1 bar-1 (more than doubled compared with the control membrane) thanks to the formation of stripe-like features and enlarged pore size. Meanwhile, the tailored membranes showed enhanced negative charge, which benefitted their rejection of HAAs and passage of Ca and Mg. The higher rejection of HAAs (e.g., > 90%) with the lower rejection of minerals (e.g., < 30% for Ca) allowed the NF membranes to achieve higher minerals/HAAs selectivity, which was significantly higher than those of commercially available NF membranes. The simultaneously enhanced membrane performance and higher minerals/HAAs selectivity would greatly boost water production efficiency and water quality. Our findings provide a novel insight to tailor the minerals/micropollutants selectivity of NF membranes for highly selective separation in membrane-based water treatment.

NO3- Promotes Nitrogen-Containing Disinfection Byproduct Formation in Corroded Iron Drinking Water Pipes

Nitrogen-containing disinfection byproducts (N-DBPs) are highly toxic DBPs in drinking water. Though, under normal conditions, NO3- could not directly participate in disinfection reactions to generate N-DBPs, here, we first found that NO3- could promote the formation of N-DBPs in corroded iron drinking water pipes. The coexistence of corrosion produced Fe(II) and iron oxides is a critical condition for the transformation of N species; meanwhile, most of the newly generated N-DBPs had aromatic fractions. The Fe-O-C bond formed between iron corrosion products and natural organic matter promoted electron transfer for the N transformation with pyrrolic N as the intermediate N species. Density functional calculation confirmed that the coexistence of Fe(II) and iron oxides effectively reduced the Gibbs free energy for NO3- reduction. ΔG of the key rate-determining step from NO* to NOH* decreased from 1.55 eV on FeOOH to 1.35 eV on Fe(II)+FeOOH. In addition, the large decrease of cell viability of the water samples from 74.3% to 45.4% further confirmed the formation of highly toxic N-DBPs. Thus, in a drinking water distribution system with corroded iron pipes, the low toxic NO3- may increase toxicity risks via N-DBP formation.

Spatiotemporal optimization of water quality degradation monitoring in water distribution systems supplied by surface sources: A chronological and critical review

Drinking water may undergo spatiotemporal changes in quality as it leaves the treatment plant and enters the distribution system. This variability means that not all consumers receive water of the same quality. Monitoring water quality in distribution networks makes it possible to verify the compliance of current regulations and reduce consumption risks associated with water quality degradation. An inaccurate interpretation of the spatiotemporal variability of water quality affects the selection of monitoring locations and the sampling frequency, which may conceal problems with the water quality and increase consumers' risk. This paper presents a chronological and critical review of the literature on the evolution, benefits and limitations of methodologies for the optimization of water quality degradation monitoring in water distribution systems supplied by surface sources. This review compares the different methodologies and examines the types of approaches, optimization objectives, variables, and types of spatial and temporal analysis, as well as the main advantages and limitations. A cost-benefit analysis was conducted to assess applicability in different-sized municipalities (small, medium and large). Future research recommendations for optimal water quality monitoring in distribution networks are also provided.

Effects of UV-based oxidation processes on the degradation of microplastic: Fragmentation, organic matter release, toxicity and disinfection byproduct formation

The occurrence and transformation of microplastics (MPs) remaining in the water treatment plants has recently attracted considerable attention. However, few efforts have been made to investigate the behavior of dissolved organic matter (DOM) derived from MPs during oxidation processes. In this study, the characteristics of DOM leached from MPs during typical ultraviolet (UV)-based oxidation was focused on. The toxicity and disinfection byproduct (DBP) formation potentials of MP-derived DOM were further investigated. Overall, UV-based oxidation significantly enhanced the aging and fragmentation of highly hydroscopic MPs. The mass scales of leachates to MPs increased from 0.03% - 0.18% at initial stage to 0.09% - 0.71% after oxidation, which were significantly higher than those leached by natural light exposure. Combined fluorescence analysis with high resolution mass spectrometer scan confirmed that the dominant MP-derived DOM are chemical additives. PET-derived DOM and PA6-derived DOM showed inhibition of Vibrio fischeri activity with corresponding EC₅₀ of 2.84 mg/L and 4.58 mg/L of DOC. Bioassay testing with Chlorella vulgaris and Microcystis aeruginosa showed that high concentrations of MP-derived DOM inhibited algal growth by disrupting the cell membrane permeability and integrity. MP-derived DOM had a similar chlorine consumption (1.63 ± 0.41 mg/DOC) as surface water (1.0 - 2.0 mg/DOC), and MP-derived DOM mainly served as precursors for the investigated DBPs. Contrary to the results of previous studies, the DBP yields from MP-derived DOM were relatively lower than those of aquatic DOM under simulated distribution system conditions. This suggests that MP-derived DOM itself rather than serving as DBP precursor might be potential toxic concern.

Removal and transformation of disinfection by-products in water during boiling treatment

Disinfection by-products (DBPs) remain an ongoing issue because of their widespread occurrence and toxicity. Boiling is the most popular household water treatment method and can effectively remove some DBPs. However, the transformation behavior of DBPs during boiling is still unclear, and the key contributors to toxicity have not been identified. In this study, the changes in the concentrations of DBPs in the single-DBP systems and the multi-DBP systems during boiling were monitored, and in-depth discussions on the removal and transformation of DBPs in both systems were carried out. The results showed that boiling was effective in removing volatile DBPs (over 90% for TCAL, TCAN, and DCAN, and over 60% for TCM), but ineffective for non-volatile DBPs (around 20% for TCAA and below 10% for DCAA and MCAA). By hydrolysis and decarboxylation, the transformation occurred among DBPs, i.e., 55% TCAL to TCM, followed by 23% DCAN to DCAA, 22% TCAN to TCAA, and 10% TCAA to TCM. The transformations were found to be significantly influenced by other co-existing DBPs. In multi-DBP systems, the transformations of DCAN to DCAA and TCAN to TCAA were both promoted, while the transformation of TCAN to TCAA was inhibited. Transformation and volatilization are the two processes responsible for DBP removal. Toxicity estimates indicated that boiling was effective in reducing the toxicity of DBPs and improving the safety of the water, despite the interconversion of DBPs in drinking water during boiling. This study emphasized the importance of studying the interconversion behaviors of DBPs in drinking water during boiling and provided practical information for end-use drinking water safety.

Functional Carbon from Nature: Biomass-Derived Carbon Materials and the Recent Progress of Their Applications

Biomass is considered as a promising source to fabricate functional carbon materials for its sustainability, low cost, and high carbon content. Biomass-derived-carbon materials (BCMs) have been a thriving research field. Novel structures, diverse synthesis methods, and versatile applications of BCMs have been reported. However, there has been no recent review of the numerous studies of different aspects of BCMs-related research. Therefore, this paper presents a comprehensive review that summarizes the progress of BCMs related research. Herein, typical types of biomass used to prepare BCMs are introduced. Variable structures of BCMs are summarized as the performance and properties of BCMs are closely related to their structures. Representative synthesis strategies, including both their merits and drawbacks are reviewed comprehensively. Moreover, the influence of synthetic conditions on the structure of as-prepared carbon products is discussed, providing important information for the rational design of the fabrication process of BCMs. Recent progress in versatile applications of BCMs based on their morphologies and physicochemical properties is reported. Finally, the remaining challenges of BCMs, are highlighted. Overall, this review provides a valuable overview of current knowledge and recent progress of BCMs, and it outlines directions for future research development of BCMs.

The potential risks posed by micro-nanoplastics to the safety of disinfected drinking water

Micro-nanoplastics (M-NPs) have become an emerging critical issue in the environment because they migrate easily, can bioaccumulate with toxic effects, and are difficult to degrade. Unfortunately, the current technologies for removing or degrading M-NPs in drinking water are insufficient to eliminate them completely, and residual M-NPs in drinking water may pose a threat to human health by impairing human immunity and metabolism. In addition to their intrinsic toxic effects, M-NPs may be even more harmful after drinking water disinfection than before disinfection. Herein, this paper comprehensively summarizes the negative impacts of several commonly used disinfection processes (ozone, chlorine, and UV) on M-NPs. Moreover, the potential leaching of dissolved organics from M-NPs and the production of disinfection byproducts during the disinfection process are discussed in detail. Moreover, due to the diversity and complexity of M-NPs, their adverse effects may exceed those of conventional organics (e.g., antibiotics, pharmaceuticals, and algae) after the disinfection process. Finally, we propose enhanced conventional drinking water treatment processes (e.g., enhanced coagulation, air flotation, advanced adsorbents, and membrane technologies), detection of residual M-NPs, and biotoxicological assessment as promising and ecofriendly candidates to efficiently remove M-NPs and avoid the release of secondary hazards.

Occurrence and mass loads of N-nitrosamines discharged from different anthropogenic activities in Desheng River, South China

N-nitrosamines are widespread in various bodies of water, which is of great concern due to their carcinogenic risks and harmful mutagenic effects. Livestock rearing, domestic, agricultural, and industrial wastewaters are the main sources of N-nitrosamines in environmental water. However, information on the amount of N-nitrosamines these different wastewaters contribute to environmental water is scarce. Here, we investigated eight N-nitrosamines and assessed their mass loadings in the Desheng River to quantify the contributions discharged from different anthropogenic activities. N-nitrosodimethylamine (NDMA) (< 1.6-18 ng/L), N-nitrosomethylethylamine (NMEA) (< 2.2 ng/L), N-nitrosodiethylamine (NDEA) (< 1.7-2.4 ng/L), N-nitrosopyrrolidine (NPYR) (< 1.8-18 ng/L), N-nitrosomorpholine (NMOR) (< 2.0-3.5 ng/L), N-nitrosopiperidine (NPIP) (< 2.2-2.5 ng/L), and N-nitrosodi-n-butylamine (NDBA) (< 3.3-16 ng/L) were detected. NDMA and NDBA were the dominant compounds contributing 89% and 92% to the total N-nitrosamine concentrations. The mean cumulative concentrations of N-nitrosamines in the livestock rearing area (26 ± 11 ng/L) and industrial area (24 ± 4.8 ng/L) were higher than those in the residential area (16 ± 6.3 ng/L) and farmland area (15 ± 5.1 ng/L). The mean concentration of N-nitrosamines in the tributaries (22 ng/L) was slightly higher than that in the mainstem (17 ng/L), probably due to the dilution effect of the mainstem. However, the mass loading assessment based on the river's flow and water concentrations suggested the negligible mass emission of N-nitrosamines into the mainstem from tributaries, which could be due to the small water flow of tributaries. The average mass loads of N-nitrosamines discharged into the mainstem were ranked as the livestock rearing area (742.7 g/d), industrial area (558.6 g/d), farmland area (93.9 g/d), and residential areas (83.2 g/d). In the livestock rearing, residential, and industrial area, NDMA (60.9%, 53.6%, and 46.7%) and NDBA (34.6%, 33.3%, and 44.9%) contributed the most mass loads; NDMA (23.4%), NDEA (15.8%), NPYR (10.1%), NPIP (12.8%), and NDBA (37.8%) contributed almost all the mass loads in the farmland area. Photodegradation amounts of NDMA (0.65 ~ 5.25 µg/(m³·day)), NDBA (0.37 ~ 0.91 µg/(m³·day)), and NDEA (0 ~ 0.66 µg/(m³·day)) were also calculated according to the mass loading. Quantifying the contribution of different anthropogenic activities to the river will provide important information for regional river water quality protection. Risk quotient (RQ) values showed the negligible ecological risks for fish, daphnid, and green algae.

Perfluorooctanoic Acid (PFOA) Incorporated into Iron Particles Promoted the Formation of Disinfection Byproducts under Drinking Water Conditions

Perfluorooctanoic acid (PFOA) is an emerging persistent organic pollutant that is frequently detected throughout the drinking water supply system. Here, we first found that PFOA could significantly increase the formation of disinfection byproducts (DBPs) in unlined iron pipes (UIPs) during the distribution process. The increased DBPs were not due to the reaction of PFOA itself with free chlorine, but the in situ formed Fe-PFOA complex played a key role. Notably, PFOA could enhance iron release from UIPs and was greatly incorporated into the iron particles to form Fe-PFOA complex. The •OH generated by the Fe-PFOA heterogeneous reaction could break large dissolved organic matter into small molecules that had higher reactivity with chlorine. In addition, DBP precursors with more aromatic structures were favorable for forming strong Fe-π interactions with Fe-PFOA complex, resulting in more •OH for the formation of aromatic DBPs. The cytotoxicity test showed that the viability of cells exposed to DBPs from UIPs with 100 ng/L PFOA was 46.9%, while that without PFOA was 67.91%. Overall, this study provided a new perspective on the risk of PFOA, with a focus not on PFOA itself but on its potential to promote DBP-associated toxicity in iron-based drinking water distribution pipes.

Transformation of Graphitic Carbon Nitride by Reactive Chlorine Species: "Weak" Oxidants Are the Main Players

Graphitic carbon nitride (g-C₃N₄) nanomaterials hold great promise in diverse applications; however, their stability in engineering systems and transformation in nature are largely underexplored. We evaluated the stability, aging, and environmental impact of g-C₃N₄ nanosheets under the attack of free chlorine and reactive chlorine species (RCS), a widely used oxidant/disinfectant and a class of ubiquitous radical species, respectively. g-C₃N₄ nanosheets were slowly oxidized by free chlorine even at a high concentration of 200-1200 mg L^-1, but they decomposed rapidly when ClO· and/or Cl₂^•- were the key oxidants. Though Cl₂^•- and ClO· are considered weaker oxidants in previous studies due to their lower reduction potentials and slower reaction kinetics than ·OH and Cl·, our study highlighted that their electrophilic attack efficacy on g-C₃N₄ nanosheets was on par with ·OH and much higher than Cl·. A trace level of covalently bonded Cl (0.28-0.55 at%) was introduced to g-C₃N₄ nanosheets after free chlorine and RCS oxidation. Our study elucidates the environmental fate and transformation of g-C₃N₄ nanosheets, particularly under the oxidation of chlorine-containing species, and it also provides guidelines for designing reactive, robust, and safe nanomaterials for engineering applications.

Formation of disinfection by-products from microplastics, tire wear particles, and other polymer-based materials

Disinfection by-products (DBPs) are formed through the disinfection of water containing precursors such as natural organic matter or anthropogenic compounds (e.g., pharmaceuticals and pesticides). Due to the ever increasing use of plastics, elastomers, and other polymers in our daily lives, polymer-based materials (PBMs) are detected more frequently and at higher concentrations in water and wastewater. The present review provides a comprehensive and systematic analysis of the contribution of PBMs - including elastomers, tire waste, polyelectrolytes, and microplastics - as precursors of DBPs in water and wastewater. Literature shows that the presence of PBMs can lead to the leaching of dissolved organic matter (DOM) and subsequent formation of DBPs upon disinfection in aqueous media. The quantity and type of DBPs formed strongly depends on the type of polymer, its concentration, its age, water salinity, and disinfection conditions such as oxidant dosage, pH, temperature, and contact time. DOM leaching from elastomers and tire waste was shown to form N-nitrosodimethylamine up to concerning levels of 930 ng/L and 466,715 ng/L, respectively upon chemical disinfection under laboratory conditions. Polyelectrolytes can also react with chemical disinfectants to form toxic DBPs. Recent findings indicate trihalomethanes formation potential of plastics can be as high as 15,990 µg/L based on the maximum formation potential under extreme conditions. Our analysis highlights an overlooked contribution of DOM leaching from PBMs as DBP precursors during disinfection of water and wastewater. Further studies need to be conducted to ascertain the extent of this contribution in real water and wastewater treatment plants.

Ozone mechanism, kinetics, and toxicity studies of halophenols: Theoretical calculation combined with toxicity experiment

Aromatic disinfection by-products (DBPs), which are generally more toxic than aliphatic DBPs, have attracted increasing attention. The toxicity of 13 typical halophenols on Scenedesmus obliquus was experimentally investigated, and the ozonation mechanism and kinetics of representative halophenols were further studied by quantum chemical calculations. The results showed that the EC₅₀ values of halophenols ranged from 2.74 to 60.23 mg/L, and their toxicity ranked as follows: di-halogenated phenols > mono-halogenated phenols, mixed halogen-substituted phenols > single halogen-substituted phenols, and iodophenols > bromophenols > chlorophenols. The toxicity of halophenols was well described by the electronegativity index (ω) as lg(EC₅₀)^-1 = 6.228ω - 3.869, indicating halophenols capturing electrons as their potential toxicity mechanism. The reactions of O₃ with halophenolate anions were dominated by three mechanisms: 1,3-dipolar cycloaddition, oxygen addition, and single electron transfer. The kinetic calculation indicated that O₃ oxidized aqueous halophenols by reacting with halophenolate anions with the reaction rate constants as high as (0.91-3.47) × 10¹⁰ M^-1 s^-1. The number of halogen substituents affected the k_{O3, cal} values of halophenolate anions, which are in the order of 2,4-dihalophenolate anions >4-halophenolate anions > 2,4,6-trihalophenolate anions. During the ozonation of 2,4,6-tribromophenol (246TBP), the toxic products (dimers and brominated benzoquinones) could be synergistically degraded by O₃ and HO^•. Thus, ozonation is feasible as a strategy to degrade aromatic DBPs.

Decomposition of Total Organic Halogen Formed during Chlorination: The Iceberg of Halogenated Disinfection Byproducts Was Previously Underestimated

Total organic halogen (TOX) is widely used as a surrogate bulk parameter to measure the overall exposure of halogenated disinfection byproducts (DBPs) in drinking water. In this study, we surprisingly found that the level of TOX in chlorinated waters had been significantly underestimated under common analytical conditions. After the addition of quenching agent sodium thiosulfate, total organic chlorine and total organic bromine exhibited a two-phase decomposition pattern with increasing contact time, and a significant decomposition was observed for different types of quenching agents, quenching doses, and pH conditions. More importantly, the decomposed TOX closely correlated with the acute toxicity of quenched water against luminous bacteria, implying that the DBPs responsible for TOX decomposition could be of important toxicological significance. Based on nontarget analysis by using high-resolution mass spectrometry, molecular formulas for the decomposed TOX were determined. After re-examining the mass balance of TOX in the context of unintentional decomposition, it was found that both the level and percentage of unknown TOX in chlorinated waters were considerably higher than historically thought. Overall, this study brings new insights into the knowledge of TOX formed during chlorination, providing important clues on the identification of toxicity driver in drinking water.

Occurrence and modeling of disinfection byproducts in distributed water of a megacity in China: Implications for human health

Disinfection byproducts (DBPs) are initially formed in the process of chlorination in the drinking water treatment plants (DWTPs), then further formed in the distribution system due to the presence of residual chlorine and reactive organic matters. However, in China, DBPs are monitored in the effluent from the DWTPs, but less is known about concentrations of DBPs in tap water since they are usually monitored once per half a year. The smart water service system is establishing real-time monitoring of water indices, although DBPs are an urgent need, they are difficult to monitor in real-time due to their diversity and complicated detection methods. If the correlation between DBP concentration and routinely real-time monitored water quality parameters (e.g., pH value, residual chlorine, ammonia) can be evaluated, the concentration of DBPs can be predicted, which will strengthen the control of tap water safety. This article comprehensively assessed the physicochemical parameters and the occurrence of DBP formation in the tap water with an 18-month investigation in Z city (China). DBP formation in tap water of different seasons and different water sources were compared. Based on the relationship between DBPs and physicochemical parameters, linear prediction and nonlinear prediction models of trihalomethanes (THMs), haloacetonitriles (HANs) and haloacetic acids (HAAs) were established, and the accuracy of these models was verified by measured data. Finally, the toxicity and carcinogenic and non-carcinogenic health risk assessment of DBPs in tap water were analyzed.

Does Snowfall Introduce Disinfection By-product Precursors to Surface Water?

Snow with large specific surface area and strong adsorption capacity can effectively adsorb atmospheric pollutants, which could/might lead to the increase of disinfection by-product (DBP) precursors in surface water. In this study, the contents and characteristics of dissolved organic matter (DOM) in meltwater were investigated, and DBP formation and the DBP-associated cytotoxicity index during chlorination of meltwater was first explored. Overall, meltwater exhibited high nitrogen contents. Meltwater-derived DOM was mainly composed of organics with low molecular weights, low aromaticity, and high unsaturated degrees. DBP formation potentials and cytotoxicity indexes in chlorinated meltwater were positively correlated with air quality index and were significantly impacted by snowfall stages. The trihalomethane and haloacetic acid yields from meltwater were relatively low, while yields of highly cytotoxic DBPs, especially halonitromethanes (6.3-10.8 μg-HNMs/mg-DOC), were significantly higher than those of surface water (1.7 μg-HNMs/mg-DOC). Notably, unsaturated nonaromatic organic nitrates in meltwater were important precursors of halonitromethanes. The actual monitoring results showed that snowfall significant increased the haloacetaldehydes and nitrogenous DBP formation levels of surface water. Considering increased DBP formation and DBP-associated toxicity, it was demonstrated that DOM derived from snowfall in atmosphere-polluted areas could deteriorate surface water quality and pose potential risks to drinking water.

Insights into the formation and mitigation of iodinated disinfection by-products during household cooking with Laminaria japonica (Haidai)

Iodinated disinfection by-products (I-DBPs) have attracted extensive interests because of their higher cytotoxicity and genotoxicity than their chlorinated and brominated analogues. Our recent studies have firstly demonstrated that cooking with seaweed salt could enhance the formation of I-DBPs with several tens of μg/L level. Here, I-DBP formation and mitigation from the reaction of disinfectant with Laminaria japonica (Haidai), an edible seaweed with highest iodine content, upon simulated household cooking process was systematically investigated. The total iodine content in Haidai ranged from 4.6 mg-I/g-Haidai to 10.0 mg-I/g-Haidai, and more than 90% of iodine is soluble iodide. During simulated cooking, the presence of disinfectant simultaneously decreased iodide by 15.0-32.8% to 2.7-5.8 mg/L and increased total organic iodine by 1.3-10.9 times to 0.5-1.8 mg/L in Haidai soup, proving I-DBP formation. The concentrations of iodinated trihalomethanes and haloacetic acids were at the levels of several hundreds of μg/L and several μg/L, respectively, which are 2-3 orders and 1-2 orders of magnitude more than those in drinking water. Effects of key factors including disinfectant specie, disinfectant dose, temperature and time on I-DBP formation were also ascertained, and temperature and disinfectant specie played a decisive role in the formation and speciation of I-DBPs. In order to avoid the potential health risk from the exposure of I-DBPs in Haidai soup, it is prerequisite to soak and wash dry Haidai sample over 30.0 min before cooking, which could effectively remove major soluble iodide. In general, this study provided the new insight into I-DBP formation from daily household cooking with Haidai and the corresponding enlightenment for inhabitants to eat Haidai in daily life.

Impact of initial chlorine concentration on water quality change in old unlined iron pipes

Unlined iron pipe (UIP) is still widely in use in drinking water distribution systems (DWDS), discoloration easily happens after a long-time retention due to iron release, but the influence of initial chlorine on water quality under this condition is not clear. Here, we studied the water quality changes in UIP section reactors under different initial chlorine dosages. Results showed that chlorine could disappeared rapidly within 0.5 h in the UIP. The water with higher initial chlorine (5 mg/L) had higher turbidity in a short time (within 1.5 h), but for a longer retention time (2∼12 h), the highest turbidity was in the iron pipe without initial chlorine. Interestingly, a clear increase in adenosine triphosphate in the UIPs was observed with the increase of initial chlorine, which was in accordance with the results of heterotrophic plate count. Polysaccharide and protein increased with the increase of initial chlorine, which would benefit the formation of a protective layer to inhibit corrosion. This study reflects that during the overnight retention in UIP, raising chlorine would be effective to control discoloration, but chemical and microbiological risks may increase.

Formation of halogenated disinfection byproducts in chlorinated real water during making hot beverage: Effect of sugar addition

Chlorine disinfection is widely applied in drinking water treatment plant to inactivate pathogens in drinking water, but it unintentionally reacts with organic matter present in source waters and generates halogenated disinfection byproducts (DBPs). Sugar is one of the most commonly used seasoning in our diet. The addition of sugar could significantly improve the taste of the beverages; however, the effects of sugar on DBP formation and transformation remain unknown. In this study, the effects of sugar type and dose on the halogenated DBP formation in chlorinated boiled real tap water were evaluated during making hot beverages. We found that sugar can react with chlorine residual in tap water and generate halogenated DBPs. As the most commonly used table sugar, the addition of sucrose in the water sample at 100 or 500 mg/L as C could increase the level of total organic halogen (TOX) by ∼35%, when compared with the boiled tap water sample without sugar addition. In addition, fifteen reported and new polar brominated and chlorinated DBPs were detected and proposed from the reaction between chlorine and sucrose; accordingly, the corresponding transformation pathways were also proposed. Moreover, the DBP formation in the chlorinated boiled real tap water samples with the addition of xylose, glucose, sucrose, maltose and lactose were also investigated. By comparing with the TOX levels in the water samples with different sugar addition and their calculated TOX risk indexes, it was suggested that applying xylose as a sweetener in beverages could not only obtain a relatively high sweetness but also minimize the adverse effect inducing by halogenated DBPs during making hot beverages.

Insight into disinfection byproduct formation potential of aged biochar and its effects during chlorination

Biochar can achieve multiple benefits including solid waste management, polluted water remediation, carbon sequestration, and emission reduction. However, various environmental factors (such as temperature variations and dry-wet alternation) and microbial activity may lead to the fragmentation, dissolution, and oxidation of biochar. These accelerate the dissolution of biochar-derived dissolved organic matter (DOM) and then influence disinfection byproducts formation potential (DBPFP) throughout the water treatment process. In this paper, biochars from six biomass feedstocks with five aging processes were prepared, and the DBPFP of biochar and its derived DOM were first studied systematically. Different aging processes might increase the DBPFP of biochar by increasing DOM content and changing the fraction distribution of DOM derived from biochar. Especially, the DBPFP of biochar increased apparently with the chemical aging process. Coexisting with the environmental concentration of humic acid, even aged biochar showed the potential to reduce DBPFP and integrated toxic risk value of the mixed system. In this study, the DBPFP of biochar-derived DOM during the disinfection process is confirmed, and the results can give information to the selection of biomass feedstocks of biochar and its service life in the water treatment process.

A comprehensive analysis of evolution and underlying connections of water research themes in the 21st century

This work aimed to reflect the advancements in water-related science, technology, and policy and shed light on future research opportunities related to water through a systematic overview of Water Research articles published in the first 21.5 years of the 21st century. Specific bibliometric analyses were performed to i) reveal the temporal and spatial trends of water-related research themes and ii) identify the underlying connections between research topics. The results showed that while top topics including wastewater (treatment), drinking water, adsorption, model, biofilm, and bioremediation remained constantly researched, there were clear shifts in topics over the years, leading to the identification of trending-up and emerging research topics. Compared to the first decade of the 21st century, the second decade not only experienced significant uptrends of disinfection by-products, anaerobic digestion, membrane bioreactor, advanced oxidation processes, and pharmaceuticals but also witnessed the emerging popularity of PFAS, anammox, micropollutants, emerging contaminants, desalination, waste activated sludge, microbial community, forward osmosis, antibiotic resistance genes, resource recovery, and transformation products. On top of the temporal evolution, distinct spatial evolution existed in water-related research topics. Microplastics and Covid-19 causing global concerns were hot topics detected, while metagenomics and machine learning were two technical approaches emerging in recent years. These consistently popular, trending-up and emerging research topics would most likely attract continuous/increasing research input and therefore constitute a major part of the prospective water-related research publications.

Generation of iodinated trihalomethanes during chloramination in the presence of solid copper corrosion products

Copper water pipelines are widely used in water distribution systems, but the effects of solid copper corrosion products (CCPs) including CuO, Cu₂O and Cu₂(OH)₂CO₃ on the generation of iodinated trihalomethanes (I-THMs) during chloramination remain unknown. This study found that the formation of I-THMs during chloramination of humic acid (HA) was inhibited by the presence of CuO and Cu₂O, but promoted with the addition of Cu₂(OH)₂CO₃. The negative effect of CuO and Cu₂O is mainly exerted by promoting the decay of both NH₂Cl and HOI. Although Cu₂(OH)₂CO₃ also accelerated the decomposition of NH₂Cl and HOI, it was found that the complexes formed between Cu₂(OH)₂CO₃ and HA facilitated, through carboxyl functional groups, the reaction between HA and HOI, leading to an enhancement of I-THM generation during chloramination, which was further confirmed by model compound experiments. Additionally, this study demonstrated that the effects of solid CCPs on I-THM generation during chloramination were solid CCP- and HA-concentration dependent, but almost unaffected by different initial I^- and Br^- concentrations. This study provides new insights into the health risks caused by the corrosion of copper water pipelines, especially in areas intruded by sea water.

Evaluation of N-acetylcysteine and glutathione as quenching agents for the analysis of halogenated disinfection by-products

Disinfection by-products (DBPs), formed from the reactions of disinfectants with natural organic matter and halides in drinking water, were considered to be cytotoxic and genotoxic, and might trigger various cancers. The relatively low concentration of DBPs in finished water (low µg/L or even ng/L levels) and the interference from water matrix inhibited in situ determination of DBPs. Moreover, the further formation and degradation of DBPs by disinfectants during the holding time (several hours to several days) from sample collection to analysis could adversely affect the determination of DBPs. To obtain accurate, precise and reliable data of DBP occurrence and formation, robust and reliable sample preservation is indispensable. However, the commonly used quenching agents (e.g., sodium sulfite, sodium thiosulfate, and ascorbic acid) for sample preservation can decompose reactive DBPs by reductive dehalogenation. This study evaluated the performance of N-acetylcysteine (NAC) and glutathione (GSH) as quenching agents for the analysis of halogenated DBPs by investigating the stoichiometry of the disinfectant-quenching agent reaction, the formation of DBPs during chlor(am)ination of NAC or GSH, and the effects of NAC or GSH on the stability of 18 individual DBPs and total organic halogen (TOX). Based on the results of this study, NAC and GSH were considered to be ideal quenching agents for the analysis of most DBPs and TOX, except halonitromethanes.

Metabonomic and transcriptomic modulations of HepG2 cells induced by the CuO-catalyzed formation of disinfection byproducts from biofilm extracellular polymeric substances in copper pipes

Cupric oxide (CuO) is able to catalyze the reactions among disinfectant, extracellular polymeric substances (EPS) and bromide (Br^-) in copper pipes, which may deteriorate the water quality. This study aimed to investigate the metabonomic and transcriptomic modulations of HepG2 cells caused by the CuO-catalyzed formation of disinfection byproducts (DBPs) from EPS. The presence of CuO favored the substitution reactions of chlorine and bromine with EPS, inducing a higher content of total organic halogen (TOX). In addition, DBPs were shifted from chlorinated species to brominated species. A total of 182 differential metabolites (DMs) and 437 differentially expressed genes (DEGs) were identified, which were jointly involved in 38 KEGG pathways. Topology analysis indicates that glycerophospholipid and purine metabolism were disturbed most obviously. During glycerophospholipid metabolism, the differential expression of genes GPATs, AGPATs, LPINs and DGKs impacted the conversion of glycerol-3-phosphate to 2-diacyl-sn-glycerol, which further affected the conversion among phosphatidylcholine, phosphatidylserine and phosphocholines. During purine metabolism, it was mainly the differential expression of genes POLRs, RPAs, RPBs, RPCs, ENTPDs and CDs that impacted the transformation of RNA into guanine-, xanthosine-, inosine- and adenosine monophosphate, which were further successively transformed into their corresponding nucleosides and purines. The study provides an omics perspective to assess the potential adverse effects of overall DBPs formed in copper pipes on human.