N-nitrosodimethylamine Formation Potential Research Articles

Natural vs. anthropogenic sources of N-Nitrosodimethylamine precursors in surface water

N-nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct formed from reactions between dichloramine and organic nitrogen-containing precursors. It is unclear if NDMA precursors in surface water intakes originate in anthropogenic (i.e., wastewater) or natural sources. The Truckee River has a single point source release of treated wastewater effluent, making it an ideal system to study the relative importance of precursor sources. Three Lagrangian sampling events were conducted. NDMA formation potential (FP, a measurement of precursors) above the wastewater outfall indicated that the natural background of NDMA precursors was 2-28 ng/L. NDMA FP increased to 18-31 ng/L immediately downstream of the wastewater outfall, but decreased rapidly in a first order manner, and were not statistically different from the upstream samples in only ∼6 km. This suggests that the dominant source of NDMA precursors may be wastewater derived only near wastewater outfalls and deviates from the previous belief that wastewater-derived precursors are responsible for NDMA formation in drinking water sources located further downstream. Additionally, given the rapid loss of the wastewater precursors in this study, precursors which are slow to biodegrade/photolyze/adsorb to sediment are likely to be poor surrogates for the overall wastewater NDMA precursor pool. To understand temporal changes in the wastewater impact on environmental NDMA precursor loading, two 24-hour sampling events were conducted near (<3 km) the wastewater outfall and demonstrated that temporal changes in the NDMA precursors directly downstream of the wastewater outfall are directly linked to the wastewater flow contribution.

Bacterial dealkylation of benzalkonium chlorides in wastewater produces benzyldimethylamine, a potent N-nitrosodimethylamine precursor

N-nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct that forms during chloramine disinfection of municipal wastewater effluents which are increasingly used to augment drinking water supplies due to growing water scarcity. Knowledge of wastewater NDMA precursors is limited and the known pool of NDMA precursors has not closed the mass balance between precursor loading, precursor NDMA yield, and formed NDMA. Benzalkonium chlorides (BACs) are the most prevalent quaternary ammonium surfactants and have antimicrobial properties. The extensive utilization of BACs in household, commercial and industrial products has resulted in their detection in wastewater at elevated concentrations. We report the formation of a potent NDMA precursor, benzyldimethylamine (BDMA) from the biodegradation of BACs during activated sludge treatment. BDMA formation and NDMA formation potential (FP) were functions of BAC and mixed liquor suspended solids concentration at circumneutral pH, and the microbial community source. Sustained exposure to microorganisms reduced NDMA FP through successive dealkylation of BDMA to less potent precursors. BAC alkyl chain length (C8 – C16) had little impact on NDMA FP and BDMA formation because chain cleavage occurred at the C–N bond. Wastewater effluents collected from three facilities contained BDMA from 15 to 106 ng/L, accounting for an estimated 4 to 38 % of the NDMA precursor pool.

Complete removal of N-nitrosamines using in-situ constructed sequential microreactors: Synergies of catalysis-adsorption between N-nitrosamines and their degradation products

The removal of N-nitrosamines from water faces the challenges of their difficult adsorption, and incomplete mineralization of degradation products. Herein, we report a new strategy by in-situ constructing microreactor on carbon cloth arrayed CoNi spinel oxide through membrane encapsulation. The NiCo2O4-nanoarrays activate peroxonosulfate, generating reactive oxygen species that rapidly degrade N-nitrosamines. The breaking N-N bond of N-nitrosamines provides an effective binding site for adsorbing degradation products (secondary amines). Meanwhile, electrons conducted from secondary amines adsorbed on Ni sites reconstruct the charge of CoNi sites, bolstering the peroxonosulfate activation to further remove N-nitrosamines and secondary amines. Moreover, the microreactive interface formed between membrane substrate and NiCo2O4-nanoarrays improved the reaction efficiency. It maintains efficient N-nitrosamines removal (96–99%) even in the presence of humic acid. Actual wastewater experiments confirmed its effective control of both N-nitrosamines and N-nitrosodimethylamine formation potential. This study provides a novel approach for eliminating the risk of N-nitrosamines in water.

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.

Effect of activated sludge treatment on the formation of N[sbnd]nitrosamines 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.

Nitrite-enhanced N-nitrosamines formation during the simulated tetracycline polluted groundwater chlorination: Experimental and theoretical investigation

N-nitrosamines (NAs), a class of emerging nitrogenous disinfection byproducts, have been detected remarkably in drinking/reclaimed water. There is a significant risk of excessive levels of NAs in the chlorination of the polluted source water, especially in the direct chlorination of nitrite-enriched groundwater. Considering the co-pollution of nitrite and micro-organic pollutants on groundwater, experiments were conducted on chlorination of nitrite-enriched water with precursor of antibiotics, and it was confirmed that the Cl 2 : N (molar ratio of chlorine to nitrite), contacting time, pH, and DO appreciably influenced the NAs formation potential. The molecular electric potential revealed that different dissociation status of precursors has a specific correlation with NAs formation potential (FP). The nitrite significantly increased the NAs FP because the reactive nitrogen species (RNS) formed in the oxidation process from nitrite to nitrate. Sequences of transformation products are determined to support the RNS promoted hypothesis of N-nitrosodimethylamine (NDMA) formation mechanism; furthermore, theoretical investigation in the reaction of dimethylamine (DMA) with different RNS verified the above hypothesis. • NDMA FP significantly promoted in chlorination of nitrite-enriched groundwater. • DO is not a key factor to NDMA formation in nitrite-enriched situation. • RNS enhanced-nitrosation pathway was proposed. • NDEA has been detected along with NDMA formation.

Predictable Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry Fragmentation of Ozone-Reactive N-Nitrosodimethylamine Precursors Coupled with In Silico Fragmentation and Ion Mobility-Quadrupole Time-of-Flight Facilitates Their Identification in Sewage

This study investigated the liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS) fragmentation of 10 potent model ozone (O3)-reactive N-nitrosodimethylamine (NDMA) precursors bearing (CH3)2N-N or (CH3)2N-(SO2)-N. Fragments (m/z 61.0766, 60.0688 Da loss, and 72.0688 Da loss) were discovered as pertinent diagnostic fragments for precursors bearing (CH3)2N-N, whereas a loss of 108.0119 Da was consistent for precursors bearing (CH3)2N-S(O2)-N. Using the fragments as structural hints on a sewage fraction with a high concentration of O3-reactive precursors, peaks of precursors sharing m/z 61.0766, a 60.0688 Da loss, or both were flagged. Then, using in silico fragmenters and (CH3)2N-N as a substructure filter on online-chemical structure databases, we identified PubChem's compound identifier (PCCID) 141210417 and 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene)disemicarbazide (TMDS). TMDS was confirmed using an authentic standard, and ion mobility (IM)-QTOF/MS confirmed its rider peak as PCCID 141210417. PCCID 141210417 is an isomer of TMDS, and its environmental occurrence is associated with technical-grade TMDS and industrial effluents. The estimated contribution of TMDS to the total NDMA formation potential of the sewage fraction was 20-24%, which was suggestive of the significance of PCCID 141210417 and other precursors.

Motivation of reactive oxidation species in peracetic acid by adding nanoscale zero-valent iron to synergic removal of spiramycin under ultraviolet irradiation: Mechanism and N-nitrosodimethylamine formation potential assessment

In this study, nanoscale zero-valent iron (nZVI) was added to motivate the functions of all the reactive oxidation species in peracetic acid (PAA) mixture under ultraviolet (UV) irradiation, and to enhance the removal of spiramycin, which is a typical precursor of N-nitrosodimethylamine (NDMA). Spiramycin (≤ 10 mg/L) could be completely removed within 20 min under the conditions of an initial pH of 4.0, a nZVI dose of 0.02 g/L and a PAA dose of 3.0 mg/L; additionally, 95.8% and 78.8% of PAA and H2O2 were consumed during the process. Electron paramagnetic resonance analysis and quenching experiments confirmed that 52.4% and 44.8% of spiramycin removal was contributed by hydroxyl radical (•OH) and carbon-centered radicals (R-C•), respectively; and Fe2+ released from nZVI played a critical role in radicals generation. Four degradation pathways of spiramycin were proposed and verified by the density of functional theory analysis. 65.2% of the NDMA formation potential (FP) was reduced after the reaction, and its residual was mainly contributed by the undegraded intermediate of dimethylamine. The results of multiple characterizations and continuous degradation experiments indicated that nZVI was stable in the system as the removal of spiramycin was hardly influenced even if reused three times. The nZVI/UV/PAA process is a promising advanced oxidation technology not only for the removal of refractory NDMA precursors (such as spiramycin) but also for significantly lowering the NDMA FP.

Degradation of ranitidine and changes in N-nitrosodimethylamine formation potential by advanced oxidation processes: Role of oxidant speciation and water matrix

This study investigated the effects of thirteen (photo/electro) chemical oxidation processes on the formation potential (FP) of N-nitrosodimethylamine (NDMA) during the chloramination of ranitidine in reverse osmosis (RO) permeate and brine. The NDMA-FP varied significantly depending on the pretreatment process, initial pH, and water matrix types. At higher initial pH values (> 7.0), most pretreatments did not reduce the NDMA-FP, presumably because few radical species and more chloramine-reactive byproducts were generated. At pH < 7.0, however, electrochemical oxidation assisted by chloride and Fe2+/H2O2, catalytic wet peroxide oxidation and peroxydisulfate-induced pretreatments removed up to 85% of NDMA-FP in the RO brine. Ultraviolet (UV) irradiation or prechlorination alone did not reduce the NDMA-FP effectively, but combined UV/chlorine treatment effectively reduced the NDMA-FP. In contrast, after UV irradiation (2.1 mW cm−2 for 0.5 h) in the presence of H2O2 and chloramine, NDMA formation increased substantially (up to 26%) during the post-chloramination of the RO permeate. Mass spectrometric analysis and structural elucidation of the oxidation byproducts indicated that compared with the reactive nitrogen species generated by UV/NH2Cl, sulfate radicals and (photo/electro)chemically generated reactive chlorine species were more promising for minimizing NDMA-FP. Unlike, the hemolytic •OH driven by UV/H2O2, the •OH from Fe(IV)-assisted pretreatments showed a significant synergistic effect on NDMA-FP reduction. Overall, the results suggest the need for a careful assessment of the type of radical species to be used for treating an RO water system containing amine-functionalized compounds.

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.

Green synthesis of sulfur‐doped g‐C3N4 nanosheets for enhanced removal of oxytetracycline under visible‐light irradiation and reduction of its N‐nitrosodimethylamine formation potential

AbstractBACKGROUNDIn this study, sulfur‐doped g‐C3N4 (SCN) nanosheets were synthesized using thiourea as a precursor, and then used to catalyze the degradation of oxytetracycline (OTC) under visible‐light irradiation. OTC was chosen as target contaminant because of it being an important precursor of N‐nitrosodimethylamine (NDMA).RESULTSThe removal of OTC was influenced by its initial concentration, initial pH, SCN dosage and water matrices. OTC (≤10 mg L−1) was almost completely removed in 40 min under the conditions of an initial pH of 7.0 and a SCN dose of 1.0 g L−1, and its degradation was well described by the pseudo‐first‐order kinetics model. Water matrices would also influence the degradation of OTC in the system. Electron paramagnetic resonance analysis and trapping experiments confirmed that the function of the radicals for OTC removal followed the order of •O2− &gt; •OH &gt; h+. Eight transformation products were determined during the degradation of OTC, it being removed through four pathways: methyl oxidization, demethylation, decarbonylation and secondary alcohol oxidation. SCN was stable in the system, as the removal efficiency of OTC was not significantly reduced even after three recycles. In addition, 55.5% of NDMA formation potential of OTC was reduced after SCN catalytic oxidation.CONCLUSIONSThe results imply that the visible‐light‐driven SCN catalytic oxidation is an effective technology not only for the removal of OTC but also for the reduction of NDMA formation potential. © 2021 Society of Chemical Industry

Fabricating a novel ternary recyclable Fe3O4/graphene/sulfur-doped g-C3N4 composite catalyst for enhanced removal of ranitidine under visible-light irradiation and reducing of its N-nitrosodimethylamine formation potential

A novel ternary recyclable Fe3O4/graphene/sulfur-doped g-C3N4 (Fe3O4/GE/SCN) composite catalyst was synthesized and adopted in a visible-light driven catalytic system for the degradation of ranitidine, which is an important precursor of the emerging disinfection by-product of N-nitrosodimethylamine (NDMA). The addition of GE and Fe3O4 significantly improved the interface charge transfer of SCN, increased the light collection efficiency and decreased the photogenerated charge recombination efficiency. Considering both the ranitidine removal efficiency and catalyst recovery, the Fe3O4 mass fraction of 20% (20%-Fe3O4/GE/SCN) was recommended. Ranitidine (≤2 mg/L) was completely removed in 60 min under the conditions of an initial pH of 7.0 and a 20%-Fe3O4/GE/SCN dose of 1.0 g/L, and its degradation fitted well with the pseudo first-order kinetics model. Electron paramagnetic resonance analysis and trapping experiments confirmed that ·O2−, ·OH and h+ participated in the degradation of ranitidine. Ranitidine was removed through the pathways of demethylation and hydroxylation based on the analysis of the detected degradation intermediates, and 57.3% of the NDMA formation potential (FP) was reduced after the reaction. The visible-light driven 20%-Fe3O4/GE/SCN catalytic technology is a promising method not only for the control of NDMA FP but also the catalyst could be recovered and reused.

Enhanced removal of oxytetracycline by UV-driven advanced oxidation with peracetic acid: Insight into the degradation intermediates and N-nitrosodimethylamine formation potential

In this study, UV-driven advanced oxidation with peracetic acid (PAA) was adopted to enhance the removal of oxytetracycline (OTC) as well as to lower the formation potential of N-nitrosodimethylamine (NDMA). Results implied that the combination of UV and PAA had a synergetic effect on both the removal and mineralization of OTC. OTC (≤5 mg L−1) could be completely removed in 45 min in the UV/PAA system under the conditions of an initial pH of 7.10 and a PAA dose of 5 mg L−1; additionally, 50.9% of mineralization rate of OTC was obtained. Electron paramagnetic resonance analysis and quenching experiments indicated that ·OH was the main oxidizer for the removal of OTC, while UV, PAA and carbon-centered radicals (R–C·) also participated in its removal. During the degradation of OTC, 31 kinds of degradation intermediates were traced, and 20 kinds of them were first detected in the UV/PAA system. OTC was removed through five pathways, and the hydroxylation pathway was involved in nearly the entire degradation period. The NDMA formation potential decreased by 65.8% after the reaction, and residual dimethylamine accounted for 15.1% of its total composition. The proposed UV/PAA process is a promising method not only for the removal of refractory antibiotics but also for controlling the formation of NDMA.

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.

N-nitrosodimethylamine formation potential (NDMA-FP) of ranitidine remains after chlorination and/or photo-irradiation: Identification of transformation products in combination with NDMA-FP test

N-nitrosodimethylamine (NDMA), a probable carcinogenic disinfection by-product, can be formed with high molar yields following chloramination of ranitidine (RNTD), a histamine H2-receptor antagonist. Although RNTD and some of its transformation products (TPs) have been studied under chlorination and photo-irradiation, the relationship between RNTD TPs and NDMA formation potential (NDMA-FP) remaining after those processes is still unclear. This study investigated the effects of chlorination and/or photo-irradiation on NDMA-FP derived from RNTD, simulating an urban water environment receiving treated wastewater. After chlorination and/or photo-irradiation of RNTD, ten TPs including five new ones were identified by liquid chromatography–quadrupole time-of-flight mass spectrometry (LC-QTof-MS). In addition, important RNTD TPs responsible for NDMA-FP (e.g., chlorinated and hydroxylated RNTD: TP-364) were also confirmed by the relationship between detected peak area and NDMA-FP. The results showed that NDMA-FP remained due to the presence of RNTD TPs, although RNTD itself was significantly removed by chlorination and/or photo-irradiation. TP-364 was only formed by chlorination of RNTD and could not be removed by photo-irradiation. TP-314 (a stereoisomer of RNTD), -299, and -286, which were mainly formed by photo-irradiation of RNTD but not by photo-irradiation after chlorination, had strong positive correlations with NDMA-FP (R2 > 0.90; F-test, P < 0.01).

Phenylurea herbicide degradation and N-nitrosodimethylamine formation under various oxidation conditions: Relationships and transformation pathways.

Four phenylurea herbicides (PUHs) were assessed for degradation and transformation into N-nitrosodimethylamine (NDMA) under three oxidation conditions (chlorine (Cl2), chlorine dioxide (ClO2), and ozone (O3)) from an aqueous solution. Removal ratios correlated with the numbers of halogen elements contained in PUHs (isoproturon (0)>chlorotoluron (1 Cl)>diuron (2 Cl)>fluometuron (3F)), and the degradation efficiencies of oxidants from fastest to slowest were: O3, ClO2, and Cl2. NDMA can be generated directly from the ozonation of PUHs. Further, compared with chloramination alone, ozonation prominently promoted NDMA formation potential (NDMA-FP) during post-chloramination, and NDMA-FPs increased approximately 23-68 times than those during ozonation only at 2.5mg/L O3 over 10min; molar yields of NDMA from highest to lowest were 11.1% (isoproturon), 1.17% (chlorotoluron), 1.0% (diuron), and 0.73% (fluometuron). The PUH degradation kinetics data during ozonation agreed with the pseudo-first-order model. The rate constant kobs were 0.31×10-3-19.8×10-3s-1. The kobs and removal ratios of PUHs during ozonation partially scaled with the mass, LogKow, and Henry's constants of PUHs. Comparisons of measured NDMA-FPs with calculated NDMA-FPs from residual PUH after oxidation showed that the intermediates produced during ozonation facilitated NDMA-FPs; this contribution was also observed for chlorotoluron and isoproturon during ClO2 oxidation. Examination of reaction mechanisms revealed that tertiary amine ozonation, N-dealkylation, hydroxylation, the cleavage of N-C bonds, ammonification, and nitrification occurred during the ozonation of PUHs, and the dimethylamine (DMA) functional groups could be decomposed directly and transformed into NDMA via the formation of the intermediate unsymmetrical dimethylhydrazine. NDMA is also formed from the reaction between DMA and phenylamino-compounds. Clarifying primary degradation products of PUHs and transformation pathways of NDMA during oxidation processes is useful to optimize treatment processes for water supplies.

Heterogeneous activation of peroxydisulfate by sulfur-doped g-C3N4 under visible-light irradiation: Implications for the degradation of spiramycin and an assessment of N-nitrosodimethylamine formation potential

In this study, peroxydisulfate (PDS) was activated by synthesized sulfur-doped g-C3N4 (SCN) under visible-light irradiation and was adopted to enhance the removal of spiramycin, which is an important precursor of N-nitrosodimethylamine (NDMA). Specifically, 95.4% of spiramycin (≤10 mg/L) was removed in 60 min under the conditions of an initial value of pH of 7.0, an SCN dose of 1.0 g/L, and a PDS dose of 200 mg/L, and its degradation fitted well with the pseudo first-order kinetics. Electron paramagnetic resonance analysis and trapping experiments confirmed that ·O2− and h+ were the main oxidizers for the degradation of spiramycin, and ·SO4− and ·OH also participated in the removal of spiramycin. The removal of spiramycin in the PDS/SCN visible-light catalytic system occurred through three different pathways: aldehyde oxidation, cleavage of C-O bond and demethylation. Notably, 61.4% of NDMA formation potential (FP) was reduced after the reaction. The SCN catalyst was stable and its catalytic performance was excellent in the PDS/SCN system, as the spiramycin removal efficiency decreased only slightly from 95.4% to 87.3% after being reused three times. Therefore, our study not only provides an alternative method for removing spiramycin but can also can significantly reduce NDMA FP.

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.

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.