N-nitrosodimethylamine Yields Research Articles

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.

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.

Comparison of the formation of N-nitrosodimethylamine (NDMA) from algae organic matter by chlor(am)ination and UV irradiation

Microcystis aeruginosa (M. aeruginosa, blue-green algae) blooms frequently in drinking water reservoirs and subsequently causes the formation of disinfection by-products (DBPs) after disinfection, which may pose a potential health risk. In this study, the formation of N-nitrosodimethylamine (NDMA) was evaluated from algal organic matter (AOM) including extracellular organic matter (EOM) and intracellular organic matter (IOM) during the disinfection process of chlorination, chloramination, or ultraviolet (UV) irradiation. The effects of a variety of factors, including reaction times, disinfectant dosages and pH, on the NDMA formation by three different disinfection methods were investigated. Additionally, this study evaluated the nitrogen sources involved in NDMA formation during chloramination of EOM and IOM using 15N-labeled monochloramine. The results showed that the NDMA formation by three different disinfection methods were ranked in the order of chlorination > UV irradiation ≈ chloramination and the specific yield from EOM was greater than that from IOM regardless of disinfection method. The yields of NDMA firstly increased and then plateaued as time prolonged during the chlorination and chloramination of AOM. Similarly, the NDMA formation from EOM was firstly increased and then remained constant with the increase of the disinfectant dosage, while it was gradually increased for IOM. The solution pH highly influenced the NDMA formation during chlorination and chloramination, while exhibited a little impact under UV irradiation. Moreover, fluorescence excitation-emission (EEM) analysis confirmed that soluble microbial by-product-like (SMPs) in EOM and IOM were the major precursors in algal-derived organic matter that contributed to the NDMA formation. Chloramination of EOM and IOM using isotope 15N-labeled monochloramine indicated that the nitroso group of the formed NDMA originates mainly from EOM and IOM of algal cells.

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.

The characteristic of N-nitrosodimethylamine precursor release from algal organic matter and degradation performance of UV/H2O2/O3 technology

Seasonal cyanobacterial blooms in eutrophic water releases algal organic matter (AOM), which contains large amount of dissolved organic nitrogen (DON) and is difficult to be removed effectively by conventional treatment processes (e.g., coagulation and sand filtration) because of its high hydrophilicity. Moreover, N-nitrosodimethylamine (NDMA) can be generated by the reaction of AOM with disinfectants in the subsequent disinfection process. In this study, the formation of NDMA from different AOM components was explored and the control of algal-derived NDMA precursors by UV/H2O2/O3 was evaluated. The results showed that the hydrophilic and polar components of AOM with the low molecular weight had higher NDMA yields. UV-based advanced oxidation process (AOPs) is effective in degrading NDMA precursors, while the removal rate can be affected greatly by UV doses. The removal rate of NDMA precursors by UV/H2O2/O3 is higher than by UV/H2O2 or UV/O3 which can reach 95% at the UV dose of 400 mJ/cm2. An alkaline environment reduces the oxidation efficiency of UV/H2O2/O3 technology, while an acidic environment is conducive to its function. Inorganic anions such as HCO3−, SO42−, Cl− and NO3− are potential to compete with target algal-derived NDMA precursors for the oxidants reaction and inhibit the degradation/removal of these precursors. The degradation of algal-derived NDMA precursors by UV/H2O2/O3 is mainly accomplished by the oxidation of DON with secondary amide groups, and the main degradation mechanism by UV/H2O2/O3 was through the initial decomposition of macromolecular organic compounds such as biopolymers and humic substances and the further degradation of resulting small molecular components.

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.

The competitive effect of different chlorination disinfection methods and additional inorganic nitrogen on nitrosamine formation from aromatic and heterocyclic amine-containing pharmaceuticals

Amine-containing pharmaceuticals formed nitrosamines that are nitrogenous disinfection byproducts of public concerns due to their carcinogenicity. The objective of this study was to investigate the co-effect of additional inorganic nitrogen in different forms (ammonium, nitrite, and nitrate) and different disinfection approaches (chlorination, monochloramination, dichloramination, and two-step chlorination) on eight nitrosamine formation from four widely used pharmaceuticals. N-nitrosodimethylamine (NDMA) was the main species formed. The presence of N-nitrosomethylethylamine (NMEA), nitrosomorpholine (NMor), and N-nitrosopiperidine (NPip) was found in certain experiments. For one-step chlorination, the influential factors, in decreasing order of importance, were the molecular structural characteristics of the pharmaceutical, oxidation method, and presence and form of additional nitrogen. In four pharmaceuticals with comparative structures, the availability of amine intermediates during degradation was the key to higher nitrosamine yields. Monochloramine significantly enhanced nitrosamine formation from four pharmaceuticals. NDMA formation by adding hypochlorous acid and ammonium separately were lower than those during monochloramination. During two-step chlorination, NDMA formation was enhanced at certain pre-chlorine doses (e.g., a Cl/N molar ratio of 20 or 4). The pre-chlorine dose changed the Cl/N ratio. As the ratio was increased, the combined chlorine residual was formed and decreased. When the ratio was high, breakpoint chlorination possibly occurred enhancing NDMA formation. While NDMA formation was successfully inhibited by two-step chlorination, ammonium brought the NDMA yields of these pharmaceuticals back to the range observed in chloramination, suggesting the importance of ammonium control for limiting NDMA formation from pharmaceuticals during two-step chlorination.

Role of reactive nitrogen species in ranitidine degradation in UV/chloramine process: Transformation pathways and NDMA formation

Chloramine under UV photolysis could not only produce the widely known hydroxyl radical (HO•) and reactive chlorine species (RCS; e.g., ClO•, Cl2•− and Cl•), but also produce reactive nitrogen species (RNS; e.g., •NH2, •NO and •NO2). In this study, the kinetic mechanisms, degradation products, N-Nitrosodimethylamine (NDMA) formation of RAN in the UV/chloramine process were investigated. The RAN degradation by UV/chloramine process well fitted the pseudo-first order kinetic model and exhibited a synergistic improvement compared with UV photolysis and chloramination alone. HO• is the predominant radical that contributes to RAN degradation in the range of solution pH from 6.0 to 8.0 (from 43.4% to 56.3%), and RNS was confirmed to contribute to RAN degradation through experiments. As the concentrations of HCO3−, Cl− and NO3− (0 ~ 4 mM), chloramine dosage (200 ~ 300 μM), solution pH (6.0 ~ 8.0) and natural organic matter (0 ~ 4 mg-C L-1) increased, the RAN degradation in UV/chloramine process was inhibited. Besides, the second-order rate constant between CO3•- and RAN was determined to be 8.05 × 106 M−1 s−1 in this study. A possible pathway and reaction schemes of RAN degradation by UV/chloramine process were proposed, which could also be used to explain the role of RNS in the NDMA formation. During the treatment of RAN by chloramination alone and UV/chloramine, NDMA has a better formation potential at both pH = 7.0 and pH = 8.0. Although RNS were responsible for NDMA formation during the RAN degradation by UV/chloramine process, UV photolysis and extending the photolysis time from 5 to 10 min could degrade NDMA and its precursors. Overall, the high yield and toxicity of NDMA should be concerned when choosing the UV/chloramine process.

Investigation on the compositions of unsymmetrical dimethylhydrazine treatment with different oxidants using solid-phase micro-extraction-gas chromatography-mass spectrometer.

The majority of unsymmetrical dimethylhydrazine (UDMH) treatments produce lots of toxic by-products, among which N-Nitrosodimethylamine (NDMA) is a strong carcinogen. The compositions of the by-products are important for evaluating the treatment efficiency and understanding the UDMH degradation mechanism to achieve UDMH mineralization. The intermediate and end products of UDMH treatment with different oxidants were investigated by using a simple and fast method, solid-phase micro-extraction (SPME) in combination with gas chromatography–mass spectrometry (GC-MS). The effects of several parameters (coating fibre, salt addition, pH, sampling time and desorption time) were studied to optimize analyte recovery. The best response can be attained by the 65 µm PDMS/DVB fibre at pH 7 during 10 min after desorption of 1 min in the GC inlet. The intermediate and final oxidative products of UDMH wastewater treatment with different oxidants (O3, Mn2+/O3, Fe2+/H2O2) were investigated. The results showed that the UDMH treatment with O3 could lead to high yields of NDMA. Metal catalytic ozonation could largely minimize the formation of NDMA. No NDMA was observed in the final decontaminated samples after treatment with Fe2+/H2O2. The NDMA formation and degradation mechanism were discussed based on the intermediates. This study is expected to provide useful information for controlling NDMA formation during UDMH wastewater treatment.

Formation Characteristics of N-Nitrosodimethylamine during Chloramines of PolyDADMAC

Interactions of chloramine with organic nitrogen compounds during purification of water for drinking may generate carcinogenic N-nitrosodime-thylamine (NDMA) as byproduct, and it has been found that cationic amine-based water treatment polymers may be one of the important precursors of NDMA. We have analyzed experimentally the influence rule of NDMA formation during chlorination and disinfection, in order to provide technical support for reducing or even avoiding the formation of NDMA. The formation characteristics of nitrosamines during the chlorination of poly-diallyldimethylammonium chloride (polyDADMAC) have been studied during our experiments. The results show that the type of chlorinating agent is crucial for the generation of NDMA; if pH = 7, NDMA has the great potential formation; the NDMA potential formation increases with temperature. The yield of NDMA will be higher as the concentration of monochloramine is 1.5 to 2.5 times of the precursor; the variation of polymer with reaction time can explain the concentration of NDMA in terminal water of pipe network is higher than that in drinking water.

NDMA formation from 4,4'-hexamethylenebis (HDMS) during ozonation: influencing factors and mechanisms.

N-nitrosodimethylamine (NDMA), a toxic disinfection byproduct commonly associated with chloramination, has recently been found to form from an anti-yellowing agent (4,4'-hexamethylenebis (1,1-dimethylsemicarbazide) (HDMS)) during ozonation but the mechanisms are unclear. In this paper, the potential roles of molecular ozone (O3) and hydroxyl radical (∙OH) on NDMA formation from HDMS were investigated under various oxidation conditions (ozone dosages, pH) and different components in water (bromide ion (Br-), bicarbonate ion (HCO3-), sulfate ion (SO42-), and humic acid (HA), as well as natural organic matter (NOM) from a lake). Moreover, HDMS transformation pathways by ozonation were determined. The results indicated that the formation of NDMA was enhanced through the combined effect of O3 and ∙OH compared to that by O3 alone (addition of tert-butyl alcohol (tBA) as ∙OH scavenger). ∙OH itself cannot generate NDMA directly; however, it can transform HDMS to intermediates with higher NDMA yield than parent compound. The NDMA generation was affected (small dosages promoted but high dosages inhibited) by HA or Br- no matter with or without tBA. The presence of SO42- and HCO3- ions lowered NDMA formation through ∙OH scavenging effect. Increasing pH not only increased degradation rate constant by enhancing ∙OH generation but also affected HDMS dissociation ratio, reaching the maximum NDMA formation at pH 7-8. Natural constituents in selected water matrix inhibited NDMA formation. Impacts of these influencing factors on NDMA formation by only O3 however were significantly less pronounced over that by the joint roles of O3 and ∙OH. Based on the result of Q-TOF, LC/MS/MS, and GC/MS, the possible transformation pathways of HDMS by ozonation were proposed. The NDMA enhancement mechanism by the combined effect of O3 and ∙OH can be attributed to greater amounts of intermediates with higher NDMA yield (such as unsymmetrical dimethylhydrazine (UDMH)) produced. These findings provide new understanding of NDMA formation upon ozonation of typical amine-based compounds.

Reaction patterns of NDMA precursors during the sequential chlorination process of short-term free chlorination and monochloramination

Abstract The sequential chlorination process of short-term free chlorination and monochloramination was designed to achieve the simultaneously control of pathogen, trihalomethanes and haloacetic acids. Its efficiency for N-nitrosodimethylamine (NDMA) control was tested with four model NDMA precursors, i.e. dimethylamine (DMA), chlordimeform, chlortoluron and pirimicarb as well as real water sample. The results showed that DMA or chlordimeform formed much less NDMA during the sequential chlorination process than during monochloramination. However, chlortoluron or pirimicarb formed more NDMA during the sequential chlorination process than during monochloramination. Seven sub-patterns were concluded for the reactions of NDMA precursors during the sequential chlorination process and some of them would lead to the decrease of NDMA. The mechanism of NDMA control during the sequential chlorination process was attributed to the quick oxidation of NDMA precursors by free chlorine, which products presented less or no yield of NDMA during the following monochloramination.

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.

Nitrite ion mitigates the formation of N-nitrosodimethylamine (NDMA) during chloramination of ranitidine

Ranitidine (RNT) has been an important tertiary amine precursor of N-nitrosodimethylamine (NDMA) in chlorine-based water treatment, due to reaction with monochloramine (NH2Cl) with exceptionally high molar yields up to 90%. This study examined the effects of nitrite ions (NO2−) on the kinetics of NDMA formation during the chloramination of RNT under variable concentrations of dissolved oxygen (DO, 0.7–7.5mg/L), RNT (5–30μM), NH2Cl (5–20mM), NO2− or NO3− (0–2mM) and pH (5.6–8.6). In the absence of the NO2−, the ultimate molar yield of NDMA after 6h of reaction was primarily influenced by [DO] and pH, while marginally affected by initial [RNT] and [NH2Cl]. A kinetic model, prepared in accordance with the reaction sequence of NDMA formation, suggested that the rate determining step was accelerated with increasing [NH2Cl]0, [DO], and pH. A Kinetic study together with ultra-performance liquid chromatography-quadrupole-time of flight mass spectrometer (UPLC-Q-TOF MS) and gas chromatography (GC)/TOF MS analyses in parallel demonstrated that the nitrite ion inhibited the nucleophilic substitution of the terminal amine on NH2Cl, and reduced the pseudo-steady state concentration of N-peroxyl radicals, significantly decreasing the ultimate yields of NDMA.

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 (0.5mg/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 pH8 with 0.5mg/L O3 but decreased with the increasing pH with 1mg/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.

Characterization and C-, N-disinfection byproduct formation of dissolved organic matter in MBR and anaerobic-anoxic-oxic (AAO) processes

This study investigated distinguishing characteristic of dissolved organic matter (DOM) in MBR and AAO effluents by UF fractionation, XAD-8 resin adsorption isolation, excitation and emission matrix fluorescence spectroscopy and fourier transform infrared spectroscopy analysis. Halogenated carbonaceous and nitrogenous disinfection byproducts (DBPs) especially N-nitrosodimethylamine (NDMA) formation reactivity of various DOM fractions were also analyzed. Results showed that although the MBR effluent contained lower DOM than the AAO effluent, more halogenated C, N-DBPs in the MBR effluent were formed than in the AAO effluent after chlorination due to its higher percentage of molecular weight (MW)>1kDa materials, fulvic acid-like substances and polysaccharides. For example, the content of TCM in MBR effluent was high as 526μg/mg-C, which was about 13 times as that in AAO effluent. In contrast, the NDMA yield of AAO effluent was more than that of MBR effluent because AAO contained higher percentage of MW<1kDa materials, aromatic proteins, polypeptides and amino acids especially secondary amines.

Formation of N-Nitrosodimethylamine during Chloramination of Secondary and Tertiary Amines: Role of Molecular Oxygen and Radical Intermediates.

N-Nitrosodimethylamine (NDMA) is a carcinogenic disinfection byproduct from water chloramination. Despite the identification of numerous NDMA precursors, essential parts of the reaction mechanism such as the incorporation of molecular O2 are poorly understood. In laboratory model systems for the chloramination of secondary and tertiary amines, we investigated the kinetics of precursor disappearance and NDMA formation, quantified the stoichiometries of monochloramine (NH2Cl) and aqueous O2 consumption, derived 18O-kinetic isotope effects (18O-KIE) for the reactions of aqueous O2, and studied the impact of radical scavengers on NDMA formation. Although the molar NDMA yields from five N,N-dimethylamine-containing precursors varied between 1.4% and 90%, we observed the stoichiometric removal of one O2 per N,N-dimethylamine group of the precursor indicating that the oxygenation of N atoms did not determine the molar NDMA yield. Small 18O-KIEs between 1.0026 ± 0.0003 and 1.0092 ± 0.0009 found for all precursors as well as completely inhibited NDMA formation in the presence of radical scavengers (ABTS and trolox) imply that O2 reacted with radical species. Our study suggests that aminyl radicals from the oxidation of organic amines by NH2Cl and N-peroxyl radicals from the reaction of aminyl radicals with aqueous O2 are part of the NDMA formation mechanism.

Comparison of N-nitrosodimethylamine formation mechanisms from dimethylamine during chloramination and ozonation: A computational study

N-nitrosodimethylamine (NDMA) as a disinfection by-product has recently become the focus of considerable research interest due to its unusually high carcinogenicity. In this study, the formation mechanisms of NDMA from dimethylamine (DMA) during chloramination and ozonation were investigated by using the quantum chemical G4 method. The reactivity of haloamines and hydroxylamine reacting with DMA was found in the order: NHCl2∼NHBrCl (Brˉleaving)>NHBr2>NH2Cl∼NH2Br>>NH2OH. This offers a theoretical support for the experimentally proposed mechanism that dimethylamine reacts with NHCl2 rather than NH2Cl to form chlorinated unsymmetrical dimethylhydrazine intermediate and the existence of bromochloramine in the presence of bromide during chloramination, and explains the observation that NDMA yield during ozonation is much lower than that during chloramination. Importantly, an N,N-dimethylaminonitrene was found to be a significant intermediate to form NDMA in oxidation reactions by molecular oxygen and ozone. Additionally, results suggest that the amines containing the second nitrogen source directly connecting or close to the N-(CH3)2 moiety are potential significant NDMA precursors upon ozonation. The findings of this study are helpful for expanding the knowledge of NDMA formation mechanism, and predicting potential NDMA precursors during disinfection.

N-nitrosodimethylamine (NDMA) formation during ozonation of N,N-dimethylhydrazine compounds: Reaction kinetics, mechanisms, and implications for NDMA formation control

Compounds with N,N-dimethylhydrazine moieties ((CH3)2N-N-) form N-nitrosodimethylamine (NDMA) during ozonation, but the relevant reaction chemistry is hitherto poorly understood. This study investigated the reaction kinetics and mechanisms of NDMA formation during ozonation of unsymmetrical dimethylhydrazine (UDMH) and daminozide (DMZ) as structural model N,N-dimethylhydrazine compounds. The reaction of ozone with these NDMA precursor compounds was fast, and kO3 at pH 7 was 2 × 106 M−1 s−1 for UDMH and 5 × 105 M−1 s−1 for DMZ. Molar NDMA yields (i.e., Δ[NDMA]/Δ[precursor] × 100) were 84% and 100% for UDMH and DMZ, respectively, determined at molar ozone dose ratio ([O3]0/[precursor]0) of ≥4 in the presence of tert-butanol as hydroxyl radical (OH) scavenger. The molar NDMA yields decreased significantly in the absence of tert-butanol, indicating OH formation and its subsequent reaction with the parent precursors forming negligible NDMA. The kOH at pH 7 was 4.9 × 109 M−1 s−1 and 3.4 × 109 M−1 s−1 for UDMH and DMZ, respectively. Reaction mechanisms are proposed in which an ozone adduct is formed at the nitrogen next to N,N-dimethylamine which decomposes via homolytic and heterolytic cleavages of the –N+-O-O-O− bond, forming NDMA as a final product. The heterolytic cleavage pathway explains the significant OH formation via radical intermediates. Overall, significant NDMA formation was found to be unavoidable during ozonation or even O3/H2O2 treatment of waters containing N,N-dimethylhydrazine compounds due to their rapid reaction with ozone forming NDMA with high yield. Thus, source control or pre-treatment of N,N-dimethylhydrazine precursors and post-treatment of NDMA are proposed as the mitigation options.

Concentration, composition, bioavailability, and N-nitrosodimethylamine formation potential of particulate and dissolved organic nitrogen in wastewater effluents: A comparative study

Wastewater-derived organic nitrogen (org-N) can act as both nutrients and carcinogenic nitrogenous disinfection byproduct precursors. In this study, the concentration, composition, bioavailability, and N-nitrosodimethylamine (NDMA) formation potential of particulate organic nitrogen (PON) from three different municipal wastewater treatment plants were characterized and compared with that of effluent dissolved organic nitrogen (DON). The average effluent PON and DON concentrations ranged from 0.09 to 0.55mgN/L and from 0.91 to 1.88mgN/L, respectively. According to principal component analysis, org-N composition and characterization differed in PON and DON samples (n=20). Compared with DON, PON tended to be enriched in protein and nucleic acids, and showed a more proteinaceous character. Composition of org-N functional groups estimated from the X-ray photoelectron spectroscopy N 1s spectra indicate no significant differences in the molecular weight distribution of the protein-like materials between PON and DON. Moreover, PON exhibited a significantly higher bioavailability (61.0±13.3%) compared to DON (38.5±12.4%, p˂0.05, t-test) and a significantly higher NDMA yields (791.4±404.0ng/mg-N) compared to DON (374.8±62.5ng/mg-N, p˂0.05, t-test). Accordingly, PON contributed to approximately 12.3–41.7% of the total bioavailable org-N and 22.0–38.4% of the total NDMA precursors in wastewater effluents. Thus, the potential adverse effects of PON on wastewater discharge and reuse applications should not be overlooked, even though it only accounted for 7.4–26.8% of the total effluent org-N.