Formation Of Haloacetamides Research Articles

Effect of copper corrosion products on the formation and speciation of haloacetamides and haloacetonitriles during chlorination

The catalytic effect of copper corrosion products, including copper ions, cupric oxide, and cuprous oxide, on the formation of haloacetamides and haloacetonitriles during chlorination of natural organic matter (NOM), model nitrogenous precursors, and real water samples was investigated. During chlorination of NOM, the presence of these copper corrosion products facilitated chlorine decay, and enhanced the formation of dichloroacetonitrile (DCAN) and dichloroacetamide (DCAcAm) with enhancement ratios of 45–59% and 64–137% after 10 h contact time, respectively. Six amino acids were selected as nitrogenous NOM surrogates for chlorination, and the results show that the enhancement of DCAN and DCAcAm formation by copper corrosion products was only observed for slow reacting amino acids, including glutamine, glutamic acid, and phenylamine, suggesting that copper corrosion products may enhance DCAN and DCAcAm formation by catalyzing NOM portions that are relatively inefficient precursors. When bromide and copper corrosion products were present, the formation of dihaloacetonitriles (DHANs) and dihaloacetamides (DHAcAms) could be enhanced during chlorination of NOM, but the degrees of bromine substitution for DHANs and DHAcAms decreased. Although copper corrosion products facilitated DHAN and DHAcAm hydrolysis with the facilitation increasing as the halogens shifted from chlorine to bromine, increased DHAN and DHAcAm concentrations was observed during chlorination of real water samples in the presence of copper corrosion products, confirming that the copper corrosion products had a catalytic effect on DHAN and DHAcAm formation that exceeded their catalytic effect on DHAN and DHAcAm hydrolysis. This study provides basic knowledge of disinfectant residuals and the fate of haloacetonitriles and haloacetamides in drinking water distribution systems where copper is used, which will be helpful for the management of safe water distribution.

Formation and speciation of chlorinated, brominated, and iodinated haloacetamides in chloraminated iodide-containing waters

Haloacetamides (HAMs), an emerging class of disinfection by-products, have received increasing attention due to their elevated cyto- and genotoxicity. However, only limited information is available regarding the iodinated analogues. This study investigated the formation and speciation of iodinated haloacetamides (I-HAMs) and their chlorinated/brominated analogues during the chloramination of bromide and/or iodide-containing waters and a model compound solution over various time periods. The rapid formation of diiodoacetamide (DIAM) was observed during chloramination of three simulated samples, whereas brominated (Br-HAMs) and chlorinated haloacetamides (Cl-HAMs) increased slowly with increasing reaction time. To further understand the differences in the formation of HAMs containing different halogens, experiments with the model compound asparagine in the presence/absence of iodide were conducted. Moreover, iodine utilisation factors and iodine incorporation factors were observed to increase significantly faster and were substantially higher than those of bromine. This implied that, compared with bromide, iodide has substantially greater potential to be transformed to the corresponding HAMs during chloramination, similar to that of other classes of DBPs. That is, I-HAMs formed faster than the other species investigated, including Cl-HAMs and Br-HAMs, in the early reaction stages (0–3 h). The effect of the bromide/iodide ratio (i.e., constant iodide, increasing bromide) on I-HAM formation was also examined. With increasing bromide/iodide ratio, the formation of Br-HAMs increased and dichloroacetamide decreased, but the formation of DIAM was largely unchanged. This was consistent with the constant level of iodide in spite of the increasing bromide. Chlorine and ammonia are applied separately during chloramination in water treatment, so the effect of pre-chlorination (before adding ammonia) on the formation and speciation of I-HAMs during in situ chloramination was also evaluated. Effective mitigation of DIAM formation with in situ chloramination was achieved, and the efficiency improved with increasing pre-chlorination time, where iodide was oxidised to iodate. The HAM-associated cytotoxicity was calculated to determine the change in toxicity at different reaction times, bromide/iodide ratios, and pre-chlorination times. A similar trend as the formation of I-HAMs was observed, which increased rapidly in the first 3 h, but decreased somewhat subsequently. When the bromide/iodide ratio and pre-chlorination time was increased, the calculated toxicity of the HAMs increased (due to more formation of Br-HAMs and less Cl-HAMs) and decreased (due to less DIAM formation), respectively.

The formation of haloacetamides, as an emerging class of N-DBPs, from chlor(am)ination of algal organic matter extracted from Microcystis aeruginosa, Scenedesmus quadricauda and Nitzschia palea

The formation of haloacetamides, as an emerging class of N-DBPs, from AOM disinfection extracted from Microcystis aeruginosa, Scenedesmus quadricauda and Nitzschia palea.

Occurrence and formation of haloacetamides from chlorination at water purification plants across Japan

The occurrence of six haloacetamides (HAcAms), which are a group of emerging nitrogenous disinfection byproducts, was investigated in drinking water across Japan in September 2015 and February 2016. At least one of the six HAcAms were found in all of the drinking water samples and their total concentrations ranged from 0.3 to 3.8 μg/L. The detection frequencies and concentrations of 2,2-dichloroacetamide (DCAcAm) and 2-bromo-2-chloroacetamide (BCAcAm) were the largest among the targeted HAcAm species. The total HAcAm concentrations in the raw water after chlorination ranged from 0.8 to 11 μg/L. The bromine incorporation factors (BIFs) of the targeted dihalogenated HAcAms (di-HAcAms) (DCAcAm, BCAcAm, and 2,2-dibromoacetamide) in the drinking water samples correlated well with those in the raw water after chlorination. The total HAcAm concentrations and the BIF of the di-HAcAms in the raw water after chlorination correlated with trihalomethane concentrations. HAcAm concentrations after chlorination increased with chlorination time. While the formation of di-HAcAms after chlorination was higher at higher pH, that of 2,2,2-trichloroacetamide remained unaffected by pH.

Formation and speciation of haloacetamides and haloacetonitriles for chlorination, chloramination, and chlorination followed by chloramination

The formation of haloacetamides (HAcAms) and haloacetonitriles (HANs) from a solution containing natural organic matter and a secondary effluent sample was evaluated for disinfection by chlorination, chloramination, and chlorination followed by chloramination (Cl2NH2Cl process). The use of preformed monochloramine (NH2Cl) produced higher concentrations of HAcAms and lower concentrations of HANs than chlorination, while the Cl2NH2Cl process produced the highest concentrations of HAcAms and HANs. These results indicate that the Cl2NH2Cl process, which inhibited the formation of regulated trihalomethanes compared with chlorination, enhanced the formation of HAcAms and HANs. For disinfection in the presence of bromide, brominated dihaloacetamides and dihaloacetonitriles were formed, and the trends were similar to those observed for chlorinated species in the absence of bromide. The degrees of bromine substitution of dihaloacetamides and dihaloacetonitriles were highest for chlorination, followed by the Cl2NH2Cl process and then by the NH2Cl process. For the Cl2NH2Cl process, HAN formation kept gradually increasing with prechlorination time increasing from 0 to 120 min, while HAcAm formation increased only until it reached a maximum at around 10–30 min. These results suggest that the prechlorination time could be reduced to control the formation of HAcAms and HANs. During chloramination, the formation of HAcAms and HANs was lower when using preformed NH2Cl than when chloramines were formed in situ, with higher formation of HAcAms and HANs when chlorine was added before ammonia than vice versa for the secondary effluent; this finding suggests that preformed NH2Cl could be used to inhibit the formation of HAcAms and HANs during chloramination.

The role of aromatic precursors in the formation of haloacetamides by chloramination of dissolved organic matter

Water treatment utilities are diversifying their water sources and often rely on waters enriched in nitrogen-containing compounds (e.g., ammonia, organic nitrogen such as amino acids). The disinfection of waters exhibiting high levels of nitrogen has been associated with the formation of nitrogenous disinfection byproducts (N-DBPs) such as haloacetonitriles (HANs) and haloacetamides (HAcAms). While the potential precursors of HANs have been extensively studied, only few investigations are available regarding the nature of HAcAm precursors. Previous research has suggested that HAcAms are hydrolysis products of HANs. Nevertheless, it has been recently suggested that HAcAms can be formed independently, especially during chloramination of humic substances. When used as a disinfectant, monochloramine can also be a source of nitrogen for N-DBPs. This study investigated the role of aromatic organic matter in the formation of N-DBPs (HAcAms and HANs) upon chloramination. Formation kinetics were performed from various fractions of organic matter isolated from surface waters or treated wastewater effluents. Experiments were conducted with 15N-labeled monochloramine (15NH2Cl) to trace the origin of nitrogen. N-DBP formation showed a two-step profile: (1) a rapid formation following second-order reaction kinetics and incorporating nitrogen atom originating from the organic matrix (e.g., amine groups); and (2) a slower and linear increase correlated with exposure to chloramines, incorporating inorganic nitrogen (15N) from 15NH2Cl into aromatic moieties. Organic matter isolates showing high aromatic character (i.e., high SUVA) exhibited high reactivity characterized by a major incorporation of 15N in N-DBPs. A significantly lower incorporation was observed for low-aromatic-content organic matter. 15N-DCAcAm and 15N-DCAN formations exhibited a linear correlation, suggesting a similar behavior of 15N incorporation as SUVA increases. Chloramination of aromatic model compounds (i.e., phenol and resorcinol) showed higher HAcAm and HAN formation potentials than nitrogenous precursors (i.e., amino acids) usually considered as main precursors of these N-DBPs. These results demonstrate the importance of aromatic organic compounds in the formation of N-DBPs, which is of significant importance for water treatment facilities using chloramines as final disinfectant.

The formation of haloacetamides and other disinfection by-products from non-nitrogenous low-molecular weight organic acids during chloramination

Low-molecular weight organic acids (LMWOAs) are widespread in nature, and many are recalcitrant during conventional drinking water treatment, due to their LMW and hydrophilic character. This study assessed the formation of a range of disinfection by-products (DBPs) from the chloramination of seven non-nitrogenous LMWOA precursors, with an emphasis on the contribution of N-chloramine incorporation to haloacetamide (HAcAm) formation. The other DBPs comprised chlorinated halomethanes, haloacetonitriles and haloacetic acids. Citric acid generated higher yields of trichloromethane and two chloroacetic acids than the other LMWOAs. Further, the unsaturated acids (fumaric acid and itaconic acid) formed more chloroacetic acids than saturated acids (oxalic acid, succinic acid, adipic acid). Importantly, non-nitrogenous LMWOAs formed three nitrogenous DBPs (dichloroacetamide, trichloroacetamide, and small amounts of dichloroacetonitrile) during chloramination, firstly indicating the monochloramine can supply the nitrogen in nitrogenous DBPs, and the formation of haloacetamides at least in part is independent of the hydrolysis of haloacetonitriles. To the authors’ knowledge, this is the first time formation of halogenated nitrogenous DBPs (N-DBPs) has been reported from chloramination of non-nitrogenous LMWOA precursors. This indicates that concentrations of dissolved organic nitrogen compounds in drinking water are not a reliable surrogate for formation of N-DBPs during chloramination. Bromine incorporation factor increased with increasing bromide during chloramination of citric acid, and bromine was easier to incorporate into di-HAcAms than mono- and tri-HAcAms during chloramination.

Impact of UV/H2O2 pre-oxidation on the formation of haloacetamides and other nitrogenous disinfection byproducts during chlorination.

Haloacetamides (HAcAms), an emerging class of nitrogen-based disinfection byproducts (N-DBPs) of health concern in drinking water, have been found in drinking waters at μg/L levels. However, there is a limited understanding about the formation, speciation, and control of halogenated HAcAms. Higher ultraviolet (UV) doses and UV advanced oxidation (UV/H2O2) processes (AOPs) are under consideration for the treatment of trace organic pollutants. The objective of this study was to examine the potential of pretreatment with UV irradiation, H2O2 oxidation, and a UV/H2O2 AOP for minimizing the formation of HAcAms, as well as other emerging N-DBPs, during postchlorination. We investigated changes in HAcAm formation and speciation attributed to UV, H2O2 or UV/H2O2 followed by the application of free chlorine to quench any excess hydrogen peroxide and to provide residual disinfection. The results showed that low-pressure UV irradiation alone (19.5-585 mJ/cm(2)) and H2O2 preoxidation alone (2-20 mg/L) did not significantly change total HAcAm formation during subsequent chlorination. However, H2O2 preoxidation alone resulted in diiodoacetamide formation in two iodide-containing waters and increased bromine utilization. Alternatively, UV/H2O2 preoxidation using UV (585 mJ/cm(2)) and H2O2 (10 mg/L) doses typically employed for trace contaminant removal controlled the formation of HAcAms and several other N-DBPs in drinking water.

Formation of haloacetamides during chlorination of dissolved organic nitrogen aspartic acid

The stability of haloacetamides (HAcAms) such as dichloroacetamide (DCAcAm) and trichloroacetamide (TCAcAm) was studied under different experimental conditions. The yield of HAcAms during aspartic acid (Asp) chlorination was measured at different molar ratio of chlorine atom to nitrogen atom (Cl/N), pH and dissolved organic carbon (DOC) mainly consisted of humic acid (HA) mixture. Ascorbic acid showed a better capacity to prevent the decay of DCAcAm and TCAcAm than the other two dechlorinating agents, thiosulfate and sodium sulfite. Lower Cl/N favored the DCAcAm formation, implying that breakpoint chlorination might minimize its generation. The pH decrease could lower the concentration of DCAcAm but favored dichloroacetonitrile (DCAN) formation. DCAcAm yield was sensitive to the DOC due to higher chlorine consumption caused by HA mixture. Two possible pathways of DCAcAm formation during Asp chlorination were proposed. Asp was an important precursor of DCAN, DCAcAm and dichloroacetic acid (DCAA), and thus removal of Asp before disinfection may be a method to prevent the formation of DCAcAm, DCAN and DCAA.