Formation Of Nitrogenous Disinfection By-products Research Articles

Synergistic removal of ammonium by monochloramine photolysis

The presence of ammonium (NH4+) in drinking water treatment results in inhibition of disinfection efficiency and formation of nitrogenous disinfection by-products. Our previous study found monochloramine (NH2Cl) photolysis under 254 nm UV irradiation can be effective for removal of NH4+; however, the mechanisms of NH4+ degradation in this process were unknown. The kinetics and fundamental radical chemistry responsible for NH4+ removal in the UV/NH2Cl process were investigated in this study. The results showed that the pseudo first-order rate constant for NH4+ degradation in the UV/NH2Cl process ranged between 3.6 × 10-4 to 1.8 × 10-3 s-1. Solution pH affected radical conversion and a higher NH4+ degradation efficiency was achieved under acidic conditions. The effects of chloride were limited; however, the presence of either bicarbonate or natural organic matter scavenged radicals and inhibited NH4+ removal. NH2Cl photolysis generated an aminyl radical (NH2•) and a chlorine radical (Cl•) that further transformed to a chlorine dimer (Cl2•-) and a hydroxyl radical (HO•). The second-order rate constants for Cl• and Cl2•- reacting with NH4+ were estimated as 2.59 × 108 M-1s-1 and 3.45 × 105 M-1s-1 at pH 3.9, respectively. Cl•, Cl2•-, and HO• contributed 95.2%, 3.5%, and 1.3% to NH4+ removal, respectively, at the condition of 3 mM NH2Cl and pH 7.5. Major products included nitrite and nitrate, possibly accompanied by nitrogen-containing gases. This investigation provides insight into the photochemistry of NH4+ degradation in the UV/NH2Cl process and offers an alternative method for drinking water production.

Role of ammonia on haloacetonitriles and halonitromethanes formation during Ultraviolet irradiation followed by chlorination/chloramination

Combination of ultraviolet (UV) disinfection and chlorination became a common multi-barrier approach taken by water utilities against microbial pathogens in drinking water disinfection. Halogenated disinfection byproducts (DBPs) have been monitored and regulated in drinking water under various jurisdictions around the world for decades. More recently, several nitrogenous DBPs (N-DBPs), like haloacetonitriles (HANs) and halonitromethanes (HNMs), have been identified in chlorinated drinking waters, whose precursors are N-containing organic compounds of various origins and structures. Rising concerns over the N-DBPs formation due to their more potent genotoxic and cytotoxic activity than the regulated carbonaceous-DBPs have prompted extensive research on drinking water disinfection processes. To examine the effect of ammonia nitrogen (NH3-N) on N-DBPs formation during UV disinfection of drinking water followed by chlorination/chloramination, as a first attempt, synthetic waters prepared by humic acid with different NH3-N concentrations were exposed to UV dose up to 300 mJ/cm2 from either low pressure (LP) or medium pressure (MP) lamps, followed by chlorination/chloramination. To investigate trends, the study employed synthetic waters with elevated precursor concentrations and disinfectant exposures to generate significant byproduct formation possible. LP UV treatment had no obvious effect on N-DBP formation, whereas MP UV irradiation produced more dichloroacetonitrile (DCAN). The existence of ammonia (≤1 mg/L-N) increased DCAN concentration in high organics synthetic waters under varying MP UV doses, respectively. In high organics synthetic water samples exposed to a MP UV dose of 300 mJ/cm2 DCAN reached a maximum yield of 13.7 μg/L in the presence of 0.5 mg/L NH3-N, whereas lower yields were observed at NH3-N ≥ 2 mg/L, i.e. 2.9 μg /L and 1.8 μg/L at 2 and 10 mg/L NH3-N, respectively.

Comparison of drinking water treatment processes combinations for the minimization of subsequent disinfection by-products formation during chlorination and chloramination

Micro-ozone, permanganate, ferrate, and chlorine dioxide were applied as pre-oxidants to meet conventional requirements for water quality and algal control. The formation of typical carbonaceous disinfection by-products (C-DBPs) and emerging nitrogenous disinfection by-products (N-DBPs) during both chlorination and chloramination were investigated with combinations of different processes: (i) coagulation-sedimentation-filtration (CSF), (ii) pre-KMnO4/O3/K2FeO4/ClO2 matched with CSF, and (iii) pre-KMnO4/O3/K2FeO4/ClO2 coupled with CSF and followed by granular activated carbon (GAC)/O3-GAC advanced treatment. All conventional water quality indexes met the requirements of the national standards for drinking water quality of China (GB5749-2006) when the system was under stable operation; only NH4+-N, which only met the requirement with either pre-oxidation or post-ozonation, failed to do so. Micro-ozone pre-treatment coupled with CSF and O3-GAC showed the best performance in removing chloroform (CF) and dichloracetonitrile (DCAN) precursors. Pre-oxidation had a negative impact on chloropicrin (TCNM) and chloral hydrate formation, but a positive effect on DCAN. The trade-off analysis based on the toxicity of the selected DBPs indicated that pre-oxidation (KMnO4, O3, K2FeO4, and ClO2) had a positive influence on the control of overall cytotoxicity, and O3 pre-oxidation coupled with CSF followed by O3-GAC performed the best. However, for the control of overall genotoxicity, the ClO2 pre-treatment showed best results, whether or not GAC or O3-GAC was involved. These results are important for optimizing the design of the treatment processes in drinking water treatment plants using eutrophic lake water where precursors for regulated C-DBP and unregulated N-DBP formation are prevalent.

Transformation of Disinfection Byproduct Precursors During the Wastewater Regeneration Processes

Disinfection byproduct(DBP) precursors during the wastewater regeneration processes were separated into hydrophilic fraction(HPI), hydrophobic fraction(HPO) and transphilic fraction(TPI) with macroporous resin. DBP precursors in these water samples were characterized with fluorescence excitation emission matrix, Fourier transformation infrared and nuclear magnetic resonance, and were further tested for their DBP formation potential(DBPFP) after chlorination. The results indicated that main DBP precursors in sewage were humic acid and aliphatic hydrocarbons, and were mainly dominated by HPI. Primary treatment(sedimentation) could effectively remove hydrophobic humic acid through the mutual exclusion between HPO and water. The removal of humic acid would lead to the obvious reduction of carbonaceous disinfection byproduct formation potential(C-DBPFP). In addition, nitrogenous disinfection byproduct formation potential(N-DBPFP) was found to be increased due to the increase of DON/DOC value. Although secondary treatment(biotreatment) was effective in removing humic acid and aliphatic hydrocarbons, it could produce a large amount of soluble microbial products(SMP), which led to the enhancement of HPO percentage. And the accumulation of SMP resulted in the significant increase of C-DBPFP and N-DBPFP. Humic acid and hydrophobic SMP could be removed by the advanced treatment(cloth filtration), leading to the reduction of HPO percentage and the increase of HPI percentage. The decrease of humic acid and hydrophobic SMP would cause the reduction of C-DBPFP and N-DBPFP in the advanced treatment.

Carbonaceous and nitrogenous disinfection byproduct precursor variation during the reversed anaerobic–anoxic–oxic process of a sewage treatment plant

Disinfection byproduct (DBP) precursors in wastewater during the reversed anaerobic–anoxic–oxic (A2/O) process, as well as their molecular weight (MW) and polarity-based fractions, were characterized with UV scanning, fluorescence excitation emission matrix, Fourier transform infrared and nuclear magnetic resonance spectroscopy. Their DBP formation potentials (DBPFPs) after chlorination were further tested. Results indicated that the reversed A2/O process could not only effectively remove the dissolved organic carbon (DOC) and dissolved total nitrogen in the wastewater, but also affect the MW distribution and hydrophilic–hydrophobic properties of dissolved organic matter (DOM). The accumulation of low MW and hydrophobic (HPO) DOM was possibly due to the formation of soluble microbial product-like (SMP-like) matters in the reversed A2/O treatment, especially in the anoxic and aerobic processes. Moreover, DOM in the wastewater displayed a high carbonaceous disinfection byproduct formation potential (C-DBPFP) in the fractions of MW>100kDa and MW<5kDa, and revealed an increasing tendency of nitrogenous disinfection byproduct formation potential (N-DBPFP) with decrease of MW. For polarity-based fractions, the HPO fraction of wastewater showed significantly higher C-DBPFP and N-DBPFP than hydrophilic and transphilic fractions. Therefore, although the reversed A2/O process could remove most DBP precursors by DOC reduction, it led to the enhancement of DBPFP with the formation and accumulation of low MW and HPO DOM. In addition, strong correlations between C-DBPFPs and SUVA, and between N-DBPFPs and DON/DOC, were observed in the wastewater, which might be helpful for DBPFP prediction in wastewater and reclaimed water chlorination.

Chloramination of wastewater effluent: Toxicity and formation of disinfection byproducts

The reclamation and disinfection of waters impacted by human activities (e.g., wastewater effluent discharges) are of growing interest for various applications but has been associated with the formation of toxic nitrogenous disinfection byproducts (N-DBPs). Monochloramine used as an alternative disinfectant to chlorine can be an additional source of nitrogen in the formation of N-DBPs. Individual toxicity assays have been performed on many DBPs, but few studies have been conducted with complex mixtures such as wastewater effluents. In this work, we compared the cytotoxicity and genotoxicity of wastewater effluent organic matter (EfOM) before and after chloramination. The toxicity of chloraminated EfOM was significantly higher than the toxicity of raw EfOM, and the more hydrophobic fraction (HPO) isolated on XAD-8 resin was more toxic than the fraction isolated on XAD-4 resin. More DBPs were also isolated on the XAD-8 resin. N-DBPs (i.e., haloacetonitriles or haloacetamides) were responsible for the majority of the cytotoxicity estimated from DBP concentrations measured in the XAD-8 and XAD-4 fractions (99.4% and 78.5%, respectively). Measured DBPs accounted for minor proportions of total brominated and chlorinated products, which means that many unknown halogenated compounds were formed and can be responsible for a significant part of the toxicity. Other non-halogenated byproducts (e.g., nitrosamines) may contribute to the toxicity of chloraminated effluents as well.

Removal of Selected C‐ and N‐DBP Precursors in Biologically Active Filters

The performance of four pilot‐ and full‐scale biologically active filters (biofilters) was evaluated in terms of change in water quality parameters and removal of disinfection by‐product (DBP) precursors. Biologically active filtration successfully decreased dissolved organic carbon (DOC) by 5–25% and dissolved organic nitrogen (DON) by 5–38%. The removal of these parameters corresponded to some decreases in carbonaceous and nitrogenous DBP formation. Formation potential tests showed 13–45% and 18–57% reduction in the formation of trihalomethanes and haloacetic acids, respectively. Bromine incorporation factors of trihalomethanes and haloacetic acids increased across the biofilters. Biofilters also showed 25–48%, 15–20%, and 34–50% removal of halonitromethane, haloacetonitrile, and N‐nitrosodimethylamine precursors, respectively. The effects of filter media and phosphate amendment were also evaluated in full‐ and pilot‐scale systems. Results showed that replacing the anthracite layer with granular activated carbon increased the removal of DOC, DON, and DBP precursors. Phosphate amendment had no distinct effect on the removal of DOC, DON, or DBP precursors.

Formation of Haloacetonitriles, Haloacetamides, and Nitrogenous Heterocyclic Byproducts by Chloramination of Phenolic Compounds.

The potential formation of nitrogenous disinfection byproducts (N-DBPs) was investigated from the chloramination of nitrogenous and non-nitrogenous aromatic compounds. All molecules led to the formation of known N-DBPs (e.g., dichloroacetonitrile, dichloroacetamide) with various production yields. Resorcinol, a major precursor of chloroform, also formed di/trichloroacetonitrile, di/trichloroacetamide, and haloacetic acids, indicating that it is a precursor of both N-DBPs and carbonaceous DBPs (C-DBPs) upon chloramination. More detailed experiments were conducted on resorcinol to understand N-DBPs formation mechanisms and to identify reaction intermediates. Based on the accurate mass from high resolution Quadrupole Time-of-Flight GC-MS (GC-QTOF) and fragmentation patterns from electronic impact and positive chemical ionization modes, several products were tentatively identified as nitrogenous heterocyclic compounds (e.g., 3-chloro-5-hydroxy-1H-pyrrole-2-one with dichloromethyl group, 3-chloro-2,5-pyrroledione). These products were structurally similar to the heterocyclic compounds formed during chlorination, such as the highly mutagenic MX (3-chloro-4-(dichloromethyl)-5-hydroxy-2(5H)-furanone) or halogenated pyrroles. To our knowledge, this is the first time that the formation of halogenated nitrogenous heterocyclic compounds is reported from chloramination process. The formation of these nitrogenous byproducts during chloramination might be of concern considering their potential toxicity.

Carbonaceous and nitrogenous disinfection by-product formation from algal organic matter

Seasonal algal blooms in drinking water sources release intracellular and extracellular algal organic matter (AOM) in significant concentrations into the water. This organic matter provides precursors for disinfection by-products (DBPs) formed when the water is subsequently chlorinated at the final disinfection stage of the potable water treatment process. This paper presents results of AOM characterisation from five algal species (three cyanobacteria, one diatom and one green) alongside the measurement of the DBP formation potential from the AOM of six algal species (an additional diatom). The character was explored in terms of hydrophilicity, charge and protein and carbohydrate content. 18 DBPs were measured following chlorination of the AOM samples: the four trihalomethanes (THMs), nine haloacetic acids (HAAs), four haloacetonitriles (HANs) and one halonitromethane (HNM).The AOM was found to be mainly hydrophilic (52 and 81%) in nature. Yields of up to 92.4 μg mg−1 C carbonaceous DBPs were measured, with few consistent trends between DBP formation propensity and either the specific ultraviolet absorbance (SUVA) or the chemical characteristics. The AOM from diatomaceous algae formed significant amounts of nitrogenous DBPs (up to 1.7 μg mg−1 C). The weak trends in DBPFP may be attributable to the hydrophilic nature of AOM, which also makes it more challenging to remove by conventional water treatment processes.

The enhanced reduction of C- and N-DBP formation in treatment of source water containing Microcystis aeruginosa using a novel CTSAC composite coagulant.

This study investigated the effect of a chitosan-aluminium chloride (CTSAC) composite coagulation process on reducing the formation of algal organic matters (AOM) related carbonaceous disinfection by-products (C-DBPs) and nitrogenous disinfection by-products (N-DBPs), by removing or adsorbing their precursors. Compared with aluminium chloride (AC) and chitosan (CTS) alone, CTSAC significantly enhanced the removal of dissolved organic matter (DOC), polysaccharide, protein and humic acids, attaining removals of 64.95%, 80.78%, 70.85% and 44.50%, respectively. Notably, the three-dimensional excitation and emission matrix (3D-EEM) combined with molecular weight (MW) fractionation analysis revealed that CTSAC was not only effective for removing high-MW AOM, but also for the low-MW fractions that are important in forming DBPs. In addition, the CTSAC coagulation was proven to enhance the removal of aromatic polypeptide/amino acid-like materials and aliphatic amines, which have high N-nitrosodimethylamine formation potential. Efficient AOM removal by the CTSAC coagulation resulted in significant reduction of both AOM-related C-DBPs (63.54%) and N-DBPs (71%), while AC coagulation did not substantially reduce the formation of tribromomethane, 1,1,1-trichloropropanone or N-nitrosodimethylamine, and CTS coagulation alone did not achieve any obvious reduction in trichloronitromethane. Fourier transform infrared (FT-IR) spectroscopy analysis confirmed the interaction of CTS and AC in the CTSAC composite coagulation, which contributed to the improved AOM removal performance of CTSAC, and, in this case, reduced the formation of C- and N-DBPs.

Factors affecting the formation of nitrogenous disinfection by-products during chlorination of aspartic acid in drinking water

The formation of emerging nitrogenous disinfection by-products (N-DBPs) from the chlorination of aspartic acid (Asp) was investigated. The yield of dichloroacetonitrile (DCAN) was higher than other N-DBPs, such as dichloroacetamide(DCAcAm) and chloropicrin (TCNM) during the chlorination of Asp. The formation of DCAN, DCAcAm, and TCNM all showed a trend of first increasing and then decreasing during the chlorination of Asp with increasing contact time. The dosage of chlorine had an impact on the formation of DCAN, DCAcAm, and TCNM. The highest yields of DCAN and DCAcAm appeared when the Cl2/Asp molar ratio was about 20, the yield of TCNM increased with increasing the Cl2/Asp molar ratio from 5 to 30 and TCNM was not produced when the ratio was less than 5. Cyanogen chloride (CNCl) was detected when the Cl2/Asp molar ratio was lower than 5. N-DBPs formation was influenced by pH. DCAN formation increased with increasing pH from 5 to 6 and then decreased with increasing pH from 6 to 9, but DCAcAm and TCNM increased with increasing pH from 5 to 8 and then decreased. Higher temperatures reduced the formation of DCAN and DCAcAm, but increased TCNM formation. DCAN and DCAcAm formation decreased, and relatively stable TCNM formation increased, with increasing free chlorine contact time during chloramination. N-nitrosodimethylamine (NDMA) was produced during chloramination of Asp and increased with prolonged chloramination contact time. The presence of bromide ions enhanced the yields of haloacetonitriles and shifted N-DBPs to more brominated species.

Formation of nitrogenous disinfection by-products in 10 chlorinated and chloraminated drinking water supply systems.

The presence of nitrogenous disinfection by-products (N-DBPs) in drinking water supplies is a public health concern, particularly since some N-DBPs have been reported to be more toxic than the regulated trihalomethanes and haloacetic acids. In this paper, a comprehensive evaluation of the presence of N-DBPs in 10 drinking water supply systems in Western Australia is presented. A suite of 28 N-DBPs, including N-nitrosamines, haloacetonitriles (HANs), haloacetamides (HAAms) and halonitromethanes (HNMs), were measured and evaluated for relationships with bulk parameters in the waters before disinfection. A number of N-DBPs were frequently detected in disinfected waters, although at generally low concentrations (<10ng/L for N-nitrosamines and <10μg/L for other N-DBPs) and below health guideline values where they exist. While there were no clear relationships between N-DBP formation and organic nitrogen in the pre-disinfection water, N-DBP concentrations were significantly correlated with dissolved organic carbon (DOC) and ammonia, and these, in addition to high bromide in one of the waters, led to elevated concentrations of brominated HANs (26.6μg/L of dibromoacetonitrile). There were significant differences in the occurrence of all classes of N-DBPs between chlorinated and chloraminated waters, except for HNMs, which were detected at relatively low concentrations in both water types. Trends observed in one large distribution system suggest that N-DBPs can continue to form or degrade within distribution systems, and redosing of disinfectant may cause further by-product formation.

Formation of organic chloramines during chlor(am)ination and UV/chlor(am)ination of algae organic matter in drinking water

Surface water are frequently subjected to problems of algal blooms and release of algae organic matter (AOM) from the algae cells, which cause many water quality issues. This study investigated the formation of organic chloramines and nitrogenous disinfection by-products (N-DBPs) during chlor(am)ination and UV/chlor(am)ination of AOM in drinking water. AOM caused higher organic chloramine formation than humic acid and fulvic acid during chlor(am)ination. The formation of organic chloramines increased first and then decreased with the increase of free chlorine dosage, but kept increasing with the increase of NH2Cl dosage. During AOM chlorination, the formation of organic chloramines kept decreasing as the reaction time went by, and the maximum organic chloramine proportion (79.1%) in total chlorine occurred at 8 h. However, during AOM chloramination, the formation of organic chloramines increased first, decreased in the following and then increased again as the reaction time went by, and the maximum organic chloramine proportion (22.1%) in total chlorine occurred at 24 h. UV irradiation pretreatment did not effectively influence organic chloramine formation during AOM chlor(am)ination, but accelerated the degradation of organic chloramines during chloramination. Besides, UV pretreatment enhanced the formation of N-DBPs during the subsequent chlor(am)ination of AOM, especially dichloroacetonitrile.

Effects of ozonation and biological filtration on the formation of nitrogenous disinfection byproducts during chloramination

This study investigates the formation potential (FP) of nitrogenous disinfection byproducts and haloacetic acids (HAAs) during ozonation and biofiltration. Ozonation of raw waters was performed in batches with 1 mg O3/mg dissolved organic carbon (DOC). The ozonized waters were subsequently passed through a biofilter with 25 minutes of empty bed contact time. The results show that the increases of biodegradable DOC in hydrophobic fractions were higher than those in hydrophilic (HPI) or transphilic fractions. Ozonation reduced the DOC (<10%), and FPs of haloacetonitriles (HANs) and HAAs by 23–70%. Subsequent biofiltration removed up to 35% of DOC, whereas the additional removals of HAN and HAA FPs were negligible during biofiltration. Trichloronitromethane FPs tended to increase by a factor of 5–10 after ozonation and slightly decrease (15–20%) during biofiltration. In the two nitrogen-rich natural organic matters (NOMs), transphilics and HPIs constituted half of the organic carbons and contributed 64–70% of the total N -nitrosodimethylamine (NDMA) formation. Ozonation-biofiltration reduced NDMA precursors in these two water sources but significantly enhanced NDMA formation in Suwannee River NOM. The increase of NDMA formation was attributable to the alteration of NOM characteristics of the HPI fraction by ozonation; the NDMA FP increased 214% in the HPI fraction after ozonation.

Precursors and factors affecting formation of haloacetonitriles and chloropicrin during chlor(am)ination of nitrogenous organic compounds in drinking water

This study investigated the precursors and factors affecting formation of haloacetonitriles (HANs) and chloropicrin (TCNM) during chlorination/chloramination of eight amino acids in the effluent water of V-type clarifying filtration from a drinking water treatment plant. The yields of trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN) and TCNM were higher during chlorination than during chloramination. Tyrosine and tryptophan produced the greatest amount of DCAN and also generated a small amount of TCAN during chlorination process. Besides, the yields of DCAN were higher than TCNM during chlorination/chloramination. Contact time, Cl2:org-N molar ratios, pH, temperature and bromide ion affected nitrogenous disinfection by-products (N-DBPs) formation during chlorination of tryptophan in different degrees. TCAN, DCAN and TCNM formation showed the increasing and then decreasing with prolonged contact time. Higher Cl2:org-N molar ratios improved N-DBPs formation within a certain range. The pH affected N-DBPs formation differently. HANs increased with increasing pH from 5 to 6 and decreased with increasing pH from 6 to 9, while TCNM increased with increasing pH from 5 to 9. Higher temperatures enhanced TCNM formation, but reduced the formation of TCAN and DCAN. The presence of bromide ions improved the yields of HANs and TCNM and shifted N-DBPs to more brominated ones.

Comparison of chlorination and chloramination in carbonaceous and nitrogenous disinfection byproduct formation potentials with prolonged contact time

Due to decreasing water demands in Japan, hydraulic retention times of water in piped supply systems has been extended, resulting in a longer contact time with disinfectants. However, the effects of extended contact time on the formation of various disinfection byproducts (DBPs), including carbonaceous DBPs such as trihalomethane (THM) and haloacetic acid (HAA), and nitrogenous DBPs such as nitrosodimethylamine (NDMA) and nitrosomorpholine (NMor), have not yet been investigated in detail. Herein, we compared the formation of these DBPs by chlorination and chloramination for five water samples collected from rivers and a dam in Japan, all of which represent municipal water supply sources. Water samples were treated by either filtration or a combination of coagulation and filtration. Treated samples were subjected to a DBP formation potential test by either chlorine or chloramine for contact times of 1 day or 4 days. Four THM species, nine HAA species, NDMA, and NMor were measured by GC-ECD or UPLC-MS/MS. Lifetime cancer risk was calculated based on the Integrated Risk Information System unit risk information. The experiment and analysis focused on (i) prolonged contact time from 1 day to 4 days, (ii) reduction efficiency by conventional treatment, (iii) correlations between DBP formation potentials and water quality parameters, and (iv) the contribution of each species to total risk. With an increased contact time from 1 day to 4 days, THM formation increased to 420% by chloramination. Coagulation-filtration treatment showed that brominated species in THMs are less likely to be reduced. With the highest unit risk among THM species, dibromochloromethane (DBCM) showed a high correlation with bromine, but not with organic matter parameters. NDMA contributed to lifetime cancer risk. The THM formation pathway should be revisited in terms of chloramination and bromine incorporation. It is also recommended to investigate nitrosamine formation potential by 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.

Peptide bonds affect the formation of haloacetamides, an emerging class of N-DBPs in drinking water: free amino acids versus oligopeptides.

Haloacetamides (HAcAms), an emerging class of nitrogenous disinfection by-products (N-DBPs) of health concern, have been frequently identified in drinking waters. It has long been appreciated that free amino acids (AAs), accounting for a small fraction of the dissolved organic nitrogen (DON) pool, can form dichloroacetamide (DCAcAm) during chlorination. However, the information regarding the impacts of combined AAs, which contribute to the greatest identifiable DON portion in natural waters, is limited. In this study, we compared the formation of HAcAms from free AAs (tyrosine [Tyr] and alanine [Ala]) and combined AAs (Tyr-Ala, Ala-Tyr, Tyr-Tyr-Tyr, Ala-Ala-Ala), and found that HAcAm formation from the chlorination of AAs in combined forms (oligopeptides) significantly exhibited a different pattern with HAcAm formation from free AAs. Due to the presence of peptide bonds in tripeptides, Tyr-Tyr-Tyr and Ala-Ala-Ala produced trichloroacetamide (TCAcAm) in which free AAs was unable to form TCAcAm during chlorination. Moreover, peptide bond in tripeptides formed more tri-HAcAms than di-HAcAms in the presence of bromide. Therefore, the peptide bond may be an important indicator to predict the formation of specific N-DBPs in chlorination. The increased use of algal- and wastewater-impacted water as drinking water sources will increase health concerns over exposure to HAcAms in drinking water.

Impact of UV/persulfate pretreatment on the formation of disinfection byproducts during subsequent chlorination of natural organic matter

Ultraviolet/persulfate (UV/PS) has been widely used to generate sulfate radicals (SO4−) in degrading organic pollutants. However, its impact on chlorinated disinfection byproducts (DBPs) is unclear. Impact of UV/PS pretreatment on the formation of DBPs during subsequent chlorination of natural organic matter was evaluated in this study. For the samples pretreated by UV/PS, the formation of some carbonaceous disinfection byproducts (C-DBPs) such as chloroform and haloacetic acids only increased a little, but the formation of nitrogenous disinfection byproducts (N-DBPs) including haloacetonitriles and trichloronitromethane decreased slightly. UV/H2O2 pretreatment increased the formation of both C-DBPs and N-DBPs significantly with the initial dosage of H2O2 being 30μM. Chloral hydrate and haloketones followed an increasing and then decreasing pattern, but dichloroacetonitrile and trichloronitromethane followed an opposite pattern with increasing UV/PS pretreatment time. Most of the C-DBPs rose monotonically with increasing dosages of PS, but N-DBPs declined at the dosage of PS being 10μM by UV/PS pretreatment. Preoxidation pH and the presence of nitrate played little role in DBP formation. In the presence of 2.5mg/L ammonia, UV/PS pretreatment increased most of the DBPs except for trichloroacetonitrile and trichloronitromethane. Bromine incorporation factors for trihalomethanes, haloacetic acids and dihaloacetonitriles were affected by UV/PS preoxidation insignificantly. It is suggested that the combination of UV/PS and post chlorination was expected to be a good choice in controlling the formation of DBPs.