Challenges to Accurate Estimation of Methane Emission from Septic Tanks with Long Emptying Intervals.

Septic tanks in low- and middle-income countries are often not emptied for a long time, potentially resulting in poor pollutant removal efficiency and increased greenhouse gas emissions, including methane (CH4). We examined the impact of long emptying intervals (4.0-23 years) on the biochemical oxygen demand (BOD) removal efficiency of 15 blackwater septic tanks and the CH4 emission rates of 23 blackwater septic tanks in Hanoi. The average BOD removal efficiency was 37% (-2-65%), and the average CH4 emission rate was 10.9 (2.2-26.8) g/(cap·d). The emptying intervals were strongly negatively correlated with BOD removal efficiency (R = -0.676, p = 0.006) and positively correlated with CH4 emission rates (R = 0.614, p = 0.001). CH4 emission rates were positively correlated with sludge depth (R = 0.596, p = 0.002), but against expectation, negatively correlated with BOD removal efficiency (R = -0.219, p = 0.451). These results suggest that shortening the emptying interval improves the BOD removal efficiency and reduces the CH4 emission rate. Moreover, the CH4 emission estimation of the Intergovernmental Panel on Climate Change, which is a positive conversion of BOD removal, might be inaccurate for septic tanks with long emptying intervals. Our findings suggest that emptying intervals, sludge depth, and per-capita emission factors reflecting long emptying intervals are potential parameters for accurately estimating CH4 emissions from septic tanks.

High formation of trichloroacetic acid from high molecular weight and ultra-hydrophilic components in freshwater raphidophytes upon chlorination.

Raphidophytes are flagellate unicellular algae that causes algal blooms in drinking water sources. In Japan, it was recently reported that the concentration of trichloroacetic acid (TCAA), a major chlorinated disinfection byproduct (DBP), increased dramatically in drinking water when the source water contained raphidophytes. Additionally, raphidophytes produced haloacetic acid (HAA) precursors, especially TCAA precursors, in high concentrations. However, their properties are still unknown, and thus, well-designed countermeasures against DBP formation have not yet been established. Therefore, in this study, the HAA precursors originated from raphidophytes in natural water collected from the algal blooms in Muro Dam (Nara Prefecture, Japan) and Gonyostomum semen (G. semen), a raphidophyte species, cultivated in the laboratory, were characterized to provide the information for establishing suitable treatment strategies. Using several high-performance liquid chromatography columns, solid-phase extraction cartridges, and ultrafiltration devices, and the spectral profiles, we discovered that the HAA precursors are highly hydrophilic and high-molecular-weight compounds with acidic and phenolic functional groups. Further characterization of the high-molecular-weight fraction (> 3 kDa) from the G. semen culture showed that the HAA precursors had a molecular weight of ~10-60 kDa, and that they were not protein molecules despite containing a large amount of nitrogen atoms. Furthermore, the TCAAFP of the fraction (310 ± 25 µg/mg C) were as high as phenol, known as a reactive TCAA model precursor. The presence of unique and unreported DBP precursors was confirmed.

Global assessment of chemical quality of drinking water: The case of trihalomethanes.

BACKGROUND: Trihalomethanes (THM), a major class of disinfection by-products, are widespread and are associated with adverse health effects. We conducted a global evaluation of current THM regulations and concentrations in drinking water. METHODS: We included 120 countries (∼7000 million inhabitants in 2016), representing 94% of the world population. We searched for country regulations and THM routine monitoring data using a questionnaire addressed to referent contacts. Scientific and gray literature was reviewed where contacts were not identified or declined participation. We obtained or estimated annual average THM concentrations, weighted to the population served when possible. RESULTS: Drinking water regulations were ascertained for 116/120 (97%) countries, with 89/116 (77%) including THM regulations. Routine monitoring was implemented in 47/89 (53%) of countries with THM regulations. THM data with a varying population coverage was obtained for 69/120 (58%) countries consisting of ∼5600 million inhabitants (76% of world's population in 2016). Population coverage was ≥90% in 14 countries, mostly in the Global North, 50-89% in 19 countries, 11-49% among 21 countries, and ≤10% in 14 countries including India, China, Russian Federation and Nigeria (40% of world's population). DISCUSSION: An enormous gap exists in THM regulatory status, routine monitoring practice, reporting and data availability among countries, especially between high- vs. low- and middle-income countries (LMICs). More efforts are warranted to regulate and systematically assess chemical quality of drinking water, centralize, harmonize, and openly report data, particularly in LMICs.

Effects of the chlorination on organic matter removal and microbial communities during soil aquifer treatment for wastewater reclamation.

Soil aquifer treatment (SAT) has been widely applied for wastewater reclamation, which cooperates secondary treatment (i.e. A2O process) and disinfection treatment (chlorination) in wastewater treatment plants (WWTPs), to remove organic matter. This study compared dissolved organic carbon (DOC) characteristics, substrate utilisation patterns, and microbial communities between pre-chlorination SAT and SAT columns, and effective removals of DOC were observed in the pre-chlorination SAT and SAT columns. However, the composition of HiA in SAT columns without chlorination was less than in pre-chlorination SAT columns for DOC fraction. In comparison to A2O effluent, different metabolic patterns and the composition of the microbial community were demonstrated by the top layer of SAT column and pre-chlorination SAT column. Furthermore, deeper layers showed similarities in the metabolic pattern and composition of the microbial community. Overall, pre-chlorination minimised the change of the microbial communities from A2O effluent in the top layer of SAT except for deeper layers, and DOC concentrations decreased in pre-chlorination SAT column. Thus, the cooperation of SAT and wastewater treatments could be suitable for wastewater reclamation.

Predictable Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry Fragmentation of Ozone-Reactive N-Nitrosodimethylamine Precursors Coupled with In Silico Fragmentation and Ion Mobility-Quadrupole Time-of-Flight Facilitates Their Identification in Sewage.

This study investigated the liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QTOF/MS) fragmentation of 10 potent model ozone (O3)-reactive N-nitrosodimethylamine (NDMA) precursors bearing (CH3)2N-N or (CH3)2N-(SO2)-N. Fragments (m/z 61.0766, 60.0688 Da loss, and 72.0688 Da loss) were discovered as pertinent diagnostic fragments for precursors bearing (CH3)2N-N, whereas a loss of 108.0119 Da was consistent for precursors bearing (CH3)2N-S(O2)-N. Using the fragments as structural hints on a sewage fraction with a high concentration of O3-reactive precursors, peaks of precursors sharing m/z 61.0766, a 60.0688 Da loss, or both were flagged. Then, using in silico fragmenters and (CH3)2N-N as a substructure filter on online-chemical structure databases, we identified PubChem's compound identifier (PCCID) 141210417 and 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene)disemicarbazide (TMDS). TMDS was confirmed using an authentic standard, and ion mobility (IM)-QTOF/MS confirmed its rider peak as PCCID 141210417. PCCID 141210417 is an isomer of TMDS, and its environmental occurrence is associated with technical-grade TMDS and industrial effluents. The estimated contribution of TMDS to the total NDMA formation potential of the sewage fraction was 20-24%, which was suggestive of the significance of PCCID 141210417 and other precursors.

Data-independent acquisition with ion mobility mass spectrometry for suspect screening of per- and polyfluoroalkyl substances in environmental water samples.

Per- and polyfluoroalkyl substances (PFASs) have environmentally persistent, and the various types of PFASs have been detected in water environments. Many previous studies have performed data-dependent acquisition (DDA) of mass spectra from an environmental sample by high-resolution mass spectrometry to identify PFAS suspects individually. In comparison, the data-independent acquisition (DIA) of comprehensive mass spectra of the sample is a technology which enables to know the occurrences of suspects and non-targets simultaneously. However, it is difficult to associate the fragment ions of targeted precursor ions by retention time only, because of the existence of co-eluting ions derived from environmental samples. Since the separation of ions is not enough with only the conventional DIA method, here, we attempted to support it using ion mobility mass spectrometry (IMS) to distinguish the relevant ions from co-eluting ions by drift time. Firstly, suspect screening of PFASs with eternal database resulted in determining 32-96 PFAS suspects in firefighting foam impacted groundwater samples (n = 8) by suspect screening. Among all the pairs of respective precursor ions and fragment ions of the PFAS suspects, 5%-19% (4-9 PFASs) of them were associated without considering the drift time of IMS, while 37%-49% (15-43 PFASs) of them were associated with considering the drift time. The consideration of the drift time increased the association ratios in all samples. In a sample, most precursor ions could be associated with their fragment ions (41 of 43 PFASs) because at least one probable fragment ion was observed among three of maximum intensity fragment ions. Thus, the method improved the identification by excluding the unrelated co-eluting ions by IMS. Moreover, the method can acquire a certain reliable MS/MS spectra of suspects in environmental samples in one analysis. It is not essential to conduct instrumental analyses again for samples stored for a long time even when the data sets and/or methodologies of data analyses are modified (e.g., the original database, screening list, or statistical filtering/data cleaning approach). It will be particularly useful for studies that must analyze a large number of environmental samples.

Effect of coexisting manganese ion on the formation of haloacetic acids during chlorination.

Haloacetic acids (HAAs) are a group of disinfection by-products formed by the reaction of dissolved organic matter (DOM) in source water and disinfectants in the drinking water treatment process. The formation of HAAs is known to be affected by several factors (e.g., pH, temperature, concentration, and DOM components in source water). However, the effects of coexisting substances, such as metal ions, on HAA formation are not well understood. In this study, HAA formation potentials (FPs) of model compounds of DOM and environmental waters in the presence or absence of manganese ion upon chlorination were compared. The results of experiments with model compounds of DOM showed that manganese ion promoted the formation of HAA from citric acid, trans-aconitic acid, and cis-aconitic acid. Even for a manganese concentration of less than 50 µg/L, which is the standard value of manganese in drinking water in the USA, EU, and Japan, manganese had great influence on the dichloroacetic acid FPs of these compounds. However, the manganese ion did not enhance the HAAFPs of the environmental waters tested. Nevertheless, manganese may have an effect on HAAFPs of environmental waters collected at the occurrence of an unusual growth of microorganisms, such as algal bloom.

Predicting formation of haloacetic acids by chlorination of organic compounds using machine-learning-assisted quantitative structure-activity relationships.

The presence of disinfection byproducts (DBPs) in drinking water is a major public health concern, and an effective strategy to limit the formation of these DBPs is to prevent their precursors. In silico prediction from chemical structure would allow rapid identification of precursors and could be used as a prescreening tool to prioritize testing. We present models using machine learning algorithms (i.e., support vector regressor, random forest regressor, and multilayer perceptron regressor) and chemical descriptors as features to predict the formation of haloacetic acids (HAAs). A robust model with good predictivity (i.e., leave-one-out cross-validated Q2 > 0.5) to predict the formation of trichloroacetic acid (TCAA) was developed using a random forest regressor. The number of aromatic bonds, hydrophilicity, and electrotopological descriptors related to electrostatic interactions and the atomic distribution of electronegativity were identified as important predictors of TCAA formation potentials (FPs). However, the prediction of dichloroacetic acid was less accurate, which is congruent with the presence of different types of precursors exhibiting distinct mechanisms. This study demonstrates that nonlinear combinations of general chemical descriptors can adequately estimate HAAFPs, and we hope that our study can be used to predict precursors of other disinfection byproducts based on chemical structures using a similar workflow.

A profile analysis with suspect screening of per- and polyfluoroalkyl substances (PFASs) in firefighting foam impacted waters in Okinawa, Japan.

Per- and polyfluoroalkyl substances (PFASs) are a group of persistent contaminants detected in firefighting foam impacted waters. Previous studies have performed suspect and non-target screening by high-resolution mass spectrometry (HRMS) to determine the composition of PFAS contamination and to discover unknown PFASs. Here, we performed a profile analysis with suspect screening against two lists in the NORMAN Suspect List Exchange in firefighting foam impacted environmental and drinking water (n = 18) collected in Okinawa, Japan, in April 2019. Samples were analyzed by liquid chromatography (LC) quadrupole time-of-flight (QTOF) MS in electron spray ionization mode. Suspect screening returned 116 candidate PFASs with their molecular weights, functional groups, and perfluoroalkyl chain lengths. Long-chain perfluoroalkyl acids (PFAAs) and some of their precursors were specifically found around the firefighting training area. Short-chain PFAAs were assumed to be formed from precursors by environmental processes. Perfluoroalkyl sulfonamide precursors were found to be transformed to perfluoroalkyl sulfonic acids (PFSAs) in the drinking water treatment process. In contrast, biological activated carbon filtration formed perfluoroalkyl carboxylic acids (PFCAs). The PFAS profile showed that a large number of different substances needs to be considered.

Effect of biodegradation on haloacetic acid formation potentials of anthropogenic compounds during chlorination.

During drinking water treatment processes, anthropogenic compounds act as important precursors of disinfection by-products such as haloacetic acids (HAAs). Several transformations in these precursors occur prior to the disinfection stage, such as partial biodegradation. We hypothesized that this partial biodegradation of anthropogenic compounds potentially affects their HAA formation potentials (HAAFPs). In this study, the HAAFPs of 51 anthropogenic compounds after short-term contact (less than 1 h) and long-term contact (24 h) with activated sludge were compared. Considerable changes were observed particularly in trichloroacetic acid (TCAA) formation potentials (FPs) of phenols, demonstrating that biodegradation should be considered in investigations of potential precursors of HAAs. Phenols with low HAAFPs, such as hydroquinone, show higher HAAFPs after biodegradation, but HAAFPs of most phenols and anilines decreased after biodegradation. Thus, biodegradation will most likely have a positive impact on water quality from the standpoint of HAAFP reduction. For most aliphatic compounds, changes in HAAFP were negligible, but the dichloroacetic acid (DCAA) FP of acrylic acid largely increased. This study illustrates that biodegradation may have a large effect on the HAAFPs of anthropogenic compounds.

Biodegradation of pharmaceuticals and personal care products in the sequential combination of activated sludge treatment and soil aquifer treatment.

Soil aquifer treatment (SAT), applied after activated sludge treatment (AST), has been widely used for wastewater reclamation. AST and SAT show potential for removing micropollutants, including pharmaceuticals and personal care products (PPCPs). However, the role of sequential combination of AST and SAT on the biodegradation of PPCPs was not clear in previous studies. In this study, the removal characteristics of PPCPs in AST and SAT were evaluated to assess the legitimacy of sequential combination of AST and SAT. SAT showed effective removals of antibiotics (> 80%), including fluoroquinolones and macrolides by sorption, but poor removals of amide pharmaceuticals (i.e. carbamazepine and crotamiton) were observed in both AST and SAT. Additionally, biodegradation contributed to the effective removal of carboxylic PPCPs (i.e. ketoprofen and gemfibrozil) in both ASTs and SAT, but effective biodegradation of halogenated acid and polycyclic aromatic compounds (i.e. clofibric acid and naproxen) was observed only in SAT (82.1% and 81.8%, respectively). Furthermore, the microbial substrate metabolic patterns showed that amino acids, amines, and polymers were biodegradable in SAT, which was fit for the biodegradation characteristics of PPCPs in SAT. For microbial communities, Proteobacteria were dominant in AST and SAT, but Acidobacteria and Actinobacteria were more abundant in SAT than AST, which could contribute to the effective removals of halogenated acid in SAT. Considering PPCP biodegradation and substrate metabolism, SAT displays a wider range on the biodegradation than AST. Therefore, we conclude that these two processes can complement each other when used for controlling PPCPs.

A new method to search for per- and polyfluoroalkyl substances (PFASs) by linking fragmentation flags with their molecular ions by drift time using ion mobility spectrometry.

Per- and polyfluoroalkyl substances (PFASs) are a group of anthropogenic organic fluorinated compounds that have been detected widely. To discover unknown PFASs, previous researchers have applied high-resolution mass spectrometer using fragmentation flagging approach with common fragment ion at the same retention time as the flags. However, it was difficult to search for their molecular ion from co-eluting peaks in the full-scan spectrum at a specific retention time. Here, we attempted to utilize drift time acquired by ion mobility spectrometry for making linkages between fragment ions and their molecular ions. For validating the process, standard solution spiked with PFASs were analyzed by liquid chromatography/ion mobility - quadrupole time-of-flight mass spectrometry (LC/IM-QTOF-MS). Fluorinated fragment ions (fragmentation flags) were categorized into three classes: Class 1 (120 types of [CxFy]-), Class 2 (123 types of [CxFyO]-), Class 3 (131 types of [CxFyO3S]-) and all overlapping fragmentation flags detected at an identical retention time were bundled together as a "flag set". Injecting standard mixed solution of 20 types of PFASs resulted in picking up 20 flag sets by fragmentation flagging. All the fragmentation flags were detected within a designated range of drift time, and their molecular ion was confirmed as a PFAS spiked in the standard solution even when co-eluting compounds were found at almost same retention time. This method was applied to a household fire extinguisher liquid, resulting in finding out nine molecular ions. Therefore, the new linking method achieved rapid searching for the prospective molecular ions using LC/IM-QTOF-MS.

Formation of N-nitrosodimethylamine by chloramination of anthropogenic nitrogenous compounds with dimethylamine monitored by Japanese water authorities.

Pollutant release and transfer registers (PRTRs) compounds accidentally released to source waters can be important precursors of the carcinogenic N-nitrosodimethylamine (NDMA) during drinking water treatment. The NDMA formation potentials (NDMAFPs) of 31 anthropogenic nitrogenous compounds with dimethylamine (DMA) moiety on the Japanese PRTR and the registered precursors listed by the Ministry of Health, Labour and Welfare of Japan are investigated as well as influencing factors (i.e., NH2Cl dose and water matrices) on the NDMAFPs of precursors. Tertiary amines with aryl groups ß-positioned to the nitrogen atom of the DMA moiety formed high concentrations of NDMA (35-51%) during chloramination. Moreover, dimethylcarbamoyl chloride (DMCCl) was considered a new NDMA precursor with NDMAFP of 1.1%, higher than DMA, a traditional NDMA precursor. Excessive NH2Cl dose enhanced the NDMA formation, and the NDMAFP of DMCCl significantly decreased in river water; the effect of the matrix in river water varied and was compound-specific. Among the selected nitrogenous compounds, NDMAFPs of 15 excessed the current guideline concentration for NDMA in Japan (100 ng/L) assuming an accidental release of 0.144 mg C/L (the concentration in previous Japanese water quality accident in May 2012), and 2-(dimethylaminomethyl) thiophene (DMAMT) showed the highest NDMAFP at 58 µg/L.

Ferroferric Oxide Significantly Affected Production of Soluble Microbial Products and Extracellular Polymeric Substances in Anaerobic Methanogenesis Reactors.

Conductive materials facilitate direct interspecies electron transfer between acidogens and methanogens during methane (CH4) production. Soluble microbial products (SMP) and extracellular polymeric substances (EPS) produced by microorganisms might act as the electron shuttle between microorganisms and conductive materials. In this study, effects of conductive ferroferric oxide (Fe3O4) on anaerobic treatment process and the production of SMP and EPS were investigated. The maximum CH4 production rate was enhanced by 23.3% with the dosage of Fe3O4. The concentrations of proteins, polysaccharides, and humic substances in tightly bound EPS (T-EPS) were promoted, suggesting that extracellular metabolisms were induced by conductive materials. Distribution of potential electron shuttles such as quinone-like substances, flavins, aromatic amino acids, and dipeptides in SMP and EPS phases were comprehensively investigated and these electron shuttles were significantly affected by Fe3O4. Dipeptides consisting of phenylalanine were widely detected in T-EPS of the Fe3O4 reactor, indicating a potential different extracellular electron exchange pattern with the addition of conductive materials.

Determination of quorum-sensing signal substances in water and solid phases of activated sludge systems using liquid chromatography-mass spectrometry.

The detection of acyl homoserine lactones (AHLs) in activated sludge is essential for clarifying their function in wastewater treatment processes. An LC-MS/MS method was developed for the detection of AHLs in both the aqueous and solid phases of activated sludge. In addition, the effects of proteases and extracellular polymeric substances (EPS) on the detection of AHLs were evaluated by adding protease inhibitors and extracting EPS, respectively. Recoveries of each AHL were improved by adding 50µL of protease inhibitor, and recoveries were also improved from 0 to 56.9% to 24.2%-105.8% by EPS extraction. Applying the developed method to determine the type and concentration of AHLs showed that C4-HSL, C6-HSL, C8-HSL and 3-oxo-C8-HSL were widely detected in a suspended activated sludge system. The dominant AHL was C8-HSL, with a highest concentration of 304.3ng/L. C4-HSL was mainly distributed in the aqueous phase, whereas C6-HSL, C8-HSL and 3-oxo-C8-HSL were preferentially distributed in the sludge phase.

Determination of Caffeine and Its Metabolites in Wastewater Treatment Plants Using Solid-Phase Extraction and Liquid Chromatography-Tandem Mass Spectrometry.

For caffeine and its seven major metabolites (i.e., theobromine, theophylline, paraxanthine, 1-methylxanthine, 3-methylxanthine, 7-methylxanthine, and xanthine), an optimized analytical method using liquid chromatography-tandem mass spectrometry (LC-MS/MS) for their detection in wastewater samples was developed in this study. Extraction of these compounds (recoveries ranged from 60.3 to 83.2%) was made possible by combining universal polymeric reversed-phase cartridge and polymeric strong cation exchange cartridge. This method was applied to the determination of caffeine and its metabolites in the influent and effluent of an anaerobic-anoxic-oxic (A2O) process. In the A2O influent, caffeine and its metabolites (except xanthine) ranged from 1.39 to 5.45 µg/L, and their concentrations in the A2O effluent ranged from 10.2 to 171.3 ng/L. The mass load of caffeine was 14.9 g/day/1000 inhabitants, considering the population served by the target wastewater treatment plant (WWTP). The concentration of caffeine derivatives in wastewater influent is a tool for estimating the population size in the area served by WWTPs.

Formation of chlorinated haloacetic acids by chlorination of low molecular weight compounds listed on pollutant release and transfer registers (PRTRs).

Anthropogenic compounds accidentally released to the environment could be important precursors of disinfection byproducts (DBPs) in drinking water treatment processes. In this study, the haloacetic acid formation potentials (HAAFPs) of 155 anthropogenic compounds listed on the Japanese pollutant release and transfer register (PRTR) system were evaluated. The results showed that phenolic and aromatic amine compounds were important HAA precursors, and chlorinated phenols showed high HAAFPs (>400 µg/mgC). Moreover, trichlorfon and ethyl chloroacetate (HAAFP of 104.9 and 602.3 µg/mgC, respectively) were also important HAA precursors because of their ability to undergo hydrolysis. Although most anthropogenic compounds with high HAAFPs showed high chlorine consumptions, no clear correlation between HAAFPs and chlorine consumptions was found in this study. In addition, the quantitative structure-activity relationship (QSAR) approach was a useful tool for predicting the chlorine consumption of organic compounds but was not effective for predicting HAAFPs based on the information currently available. A scenario study assuming a hypothetical accidental release predicted that the release of 3,4-dichloroaniline (HAAFP of 407.6 µg/mgC) would lead to a violation of the current drinking water quality standards for HAAs in Japan.

Effect of operating conditions in soil aquifer treatment on the removals of pharmaceuticals and personal care products.

Soil aquifer treatment (SAT) is an alternative advanced treatment for wastewater reclamation, and it has the potential to control micropollutants including pharmaceuticals and personal care products (PPCPs). However, the relationship of operating conditions in SAT and removals of micropollutants was not clear. In this study, the effects of operating conditions on the removals of PPCPs were evaluated by using lab-scale columns and plant pilot-scale reactors under different operating conditions. Firstly, weathered granite soil (WGS), standard sand (SAND) and Toyoura standard sand (TS) have different soil characteristics such as total organic carbon (TOC) and cation exchange capacity (CEC). In the columns with these packing materials, the removals of carboxylic analgesics and antilipidemics were effective regardless packing materials. The removals of antibiotics were more effective in WGS than in TS and SAND, indicating high TOC and CEC enhance the sorption in SAT. Secondly, with the extension of hydraulic retention time (HRT), the removals of sulfamethoxazole, acetaminophen, crotamiton, and antipyrine were improved in WGS columns, and adaptable biodegradation for moderately removable PPCPs was formed. Thirdly, the removal efficiencies of sulfamethoxazole and crotamiton were higher in the WGS column under vadose condition than in the WGS column under saturated condition, because of aerobic condition in WGS column under vadose condition. Though long HRT and vadose condition had positive influence on the removals of several PPCPs such as sulfamethoxazole, WGS column with an HRT of 7days under saturated condition removed most PPCPs.

Characterization of organic precursors for chlorinous odor before and after ozonation by a fractionation technique.

To identify the primary fraction of dissolved organic matter (DOM) responsible for chlorinous odor, waters treated by the conventional treatment (i.e., coagulation, flocculation, sedimentation and rapid sand filtration (RSF)) and ozonation were characterized by a fractionation technique prior to chlorination. Furthermore, chlorinous odor strengths originated from organic fractions were compared with that resulted from trichloramine (NCl3). Odor strengths and trichloramine concentrations were determined by the triangle sensory test and head space-GC/MS, respectively. The major DOM fraction for outlet water of RSF was hydrophobic acid (HoA), whereas the hydrophilic acid (HiA) fraction was dominant in the ozonated water. For a fixed DOC level (1 mgC/L), the base (Bas) or hydrophilic base (HiB) fraction was found to be the major organic precursor of chlorinous odor for the effluent of RSF. Even the mass percentages of DOM fractions in RSF water were considered, Bas was the major DOM fractions responsible for chlorinous odor. For ozonated water, two major precursors of chlorinous odor were HiA and hydrophilic neutral (HiN) fractions. Furthermore, the influence of trichloramine on chlorinous odor intensity for ozonated water should not be negligible. Under variation of seasonal organic contents, changes in precursors of chlorinous odor were observed.

Identification of a new N-nitrosodimethylamine precursor in sewage containing industrial effluents.

N-Nitrosodimethylamine (NDMA), a potential human carcinogen, is known to be a disinfection byproduct of chloramination and ozonation. NDMA is formed during ozonation at water purification plants in the Yodo River basin, a major drinking water source in western Japan. An NDMA precursor, 1,1,5,5-tetramethylcarbohydrazide (TMCH) was identified in sewage containing industrial effluents via ultrahigh performance liquid chromatography-tandem mass spectrometry, and ultrahigh performance liquid chromatography-time-of-flight mass spectrometry, as well as nuclear magnetic resonance spectroscopy. The mean of the NDMA molar formation yield of TMCH upon ozonation in four water matrices was 140%. TMCH removal was low during biological treatment processes at a sewage treatment plant. The mean TMCH contribution to total NDMA precursors upon ozonation of the primary, secondary, and final effluents of the sewage treatment plant in January and February of 2014 was 43-72%, 51-72%, and 42-60%, respectively, while the contributions of 4,4'-hexamethylenebis(1,1-dimethylsemicarbazide) and 1,1,1',1'-tetramethyl-4,4'-(methylene-di-p-phenylene)disemicarbazide, two other known NDMA precursors, were limited to 0.6% and 6.9%, respectively. Thus, TMCH was identified as the primary precursor yielding NDMA upon ozonation in the Yodo River basin.