Formation Of Halonitromethanes Research Articles

Formation and toxicity alteration of halonitromethanes from Chlorella vulgaris during UV/chloramination process involving bromide ion

Frequent algal blooms cause algal cells and their algal organic matter (AOM) to become critical precursors of disinfection by-products (DBPs) during water treatment. The presence of bromide ion (Br−) in water has been demonstrated to affect the formation laws and species distribution of DBPs. However, few researchers have addressed the formation and toxicity alteration of halonitromethanes (HNMs) from algae during disinfection in the presence of Br−. Therefore, in this work, Chlorella vulgaris was selected as a representative algal precursor to investigate the formation and toxicity alteration of HNMs during UV/chloramination involving Br−. The results showed that the formation concentration of HNMs increased and then decreased during UV/chloramination. The intracellular organic matter of Chlorella vulgaris was more susceptible to form HNMs than the extracellular organic matter. When the Br−: Cl2 mass ratio was raised from 0.004 to 0.08, the peak of HNMs total concentration increased 33.99%, and the cytotoxicity index and genotoxicity index of HNMs increased 67.94% and 22.80%. Besides, the formation concentration and toxicity of HNMs increased with increasing Chlorella vulgaris concentration but decreased with increasing solution pH. Possible formation pathways of HNMs from Chlorella vulgaris during UV/chloramination involving Br− were proposed based on the alteration of nitrogen species and fluorescence spectrum analysis. Furthermore, the formation laws of HNMs from Chlorella vulgaris in real water samples were similar to those in deionized water samples. This study contributes to a better comprehension of HNMs formation from Chlorella vulgaris and provides valuable information for water managers to reduce hazards associated with the formation of HNMs.

Effects of Fe(III) on the formation and toxicity alteration of halonitromethanes, dichloroacetonitrile, and dichloroacetamide from polyethyleneimine during UV/chlorine disinfection

Trace iron ions (Fe(III)) are commonly found in water and wastewater, where free chlorine is very likely to coexist with Fe(III) affecting the disinfectant's stability and N-DBPs’ fate during UV/chlorine disinfection, and yet current understanding of these mechanisms is limited. This study investigates the effects of Fe(III) on the formation and toxicity alteration of halonitromethanes (HNMs), dichloroacetonitrile (DCAN), and dichloroacetamide (DCAcAm) from polyethyleneimine (PEI) during UV/chlorine disinfection. Results reveal that the maxima concentrations of HNMs, DCAN, and DCAcAm during UV/chlorine disinfection with additional Fe(III) were 1.39, 1.38, and 1.29 times higher than those without additional Fe(III), instead of being similar to those of Fe(III) inhibited the formation of HNMs, DCAN and DCAcAm during chlorination disinfection. Meanwhile, higher Fe(III) concentration, acidic pH, and higher chlorine dose were more favorable for forming HNMs, DCAN, and DCAcAm during UV/chlorine disinfection, which were highly dependent on the involvement of HO· and Cl·. Fe(III) in the aquatic environment partially hydrolyzed to the photoactive Fe(III)-hydroxyl complexes Fe(OH)2+ and [Fe(H2O)6]3+, which undergone UV photoactivation and coupling reactions with HOCl to achieve effective Fe(III)/Fe(II) interconversion, a process that facilitated the sustainable production of HO·. Extensive product analysis and comparison verified that the HO· production enhanced by the Fe(III)/Fe(II) internal cycle played a primary role in increasing HNMs, DCAN, and DCAcAm productions during UV/chlorine disinfection. Note that the incorporation of Fe(III) increased the cytotoxicity and genotoxicity of HNMs, DCAN, and DCAcAm formed during UV/chlorine disinfection, and yet Fe(III) did not have a significant effect on the acute toxicity of water samples before, during, and after UV/chlorine disinfection. The new findings broaden the knowledge of Fe(III) affecting HNMs, DCAN, and DCAcAm formation and toxicity alteration during UV/chlorine disinfection.

Regression model and pathways of halonitromethane formation from amino acids in the presence of bromide ion under UV/monochloramine disinfection

Halonitromethanes (HNMs) including chlorinated and brominated HNMs, a category of nitrogenous disinfection by-products with high toxicity, were formed from amino acids (AAs) in the presence of bromide ion (Br-) under UV/monochloramine (UV/NH2Cl) disinfection. This study developed a regression model using water characteristics (pH, HCO3– and Br-) and disinfection conditions (disinfection time and NH2Cl doses) to predict HNM formation from AAs (tyrosine (Tyr), tryptophan (Trp) and aspartic acid (Asp)) in the presence of Br- under UV/NH2Cl disinfection. Main contributors to the abatement of Tyr and Trp were UV (6.1%-18.7%), HO (18.5%-62.3%), Cl2− (0.3%-17.9%), Br (2.4%-41.3%, kBr•,AA=∼109-1010 M−1·s−1), Br2− (1.3%-11.0%, kBr2•-,AA=∼108-109 M−1·s−1), NO (2.6%-43.0%) and CO3− (0%-43.2%) based on the first-principle kinetic model of UV/NH2Cl/Br- process, while the removal ratio of Asp was low. It was responsible for higher HNM concentrations from Tyr and Trp than those from Asp. Due to the decline in HNM concentrations with prolongation of reaction time, HNM concentrations were considered as the quadratic function of disinfection time with coefficients related to water characteristics and NH2Cl doses. The regression model with backward stepwise regression described HNM formation well. After introducing specific UV absorbance at 254 nm (SUVA254) and interaction terms associated with SUVA254, HNM formation from three AAs was successfully predicted by one regression equation (R2 = 0.91, mean absolute error = 0.46, mean relative error = 37%, root-mean-square error = 0.81). Using the optimal regression model, increasing NH2Cl doses was found to advance the peak time for HNM formation. Besides, obtained heatmaps of HNM formation revealed that a high NH2Cl dose with a high UV dose or low NH2Cl dose helped to limit HNM formation. Lastly, the possible formation pathways of HNMs were presented.

Formation of halonitromethanes from benzylamine during UV/chlorination: Impact factors, toxicity alteration, and pathways.

Halonitromethanes (HNMs), a representative nitrogen-containing disinfection byproduct, have gained significant concerns due to their higher cytotoxicity and genotoxicity. UV/chlorination is considered a promising alternative disinfection technology for chlorination. This study aimed to investigate the HNMs formation from benzylamine (BZA) during UV/chlorination. The experimental results revealed that the yields of HNMs initially raised to a peak then dropped over time. Higher chlorine dosage and BZA concentration promoted the formation of HNMs, whereas alkaline pH inhibited their formation. The presence of bromine ion (Br-) not only converted chlorinated-HNMs (Cl-HNMs) to brominated (chlorinated)-HNMs Br (Cl)-HNMs) and brominated-HNMs (Br-HNMs) but also enhanced the total concentration of HNMs. Besides, the calculated cytotoxicity index (CTI) and genotoxicity index (GTI) of HNMs were elevated by 68.97% and 60.66% as Br- concentration raised from 2 to 6µM. The possible formation pathways of HNMs from BZA were proposed based on the intermediates identified by a gas chromatography/mass spectrometry (GC/MS). In addition, the formation rules of HNMs in actual water verified the results in deionized water during UV/chlorination. The results of this study provide basic data and a theoretical basis for the formation and control of HNMs, which is conducive to applying UV/chlorination.

Insights into the formation of halonitromethanes from dimethylamine involving bromide ion during UV/chloramine disinfection

Aliphatic amines are vital precursors of halonitromethane (HNMs), which pose a potential hazard to water safety. Bromide ions (Br−) have been reported to exert a significant effect on HNMs formation. However, the formation of HNMs from secondary aliphatic amine during UV/chloramine disinfection in the presence of Br− has rarely been studied. Hence, this work selected dimethylamine (DMA) as the model precursor and focused on the mechanism and impact factors of HNMs formation involving Br− during UV/chloramine disinfection. The results indicated that after adding 2 mg/L Br−, the total concentration of HNMs at 4 min increased up to 1.86-fold compared with adding 0.3 mg/L Br−. Moreover, brominated (chlorinated)-HNMs (Br(Cl)-HNMs) were gradually transformed into brominated-HNMs (Br-HNMs) with increased Br− concentration. While Br-HNMs would be transformed into Br(Cl)-HNMs with the increase of monochloramine concentration. The peak values of HNMs were promoted with the increase of DMA concentration but inhibited with the increase of pH. Notably, tribromonitromethane was the dominant species of HNMs involving Br− during UV/chloramine disinfection. The possible formation pathways of HNMs from DMA involving Br− during UV/chloramine disinfection were deduced. Finally, it was discovered that the formation of HNMs in real water was basically consistent with that in simulated water. The findings of this research are beneficial for comprehending the formation mechanism of HNMs from aliphatic amines and provide scientific measures to minimize the HNMs production during UV/chloramine disinfection.

Formation of halonitromethanes from glycine during LED-UV265/chlorine disinfection

LED-UV265/chlorine is a promising alternative disinfection technology that emits mono-wavelength light for high germicidal efficiency. Halonitromethanes (HNMs) are highly cytotoxic and genotoxic disinfection byproducts that can be formed during LED-UV265/chlorine disinfection. Thus, this work aimed to investigate the HNMs formation from glycine (Gly) during LED-UV265/chlorine disinfection. The results indicated that the concentrations of chlorinated-HNMs (Cl-HNMs) increased first and then decreased as the reaction proceeded. Besides, the effects of operating parameters (UV intensity, free chlorine dosage, and pH) and coexisting ions (Cu2+ and Br−) on HNMs formation were investigated. It was found that the formation concentrations of Cl-HNMs increased with the increase of LED-UV265 intensity and free chlorine dosage but decreased with increased pH. The presence of Cu2+ promoted the formation of Cl-HNMs. The total concentration of HNMs (at 3 min) with adding 1.5 mg/L Cu2+ was 30.90% higher than that without Cu2+. Notably, nine species of HNMs were detected after adding Br−, and the total concentrations of HNMs were enhanced. Moreover, Cl-HNMs were gradually transformed into brominated (chlorinated)-HNMs and brominated-HNMs as Br− concentration increased. According to the findings, the possible formation mechanism of HNMs from Gly during LED-UV265/chlorine disinfection was deduced. Finally, it was demonstrated that the formation laws of HNMs from Gly in real water samples were basically consistent with those in simulated water. Insights obtained in this study help to comprehend the HNMs formation from Gly and provide strategies for controlling the production of HNMs during LED-UV265/chlorine disinfection.

Impact factors and pathways of halonitromethanes formation from aspartic acid during LED-UV265/chlorine disinfection

Impact factors and pathways of halonitromethanes formation from aspartic acid during LED-UV265/chlorine disinfection

Degradation of metronidazole during the UV365-LED /chlorine process: Kinetics, influencing factors, and halonitromethanes formation

Effective removal of refractory metronidazole (MNZ) from the aquatic environment is important for the safeguarding of human health and ecological safety. Herein, the combination of ultraviolet light-emitting diode at 365 nm wavelength and free chlorine (UV365-LED/chlorine) was used for the removal of MNZ. The UV365-LED/chlorine presented higher MNZ degradation efficiency (90.6%) compared to UV365-LED photolysis (29.96%) and chlorination alone (negligible). The degradation of MNZ by the UV365-LED photolysis and UV365-LED/chlorine process followed pseudo-first-order kinetics, and the corresponding degradation rate constants were 8.23 × 10–3 and 5.505 × 10–2 min–1, respectively. Quenching experiments indicated that hydroxyl radicals (·OH), ozone (O3), and reactive chlorine species (RCS) were responsible for MNZ removal during the UV365-LED/chlorine process. Meanwhile, probe experiments found that·OH and RCS were the major reactive species for MNZ elimination. Increasing chlorine dosage, raising UV power, and lowering pH of solution were beneficial to the MNZ degradation and corresponding halonitromethanes (HNMs) formation. HCO3–, NH4+, and Cl– presented inhibitory effects on MNZ degradation to different degrees, while Br– slightly improved MNZ degradation rate constants. Based on the analysis of MNZ degradation intermediates, the possible MNZ degradation pathways were proposed. Besides, energy consumption of UV365-LED/chlorine process decreased by 85.05% compared with UV365-LED photolysis. These findings contribute to the practical application of UV365-LED/chlorine process for MNZ removal in water systems and wastewater.

Degradation of natural organic matter and disinfection byproducts formation by solar photolysis of free available chlorine

Environment disinfection effectively curbs transmission of the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2). However, elevated concentration of free available chlorine (FAC) in disinfectants can be discharged into surface water, generating toxic disinfection byproducts (DBPs). The impact of solar photolysis of FAC on natural organic matter (NOM) to form DBPs has not been well studied. In this work, solar photolysis of FAC was found to result in higher formation of DBPs, DBPs formation potential (DBPsFP), total organic chlorine (TOCl) and lower specific ultraviolet absorbance at 254 nm (SUVA254), compared to dark chlorination. In solar photolysis of FAC, formation of total DBPs was promoted by pH=8, but hindered by the addition of HCO3−, radical scavenger or deoxygenation, while addition of NO3−and NH4+both enhanced the formation of nitrogenous DBPs. Differences in the formation of DBPs in solar photolysis of FAC under various conditions were influenced by reactive species. The formation of trichloromethane (TCM) and haloacetic acids (HAAs) in solar photolysis of FAC positively correlated with the steady-state concentrations of ClO• and O3. The steady-state concentrations of •NO and •NH2 positively correlated with the formation of halonitromethanes (HNMs). HAAs and haloacetonitriles (HANs) mainly contributed to calculated cytotoxicity of DBPs. This study demonstrates that solar photolysis of FAC may significantly impact the formation of DBPs in surface water due to extensive use of disinfectants containing FAC during SARS-CoV-2 pandemic.

Formation, toxicity, and mechanisms of halonitromethanes from poly(diallyl dimethyl ammonium chloride) during UV/monochloramine disinfection in the absence and presence of bromide ion

Bromide ion (Br−) is known as a prevalent component in water environments, which exhibits significant impacts on halonitromethanes (HNMs) formation. This study was performed to explore and compare the formation, toxicity, and mechanisms of HNMs from poly(diallyl dimethyl ammonium chloride) (PDDACl) in the absence and presence of Br− in the UV/monochloramine (UV/NH2Cl) disinfection process. The results showed that chlorinated HNMs were found in the absence of Br−, while brominated (chlorinated) HNMs and brominated HNMs were found in the presence of Br−. Furthermore, the peaks of total HNMs were promoted by 2.0 and 2.4 times, respectively when 1.0 and 2.0 mg L−1 Br− were added. Also, the peaks of total HNMs were enhanced with the increase of the NH2Cl dosage, which were reduced with the increase of pH. It should be noted that Br− induced higher toxicity of HNMs, and the cytotoxicity and genotoxicity of HNMs with the addition of 2.0 mg L−1 Br− were 78.0 and 3.7 times those without the addition of Br−, respectively. Meanwhile, both the reaction mechanisms of HNMs produced from PDDACl were speculated in the absence and presence of Br−. Finally, different HNMs species and yields were discovered in these two real water samples compared to those in simulated waters. These findings of this work will be conducive to understanding the significance of Br− affecting HNMs formation and toxicity in the disinfection process.

Comparison of UV/chloramine disinfection of methylamine water in the absence and presence of bromide: Halonitromethanes formation, toxicity alteration, and reaction mechanisms

UV/chloramine is considered a new potential disinfection process to substitute traditional disinfection methods, and the participation of bromide (Br−) significantly influences halonitromethanes (HNMs) formation during UV/chloramine disinfection. Herein, the formation laws of HNMs from methylamine were explored and compared during UV/chloramine disinfection with and without the existence of Br−. The results indicated that there were similar formation laws of HNMs between the disinfection processes with and without the existence of Br− but different species and productions of HNMs were observed. Furthermore, both the total HNMs productions during UV/chloramine disinfection with and without the existence of Br− were markedly enhanced when increasing chloramine dosage while those were significantly reduced when increasing solution pH from 6.0 to 8.0. Also, it was pointed out that Br− dramatically strengthened the toxicity of HNMs, and the toxicity alteration of HNMs was consistent with the changes in the yields of total HNMs with reaction time. Meanwhile, the reaction mechanisms of HNMs formed from methylamine were speculated during UV/chloramine disinfection with and without the existence of Br−, and Br− presented a non-negligible impact on the formation mechanisms. Finally, the formation laws of HNMs in two real water samples were found to be similar to that in simulated water samples during UV/chloramine disinfection, while different species and yields of HNMs were simultaneously observed. This work illustrated HNMs formation from methylamine and the significant impacts of Br− on HNMs generation during UV/chloramine disinfection.

Effects of bromide ion on the formation and toxicity alteration of halonitromethanes from nitrate containing humic acid water during UV/chlor(am)ine disinfection

UV/chlor(am)ine are efficient for achieving multiple-barrier disinfection and maintaining residuals, while bromide (Br−) has notable impacts on the formation and toxicity of halonitromethanes (HNMs) during UV/chlor(am)ine disinfection. This study investigated the effects of Br− on HNMs formation and toxicity alteration during UV/chlor(am)ine disinfection of nitrate containing humic acid (HA) water. Results reveal that the maximum concentration of HNMs during UV/chlorine disinfection was 12.03 μg L−1 with 0.2 mg L−1 Br−, which was 22.5% higher than that without Br−, and the predominant species of HNMs were converted from trichloronitromethane (TCNM) to dibromonitromethane (DBNM) and tribromonitromethane (TBNM). However, the maximum concentration of HNMs during UV/chloramine disinfection was 3.69 μg L−1 with 0.2 mg L−1 Br−, which was increased by 26.0% than that without Br−, and the predominant species of HNMs were converted from dichloronitromethane (DCNM) to bromochloronitromethane (BCNM) and DBNM. Notably, the HNMs species and yields during UV/chloramine disinfection were less than those during UV/chlorine disinfection, primarily due to the higher concentrations of HO· and reactive chlorine/bromine species in UV/chlorine. Also, in the ranges of the Br−:Cl2 molar ratio from 0 to 0.32 and pH from 6.0 to 8.0, the Br−:Cl2 molar ratio of 0.16 and acidic pH contributed to the HNMs formation during UV/chlorine disinfection, and a high Br−:Cl2 molar ratio and neutral pH contributed to the HNMs formation during UV/chloramine disinfection. Note that the incorporation of Br− significantly improved the calculated cytotoxicity (CTI) and genotoxicity (GTI) of HNMs formed, and the calculated CTI and GTI of HNMs formed during UV/chloramine disinfection were 28.19 and 48.90% of those during UV/chlorine disinfection. Based on the diversity of nitrogen sources, the possible formation pathways of HNMs from nitrate containing HA water were proposed during UV/chlor(am)ine disinfection in the presence of Br−. Results of this study indicated that UV/chloramine can reduce the formation and toxicity of HNMs efficiently.

Düşük SUVA Değerine Sahip Kaynak Sularında Farklı Dezenfeksiyon Senaryolarında Halonitrometan Oluşum Potansiyellerinin Değerlendirilmesi

The main objective of this project is to investigate the formation of halonitromethanes, an emerging class of disinfection by-products (DBPs) identified in drinking waters in recent years, which are currently unregulated but highly toxic. Halonitromethanes formation potentials tests were investigated under five different disinfection conditions in Egirdir Lake with low specific ultraviolet absorbance (SUVA) value. The results showed that ozone/chlorine formed the highest halonitromethanes followed by in the order of ozone/chloramine and chlorine only. When chloramine or ozone were used alone, the halonitromethanes concentration was below the minimum detection limits. The highest halonitromethanes was determined 2.5 µg/L for ozone /chlorine scenario and the lowest halonitromethanes concentration was 1.7 µg/L in ozone /chlorine scenario. In the ozone/chlorine scenario, a dramatic decrease for halonitromethane formation was detected from spring to winter. Chloropicrin has been the only measurable halonitromethanes species. In the correlation analysis between halonitromethanes and water quality parameters, the highest correlation was found between halonitromethanes and dissolved organic nitrogen. Besides dissolved organic nitrogen, different organic/inorganic compounds and disinfectants also contribute to the formation of halonitromethanes. These results can be used to control the formation of N-DBPs in the disinfection of low SUVA waters.

Efficient degradation of dimetridazole during the UV/chlorine process: Kinetics, pathways, and halonitromethanes formation

Dimetridazole (DMZ) is widely used as a veterinary antibiotic, but it is recalcitrant in the water environment. The residual of DMZ has raised widespread concern because of its harmful effects on human health and environmental safety. This work aimed to investigate the degradation of DMZ and the corresponding formation of halonitromethanes (HNMs) during the ultraviolet (UV)/chlorine process. The UV/chlorine process presented an excellent performance in DMZ degradation.The observed degradation rate constant of DMZ by UV/chlorine was 1.4 × 10−1 min−1. The hydroxyl radicals (·OH) and chlorine radicals (·Cl) were the predominant reactive species for DMZ degradation, and corresponding contributions were 79.8% and 13.7%, respectively. With the increase of free chlorine dosage, the degradation efficiency of DMZ firstly increased and then slightly decreased, while the formation of HNMs increased after 40 min UV/chlorine treatment. The higher degradation efficiency of DMZ was observed at acid circumstances, while higher HNMs formation was found at alkaline conditions due to base-catalyzed hydrolysis and less degradation of HNMs. The presences of Cl–, Br–, HCO3– and humic acid (HA) inhabited the degradation of DMZ. Furthermore, the possible degradation pathways of DMZ were proposed based on five intermediate products identified by UPLC/MS. Overall, the UV/chlorine was an efficient method for DMZ removal, but the formation of HNMs from DMZ should be evaluated before using UV/chlorine.

Impact of bromide ion on the formation and transformation of halonitromethanes from poly(diallyldimethylammonium chloride) during the UV/chlorine treatment

The formation of halonitromethanes (HNMs) is one of the major concerns when considering the application of UV/chlorine in the treatment of water containing bromide (Br-). The effects of Br- on the formation and transformation of HNMs from poly(diallyldimethylammonium chloride) during the UV/chlorine treatment were investigated in this study. The results showed that the incorporation of Br- was beneficial for producing reactive bromine species resulting in the changes of yields and dominant species of HNMs. With the increase of Br- concentration, the formations of brominated-HNMs (Br-HNMs) were promoted and the predominant species of HNMs were gradually converted from chlorinated-HNMs (Cl-HNMs) to brominated (chlorinated)-HNMs (Br(Cl)-HNMs) and Br-HNMs. Besides, the formation of HNMs increased with the increase of the ratio of Cl2:Br- and decreased with increasing pH from 6.0 to 8.0. According to the findings, the possible formation and transformation pathways of HNMs in the presence of Br- were proposed during the UV/chlorine treatment. Finally, it was proved that the effects of Br– on the formation and transformation of HNMs in real water were similar to that in deionized water. This study can help to understand the formation and transformation of HNMs better and develop effective measures for the control of HNMs (especially Br-HNMs) during the UV/chlorine treatment.

Formation of halonitromethanes from methylamine in the presence of bromide during UV/Cl2 disinfection

The UV/Cl2 process is commonly used to achieve a multiple-barrier disinfection and maintain residuals. The study chose methylamine as a precursor to study the formation of high-toxic halonitromethanes (HNMs) in the presence of bromide ions (Br−) during UV/Cl2 disinfection. The maximum yield of HNMs increased first and then decreased with increasing concentration of Br−. An excessively high concentration of Br− induced the maximum yield of HNMs in advance. The maximum bromine incorporation factor (BIF) increased, while the maximum bromine utilization factor (BUF) decreased with the increase of Br− concentration. The maximum yield of HNMs decreased as pH value increased from 6.0 to 8.0 due to the deprotonation process. The BUF value remained relatively higher under an acidic condition, while pH value had no evident influence on the BIF value. The maximum yield of HNMs and value of BUF maximized at a Cl2:Br− ratio of 12.5, whereas the BIF value remained relatively higher at low Cl2:Br− ratios (2.5 and 5). The amino group in methylamine was first halogenated, and then released into solution as inorganic nitrogen by the rupture of C-N bond or transformed to nitro group by oxidation and elimination pathways. The maximum yield of HNMs in real waters was higher than that in pure water due to the high content of dissolved organic carbon. Two real waters were sampled to verify the law of HNMs formation. This study helps to understand the HNMs formation (especially brominated species) when the UV/Cl2 process is adopted as a disinfection technique.

Formation and transformation of halonitromethanes from dimethylamine in the presence of bromide during the UV/chlorine disinfection

Halonitromethanes (HNMs) is a typical class of nitrogenous disinfection byproducts with high toxicity. The effect of Br− on the formation and transformation of HNMs from dimethylamine (DMA) during the ultraviolet (UV)/chlorine disinfection has been investigated in current study. Results reveal that only chloronitromethane, dichloronitromethane and trichloronitromethane (TCNM) could be found during the UV/chlorine disinfection. Whereas in the presence of Br−, nine species of HNMs could be observed simultaneously. When Br− concentration increased from 0 to 15.0 mg L−1, the predominant species of HNMs were gradually changed from TCNM to dibromonitromethane and tribromonitromethane, which contributed to 23.37% and 31.07% of total HNMs concentration at 15 mg L−1 Br−, respectively. The presence of Br− not only shifted the chlorinated-HNMs (Cl-HNMs) towards brominated-HNMs (Br-HNMs) but also affected the dominant species and total concentration of HNMs. When Br− concentration was 4.0 mg L−1, the formation of HNMs decreased with the increase of pH from 6.0 to 8.0 and increased with the increase of free chlorine and DMA. When free chlorine concentration rose from 0.25 to 1.1 mmol L−1, Br-HNMs were shifted to Br(Cl)-HNMs and then to Cl-HNMs. According to the findings, possible formation and transformation pathways of HNMs from DMA were proposed in the presence of Br− during the UV/chlorine disinfection. Finally, it was proved that the effect of Br− on the trend of HNMs in real water was similar to that in deionized water, but higher HNMs concentrations and delayed peak time were observed in real water. This study can provide the scientific evidence and fundamental data for the applications of UV/chlorine disinfection in the treatment of water containing Br−.

Formation and influence factors of halonitromethanes in chlorination of nitro-aromatic compounds

Halonitromethanes (HNMs), typical nitrogenous disinfection byproducts generated during disinfection of chlorination and chloramination, are widely detected in drinking water. This study investigated the formation of two dominant HNMs, trichloronitromethane (TCNM) and dichloronitromethane (DCNM) during chlorination/chloramination of ten nitro-aromatic compounds (NACs), including six aromatic mono-nitro compounds, three aromatic di-nitro compounds and one aromatic tri-nitro compound. The results showed that 2-nitrophenol and 3-nitrophenol could be the main precursors of TCNM and DCNM, and the yields of TCNM were one order of magnitude higher than that of DCNM. HNMs formation in chlorination was much higher than that in chloramination. However, HNMs were hardly produced during chlorination and chloramination of the other eight NACs. In chlorination of 2-nitrophenol, a pH range of 5.0–7.0 facilitated the TCNM formation. Besides, the concentration of ferric and manganese ions had different influences on TCNM formation. While the concentration ranges were 0–2 mg/L, ferric ion significantly decreased TCNM formation but manganese ion had not any influence on TCNM formation. Contrary to a previous finding, nitrite significantly reduced TCNM formation, which implied that nitrite has different effects on TCNM formation from various precursors. Moreover, dissolved organic matter (DOM, 0–5 mg/L as C) significantly influenced the formation of TCNM in chlorination of 2-nitrophenol despite the low TCNM formation in chlorination of DOM. Several chlorinated intermediates were detected and identified as mono/di/tri-chloro-2-nitrophenol during chlorination of 2-nitrophenol. It is effectively to reduce the production of TCNM and DCNM formation from chlorination of 2-nitrophenol by controlling disinfection conditions in drinking water.

Oxidative degradation of ranitidine by UV and ultrasound: identification of transformation products using LC-Q-ToF-MS

Environmental contextRanitidine, a widely prescribed antiulcer drug commonly found in surface waters, has been identified as an emerging contaminant due to its toxicity and the enhanced toxicity displayed by its transformation products. Mechanisms for the formation of ranitidine transformation products and their degradation pathways induced by UV oxidation processes are presented. This work provides insight into treatment processes to remove these toxic chemicals from environmental water bodies. AbstractThe transformation products (TPs) of pharmaceuticals formed during advanced oxidation processes (AOPs) are of great significance, but there are still gaps in our knowledge regarding the persistence of such compounds in the water matrices, their impact on human health and the applicability of such techniques during water treatment processes. Ranitidine (RAN), a highly prescribed gastrointestinal drug, has been widely detected in various surface waters and experiments, along with its TPs, which show enhanced toxicity. The present study analyses the TPs formed from the degradation of RAN in aqueous solution induced by three AOPs; namely UV-photolysis, UV/peroxodisulfate (PDS) and sonolysis. The degradations followed pseudo first-order kinetics, with removal efficiencies of 99.8, 100 and 98.8% after 60min under UV photolysis, UV/PDS, and sonolysis, respectively, with a corresponding decrease in chemical oxygen demand (COD) of 25, 100 and 75%. Structures of the main TPs were elucidated by using LC-Q-ToF-MS in positive mode, and possible degradation pathways are proposed which mainly involved C-N and C-H bond cleavage, hydroxylation and reduction of nitro groups. Possible mechanisms for the formation of the identified TPs (elucidated by using electrospray ionisation–collisionally induced dissociation) support their structural assignments. Seven out of the 11 TPs presented here (namely TP-1, TP-4, TP-5, TP-6, TP-7, TP-9 and TP-10) were not reported in previous studies of RAN using any other AOPs, while four (m/z 331, 270, 288 and 286) were found to retain the NO2 group, which might contribute to the formation of halonitromethanes (HNMs) during chlorination of drinking water. Interestingly, we identified an additional sonolysis product, TP-3, whose formation can only be rationalised by invoking ozone.

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.