Degrading surface-water-based natural organic matter and mitigating haloacetonitrile formation during chlorination: Comparison of UV/persulfate and UV/hydrogen peroxide pre-treatments

Haloacetonitriles (HANs) are unregulated disinfection by-products that are more toxic than regulated species. Therefore, efficient decomposition of HAN precursors prior to disinfection is crucial for allaying the potential HAN-induced health risks. This study investigated the key roles of ultraviolet-activated persulfate (UV/PS) treatment in alleviating HAN formation. The effects of UV/PS treatment were evaluated by correlating with the characteristics of organic matter in surface water and comparing with conventional UV/H2O2 treatment. Upon irradiating raw water samples and a Suwannee River humic acid solution spiked with 10 mM PS or H2O2 with 254 nm UV light, UV/PS treatment was found to be more potent than UV/H2O2 in mitigating the HAN production and degrading organic substances; moreover, UV/PS treatment effectively decreased the dissolved organic nitrogen (DON) content. In contrast, UV/H2O2 treatment did not induce any noticeable reduction in DON level. Furthermore, both UV/PS and UV/H2O2 treatments reduced the dichloroacetonitrile (DCAN) formation potential (FP), leading to strong correlations with the degradation of aromatic and humic-acid-like compounds. Notably, UV/PS treatment efficiently decreased the FP of bromochloroacetonitrile (BCAN) and dramatically reduced that of dibromoacetonitrile (DBAN) after a sharp increase; however, UV/H2O2 treatment gradually increased the DBAN-FP. Bromide was activated by sulfate radicals during UV/PS treatment, negatively correlating with the BCAN-FP and DBAN-FP, indicating that the formation of reactive bromine species increased the DBAN-FP; however, excessive oxidation possibly led to the recovery of inorganic bromine for decreasing the BCAN-FP and DBAN-FP. Additionally, UV/PS treatment effectively suppressed toxicity owing to its high reduction rate for brominated HANs; in contrast, UV/H2O2 treatment resulted in less significant BCAN and DBAN reductions, leading to minimal net reduction in toxicity. Overall, UV/PS treatment was remarkably effective at diminishing the toxicity of brominated HANs, underscoring its potential to mitigate drinking-water-related health risks.

Formation of halogenated forms of bisphenol A (BPA) in water: Resolving isomers with ion mobility - mass spectrometry and the role of halogenation position in cellular toxicity

Halogenated BPA (XBPA) forms resulting from water chlorination can lead to increased toxicity and different biological effects. While previous studies have reported the occurrence of different XBPAs, analytical limitation have hindered the analysis and differentiation of the many potential isomeric forms. Using online solid-phase extraction - liquid chromatography - ion-mobility - high-resolution mass spectrometry (OSPE-LC-IM-HRMS), we demonstrated a rapid analysis method for the analysis of XBPA forms after water chlorination, with a total analysis time of less than 10 min including extraction and concentration and low detection limits (∼5-80 ng/L range). A multi in-vitro bioassay testing approach for the identified products revealed that cytotoxicity and bioenergetics impacts were largely associated with the presence of halogen atoms at positions 2 or 2' and the overall number of halogens incorporated into the BPA molecule. Different XBPA also showed distinct impacts on oxidative stress, peroxisome proliferator-activated receptor gamma - PPARγ, and inflammatory response. While increased DNA damage was observed for chlorinated water samples (4.14 ± 1.21-fold change), the additive effect of the selected 20 XBPA studied could not explain the increased DNA damage observed, indicating that additional species or synergistic effects might be at play.

Assessing the impact of low organic loading on effluent safety in wastewater treatment: Insights from an activated sludge reactor study

In this study, an organic loading (OL) of 300 mg/(L d) was set as the relative normal condition (OL-300), while 150 mg/(L d) was chosen as the condition reflecting excessively low organic loading (OL-150) to thoroughly assess the associated risks in the effluent of the biological wastewater treatment process. Compared with OL-300, OL-150 did not lead to a significant decrease in dissolved organic carbon (DOC) concentration, but it did improve dissolved organic nitrogen (DON) levels by ∼63 %. Interestingly, the dissolved organic matter (DOM) exhibited higher susceptibility to transformation into chlorinated disinfection by-products (Cl-DBPs) in OL-150, resulting in an increase in the compound number of Cl-DBPs by ∼16 %. Additionally, OL-150 induced nutrient stress, which promoted engendered human bacterial pathogens (HBPs) survival by ∼32 % and led to ∼51 % increase in the antibiotic resistance genes (ARGs) abundance through horizontal gene transfer (HGT). These findings highlight the importance of carefully considering the potential risks associated with low organic loading strategies in wastewater treatment processes.

Synergistic effects of trace sulfadiazine and corrosion scales on disinfection by-product formation in bulk water of cast iron pipe

The effects of trace sulfadiazine (SDZ) and cast-iron corrosion scales on the disinfection by-product (DBP) formation in drinking water distribution systems (DWDSs) were investigated. The results show that under the synergistic effect of trace SDZ (10 μg/L) and magnetite (Fe3O4), higher DBP concentration occurred in the bulk water with the transmission and distribution of the drinking water. Microbial metabolism-related substances, one of the important DBP precursors, increased under the SDZ/Fe3O4 condition. It was found that Fe3O4 induced a faster microbial extracellular electron transport (EET) pathway, resulting in a higher microbial regrowth activity. On the other hand, the rate of chlorine consumption was quite high, and the enhanced microbial EET based on Fe3O4 eliminated the need for microorganisms to secrete excessive extracellular polymeric substances (EPS). More importantly, EPS could be continuously secreted due to the higher microbial activity. Finally, high reactivity between EPS and chlorine disinfectant resulted in the continuous formation of DBPs, higher chlorine consumption, and lower EPS content. Therefore, more attention should be paid to the trace antibiotics polluted water sources and cast-iron corrosion scale composition in the future. This study reveals the synergistic effects of trace antibiotics and corrosion scales on the DBP formation in DWDSs, which has important theoretical significance for the DBP control of tap water.

Rainwater extracting characteristics and its potential impact on DBPs generation: A case study

Frequent extreme precipitation events due to global warming can lead to large amounts of pollutants entering source water bodies via surface runoff and wet deposition, thus posing a threat to water supply security. In order to better understand the source characteristics and leaching mechanisms of rainwater dissolved organic matter (DOM), as well as its disinfection by-products formation potential (DBPsFP) during disinfection processes, rainwater samples were collected and extracting experiments were conducted. Three components were identified in rainwater through Parallel factor (PARAFAC) analysis, which were microbial humic-like component C1 (63.1 %), protein (tryptophan-like) component C2 (28.9 %), marine or terrestrial humic-like component C3 (8.1 %). The average molecular weight of rainwater fractions was ordered: hydrophobic neutral (HON) < hydrophobic bases (HOB) < hydrophobic acidic (HOA) < hydrophilic (HIS). The HOA and HON fractions of rainwater were the dominant precursors of trihalomethanes (THMs), while the rainwater HON fraction and hydrophilic fraction were the main precursor of haloacetic acids (HAAs) and trihloroacetonitrile (TCAN), respectively. Subsoil extracts had a higher concentration of dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) than topsoil extracts. Partial least squares path modeling (PLS-PM) demonstrated that the extraction temperature was the dominant factor affecting the abundance of DOM in the topsoil extracts (R2 = 0.28), while the extraction time accounted more for the abundance of fluorescence substance and physicochemical indices in the subsoil extracts (R2 = 0.23 and 0.32, respectively). These results provide key information for controlling the impacts of global warming, in particular the risk of water sources being heavily contaminated by request rainfalls.

Tailoring the topology of ZIF-67 metal-organic frameworks (MOFs) adsorbents to capture humic acids

Chlorination is a versatile technique to combat water-borne pathogens. Over the last years, there has been continued research interest to abate the formation of chlorinated disinfection by-products (DBPs). To prevent hazardous DBPs in drinking water, it is decided to diminish organic precursors, among which humic acids (HA) resulting from the decomposition and transformation of biomass. Metal-organic frameworks (MOFs) such as zeolitic imidazolate frameworks (ZIFs) have recently received tremendous attention in water purification. Herein, customized ZIF-67 MOFs possessing various physicochemical properties were prepared by changing the cobalt source. The HA removal by ZIF-67-Cl, ZIF-67-OAc, ZIF-67-NO3, and ZIF-67-SO4 were 85.6%, 68.9%, 86.1%, and 87.4%, respectively, evidently affected by the specific surface area. HA uptake by ZIF-67-SO4 indicated a removal efficiency beyond 90% in 4  90% after 60 min mixing the solution with 0.3 g L-1 ZIF-67-SO4. Notably, an acceptable removal performance (∼72.3%) was obtained even at HA concentrations up to 100 mg L-1. The equilibrium data fitted well with the isotherm models in the order of Langmuir> Hill > BET> Khan > Redlich-Peterson> Jovanovic> Freundlich > and Temkin. The maximum adsorption capacity qm for HA uptake by ZIF-67-SO4 was 175.89 mg g-1, well above the majority of adsorbents. The pseudo-first-order model described the rate of HA adsorption by time. In conclusion, ZIF-67-SO4 presented promising adsorptive properties against HA. Further studies would be needed to minimize cobalt leaching from the ZIF-67-SO4 structure and improve its reusability safely, to ensure its effectiveness and the economy of adsorption system.

Trihalomethanes in developed and developing countries

The reactions between natural organic matter, anthropogenic contaminants, ions, and disinfectants lead to the formation of disinfection by-products (DBPs) such as trihalomethanes (THMs) in drinking water. The formation of THMs is strongly related to the chlorination of water. The study's central objective was to compare the concentration of THMs in twenty developed and developing countries and their disinfection techniques. The THM concentration in 11 developed and 9 developing countries ranged from 0.5 µg/L (Germany) to 215 µg/L (Russia) and 3 µg/L (China) to 439.2 µg/L (Bangladesh), respectively. The developed country has partially succeeded in reducing THM concentration in drinking water, whereas significant steps are needed in developing countries to reduce the existing high THM concentration. The concentration of THMs in water varies among these countries because of the different water sources, water quality, environmental conditions, and efficiency of water treatment technologies. A meaningful relationship has been observed between the properties of water and the THM formation. The use of chemical disinfectants will result in new forms of DBPs that are undesirable due to their carcinogenic and mutagenic effects on human health. The DBP guidelines by various national and international agencies have helped to control and manage the THM concentration in drinking water. However, these regulatory standards are not continuously monitored. Therefore, the formation of these compounds should be prevented either by removing THMs forming precursors or by using an integrated approach for controlling THM formation by implementing advanced water treatment technology. Extensive research is desirable in domains like THM minimization strategies which are easy to deploy, scalable, and cost-effective.

The combination of multiple linear regression and adaptive neuro-fuzzy inference system can accurately predict trihalomethane levels in tap water with fewer water quality parameters

Artificial Neural Network (ANN) models are accurate in predicting the levels of disinfection by-products (DBPs) in drinking water. However, these models are not yet practical due to the large number of parameters involved, which should take a significant amount of time and cost to detect. Developing accurate and reliable prediction models of DBPs with fewest parameters is essential in the management of drinking water safety. This study used the adaptive neuro-fuzzy inference system (ANFIS) and radial basis function artificial neural network (RBF-ANN) to predict the levels of trihalomethanes (THMs), the most abundant DBPs in drinking water. Two water quality parameters identified by multiple linear regression (MLR) models were used as model inputs, and the quality of the models was assessed based on criteria such as correlation coefficient (r), mean absolute relative error (MARE), and the percentage of predictions with absolute relative error less than 25% (NE<25%) and over than 40% (NE>40%), etc. The results showed that the ANFIS models had higher correlation coefficients (r = 0.853-0.898) and prediction accuracy (NE<25% = 91%-94%) compared to RBF-ANN models (r = 0.553-0.819; NE<25% = 77%-86%) and traditional MLR models (r = 0.389-0.619; NE<25% = 67%-77%). Conversely, the prediction error, as indicated by MARE and NE>40%, showed the opposite trend: ANFIS models (MARE = 8%-11%; NE>40% = 0-5%) < RBF-ANN models (MARE = 15%-18%; NE>40% = 5%-11%) < MLR models (MARE = 19%-21%; NE>40% = 11%-17%). The present study provided a novel approach for constructing high-quality prediction models of THMs in water supply systems using only two parameters. This method holds promise as a viable alternative for monitoring THMs concentrations in tap water, thereby contributing to the improvement of water quality management strategies.

Potential and mechanism of disinfection by-products removal in drinking water by bubbling corona discharge

Disinfection by-products (DBPs) with significant teratogenic and carcinogenic properties have become a growing concern among the public. As an efficient and environmentally friendly technology, non-thermal plasma offers potential for removing emerging micro-pollutants. In this study, the degradation performance of bubbling corona discharge was evaluated on 24 halogenated alicyclic and aliphatic DBPs present in drinking water at concentrations ranging from ng/L to μg/L. The degradation of DBPs followed pseudo-first-order kinetics with rate constants (kobs) in the descending order of halonitromethanes (HNMs), halogenated benzoquinones (HBQs), haloacetonitriles, trihalomethanes (THMs), haloketones, halogenated aldehydes, and haloacetic acids (HAAs). THMs, HNMs, and HBQs were effectively removed within 5 min under a discharge power of 28 W. Degradation rates achieved by plasma treatment surpass those of other conventional treatment technologies. The required energy consumption was in the range of 5-30 kW·h/m3/order. Furthermore, the study investigated the effects of discharge power, initial concentration, and economic analysis on the degradation of four selected DBPs as representatives of mono-, di- and multi-carbon-containing DBPs, namely chloroform (TCM) and bromoform (TBM), tribromoacetic acid (TBAA), and 2,3,5,6-tetrachloro-1,4-benzoquinone (TetraC-BQ). Reactive radicals in the plasma system were investigated using electron paramagnetic resonance, optical emission spectroscopy, fluorimetry, and radical scavengers. Hydrated electrons and hydroxyl radicals played an important role in the removal of DBPs. The intermediates generated during the degradation of TCM, TBM, TBAA, and TetraC-BQ were identified, and the possible degradation pathways for mono- and binary C-DBPs and HBQs were deduced. The breakdown of HBQs did not produce secondary contamination with aliphatic DBPs. The carbon in DBPs was primarily converted to formic acid, acetic acid, and oxalic acid, and the halogens were mainly converted to halogen ions. Additionally, luminescent bacteria toxicity testing confirmed that plasma treatment could reduce the acute toxicity of water samples. These findings demonstrate the potential of plasma treatment as a post-treatment device at the household level.

Residual chlorine persistently changes antibiotic resistance gene composition and increases the risk of antibiotic resistance in sewer systems

During the COVID-19 pandemic, excessive amounts of disinfectants and their transformation products entered sewer systems worldwide, which was an extremely rare occurrence before. The stress of residual chlorine and disinfection by-products is not only likely to promote the spread of antibiotic resistance genes (ARGs), but also leads to the enrichment of chlorine-resistant bacteria that may also be resistant to antibiotics. Therefore, the potential impact of such discharge on ARG composition should be studied and the health risks should be assessed. Thus, this study combined high-throughput 16S rRNA gene amplicon sequencing and metagenomic analysis with long-term batch tests that involved two stages of stress and recovery to comprehensively evaluate the impact of residual chlorine on the microbial community and ARG compositions in sewer systems. The tests demonstrated that the disturbance of the microbial community structure by residual chlorine was reversible, but the change in ARG composition was persistent. This study found that vertical propagation and horizontal gene transfer jointly drove ARG composition succession in the biofilm, while the driving force was mainly horizontal gene transfer in the sediment. In this process, the biocide resistance gene (BRG) subtype chtR played an important role in promoting co-selection with ARGs through plasmids and integrative and conjugative elements. Moreover, it was further shown that the addition of sodium hypochlorite increased the risk of ARGs to human health, even after discontinuation of dosing, signifying that the impact was persistent. In general, this study strengthens the co-selection theory of ARGs and BRGs, and calls for improved disinfection strategies and more environmentally friendly disinfectants.

Novel insights into impacts of the "7.20" extreme rainstorm event on water supply security of Henan Province, China: Levels and health risks of tap water disinfection by-products

Spatial distributions, levels, and comprehensive assessments of post-flood tap water disinfection by-products (DBPs) were first studied in Henan Province after the "7.20" Extreme Rainstorm Event in 2021. DBPs levels and health risks in tap water were higher in areas flooded (waterlogged) by storm or upstream flood discharge (WA) and rainstorm-affected areas (RA) compared with other areas (OA), suggesting that extreme rainstorm and flooding events may somehow exacerbate DBPs contamination of tap water through disinfection. WA sites were characterized as contamination hotspots. The results revealed high haloacetic acids (HAAs) levels in WA (Avg: 57.79 μg·L^-1) and RA (Avg: 32.63 μg·L^-1) sites. Compared with normal period, DBPs-caused cancer risk increased by 3 times, exceeding the negligible risk level. Cancer risk came primarily from the ingestion of trihalomethanes (THMs) (>80%), children were the sensitive group. Those between 30 and 69 showed approximately 1.7 times higher disability-adjusted life yearsper person-yearthan other age groups. Apart from regulated DBPs, bromochloracetic acid (BCAA) and dibromoacetonitrile (DBAN) appear to be the main toxicity contributors in these samples. Our results provide a scientific basis for preventing and controlling health risks from tap water DBPs and for assessing the social benefits and burdens of emergency disinfection.

Performance evaluation of the UV activated chlorite process on trimethoprim: Degradation efficiency, energy consumption and disinfection by-products formation

As the primary inorganic by-product species of ClO₂, chlorite is believed to have negative toxicological effects on human health and therefrom greatly limits the wide application of ClO₂ in water treatment. The synergistic trimethoprim (TMP) removal concerning degradation efficiency, energy consumption and disinfection by-products (DBPs) formation in the UV activated chlorite process accompanied by the simultaneously elimination of chlorite was comprehensively evaluated. UV/chlorite integrated process removed TMP far more rapidly than UV (1.52%) or chlorite (3.20%) alone due to the endogenous radicals (Cl•, ClO• and •OH), the contributing proportions of which were 31.96%, 19.20% and 44.12%. The second-order rate constants of TMP reaction with Cl•, ClO• and •OH were determined to be 1.75 × 10¹⁰, 1.30 × 10⁹ and 8.66 × 10⁹ M^-1 s^-1. The effects of main water parameters including chlorite dosage, UV intensity, pH as well as water matrixes (nature organic matter, Cl^- and HCO₃^-) were examined. k_obs obeyed the order as UV/Cl₂>UV/H₂O₂≈UV/chlorite>UV, and the cost ranking via electrical energy per order (EE/O, kWh m^-3 order^-1) parameter was UV/chlorite (3.7034) > UV/H₂O₂ (1.1625) >UV/Cl₂ (0.1631). The operational scenarios can be optimized to achieve the maximum removal efficiencies and the minimum energy costs. The destruction mechanisms of TMP were proposed by LC-ESI-MS analysis. The overall weighted toxicity in subsequent disinfection was assessed as UV/Cl₂>UV/chlorite > UV, the values of which in post-chlorination were 6.2947, 2.5806 and 1.6267, respectively. Owing to the vital roles of reactive chlorine species (RCS), UV/chlorite displayed far higher TMP degradation efficiency than UV, and concurrently presented much less toxicity than UV/Cl₂. In an effort to determine the viability of the promising combination technology, this study was devoted to reduce and reuse chlorite and synchronously realize the contaminants degradation efficiently.

Removal and transformation of disinfection by-products in water during boiling treatment

Disinfection by-products (DBPs) remain an ongoing issue because of their widespread occurrence and toxicity. Boiling is the most popular household water treatment method and can effectively remove some DBPs. However, the transformation behavior of DBPs during boiling is still unclear, and the key contributors to toxicity have not been identified. In this study, the changes in the concentrations of DBPs in the single-DBP systems and the multi-DBP systems during boiling were monitored, and in-depth discussions on the removal and transformation of DBPs in both systems were carried out. The results showed that boiling was effective in removing volatile DBPs (over 90% for TCAL, TCAN, and DCAN, and over 60% for TCM), but ineffective for non-volatile DBPs (around 20% for TCAA and below 10% for DCAA and MCAA). By hydrolysis and decarboxylation, the transformation occurred among DBPs, i.e., 55% TCAL to TCM, followed by 23% DCAN to DCAA, 22% TCAN to TCAA, and 10% TCAA to TCM. The transformations were found to be significantly influenced by other co-existing DBPs. In multi-DBP systems, the transformations of DCAN to DCAA and TCAN to TCAA were both promoted, while the transformation of TCAN to TCAA was inhibited. Transformation and volatilization are the two processes responsible for DBP removal. Toxicity estimates indicated that boiling was effective in reducing the toxicity of DBPs and improving the safety of the water, despite the interconversion of DBPs in drinking water during boiling. This study emphasized the importance of studying the interconversion behaviors of DBPs in drinking water during boiling and provided practical information for end-use drinking water safety.

Oxidative treatment of NOM by selective oxidants in drinking water treatment and its impact on DBP formation in postchlorination

Natural organic matter (NOM), as a ubiquitous component in aqueous environments, has raised continuous scientific concerns due to its role as an organic precursor to disinfection by-products (DBPs) in the subsequent chlorination process. Selective oxidants, including ozone (O₃), chlorine dioxide (ClO₂), permanganate (Mn(VII)), and ferrate (Fe(VI)) are widely used in the preoxidation stage in drinking water treatment. The selective reactivity of those oxidants toward NOM is expected to alternate NOM properties and consequently DBP formation in postchlorination. Despite extensive studies on the interactions of NOM with selective oxidants, there is currently a lack of an overview of this area. To fill this gap, this study presents the current knowledge of the modification of NOM properties by selective oxidants and its impact on DBP formation in postchlorination. The NOM property changes in three aspects, including bulk property (e.g., total organic carbon, ultraviolet absorbance), fractional constituent (e.g., molecular size, hydrophilicity/hydrophobicity), and elemental composition (e.g., functional group) by the four selective oxidants (i.e., O₃, ClO₂, Mn(VII), and Fe(VI)) were discussed. Thereafter, the impacts of alteration of NOM properties by those selective oxidants on DBP formation in the subsequent chlorination were summarized, wherein the key influencing factors were discussed. Finally, the future perspectives in this area were forwarded, which highlighted the significance of process optimization, the attention to the less studied but more toxic DBPs, and the need for the identification of unknown DBPs. This review presented a state-of-the-art knowledge pool of the fate of NOM in oxidation and chlorination processes, promoted our understanding of the relationship between NOM properties and DBP formation, and identified further research needs in this area.

The involvement of branched-chain amino acids (BCAAs) in aromatic trihalogenated DBP exposure-induced kidney damage in mice

Disinfection by-products (DBPs) are inevitably generated in the process of disinfection. Among them, aromatic halogenated DBPs, such as 2,4,6-trichlorophenol (TCP), 2,4,6-tribromophenol (TBP) and 2,4,6-triiodophenol (TIP), have attracted considerable interest for their high toxicity. A systematic nephrotoxicity evaluation of 2,4,6-trihalophenols is still lacking. In this study, mice were exposed to TCP, TBP and TIP ranging from environmental-related low concentration to high concentration that commonly used in animal study (0.5-200 μg/L). Kidney histopathology, urine protein detection and urine metabolomics were performed. Remarkable changes including kidney damage, proteinuria and glomerular mesangial cell proliferation were observed after three 2,4,6-trihalophenol exposure, even at low concentration of 0.5 μg/L. The nephrotoxicity rank order was TIP > TBP > TCP. Additionally, in vivo exposure to 2,4,6-trihalophenols also led to apparent changes in urinary metabolic profiles. Biosynthesis pathways of branched-chain amino acids (BCAAs, containing valine, leucine and isoleucine) were disturbed even at the early stage of exposure (4 weeks). Intriguingly, it has been reported that BCAAs could promote the proliferation of glomerular mesangial cells. Thus, in vitro cell experiments were further performed on mouse glomerular mesangial cell line MES-13. Consistently with in vivo results, cell proliferation was observed in MES-13 cells after exposure to 2,4,6-trihalophenols, especially to TBP and TIP. Meanwhile, TCP at high concentration, TBP and TIP at not only high concentration but also low concentration, induced BCAAs accumulation in glomerular mesangial cells, which was completely commensurate to that observed in cell proliferation assay. Then the proliferation of MES-13 cells induced by 2,4,6-trihalophenols was remarkably inhibited after BCAAs interference. Here we provide direct link between disturbed BCAAs and the nephrotoxicity of 2,4,6-trihalophenols. 2,4,6-trihalophenols could induce excess BCAAs, which further led to proliferation of glomerular mesangial cells and renal injury. This study revealed the nephrotoxicity of aromatic trihalogenated DBPs and provided new insights into the potential toxic mechanisms.

Multivariate experimental design provides insights for the optimisation of rechloramination conditions and water age to control disinfectant decay and disinfection by-product formation in treated drinking water

The stability of drinking water disinfectant residuals is known to be influenced by multiple variables. To evaluate the effects of various influencing variables on disinfectant stability, a multivariate analysis of chloramine decay and associated disinfection by-products (DBPs) formation was investigated in a series of bench-scale experiments. Of nine water quality variables previously identified, monochloramine dose, pH, and bromide concentration were selected as key water quality variables based on previous investigations and modelling. Co-effects of these key variables on monochloramine decay and formation of 33 halogenated and nitrogen-containing DBPs were investigated using response surface experimental design. Rechloramination conditions, including monochloramine dose, pH and bromide concentration, were optimised via a 3-factorial multivariate analysis of monochloramine stability in post-treatment drinking water. Effects of influencing variables on disinfectant decay and DBP formation were assessed and graphically presented as response surfaces with minimal experiments using Doehlert matrix experimental design compared to other multivariate experimental designs. Concentrations of trihalomethanes (THMs), haloacetic acids (HAAs), and N-nitrosamines were found to increase with water age, whereas opposite phenomenon was observed in the net production of haloacetonitriles (HANs). Increasing pH was found to stabilise monochloramine but it could cause DBP speciation to shift. Furthermore, increasing bromide concentration elevated Br-DBP formation. In bromide-containing water, pH = 7.8-8.0 should be considered as higher pH increases Br-THMs formations and lower pH increases formations of Br-HAAs and Br-HANs. However, water age or pH has insignificant impacts on DBP formation after significant monochloramine decay or at low initial monochloramine dose. These findings indicate that effective combined control measures to maintain monochloramine stability should include the application of high monochloramine dose (>1.5 mg-Cl₂.L^-1) under conditions of moderate to high pH (pH = 7.8-8.0) and minimal bromide concentration. This study provides relevant insights to water utilities aiming to design effective disinfectant residual management strategies for controlling monochloramine decay and DBP formation.

Micropollutant removal and disinfection byproduct control by sequential peroxymonosulfate-UV treatment in water: A case study with sulfamethoxazole

UV/peroxymonosulfate (UV/PMS) advanced oxidation process has attracted significant attention for removal of micropollutants in water. However, during practical water treatment applications, the PMS treatment must be performed before the UV treatment to achieve full contact. In this study, sulfamethoxazole (SMX) was selected as the target micropollutant. Four different operational approaches, including UV alone, PMS alone, simultaneous UV/PMS and sequential PMS-UV, were compared for their differences in SMX removal and disinfection by-product (DBP) formation potentials during chlorine-driven disinfection. Among the four approaches, UV/PMS and PMS-UV achieved over 90% removal efficiencies for SMX without substantial differences. For raw water, the trichloronitromethane (TCNM) formation potential after treatment with PMS-UV was lower than that after UV/PMS treatment. The time interval over which the PMS-UV process was conducted had little effect on the final removal efficiency for SMX. However, a brief (5 min) pre-PMS treatment significantly reduced the TCNM formation potential and the genotoxicity from DBPs. The formation risk for TCNM during chlorination increased markedly with increasing PMS dosages, and the appropriate dosage under these experimental conditions was suggested to be 0.5-1.0 mmol/L. Under alkaline conditions, PMS-UV treatment can enhance SMX degradation as well as dramatically reduced the formation potentials for haloketones, haloacetonitriles and halonitromethanes. This study suggests that proper optimization of UV/PMS processes can remove SMX and reduce its DBP formation.

Formation and control of organic chloramines and disinfection by-products during the degradation of pyrimidines and purines by UV/chlorine process in water

Pyrimidine and purine bases (adenine, cytosine, guanine and thymine) are important precursors of organic chloramines (OC) and disinfection by-products (DBPs) during chlor(am)ination. In this study, OC and DBP formation derived from pyrimidine and purine bases during chlor(am)ination, post-chlor(am)ination after pretreated by UV alone and UV/chlorination were systematically investigated with ultraviolet light-emitting diodes (UV-LEDs, 265 and 275 nm) and low pressure mercury lamp (LPUV, 254 nm). The results revealed that higher OC formation was observed during chlorination than that during chloramination of pyrimidine and purine bases. The degradation of pyrimidine and purine bases followed the pseudo-first-order kinetics. Both solution pH and UV wavelength played vital influence on the degradation of pyrimidine and purine bases. In terms of fluence-based rate constants (k_obs), the degradation rates of pyrimidine and purine bases decreased in the order of 275 nm > 265 nm > 254 nm in alkaline conditions. The synergistic effects of k_{obs, chlorine,}k_{obs, •OH} and k_{obs, RCS} contributed to the differences of pyrimidine and purine bases degradation at different pH values and UV wavelengths. A vital suppression of OC formation was observed during post-chlorination after pretreated by 275 nm UV-LED/chlorination. In addition, compared with LPUV (254 nm), less DBP formation was observed at UV-LED (275 nm), especially during the UV/chlorine process. The phenomena obtained in this study indicated that 275 nm UV-LED combined with chlorine could be a preferred method to promote pyrimidine and purine bases degradation and control OC and DBP formation in practical water treatment.

Investigation into the content and formation of trihalomethanes and molecular change of dissolved organic matter from a typical water plant in south China

Trihalomethanes (THMs) are a class of disinfection by-products that were proved to have adverse effects to human health. Investigation into its content change and molecular composition variation of its main precursor, which is believed to be dissolved organic matter (DOM) during water purification process, can help understand the formation mechanism of THMs and optimize the processes in drinking water treatment plant (DWTP). This is of great significance to ensure the safety of urban water supply. In this study, detailed changes of THMs' content and formation potential were determined during the water purification process in summer and winter at a typical DWTP in south China. Specific molecular composition changes of DOM were also characterized by ultrahigh-resolution mass spectrometry, to comprehensively study its correlation with the formation of THMs in different water processing units and seasons. The result showed that chlorination will cause drastic changes of water quality and a sharp increase in the concentration of THMs (18.7 times in summer and 13.9 times in winter). Molecular-level characterization of DOM indicates that a range of lignin-like substance with lower O/C (< 0.5) and H/C (< 1.25) vanished and considerable amount of protein-like and tannins-like substance with higher H/C (> 1.25) and O/C (> 0.5) was formed after chlorination. Analysis of Cl-containing products demonstrated that a bulk of CHOCl₁ and CHOCl₂ compounds with moderate molecular weights were formed in both winter and summer. However, the newly formed CHOCl₁ molecules showed a relatively higher mass weight in summer (> 500 Da) compared to winter (300-500 Da). Seasonal differences also emerged in the result of correlation between the trihalomethanes formation potential and total organic carbon. The correlation coefficient in summer (0.500) was lower than that in winter (0.843). The results suggested that the exhaustive reaction and contribution of DOM to THMs may vary in different seasons.

Degradation kinetics of prometryn and formation of disinfection by-products during chlorination

Prometryn is a herbicide that is widely used and frequently detected in aqueous environment and soil. Prometryn is chemically stable, biologically toxic, and easily to accumulate in living bodies, which can cause accumulate in the environment and acute and chronic toxicity to living creatures. In this study, factors affecting the degradation kinetics of prometryn chlorination were studied, including solution pH, bromide and ammonium concentrations, and temperature. Prometryn reacted quickly with aqueous chlorine following the pseudo-first-order kinetics. The maximum pseudo-first-order rate constant (k_app) appeared at pH 5 with the observed rate constant (k_obs) as 190. 08 h^-1; the minimum value of k_app reached at pH 9 with k_obs as 5.26 h^-1. The presence of Br^- and increase of temperature both accelerated the degradation rate of prometryn during chlorination. The activation energy was calculated as 31.80 kJ/mol. Meanwhile 6 disinfection by-products (DBPs) were detected, namely: chloroform (CF), trichloroacetonitrile (TCAN), dichloroacetonitrile (DCAN), dichloroacetone, trichloronitromethane (TCNM), and trichloroacetone. Solution pH significantly affected the formation and distribution of DBPs. CF was the most formed carbonated DBP (C-DBP) with the maximum of 217.9 μg/L at pH 8, and its formation was significantly higher in alkaline conditions. For nitrogenated DBPs (N-DBPs), the yields of DCAN and TCAN were significantly higher in acidic conditions, while the maximum of TCNM achieved in neutral conditions. Because the toxicity of N-DBPs is higher than that of C-DBPs, the pH should be controlled in neutral or slight alkaline conditions during prometryn chlorination to effectively control DBP formation and reduce the related toxicity.

Destruction of microbial stability in drinking water distribution systems by trace phosphorus polluted water source

The effects of trace phosphate concentrations (0, 0.3 and 0.6 mg/L) in water source were investigated on microbial stability of the drinking water distribution systems (DWDSs). Obviously, the results verified that in the effluent of DWDSs simulated by annular reactors (ARs), the total microbial biomass and the absolute concentration of opportunistic pathogens such as Legionella pneumophila, Mycobacterium avium, and Hartmanella vermiformis increased significantly with phosphate concentration increasing. Based on X-ray powder diffractometer and zeta potentials measurement, trace phosphate did change physicochemical properties of corrosion products, hence promoting microbes escape from corrosion products to bulk water to a certain extent. Stimulated by chlorine disinfectant and phosphate, the extracellular polymeric substances (EPS) from the suspended biofilms of AR-0.6 gradually exhibited superior characteristics including higher content, flocculating efficiency, hydrophobicity and tightness degree, contributing to formation of large-scale suspended biofilms with strong chlorine-resistance ability. However, the disinfection by-products concentration in DWDSs barely changed due to the balance of EPS precursors contribution and biodegradation effect, covering up the microbiological water quality risk. Therefore, more attention should be paid to the trace phosphorus polluted water source though its concentration was much lower than wastewater. This is the first study successfully revealing the influence mechanism of trace phosphate on microbial stability in DWDSs, which may help to fully understand the biofilms transformation and microbial community succession in DWDSs.

Trade-off control of organic matter and disinfection by-products in the drinking water treatment chain: Role of pre-ozonation

Ozone is a strong oxidant commonly used in drinking water treatment, but its role in the transformation/formation of organic matters (OMs) and disinfection by-products (DBPs) in the drinking water treatment chain had not been systematically studied. In this work the occurrence and building up of OMs, DBPs of trihalomethanes (THMs) and nitrosamines (NAs) during water purification steps under different pre-ozonation dosages have been studied through lab-scale and pilot-scale studies. Results indicated that 0-0.4 mg/L of pre-ozonation dosage could reduce organic load of following-up process steps but insufficient to control DBPs. Seasonal performances of a pilot plant indicated that the accumulation of DBPs was much less in summer than in winter. Furthermore the formation potential of NAs was higher in winter than summer when 0.4 mg/L pre-ozonation was dosed while the maximum removal efficiency of organic matter was found at a pre-ozonation dosage of 0.8 mg/L in summer. Finally a seasonal trade-off control strategy for both OMs and DBPs was proposed with an elucidated role of pre-ozonation in the drinking water treatment chain. This study provided working principles on optimizing pre-ozonation dosage and a seasonal control strategy for trade-off control of both OMs and DBPs in drinking water treatment plants.

Formation of disinfection by-products in a UV-activated mixed chlorine/chloramine system

In recent years, ultraviolet (UV) irradiation coupled with chlor(am)ination process is ubiquitous in secondary water supply systems in many cities of China. However, the disinfection by-products (DBPs) formation in a UV-activated mixed chlorine/chloramine system (MCCS) still remains unclear. In this study, the DBPs formation in a UV-activated MCCS was systematically investigated, considering influencing factors including the mass ratios of free chlorine to NH₂Cl, UV irradiation, pH values, NOM types, Br^- concentration and toxicity of the DBPs. Results indicated that DBPs formation decreased remarkably as mass ratio of free chlorine to NH₂Cl changed from 5:0 to 0:5. The DBPs formation in humic acid (HA)-containing water was the highest, followed by those in fulvic acid (FA) and algal organic matter (AOM). Besides, better control of the DBP-related calculated toxicity can be achieved in acidic conditions regardless of the UV irradiation. Furthermore, in the presence of Br^-, a significant reduction of DBPs formation could be achieved in a UV-activated MCCS. The findings also demonstrated that DBPs formation in real water can be effectively reduced at high UV fluence in a MCCS.

A multivariate Bayesian network analysis of water quality factors influencing trihalomethanes formation in drinking water distribution systems

Controlling disinfection by-products formation while ensuring effective drinking water disinfection is important for protecting public health. However, understanding and predicting disinfection by-product formation under a variety of conditions in drinking water distribution systems remains challenging as disinfection by-product formation is a multifactorial phenomenon. This study aimed to assess the application of Bayesian Network models to predict the concentration of trihalomethanes, the dominant halogenated disinfection by-product class, using various water quality parameters. Naïve Bayesian and semi-naïve Bayesian models were constructed from Sydney and South East Queensland datasets across 15 drinking water distribution systems in Australia. The targeted variable, total trihalomethanes concentration, was discretised into 3 bins (<0.1 mg L^-1, 0.1 - 0.2 mg L^-1 and >0.2 mg L^-1). The Bayesian network structures were built using water quality parameters including concentrations of individual and total trihalomethanes, disinfectant species (free chlorine, monochloramine, dichloramine, total chlorine), nitrogen species (free ammonia, total ammonia, nitrate, nitrite), and other physical/chemical parameters (temperature, pH, dissolved organic carbon, total dissolved solids, conductivity and turbidity). Seven performance parameters, including predictive accuracy and the rates of true and false positive and negative results, were used to assess the accuracy and precision of the Bayesian network models. After evaluating the model performance, the optimum models were selected to be Bayesian network augmented naïve models. These were observed to have the highest predictive accuracies for Sydney (78%) and South East Queensland (94%). Although disinfectant residuals are among the key variables that lead to trihalomethanes formation, potential concentrations of trihalomethanes in distribution systems can be more confidently predicted, in terms of probability associated with a wider range of water quality variables, using Bayesian networks. The modelling procedure developed in this work can now be applied to develop system-specific Bayesian network models for trihalomethanes prediction in other drinking water distribution systems.

Temporospatial variation and health risk assessment of trihalomethanes (THMs) in drinking water (northwest Iran)

Trihalomethanes (THMs) are one of the most common classes of disinfection by-products. In this study, the temporospatial trends and health risks due to exposure to THMs in the Tabriz water distribution network were investigated. THM series were analyzed using gas chromatography equipped with electron capture detector. The non-carcinogenic and carcinogenic risks due to exposure to THMs were calculated using Monte Carlo simulations. Mean concentrations of THMs in winter and spring were 10.2 ± 9.3 μg/l and 252 ± 185.9 μg/l, respectively. More than 80% of THMs identified were bromodichloromethane. The mean values of lifetime cancer risk (LTCR) of THMs were calculated as 4.23E-06 and 2.38E-04 for winter and spring, respectively. This study showed that there were noticeable levels of THMs in Tabriz water distribution network, especially in the center of the city. Although the non-cancer risk through THMs was below permissible recommended levels, the cancer risk likely remains due to high levels of THMs in some locations.

Mechanistic insight for DBP induced growth inhibition in Vigna radiata via oxidative stress and DNA damage

Chlorination is important to the safeness of recouped water; though it shows concern about disinfection by-products (DBPs) formation and its toxic effects. DBPs generation mostly specified by category of disinfectant utilized and naturally occurring organic matter present in the water pre and post disinfection. Plants are exposed to diverse stresses of environment across their lifespan. Reactive oxygen species (ROS) perform significant roles in preserving ordinary plant growth and enhancing their tolerance towards stress. This study is focused on the generation and elimination of ROS in apical meristematic growth and responses in Vigna radiata towards DBPs exposure. Phytotoxic and genotoxic effect of selected DBPs, TCAA (trichloroacetic acid), TCM (trichloromethane), TBM (tribromomethane) revealed concentration-dependent root length inhibition, germination index, vigour index, tolerance index, root/shoot ratio with higher EC₅₀ value for TCM (6000 mg/L, 50.26 mM) over TCAA and TBM (1850 mg/L, 11.32 mM; 4000 mg/L, 15.83 mM). DNA laddering assay demonstrated DBP induced DNA damage to be concentration-dependent too. The concentration-dependent increase in the lipid peroxidation, H₂O₂ generation for each DBPs examined with highest oxidative stress for TCAA over TBM and TCM at fixed concentration illustrates that possible mechanism behind observed toxicity may be via ROS. Its regulation by antioxidative defense enzymes activities can be attributed to observed decline in these enzymes (catalase, ascorbate peroxidase, guaiacol peroxidase) activities with increasing concentration again where TCAA found more significantly affected than TBM and TCM over control. Results thus provide a useful understanding of the mechanism of DBP induced phytotoxicity and genotoxicity in V.radiata.

Variability of TOC and DBPs (THMs and HAA5) in drinking water sources and distribution system in drought season: the North Iran case study

The aim of this study is tracing seasonal variability of total organic carbon (TOC), trihalomethanes (THMs) and haloacetic acids (HAA5) as disinfection by-products (DBPs) in drinking water sources and the distribution system in the north of Iran. The results showed that the concentrations of TOC were within the range of 0.013-1.42 mg/L. In addition, the results showed that most of the water sources had nearly the same concentration level (i.e. <1 mg/L), with the exception of one peak for groundwater source and middle drinking water distribution system in the city of Sari (1.42 mg/L) and Babol (1.37 mg/L). It was demonstrated that brominated HAA (MBAA) presented the highest concentration in the Sari City (17.3 µg/L) followed by the City of Behshahr (8.9-11.19 µg/L). The Babol City showed the highest concentration of chlorinated HAA (22.403 and 22.503 µg/L for DCAA and TCAA, respectively). Among the different compounds of THMs, the concentration of CHBr₃ was nearly in the same order of magnitude in the cities of Sari, Babol and Behshahr for both spring and summer seasons. The brominated THM (BDCM) concentrations were also high (14.7 µg/L) in the Behshahr City. The results of independent t-test indicated that the seasonal (spring and summer) difference was statistically significant in the case of temperature and TTHM (p < 0.05). Furthermore, total HAA₅ ≤ 60 µg/L and THM ≤100 µg/L in all the considered cities over the period of the study. The TTHMs concentration was 56 µg/L in treating surface water (TSW) source in the summer season at the Sari city.

Chlorination of soil-derived dissolved organic matter: Long term nitrogen deposition does not increase terrestrial precursors of toxic disinfection byproducts

Terrestrial dissolved organic matter (DOM) in forested watersheds is a known precursor of disinfection byproducts (DBPs) in drinking water. Although the characteristics of terrestrial DOM may change with increasing nitrogen (N) deposition in forests, how these changes alter formation potential and toxicity of DBPs remains unexplored. We analyzed the speciation and toxicity of DBPs from chlorination of DOM derived from soils (O, A, and B horizons) in an experimental temperate forest with 22 years of N addition. With long-term N addition, the DOM reactivity toward the formation of trihalomethanes (from 27.7-51.8 to 22.8-31.1 µg/mg-dissolved organic carbon (DOC)) and chloral hydrate (from 1.25-1.63 to 1.14-1.36 µg/mg-DOC) decreased, but that toward the formation of haloketones increased (from 0.23-0.26 to 0.26-0.33 µg/mg-DOC). The DOM reactivity toward the formation of haloacetonitriles was increased in the deeper soil but reduced in the surface soil. The DBP formation potential of DOM draining from a certain area of forest soils (in µg-DBP/m²-soil) was estimated to be reduced by 20.3% for trihalomethanes and increased by 37.5% for haloketones and have minor changes for haloacetonitriles and chloral hydrate (both <7%). Furthermore, the DBPs from chlorination of the soil-derived DOM showed lowered microtoxicity with N addition possibly due to reduced brominated DBP formation. Overall, this study highlights that N deposition may not increase drinking water toxicity through altering terrestrial DOM characteristics.

Mechanistic study on chlorine/nitrogen transformation and disinfection by-product generation in a UV-activated mixed chlorine/chloramines system

The conversion mechanisms of chlorine species (including free chlorine, monochloramine (NH₂Cl), dichloramine, and total chlorine), nitrogen species (including ammonium (NH₄⁺), nitrate (NO₃^-), and nitrite (NO₂^-)) as well as the formation of disinfection by-products (DBPs) in a UV-activated mixed chlorine/chloramines system in water were investigated in this work. The consumption rates of free chlorine and NH₂Cl were significantly promoted in a HOCl/NH₂Cl coexisting system, especially in the presence of UV irradiation. Moreover, the transformation forms of nitrogen in both ultrapure and HA-containing waters were considerably affected by UV irradiation and the mass ratio of free chlorine to NH₂Cl. NO₃^- and NO₂^- can be easily produced under UV irradiation, and the removal efficiency of total nitrogen with UV was obvious higher than that without UV when the initial ratio of HOCl/NH₂Cl was less than 1. The roles of different radicals in the degradation of free chlorine, NH₂Cl and NH₄⁺ were also considered in such a UV-activated mixed chlorine/chloramines system. The results indicated that OH• was important to the consumption of free chlorine and NH₂Cl, and showed negligible influence on the consumption of NH₄⁺. Besides, the changes of DOC and UV₂₅₄ in HA-containing water in UV-activated mixed chlorine/chloramines system indicated that the removal efficiency of DOC (24%) was much lower than that of UV₂₅₄ (94%). The formation of DBPs in a mixed chlorine/chloramines system was also evaluated. The yields of DBPs decreased significantly as the mass ratio of HOCl/NH₂Cl varied from 1 : 0 to 0 : 1. Moreover, compared to the conditions without UV irradiation, higher DBPs yields and DBP-associated calculated toxicity were observed during the UV-activated mixed chlorine/chloramine process.

Efficient removal of disinfection by-products precursors and inhibition of bacterial detachment by strong interaction of EPS with coconut shell activated carbon in ozone/biofiltration

The change of water quality was investigated in pilot-scale ozone-biological activated carbon (O₃-BAC) filters using an emerging coconut shell-based granular activated carbon (CAC) or traditional granular activated carbon (GAC), respectively. More dissolved organic carbon (DOC) and disinfection by-products (DBPs) precursors were removed, meanwhile, less microbes, less metabolites and smaller microbial clusters were detected in the effluent of CAC compared with GAC. Sequentially, lower DBPs formation and higher disinfection efficiency were achieved in drinking water distribution systems (DWDSs). Furthermore, it was observed that extracellular electron transfer was enhanced in the attached biofilms of CAC, hence improving the microbial metabolic activity and biological removal of DOC. The results were attributed to the strong interaction of extracellular polymeric substances (EPS) with highly graphitized CAC. In addition, CAC resulted in totally different EPS in attached biofilms with superior characteristics including stronger viscosity, higher flocculating efficiency, mechanical stability and numerous binding sites for bacterial cells. Consequently, a wide range of compact interconnected biofilms formed on the surface of CAC and exhibited certain binding effect for microbial flocs and metabolites. Therefore, CAC resulted in higher microbial metabolic activity and lower release of microbes and metabolites, which was beneficial to maintain water quality safety in downstream DWDSs.

Characterization of dissolved organic matter derived from atmospheric dry deposition and its DBP formation

Disinfection by-products (DBPs) precursors can be regarded mainly from the drinking water sources and the water treatment processes. A recent study showed that dissolved organic matter (DOM) in atmosphere is an important precursor source of DBPs through atmospheric wet deposition. However, little information is available on the characteristics of DOM derived from dry deposition particulate matter (PM) and the impact of dry deposition on CX₃R-type DBP formation. This study determined whether dry deposition directly contributed the production of DBPs during chlor (am)ination and investigated the mechanism behind the contribution based on the combination of the resin and membrane for fractionating DOM fractions. The results showed that the hydrophilic fraction (HPI) contributed the most DOM and low molecular weight DOM (<10 kDa) was the main component of HPI. In addition, aromatic proteins and soluble microbial products-like compounds were the dominant fluorescent species in DOM derived from PM, and <10 kDa transphilic was the most abundant. The concentrations of C-DBPs and N-DBPs in disinfected PM solution were trihalomethanes (THMs) > haloacetic acids (HAAs) > haloaldehydes and haloacetamides > haloacetonitriles > halonitromethanes for both chlorination and chloramination. The main contributors of calculated toxicity are transphilic and hydrophobic in chlorination and chloramination respectively. Dry deposition PM was deduced to contribute DOM and DBP formation after chlorination in surface water, especially THMs and HAAs. These results presented herein provide key information for controlling DBPs from the perspectives of atmospheric dry deposition, especially in the case of heavy air pollution.

Comparison of different disinfection processes for controlling disinfection by-product formation in rainwater

With increasing shortage of clean water, rainwater has been considered as a precious alternative drinking water source. The processes applied to rainwater treatment are responsible for the safety of drinking water. Therefore, we systematically compared different disinfection processes to evaluate the control of disinfection by-product (DBP) formation and integrated cyto- and genotoxicity of the treated rainwater for the first time. The evaluated disinfection processes included chlorination and chloramination, pre-oxidation by potassium permanganate (KMnO₄) and potassium ferrate (K₂FeO₄), ultraviolet/hydrogen peroxide (UV/H₂O₂), and ultraviolet/persulfate (UV/PS) processes. The results revealed that chloramination was effective for controlling the formation of carbonaceous DBPs (C-DBPs), but not nitrogenous DBPs (N-DBPs). Compared to KMnO₄ pre-oxidation, better reduction of almost all DBPs was observed during K₂FeO₄ pre-oxidation. According to the calculation of cytotoxicity index (CTI) and genotoxicity index (GTI), cyto- and genotoxicity of the samples decreased obviously at the dosage of ≥ 2.0 mg/L KMnO₄ and K₂FeO₄. The control of the cyto- and genotoxicity of the formed DBPs from the two UV-related AOPs was more effective at the dosage of ≥ 1.0 mM PS and ≥ 5.0 mM H₂O₂. Moreover, UV/PS was much more powerful to alter the structure of DBP precursors in rainwater.

Dominant formation of unregulated disinfection by-products during electrocoagulation treatment of landfill leachate

During the electrocoagulation (EC) treatment of landfill leachate, the production of chlorine species may result in the formation of harmful disinfection by-products (DBPs). This formation was investigated in the present study by monitoring five classes of DBPs (haloacetic acids-HAA, trihalomethanes-THM, haloacetonitriles-HAN, haloketones-HK, and halonitromethanes-HNM) in two leachate samples treated by EC. It was shown that the applied current has stimulated the formation of DBPs, which were dominated by unregulated DBPs. With a current density of 100 mA cm^-2, the unregulated HK dominated the weight-based DBP concentration (96% in Leachate A and 44.3% in Leachate B), while the unregulated HAN contributed to >80% of the DBP additive toxicity in both leachates. The concentrations of regulated THM and HAA species were below US EPA regulations. The in situ generation of active chlorine has resulted in the DBP formation, as demonstrated in the scavenging test. Applying granular activated carbon as a post-treatment step could successfully reduce the total DBP concentration from 295.33 μg L^-1 to 82.04 μg L^-1 in Leachate A, leading to a total DBP removal of 72.2% and a toxicity removal of 50%. Given the dominant concentration and lack of toxicity information, the unregulated DBPs should receive more attention.

The impact of UV treatment on microbial control and DBPs formation in full-scale drinking water systems in northern China

To manage potential microbial risks and meet increasingly strict drinking water health standards, UV treatment has attracted increasing attention for use in drinking water systems in China. However, the effects of UV treatment on microbial control and disinfection by-products (DBPs) formation in real municipal drinking water systems are poorly understood. Here, we collected water samples from three real drinking water systems in Beijing and Tianjin to investigate the impacts of UV treatment on microbial control and DBP formation. We employed heterotrophic plate count (HPC), flow cytometry (FCM), quantitative PCR analysis, and high-throughput sequencing to measure microorganisms in the samples. Different trends were observed between HPC and total cell count (measured by FCM), indicating that a single indicator could not reflect the real degree of biological re-growth in drinking water distribution systems (DWDSs). A significant increase in the 16S rRNA gene concentration was observed when the UV system was stopped. Besides, the bacterial community composition was similar at the phylum level but differed markedly at the genera level among the three DWDSs. Some chlorine-resistant bacteria, including potential pathogens (e.g., Acinetobacter) showed a high relative abundance when the UV system was turned off. It can be concluded that UV treatment can mitigate microbial re-growth to some extent. Finally, UV treatment had a limited influence on the formation of DBPs, including trihalomethanes, haloacetic acids, and nitrogenated DBPs. The findings of this study may help to understand the performance of UV treatment in real drinking water systems.

Removal of mutagen X "MX" from drinking water using reduced graphene oxide coated sand particles

PURPOSE

Mutagen X is a hazardous by-product of disinfection by chlorine, which is responsible for most of the mutagenicity in chlorinated drinking water. It has the cancer potency value of 100-fold higher than bromodichloromethane and 6000-fold higher than chloroform, In this study, Mutagen X was removed from aqueous media by a thermally reduced graphene oxide bonded on the surface of amino-functionalized sand particles.

METHOD

A Box-Behnken design was applied to optimize the adsorption process. Characterization of the adsorbent and graphene oxide was accomplished using scanning electron microscopy (SEM), Energy-dispersive X-ray spectroscopy (EDS), X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and Raman analysis. The effects of three independent parameters, including initial concentration (20-200 μg L^-1), temperature (5-30 °C), and adsorbent dose (2-80 g L^-1) were examined using batch experiments.

RESULTS

Characterization results confirmed that the graphene oxide was successfully coated on the surface of sand particles. Regression analysis of experimental results showed a great fit with a quadratic polynomial model with the R² = 0.999. Optimum conditions (initial concentration: 20 μg L^-1, temperature: 30 °C, and adsorbent dose: 80 g L^-1) with the desirability of 1.0 resulted in the minimum residual concentration of Mutagen X (2 μg L^-1). Equilibrium study results depicted that the experimental data were fitted well to the Freundlich and UT isotherm models.

Conversion of chlorine/nitrogen species and formation of nitrogenous disinfection by-products in the pre-chlorination/post-UV treatment of sulfamethoxazole

Pre-chlorination and UV disinfection are two common processes in drinking water treatment plants. Sulfamethoxazole (SMX), an antibiotic widely detected in source water, was selected as a precursor to study the conversion of chlorine/nitrogen species and DBP formation in pre-chlorination/post-UV process. The combined chlorine (mainly organic chloramines) produced in pre-chlorination of SMX can self-degrade and release free chlorine back again as pre-chlorination time goes on. With free chlorine dose increasing, the self-degradation rate of combined chlorine increased obviously. But the combined chlorine stopped self-degrading and remained stable around 1 mg-Cl₂/L after adding 0.30 mM chlorine for 30 min. Post-UV treatment after pre-chlorination can enhance the degradation and achieve a complete removal of combined chlorine (including organic chloramines). Deamination occurred during pre-chlorination/post-UV process and deamination amount (-NH₂) per SMX concentration was 0.19 M/M. Radicals in this process had no obvious influence on chlorine/nitrogen species conversion. Direct chlorination of SMX had the lowest DBP formation potentials while the application of pre-chlorination and UV enhanced them. Compared with UV treatment only, dichloroacetonitrile formation potential of SMX reduced by 1.58 × 10^-3 mol/mol-SMX (17.37 μg/l) after pre-chlorination/post-UV treatment. During pre-chlorination/post-UV/final-chlorination treatment of SMX, Br^- and natural organic matter can enhance DBP formation and toxicity-weighted values. Acid conditions showed a very high DBP risk, while alkaline conditions could cut this risk obviously, especially for the toxicity-weighted values of these DBPs.

Advantages of a ClO2/NaClO combination process for controlling the disinfection by-products (DBPs) for high algae-laden water

Chlorine dioxide (ClO₂) has been widely used in the process of preoxidation and disinfection as an excellent water treatment reagent. However, the inorganic by-products produced by ClO₂, such as chlorite (ClO₂^-) and chlorate (ClO₃^-) are harmful to human health, and this has become a potential problem when using ClO₂ in drinking water treatment. In this study, ClO₂ alone and a ClO₂/NaClO combination process were carried out to evaluate the algae removal efficiency of the treatment and the formation of disinfection by-products (DBPs: chlorite, chlorate, trihalomethanes and haloacetic acids) for high algae-laden water with 124.16 µg L^-1 chlorophyll a (Chl.a) content. The results show that disinfection with 1.5 mg L^-1 ClO₂ alone results in a ClO₂^- concentration exceeding 0.7 mg L^-1. ClO₂ preoxidation/ClO₂ disinfection is applicable for the control of effluent quality, but the ClO₂^- concentration still has an excessive risk when using 0.8 mg L^-1 and 0.6 mg L^-1 ClO₂ for the two process, respectively. In the ClO₂/NaClO combination process, the ClO₂^- concentration is below 0.6 mg L^-1, and trihalomethane (THM) and haloacetic acid (HAA) concentrations are lower than 60% of the maximum contaminant levels (MCLs) set by the World Health Organization (WHO). Further, the formation of ClO₂^- is more effectively controlled by NaClO preoxidation/ClO₂ disinfection than ClO₂ preoxidation/NaClO disinfection.

Disinfectant residual stability leading to disinfectant decay and by-product formation in drinking water distribution systems: A systematic review

Secondary disinfectants, such as chlorine and chloramine, have been widely applied to minimise microbial risks in drinking water during distribution. Key challenges have included the maintenance of stable concentrations of disinfectant residuals and the control of disinfection by-products that may form as a consequence of residual decay processes. Many factors may influence disinfectant residual stability and the consequential formation of by-products. Thus predictions of disinfectant stability and by-product formation are multifactorial problems, complete with numerous complications of parameter co-dependence and feedback amplification of some key parameters. The aim of this review was to derive an understanding of how disinfectant residual stability in drinking water distribution systems is impacted by various influencing factors such as water quality and operational parameters. Factors known to influence disinfectant stability and by-product formation were critically reviewed. A systematic review method was applied to identify 1809 journal articles published in the two decades from January 1998 to December 2017. From the initial screening, 161 papers were selected for detailed assessment. Important factors were identified to include temperature, water age, piping material, corrosion products, pH, hydraulic condition, disinfectant residual type and dosage and microbial activity. Microbial activity is a particularly complex parameter on which to base predictions since many factors are known to influence the degree and nature of such activity. These include temperature, water age, piping material, corrosion products, nutrients, natural organic matter, hydraulic condition and disinfectant residual type and dosage. Disinfectant types and dosages were found to be among the most important factors. Many knowledge gaps and research needs still remain, including the need for a more complete understanding of the factors that influence the production of nitrogenous disinfection by-products.

Electrochemical oxidation for stormwater disinfection: How does real stormwater chemistry impact on pathogen removal and disinfection by-products level?

Preliminary laboratory work has shown that electrochemical oxidation (ECO) is a promising technology for disinfection of harvested stormwater. This paper focuses on understanding how stormwater chemistry (e.g. pH, chloride, bicarbonate, ammonia and total organic carbon - that can vary substantially between sites) impacts the disinfection performance of ECO. Real stormwater samples from four different urban catchments were collected and tested for ECO performance in disinfecting stormwater pathogens using a boron doped diamond anode under the current density of 4.2 mA/cm². Results showed that total disinfection of indigenous Escherichia coli (E. coli), as well as three different stormwater pathogens (Enterococci, Campylobacter and C. perfringens) was achievable for all four tested stormwater within 30 min. Compared to the synthetic stormwater, lower disinfection rates were observed in real stormwater which has more complex chemistry. Stormwater chloride concentration was the only tested parameter that had significant impact on the treatment performance, with higher initial stormwater chloride concentration leading to an increased disinfection rate. Disinfection by-products in the treated stormwater were well below the Australian Drinking Water Guideline value for health, with its production level positively correlated to the pH values of stormwater.

Formation of disinfection by-products during chlorination of organic matter from phoenix tree leaves and Chlorella vulgaris

To better understand the precursor of disinfection by-products (DBPs) and provide useful information for water utilities to manage the drinking water, a study of DBP formation was conducted through chlorination of leaf organic matter (OM) from phoenix tree and algal OM from Chlorella vulgaris. DBPs investigated include trichloromethane (TCM), trichloroacetic acid (TCAA), dichloroacetic acid (DCAA), chloroacetic acid (CAA), dichloroacetonitrile (DCAN) and trichloroacetonitrile (TCNM). Results show that the specific yields (μg/mg C) of C-DBPs (TCM, CAA, DCAA and TCAA) from leaf OM were higher but the specific yields of N-DBPs (DCAN and TCNM) were lower than those from algal OM. Correlation analysis revealed that C-DBPs yields (μg/L) were significantly (p < 0.01) interrelated with each other (r = 0.937-0.996), and for each C-DBP, the hydrophobic OM contributed more to their formation (61-90% of total yields) as compared with hydrophilic OM. In spite of these characteristics, an in-depth examination was conducted revealing that the hydrophobicity and aromaticity of C-DBPs precursors were in the order of TCAA > DCAA & TCM > CAA. DCAN precursors were highly variable: they were dominated by hydrophobic OM (leaf OM: 86%) or hydrophilic OM (algal OM: 61%). Hydrophilic OM was the most important precursor for TCNM (76-79% of total yields), followed by hydrophobic neutral and base substances (29-45% of total yields), but the hydrophobic acids exhibited an inhibition role in TCNM formation.

Formation of iodinated trihalomethanes during breakpoint chlorination of iodide-containing water

This study investigated the formation of toxic iodinated trihalomethanes (I-THMs) during breakpoint chlorination of iodide-containing water. Impact factors including I^- concentration, natural organic matter (NOM) concentration and type, pH as well as Br^-/I^- molar ratio were systematically investigated. Moreover, the incorporation of I^- into I-THM formation was also calculated. The results showed that I-THM formation varied in different zones of the breakpoint curves. I-THMs increased with increasing chlorine dosage to breakpoint value and then dropped significantly beyond it. Iodoform (CHI₃) and chlorodiiodomethane (CHClI₂) were the major I-THMs in the pre-breakpoint zone, while dichloroiodomethane (CHCl₂I) was the dominant one in the post-breakpoint zone. The formation of I-THMs increased remarkably with I^- and dissolved organic carbon (DOC) concentrations. More bromine-containing species were formed as Br^-/I^- molar ratio increased from 0.5 to 5. In addition, the major I-THM compound shifted from CHCl₂I to the more toxic CHClBrI. As pH increased from 6.0 to 8.0, I-THM formation kept increasing in the pre-breakpoint zone and the speciation of I-THMs changed alongside the breakpoint curves. The incorporation of I^- during breakpoint chlorination was highly dependent on chlorine, I^-, and NOM concentrations, NOM type, solution pH and Br^-/I^- molar ratio.

Degradation kinetics of organic chloramines and formation of disinfection by-products during chlorination of creatinine

Organic chloramines can interfere with the measurement of effective combined chlorine in chlorinated water and are potential intermediate products of highly toxic disinfection by-products (DBPs). In order to know more about the degradation and transformation of organic chloramines, a typical organic chloramine precursor creatinine was selected for investigation and a corresponding individual organic chloramine chlorocreatinine was prepared in this study. The preparation condition of chlorocreatinine by chlorination was established as chlorine/creatinine = 1 M/M, reaction time = 2 h and pH = 7.0. Then the degradation kinetics of chlorocreatinine during further chlorination was studied, and a second-order rate constant of 1.16 (±0.14) M^-1 s^-1 was obtained at pH 7.0. Solution pH significantly influenced the degradation rate, and the elementary rate constants of chlorocreatinine with HOCl+H⁺, HOCl, OCl^- and chlorocreatinine^- with OCl^- were calculated as 2.43 (±1.55) × 10⁴ M^-2 s^-1, 1.05 (±0.09) M^-1 s^-1, 2.86 (±0.30) M^-1 s^-1 and 3.09 (±0.24) M^-1 s^-1, respectively. Besides, it was found that chlorocreatinine could be further converted into several C-DBPs (chloroform and trichloroacetone) and N-DBPs (dichloroacetonitrile (DCAN) and trichloronitromethane (TCNM)) during chlorination. The total yield of DBPs increased obviously with increasing pH, especially for TCNM. In addition, the presence of humic acid in creatinine solution could increase the formation of DCAN obviously during chlorination. Based on the UPLC-Q-TOF-MS analysis, the conversion pathways of chlorocreatinine were proposed. Several kinds of intermediate products were also identified as organic chloramines and some of them could even exist stably during the further chlorination.

Degradation of acrylamide during chlorination as a precursor of haloacetonitriles and haloacetamides

Acrylamide is a monomer of polyacrylamide, which is widely used in the water treatment process as a flocculant. The degradation kinetics and formation of disinfection by-products (DBPs) during acrylamide chlorination were investigated in this study. The reaction between chlorine and acrylamide followed a pseudo-first-order kinetics. A kinetic model regarding acrylamide chlorination was established and the rate constants of each predominant elementary reaction (i.e., the base-catalyzed reaction of acrylamide with ClO^- as well as the reactions of acrylamide with HOCl and ClO^-) were calculated as 7.89×10⁷M^-2h^-1, 7.72×10¹M^-1h^-1, and 1.65×10³M^-1h^-1, respectively. The presence of Br^- in water led to the formation of HOBr and accelerated the rate of acrylamide degradation by chlorine. The reaction rate constant of acrylamide with HOBr was calculated as 1.33×10³M^-1h^-1. The degradation pathways of acrylamide chlorination were proposed according to the intermediates identified using ultra-performance liquid chromatography and electrospray ionization-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS). Five chlorinated DBPs including chloroform (CF), dichloroacetonitrile (DCAN), trichloroacetonitrile (TCAN), dichloroacetamide (DCAcAm), and trichloroacetamide (TCAcAm) were identified during acrylamide chlorination. The formation of CF, DCAN, DCAcAm, and TCAcAm kept increasing, while that of TCAN increased and then decreased with increasing reaction time. As the chlorine dosage increased from 0.75 to 4.5mM, DCAN became the dominant DBP. Large amounts of CF, DCAN, and TCAN were formed at basic pHs. The hydrolysis of DCAN and TCAN led to the formation of DCAcAm and TCAcAm, respectively. The results of this study elucidated that acrylamide can be a precursor for the formation of haloacetonitriles (HANs) and haloacetamides (HAcAms) during drinking water treatment.

Comparison of the effects of chloramine and chlorine on the aromaticity of dissolved organic matter and yields of disinfection by-products

This study compared effects of chlorination and chloramination on the chromophores of dissolved organic matter (DOM) and attendant formation of disinfection by-products (DBPs) in raw and treated surface waters. Comparison of the differential absorbance spectra of chloraminated and chlorinated waters shows that interactions of chloramine with DOM chromophores result in changes that are in many respects similar to those observed for chlorine although the extent of degradation of DOM chromophores and the attendant decrease of DOM aromaticity by chloramine are less pronounced than that caused by free chlorine. The degradation of DOM chromophores caused by the examined disinfectants indicated that in both cases a gradual decrease of DOM took place. Decreases of DOM aromaticity estimated based on the changes of DOM absorbance at 254 or 280 nm were correlated with chlorine consumption in a similar way for both examined disinfectants. Correlations between changes of DOM absorbance and yields of dihaloacetic acids (DHAA) were also similar for chlorination and chloramination. This was interpreted to indicate that the generation of DHAA proceeds via the degradation of the reactive sites associated with DOM chromophores irrespective of whether these sites are engaged by chlorine or chloramine. Correlations between the decrease of DOM aromaticity and formation of other DBP (e.g. trihalomethanes - THM, trihaloacetic acids - THAA and dihaloacetonitriles - DHAN) for chloramine and chlorine were also observed but, as opposed to the observations for DHAA, the correlations between degradation of DOM aromaticity and yields of THM, THAA or DHAN were different for chlorination and chloramination.

Comparative assessment of ceramic media for drinking water biofiltration

Media type is a critical design consideration when implementing biofiltration for drinking water treatment. Granular activated carbon (GAC) has been shown to provide superior performance when compared to a wide range of media types, largely due to its higher surface area. Engineered ceramic media is an attractive alternative to GAC as it has a similar surface area but at a lower cost. This pilot-scale biofiltration study compared the performance of GAC, anthracite and two different effective sizes of ceramic (CER) media (1.0 mm and 1.2 mm), in terms of dissolved organic carbon (DOC), head loss, turbidity, and disinfection by-product formation potential (DBPFP). Biological acclimation was monitored using adenosine tri-phosphate (ATP) measurements; biomass was further examined using laccase and esterase enzyme activity assays. When compared to other media types examined, biological GAC had higher (p > 0.05) removals of DOC (9.8 ± 3.8%), trihalomethane formation potential (THMFP, 26.3 ± 10.2%), and haloacetic acid formation potential (HAAFP, 27.2 ± 14.0%). CER media required 6-7 months to biologically acclimate, while filters containing GAC and anthracite were biologically active (>100 ng of ATP/g media) following 30-45 days of operation. Once acclimated, ATP values of 243 and 208 ng/g attained for CER 1.0 and 1.2, respectively, were statistically comparable to GAC (244 ng/g) and higher than anthracite (110 ng/g), however this did not translate into greater organics removal. Esterase and laccase enzyme kinetics were highest for GAC, while CER was shown to have greater biodegradation potential than anthracite. The four media types attained similar turbidity reduction (p > 0.05), however ceramic media filters were observed to have run times which were 1.5-2.3 times longer when compared to anthracite, which could represent potential cost savings in terms of energy for pumping and backwash requirements. Overall, ceramic media was shown to be a potential alternative to anthracite when considering biofiltration, especially during cold water conditions (T < 10 °C).

Occurrences and changes of disinfection by-products in small water supply systems

The small water supply systems (WSSs) often report high concentrations of disinfection by-products (DBPs) in drinking water. In this study, occurrences of trihalomethanes (THMs) and haloacetic acids (HAAs) in Newfoundland and Labrador (NL), Canada, were investigated from 441 WSSs for a period of 18 years (1999-2016). The WSSs were divided into groundwater (GWP) and surface water (SWP) systems, which were further classified into eight sub-groups (P1-P8) based on the population served (≤ 100; 101-250; 251-500; 501-1000; 1001-3000; 3001-5000; 5001-10,000; and 10,000+, respectively). The DBPs with probable and possible carcinogenic forms were estimated. Overall, 31.1% of WSSs were GWP, in which averages of THMs and HAAs were 32.2 and 27.7 μg/L, respectively, while the SWP had averages of THMs and HAAs of 97.6 and 129.2 μg/L, respectively. The very small WSSs (P1-P3) of GWP had averages of THMs and HAAs in the ranges of 29.1-43.5 and 15.8-64.3 μg/L, respectively. The P1-P3 of SWP had averages of THMs and HAAs in the ranges of 92.6-112.8 and 108.0-154.0 μg/L, respectively, which often exceeded the Canadian guideline limits. If the samples represented the populations homogenously, the total populations exposed to THMs or HAA₅ above the guideline values would be in the range of 132.08-181.38 in thousands (30.3-41.6% of total populations). The probable and possible carcinogenic forms of THMs in GWP and SWP were in the ranges of 4.8-48.8 and 4.4-7.0% of THMs, respectively. In HAAs, carcinogenic forms were in the ranges of 82.6-98.4 and 97.6-98.7%, respectively. The findings indicated that the SWP might need further attention to better protect human health.

Iodinated trihalomethane formation during chloramination of iodate-containing waters in the presence of zero valent iron

Iodide (I^-) and iodinated X-ray contrast media (ICM) are the primary iodine sources for the formation of iodinated disinfection byproducts (I-DBPs), and iodate (IO₃^-) is believed to be a desired sink of iodine in water. This study found that highly cytotoxic iodinated trihalomethanes (I-THMs) also can be generated from iodate-containing waters (without any other iodine sources) in the presence of zero valent iron (ZVI) during chloramination, which could be a big issue in the wide usage of iron pipes. The effect of major factors including ZVI dosage, NH₂Cl and IO₃^- concentrations, initial pH, Br^-/IO₃^- molar ratio, phosphate concentration, iron corrosion scales (goethite and hematite) on the formation of I-THMs were investigated. Formation of I-THMs from IO₃^- increased with the increase of ZVI dosage, IO₃^- and NH₂Cl concentrations. Chloramines can also remarkably accelerate the reduction of IO₃^- by ZVI. Peak I-THM formation was found at pH 8. As the Br^-/IO₃^- molar ratio increased from 0 to 20, I-THM formation considerably enhanced, especially for the bromine-incorporated species. Goethite and hematite enhanced the formation of I-THMs in the presence of ZVI. Additionally, a significant suppression on I-THM formation was observed with the addition of phosphate. Considering that a large number of water distribution networks contain unlined cast iron pipes, transformation of IO₃^- in the presence of ZVI during chloramination may contribute to the formation of I-THMs in such systems.

Chlor(am)ination of iopamidol: Kinetics, pathways and disinfection by-products formation

The degradation kinetics, pathways and disinfection by-products (DBPs) formation of iopamidol by chlorine and chloramines were investigated in this paper. The chlorination kinetics can be well described by a second-order model. The apparent second-order rate constants of iopamidol chlorination significantly increased with solution pH. The rate constants of iopamidol with HOCl and OCl^- were calculated as (1.66 ± 0.09) × 10^-3 M^-1 s^-1 and (0.45± 0.02) M^-1 s^-1, respectively. However, the chloramination of iopamidol fitted well with third-order kinetics and the maximum of the apparent rate constant occurred at pH 7. It was inferred that the free chlorine (i.e., HOCl and OCl^-) can react with iopamidol while the combined chlorine species (i.e., NH₂Cl and NHCl₂) were not reactive with iopamidol. The main intermediates during chlorination or chloramination of iopamidol were identified using ultra performance liquid chromatography - electrospray ionization-mass spectrometry (UPLC-ESI-MS), and the destruction pathways including stepwise deiodination, hydroxylation as well as chlorination were then proposed. The regular and iodinated DBPs formed during chlorination and chloramination of iopamidol were measured. It was found that iodine conversion from iopamidol to toxic iodinated DBPs distinctly increased during chloramination. The results also indicated that although chloramines were much less reactive than chlorine toward iopamidol, they led to the formation of much more toxic iodinated DBPs, especially CHI₃.

Total organic halogen (TOX) in human urine: A halogen-specific method for human exposure studies

Disinfection by-products (DBPs) are a complex mixture of compounds unintentionally formed as a result of disinfection processes used to treat drinking water. Effects of long-term exposure to DBPs are mostly unknown and were the subject of recent epidemiological studies. However, most bioanalytical methods focus on a select few DBPs. In this study, a new comprehensive bioanalytical method has been developed that can quantify mixtures of organic halogenated compounds, including DBPs, in human urine as total organic chlorine (TOCl), total organic bromine (TOBr), and total organic iodine (TOI). The optimized method consists of urine dilution, adsorption to activated carbon, pyrolysis of activated carbon, absorption of gases in an aqueous solution, and halide analysis with ion chromatography and inductively coupled plasma-mass spectrometry. Spike recoveries for TOCl, TOBr, and TOI measurements ranged between 78% and 99%. Average TOCl, TOBr, and TOI concentrations in five urine samples from volunteers who consumed tap water were 1850, 82, and 21.0μg/L as X^-, respectively. Volunteers who consumed spring water (control) had TOCl, TOBr, and TOI average concentrations in urine of 1090, 88, and 10.3μg/L as X^-, respectively. TOCl and TOI in the urine samples from tap water consumers were higher than the control. However, TOBr was slightly lower in tap water urine samples compared to mineral water urine samples, indicating other sources of environmental exposure other than drinking water. A larger sample population that consumes tap water from different cities and mineral water is needed to determine TOCl, TOBr, and TOI exposure from drinking water.

Bromine incorporation into five DBP classes upon chlorination of water with extremely low SUVA values

The main objective of this study was to assess the effects of disinfection conditions on bromine incorporation into disinfection by-products (DBPs) during chlorination of water with low specific UV absorbance (SUVA). Five classes of DBPs were included: trihalomethanes (THMs), dihaloacetic acids (di-HAAs), trihaloacetic acids (tri-HAAs), dihaloacetonitriles (DHANs) and trihalonitromethanes (THNMs). Results showed that the bromine utilization in DBPs formation was positive related with reaction time, pH and temperature. On the other hand, the bromine substitution factors (BSFs) of DBPs were generally increased with pH (except tri-HAAs) and bromide concentration, but decreased with the reaction time, temperature and chlorine dose. Moreover, the BSFs values varied with DBP classes with the ranking being as following: THNMs≫DHANs≫tri-HAAs>THM≈di-HAAs. These results were mostly similar with the references, yet the pH effect on BSFs as well as the rank of BSFs for different DBP classes may differ with the specific UV absorbance of organic matter.