Precursors Of Nitrogenous Disinfection Byproducts Research Articles

The ideal model for determination the formation potential of priority DBPs during chlorination of free amino acids

Amino acids (AAs) account for about 15–35% of dissolved organic nitrogen (DON), and are known as the important precursors of nitrogenous disinfection by-products (N-DBPs). Determining the formation potential (FP) of AAs to DBPs is used to reveal the key precursors of DBPs for further control, while the ideal method for N-DBPs FP of AAs during chlorination is not revealed. In this study, the ideal FP test models for five classes of priority DBPs during chlorination of four representative AAs (accounted for about 35% of total AAs) were analyzed. For haloaldehydes (HALs), haloketones (HKs), haloacetonitriles (HANs), haloacetamides (HAMs), and halonitromethanes (HNMs), their FPs during chlorination of four AAs were 0.1–13.0, 0.01–1.1, 0.1–104, not detectable (nd)-173, and nd-0.4 μg/mg, respectively. The FPs of priority DBPs had significant deviations between different FP test models and different tested AAs. For HALs, the model, whose chlorine dosage was determined by 15 × molar concentration of AAs [Cl (mM) = 15 × M](named: model II), was the ideal model. For HKs, model II was also the ideal FP test model for AAs with ≤3 carbons, while for AAs with 4 carbons, the model, whose chlorine dosage was determined by keeping the residual chlorine at 1 ± 0.2 mg/L after 24 h of reaction (named: model 4), was the ideal model. For HANs and HNMs, model 4 was the ideal FP test model for most of the studied AAs. The performance of HAMs during chlorination of amino acids was totally different from other P-DBPs, and model 3 was recommended to be the ideal model, in which chlorine dosage was determined by 3 × mass concentration of AAs [Cl (mg/L) = X × DOC]. This study is a reference that helps researchers select an ideal model for N-DBPs FP study of AAs.

Effect of micropollutants on disinfection byproducts and antibiotic resistance genes in drinking water in the process of biological activated carbon treatment

The biofilm stress response of biological activated carbon (BAC) was investigated under prolonged exposure to sulfadiazine and 2,4-Dichlorophenoxyacetic acid, simulating complex emerging organic contaminants (EOCs) that are mainly involved in the formation of nitrogenous disinfection byproducts (N-DBPs) and antibiotic resistance genes (ARGs). Under trace complex EOCs condition (2 µg/L), N-DBP precursors and abundance of ARGs increased significantly in BAC effluent. The total formation potential of haloacetonitriles (HANs) and halonitromethanes (HNMs) was 751.47 ± 2.98 ng/L, which was much higher than the control group (440.67 ± 13.38 ng/L without EOCs). Similarly, the relative abundance of ARGs was more than twice that in the control group. The complex EOCs induce excessive extracellular polymeric substance secretion (EPS), thereby causing more N-DBP precursors and stronger horizontal gene transfer. Metagenome analysis revealed that functional amino acid and protein biosynthesis genes were overexpressed compared to the control group, causing more EPS to be secreted into the external environment. Complex EOCs promote Cobetia, Clostridium, and Streptomyces dominance, contributing to the production of N-DBP precursors and ARGs. For the first time, in addition to the direct hazards of the EOCs, this study successfully revealed the indirect water quality risks of complex EOCs from the microbial stress response during BAC treatment. Synergistic regulation of EOCs and microorganisms is important for tap water security.

Removal of carbonaceous and nitrogenous disinfection by-product precursors in biological activated carbon process of drinking water: Is service life a pivotal factor?

Biological activated carbon (BAC) process is commonly used for drinking water treatment. Granular activated carbon (GAC) serving as the initial filter media can be converted to BAC with biofilm development during extending service life. Consequently, GAC/BAC effectiveness for disinfection by-product (DBP) precursors removal varies over service life. Effluents of full-scale ozonation and BACs operated for 1–3 months (1-month GAC), 4–6 months (4-month BAC), and about 7 years (7-year BAC) were analyzed. All BACs were efficient in fluorescence components removal, with decreasing efficiency in the order of 1-month GAC > 4-month BAC > 7-year BAC. Accordingly, reduction ratios of total DBPs concentration formed in post-chlorination dropped from 39% to 21% and 8% by BACs with different ages. Due to varied toxic potencies of DBPs, toxicities reduction was not completely related to DBPs concentration reduction. Haloacetonitriles (HANs) group accounted for small proportion of DBPs concentration but drove both of cytotoxicity and genotoxicity. Hence, the precursor removals of carbonaceous (C-) DBPs and nitrogenous (N-) DBPs were further compared in detail. 1-month GAC exhibited relatively higher effectiveness for protein-like components removal than humic-like component removal, for HANs formation reduction than trihalomethanes (THMs) formation reduction, and for HANs cytotoxicity reduction than THMs cytotoxicity reduction. A similar pattern was observed for 4-month BAC, while 7-year BAC exhibited the opposite pattern. Given the complexity of real water, this full-scale study provides valuable insights into the differences in precursor removals of C-DBPs and N-DBPs by BACs with different ages, which is critical for advancing our understanding of BAC process.

Relating algal-derived extracellular and intracellular dissolved organic nitrogen with nitrogenous disinfection by-product formation

The dissolved organic nitrogen (DON) pool from algal-derived extracellular and intracellular organic matter (EOM and IOM) comprises proteins, peptides, free amino acids and carbohydrates, of which, proteins can contribute up to 100% of the DON. Previous reports of algal-derived DON character have focused on bulk properties including concentration, molecular weight and hydrophobicity. However, these can be similar between algal species and between the EOM and IOM even when the inherent molecular structures vary. A focus on bulk character presents challenges to the research on algal-derived nitrogenous-disinfection by-product (N-DBP) formation as N-DBP formation is sensitive to the changes in molecular structure. Hence, the main aim of this study was to characterize algal EOM and IOM-derived DON, specifically proteinaceous-DON, using a combination of bulk and molecular characterization techniques to enable a more detailed exploration of the relationship between the character of algal-derived proteins and the N-DBP formation potential. DON from the EOM and IOM of four commonly found algae and cyanobacteria in natural waters were evaluated, namely Chlorella vulgaris, Microcystis aeruginosa, Dolichospermum circinale, and Cylindrospermopsis raciborskii. It was observed that 77-96% of total DON in all EOM and IOM samples was of proteinaceous origin. In the proteins, DON concentrations were highest in the high molecular weight fraction of IOM-derived bulk proteins (0.13–0.75 mg N L−1) and low to medium molecular weight fraction of EOM-derived bulk proteins (0.15–0.63 mg N L−1) in all species. Similar observations were also made via sodium dodecyl sulphate polyacrylamide gel electrophoresis and liquid chromatography-high resolution mass spectrometry. Solid-state 15N nuclear magnetic resonance (NMR) spectroscopy of the EOM and IOM revealed the existence of common aliphatic and heterocyclic N-groups in all samples, including a dominant 2° amide peak. Species dependent variability was also observed in the spectra, particularly in the EOM; e.g. nitro signals were found only in the Cylindrospermopsis raciborskii EOM. Dichloroacetonitrile (DCAN) and N-nitrosamine concentrations from the EOM of the species evaluated in this study were lower than the guideline limits set by regulatory agencies. It is proposed that the dominant 2° amide in all samples decreased N-DBP formation upon chlorination. For chloramination, the presence of nitro groups and aliphatic and heterocyclic N-DBP precursors could cause variable N-nitrosamine formation. Compared to non-algal impacted waters, algae-laden waters are characterised by low organic carbon: organic nitrogen ratios of ∼7–14 and elevated DON and protein concentrations. Hence, relying only on bulk characterization increases the perceived risk of N-DBP formation from algae-laden waters.

Exploring the impacts of service life of biological activated carbon on dissolved organic nitrogen removal

The biological activated carbon (BAC) process has been widely used in drinking water treatment to improve the removal of pollutants, including the precursors of nitrogenous disinfection byproducts (N-DBPs). Nevertheless, old BAC filter effluent DON concentration is heightened, increasing the highly toxic N-DBPs formation potential. Herein, the variation of dissolved organic nitrogen (DON) was comprehensively explored during one backwashing cycle, focusing on four BAC age (0.3, 2, 5, and 10 years) for BAC filters in drinking water. Comparatively, the removal rate of DON by four BAC followed the order 0.3-yr BAC (39.69%–66.96%) >2-yr BAC (10.10%–39.78%) >5-yr BAC (−4.18%-29.63%)>10-yr BAC (−20.88%-19.87%). When at day 7 after backwashing, 10-yr BAC filter effluent increased at least 13.71% of DON and considerably elevated the N-DBPs formation potential, which was attributed to the ultimate production of more various proteins/amino sugars-like compounds by microbes. In comparisons of microbial community between all BAC samples, Rhizobials were more prevalent in 10-yr BAC and could produce microbe-derived DON associated with amino acids. Moreover, microbes regulated metabolic pathways, including amino acid biosynthesis, TCA cycle, purine metabolism, and pyrimidine metabolism, to enhance the adaptive cellular machinery in response to environmental stressors, and therefore accelerated microbial secretion of microbe-derived DON. Structural equation model (SEM) analysis investigated that BAC age had bio-effects on N-DBPs formation potential, which were delivered via the linkage of " BAC age, microbial community, microbial metabolism, and DON molecular characteristics”. Our findings demonstrate the necessity of reconsidering the feasibility of BAC filters for long-time operation, which has implications for future N-DBPs precursors control in drinking water.

Transfer organic chloramines to monochloramine using two-step chlorination: A method to inhibit N-DBPs formation in algae-containing water treatment.

Organic chloramines formed in chlorination of algae-containing water are typical precursors of nitrogenous disinfection byproducts (N-DPBs). The objective to simultaneously enhance the removal efficiency of organic chloramines and control DBP formation remains a challenge. In this study, we report a two-step chlorination strategy for transferring organic chloramines to monochloramine based on the decomposition mechanisms of mono- and di-organic chloramines, which could limit organic chloramines formation and inhibit N-DBPs formation. We demonstrated that two-step chlorination could decrease the organic chloramines formation by nearly 50% than conventional one-step chlorination. Furthermore, two-step chlorination not only blocked the pathway that organic chloramines decomposed to nitriles, but also led to the conversion of organic chloramines to monochloramine. During two-step chlorination of algal organic matter, the organic chloramine transfer proportion decreased by 6.5% and the monochloramine transfer proportion increased by 17.0%. The N-DBP formation, especially haloacetonitriles (HANs), decreased significantly as organic nitrogen became inorganic nitrogen (monochloramine) in two-step chlorination. This work further clarified the process from algal organic matter to N-DBPs, which could expand our understanding of algae-derived organic chloramines removal and DBPs control.

Enhanced formation of 2,6-dichloro-4-nitrophenol during chlorination after UV/chlorine process: Free amino acid versus oligopeptide

Halonitrophenols (HNPs) are emerging aromatic nitrogenous disinfection by-products (N-DBPs) with high cyto- and genotoxicity. However, limited information is available regarding the formation mechanism of HNP during chlorination after the UV/chlorine process. In the past, dissolved organic nitrogen (DON) constitutes a vast array of N-DBP precursors due to its heterogeneous nature. Amino acids (AAs) are an important class of DON in water, where combined AAs (i.e., peptides and proteins) make up a larger identifiable section. In this study, three AAs including free tyrosine (Tyr) and two oligopeptides (i.e., tyrosine-alanine (Tyr-Ala) and tyrosine-tyrosine-tyrosine (Tyr-Tyr-Tyr)) were selected as model AAs to evaluate the effect of the UV/chlorine process on the formation of 2,6-dichloro-4-nitrophenol (DCNP). We found an enhanced formation of DCNP after the UV/chlorine process in comparison with direct chlorination, which indicated the nitrogen sources in AAs can contribute to the formation of HNPs. The presence of NO• in the UV/chlorine process was demonstrated by electron spin-resonance spectroscopy (ESR) test. The effects of three typical factors (i.e., UV fluence, pH, and Cl2/AA) on the formation of DCNP in the UV/chlorine process were investigated to optimize parameters to minimize the formation of HNPs. Furthermore, it was observed that oligopeptides exhibited higher yields of DCNP than free Tyr. Based on this, we propose a possible formation pathway of DCNP from 2 oligopeptides to elucidate the formation mechanisms more intuitively. We observed and confirmed a convertible tendency from HNPs to aliphatic DBPs (e.g., trichloronitromethane). Overall, this study provided a reliable theoretical basis for a comprehensive understanding of the precursors, formation mechanisms and control methods of HNPs.

Reaction of Amino Acids with Ferrate(VI): Impact of the Carboxylic Group on the Primary Amine Oxidation Kinetics and Mechanism.

Ferrate (Fe(VI)) is a novel oxidant that can be used to mitigate disinfection byproduct (DBP) precursors. However, the reaction of Fe(VI) with organic nitrogen, which is a potential precursor of potent nitrogenous DBPs, remains largely unexplored. The present work aimed to identify the kinetics and products for the reaction of Fe(VI) with primary amines, notably amino acids. A new kinetic model involving ionizable intermediates was proposed and can describe the unusual pH effect on the Fe(VI) reactivity toward primary amines and amino acids. The Fe(VI) oxidation of phenylalanine produced a mixture of nitrile, nitrite/nitrate, amide, and ammonia, while nitroalkane was an additional product in the case of glycine. The product distribution for amino acids significantly differed from that of uncarboxylated primary amines that mainly generate nitriles. A general reaction pathway for primary amines and amino acids was proposed and notably involved the formation of imines, the degradation of which was affected by the presence of a carboxylic group. In comparison, ozonation led to higher yields of nitroalkanes that could be readily converted to potent halonitroalkanes during chlor(am)ination. Based on this study, Fe(VI) can effectively mitigate primary amine-based, nitrogenous DBP precursors with little formation of toxic halonitroalkanes.

Contribution of filtration and photocatalysis to DOM removal and fouling mechanism during in-situ UV-LED photocatalytic ceramic membrane process

The use of ceramic membranes and ultraviolet light-emitting diodes (UV-LEDs) has advanced the application of photocatalytic membrane for water treatment. We systematically evaluated the contribution of filtration and photocatalysis to dissolved organic matter (DOM) removal and fouling mechanism during in-situ UV-LED photocatalytic ceramic membrane filtration. The results showed that physical rejection primarily led to removal of 4–15 kDa molecules and photocatalysis further increased the removal of 1-4 kDa molecules, causing small sized microbial humic-like or protein-like materials in the permeate. In-situ UV-LED photocatalysis had an excellent effect on membrane fouling mitigation regardless of DOM sources. The dominant fouling mechanism changed from partial blockage to gel layer formation with increasing Ca2+ concentration but did not change with UV treatment. Correlation analysis revealed that the removal of 1-4 kDa molecules contributed to the mitigation of both reversible and irreversible fouling resistance, and the small molecules were the major cause of irreversible fouling resistance. Removal of 1–4 kDa terrestrial humic acid-like contributed to the pore blockage mechanism for synthetic water. Removal of 4-15 kDa protein-like materials was closely correlated to the pore blockage mechanism for real water. Trihalomethanes (THMs) and haloacetic acids (HAAs) formation potential (FP) were both significantly reduced after photocatalytic ceramic membrane process, but precursors of nitrogenous disinfection by-products (N-DBPs) with high toxicity were not removed by filtration or by photocatalysis, which deserves attention. Membrane rejection made higher contribution to better DBPFP control than photocatalysis. This study provides novel insights into the impact of UV-LED on DOM removal, DBPFP control and fouling mitigation, promoting the development of photocatalytic ceramic membrane filtration.

Dissolved organic nitrogen derived from wastewater denitrification: Composition and nitrogenous disinfection byproduct formation

Microbially derived dissolved organic nitrogen (mDON) is a major fraction of effluent total nitrogen at wastewater treatment plants with enhanced nutrient removal, which stimulates phytoplankton blooms and formation of toxic nitrogenous disinfection by-products (N-DBPs). This study identified denitrifiers as major contributors to mDON synthesis, and further revealed the molecular composition, influential factors and synthetic microorganisms of denitrification-derived mDON compounds leading to N-DBP formation. The maximum mDON accumulated during denitrification was 8.92% of converted inorganic nitrogen, higher than that of anammox (4.24%) and nitrification (2.76%). Sodium acetate addition at relatively high C/N ratio (5−7) favored mDON formation, compared with methanol and low C/N (1−3). Different from acetate, methanol-facilitated denitrification produced 13–69% more lignin-like compounds than proteins using Orbitrap LC-MS. The most abundant N-DBPs formed from denitrification-derived mDON were N-nitrosodibutylamine and dichloroacetonitrile (13.32 μg/mg mDON and 12.21 μg/mg mDON, respectively). Major amino acids, aspartate, glycine, and alanine were positively correlated with typical N-DBPs. Biosynthesis and degradation pathways of these N-DBP precursors were enriched in denitrifiers belonging to Rhodocyclaceae, Mycobacteriaceae and Hyphomicrobiaceae. As intensive disinfection is applied at worldwide wastewater treatment plants during COVID-19, carbon source facilitated denitrification should be better managed to reduce both effluent inorganic nitrogen and DON, mitigating DON and N-DBP associated ecological risks in receiving waters.

Transformation of dissolved organic matter during biological wastewater treatment and relationships with the formation of nitrogenous disinfection byproducts

Nitrogenous disinfection byproducts (N-DBPs) can be produced from dissolved organic matter (DOM) during the disinfection of secondary wastewater effluent. This study examined the transformation of DOM and the abatement of N-DBP precursors during different types of biological wastewater treatment (e.g., anaerobic/anoxic/oxic activated sludge processes and membrane bioreactor) using high-performance size exclusion chromatography (HPSEC) with dissolved organic carbon, UV, and fluorescence detectors. DOM with molecule weight (MW) larger than 3 kDa and protein-like substances smaller than 0.3 kDa was effectively bio-transformed, whereas DOM fractions with MW in the range of 0.3–3 kDa were the most bio-refractory. Complete nitrification was beneficial to the removal of small amino sugar-like and protein-like molecules (< 0.3 kDa). Haloacetonitrile (HAN) precursors were recalcitrant to biological treatment with a median removal of 17%. Halonitromethane (HNM) and N-nitrosamine (NA) precursors tended to be effectively removed in complete nitrification conditions. The abundance of low-molecular-size protein-like substances (< 0.3 kDa) was significantly correlated with the formation potential of HNM, NA, and total N-nitrosamine (TONO) in post-chloramination (r = 0.81, 0.62, and 0.68, respectively, p < 0.01). This study improved the understanding of DOM transformation and the removal of N-DBPs precursors in wastewater treatment and pointed out the benefit of provision of complete nitrification in removing low-molecular-size protein-like substances and NA and HNM precursors.

Fermentation liquid as a carbon source for wastewater nitrogen removal reduced nitrogenous disinfection byproduct formation potentials of the effluent

Sludge alkaline fermentation liquid (SAFL) is an alternative to sodium acetate (NaAc) in enhancing wastewater nitrogen removal. Upon SAFL addition, dissolved organic nitrogen (DON) can be externally introduced or biologically synthesized during nitrogen removal, which is an important precursor to toxic nitrogenous disinfection by-products (N-DBPs). This study aims to evaluate the effects of different carbon source addition on effluent DON concentration, composition, and N-DBP formation potentials. A lab-scale A2O system treating real municipal wastewater was operated with NaAc or SAFL as external carbon sources. DON molecules and potential N-DBP precursors were identified by Orbitrap mass spectrometry. Subsequently, major microorganisms contributing to DON biosynthesis were suggested based on metagenomics. It was found that effluent DON was higher with SAFL as the carbon source than NaAc (1.51 ± 0.24 v.s. 0.56 ± 0.08 mg N/L, p < 0.05). Nevertheless, dichloroacetonitrile and nitrosamine formation potentials (7.14 ± 1.02 and 1.57 ± 0.07 μg/mg DON-N, respectively) of the effluent with SAFL addition were 42.79 ± 2.42% and 54.89 ± 1.70% lower than those of NaAc. Protein- and lignin-like compounds were the most abundant DON molecules in the effluent, where alanine, glycine and tyrosine were important precursors to N-DBPs. Azonexus and Flavobacterium spp. were positively correlated with these precursors, and possessed key genes involved in precursor synthesis. SAFL is a promising carbon source, not only for achieving efficient inorganic nitrogen and DON removals, but also for reducing N-DBP formation potentials of chlorinated effluent.

Formation of disinfection byproducts from chlorinated soluble microbial products: Effect of carbon sources in wastewater denitrification processes

Carbon sources are crucial for biological denitrification in wastewater treatment that significantly affects the production of soluble microbial products (SMPs), thereby affecting the formation of disinfection byproducts (DBPs) during subsequent chlorination. However, the effect of carbon sources on DBPs formation has not been studied. In this work, sodium acetate, sodium lactate, and glucose were used as carbon sources, and denitrifying SMPs derived from different carbon sources were used as DBPs precursors to investigate the formation potential (FP) of 16 carbonaceous DBPs and 19 nitrogenous DBPs. Results showed that the carbonaceous DBPs FP of SMPs derived from acetate, lactate, and glucose were 502.1–584.3, 250.3–288.9, and 374.7–439.1 μg/L, respectively, and the nitrogenous DBPs FP were 19.1–45.6, 12.8–21.9, and 7.9–9.0 μg/L, respectively. After chlorination, the genotoxicity of SMPs measured by the SOS/umu test was also evaluated with 364 ng 4-NQO/L for acetate, 212 ng 4-NQO/L for lactate, and 138 ng 4-NQO/L for glucose. Based on X-ray photoelectron spectroscopy, chemical structures of SMPs were characterized, and their relationship with DBPs FP was investigated to explain the mechanism of DBPs formation. Aromatic C and C-O were found to be the major precursor structures to form carbonaceous DBPs, and their lowest proportions in lactate-derived SMPs caused the lowest carbonaceous DBPs FP. Organic nitrogen, including aromatic N, amide/peptide N, and primary amine N, was the precursor of nitrogenous DBPs. The lowest concentration of dissolved organic nitrogen for glucose-derived SMPs caused the lowest nitrogenous DBPs FP and genotoxicity. Glucose may be a better choice among the three carbon sources in terms of reducing genotoxicity.

Study on the Control of Dichloroacetonitrile Generation by Two-Point Influent Activated Carbon-Quartz Sand Biofilter.

Aiming at the problem of highly toxic Nitrogenous disinfection by-products (N-DBPs) produced by disinfection in the process of drinking water, two-point influent activated carbon-quartz sand biofilter, activated carbon-quartz sand biofilter, and quartz sand biofilter are selected. This study takes typical N-DBPs Dichloroacetonitrile (DCAN) as the research object and aromatic amino acid Tyrosine (Tyr), an important precursor of DCAN, as the model precursor. By measuring the changes of conventional pollutants in different biofilters, and the changes of Tyr, the output DCAN formation potential of the biofilters, this article investigates the control of DCAN generation of the two-point influent activated carbon-quartz sand biofilter. The results show that the average Tyr removal rate of the three biofilters during steady operation is 73%, 50%, and 20%, respectively, while the average effluent DCAN generation potential removal rate is 78%, 52%, and 23%, respectively. The two-point influent activated carbon-sand biofilter features the highest removal rate. The two-point water intake improves the hypoxia problem of the lower filter material of the activated carbon-quartz sand biofilter, and at the same time, the soluble microbial products produced by microbial metabolism can be reduced by an appropriate carbon sand ratio, which is better than traditional quartz sand filters and activated carbon-quartz sand biofilters in the performance of controlling the precursors of N-DBPs.

Removal performance and mechanism of typical amino acids in water by the peroxymonosulfate/Fe3O4 nanoparticles

Abstract Dissolved organic nitrogen (DON) as precursors of nitrogenous disinfection byproducts (N-DBPs) has become a serious issue for drinking water treatment. Here, Fe3O4/peroxymonosulfate (PMS) system was used to examine the amino acid removal and formation of N-DBPs in the system and the corresponding mechanisms. Results showed a remarked variation in removal efficiency of three typical amino acids, i.e., glutamate (78%), histidine (53%) and phenylalanine (27%) in Fe3O4/PMS system at optimum conditions (0.1 g/L Fe3O4, 1.5 mM PMS, 1 h). Notably, Fe3O4/PMS treatment led to dichloroacetonitrile (DCAN) formation caused by the chlorination of glutamate, phenylalanine and histidine being reduced by 53.3%, 9.7% and 41.9%, respectively. The degradation and subsequent N-DBPs formation in the Fe3O4/PMS system mainly depended on the types and properties of the amino acids. The formation of dichloroacetamide (DCAcAm) exhibited different trends, which may be due to the different R group structure of the three amino acids and the special aromaticity of the imidazole ring in the histidine side chain that facilitates its quick electrophilic substitution and ring-opening reaction. This study highlights that the Fe3O4/PMS system is a promising strategy to remove DON and efficiently eliminate N-DBPs formation in the drinking water treatment process depending on the amino acid type.

Removal Behavior of Protein-like Dissolved Organic Matter During Different Water Treatment Processes in Full-Scale Drinking Water Treatment Plants

Protein-like dissolved organic matter (pDOM), which is ubiquitous in natural waters, is a critical precursor of nitrogenous disinfection byproducts. Recently, the control and elimination of pDOM have been a growing concern during drinking water treatment processes. In this study, a high-performance size exclusion chromatography system coupled with photo-diode array, fluorescence detector, and online organic carbon detector (HPSEC-PDA/FLD/OCD) was used to determine the removal behaviors of different-sized pDOM from two full-scale drinking water treatment plants (DWTPs). Coagulation and activated carbon adsorption were selected for bench-scale experiments to further assess the removal behavior of pDOM during conventional water treatment processes. The results showed that different-sized pDOM fractions exhibited different removal characteristics. Pre-oxidation can effectively remove some tyrosine-like and tryptophan-like components with high MW, and as the oxidization effect was enhanced, more high MW fractions decomposed into low MW ones. Conversely, some aliphatic pDOM fractions in high MW (e.g., aliphatic proteins) were not subject to pre-oxidation removal. The coagulation-sedimentation unit was efficient in removing high MW fractions, specifically tryptophan-like fractions. Additionally, some pDOM components may be released during coagulation. pDOM with low MW and high hydrophobicity were easily removed during activated carbon filtration. However, long-term operation of the activated carbon filter may breed microorganisms, resulting in the partial release of pDOM fractions. Moreover, UV disinfection processes promoted the degradation of low MW pDOM components. Due to the complex water quality and uncontrollable microbial activities, the aforementioned water treatment units did not exhibit a synergistic effect on pDOM removal. In comparison with humic-like substances, pDOM was susceptible to water quality changes, and its removal was limited in the surveyed DWTPs. Therefore, DWTPs must strengthen pDOM monitoring in influent and effluent and adjust the operating parameters of different treatment units in a timely manner. Moreover, the combination of advanced water treatment processes, such as ozone-biological activated carbon process and nanofiltration, should also be considered to strictly control pDOM component removal.

Formation of nitrogenous disinfection by-products (N-DBPs) in drinking water: emerging concerns and current issue

Nitrogenous disinfection by-product (N-DBPs) has always been one of the most concerned disinfection by-products (DBPs) in recent years. The toxicity of regulated DBPs is generally less than that of N-DBPs, which have been widely detected in finished drinking water. Despite the fact that N-DBPs are highly toxic, there are currently no N-DBPS species officially regulated by governments around the world. This paper provides a review of the formation mechanism and precursors of nitrogen-containing disinfection by-products in drinking water treatment. Also, the spcieces and inducing factors of N-DBPs were summarized. The data were mainly collected from 2000-2002 and 2006-2007 US Survey in effluents of US WTPs. Because nitrogen source is a prerequisite for the formation of nitrogen-DBP in drinking water, the occurrence of N-DBPS may increase due to the influence of sewage and algae blooms on water sources. Chloramine disinfection are used in most of developed countries for preferred secondary disinfection to reduce the formation of chlorine-related by-products, but this increases the formation potential of N-DBPs. Furthermore, the safety control of N-DBPs and suggestions for the further exploration of for efficient drinking water are discussed. Coagulation and filtration are not very effective in removing precursors (such as amino acids) of N-DBPs and the precursors need to be removed before disinfection.

Release of nitrogenous disinfection by-product precursors in algae-laden water under UV radiation

Abstract Nitrogen-containing organic compounds and nitrogenous disinfection by-products (N-DBPs) in drinking water have attracted attention in the field of water treatment. Metabolites released during algae growth contain a variety of organic nitrogen species, which are called N-DBP precursors. The aim of this paper is to elucidate how N-DBP precursors are released under UV radiation, as well as investigate the variations of their chemical properties. The results show that through UV radiation, the physiological metabolism of algal cells was disordered and the properties of their metabolites were changed. The dissolved organic nitrogen (DON) compound concentration increased rapidly from 5.38 at the beginning to 11.11 mg/L after 30 min of radiation, and then increased steadily from 11.11 to 23.71 mg/L during a further 210 min of radiation. Derivation results of the curves for algae and DON concentration variations shows that when 1 × 1010 algal cells were destroyed, 8.31 mg DON was released into the solution during the first 30 min of radiation. Low dose UV radiation brought a slight decline of the specific N-DBP formation potential due to changes in the extracellular organic matter (EOM) structure without destroying the algal cells, which was conducive to controlling the formation potential of N-DBPs. Long-time UV radiation can bring a significant increase in N-DBP formation potential. After 4 hours of ultraviolet radiation, the total formation potential of N-DBPs in the solution increased from about 84.9 μg/L to about 213.5 μg/L, 2.5 times higher than the initial solution. The N-DBP formation potential increases obviously during the first 10–30 min UV radiation, and then decreases slightly in the subsequent 30–240 min radiation.

Precursors of typical nitrogenous disinfection byproducts: Characteristics, removal, and toxicity formation potential

The emergence of nitrogenous disinfection byproducts (N-DBPs) in drinking water has become a widespread concern. In this study, dichloroacetonitrile (DCAN), dicholoacetamide (DCAcAm) and trichloronitromethane (TCNM) were chosen as representatives to clarify the characteristics of N-DBP precursors in the raw waters of Taihu Lake, the Yangtze River, and Gaoyou Lake. Removal of DCAN and DCAcAm precursors must focus on nonpolar and positively charged organics, but more attention should be paid to micromolecular, polar and non-positively charged organics as TCNM precursors. Compared to molecular weight (MW) and hydrophilicity fractionation, polarity and electrical classification have higher selectivity to intercept N-DBP precursors. The properties of N-DBP precursors are relatively fixed and traceable in water systems, which could contribute to their targeted removal. Based on investigation of their characteristics, the removal efficiency and preferences of organic precursors under different processes were studied in three drinking water treatment plants (DWTPs). The TCNM precursors produced in preozonation can be effectively removed during coagulation. The cumulative removal efficiency of conventional processes on N-DBP precursors was approximately 20–30%, but O3/BAC process improved removal by about 40%. The key to improving the removal efficiency of N-DBP precursors by O3/BAC is that it can significantly remove low-MW, nonpolar, positively charged, hydrophilic and transphilic organics. In combined toxicity trials, both cytotoxicity and genotoxicity showed a synergistic effect when DCAN, DCAcAm, and TCNM coexisted, which means that low-level toxicity enhancement in the actual water merits attention. DCAN precursors dominated in the toxicity formation potential (TFP), followed by TCNM precursors. In addition, the removal rate of total N-DBP precursors may be higher than that of TFP, leading to overly optimistic evaluation of precursor removal in water treatment practice. Therefore, the removal effect on TFP must also be considered.

Impact of backwash on biofiltration-related nitrogenous disinfection by-product formation

Previous studies have reported that biofilm extracted from full-scale biofilters can serve as nitrogenous disinfection by-product (N-DBP) precursors. Detached biofilm materials could escape during filter ripening and form N-DBP upon chloramination. This study examined the potential breakthrough of biofilm and N-DBP precursors during filter ripening at two water treatment plants (WTPs). The presence of biofilm material in aqueous samples was estimated by total adenosine triphosphate (tATP) levels; N-DBP formation potential (FP) tests were conducted under uniform formation conditions to quantify N-nitrosodimethylamine (NDMA) and haloacetonitrile (HAN4) precursors. While tATP peaks in filter effluent were observed post backwash at both WTPs, temporary increases of effluent NDMA FP were only observed during filter ripening where particle-associated NDMA precursors served as the dominant contributor. Overall, biofilters examined in this study demonstrated a consistent removal of NDMA FP regardless of the filter ripening process.