Compounds with N,N-dimethylhydrazine moieties ((CH 3) 2 N-N-) form N-nitrosodimethylamine (NDMA) ... more Compounds with N,N-dimethylhydrazine moieties ((CH 3) 2 N-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 k O3 at pH 7 was 2 Â 10 6 M À1 s À1 for UDMH and 5 Â 10 5 M À1 s À1 for DMZ. Molar NDMA yields (i.e., D[NDMA]/D [precursor] Â 100) were 84% and 100% for UDMH and DMZ, respectively, determined at molar ozone dose ratio ([O 3 ] 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 k OH at pH 7 was 4.9 Â 10 9 M À1 s À1 and 3.4 Â 10 9 M À1 s À1 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 eN þ-O-O-O À 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 O 3 /H 2 O 2 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.
Full-scale experiments to evaluate N-nitrosodimethylamine (NDMA) formation and attenuation were p... more Full-scale experiments to evaluate N-nitrosodimethylamine (NDMA) formation and attenuation were performed within an advanced indirect potable reuse (IPR) treatment system, which includes, sequentially: chloramination for membrane fouling control, microfiltration (MF), reverse osmosis (RO), ultraviolet irradiation with hydrogen peroxide (UV/H2O2), final chloramination, and pH stabilization. Results of the study demonstrate that while RO does effectively remove the vast majority of NDMA precursors, RO permeate can still contain significant concentrations of NDMA precursors resulting in additional NDMA formation during chloramination. Thus, it is possible for this advanced treatment system to produce water with NDMA levels higher than regional requirements for potable applications (10 ng/L). The presence of H2O2 during UV oxidation reduced NDMA photolysis efficiency and increased NDMA formation (∼22 ng/L) during the secondary chloramination and lime stabilization. This is likely due to formation of UV/H2O2 degradation by-products with higher NDMA formation rate than the parent compounds. However, this effect was diminished with higher UV doses. Bench-scale experiments confirmed an enhanced NDMA formation during chloramination after UV/H2O2 treatment of dimethylformamide, a compound detected in RO permeate and used as model precursor in this study. The effect of pre-ozonation for membrane fouling control on NDMA formation was also evaluated at pilot- (ozone-MF-RO) and bench-scale. Relatively large NDMA formation (117-227 ng/L) occurred through ozone application that was dose dependent, whereas chloramination under typical dosages and contact times of IPR systems resulted in only a relatively small increase of NDMA (∼20 ng/L). Thus, this research shows that NDMA formation within a potable water reuse facility can be challenging and must be carefully evaluated and controlled.
UV-based advanced oxidation processes (AOPs) effectively degrade Nnitrosodimethylamine (NDMA) pas... more UV-based advanced oxidation processes (AOPs) effectively degrade Nnitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the reformation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (~5.5) coupled with the effective rejection of NH 4 + promotes conversion of the residual monochloramine (NH 2 Cl) in the permeate to dichloramine (NHCl 2) via the reaction: 2 NH 2 Cl + H + ↔ NHCl 2 + NH 4 +. Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA reformation by minimizing the amount of dichloramine formed prior to reaching the final target pH. INTRODUCTION Droughts in the United States Southwest and California have increased interest in purified municipal wastewater as a reliable source of potable water. Advanced treatment trains for potable reuse frequently employ Full Advanced Treatment (FAT), a combination of microfiltration (MF), reverse osmosis (RO) and advanced oxidation processes (AOPs; typically the UV/hydrogen peroxide AOP). 1 A recent water reuse risk assessment identified disinfection
Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary ... more Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most N-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation during ozonation of dimethylformamide (DMF), the other model precursor used in this study, occurred only in the presence of ammonia, and it was attributable to the oxidation of DMF by hydroxyl radicals. Filtered wastewater samples (0.7 μm) produced more NDMA than unfiltered samples, suggesting that ozone reacted with dissolved precursors and supporting the hypothesis of polymer degradation. Particularly, the total suspended solids content similarly affected NDMA formation and the UV absorbance decrease during ozonation due to the different ozone demand created in filtered and unfiltered samples.
ABSTRACT To evaluate the potential for minimizing the formation of the disinfection byproduct N-n... more ABSTRACT To evaluate the potential for minimizing the formation of the disinfection byproduct N-nitrosodimethy-lamine (NDMA) by controlling the conditions under which chlorine is added, a pilot-scale study was con-ducted under conditions that simulated a microfiltration system at an advanced wastewater treatment fa-cility. NDMA formation was detected consistently during direct addition of sodium hypochlorite to the ammonia-containing wastewater and when chloramines were formed in a dosing tank by the addition of hypochlorite after ammonium chloride in tap water preadjusted to pH 7.0. No NDMA formation was ob-served when chloramines formed at higher pH or by addition of ammonium chloride prior to sodium hypochlorite. The conditions under which NDMA was formed were accompanied by breakpoint chlori-nation and enhanced formation of dichloramine in the dosing tank. The formation of NDMA appears to be related to the enhanced reactivity of dichloramine with NDMA precursors. Although direct addition of sodium hypochlorite to ammonia-containing wastewater also has the potential to enhance the formation of dichloramine, this effect was counterbalanced by the reaction of hypochlorous acid with organic-ni-trogen containing NDMA precursors, which decreases their reactivity with inorganic chloramines. Al-though this offset may reduce some of the benefits of using preformed chloramines for disinfection, the application of preformed chloramines may still be a useful way to reduce NDMA formation, provided that the chloramines are produced under the appropriate conditions.
Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary ... more Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most <i>N</i>-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation ...
The N-nitrosamines are a group of emerging disinfection byproducts (DBPs) that are considered as ... more The N-nitrosamines are a group of emerging disinfection byproducts (DBPs) that are considered as probable human carcinogens. Of all the nitrosamines, N-Nitrosodimethylamine (NDMA) has been most commonly detected in drinking water and wastewater. Particularly, the presence of NDMA is of concern in locations where wastewater effluents are used for potable reuse. Thus, to investigate treatment processes specifically aimed at removing/transforming nitrosamine precursors is crucial to avoid high formation of these carcinogenic DBPs. In this study, coagulation with ferric chloride of a wastewater effluent destined for potable reuse was investigated to evaluate ozone NDMA precursor removal. Furthermore, the effect of carbon dioxide concentration in the effluent of an indirect potable reuse system in NDMA formation during chloramination was investigated as strategy to control NDMA formation. Results of the study showed that coagulation with ferric chloride is not effective in NDMA precursor removal and that the carbon dioxide concentration in water seems to not affect NDMA formation during chloramination.
A new concept developed for the successful implementation of integrated resource management in ur... more A new concept developed for the successful implementation of integrated resource management in urban and protected areas is the production of ‘designer’ or custom-made recycled water for various reuse purposes. The Edward C. Little Water Recycling Facility in El Segundo, California is an excellent example and the only facility in the world and the United States producing five distinct types of recycled water. This paper presents the plant design, critical milestones, water quality challenges faced and problems solved towards consistently meeting the needs of a diverse client base through delivery of a leading-edge range of custom-made recycled waters.
UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) pa... more UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH4(+) promotes conversion of the residual monochloramine (NH2Cl) in the permeate to dichloramine (NHCl2) via the reaction: 2 NH2Cl + H(+) ↔ NHCl2 + NH4(+). Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.
UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) pa... more UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH4(+) promotes conversion of the residual monochloramine (NH2Cl) in the permeate to dichloramine (NHCl2) via the reaction: 2 NH2Cl + H(+) ↔ NHCl2 + NH4(+). Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.
Abstract: Researchers investigated the use of ultralow-pressure reverse osmosis (ULPRO) and nanof... more Abstract: Researchers investigated the use of ultralow-pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes for water reuse applications where lower operating pressures and a high permeate quality are desired. A laboratory-scale investigation was ...
N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four di... more N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four different wastewater treatment plants destined for alternative reuse. Very high levels of NDMA formation were observed in wastewaters from treatment plants non operating with biological nitrogen removal. Selected experiments showed that hydroxyl radical did not have a significant role in NDMA formation during ozonation of wastewater. Furthermore, ozonation of three different polymers used for water treatment, including polyDADMAC, anionic polyacrylamide, and cationic polyacrylamide, spiked in wastewater did not increase the NDMA formation. Effluent organic matter (EfOM) likely reduced the availability of ozone in water able to react with polymers and quenched the produced ·OH radicals which limited polymer degradation and subsequent NDMA production. Excellent correlations were observed between NDMA formation, UV absorbance at 254 nm, and total fluorescence reduction. These data provide evidence that UV and fluorescence surrogates could be used for monitoring and/or controlling NDMA formation during ozonation.
Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary ... more Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most N-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation during ozonation of...
N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four di... more N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four different wastewater treatment plants destined for alternative reuse. Very high levels of NDMA formation were observed in wastewaters from treatment plants non operating with biological nitrogen removal. Selected experiments showed that hydroxyl radical did not have a significant role in NDMA formation during ozonation of wastewater. Furthermore, ozonation of three different polymers used for water treatment, including polyDADMAC, anionic polyacrylamide, and cationic polyacrylamide, spiked in wastewater did not increase the NDMA formation. Effluent organic matter (EfOM) likely reduced the availability of ozone in water able to react with polymers and quenched the produced ·OH radicals which limited polymer degradation and subsequent NDMA production. Excellent correlations were observed between NDMA formation, UV absorbance at 254 nm, and total fluorescence reduction. These data provide evidence that UV and fluorescence surrogates could be used for monitoring and/or controlling NDMA formation during ozonation.
Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary ... more Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most N-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation during ozonation of...
Full-scale experiments to evaluate N-nitrosodimethylamine (NDMA) formation and attenuation were p... more Full-scale experiments to evaluate N-nitrosodimethylamine (NDMA) formation and attenuation were performed within an advanced indirect potable reuse (IPR) treatment system, which includes, sequentially: chloramination for membrane fouling control, microfiltration (MF), reverse osmosis (RO), ultraviolet irradiation with hydrogen peroxide (UV/H2O2), final chloramination, and pH stabilization. Results of the study demonstrate that while RO does effectively remove the vast majority of NDMA precursors, RO permeate can still contain significant concentrations of NDMA precursors resulting in additional NDMA formation during chloramination. Thus, it is possible for this advanced treatment system to produce water with NDMA levels higher than regional requirements for potable applications (10 ng/L). The presence of H2O2 during UV oxidation reduced NDMA photolysis efficiency and increased NDMA formation (∼22 ng/L) during the secondary chloramination and lime stabilization. This is likely due to...
Abstract: Researchers investigated the use of ultralow-pressure reverse osmosis (ULPRO) and nanof... more Abstract: Researchers investigated the use of ultralow-pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes for water reuse applications where lower operating pressures and a high permeate quality are desired. A laboratory-scale investigation was ...
Compounds with N,N-dimethylhydrazine moieties ((CH 3) 2 N-N-) form N-nitrosodimethylamine (NDMA) ... more Compounds with N,N-dimethylhydrazine moieties ((CH 3) 2 N-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 k O3 at pH 7 was 2 Â 10 6 M À1 s À1 for UDMH and 5 Â 10 5 M À1 s À1 for DMZ. Molar NDMA yields (i.e., D[NDMA]/D [precursor] Â 100) were 84% and 100% for UDMH and DMZ, respectively, determined at molar ozone dose ratio ([O 3 ] 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 k OH at pH 7 was 4.9 Â 10 9 M À1 s À1 and 3.4 Â 10 9 M À1 s À1 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 eN þ-O-O-O À 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 O 3 /H 2 O 2 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.
Full-scale experiments to evaluate N-nitrosodimethylamine (NDMA) formation and attenuation were p... more Full-scale experiments to evaluate N-nitrosodimethylamine (NDMA) formation and attenuation were performed within an advanced indirect potable reuse (IPR) treatment system, which includes, sequentially: chloramination for membrane fouling control, microfiltration (MF), reverse osmosis (RO), ultraviolet irradiation with hydrogen peroxide (UV/H2O2), final chloramination, and pH stabilization. Results of the study demonstrate that while RO does effectively remove the vast majority of NDMA precursors, RO permeate can still contain significant concentrations of NDMA precursors resulting in additional NDMA formation during chloramination. Thus, it is possible for this advanced treatment system to produce water with NDMA levels higher than regional requirements for potable applications (10 ng/L). The presence of H2O2 during UV oxidation reduced NDMA photolysis efficiency and increased NDMA formation (∼22 ng/L) during the secondary chloramination and lime stabilization. This is likely due to formation of UV/H2O2 degradation by-products with higher NDMA formation rate than the parent compounds. However, this effect was diminished with higher UV doses. Bench-scale experiments confirmed an enhanced NDMA formation during chloramination after UV/H2O2 treatment of dimethylformamide, a compound detected in RO permeate and used as model precursor in this study. The effect of pre-ozonation for membrane fouling control on NDMA formation was also evaluated at pilot- (ozone-MF-RO) and bench-scale. Relatively large NDMA formation (117-227 ng/L) occurred through ozone application that was dose dependent, whereas chloramination under typical dosages and contact times of IPR systems resulted in only a relatively small increase of NDMA (∼20 ng/L). Thus, this research shows that NDMA formation within a potable water reuse facility can be challenging and must be carefully evaluated and controlled.
UV-based advanced oxidation processes (AOPs) effectively degrade Nnitrosodimethylamine (NDMA) pas... more UV-based advanced oxidation processes (AOPs) effectively degrade Nnitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the reformation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (~5.5) coupled with the effective rejection of NH 4 + promotes conversion of the residual monochloramine (NH 2 Cl) in the permeate to dichloramine (NHCl 2) via the reaction: 2 NH 2 Cl + H + ↔ NHCl 2 + NH 4 +. Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA reformation by minimizing the amount of dichloramine formed prior to reaching the final target pH. INTRODUCTION Droughts in the United States Southwest and California have increased interest in purified municipal wastewater as a reliable source of potable water. Advanced treatment trains for potable reuse frequently employ Full Advanced Treatment (FAT), a combination of microfiltration (MF), reverse osmosis (RO) and advanced oxidation processes (AOPs; typically the UV/hydrogen peroxide AOP). 1 A recent water reuse risk assessment identified disinfection
Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary ... more Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most N-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation during ozonation of dimethylformamide (DMF), the other model precursor used in this study, occurred only in the presence of ammonia, and it was attributable to the oxidation of DMF by hydroxyl radicals. Filtered wastewater samples (0.7 μm) produced more NDMA than unfiltered samples, suggesting that ozone reacted with dissolved precursors and supporting the hypothesis of polymer degradation. Particularly, the total suspended solids content similarly affected NDMA formation and the UV absorbance decrease during ozonation due to the different ozone demand created in filtered and unfiltered samples.
ABSTRACT To evaluate the potential for minimizing the formation of the disinfection byproduct N-n... more ABSTRACT To evaluate the potential for minimizing the formation of the disinfection byproduct N-nitrosodimethy-lamine (NDMA) by controlling the conditions under which chlorine is added, a pilot-scale study was con-ducted under conditions that simulated a microfiltration system at an advanced wastewater treatment fa-cility. NDMA formation was detected consistently during direct addition of sodium hypochlorite to the ammonia-containing wastewater and when chloramines were formed in a dosing tank by the addition of hypochlorite after ammonium chloride in tap water preadjusted to pH 7.0. No NDMA formation was ob-served when chloramines formed at higher pH or by addition of ammonium chloride prior to sodium hypochlorite. The conditions under which NDMA was formed were accompanied by breakpoint chlori-nation and enhanced formation of dichloramine in the dosing tank. The formation of NDMA appears to be related to the enhanced reactivity of dichloramine with NDMA precursors. Although direct addition of sodium hypochlorite to ammonia-containing wastewater also has the potential to enhance the formation of dichloramine, this effect was counterbalanced by the reaction of hypochlorous acid with organic-ni-trogen containing NDMA precursors, which decreases their reactivity with inorganic chloramines. Al-though this offset may reduce some of the benefits of using preformed chloramines for disinfection, the application of preformed chloramines may still be a useful way to reduce NDMA formation, provided that the chloramines are produced under the appropriate conditions.
Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary ... more Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most <i>N</i>-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation ...
The N-nitrosamines are a group of emerging disinfection byproducts (DBPs) that are considered as ... more The N-nitrosamines are a group of emerging disinfection byproducts (DBPs) that are considered as probable human carcinogens. Of all the nitrosamines, N-Nitrosodimethylamine (NDMA) has been most commonly detected in drinking water and wastewater. Particularly, the presence of NDMA is of concern in locations where wastewater effluents are used for potable reuse. Thus, to investigate treatment processes specifically aimed at removing/transforming nitrosamine precursors is crucial to avoid high formation of these carcinogenic DBPs. In this study, coagulation with ferric chloride of a wastewater effluent destined for potable reuse was investigated to evaluate ozone NDMA precursor removal. Furthermore, the effect of carbon dioxide concentration in the effluent of an indirect potable reuse system in NDMA formation during chloramination was investigated as strategy to control NDMA formation. Results of the study showed that coagulation with ferric chloride is not effective in NDMA precursor removal and that the carbon dioxide concentration in water seems to not affect NDMA formation during chloramination.
A new concept developed for the successful implementation of integrated resource management in ur... more A new concept developed for the successful implementation of integrated resource management in urban and protected areas is the production of ‘designer’ or custom-made recycled water for various reuse purposes. The Edward C. Little Water Recycling Facility in El Segundo, California is an excellent example and the only facility in the world and the United States producing five distinct types of recycled water. This paper presents the plant design, critical milestones, water quality challenges faced and problems solved towards consistently meeting the needs of a diverse client base through delivery of a leading-edge range of custom-made recycled waters.
UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) pa... more UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH4(+) promotes conversion of the residual monochloramine (NH2Cl) in the permeate to dichloramine (NHCl2) via the reaction: 2 NH2Cl + H(+) ↔ NHCl2 + NH4(+). Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.
UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) pa... more UV-based advanced oxidation processes (AOPs) effectively degrade N-nitrosodimethylamine (NDMA) passing through reverse osmosis (RO) units within advanced treatment trains for the potable reuse of municipal wastewater. However, certain utilities have observed the re-formation of NDMA after the AOP from reactions between residual chloramines and NDMA precursors in the AOP product water. Using kinetic modeling and bench-scale RO experiments, we demonstrate that the low pH in the RO permeate (∼5.5) coupled with the effective rejection of NH4(+) promotes conversion of the residual monochloramine (NH2Cl) in the permeate to dichloramine (NHCl2) via the reaction: 2 NH2Cl + H(+) ↔ NHCl2 + NH4(+). Dichloramine is the chloramine species known to react with NDMA precursors to form NDMA. After UV/AOP, utilities generally use lime or other techniques to increase the pH of the finished water to prevent distribution system corrosion. Modeling indicated that, while the increase in pH halts dichloramine formation, it converts amine-based NDMA precursors to their more reactive, neutral forms. With modeling, and experiments at both bench-scale and field-scale, we demonstrate that reducing the time interval between RO treatment and final pH adjustment can significantly reduce NDMA re-formation by minimizing the amount of dichloramine formed prior to reaching the final target pH.
Abstract: Researchers investigated the use of ultralow-pressure reverse osmosis (ULPRO) and nanof... more Abstract: Researchers investigated the use of ultralow-pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes for water reuse applications where lower operating pressures and a high permeate quality are desired. A laboratory-scale investigation was ...
N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four di... more N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four different wastewater treatment plants destined for alternative reuse. Very high levels of NDMA formation were observed in wastewaters from treatment plants non operating with biological nitrogen removal. Selected experiments showed that hydroxyl radical did not have a significant role in NDMA formation during ozonation of wastewater. Furthermore, ozonation of three different polymers used for water treatment, including polyDADMAC, anionic polyacrylamide, and cationic polyacrylamide, spiked in wastewater did not increase the NDMA formation. Effluent organic matter (EfOM) likely reduced the availability of ozone in water able to react with polymers and quenched the produced ·OH radicals which limited polymer degradation and subsequent NDMA production. Excellent correlations were observed between NDMA formation, UV absorbance at 254 nm, and total fluorescence reduction. These data provide evidence that UV and fluorescence surrogates could be used for monitoring and/or controlling NDMA formation during ozonation.
Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary ... more Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most N-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation during ozonation of...
N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four di... more N-Nitrosodimethylamine (NDMA) formation by ozonation was investigated in the effluents of four different wastewater treatment plants destined for alternative reuse. Very high levels of NDMA formation were observed in wastewaters from treatment plants non operating with biological nitrogen removal. Selected experiments showed that hydroxyl radical did not have a significant role in NDMA formation during ozonation of wastewater. Furthermore, ozonation of three different polymers used for water treatment, including polyDADMAC, anionic polyacrylamide, and cationic polyacrylamide, spiked in wastewater did not increase the NDMA formation. Effluent organic matter (EfOM) likely reduced the availability of ozone in water able to react with polymers and quenched the produced ·OH radicals which limited polymer degradation and subsequent NDMA production. Excellent correlations were observed between NDMA formation, UV absorbance at 254 nm, and total fluorescence reduction. These data provide evidence that UV and fluorescence surrogates could be used for monitoring and/or controlling NDMA formation during ozonation.
Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary ... more Ozone doses normalized to the dissolved organic carbon concentration were applied to the primary influent, primary effluent, and secondary effluent of a wastewater treatment plant producing water destined for potable reuse. Results showed the most N-Nitrosodimethylamine (NDMA) production from primary effluent, and the recycle streams entering the primary clarifiers were identified as the main source of NDMA precursors. The degradation of aminomethylated polyacrylamide (Mannich) polymer used for sludge treatment was a significant cause of precursor occurrence. A strong correlation between NDMA formation and ammonia concentration was found suggesting an important role of ammonia oxidation on NDMA production. During ozonation tests in DI water using dimethylamine (DMA) as model precursor, the NDMA yield significantly increased in the presence of ammonia and bromide due to the formation of hydroxylamine and brominated nitrogenous oxidants. In addition, NDMA formation during ozonation of...
Full-scale experiments to evaluate N-nitrosodimethylamine (NDMA) formation and attenuation were p... more Full-scale experiments to evaluate N-nitrosodimethylamine (NDMA) formation and attenuation were performed within an advanced indirect potable reuse (IPR) treatment system, which includes, sequentially: chloramination for membrane fouling control, microfiltration (MF), reverse osmosis (RO), ultraviolet irradiation with hydrogen peroxide (UV/H2O2), final chloramination, and pH stabilization. Results of the study demonstrate that while RO does effectively remove the vast majority of NDMA precursors, RO permeate can still contain significant concentrations of NDMA precursors resulting in additional NDMA formation during chloramination. Thus, it is possible for this advanced treatment system to produce water with NDMA levels higher than regional requirements for potable applications (10 ng/L). The presence of H2O2 during UV oxidation reduced NDMA photolysis efficiency and increased NDMA formation (∼22 ng/L) during the secondary chloramination and lime stabilization. This is likely due to...
Abstract: Researchers investigated the use of ultralow-pressure reverse osmosis (ULPRO) and nanof... more Abstract: Researchers investigated the use of ultralow-pressure reverse osmosis (ULPRO) and nanofiltration (NF) membranes for water reuse applications where lower operating pressures and a high permeate quality are desired. A laboratory-scale investigation was ...
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Papers by Gregg Oelker