A N-Nitrosodimethylamine (NDMA) precursor analysis for chlorination of water and wastewater

Locally enhanced mixed-order model for chloramine decay in drinking water disinfection

Chloramine is the second most popular disinfectant and is widely used in the disinfection of drinking water. For chloramine disinfection, some standards require the total chlorine concentration to be maintained in an appropriate range in the water distribution system. Therefore, exploring the mechanism of chloramine decay and deriving an accurate chloramine decay model helps to optimize the disinfection process and ensure water quality safety. This paper proposed a locally enhanced mixed-order(LEM) model consisting of the first order model and the mixed order model to describe chloramine auto-decomposition and decays caused by other reactions respectively. Via proving the parameter a and k2 related to temperatures instead of initial chloramine concentration, the model had been further simplified. Nine chloramine decay experiments with different initial chloramine concentrations and temperatures were designed and carried out to evaluate the new model performance for chloramine decay simulation. The research results showed that the simplified LEM model could simulate the whole process of chloramine decay well. Its accuracy evaluation indexes (R2 and SSE) were better than that obtained from the first order model and the mixed order model. This paper proposed a simple and accurate method to simulate the process of chloramine decay and had a guiding significance for water quality safety assurance.

Identification of transformation products during Doxylamine chloramination for NDMA mitigation

N-nitrosodimethylamine (NDMA) is a disinfection byproduct that forms at the presence of an organic nitrogen precursor. Doxylamine, an antihistaminic pharmaceutical, is a precursor of NDMA and has been shown to form NDMA in the presence of chloramine. In this study, the effect of Doxylamine as an NDMA precursor has been further studied during chloramination. The end product and byproducts during chloramination were investigated using a high-resolution mass spectrometer by taking samples at different time intervals. Results suggest that NDMA is not the only end product forming during chloramination of Doxylamine and several transformation products that do not end up as NDMA may form. A group of these transformation products have been selected based on their relative amounts during chloramination with time and notated as Focus Tentative Transformation Products (FTTPn). The identification of these byproducts will make it easier to study the conditions during chloramination that may favour these 'known' transformation products with the use of less sophisticated analytical instruments. Then, it might lead to the establishment of chloramination protocols that will minimise the formation of NDMA from its precursors.

N-Nitrosamines and their precursors in wastewater effluents from selected industries in Spain

N-nitrosamines (NAs), and N-nitrosodimethylamine (NDMA) in particular, are hazardous disinfection byproducts (DBPs) relevant when wastewater impacts drinking water sources and, in water reuse practices. Our study investigates the concentrations of NDMA and five additional NAs and their precursors in industrial wastewater effluents. Aiming to identify potential differences between industrial typologies, wastewaters from 38 industries belonging to 11 types of the UN International Standard Industrial Classification of All Economic Activities system (ISIC) were analysed. Results show that the presence of most NAs and their precursors cannot be linked to a specific industry type as these were in general very different within the classes. Nevertheless, N-nitrosomethylethylamine (NMEA) and N-nitrosopiperidine (NPIP) as well as precursors for N-nitrosodiethylamine (NDEA), NPIP and N-nitrosodibuthylamine (NDBA) could be rank with different concentrations between ISIC classes (p-value < 0.05). Specific industrial wastewater with notable high concentrations of NAs and their precursors were identified too. The effluents with the highest concentration of NDMA belong to the ISIC C2011 class (Manufacture of basic chemical), while the effluents with the highest concentration of NDMA precursors were from the ISIC C1511 class (Tanning and dressing of leather; dressing and dyeing of fur). Other relevant NAs found were NDEA in ISIC class B0810 (Quarrying of stone, sand, and clay) and ISIC class C2029 (Manufacture of other chemical products).

Study on characteristic and mechanism involved in the formation of N-nitrosodimethylamine precursors during microbial metabolism of amino acids

Amino acid metabolism by microorganisms is a new but important pathway for the formation of NDMA precursors in water. We investigated the properties of nitrosamine precursors produced through microbial metabolism of amino acids by polarity rapid assessment method and molecular weight fractionation by ultrafiltration method. The PRAM results showed that the positively charged fraction and the non-polar fraction accounted for most (45 %-79 % and 6 %-82 %, respectively) of the NDMA precursors. The MW fractionation results also indicate the dominant precursors had MWs <1 kDa or over 10 kDa. NDMA precursors produced through amino acid metabolism were identified and quantified. Dimethylamine, N-methyl-alanine and alanine methyl ester were produced during the metabolism of alanine and peptone. Together, N-methyl-alanine and dimethylamine averagely contributed 24 % (12 %-44 %) of the NDMA precursors in the alanine medium. The NDMA precursor formation pathway during alanine metabolism involves the methylation of alanine to form N-methyl-alanine and the decomposition of alanine anabolism products to form dimethylamine. Nitrosamine precursors are generally formed through anabolism or methylation, but biogenic amines or NH₃ can be produced through catabolism before nitrosamine precursor synthesis. Microbial community analysis was performed and Ralstonia was found to be a likely key genus contributing to NDMA precursor formation during alanine metabolism.

Adsorption of trichloroacetic acid from drinking water using polyethylene terephthalate waste carbon and periwinkle shells–based chitosan

Toxins are formed because of massive anthropogenic activities, polluting freshwater bodies. Most disinfectants used in water purification produce disinfection by-products (DBPs) such as trichloroacetic acid (TCA). TCA is a strong acid, and TCA uptake could harm gastrointestinal tract tissues or result in systemic acidosis. Activated carbons were investigated to remove TCA from drinking water in this study. Elemental and Energy Dispersive X-ray (EDX) and scanning electron microscope methodologies were employed to characterize the surface morphological features of the activated carbons (SEM). Activated carbons’ chemical functional groups were identified through using Fourier transform-infrared (FT-IR) spectroscopy technique. Using a UV-vis spectrophotometer, the TCA concentrations in water samples were examined at 530 nm. The levels of TCA in raw and conventionally treated water were 0.9900 and 2.8900 mg/L, respectively. The polyethylene terephthalate activated carbon (PETAC), polyethylene terephthalate modified activated carbon (PETMAC), and commercial activated carbon (CAC) gave mean TCA removal efficiencies of 80.80%, 90.90%, and 90.90% for raw water and 95.16%, 96.13%, and 100% for conventionally treated water, respectively. The reusability efficiencies of PETAC and PETMAC were 78.4% and 82.4%, respectively. The PETAC with R 2 = 0.9377 showed that Langmuir model best fit the TCA adsorption in the isotherm models. According to the findings, PETAC was effective at removing TCA from water sources and could be improved by incorporating chitosan.

A Bioanalytical Method for Quantification of N-nitrosodimethylamine (NDMA) in Human Plasma and Urine with Different Meals and following Administration of Ranitidine

Control of N-nitrosoamine impurities is important for ensuring the safety of drug products. Findings of nitrosamine impurities in some drug products led FDA to develop new guidance providing recommendations for manufacturers towards prevention and detection of nitrosamine impurities in pharmaceutical products. One of these products, ranitidine, also had a published in vivo study, which has since been retracted by its authors, suggesting a potential for in vivo conversion of ranitidine to the probable human carcinogen, N-nitrosodimethylamine (NDMA). FDA subsequently initiated a randomized, double-blind, placebo-controlled, crossover clinical investigation to assess the potential for in vivo conversion of ranitidine to NDMA with different meals. A bioanalytical method toward characterization of NDMA formation was needed as previously published methods did not address potential NDMA formation after biofluid collection. Therefore, a bioanalytical method was developed and validated as per FDA's Bioanalytical Method Validation guidance. An appropriate surrogate matrix for calibration standards and quality control sample preparation for both liquid matrices (human plasma and urine) was optimized to minimize the artifacts of assay measurements and monitor basal NDMA levels. Interconversion potential of ranitidine to NDMA was monitored during method validation by incorporating the appropriate quality control samples. The validated methods for NDMA were linear from 15.6 pg/mL to 2000 pg/mL. Low sample volumes (2 mL for urine and 1 mL for plasma) made this method suitable for clinical study samples and helped to evaluate the influence of ranitidine administration and meal types on urinary excretion of NDMA in human subjects.

Silica sand-supported nano zinc oxide-graphene oxide composite induced rapid photocatalytic decolorization of azo dyes under sunlight and improved antimicrobial activity

Here, silica sand-supported heterojunction composite of nano zinc oxide (nZnO) and graphene oxide nanosheet (nZnO-GO@SS) was prepared, and its potential as an efficient photocatalyst for the degradation of methylene blue (MB) and Rhodamine-B (Rh-B) under sunlight was demonstrated. Transmission electron microscopy confirmed the uniform distribution of spherically shaped nZnO of average size of approximately 8 nm over graphene oxide nanosheet (GO) in the composites. Photodegradation yields of 95.3% and 97.5% for 100 ppm of MB and Rh-B dye within 150 and 220 min, respectively, were achieved under sunlight by the prepared nanocatalyst (nZnO-GO), while sand microparticle-supported nanocatalyst (nZnO-GO@SS) demonstrated faster degradation of MB and Rh-B, i.e., within 120 and 160 min, respectively. Furthermore, when the recyclability of the photocatalyst was studied, the nZnO-GO exhibited more than 80% degradation efficiency after five cycles for both the dyes and nZnO-GO@SS demonstrated 10% higher (~90%) removal capability after five cycles of reuse. Furthermore, the antibacterial assay showed complete inactivation of Escherichia coli and Staphylococcus aureus bacterial strain by nZnO-GO@SS. Hence, our proposed strategy for the removal of toxic dyes from the aquatic environment under sunlight proved that sand microparticle-supported nanocatalyst (nZnO-GO@SS) might be a superior, cost-effective, and suitable photocatalytic system for industrial applications toward toxic dye removal and decontamination from industrial wastewater.

Metformin Contamination in Global Waters: Biotic and Abiotic Transformation, Byproduct Generation and Toxicity, and Evaluation as a Pharmaceutical Indicator

Metformin is the first-line antidiabetic drug and one of the most prescribed medications worldwide. Because of its ubiquitous occurrence in global waters and demonstrated ecotoxicity, metformin, as with other pharmaceuticals, has become a concerning emerging contaminant. Metformin is subject to transformation, producing numerous problematic transformation byproducts (TPs). The occurrence, removal, and toxicity of metformin have been continually reviewed; yet, a comprehensive analysis of its transformation pathways, byproduct generation, and the associated change in adverse effects is lacking. In this review, we provide a critical overview of the transformation fate of metformin during water treatments and natural processes and compile the 32 organic TPs generated from biotic and abiotic pathways. These TPs occur in aquatic systems worldwide along with metformin. Enhanced toxicity of several TPs compared to metformin has been demonstrated through organism tests and necessitates the development of complete mineralization techniques for metformin and more attention on TP monitoring. We also assess the potential of metformin to indicate overall contamination of pharmaceuticals in aquatic environments, and compared to the previously acknowledged ones, metformin is found to be a more robust or comparable indicator of such overall pharmaceutical contamination. In addition, we provide insightful avenues for future research on metformin.

Effect of activated sludge treatment on the formation of Nnitrosamines under different chloramination conditions

Municipal wastewater discharge is considered as one of the main sources of N-nitrosamine precursors which can impact the qualities of downstream source waters and reclaimed wastewaters for potable reuse. NNitrosamine precursors can be removed to various degrees during biological wastewater treatment (e.g., the activated sludge (AS) process). So far, little is known about the impact of the AS process on N-nitrosamine formation under practical disinfection condition (e.g., uniform formation condition (UFC)). In this study, N-nitrosamine UFC from selected model compounds, sewage components (i.e., blackwaters and greywaters) and sewage samples were comprehensively investigated during batch AS treatment tests. NNitrosodimethylamine (NDMA) formation from the tested precursor compounds (i.e., trimethylamine (TMA) and sumatriptan (SMTR)) under UFC chloramination decreased mostly after 6 or 24 hr treatment with different types of AS (i.e., domestic rural AS, domestic urban AS, and textile AS), and the reductions in NDMA UFC were comparable to their NDMA formation potential (FP) reductions. In urine and feces blackwaters, NDMA UFC increased after 6 or 24 hr treatment with the domestic (i.e., rural and urban) AS, while NDMA FP decreased substantially. The increases in NDMA UFC after AS treatment was presumably attributed to the removal of bulk organic matters (e.g., dissolved organic carbon (DOC)) which favored NDMA formation under UFC. On the other hand, in laundry greywaters having relatively abundant DOC, N-nitrosamine UFC was less affected by DOC removal before or after AS treatment, but decreased to similar degrees with N-nitrosamine FP. In sewage samples collected from wastewater treatment plants, N-nitrosamines UFC tended to increase or remain constant during AS treatment, despite the decreases in their FPs. These results suggest that biological wastewater treatment (e.g., the AS process) may not effectively reduce N-nitrosamine formation (e.g., measured under UFC) partially because the concurrent removal of bulk organic matters (e.g., DOC) favored N-nitrosamine formation in s econdary effluents.

High concentrations of dissolved organic nitrogen and N-nitrosodimethylamine precursors in effluent from biological nutrient removal process with low dissolved oxygen conditions

The presence of dissolved organic nitrogen (DON) in biological nutrient removal (BNR) effluent has led to increased concern about its adverse effects on wastewater discharge and reuse applications. Previous studies have demonstrated efficient biological inorganic nitrogen removal in BNR under low dissolved oxygen (DO) conditions; however, information on DON is scarce. This study investigated low-DO effects on DON and N-nitrosodimethylamine (NDMA) precursor concentrations in BNR effluents. Identical BNR reactors consisting of an external real-time DO intelligent control system were operated at three different DO concentrations (0.3, 1.0, and 4.0 mgO₂/L). Surprisingly, significantly higher values of effluent DON (p<0.05, t-test) and NDMA precursors (p<0.01, t-test) were observed at lower DO levels. Ultrahigh-resolution mass spectrometry analysis showed that molecules produced by microbes at low-DO levels exhibited high proteins/amino sugars-like and low normal oxidation state of carbon characteristics, which possibly acted critical roles in NDMA formation. Furthermore, path analysis by partial least-squares path modeling suggested that NDMA formation potential had strong associations with microbe-DON network stability of microbe-DON co-occurrence interactions (r=0.979, p<0.01). These results highlight the necessity of reconsidering the feasibility of BNR systems operating at low-DO concentrations considering the adverse effects of DON on wastewater discharge and reuse applications.

Ozonation of organic compounds in water and wastewater: A critical review

Ozonation has been applied in water treatment for more than a century, first for disinfection, later for oxidation of inorganic and organic pollutants. In recent years, ozone has been increasingly applied for enhanced municipal wastewater treatment for ecosystem protection and for potable water reuse. These applications triggered significant research efforts on the abatement efficiency of organic contaminants and the ensuing formation of transformation products. This endeavor was accompanied by developments in analytical and computational chemistry, which allowed to improve the mechanistic understanding of ozone reactions. This critical review assesses the challenges of ozonation of impaired water qualities such as wastewaters and provides an up-to-date compilation of the recent kinetic and mechanistic findings of ozone reactions with dissolved organic matter, various functional groups (olefins, aromatic compounds, heterocyclic compounds, aliphatic nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, carbanions, β-diketones) and antibiotic resistance genes.

Effects of chlorination on the nitrosamines formation from two algae species in drinking water source-M. aeruginosa and C. meneghiniana

The effects of chlorine dosage, reaction time, algae concentration, and cell components, including extracellular organic matter (EOM), intracellular organic matter (IOM) and cell debris (CD), were evaluated on the formation of nitrosamines (NAs), including N-Nitrosodimethylamine (NDMA), -Nitrosomethylethylamine (NMEA), N-Nitrosodi-n-propylamine (NDPA), N-nitrosodi-n-butylamine (NDBA), N-Nitrosopyrollidine (NPyr), during the chlorination of Microcystis aeruginosa (M. aeruginosa) and Cyclotella meneghiniana (C. meneghiniana) in drinking water treatment. In addition, the NAs formation from Chlorophyll-a and Microcystin-LR (MC-LR) chlorination was investigated. The results showed that NDMA was the most dominant product of two algae, while only a small yield of NPyr, NMEA and NDBA was generated with NDPA as the least. The nitrosamines formation potential (NAsFP) of M. aeruginosa was positively correlated with the chlorine concentration, while the highest NAsFP of C. meneghiniana was observed at 10 mg/L chlorine. With the increase of reaction time, the NAsFP from C. meneghiniana was higher than M. aeruginosa. The NAs formation enhanced with the increase of cell concentration. Moreover, the impacts of cellular components on the NAsFP followed the order of CD > IOM > EOM and IOM > EOM > CD for M. aeruginosa and C. meneghiniana, respectively. The results indicated that proteins and soluble microbial products (SMPs) were the main cellular components to contribute to NAs formation and IOM was the primary source of NAs precursor for both algae. Chlorination of Chlorophyll-a and MC-LR showed that chlorophyll-a formed only a small yield of NDMA and NDBA, while MC-LR made a more significant contribution to the types of NAs.

Formation of nitrosamines during chloramination of two algae species in source water-Microcystis aeruginosa and Cyclotella meneghiniana

The contribution of two algae species, Microcystis aeruginosa (M. aeruginosa) and Cyclotella meneghiniana (C. meneghiniana), to the formation of nitrosamines (NAs) during chloramination in drinking water treatment was investigated. A variety of factors including contact time, algae cell concentration, chloramine dosages, and algal cell components (cell debris (CD), intracellular organic matter (IOM), and extracellular organic matter (EOM)) were evaluated for influencing the formation of different NAs, such as N-Nitrosodiethylamine (NDMA), N-Nitrosomethylethylamine (NMEA), N-Nitrosodibutylamine (NDBA), N-Nitrosodi-n-propylamine (NDPA), and N-nitrosopyridine (NPyr). In addition, NAs formation from Chlorophyll-a and Microcystin-LR (MC-LR) after chloramination was studied. These results showed that the increase of reaction time and algae cell concentration enhanced the formation potential of five types of NAs from both algae species, except for the NDMA formation from C. meneghiniana, which increased first and then decreased with increased reaction time. The generation of NDMA was detected as the dominated type of NAs. The formation of total NAs from both algae species followed same pattern of increasing first and then decreasing with the increase of chloramine dosage. The largest NAs formation potential (NAsFP) of M. aeruginosa and C. meneghiniana showed at 1.5 mM and 1.0 mM monochloramine, respectively. Moreover, the impacts of algae cellular components on the formation potential of NAs followed the order of IOM > EOM ≫ CD and IOM ≫ CD > EOM for M. aeruginosa and C. meneghiniana, respectively, indicating that IOM was the main source of NAs precursors for both algae. Furthermore, EEM analysis before and after chloramination confirmed that the soluble microbial products (SMPs) and protein-like substances were the main cellular components that contributed to NAs formation for both algae. The NAs formation potential of Microcystin-LR was much higher than that of Chlorophyll-a chloramination.

Formation of N-nitrosodimethylamine (NDMA) from tetracycline antibiotics during the disinfection of ammonium-containing water: The role of antibiotics dissociation and active chlorine species

N-nitrosodimethylamine (NDMA), a nitrosamine, is a typical nitrogenous disinfection byproduct. In this study, NDMA formation potential and mechanism, from tetracycline and oxytetracycline (as model precursors) in an ammonium-contaminating water, were investigated. The results indicated that both monochloramine and dichloramine played a vital role in NDMA formation. Additionally, the determination of NDMA formation potential (NDMA FP) at a wide range of pH showed that the unprotonated tetracycline tended to have a higher NDMA conversion ratio. We also found that the dissociation of hydroxyl on the meta-position of dimethylamine group promoted on NDMA formation. The detection of significant intermediate products showed that N-chloro unsymmetrical dimethylhydrazine (UDMH-Cl) and sequences of chlorine substitution products were key intermediates, indicating that NDMA formation occurred via the UDMH mechanism pathway. These results improve the knowledge on NDMA formation mechanism and the control strategies during the disinfection of ammonium-containing water.

Fate of N-nitrosodimethylamine and its precursors during a wastewater reuse trial in the Llobregat River (Spain)

In summer 2019, a full-scale trial was carried out to investigate the effects in drinking water quality when tertiary treated wastewater was discharged into the Llobregat River upstream of the intake of one of the major drinking water treatment plants of Barcelona and its metropolitan area. Two scenarios were investigated, i.e. discharging the reclaimed water with and without chemical disinfection with chlorine. This study investigates the concentration of N-nitrosodimethylamine (NDMA) as the specific disinfection conditions employed in this trial may favor its formation. To this aim, both NDMA and NDMA formation potential, were measured. The river contained NDMA at very low concentrations, but the concentration of NDMA precursors was already high. The NDMA concentration was reduced from discharge to the river to drinking water intake probably due to a combined effect of dilution and photolysis. The formation potential was also reduced probably due to dilution and biodegradation. The concentration of NDMA in the drinking water was always low (<7.3 ng/L), although the formation potential was above 10 ng/L in one sample. Dissolved organic matter characterization by high resolution mass spectrometry revealed differences between the nature of the organic matter in the river before and after reclaimed water discharge.

NDMA and NDMA precursor attenuation in environmental buffers prior to groundwater recharge for potable reuse

Natural attenuation of N-nitrosodimethylamine (NDMA) and NDMA precursors was evaluated in infiltration basins, a riverbed filtration system, and constructed wetlands operated as part of a managed aquifer recharge system. Initial NDMA concentrations up to 9.0 ng/L in infiltration basins (advanced purified, recycled water) before sunrise declined to non-detect (<1.5 ng/L) by 10:00 A.M due to natural photolysis (half-life of 33 to 86 min dependent on solar irradiance). NDMA fortified controls adjacent to the infiltration basin showed similar results, while concentrations in dark controls did not change over the basin's hydraulic retention time. NDMA precursor concentrations did not change significantly in the basin containing advanced-treated water from a potable reuse treatment plant, indicating that photolysis did not remove NDMA precursors nor did photolysis produce a significant amount of precursors. For the other environmental buffers evaluated, NDMA removal was variable through laboratory scale soil columns (22 cm height), in full-scale riverbed filtration system that pre-filters water prior to infiltration basin recharge, and in the constructed wetland. Variability in NDMA removal through the wetlands is attributed to high turbidity. In the case of the riverbed filtration system, variability is likely due to short exposure times to sunlight. For the soil columns, limited NDMA removal is attributed to inefficacy of soil aquifer treatment in removing NDMA over short travel times/distances. NDMA precursors were also ineffectively removed in these systems, with effluent concentrations occasionally exceeding influent concentrations. Overall, the removal of NDMA in environmental buffers utilized for planned or de facto indirect potable reuse is dependent on the system's capacity for photolysis, while NDMA precursors are more recalcitrant and unlikely to be removed in such systems without enhancement or sufficient hydraulic residence times.

Contribution of N,N-dimethylformamide to formation of N-nitrosodimethylamine by chloramination in sewage treatment plants and receiving rivers

The contribution of specific precursors to N-nitrosodimethylamine formation potential (NDMA FP) upon chloramination depends not only on their NDMA molar yields but also on their concentrations in the actual environment. We investigated the seasonal and diurnal patterns of the NDMA precursor N,N-dimethylformamide (DMF) and NDMA FP in the Yodo River basin, Japan, by examining water samples taken from inside the basin's largest sewage treatment plant (STP) as well as samples from five final effluents from four STPs, two main stream sites, and two tributary sites in the same basin. DMF and NDMA FP were found to be high in influent (raw sewage), and were found to be mostly removed during the STP treatment processes (especially with biological treatment). Nevertheless, DMF was found in concentrations of 0.06 to 31.7 µg/L in chlorinated effluents and in receiving rivers, while NDMA FP was detected in concentrations of 3.57 to 306 ng/L. Thus, STPs were shown to be an important source of DMF and NDMA FP to rivers. A strong positive correlation between NDMA FP and DMF was confirmed in the receiving river (K-M), indicating that DMF was an important NDMA precursor in the Yodo River basin. The contribution of DMF to NDMA FP was 15.8±11.2% (n = 4) in summer and 82.1±10.2% (n = 4) in winter in the main stream (site K-M) of the river due to insufficient dilution of chlorinated effluents from the largest STP. From the viewpoint of NDMA and NDMA FP control at downstream sites, monitoring and control of DMF at upstream sites are important.

Intake of volatile nitrosamines by Chinese residents in different provinces via food and drinking water

N-nitrosamines are potent carcinogens, particularly N-nitrosodimethylamine (NDMA) and N-nitrosodiethylamine (NDEA), which are commonly found in a variety of foods and drinking water. We calculated the food and drinking water intakes of NDMA, NDEA, and total volatile nitrosamines (TVNA) by Chinese residents in different provinces by multiplying the reported total diet study results by the nitrosamine contents in food and drinking water. The weighted content of nitrosamines in each category of foods and the concentration of nitrosamines in drinking water was obtained through literature review. The exogenous NDMA, NDEA and TVNA intakes of adult residents in 20 provinces ranged from 171 to 425 ng/d, 41 to 140 ng/d and 373 to 1028 ng/d, respectively. The main contributors to NDMA and TVNA intakes were vegetables, cereals, aquatic products, and meats while the main sources of NDEA intake were vegetables and cereals. The average total NDMA intake per capita in China (251 ng/d) was similar to that in Germany in 1991 (231 ng/d) but higher than that in the United States (136 ng/d), Canada (87.6 ng/d) and France (188 ng/d). Large differences in nitrosamine intakes were observed between the coastal provinces and inland provinces. Drinking water was estimated to contribute 13.1%, 1.3% and 10.8% of the exogenous intakes of NDMA, NDEA and TVNA, respectively. Based on our results, we recommend setting the NDMA drinking water criterion of 40 ng/L. Overall, this study presents basic information regarding nitrosamines intake via food and drinking water in China that will facilitate risk assessment, generation of health advisories and policy making.

The Roles of Sono-induced Nitrosation and Nitration in the Sono-degradation of Diphenylamine in Water: Mechanisms, Kinetics and Impact Factors

The potential risks of sono-induced nitrosation and nitration side reactions and consequent toxic nitrogenous byproducts were first investigated via sono-degradation of diphenylamine (DPhA) in this study. The kinetic models for overall DPhA degradation and the formation of nitrosation byproduct (N-nitrosodiphenylamine, NDPhA) and nitration byproducts (2-nitro-DPhA and 4-nitro-DPhA) were well established and fitted (R² > 0.98). Nitrosation contributed much more than nitration (namely, 43.3 - 47.3 times) to the sono-degradation of DPhA. The contribution of sono-induced nitrosation ranged from 0.4 to 56.6% at different conditions. The maximum NDPhA formation rate and the contribution of sono-induced nitrosation were obtained at 600 and 200 kHz, respectively, as ultrasonic frequencies at 200 to 800 kHz. Both NDPhA formation rate and the contribution of sono-induced nitrosation increased with increasing power density, while decreased with increasing initial pH and DPhA concentration. PO₄^3-, HCO₃^-, NH₄⁺ and Fe²⁺ presented negative impacts on sono-induced nitrosation in order of HCO₃^- >> Fe²⁺ > PO₄^3- > NH₄⁺, while Br^- exhibited a promoting effect. The mechanism of NDPhA formation via sono-induced nitrosation was first proposed.

Dissolved organic nitrogen in wastewater treatment processes: Transformation, biosynthesis and ecological impacts

With the upgrade of wastewater treatment plants (WWTPs) to meet more stringent discharge limits for nutrients, dissolved organic nitrogen (DON) is present at an increasing percentage (up to 85%) in the effluent. Discharged DON is of great environmental concern due to its potentials in stimulating algal growth and forming toxic nitrogenous disinfection by-products (N-DBPs). This article systematically reviewed the characteristics, transformation and ecological impacts of wastewater DON. Proteins, amino acids and humic substances are the abundant DON compounds, but a large fraction (nearly 50%) of DON remains uncharacterized. Biological treatment processes play a dominant role in DON transformation (65-90%), where DON serves as both nutrient and energy sources. Despite of the above progress, critical knowledge gaps remain in DON functional duality, relationship with dissolved inorganic nitrogen (DIN) species, and coupling/decoupling with the dissolved organic carbon (DOC) pool. Development of more rapid and accurate quantification methods, modeling transformation processes, and assessing DON-associated eutrophication and N-DBP formation risks should be given priority in further investigations.

N-Nitrosodimethylamine Formation during UV/Hydrogen Peroxide and UV/Chlorine Advanced Oxidation Process Treatment Following Reverse Osmosis for Potable Reuse

Chloramines applied to control microfiltration and reverse osmosis (RO) membrane biofouling in potable reuse trains form the potent carcinogen, N-nitrosodimethylamine (NDMA). In addition to degrading other contaminants, UV-based advanced oxidation processes (AOPs) strive to degrade NDMA by direct photolysis. The UV/chlorine AOP is gaining attention because of its potential to degrade other contaminants at lower UV fluence than the UV/hydrogen peroxide AOP, although previous pilot studies have observed that the UV/chlorine AOP was less effective for NDMA control. Using dimethylamine (DMA) as a model precursor and secondary municipal wastewater effluent, this study evaluated NDMA formation during the AOP treatment via two pathways. First, NDMA formation by UV treatment of monochloramine (NH₂Cl) and chlorinated DMA (Cl-DMA) passing through RO membranes was maximized at 350 mJ/cm² UV fluence, declining at higher fluence, where NDMA photolysis outweighed NDMA formation. Second, this study demonstrated that chlorine addition to the chloramine-containing RO permeate during the UV/chlorine AOP treatment initiated rapid NDMA formation by dark breakpoint reactions associated with reactive intermediates from the hydrolysis of dichloramine. At pH 5.7, this formation was maximized at a chlorine/ammonia molar ratio of 3 (out of 0-10), conditions typical for UV/chlorine AOPs. At 700 mJ/cm² UV fluence, which is applicable to current practice, NDMA photolysis degraded a portion of the NDMA formed by breakpoint reactions. Lowering UV fluence to ∼350 mJ/cm² when switching to the UV/chlorine AOP exacerbates effluent NDMA concentrations because of concurrent NDMA formation via the UV/NH₂Cl/Cl-DMA and breakpoint chlorination pathways. Fluence >700 mJ/cm² or chlorine doses greater than the 3:1 chlorine/ammonia molar ratios under consideration for the UV/HOCl AOP treatment are needed to achieve NDMA control.

Impact of biological wastewater treatment on the reactivity of N-Nitrosodimethylamine precursors

N-Nitrosodimethylamine (NDMA) is a probable human carcinogen which forms during chloramination of wastewater-impacted drinking waters. Municipal wastewater effluents are considered as major sources of NDMA precursors affecting downstream water quality. To evaluate the deactivation mechanisms and efficiencies of NDMA precursors during secondary treatment with the activated sludge (AS) process, NDMA formation potentials (FPs) of selected model precursor compounds and sewage components (i.e., blackwaters and greywaters) were monitored in batch AS treatment tests. After 24-h incubation with four different types of AS (i.e., domestic rural, domestic urban, textile and lab-grown AS), NDMA FP of trimethylamine (TMA) and minocycline (MNCL) decreased by 77-100%, while there was only 29-46% reduction in NDMA FP of sumatriptan (SMTR). The reduction in NDMA FP associated with ranitidine (RNTD) varied between 34% and 87%. The decrease in NDMA FP of RNTD depended on the AS type, hydraulic retention time (HRT) and solids retention time (SRT). The domestic AS (rural and urban) achieved higher decreases in NDMA FPs of the tested model precursors than the textile AS or lab-grown AS. Increasing the HRT or SRT enhanced NDMA FP decrease for RNTD. Among different processes tested (i.e., biodegradation, biosorption and volatilization), biosorption was the major mechanism responsible for the NDMA FP decrease of RNTD, MNCL and SMTR, while biodegradation was the major NDMA FP reduction mechanism for TMA. The reduction in NDMA FP of RNTD via biodegradation depended on the AS activity which may vary with sampling seasons and SRT. NDMA FPs in all tested sewage components (i.e., blackwaters and greywaters) decreased after 24-h AS treatment. Urine in blackwater was the predominant (i.e., >90%) contributor to NDMA FP in domestic sewage and AS-treated effluents.

Oxidation of betrixaban to yield N-nitrosodimethylamine by water disinfectants

Degradation of betrixaban, an oral anticoagulant recently approved by the U.S. Food and Drug Administration (FDA), and its N-nitrosodimethylamine (NDMA) formation potential were studied mechanistically in the presence of monochloramine (NH₂Cl), free chlorine, and ozone. Upon monochloramination, the formation of NDMA exceeded 1% at basic pH and was significant at circumneutral pH as well. The kinetic studies revealed that the reaction between betrixaban and monochloramine followed pseudo-first-order reaction kinetics. Increasing monochloramine concentration, its reaction time, and pH all significantly enhanced the NDMA formation yield, which also increased three-fold in the presence of bromide during monochloraminantion. The presence of nitrite inhibited the formation of NDMA under the same conditions. This study revealed a new potent and significant precursor of NDMA, indicating that monochloramination of waters containing betrixaban can lead to the formation of NDMA and other disinfection by-products such as dichloroacetonitrile (DCAN) and dimethylformamide (DMF). Moreover, chlorination of betrixaban by hypochlorite also yielded NDMA, albeit at two orders of magnitude lower yield than chloramination, while no NDMA formation was observed from ozonation of betrixaban.

Formation of N-nitrosodimethylamine precursors through the microbiological metabolism of nitrogenous substrates in water

N-nitrosodimethylamine (NDMA) as one emerging disinfection by-product has been investigated globally since 1990s. However, its main precursors are still unclear. We found that NDMA formation potential (NDMAFP) of various water samples increased firstly and then decreased gradually during incubation with microorganism. We hypothesized that NDMA precursors could be produced through metabolism of nitrogenous components and then gradually be biodegraded. To verify this hypothesis, six amino acids (AAs), peptone and ammonium were separately incubated with microorganism and NDMAFP was measured regularly. The average molar yield of the substrates to NDMAFP were 60-200 × 10^-6 for the AAs, 350 × 10^-6 for peptone under aerobic condition. The extracellular fraction with molecular weight (MW) less than 1 k Dalton contributed the majority to NDMAFP in the peptone experiment, followed by that with MW between 10 k and 0.22 μm and the intracellular materials. Dimethylamine and methylamine were detected during the experiments but their contribution to NDMAFP is quite limited. The results indicate that the nitrosamine precursors may not be the direct metabolite of AAs or peptones but the excretion of living bacteria or the components in dead bacteria body. Our results inferred that AA metabolism may give an NDMAFP of 0.12 nmol/L (maximum) or 0.09 nmol/L (average) in water under aerobic condition. This estimation of NDMAFP from AA metabolism can account for 38% (maximum) or 27% (average) of the median NDMAFP in waters of China (0.32 nmol/L) reported before.

Formation and Fate of Carbonyls in Potable Water Reuse Systems

Low molecular weight, uncharged compounds have been the subject of considerable study at advanced treatment plants employed for potable water reuse. However, previously identified compounds only account for a small fraction of the total dissolved organic carbon remaining after reverse osmosis treatment. Uncharged carbonyl compounds (e.g., aldehydes and ketones) formed during oxidation have rarely been monitored in potable water reuse systems. To determine the relative importance of these compounds to final product water quality, samples were collected from six potable water reuse facilities and one conventional drinking water treatment plant. Saturated carbonyl compounds (e.g., formaldehyde, acetone) and α,β-unsaturated aldehydes (e.g., acrolein, crotonaldehyde) were quantified with a sensitive new analytical method. Relatively high concentrations of carbonyls (i.e., above 7 μM) were observed after ozonation of wastewater effluent. Biological filtration reduced concentrations of carbonyls by over 90%. Rejection of the carbonyls during reverse osmosis was correlated with molecular weight, with concentrations decreasing by 33% to 58%. Transformation of carbonyls resulted in decreases in concentration of 10% to 90% during advanced oxidation, with observed decreases consistent with rate constants for reactions of the compounds with hydroxyl radicals. Overall, carbonyl compounds accounted for 19% to 38% of the dissolved organic carbon in reverse osmosis-treated water.

Safety and Effectiveness of Monochloramine Treatment for Disinfecting Hospital Water Networks

The formation of potentially carcinogenic N-nitrosamines, associated with monochloramine, requires further research due to the growing interest in using this biocide for the secondary disinfection of water in public and private buildings. The aim of our study was to evaluate the possible formation of N-nitrosamines and other toxic disinfection by-products (DBPs) in hospital hot water networks treated with monochloramine. The effectiveness of this biocide in controlling Legionella spp. contamination was also verified. For this purpose, four different monochloramine-treated networks, in terms of the duration of treatment and method of biocide injection, were investigated. Untreated hot water, municipal cold water and, limited to N-nitrosamines analysis, hot water treated with chlorine dioxide were analyzed for comparison. Legionella spp. contamination was successfully controlled without any formation of N-nitrosamines. No nitrification or formation of the regulated DBPs, such as chlorites and trihalomethanes, occurred in monochloramine-treated water networks. However, a stable formulation of hypochlorite, its frequent replacement with a fresh product, and the routine monitoring of free ammonia are recommended to ensure a proper disinfection. Our study confirms that monochloramine may be proposed as an effective and safe strategy for the continuous disinfection of building plumbing systems, preventing vulnerable individuals from being exposed to legionellae and dangerous DBPs.

Monitoring NDMA precursors throughout membrane-based advanced wastewater treatment processes by organic matter fluorescence

This study investigates the potential of fluorescence excitation/emission matrices (EEM) measurement as a tool to predict N-Nitrosodimethylamine (NDMA) formation in water reuse applications. In particular, samples from a pilot-scale membrane biological reactor (MBR) followed by nanofiltration (NF) advanced water treatment plant, are used for the study. Concentrations of both, specific NDMA precursors and NDMA formation potential (FP) are correlated with different EEM peaks. The specific precursors investigated are: erythromycin, azithromycin, clarithromycin, venlafaxine, o-desmethylvenlafaxine, ranitidine and citalopram, while the NDMA FP is conventionally measured by the NDMA formation potential test. EEM peaks investigated are obtained by fluorescence regional integration as well as by the peak picking method generating I₁, I₂, I₃, I₄, and I₅ peaks. Results showed that protein-like materials are correlated with the bulk NDMA FP and specific NDMA precursors. Additionally, selected fluorescence peaks such as I₁, I₂ and I₄ are strongly correlated with NDMA precursors throughout the MBR-NF pilot plant. The removal of NDMA precursors and EEM peaks also correlated well (R² > 0.8). This data shows that fluorescence EEM can be a promising tool to monitor the concentration of NDMA precursors and their removal in water reuse application.

Halogenated semivolatile acetonitriles as chloramination disinfection by-products in water treatment: a new formation pathway from activated aromatic compounds

The use of monochloramine as an alternative disinfectant to chlorine in drinking water treatment can lead to increased formation of emerging nitrogenous halogenated disinfection by-products (DBPs), even when the formation of regulated halogenated DBPs has decreased. In this study, we investigated formation of the semivolatile haloacetonitriles (HANs) from model nitrogen-containing compounds (6 amines, 1 amide, 6 amino acids, and 2 nitrogen-containing aromatic chemicals) and natural organic matter (NOM) reference materials after chloramination. In agreement with previous studies, most amino acids formed dichloroacetonitrile (DCAN). Additionally, DCAN formed from two amines containing aromatic rings (N,N-dimethylaniline and 3-(dimethylamino-methyl)indole) and the two nitrogen-containing aromatic chemicals (cotinine and phenytoin). This is the first report of DCAN formation from these precursors. DCAN also formed after chloramination of NOM reference materials, with the highest formation from the NOM material with the highest aromaticity. The results provide new evidence of a DCAN formation pathway from cleavage of activated aromatic structures after electrophilic substitution of chlorine and addition of monochloramine to the ring system. In particular, the results suggest that the previously proposed aldehyde pathway from the amino acid group is not responsible for the majority of DCAN formation from amino acids with an activated aromatic ring system. This newly proposed formation pathway for DCAN from activated aromatic organic matter has significant implications for NOM removal during water treatment to minimise DBP formation. Studies using ¹⁵N-labelled monochloramine showed that there was significant incorporation of nitrogen from monochloramine into DCAN, demonstrating that monochloramine disinfection promotes the formation of HANs.

One representative water supply system in China with nitrosamine concern: Challenges and treatment strategies

Four sampling campaigns were conducted in two years to understand the fluctuation of N-Nitrosamines (NAs) and their precursors in one drinking water treatment plant (DWTP) in East China in different seasons. This water supply system has been facing several nitrosamine challenges related with source water, including the switch of water source, high concentration of ammonium, formed NAs and NA formation potential (FP) in source water. Besides, the use of ozonation in the DWTP and chloramination in networks will increase the NDMA concentration in tap water. To address these challenges, the bio-pretreatment was applied in this DWTP to decrease the concentration of ammonium and NAs. The following biological activated carbon (BAC) will neutralize the nitrosamine increase brought by ozonation. The use of free chlorine in disinfection process will also decrease the NDMA formation compared with chloramination. The results will benefit other cities in China and other countries with similar impacted water sources.

Application of stabilized hypobromite for controlling membrane fouling and N-nitrosodimethylamine formation

Chloramination is a conventional and successful pre-disinfection approach to control biological fouling for reverse osmosis (RO) treatment in water reuse. This study aimed to evaluate the possibility of using a new disinfectant-stabilized hypobromite-in controlling membrane fouling and the formation of a particular carcinogenic disinfection byproduct (DBP)-N-nitrosodimethylamine (NDMA). Our accelerated chemical exposure tests showed that the new disinfectant reduced the permeability of a polyamide RO membrane permeability from 6.7 to 4.1 L/m²hbar; however, its treatment impact was equivalent to that of chloramine. The disinfection efficacy of stabilized hypobromite was greater than that of chloramine when evaluated with intact bacterial counts, which suggests its potential for mitigating membrane biofouling. Additional pilot-scale tests using synthetic wastewater demonstrated that pre-disinfection with the use of stabilized hypobromite inhibits membrane fouling. Among 13 halogenated DBPs evaluated, the formation of bromoform by stabilized hypobromite was higher than that by chloramine at a high dose of 10 mg/L, thus suggesting the need for optimizing chemical doses for achieving sufficient biofouling mitigation. NDMA formation upon stabilized hypobromite treatment in two different types of actual treated wastewaters was found to be negligible and considerably lower than that by chloramine treatment. In addition, NDMA formation potential by stabilized hypobromite was 2-5 orders of magnitude lower than that by chloramine. Our findings suggest the potential of using stabilized hypobromite for controlling NDMA formation and biofouling, which are the keys to successful potable water reuse.

Determination of N-Nitrosamines by Gas Chromatography Coupled to Quadrupole–Time-of-Flight Mass Spectrometry in Water Samples

An analytical method based on high-resolution quadrupole–time-of-flight (QToF) mass spectrometry has been developed as an alternative to the classical method, using a low-resolution ion trap (IT) analyzer to reduce interferences in N-nitrosamines determination. Extraction of the targeted compounds was performed by solid-phase extraction (SPE) following the United States Environmental Protection Agency (USEPA) -521 method. First, both electron impact (EI) and positive chemical ionization (PCI) using methane as ionization gas were compared, along with IT and QToF detection. Then, parameters such as limits of detection (LOD) and quantification (LOQ), linearity, and repeatability were assessed. The results showed that the QToF mass analyzer combined with PCI was the best system for the determination of the N-nitrosamines, with instrumental LOD and LOQ in the ranges of 0.2–4 and 0.6–11 ng mL−1, respectively, which translated into method LOD and LOQ in the ranges of 0.2–1.3 and 0.6–3.9 ng L−1, respectively. The analysis of real samples showed the presence of 6 of the N-nitrosamines in influent, effluent, and tap water. N-nitrosodimethylamine (NDMA) was quantified in all the analyzed samples at concentrations between 1 and 27 ng L−1. Moreover, four additional nitrosamines were found in tap and wastewater samples.

Occurrence of N-Nitrosamines in the Pearl River delta of China: Characterization and evaluation of different sources

N-nitrosamines in water have drawn significant concerns for the health of water consumers due to their carcinogenic properties. N-nitrosamines are formed during disinfection of wastewater as well as different industrial and agricultural processes. This study characterized the N-nitrosamines compositions in eleven different wastewaters in the Pearl River Delta (PRD) in Southeast China, and the spatial distributions and the abundances of N-nitrosamines in the Pearl River water were detected. The results indicated that five N-nitrosamines species, including N-nitrosodimethylamine (NDMA), N-nitrosodiethylamine (NDEA), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR) and N-nitrosodibutylamine (NDBA) were found in the industrial wastewater samples in the PRD. Remarkably high concentrations of NDMA (up to 4000 ng/L) were found in the wastewaters from the textile printing and dyeing as well as the electroplating, whereas NDMA, NDEA and NMOR were detected in the domestic wastewaters at concentrations lower than 15 ng/L. Moreover, we found that certain treatment processes for the electroplating wastewater could form a significant amount of NDMA, NPYR and NMOR. Analyses of the Pearl River water samples showed occurrences of different N-nitrosamines species, including NDMA (5.7 ng/L), NDEA (1.7 ng/L), NPYR (2.2 ng/L), NMOR (2.2 ng/L) and NDBA (4.9 ng/L). The abundances of N-nitrosamines species varied spatially due to the inputs from the different sources. Thus, our study provides unique and valuable information for occurrences, abundances and source characteristics of N-nitrosamines in the PRD.

Influence of reverse osmosis membrane age on rejection of NDMA precursors and formation of NDMA in finished water after full advanced treatment for potable reuse

The influence of reverse osmosis (RO) membrane age on rejection of N-nitrosodimethylamine (NDMA) precursors was evaluated for a full-scale potable water reuse facility. The rejection of NDMA precursors decreased slightly with increased membrane age in most RO membrane products evaluated, but remained high overall (91% average). Chloride rejection was well-correlated with rejection of NDMA precursors. Precursor removal varied (75-98%) by membrane product, with certain membrane products maintaining better precursor rejection over time. NDMA rejection, however, did not decline significantly over time, while passage of other low molecular weight organics (LMWOs) increased with membrane age. Thus, rejection of NDMA was not highly correlated with rejection of these LMWOs, suggesting that NDMA is not a good surrogate for these compounds. Incomplete removal of NDMA precursors by RO and a UV/advanced oxidation process (UV/AOP) led to NDMA formation in the finished water and miles downstream in the transmission pipelines. An average NDMA formation rate of 0.7 ng/L/hr in the transmission lines was observed, despite typical removal of NDMA by UV/AOP to non-detect levels. The study indicates that RO membranes throughout their lifetime are not an absolute barrier to NDMA precursors, and that while older membranes continue to sufficiently remove NDMA precursors to a high degree, NDMA precursor rejection may decrease slightly as membranes age. Thus, the potential exists for NDMA to form from these precursors in purified, potable reuse water after treatment despite the effective removal of NDMA by UV/AOP.

Transformation and fate of dissolved organic nitrogen in drinking water supply system: A full scale case study from Yixing, China

The transformation of dissolved organic nitrogen (DON) in the drinking water treatment plants could be closely associated with nitrogenous disinfection by-product (N-DBP) formation. In this study, we have assessed the molecular transformation of DON and its impact on N-DBP formation in a full scale drinking water treatment plant. Based on the result of Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) analysis, DON compounds with low molecular weight (<1 kDa) were classified as CHON, CHON₂ and CHON₃ according to the number of nitrogen atoms. Via the analytical window of van Krevelen diagrams, we found that the molecular structural features of CHON, CHON₂ and CHON₃ were not altered before the chlorination process. In detail, the CHON₂ and CHON₃ compositions were concentrated on the regions assigned to a lignin-structure while CHON compositions were also distributed in other compounds including proteins, carbohydrates and tannin. Furthermore, CHON formation was more difficult to be removed before the V-filter process. For N-DBP, chlorine-containing DON (Cl-DON) composition was likely to be removed through flocculation and sedimentation processes, whereas N-nitrosamine compounds were removed in V-filter and biological activated carbon filter processes. The health risks of aromatic structure N-nitrosamines due to the pre-chlorination of the raw water should be further studied.

Orbitrap molecular fingerprint of dissolved organic matter in natural waters and its relationship with NDMA formation potential

N-nitrosodimethylamine (NDMA) is a disinfection byproduct that has been classified as probable human carcinogen by the US Environmental Protection Agency. According to the published literature, natural dissolved organic matter (DOM) can be a source of NDMA precursors in drinking water. New advances in chemical characterization of DOM with high resolution mass spectrometry (HRMS) are allowing researchers to understand these ultra-complex mixtures. The objective of this study is to investigate analytical methodologies based on HRMS to explore NDMA formation from natural waters. To this aim, different waters from drinking water reservoirs in Spain containing NDMA precursors (quantified by means of NDMA formation potential) in concentrations between 17 and 60 ng/L have been studied. The workflow includes DOM solid-phase extraction and Orbitrap analysis with and without chromatographic separation. Here, we show that the molecular composition of DOM across the studied drinking water reservoirs is correlated with the NDMA formation potential. In particular, we found that NDMA formation potential is associated with compounds with high hydrogen saturation (H/C ≥ 1.5), corresponding also to reservoirs with higher background nutrient concentrations and wastewater indicators. Further chromatographic fractionation did not allow better definition of these possible precursors as they were present in different fractions of the chromatogram, suggesting that they were isomerically complex.

Formation potential of nine nitrosamines from polyacrylamide during chloramination

Cationic polymers, which are commonly used as flocculants and coagulant aids in water and wastewater treatment, have been recently reported to promote the formation of nitrosamines. Most of the findings to date are based on poly (epichlorohydrin dimethylamine) and poly (diallyldimethylammonium chloride), while few studies have considered nitrosamines formation of polyacrylamides. In this work, the nitrosamines formation from non-ionic, anionic and cationic polyacrylamides was evaluated. Moreover, the effects of chemical structures of cationic polyacrylamides (including molecular weight, charge density, and monomers) on nitrosamines formation were investigated. The results revealed that the highest amount of nitrosamines formation was formed from cationic polyacrylamide, followed by non-ionic polyacrylamide and anionic polyacrylamide. Molecular weight and various cationic monomers showed no significant effects on nitrosamines formation, but monomers generated significantly higher amount of nitrosamines formation than cationic polyacrylamides. Nitrosamines formation increased with the increasing charge density of cationic polyacrylamides, and FTIR analysis results showed that the quaternary amine groups preferentially reacted with chloramines than with amide groups. This work shed new light on the nitrosamines formation from water and wastewater treatment polymers.

Carcinogenic risk of N-Nitrosamines in Shanghai Drinking Water: Indications for the Use of Ozone Pretreatment

N-Nitrosamines are drinking water disinfection byproducts that pose a high carcinogenic risk. We hypothesized that raw water treatment processes influence the types and concentrations of nitrosamines in drinking water, thereby posing differential health risks. We compared the finished water of two water treatment plants (WTP-A, WTP-B) serving Shanghai, China. Both plants use the Qingcaosha reservoir as a water source to generate drinking water with conventional but distinct treatment processes, namely preoxidation with sodium hypochlorite (WTP-A) vs ozone (WTP-B). Average nitrosamine concentrations, especially that of the probable human carcinogen (2A) N-nitrosodimethylamine, were higher in finished (drinking) water from WTP-A (35.83 ng/L) than from WTP-B (5.07 ng/L). Other differences in mean nitrosamines in drinking water included N-nitrosodipropylamine (42.62 ng/L) and N-nitrosomethylethylamine (26.73 ng/L) in WTP-A in contrast to N-nitrosodiethylamine (7.26 ng/L) and N-nitrosopyrrolidine (59.12 ng/L) in WTP-B. The estimated adult cancer risk from exposure to mixed nitrosamines was 1.83 times higher from WTP-A than from WTP-B drinking water. Children exposed to nitrosamines had a significantly higher cancer risk than adults ( p < 0.05). Disease burden exceeded 10⁶ person-years. Taken together, these data suggest that use of ozone in the preoxidation step can reduce nitrosamine formation in drinking water and thereby lower the population cancer health risk.

Formation of N-nitrosodimethylamine by chloramination of anthropogenic nitrogenous compounds with dimethylamine monitored by Japanese water authorities

Pollutant release and transfer registers (PRTRs) compounds accidentally released to source waters can be important precursors of the carcinogenic N-nitrosodimethylamine (NDMA) during drinking water treatment. The NDMA formation potentials (NDMAFPs) of 31 anthropogenic nitrogenous compounds with dimethylamine (DMA) moiety on the Japanese PRTR and the registered precursors listed by the Ministry of Health, Labour and Welfare of Japan are investigated as well as influencing factors (i.e., NH₂Cl dose and water matrices) on the NDMAFPs of precursors. Tertiary amines with aryl groups β-positioned to the nitrogen atom of the DMA moiety formed high concentrations of NDMA (35-51%) during chloramination. Moreover, dimethylcarbamoyl chloride (DMCCl) was considered a new NDMA precursor with NDMAFP of 1.1%, higher than DMA, a traditional NDMA precursor. Excessive NH₂Cl dose enhanced the NDMA formation, and the NDMAFP of DMCCl significantly decreased in river water; the effect of the matrix in river water varied and was compound-specific. Among the selected nitrogenous compounds, NDMAFPs of 15 excessed the current guideline concentration for NDMA in Japan (100 ng/L) assuming an accidental release of 0.144 mg C/L (the concentration in previous Japanese water quality accident in May 2012), and 2-(dimethylaminomethyl) thiophene (DMAMT) showed the highest NDMAFP at 58 μg/L.

Fungal biodegradation of the N-nitrosodimethylamine precursors venlafaxine and O-desmethylvenlafaxine in water

Antidepressant drugs such as Venlafaxine (VFX) and O-desmethylvenlafaxine (ODMVFX) are emerging contaminants that are commonly detected in aquatic environments, since conventional wastewater treatment plants are unable to completely remove them. They can be precursors of hazardous by-products, such as the carcinogenic N-nitrosodimethylamine (NDMA), generated upon water chlorination, as they contain the dimethylamino moiety, necessary for the formation of NDMA. In this study, the capability of three white rot fungi (Trametes versicolor, Ganoderma lucidum and Pleurotus ostreatus) to remove both antidepressants from water and to decrease NDMA formation potential was investigated. Furthermore, transformation by-products (TPs) generated along the treatment process were elucidated and also correlated with their NDMA formation potential. Very promising results were obtained for T. versicolor and G. lucidum, both being able to remove up to 100% of ODMVFX. In the case of VFX, which is very recalcitrant to conventional wastewater treatment, a 70% of removal was achieved by T. versicolor, along with a reduction in NDMA formation potential, thus decreasing the associated problems for human health and the environment. However, the NDMA formation potential remained practically constant during treatment with G. lucidum despite of the equally high VFX removal (70%). This difference was attributed to the generation of different TPs during both fungal treatments. For example, G. lucidum generated more ODMVFX, which actually has a higher NDMA formation potential than the parent compound itself.

A pilot-scale investigation of disinfection by-product precursors and trace organic removal mechanisms in ozone-biologically activated carbon treatment for potable reuse

Although granular activated carbon (GAC) has been broadly applied in ozone-biologically activated carbon filtration (O₃/BAC) systems for potable reuse of municipal wastewater, the mechanisms of various pollutant removal remain largely unknown as the regenerated GAC develops microbial populations resulting in biofiltration but loses significant adsorption capacity as it becomes spent GAC. Therefore, pilot-scale parallel performance comparisons of spent and regenerated GAC, along with a range of pre-oxidant ozone doses, were used to shed light on the mechanisms responsible for the removal of various types of treatment byproduct precursors and trace organic compounds. It was confirmed from this pilot-study that ozone alone can effectively degrade chlorinated trihalomethane (THM) and haloacetic acid (HAA) precursors, chloramine-reactive N-nitrosodimethylamine (NDMA) precursors, and 29 PPCPs. In contrast, biodegradation by microbial population on spent or regenerated GAC can remove NDMA and 22 PPCPs, while the adsorption by regenerated GAC can remove chlorinated THM and HAA precursors, PFAS, flame retardants, and 27 PPCPs. The results of this pilot study are intended to provide those interested in potable reuse with an example of the simultaneous removal capabilities and mechanisms that can be anticipated for treating a complex mixture of organics present in real municipal wastewater effluent.

Removal of N-nitrosodimethylamine precursors by cation exchange resin: The effects of pH and calcium

Cation exchange resins have proved to be efficient in removing precursors of N-nitrosodimethylamine (NDMA). NDMA is a probable human carcinogen with a calculated lifetime cancer risk of 10^-6 at 0.7 ng/L in drinking water. This paper investigated the effect of pH and calcium levels on the removal of NDMA precursors using a cation exchange resin. At pH 5 and 7, 30-50% of NDMA precursors, measured by formation potentials (FPs) changes before and after the treatment, were removed by Plus resin. However, increases in NDMA FPs were observed after the treatment at pH 10 indicating that NDMA precursors were released from the resin. NDMA FPs removals in samples containing 15 and 115 mg/L Ca²⁺ were 40% and -10% after the ion exchange treatments at pH 7, respectively. It was found that in the presence of high concentration of calcium only one out of four cation exchange resins released NDMA precursors (probably due to manufacturing impurities). Also, the release of NDMA precursors depended on the calcium concentration and the contact time of the resin with the solution containing calcium. Nonetheless, NDMA precursors release from the resin subsided significantly with increasing the number of regeneration cycles of the resin.

Removal Characteristics of N-Nitrosamines and Their Precursors by Pilot-Scale Integrated Membrane Systems for Water Reuse

This study investigated the removal characteristics of N-Nitrosamines and their precursors at three pilot-scale water reclamation plants. These plants applies different integrated membrane systems: (1) microfiltration (MF)/nanofiltration (NF)/reverse osmosis (RO) membrane; (2) sand filtration/three-stage RO; and (3) ultrafiltration (UF)/NF and UF/RO. Variable removal of N-Nitrosodimethylamine (NDMA) by the RO processes could be attributed to membrane fouling and the feed water temperature. The effect of membrane fouling on N-Nitrosamine removal was extensively evaluated at one of the plants by conducting one month of operation and chemical cleaning of the RO element. Membrane fouling enhanced N-Nitrosamine removal by the pilot-scale RO process. This finding contributes to better understanding of the variable removal of NDMA by RO processes. This study also investigated the removal characteristics of N-Nitrosamine precursors. The NF and RO processes greatly reduced NDMA formation potential (FP), but the UF process had little effect. The contributions of MF, NF, and RO processes for reducing FPs of NDMA, N-Nitrosopyrrolidine and N-Nitrosodiethylamine were different, suggesting different size distributions of their precursors.

The role of chloramine species in NDMA formation

N-nitrosodimethylamine (NDMA), a probable human carcinogen disinfection by-product, has been detected in chloraminated drinking water systems. Understanding its formation over time is important to control NDMA levels in distribution systems. The main objectives of this study were to investigate the role of chloramine species (i.e., monochloramine and dichloramine); and the factors such as pH, sulfate, and natural organic matter (NOM) influencing the formation of NDMA. Five NDMA precursors (i.e., dimethylamine (DMA), trimethylamine (TMA), N,N-dimethylisopropylamine (DMiPA), N,N-dimethylbenzylamine (DMBzA), and ranitidine (RNTD)) were carefully selected based on their chemical structures and exposed to varying ratios of monochloramine and dichloramine. All amine precursors reacted relatively fast to form NDMA and reached their maximum NDMA yields within 24 h in the presence of excess levels of chloramines (both mono- and dichloramine) or excess levels of dichloramine conditions (with limited monochloramine). When the formation of dichloramine was suppressed (i.e., only monochloramine existed in the system) over the 5 day contact time, NDMA formation from DMA, TMA, and DMiPA was drastically reduced (∼0%). Under monochloramine abundant conditions, however, DMBzA and RNTD showed 40% and 90% NDMA conversions at the end of 5 day contact time, respectively, with slow formation rates, indicating that while these amine precursors react preferentially with dichloramine to form NDMA, they can also react with monochloramine in the absence of dichloramine. NOM and pH influenced dichloramine levels that affected NDMA yields. NOM had an adverse effect on NDMA formation as it created a competition with NDMA precursors for dichloramine. Sulfate did not increase the NDMA formation from the two selected NDMA precursors. pH played a key role as it influenced both chloramine speciation and protonation state of amine precursors and the highest NDMA formation was observed at the pH range where dichloramine and deprotonated amines coexisted. In selected natural water and wastewater samples, dichloramine led to the formation of more NDMA than monochloramine.

Efficient bacterial disinfection based on an integrated nanoporous titanium dioxide and ruthenium oxide bifunctional approach

The increasing lack of drinking water around the globe is of great concern. Although UV irradiation, photocatalysis, and electrocatalysis for bacterial disinfection have been widely explored, the synergistic kinetics involved in these strategies have not been reported to date. Herein, we report on an efficient and cost-effective strategy for the remediation of a model bacterium (E. coli), through the integration of photochemistry and electrochemistry based on a bifunctional electrode, which utilizes titanium (Ti) as the substrate, nanoporous titanium dioxide (TiO₂) as a photocatalyst, and ruthenium oxide (RuO₂) nanoparticles as an electrocatalyst. The nanoporous TiO₂ was grown directly onto a Ti substrate via a three-step anodization process, and its photocatalytic activity was significantly enhanced by a facile electrochemical treatment. A high disinfection rate at 0.62 min^-1, with >99.999% bacterial removal within 20 min was achieved using the novel TiO₂/Ti/RuO₂ bifunctional electrode. Complete bacterial disinfection was attained within 30 min as assessed by a spread plate method. Bacterial survival strategies, including a viable but non-culturable state of the bacteria, were also investigated during the bifunctional treatment process. The novel strategy demonstrated in this study has strong potential to be utilized for water purification and wastewater treatment as an advanced environmentally compatible technology.

N-nitrosamines in drinking water and beer: Detection and risk assessment

Occurrence and risk related to nitrosamines, a group of carcinogenic compounds found in some drinking waters and beer, are studied. An analytical method using a solid-phase micro-extraction (SPME) along with gas chromatography (GC) and mass spectrometry (MS) was developed to determine seven N-nitrosamines in drinking water and beer, including N-nitrosomethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodimethylamine (NDMA), N-nitrosodi-n-propylamine (NDPA), N-nitrosopyrrolidine (NPyr), N-nitrosopiperidine (NPip), and N-nitrosodinbutylamine (NDBA). The analysis can be completed in 70 min, and only a 4 mL sample is required, with a detection limit of 0.1-0.8 ng/L for the seven nitrosamines in water and 6-15.7 ng/L in beer. The method was applied to analyze water samples collected from 11 reservoirs and their associated drinking water treatment plants in Taiwan and 10 beer samples from 6 brands with factories located in 6 countries. In the drinking water samples, all seven N-nitrosamines were detected, with NDMA having the highest level at 10.2 ng/L. In the beer samples, NDMA was detected at much lower concentrations (0.12-0.23 μg/L) than the 5 μg/L US standard, while NPip was detected at much higher concentrations (4.1-5.3 μg/L) compared to NDMA. The risk assessment indicates that the risk associated with NDMA is the highest among the studied N-nitrosamines in Taiwan's drinking water, with an average cancer risk of 6.4 × 10^-06. For other nitrosamines, the risks are all below 10^-6. For the risks associated with N-nitrosamines in beer, NDMA, NDEA, NDPA, and NPip are in the range of 1.5 × 10^-05 to 4.6 × 10^-04, while that for other nitrosamines are much lower. As for beer, no information for NPip and no modern information for NDEA and NDPA have previously been available, more studies about nitrosamines in beer are suggested for better estimation and control of the risks associated with consumption of beer.

Reduction of N-nitrosodimethylamine formation from ranitidine by ozonation preceding chloramination: influencing factors and mechanisms

Formation of toxic N-nitrosodimethylamine (NDMA) by chloramination of ranitidine, a drug to block histamine, was still an ongoing issue and posed a risk to human health. In this study, the effect of ozonation prior to chloramination on NDMA formation and the transformation pathway were determined. Influencing factors, including ozone dosages, pH, hydroxyl radical scavenger, bromide, and NOM, were studied. The results demonstrated that small ozone dosage (0.5 mg/L) could effectively control NDMA formation from subsequent chloramination (from 40 to 0.8%). The NDMA molar conversion was not only influenced by pH but also by ozone dosages at various pre-ozonation pH (reached the highest value of 5% at pH 8 with 0.5 mg/L O₃ but decreased with the increasing pH with 1 mg/L O₃). The NDMA molar yield by chloramination of ranitidine without pre-ozonation was reduced by the presence of bromide ion due to the decomposition of disinfectant. However, due to the formation of brominated intermediate substances (i.e., dimethylamine (DMA), dimethyl-aminomethyl furfuryl alcohol (DFUR)) with higher NDMA molar yield than their parent substances, more NDMA was formed than that without bromide ion upon ozonation. Natural organic matter (NOM) and hydroxyl radical scavenger (tert-butyl alcohol, tBA) enhanced NDMA generation because of the competition of ozone and more ranitidine left. The NDMA reduction mechanism by pre-ozonation during chloramination of ranitidine may be due to the production of oxidation products with less NDMA yield (such as DMA) than parent compound. Based on the result of Q-TOF and GC-MS/MS analysis, three possible transformation pathways were proposed. Different influences of oxidation conditions and water quality parameters suggest that strategies to reduce NDMA formation should vary with drinking water sources and choose optimal ozone dosage.