Modeling NDMA Formation Kinetics During Chloramination of Model Compounds and Surface Waters Impacted by Wastewater Discharges

Abstract

Telephone: 1-480-965-2885.N-nitrosodimethylamine (NDMA) is a chloramination disinfection by-product (DBP). Despite extensive research on NDMA occurrence and evaluation of formation potential from select precursors and in different matrices, less information exists on the kinetics of NDMA formation. A kinetic model is developed and parameterizered using the limited amount of previously published kinetic data involving addition of model compounds to pH buffered ultrapure water and/or surface waters containing organic matter. A simple second-order kinetic model was developed using a NDMA precursor concentration, based upon a measured maximum NDMA concentration as the initial precursor concentration, and measured monochloramine concentrations. The second order model was able to fit NDMA formation kinetics well by determining the best-fit apparent rate constant (k app ), suggesting the model represents a common rate limiting step and/or an intermediate product. An associated reaction may exist during the transformation of a wide variety of precursors into NDMA. Values for k app ranged by approximately one-order of magnitude and were lower in the presence of

Methadone Contributes to N-Nitrosodimethylamine Formation in Surface Waters and Wastewaters during Chloramination

“…At a dose and contact time commonly used in NDMA FP studies (18 mg of Cl 2 /L for 72 h), methadone had a molar yield of 60%. At this monochloramine dose, NDMA formation from methadone was moderately slow (Figure 2; k app = 0.035 M −1 s −1 modeled using previously published methods 47,48 ) and within the range of previously observed rates for NDMA formation in a wastewater-impacted surface water. 47,48 As the monochloramine contact time increased from 0 to 72 h, NDMA formation from methadone increased but did not plateau at longer contact times, meaning that our estimate of a 60% yield at 72 h is potentially a conservative estimate with longer contact times.…”

“…In addition to the yield under FP conditions, we investigated whether monochloramine dose would impact the total NDMA formed. In Figure , we show that an increasing monochloramine dose increased the NDMA yield of methadone (from 23 to 70% at doses of 1 to 150 mg of Cl 2 /L), a phenomenon that has been similarly observed in other natural and engineered (wastewater) water sources recently by our team. , …”

“…In Figure 2, we show that an increasing monochloramine dose increased the NDMA yield of methadone (from 23 to 70% at doses of 1 to 150 mg of Cl 2 /L), a phenomenon that has been similarly observed in other natural and engineered (wastewater) water sources recently by our team. 47,48 Methadone is one of only six compounds known to have a molar yield of NDMA in excess of 50% under 72 h formation potential conditions; the five others are ranitidine, 11 dimethylisopropylamine, 8 5-[(dimethylamino)methyl]furan-2-methanol, 9 dimethylbenzylamine, 8,10,49 and N,N-dimethyl-1-(2thienyl)methanamine. 8 The other five compounds have not been detected or have not been sought in wastewater effluents; however, published literature reports methadone occurs in both wastewater and surface water.…”

Multiple Roles of Dissolved Organic Matter in Advanced Oxidation Processes

“…Free chlorine and bromine are particularly reactive toward phenolic groups, amines, and reduce sulfur moieties in DOM, , but free bromine reacts about ten times faster with DOM than free chlorine . Monochoramine (NH 2 Cl) and dichloramine (NHCl 2 ) formed from the reaction of free chlorine with ammonia have smaller reaction rate constants with DOM. , The decomposition of O 3 , free chlorine, and free bromine in the presence of DOM follows a two-stage kinetics with a rapid initial stage (lasting less than about 20 s) and a slower consumption stage. ,, Notably, relatively high yields of • OH are formed in the rapid initial stage of ozone reactions with DOM. That helps to reduce ozone-resistant TrOCs. , Depending on the types and concentrations of DOM, the decomposition rates of these chemical oxidants vary and the generation of radicals is inhibited in the presence of DOM, except in O 3 -based processes.…”

“…111 Monochoramine (NH 2 Cl) and dichloramine (NHCl 2 ) formed from the reaction of free chlorine with ammonia have smaller reaction rate constants with DOM. 114,115 The decomposition of O 3 , free chlorine, and free bromine in the presence of DOM follows a two-stage kinetics with a rapid initial stage (lasting less than about 20 s) and a slower consumption stage. 64,111,116 Notably, relatively high yields of • OH are formed in the rapid initial stage of ozone reactions with DOM.…”