Rejection Of N-nitrosamines Research Articles

Maximizing N-Nitrosamine Rejection via RO Membrane Plugging with Hexylamine and Hexamethylenediamine.

The rapid expansion of urban areas and the increasing demand for water resources necessitate substantial investments in technologies that enable the reuse of municipal wastewater for various purposes. Nonetheless, numerous challenges remain, particularly regarding disinfection by-products (DBPs), especially carcinogenic compounds such as N-nitrosamines (NTRs). To tackle the ongoing issues associated with reverse osmosis (RO) membranes, this study investigated the rejection of NTRs across a range of commercially available RO membranes. In addition, the research aimed to improve rejection rates by integrating molecular plugs into the nanopores of the polyamide (PA) layer. Hexylamine (HEX) and hexamethylenediamine (HDMA), both linear chain amines, have proven to be effective as molecular plugs for enhancing the removal of NTRs. Given the environmental and human health concerns associated with linear amines, the study also aimed to assess the feasibility of diamine molecules as potential alternatives. The application of molecular plugs led to changes in pore size distribution (PSD) and effective pore number, resulting in a decrease in membrane permeability (from 5 to 33%), while maintaining levels suitable for RO processes. HEX and HDMA exhibited a positive effect on NTR rejection with ACM1, ACM5 and BW30LE membranes. In particular, NDMA rejection, the smallest molecule of the tested NTRs, with ACM1 was improved by 65.5% and 70.6% after treatment with HEX and HDMA, respectively.

Impact of Polymer Chain Rearrangements in the PA Structure of RO Membranes on Water Permeability and N-Nitrosamine Rejection.

The use of solvents is overall recognized as an efficient method to improve the water permeability of polyamide thin film composite membranes (PA-TFC). The objective of this work was to test the performance of the membranes after exposing them to n-propanol (n-PrOH) to improve the permeability of the membranes while maintaining the rejection factor for small uncharged organic molecules, namely N-nitrosamines (NTRs). After the membranes were exposed to n-PrOH, the water permeability of the UTC73AC membrane increased by 98%, with minimal change in rejection. N-nitrosodiethylamine (NDEA) rejection decreased (3.4%), while N-nitrosodi-n-propylamine (NDPA) and N-nitrosodi-n-butylamine (NDBA) rejection increased by 0.9% and 2.8%, respectively. In contrast, for the BW30LE membrane, water permeability decreased (by 38.7%), while rejection factors increased by 14.5% for NDEA, 6.2% for NDPA, and 15.0% for NDBA. In addition, the morphology of the membrane surface before and after exposure to n-PrOH was analyzed. This result and the pore size distribution (PSD) curves obtained indicate that the rearrangement of polymer chains affects the network or aggregate pores in the PA layer, implying that a change in pore size or a change in pore size distribution could improve the permeability of water molecules, while the rejection factor for NTRs is not significantly affected.

Role of membrane fouling substances on the rejection of N-nitrosamines by reverse osmosis

The impact of fouling substances on the rejection of four N-nitrosamines by a reverse osmosis (RO) membrane was evaluated by characterizing individual organic fractions in a secondary wastewater effluent and deploying a novel high-performance liquid chromatography-photochemical reaction-chemiluminescence (HPLC-PR-CL) analytical technique. The HPLC-PR-CL analytical technique allowed for a systematic examination of the correlation between the fouling level and the permeation of N-nitrosamines in the secondary wastewater effluent and synthetic wastewaters through an RO membrane. Membrane fouling caused by the secondary wastewater effluent led to a notable decrease in the permeation of N-nitrosodimethylamine (NDMA) while a smaller but nevertheless discernible decrease in the permeation of N-nitrosomethylethylamine (NMEA), N-nitrosopyrrolidine (NPYR) and N-nitrosomorpholine (NMOR) was also observed. Fluorescence spectrometry analysis revealed that major foulants in the secondary wastewater effluent were humic and fulvic acid-like substances. Analysis using the size exclusion chromatography technique also identified polysaccharides and proteins as additional fouling substances. Thus, further examination was conducted using solutions containing model foulants (i.e., sodium alginate, bovine serum albumin, humic acid and two fulvic acids). Similar to the secondary wastewater effluent, membrane fouling with fulvic acid solutions resulted in a decrease in N-nitrosamine permeation. In contrast, membrane fouling with the other model foulants resulted in a negligible impact on N-nitrosamine permeation. Overall, these results suggest that the impact of fouling on the permeation of N-nitrosamines by RO is governed by specific small organic fractions (e.g. fulvic acid-like organics) in the secondary wastewater effluent.

Rejection of trace organic chemicals by a hollow fibre cellulose triacetate reverse osmosis membrane

The rejection behaviours of 41 trace organic chemicals (TrOCs) by a hollow fibre cellulose triacetate (CTA) reverse osmosis (RO) membrane for potable water reuse were evaluated. Results reported here suggest that the rejection behaviours of TrOCs by the CTA RO membrane are mostly similar to those previously reported for the polyamide (PA) RO membrane. However, in comparison to the PA based RO membrane, hydrophobic interaction plays a greater role while electrostatic interaction is less significant in governing the rejection of TrOCs by the CTA RO membrane. No difference in rejection between positively and negatively charged compounds by the CTA RO membrane could be observed. The rejection of neutral TrOCs by the CTA RO membrane varied significantly from 25% to over 95%. Molecular size (i.e. minimum projection area) was found to be an important factor governing the rejection of neutral TrOCs. Further investigation using N-nitrosamines reveals that in addition to molecular size, hydrophobicity could significantly influence their rejection by the CTA RO membrane, while N-nitrosamine rejection by the PA RO membrane was mostly governed by molecular size. In contrast to the neutral TrOCs, most charged TrOCs selected in this investigation exhibited over 90% rejection, regardless of molecular size.

Modelling the rejection of N-nitrosamines by a spiral-wound reverse osmosis system: Mathematical model development and validation

A mathematical model was developed based on the irreversible thermodynamic principle and hydrodynamic calculation to predict the rejection of N-nitrosamines by spiral-wound reverse osmosis (RO) membrane systems. The developed model is able to accurately describe the rejection of N-nitrosamines under a range of permeate flux and system recovery conditions. The modelled N-nitrosamine rejections were in good agreement with values obtained experimentally using a pilot-scale RO filtration system. Simulation from the model revealed that an increase in permeate flux from 10 to 30L/m2h led to an increase in the rejection of low molecular weight N-nitrosamines such as N-nitrosodimethylamine (NDMA) (from 31% to 54%), which was validated by experimental results. The modelling results also revealed that an increase in recovery caused a decrease in the rejection of these N-nitrosamines, which is consistent with the experimental results. Further modelling investigations suggested that NDMA rejection by a spiral-wound system can drop from 49% to 35% when the overall recovery increased from 10% to 50%. The model developed from this study can be a useful tool for water utilities and regulators for system design and evaluating the removal of N-nitrosamine by RO membranes.

N-nitrosamine rejection by reverse osmosis: Effects of membrane exposure to chemical cleaning reagents

The impact of chemical cleaning on the removal of N-nitrosamines by low pressure reverse osmosis (RO) membranes was investigated. The results show that caustic chemical cleaning resulted in an increase in membrane permeability but caused a notable decrease in the rejection of N-nitrosamines. The impact of caustic chemical cleaning was particularly obvious for N-nitrosodimethylamine (NDMA) and N-nitrosomethylethylamine (NMEA), which have the lowest molecular weight amongst the N-nitrosamines investigated in this study. A correlation between the increase in permeability and the decrease in the rejection of either NDMA or NMEA could be observed. The rejection of conductivity also decreased as the membrane permeability increased, indicating that conductivity rejection can be an indicative parameter of predicting changes in NDMA and NMEA rejection during RO plant operation. The impact of caustic cleaning was not permanent and could be significantly reduced by a subsequent acidic cleaning step.

N-nitrosamine rejection by reverse osmosis membranes: A full-scale study

This study aims to provide longitudinal and spatial insights to the rejection of N-nitrosamines by reverse osmosis (RO) membranes during sampling campaigns at three full-scale water recycling plants. Samples were collected at all individual filtration stages as well as at a cool and a warm weather period to elucidate the impact of recovery and feed temperature on the rejection of N-nitrosamines. N-nitrosodimethylamine (NDMA) was detected in all RO feed samples varying between 7 and 32 ng/L. Concentrations of most other N-nitrosamines in the feed solutions were determined to be lower than their detection limits (3–5 ng/L) but higher concentrations were detected in the feed after each filtration stage. As a notable exception, in one plant, N-nitrosomorpholine (NMOR) was observed at high concentrations in RO feed (177–475 ng/L) and permeate (34–76 ng/L). Overall rejection of NDMA among the three RO systems varied widely from 4 to 47%. Data presented here suggest that the feed temperature can influence rejection of NDMA. A considerable variation in NDMA rejection across the three RO stages (14–78%) was also observed. Overall NMOR rejections were consistently high ranging from 81 to 84%. On the other hand, overall rejection of N-nitrosodiethylamine (NDEA) varied from negligible to 53%, which was considerably lower than values reported in previous laboratory-scale studies. A comparison between results reported here and the literature indicates that there can be some discrepancy in N-nitrosamine rejection data between laboratory- and full-scale studies probably due to differences in water recoveries and operating conditions (e.g. temperature, membrane fouling, and hydraulic conditions).

N-nitrosamine rejection by nanofiltration and reverse osmosis membranes: The importance of membrane characteristics

The influence of membrane characteristics on the rejection of eight N-nitrosamines was investigated using one nanofiltration (NF), one seawater reverse osmosis (SWRO) and six low pressure reverse osmosis (LPRO) membranes. The rejection of the two lowest molecular weight N-nitrosamines, namely N-nitrosodimethylamine (NDMA) and N-nitrosomethylethylamine (NMEA), varied in the range from 8–82% to 23–94%, respectively. In general, the rejection of NDMA and NMEA increased with decreasing membrane permeability. The impact of membrane characteristics became less important for higher molecular weight N-nitrosamines. Among the four LPRO membranes (i.e. ESPA2, LFC3, TFC-HR and 70LW) that are commonly used for water reclamation applications, similar rejections were obtained for NDMA (37–52%) and NMEA (69–82%). In addition, rejection values of NDMA and NMEA among two LPRO membranes (i.e. ESPA2 and 70LW) were almost identical when compared under variable permeate flux and feed temperature conditions. However, it is noteworthy that the ESPAB membrane could achieve very high rejection of NDMA (as high as 71%) despite having a similar permeability to the LPRO membranes. Results reported here suggest that membrane characteristics associated with permeability such as the pore size and thickness of the active skin layer can be a key factor determining N-nitrosamine rejection.

Effects of membrane fouling on N-nitrosamine rejection by nanofiltration and reverse osmosis membranes

The impact of fouling on N-nitrosamine rejection by nanofiltration (NF) and reverse osmosis (RO) membranes was investigated in this study. Membrane fouling was simulated using tertiary treated effluent and several model fouling solutions (that contained sodium alginate, bovine serum albumin, humic acid or colloidal silica) to elucidate the changes in rejection behaviour of N-nitrosamines. In general, the rejection of N-nitrosamines increased when the membranes were fouled by tertiary effluent. The rejection of small molecular weight N-nitrosamines was most affected by membrane fouling. In particular, the rejection of N-nitrosodimethylamine (NDMA) by the ESPA2 membrane increased from 34% to 73% after membrane fouling caused by tertiary effluent. The results also indicate that the impact was less apparent for the lowest permeability membrane (i.e., ESPAB), and the rejection of N-nitrosamines by the ESPAB membrane was over 82% regardless of membrane fouling. The effect of membrane fouling caused by model foulants on N-nitrosamine rejection was considerably less than that caused by tertiary effluent. Size exclusion chromatography analyses revealed that the tertiary effluent contains a high fraction of low molecular weight (<500g/mol) organic substances. It appears that these low molecular weight foulants present in the tertiary effluent can restrict the solute pathway within the active skin layer of membranes, resulting in the observed increase of solute rejection.

Effects of feed solution characteristics on the rejection of N-nitrosamines by reverse osmosis membranes

Abstract The rejection of eight N-nitrosamines was investigated in this laboratory-scale study, focusing on the influence of feed solution characteristics on their separation by low pressure reverse osmosis membranes. The rejection mechanisms of N-nitrosamines were first examined using one nanofiltration (NF90) and two reverse osmosis (TFC-HR and SWC5) membranes. The TFC-HR membrane was used to investigate the effects of feed solution characteristics. The rejection of a particular N-nitrosamine was generally membrane dependent and increased in the order of NF (NF90), low pressure RO (TFC-HR) and seawater RO (SWC5) membranes. In general, the rejection of N-nitrosamines by a given membrane also increased in the order of increasing molecular weight. These results suggested that steric hindrance was a dominating rejection mechanism of N-nitrosamines. Nevertheless, it was also observed from the result of N-nitrosomorpholine (NMOR) that the rejection of N-nitrosamines may also depend on other physicochemical properties such as hydrophobicity. A decrease in the feed solution pH (from 9 to 3) resulted in a decrease in the rejection of the two smallest molecular weight N-nitrosamines, namely N-nitrosodimethylamine (NDMA) and N-nitrosomethylethylamine (NMEA). Changes in the feed solution ionic strength (from 26 to 260 mM) caused a discernible decrease only in NDMA rejection, while no apparent impact on rejection was observed for an increase in the feed concentration. On the other hand, it is striking that an increase in the feed temperature led to a significant decrease in the rejection of all N-nitrosamines and the impact was more pronounced for the small molecular weight N-nitrosamines. For example, a significant drop in NDMA rejection (from 49 to 25%) was observed as the feed temperature increased from 20 to 30 °C. The results also indicate that pH, ionic strength, and temperature of the feed solution can exert some influence on the rejection of NDMA and in some cases other N-nitrosamines. The combined effects of these feed solution characteristics, particularly feed temperature, may account for some of the variation of NDMA rejection by RO membranes previously reported in the literature.

Effects of Feed Solution Characteristics and Membrane Fouling on N-Nitrosamine Rejection by Reverse Osmosis Membranes

Augmentation of potable water sources with reclaimed municipal wastewater is an option of increasing importance for water security in regions and countries where severe water stress occurs. Consequently, the presence of emerging trace contaminants in reclaimed water has been recognised as a critical issue due to their potential adverse health effects. Notable examples of these trace organic chemicals include Nnitrosodimethylamine (NDMA) and several other N-nitrosamines.