Monitoring dissolved organic matter in wastewater and drinking water treatments using spectroscopic analysis and ultra-high resolution mass spectrometry

Freeze-induced acceleration of iodide oxidation and consequent iodination of dissolved organic matter to form organoiodine compounds

Freeze-induced acceleration of I- oxidation and the consequent iodination of dissolved organic matter (DOM) contribute to the formation of organoiodine compounds (OICs) in cold regions. The formed OICs may be a potentially important source of risk and are very closely with the environment and human health. Herein, we investigated the acceleration effects of the freeze process on I- oxidation and the formation of OICs. In comparison to reactive iodine species (RIS) formed in aqueous solutions, I- oxidation and RIS formation were greatly enhanced in frozen solution and were affected by pH, and the content of I- and O2. Freeze-thaw process further promoted I- oxidation and the concentration of RIS reached 45.7 µmol/L after 6 freeze-thaw cycles. The consequent products of DOM iodination were greatly promoted in terms of both concentration and number. The total content of OICs ranged from 0.02 to 2.83 µmol/L under various conditions. About 183-1197 OICs were detected by Fourier transform ion cyclotron resonance mass spectrometry, and more than 96.2% contained one or two iodine atoms. Most OICs had aromatic structures and were formed via substitution and addition reactions. Our findings reveal an important formation pathway for OICs and shed light on the biogeochemical cycling of iodine in the natural aquatic environment.

Enhanced Mineralization of Organic Pollutants through Atomic Hydrogen-Mediated Alternative Transformation Pathways

Electrocatalytic hydrogen atom-hydroxyl radical (H*-·OH) redox system is a promising approach for contaminant removal and mineralization. However, its working mechanism, especially the effect of H*, remains unclear, hindering its practical application. Herein, we constructed an electrochemical reactor equipped with our self-made Pd-loaded Ti/TiO2 nanotube cathode and a commercial boron-doped diamond anode. After fulfilling the electrode characterization and free radical detection, we employed coumarin and 7-azido-4-methylcoumarin as probes to confirm the participation of H* in the transformation of organic compounds. A comprehensive study on the degradation kinetics, reaction, and mineralization mechanisms using benzoic acid (BA) and 4-chlorophenol (4-CP) as model compounds was further conducted. The rate constants and total organic carbon removal of BA and 4-CP in the redox system increased compared with those of the individual oxidation and reduction processes. Theoretical calculations demonstrate that H* opens up alternative pathways for BA and 4-CP ring cleavage, forming quinones as reactive intermediates. Furthermore, H* facilitates the mineralization of the typical intermediates, maleic acid and fumaric acid, through C=C bond addition and H-abstraction from the 1,1-diol structure. The presence of H* provides alternative pathways for pollutant transformation, consequently reducing the treatment duration.

Molecular-level insights into dissolved organic matter and its variations of the full-scale processes in a typical petrochemical wastewater treatment plant

Petrochemical wastewater (PCWW) treatment poses challenges due to its unique and complex dissolved organic matter (DOM) composition, originating from various industrial processes. Despite the addition of advanced treatment units in PCWW treatment plants to meet discharge standards, the mechanisms of molecular-level sights into DOM reactivity of the upgraded full-scale processes including multiple biological treatments and advanced treatment remain unclear. Herein, we employ water quality indexes, spectra, molecular weight (MW) distribution, and Fourier transform ion cyclotron resonance mass spectrometry to systematically characterize DOM in a typical PCWW treatment plant including influent, micro-oxygen hydrolysis acidification (MOHA), anaerobic/oxic (AO), and micro-flocculation sand filtration-catalytic ozonation (MFSF-CO). Influent DOM is dominated by tryptophan-like and soluble microbial products with MW fractions 〈 1 kDa and 〉 100 kDa, and CHO with lignin and aliphatic/protein structures. MOHA effectively degrades macromolecular CHO (10.86 %) and CHON (5.24 %) compounds via deamination and nitrogen reduction, while AO removes CHOS compounds with MW < 10 kDa by desulfurization, revealing distinct DOM conversion mechanisms. MFSF-CO transforms unsaturated components to less aromatic and more saturated DOM through oxygen addition reactions and shows high CHOS and CHONS reactivity via desulfurization and deamination reactions, respectively. Moreover, the correlation among multiple parameters suggests UV254 combined with AImod as a simple monitoring indicator of DOM to access the chemical composition. The study provides molecular-level insights into DOM for the contribution to the improvement and optimization of the upgraded processes in PCWW.

Spectral fusion-based machine learning classifiers for discriminating membrane breakage in multiple scenarios

Membrane breakage can lead to filtration failure, which allows harmful substances to enter the effluent, posing potential hazards to human health and the environment. This study is an innovative combination of fluorescence and ultraviolet-visible (UV-Vis) spectroscopy to identify membrane breakage. It aims to unravel more comprehensive information, improve detection sensitivity and selectivity, and enable real-time monitoring capabilities. Fluorescence and UV-Vis data are extracted through variance partitioning analysis (VPA) and integrated through a decision tree algorithm to form a superior system with enhanced discrimination capabilities. VPA improves discrimination efficiency by extracting key information from spectral data and eliminating redundancy. The decision tree algorithm, on the other hand, can process large amounts of data simultaneously. In addition, the method has a wide range of applications and can be used in various scenarios accurately. The scenarios include domestic sewage, micropollutant water, aquaculture wastewater, and secondary treated sewage. The experimental results validate the application of machine learning classifiers in membrane breakage detection with an accuracy rate of 96.8 % to 97.4 %.

Tracking the changes of dissolved organic matter throughout the city water supply system with optical indices

Dissolved organic matter (DOM) is important in determining the drinking water treatment and the supplied water quality. However, a comprehensive DOM study for the whole water supply system is lacking and the potential effects of secondary water supply are largely unknown. This was studied using dissolved organic carbon (DOC), absorption spectroscopy, and fluorescence excitation-emission matrices-parallel factor analysis (EEM-PARAFAC). Four fluorescent components were identified, including humic-like C1-C2, tryptophan-like C3, and tyrosine-like C4. In the drinking water treatment plants, the advanced treatment using ozone and biological activated carbon (O3-BAC) was more effective in removing DOC than the conventional process, with the removals of C1 and C3 improved by 17.7%-25.1% and 19.2%-27.0%. The absorption coefficient and C1-C4 correlated significantly with DOC in water treatments, suggesting that absorption and fluorescence could effectively track the changes in bulk DOM. DOM generally remained stable in each drinking water distribution system, suggesting the importance of the treated water quality in determining that of the corresponding network. The optical indices changed notably between distribution networks of different treatment plants, which enabled the identification of changing water sources. A comparison of DOM in the direct and secondary water supplies suggested limited impacts of secondary water supply, although the changes in organic carbon and absorption indices were detected in some locations. These results have implications for better understanding the changes of DOM in the whole water supply system to help ensure the supplied water quality.

Effect of interaction between dissolved organic matter and iron/manganese (hydrogen) oxides on the degradation of organic pollutants by in-situ advanced oxidation techniques

Iron and manganese (hydrogen) oxides (IMHOs) exhibit excellent redox capabilities for environmental pollutants and are commonly used in situ chemical oxidation (ISCO) technologies for the degradation of organic pollutants. However, the coexisting dissolved organic matter (DOMs) in surface environments would influence the degradation behavior and fate of organic pollutants in IMHOs-based ISCO. This review has summarized the interactions and mechanisms between DOMs and IMHOs, as well as the properties of DOM-IMHOs complexes. Importantly, the promotion or inhibition impact of DOM was discussed from three perspectives. First, the presence of DOMs may hinder the accessibility of active sites on IMHOs, thus reducing their efficiency in degrading organic pollutants. The formation of compounds between DOMs and IMHOs alters their stability and activity in the degradation process. Second, the presence of DOMs may also affect the generation and transport of active species, thereby influencing the oxidative degradation process of organic pollutants. Third, specific components within DOMs also participate and affect the degradation pathways and rates. A comprehensive understanding of the interaction between DOMs and IMHOs helps to better understand and predict the degradation process of organic pollutants mediated by IMHOs in real environmental conditions and contributes to the further development and application of IMHO-mediated ISCO technology.

Differential response of Hg-methylating and MeHg-demethylating microbiomes to dissolved organic matter components in eutrophic lake water

Methylmercury (MeHg) production in aquatic ecosystems is a global concern because of its neurotoxic effect. Dissolved organic matter (DOM) plays a crucial role in biogeochemical cycling of Hg. However, owing to its complex composition, the effects of DOM on net MeHg production have not been fully understood. Here, the Hg isotope tracer technique combined with different DOM treatments was employed to explore the influences of DOM with divergent compositions on Hg methylation/demethylation and its microbial mechanisms in eutrophic lake waters. Our results showed that algae-derived DOM treatments enhanced MeHg concentrations by 1.42-1.53 times compared with terrestrial-derived DOM. Algae-derived DOM had largely increased the methylation rate constants by approximately 1-2 orders of magnitude compared to terrestrial-derived DOM, but its effects on demethylation rate constants were less pronounced, resulting in the enhancement of net MeHg formation. The abundance of hgcA and merB genes suggested that Hg-methylating and MeHg-demethylating microbiomes responded differently to DOM treatments. Specific DOM components (e.g., aromatic proteins and soluble microbial byproducts) were positively correlated with both methylation rate constants and the abundance of Hg-methylating microbiomes. Our results highlight that the DOM composition influences the Hg methylation and MeHg demethylation differently and should be incorporated into future Hg risk assessments in aquatic ecosystems.

Coagulation pretreatment coupled with indigenous microalgal-bacterial consortium system for on-site treatment of rural black wastewater

Improper treatment of rural black wastewater (RBW) presents substantial challenges, including the wastage of resource, environmental contamination, and economic consequences. This study proposed an integrated process for RBW treatment, consisting of coagulation/flocculation (C/F) pretreatment and subsequent inoculation of indigenous microalgal-bacterial consortium (IMBC) for nitrogen recovery, namely C/F-IMBC process. Specifically, the optimal C/F conditions (polyaluminium chloride of 4 g/l, polyacrylamide of 50 mg/l, and pH of 6) were determined through a series of single-factor experiments, considering CN, turbidity, and dissolved organic matter (DOM) removal, economic cost, and potential influence on the water environment. Compared to the sole IMBC system for RBW treatment, the proposed C/F-IMBC process exhibited a remarkable 1.23-fold increase in microalgal growth and a substantial 17.6-22.6 % boost in nitrogen recovery. The altered RBW characteristic induced by C/F pretreatment was supposed to be responsible for the improved system performance. In particular, the abundance of DOM was decreased and its composition was simplified after C/F pretreatment, based on the analysis for excitation-emission matrices with parallel factor and gas chromatography-mass spectrometry, thus eliminating the potential impacts of toxic DOM components (e.g., Bis(2-ethylhexyl) phthalate) on IMBC activity. It should also be noted that C/F pretreatment modified microbial community structure as well, thereby regulating the expression of nitrogen-related genes and enhancing the system nitrogen recovery capacity. For instance, the functional Cyanobacteria responsible for nutrient recovery was enriched by 1.95-fold and genes involved in the assimilatory nitrate reduction to ammonia pathway were increased by 1.52-fold. These fundamental findings are expected to offer insights into the improvement of DOM removal and nitrogen recovery for IMBC-based wastewater treatment system, and provide valuable guidance for the development of sustainable on-site RBW treatment technologies.

Molecular insight of dissolved organic matter and chlorinated disinfection by-products in reclaimed water during chlorination with permanganate preoxidation

Permanganate is a common preoxidant applied in water treatment to remove organic pollutants and to reduce the formation of disinfection by-products. However, the effect of permanganate preoxidation on the transformation of dissolved effluent organic matter (dEfOM) and on the formation of unknown chlorinated disinfection by-products (Cl-DBPs) during chlorination remains unknown at molecular level. In this work, the molecular changes of dEfOM during permanganate preoxidation and subsequent chlorination were characterized using Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Permanganate preoxidation was found to decrease the DBE (double bond equivalent) and AImod (modified aromaticity index) of the dEfOM. The identity and fate of over 400 unknown Cl-DBPs during KMnO4-chlorine treatment were investigated. Most Cl-DBPs and the precursors were found to be highly unsaturated aliphatic and phenolic compounds. The Cl-DBPs precursors with lower H/C and lower O/C were preferentially removed by permanganate preoxidation. Additionally, permanganate preoxidation decreased the number of unknown Cl-DBPs by 30% and intensity of unknown Cl-DBPs by 25%. One-chlorine-containing DBPs were the major Cl-DBPs and had more CH2 groups and higher DBEw than Cl-DBPs containing two and three chlorine atoms. 60% of the Cl-DBPs formation was attributed to substitution reactions (i.e., +Cl-H, +2Cl-2H, +3Cl-3H, +ClO-H, +Cl2O3-2H). This work provides detailed molecular level information on the efficacy of permanganate preoxidation on the control of overall Cl-DBPs formation during chlorination.

Effect of 2,4-dichlorophenol on the production of methane from anaerobic granular sludge during anaerobic digestion through spectroscopy analysis

Chlorophenols in urban high organic wastewater increases, which plays an inhibitory role in the process of anaerobic fermentation and methanogenesis. The release rules of extracellular polymers (EPS) and soluble microbial products (SMP) and the production of methane from anaerobic granular sludge were evaluated by spectroscopic analysis. The methane production was reduced by 21.6%, 41.4% and 50.5% respectively by adding 2,4-DCP of different concentrations (25, 50 and 100 mg/L). Activity tests of methanogenic functional enzymes indicated that F420 was more susceptible to the toxic of 2, 4-DCP than Acetyl-CoA and NADH. The decrease in methane production was due to the reduction in the activity of conversion enzymes rather than the loss of crucial precursors for methanogenesis. 2,4-DCP disintegrated the protein 'shell' of anaerobic granular sludge by destroying α-helix and β-sheet structures. After the protein 'shell' in EPS was destroyed, 2, 4-DCP entered the interior of granular, which inhibited the activity of functional enzymes and affected the process of acidogenesis and methanogenesis. At the same time, due to the partial rupture of the cells after being affected by the toxicity of 2,4-DCP, the protein material could be dissolved into the aqueous phase and complexed with 2,4-DCP to reduce the toxic effect of 2,4-DCP.

Molecular formula assignment of dissolved organic matter by ultra-performance liquid chromatography quadrupole time-of-flight mass spectrometry using two non-targeted data processing approaches: A case study from recirculating aquaculture systems

BACKGROUND

The accumulation of dissolved organic matter (DOM) poses an issue in the management of the water quality from recirculating aquaculture systems (RAS), but its characterization is often not detailed enough to understand the DOM transformations in RAS. In this study, we investigated the application of two distinct non-targeted data processing approaches using ultra-performance liquid chromatography (UPLC) with quadrupole time-of-flight mass spectrometry (QTOF-MS) and two software with different algorithmic designs: PetroOrg and Progenesis QI to accurately characterize the molecular composition of DOM in RAS by UPLC-QTOF-MS.

RESULTS

The UPLC-QTOF-MS resolution in combination with PetroOrg and Progenesis QI software successfully assigned 912 and 106 unique elemental compositions, respectively, including compounds containing carbon, hydrogen, and oxygen (CHO) and nitrogen-containing CHO compounds (CHON), in the DOM samples from RAS. The results of these two distinct data processing approaches were consistent with the list of DOM formulas from RAS identified by higher resolution mass spectrometry techniques confirming their reliability. PetroOrg approach revealed only compositional information in the DOM samples from RAS, while Progenesis QI in addition to identifying new elemental compositions, increased their chemical space by giving information about their polarity and their possible key structures. DOM samples from RAS were found to be rich in unsaturated CHO compounds, with tentatively key structures of terpenoids with medium polarity indicating natural origins in their composition. The analysis also revealed probable structures of sucrose fatty acid esters and polyethylene glycol, indicating anthropogenic sources.

SIGNIFICANCE AND NOVELTY

The combination of these two non-targeted data processing approaches significantly improves the characterization of the complex mixture of DOM from RAS by UPLC-QTOF-MS reporting for the first time accurate DOM results in terms of its composition, while proposing its key structures. The presented methods can also be used to analyze different DOM samples with other HRMS techniques and software.

Purification of dredged water by magnetic coagulation: Response surface optimization and dissolved organic matter removal characteristics

In the present study, magnetic coagulation was used to treat dredged water and the response surface method was used to optimize process parameters. The dissolved organic matter (DOM) removal characteristics were characterized by three-dimensional fluorescence spectrometry and ultra-high resolution mass spectrometry. During the magnetic coagulation process, the suspended solids (SS) removal rate increased initially and then decreased under conditions of increasing magnetic powder dosage and stirring rate. After magnetic coagulation and precipitation for 20 min, the contents of SS, ammonia nitrogen, chemical oxygen demand, and total phosphorus in the treated dredged water met the requirements of the discharge standard (GB8978-1996, China). Three-dimensional fluorescence results showed that magnetic coagulation selectively removed fulvic acids and humic acid substances. After magnetic coagulation with precipitation for 10 min and 20 min, the total relative content of lignins, tannins, proteins, lipids, aminosugars, unsaturated hydrocarbons, condensed aromatic structures, and carbohydrates decreased by 26.3% and 39.4%, respectively. After magnetic coagulation, the distribution range of small molecule DOM shifted to the low H/C and high O/C regions. This study provides a novel perspective for studies on the removal of DOM in dredged water by magnetic coagulation. PRACTITIONER POINTS: SS and DOM removal were significantly enhanced by the use of magnetic coagulation. SS removal efficiency was affected by stirring rate and magnetic powder dosage. Magnetic coagulation selectively removed fulvic acids and humic acid substances. DOM molecule shifted to low H/C and high O/C regions after magnetic coagulation.

Phototransformation of Brominated Disinfection Byproducts and Toxicity Elimination in Sunlit-Ozonated Reclaimed Water

Ozonation is universally used during water treatment but can form hazardous brominated disinfection byproducts (Br-DBPs). While sunlight exposure is advised to reduce the risk of Br-DBPs, their phototransformation pathways remain insufficiently understood. Here, sunlight irradiation was found to reduce adsorbable organic bromine by 63%. Applying high-resolution mass spectrometry, the study investigated transformations of dissolved organic matter in sunlit-ozonated reclaimed water, revealing the number and abundance of assigned formulas decreased after irradiation. The Br-DBPs with O/C < 0.6 and MW > 400 Da were decreased or removed after irradiation, with the majority being CHOBr compounds. The peak intensity reduction ratio of CHOBr compounds correlated positively with double bound equivalent minus oxygen ratios but negatively with O/C, suggesting that photo-susceptible CHOBr compounds were highly unsaturated. Mass difference analysis revealed that the photodegradation pathways were mainly oxidation aligned with debromination. Three typical CHOBr molecular structures were resolved, and their photoproducts were proposed. Toxicity estimates indicated decreased toxicity in these photoproducts compared to their parent compounds, in line with experimentally determined values. Our proposed phototransformation pathways for Br-DBPs enhance our comprehension of their degradation and irradiation-induced toxicity reduction in reclaimed water, further illuminating their transformation under sunlight in widespread environmental scenarios.

Unveiling changes in the complexation of dissolved organic matter with Pb(II) by photochemical and microbial degradation using fluorescence EEMs-PARAFAC

Dissolved organic matter (DOM) is very important in determining the speciation, behaviors, and risk of metal pollutants in aquatic ecosystems. Photochemical and microbial degradation are key processes in the cycling of DOM, yet their effects on the DOM-Pb(II) interaction remain largely unknown. This was studied by examining the complexation of river DOM with Pb(II) after degradation, using fluorescence quenching titration and excitation-emission matrices-parallel factor analysis (EEMs-PARAFAC). Three humic-like and two protein-like components were identified, with strong removals of humic-like components and decreasing average molecular weight and humification degree of DOM by photo- and photo-microbial degradation. The changes in humic-like abundance and structure resulted in notable weakening of their interaction with Pb(II). The tryptophan-like C2 was also mainly removed by photo-degradation, while the tyrosine-like C3 could be either removed or accumulated. The Pb(II)-binding of protein-like components was generally weaker but was enhanced in some degradation groups, which might be related to the lowering competition from humic-like components. The binding parameters correlated significantly with the DOM indices, which were dominated by photo-degradation for humic-like components but by seasonal variations for the tyrosine-like component. These results have implications for understanding the key mechanisms underlying the variability of the DOM-metal interaction in aquatic environments.

The Future of Municipal Wastewater Reuse Concentrate Management: Drivers, Challenges, and Opportunities

Water reuse is rapidly becoming an integral feature of resilient water systems, where municipal wastewater undergoes advanced treatment, typically involving a sequence of ultrafiltration (UF), reverse osmosis (RO), and an advanced oxidation process (AOP). When RO is used, a concentrated waste stream is produced that is elevated in not only total dissolved solids but also metals, nutrients, and micropollutants that have passed through conventional wastewater treatment. Management of this RO concentrate─dubbed municipal wastewater reuse concentrate (MWRC)─will be critical to address, especially as water reuse practices become more widespread. Building on existing brine management practices, this review explores MWRC management options by identifying infrastructural needs and opportunities for multi-beneficial disposal. To safeguard environmental systems from the potential hazards of MWRC, disposal, monitoring, and regulatory techniques are discussed to promote the safety and affordability of implementing MWRC management. Furthermore, opportunities for resource recovery and valorization are differentiated, while economic techniques to revamp cost-benefit analysis for MWRC management are examined. The goal of this critical review is to create a common foundation for researchers, practitioners, and regulators by providing an interdisciplinary set of tools and frameworks to address the impending challenges and emerging opportunities of MWRC management.

Climate and Environmental Variables Drive Stream Biofilm Bacterial and Fungal Diversity on Tropical Mountainsides

High mountain freshwater systems are particularly sensitive to the impacts of global warming and relevant environmental changes. Microorganisms contribute substantially to biogeochemical processes, yet their distribution patterns and driving mechanism in alpine streams remain understudied. Here, we examined the bacterial and fungal community compositions in stream biofilm along the elevational gradient of 745-1874 m on Mt. Kilimanjaro and explored their alpha and beta diversity patterns and the underlying environmental drivers. We found that the species richness and evenness monotonically increased towards higher elevations for bacteria, while were non-significant for fungi. However, both bacterial and fungal communities showed consistent elevational distance-decay relationships, i.e., the dissimilarity of assemblage composition increased with greater elevational differences. Bacterial alpha diversity patterns were mainly affected by chemical variables such as total nitrogen and phosphorus, while fungi were affected by physical variables such as riparian shading and stream width. Notably, climatic variables such as mean annual temperature strongly affected the elevational succession of bacterial and fungal community compositions. Our study is the first exploration of microbial biodiversity and their underlying driving mechanisms for stream ecosystems in tropical alpine regions. Our findings provide insights on the response patterns of tropical aquatic microbial community composition and diversity under climate change.

Seasonal variations in dissolved organic matter concentration and composition in an outdoor system for bank filtration simulation

Dissolved organic matter (DOM) in surface waters can vary markedly in character depending on seasonal variations such as rainfall intensity, UV radiations and temperature. Changes in DOM as well as temperature and rainfall intensity over the year can affect the biochemical processes occurring in bank filtration (BF). Identification and characterization of DOM in the surface water could help to optimize the water treatment and provide stable and safe drinking water. This study investigated year-long variations of DOM concentrations and compositions in a surface water of a circulated outdoor pond (research facility) connected to a BF passage. DOM was dominated by humic substances and a changing pattern of DOM in surface water was observed throughout the year. A significant increase of DOM (∼ 38%) in surface water was noted in August compared to November. The fluorescent DOM showed that DOM in summer was enriched with the degradable fraction whilst non-degradable fraction was dominated in winter. A constant (1.7 ± 0.1 mg/L) effluent DOM was recirculated in the system throughout the year. DOM removal through BF varied between 4% to 39% and was achieved within a few meters after infiltration and significantly correlated with influent DOM concentration (R2 = 0.82, p < 0.05). However, no significant (p > 0.05) change in the removal of DOM was observed in two subsurface layers (upper and lower). This study highlights the presence of a constant non-degradable DOM in the bank filtrate, which was not affected by temperature, redox conditions and UV radiations.

Characterization of DOM released from bacteria in response to chlorine in water based on indicator bacteria E. coli

ABSTRACTIn this study, Escherichia coli (E. coli) was used as an indicator bacterium treated with five different concentrations of chlorine (0.1; 0.5; 1.0; 2.0, and 5.0 mg/L) and without chlorine (0.0 mg/L) to evaluate the changes in the DOM characteristics. The dissolved organic carbon (DOC) concentration initially increased along with the chlorine concentrations and decreased after 24 h (0.0 and 0.1 mg/L) and 168 h (0.5; 1.0; 2.0 and 5.0 mg/L). Ultra-violet absorbance at 260 nm (UV260) showed that the absorbance decreased for control without chlorine (0.0 mg/L) and 0.1 mg/L chlorine, while increased for other concentrations of chlorine within 120 h. The DOC and UV260 results indicated that the high concentrations of chlorine initiated high contents of DOM which contained more humic-like molecules than the DOM released from E. coli without chlorine. Fluorescence excitation-emission matrix (EEM) analysis suggested that the DOM released from E. coli without chlorine enriched with protein-like substances, whereas the fulvic-like and humic-like substances more intensified in the DOM for the high concentrations of chlorine (>1.0 mg/L). The molecular weight distribution of DOM showed that the intensity of high molecular weight substances and polydispersity increased along with chlorine concentration and contact time, whereas the low molecular weight substances were relatively higher in the DOM for control without chlorine. The obtained results of this study would be useful for a better understanding of the variation of DOM during treatment and could be used as an important reference for optimizing the operation condition of the water treatment plants.

Effects of disturbance modes and carbon sources on the physiological traits and nutrient removal performance of microalgae (S. obliquus) for treating low C/N ratio wastewater

Wastewater treatment with microalgae is an ecologically sustainable process. In this study, the growth characteristics, nutrient removal, and spectral changes of dissolved organic matter (DOM) in microalgae bioreactors were investigated for treating low C/N ratio wastewater under different disturbance modes (agitation and aeration) and carbon sources (sucrose and humic acid). The results showed that the biomass and chlorophyll-a contents of Scenedesmus obliquus in the aeration condition (725.32-811.16 × 104 cells mL-1, 1.58-1.69 mg L-1) were higher than those in the agitation condition (426.06-465.14 × 104 cells mL-1, 1.48-1.61 mg L-1). The better removal of nutrients (TN, 29.62-36.39 mg L-1, TP, 1.84-2.30 mg L-1) by microalgae in sucrose-containing wastewater under agitation conditions occurred on the second day, with removal efficiencies of 21.33-30.67% and 44.84-58.51%, respectively; while it was on the fifth day both in sucrose and humic acid-containing wastewater under aeration conditions (TN, 19.56-31.20 mg L-1, TP, 0.26-0.30 mg L-1), with removal efficiencies of 13.92-46.75% and 88.36-90.50%, respectively. The wastewater DOM primarily consisted of humic-like substances under agitation and aeration conditions characterized by high levels of aromaticity, molecular weight and humification. Furthermore, the aromatization and humification properties of DOM in humic acid wastewater were higher than those in sucrose wastewater, which was corresponding with the lower removal and availability of pollutants by algae. Microalgae showed good biomass accumulation and nutrients removal at incubation time of 2 days (agitation condition) and 5 days (aeration condition), respectively. Consequently, a technical reference is provided for the microalgae coupled with other treatment processes.

Comparative molecular transformations of dissolved organic matter induced by chlorination and ammonia/chlorine oxidation process

The ammonia/chlorine oxidation process can greatly degrade PPCPs in water. However, its effect on molecular transformations of natural organic matter (NOM) and effluent organic matter (EfOM) are still poorly understood. In this study, molecular transformations of NOM and EfOM occurring during ammonia/chlorine were explored and compared with those occurred during chlorination, using spectroscopy and mass spectrometry. Phenolic and highly unsaturated aliphatic compounds together with aliphatic compounds were found to be predominant in both NOM and EfOM samples, all of which were significantly degraded after two processes. The ammonia/chlorine process led to greater decreases in the molecular weights of such components but lower reductions in aromaticity. Compared with chlorination, ammonia/chlorine was found to be more likely to degrade compounds while remaining fluorophores or chromophores. The CH(N)O(S) precursors were found to be similar for both processes but their products were quite different. The CH(N)O(S) precursors that only found in ammonia/chlorine had higher molecular weights and greater degrees of oxidation but lower degrees of saturation. In contrast, the unique CH(N)O(S) products that only found in ammonia/chlorine exhibited lower molecular weights and lower degrees of oxidation degrees together with higher degrees of saturation. Lower total abundance of chlorinated byproducts was found by ammonia/chlorine compared with chlorination, although the former process provided a richer diversity. In all water samples, chlorinated byproducts were mainly generated by substitution reactions during ammonia/chlorine and chlorination. Overall, the findings of this study could provide new insights into the transformations of NOM and EfOM induced by ammonia/chlorine and chlorination.

Chemodiversity transformation of organic matters in a full scale MBR-NF wastewater reclamation plant

Membrane bioreactor (MBR) and nanofiltration (NF) process has been attractive in wastewater reclamation, and was set as the target process in this study. Dissolved organic matter (DOM) and trace organic contaminants (TrOCs), closely associated with water safety, are noteworthy pollutants. Though the general DOM characteristics and TrOCs removal in MBR-NF reclamation process have been reported in lab-/pilot-scale experiment, the molecular characteristics of DOM revealed by high resolution mass spectrometry, and the correlation between DOM and TrOCs have been rarely studied in full-scale MBR-NF wastewater reclamation plant. In this work, biological and NF processes contributed significantly to the removal of DOM and TrOCs, while MBR filtration contributed slightly. Spectroscopic analyses revealed that DOM with higher aromaticity and lower molecular weight were more recalcitrant along the treatment. Aromatic protein-like substances were preferentially removed comparing to humic-like substances. Fourier transform ion cyclotron resonance mass spectrometry was applied to investigate DOM transformation at molecular level. DOM molecules with higher H/C and lower O/C, especially the aliphatics and peptides, were readily biodegraded into higher‑oxygenate, highly unsaturated, and aromatic compounds. The generated species mainly included condensed aromatics, polyphenols, and highly unsaturated compounds. Filtration in MBR tended to reject higher oxygenated molecules. NF effectively removed most of the DOM molecules, especially higher oxygenated molecules with low H, N and S. The residual TrOCs in the NF effluent, including sulfamethoxazole, ofloxacin, and bisphenol A, still displayed above medium environmental risk. Significant correlations were found among organic compounds, spectral indices, and peptides molecules. Positive correlation between most of the TrOCs and several DOM parameters implied that they were synchronously removed in biological and membrane filtration processes. SUVA and FI might be potential indexes in monitoring the performance of MBR-NF process in both DOM and TrOC removal. These findings would expand the understanding of DOM and TrOCs behavior in wastewater reclamation process and simplify an in-depth system monitoring.

Simultaneous modulation of CHO cell cytotoxicity, turbidity, and DOC by coagulation with or without pre-oxidation in water from the Pearl River Delta region, China

Coagulation with or without pre-oxidation are important drinking water treatment processes. However, the efficacy of these processes in mitigating water toxicity remains unknown. To further improve drinking water safety, we employed water from the Pearl River Delta region of southern China to investigate a treatment approach consisting of coagulation with or without pre-oxidation to simultaneously modulate health-relevant cytotoxicity to CHO cells, on top of the conventional foci of turbidity and dissolved organic carbon (DOC) during water treatment. Three coagulants (two aluminum-based and one iron-based salts) and three pre-oxidants (ozone, permanganate, and peroxymonosulfate) were studied. For coagulation without pre-oxidation, intermediate coagulant doses and pH reached optimum cytotoxicity to CHO cells, turbidity, and DOC control simultaneously. Introducing oxidants reduced cytotoxicity to CHO cells significantly, enhanced by increasing oxidant concentrations and pre-oxidation duration. The cytotoxicity to CHO cells mitigation capabilities of three pre-oxidants were: ozone > peroxymonosulfate > potassium permanganate. Modulation of water cytotoxicity to CHO cells was mostly attributable to controlling DOC (specifically humic-acid like substances, tyrosine, tryptophan). However, the addition of pre-oxidants led to significant shifts in water cytotoxicity to CHO cells forcing drivers, rendering humic-acid like substances the sole decisive cytotoxicity-inducing fluorophores. For the first time, 'sweet spots' were identified to simultaneously monitor cytotoxicity to CHO cells alongside turbidity and DOC. These methods better modulate water cytotoxicity to CHO cells without sacrificing conventional water treatment goals while shedding light onto the mechanisms behind.

Characteristics of dissolved organic matter in point-source wastewaters at a petrochemical plant: Molecular constituents and contributions to the influent of wastewater treatment plant

Dissolved organic matter (DOM) in point-source petrochemical wastewaters (PCWs) from different operating units is closely linked to the efficiency of wastewater treatment plant (WWTP). However, systematic studies on DOM characters of point-source PCWs and their influences on WWTP influents were seldom conducted. In this study, DOM in three low-salinity point-source PCWs and four high-salinity point-source PCWs at a typical petrochemical plant were comprehensively characterized at a molecular level. Orbitrap mass spectrometry results indicated that point-source PCWs had diverse DOM constituents tightly related to the corresponding petrochemical processes. Phenols in oily wastewaters (OW), phenols and N-containing compounds in coal partial oxidation wastewater (POXW), and naphthenic acids (NAs) and aromatic acids in crude oil electric desalting unit wastewater (EDW) were characteristic DOM constituents for low-salinity point-source PCWs. While S-containing compounds (mercaptans, thiophenes) and NAs in spent caustic liquors (SCL), alcohols and esters in butanol-octanol plant wastewater (BOW), high molecular weight aromatic ketones in phenol-acetone plant wastewater (PAW), and oxygenated NAs as well as short chain N-containing compounds in concentrate from reverse osmosis unit (ROC) were characteristic DOM constituents for high-salinity point-source PCWs. Spearman correlation analysis indicated that though with relative low pollutant contents (OW) and discharge volume (EDW), N/O/S-containing compounds of OW and EDW greatly contributed to the polar DOM constituents of low-salinity influent in WWTP (R > 0.5, P < 0.001). While N-containing compounds of ROC mainly contributed to the polar DOM of high-salinity influent (R > 0.5, P < 0.001). Though N-/S-containing species in PAW had low contents, they also posed obvious impacts on DOM constituents of high-salinity influent. Interestingly, some O-/S-containing species were newly formed during the confluent process of high-salinity point-source PCWs. The results strengthened the combined contributions of pollutants contents, discharge emission and DOM constituents of point-source PCWs to the water matrix of WWTP influents, which would provide reference for the management of PCW streams.

Improving algal bloom detection using spectroscopic analysis and machine learning: A case study in a large artificial reservoir, South Korea

The prediction of algal blooms using traditional water quality indicators is expensive, labor-intensive, and time-consuming, making it challenging to meet the critical requirement of timely monitoring for prompt management. Using optical measures for forecasting algal blooms is a feasible and useful method to overcome these problems. This study explores the potential application of optical measures to enhance algal bloom prediction in terms of prediction accuracy and workload reduction, aided by machine learning (ML) models. Compared to absorption-derived parameters, commonly used fluorescence indices such as the fluorescence index (FI), humification index (HIX), biological index (BIX), and protein-like component improved the prediction accuracy. However, the prediction accuracy was decreased when all optical indices were considered for computation due to increased noise and uncertainty in the models. With the exception of chemical oxygen demand (COD), this study successfully replaced biochemical oxygen demand (BOD), dissolved organic carbon (DOC), and nutrients with selected fluorescence indices, demonstrating relatively analogous performance in either training or testing data, with consistent and good coefficient of determination (R2) values of approximately 0.85 and 0.74, respectively. Among all models considered, ensemble learning models consistently outperformed conventional regression models and artificial neural networks (ANNs). However, there was a trade-off between accuracy and computation efficiency among the ensemble learning models (i.e., Stacking and XGBoost) for algal bloom prediction. Our study offers a glimpse of the potential application of spectroscopic measures to improve accuracy and efficiency in algal bloom prediction, but further work should be carried out in other water bodies to further validate our proposed hypothesis.

Redox-directed identification of toxic transformation products during ozonation of aromatics

The toxicity assessment of transformation products (TPs) formed in oxidative water treatment is crucial but challenging because of their low concentration, structural diversity, and mixture complexity. Here, this study developed a novel redox-directed approach for identification of toxic TPs without the individual toxicity and concentration information. This approach based on sodium borohydride reduction comprised an integrated process of toxicological evaluation, fluorescence excitation-emission matrix characterization, high-resolution mass spectrometry detection, followed by ecological toxicity assessment of identified TPs. The redox-directed identification of primary causative toxicants was experimentally tested for the increased nonspecific toxicity observations in the ozonated effluents of model aromatics. Reduction reaction caused a remarkable decrease in toxicity and increase in fluorescence intensity, obtaining a good linear relation between them. More than ten monomeric or dimeric p-benzoquinone (p-BQ) TPs were identified in the ozonated effluents. The occurrence of the p-BQ TPs was further verified through parallel sodium sulfite reduction and actual wastewater ozonation experiments. In vitro bioassays of luminescent bacteria, as well as in silico genotoxicity and cytotoxicity predictions, indicate that the toxicity of p-BQ TPs is significantly higher than that of their precursors and other TPs. These together demonstrated that the identified p-BQ TPs are primary toxicity contributors. The redox-directed approach facilitated the revelation of primary toxicity contribution, illustrating emerging p-BQs are a concern for aquatic ecosystem safety in the oxidative treatment of aromatics-contaminated wastewater.

Estimation of stability constants of Fe(III) with antibiotics and dissolved organic matter using a novel UV-vis spectroscopy method

Determining conditional stability constant (Kcond) is paramount in assessing complex stability, particularly in Fe(III) complexes that are prevalent in actual surface water and wastewater matrices. In this study, existing methods of Kcond determination were evaluated and a novel UV-Vis spectroscopy method was proposed based on the evaluation of these approaches. Model ligands (ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA), and oxalic acid (OA)), as well as common antibiotics (kanamycin (Kana) and tetracycline (TTC)), were employed to determine the Kcond of the Fe(III)-ligand complexes under neutral conditions (pH 6.5). The obtained fitting results revealed that the logKcond were in the order of Fe(III)-EDTA (7.08) > Fe(III)-NTA (4.67) > Fe(III)-OA (4.32) > Fe(III)-TTC (4.28) > Fe(III)-Kana (3.07). In addition to these single ligands, the methodology was extended to the Fe(III) complexation with humic acid (HA), a complex mixture of organic components, where the fitting result indicated a logKcond of 5.02 M-1. The method's application domain was analyzed by numerical analysis and combined with experimental results. The findings demonstrate that the proposed methodology possesses satisfactory measurement capability for Kcond ranging from 103 to 107 M-1, suggesting its broad applicability to the majority of complexes. This method can provide valuable insights into the impact of Fe(III) complexes within the water matrix.

Characterization of halogenated organic compounds by the Fourier transform ion cyclotron resonance mass spectrometry: A critical review

Halogenated organic compounds (HOCs), widely present in various environments, are generally formed by natural processes (e.g., photochemical halogenation) and anthropogenic activities (e.g., water disinfection and anthropogenic discharge of HOCs), posing health and environmental risks. Therefore, in-depth knowledge of the molecular composition, transformation, and fate of HOCs is crucial to regulate and reduce their formation. Because of the extremely complex nature of HOCs and their precursors, the molecular composition of HOCs remains largely unknown. The Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) offers the most powerful resolution and mass accuracy for the simultaneous molecular-level characterization of HOCs and their precursors. However, there is still a paucity of reviews regarding the comprehensive characterization of HOCs by FT-ICR MS. Based on the FT-ICR MS, the formation mechanism, sample pretreatment, and analysis methods were summarized for two typical HOCs classes, namely halogenated disinfection byproducts and per- and polyfluoroalkyl substances in this review. Moreover, we have highlighted data analysis methods and some typical applications of HOCs using FT-ICR MS and proposed suggestions for current issues. This review will deepen our understanding of the chemical characterization of HOCs and their formation mechanisms and transformation at the molecular level in aquatic systems, facilitating the application of the state-of-the-art FT-ICR MS in environmental and geochemical research.

Binding of Dissolved Organic Matter to RNA and Protection from Nuclease-Mediated Degradation

The persistence of RNA in environmental systems is an important parameter for emerging applications, including ecological surveys, wastewater-based epidemiology, and RNA interference biopesticides. RNA persistence is controlled by its rate of biodegradation, particularly by extracellular enzymes, although the specific factors determining this rate have not been characterized. Due to prior work suggesting that nucleic acids-specifically DNA-interact with dissolved organic matter (DOM), we hypothesized that DOM may bind RNA and impede its biodegradation in natural systems. We first adapted a technique previously used to assess RNA-protein binding to differentiate RNA that is bound at all sites by DOM from RNA that is unbound or partially bound by DOM. Results from this technique suggested that humic acids bound RNA more extensively than fulvic acids. At concentrations of 8-10 mgC/L, humic acids were also found to be more effective than fulvic acids at suppressing enzymatic degradation of RNA. In surface water and soil extract containing DOM, RNA degradation was suppressed by 39-46% relative to pH-adjusted controls. Due to the ability of DOM to both bind and suppress the enzymatic degradation of RNA, RNA biodegradation may be slowed in environmental systems with high DOM concentrations, which may increase its persistence.

Electroactive biocake layer-driven advanced removal of dissolved organic matter at membrane interface of anaerobic electrochemical membrane bioreactor

The bio-cake layer is one of the most negative effects during water and wastewater filtration, but its potential behoof of biodegradation is poorly understood. In this study, we activated and reconstructed the bio-cake by using the carbon nanotube membrane (25 cm2 area, 17 LMH flux) as the anode in an anaerobic membrane bioreactor (AnMBR), and investigated its positive role in advanced removal of dissolved organic matter from up-flow anaerobic sludge bed unit (3 L/d) when treating synthetic municipal wastewater. At the anodic membrane interface, the enhanced biodegradation was proved to dominate the DOM reduction (contribution >40%), controlling the effluent COD as low as 19.2 ± 2.5 mg/L. Bio-cake characterizations suggested that the positive potential induced electroactive improvement, cell viability boost, and metabolic optimization. Metatranscriptomic analyses revealed that anode respiratory out-compete methanogenesis, forwarding a synergetic metabolism between enriched fermenters like Proteiniphilum sp. and exoelectrogens like Geobacter sp. Thus, electroactive bio-cake not only accelerated the decomposition of inside foulants to maintain the high flux, but also efficiently intercepted flow-through DOM due to reduced mass-transfer limitations and enhanced metabolic activity. An ordered, non-clogging, and potentially functional "cell filter" was established to achieve a win-win situation between fouling control and effluent improvement, which is promising to upgrade the AnMBR technology for maximizing the sustainable regeneration in future wastewater treatment.

Interpreting pH-Dependent Differential UV/VIS Absorbance Spectra to Characterize Carboxylic and Phenolic Chromophores in Natural Organic Matter

Natural organic matter (NOM) is critical for the biogeochemical cycles of energy and many elements in terrestrial and aquatic ecosystems, and protonation-active functional groups in NOM molecules, notably carboxylic and phenolic groups often mediate these critical environmental functions. Molecular heterogeneity, polydispersity and dynamic behavior of NOM complicate achieving an unambiguous description of its molecular properties and reactivity. This study demonstrates that differential ultraviolet-visible (UV/VIS) absorbance spectra (DAS) of NOM acquired at varying pH values exhibit several distinct features associated with the deprotonation of NOM molecules, independent of the environmental provenance of NOM (e.g., surface water, seawater, sediment, and wastewater). The protonation-active functionalities that contribute to the Gaussian distribution bands present in the DAS were identified here by comparing characteristic properties of the bands with the stoichiometries of NOM molecules ascertained by Ultrahigh-Resolution Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS). The protonation-active individual chromophores universally present in NOM molecules were identified by a genetic molecular network analysis. The observed DAS features were closely modeled via superimposing DAS spectra of 51 individual protonation-active chromophores. Molecular orbital theory was applied to further interpret the deprotonation of these chromophores, their molecular structure, electron distribution, and electron transitions measured using DAS. The high sensitivity and easy implementation of the DAS approach allows using it as a powerful tool to quantify the molecular properties and reactivity of NOM at environmental concentrations.

Rapid Fluorescence EEM Spectroscopy Using Super-Cycle Hadamard-Transform Multiplexing

Hadamard-transform (HT) multiplexing has recently been applied to increasingly complex spectroscopic techniques. It had been shown that the data acquisition time for fluorescence excitation emission matrix (EEM) spectroscopy can be reduced by 1 or 2 orders of magnitude using HT multiplexing of the excitation light using a programmable light source. In these previous studies, the data acquisition rate had been limited by the time it took to record an EEM, that is, to complete one cycle of multiplexed excitation spectra. The extraction of chemical information, such as concentration and chemical identity, is then obtained from parallel factor (PARAFAC) analysis of the sequence of EEMs. In this contribution, we increase the data acquisition rate by another order of magnitude, limited ultimately by the time it takes to record a single excitation spectrum. Our algorithm is entirely based on improved data processing, that is, it can be applied to previously recorded HT multiplexed data sets. The algorithm is based on three previously unexplored approaches: (1) we perform a PARAFAC multivariate analysis on the raw (multiplexed) data set, (2) the time-independent PARAFAC loading vectors are obtained prior to obtaining the time-dependent score vectors, and (3) when loading vectors are difficult to obtain from the EEMs, we instead use a rolling-average approach to considerably increase the stability of the fit. Analysis of experimental data shows that the scores of fluorescence EEMs with seven excitation wavelengths and over 1000 emission wavelengths can be obtained in less than 20 ms.

Mechanistic insight into humic acid-enhanced sonophotocatalytic removal of 17β-estradiol: Formation and contribution of reactive intermediates

In this study, humic acid (HA) enhanced 17β-estradiol (17β-E2) degradation by Er3+-CdS/MoS2 (ECMS) was investigated under ultrasonic and light conditions. The degradation reaction rate of 17β-E2 was increased from (14.414 ± 0.315) × 10-3 min-1 to (122.677 ± 1.729) × 10-3 min-1 within 90 min sonophotocatalytic (SPC) reaction with the addition of HA. The results of quenching coupled with chemical probe experiments indicated that more reactive intermediates (RIs) including reactive oxygen species (ROSs) and triplet-excited states were generated in the HA-enhanced sonophotocatalytic system. The triplet-excited states of humic acid (3HA*), hydroxyl radical (•OH), and superoxide radical (•O2-) were the dominant RIs for 17β-E2 elimination. In addition, the energy- and electron-transfer process via coexisting HA also account for 12.86% and 29.24% contributions, respectively. The quantum yields of RIs in the SPC-ECMS-HA system followed the order of 3HA* > H2O2 > 1O2 > •O2-> •OH. Moreover, the spectral and fluorescence characteristics of HA were further analyzed during the sonophotocatalytic reaction process. The study expanded new insights into the comprehension of the effects of omnipresent coexisting HA and RIs formation for the removal of 17β-E2 during the sonophotocatalytic process.

Photochemical behaviors of dissolved organic matter in aquatic environment: Generation, characterization, influencing factors and practical application

Dissolved organic matter (DOM) widely exists in aquatic environment and plays a critical role in environmental photochemical reaction. The photochemical behaviors of DOM in sunlit surface waters have received widely attention because its photochemical effects for some coexisted substances in aquatic environment, especially for organic micropollutants degradation. Therefore, to gain a comprehensive understanding of the photochemical properties and environmental effects of DOM, we reviewed the influence of sources on the structure and composition of DOM with relevant identified techniques to analysis functional groups. Additionally, identification and quantification for reactive intermediates are discussed with a focus on influencing factors to produce reactive intermediates by DOM under solar irradiation. These reactive intermediates can promote the photodegradation of organic micropollutants in the environmental system. In future, attention should be paid to the photochemical properties of DOM and environmental effects in real environmental system and development of advanced techniques to study DOM.

Molecular insights into the dissolved organic matter of leather wastewater in leather industrial park wastewater treatment plant

Leather wastewater (LW) effluent is characterized by complex organic matter, high salinity, and poor biodegradability. To meet the discharge standards, LW effluent is often mixed with municipal wastewater (MW) before being treated at a leather industrial park wastewater treatment plant (LIPWWTP). However, whether this method efficiently removes the dissolved organic matter (DOM) from LW effluent (LWDOM) remains debatable. In this study, the transformation of DOM during full-scale treatment was revealed using spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. LWDOM exhibited higher aromaticity and lower molecular weight than DOM in MW (MWDOM). The DOM properties in mixed wastewater (MixW) were similar to those in LWDOM and MWDOM. The MixW was treated using a flocculation/primary sedimentation tank (FL₁/PST), anoxic/oxic (A/O) process, secondary sedimentation tank (SST), flocculation/sedimentation tank, denitrification filter (FL₂/ST-DNF), and an ozonation contact reactor (O₃). The FL₁/PST unit preferentially removed the peptide-like compounds. The A/O-SST units had the highest removal efficiencies for dissolved organic carbon (DOC) (61.34 %) and soluble chemical oxygen demand (SCOD) (52.2 %). The FL₂/ST-DNF treatment removed the lignin-like compounds. The final treatment showed poor DOM mineralization efficiency. The correlation between water quality indices, spectral indices, and molecular-level parameters indicated that lignin-like compounds were strongly correlated with spectral indices and CHOS compounds considerably contributed to the SCOD and DOC. Although the effluent SCOD met the discharge standard, some refractory DOM from LW remained in the effluent. This study illustrates the composition and transformation of DOM and provides theoretical guidance for improving the current treatment processes.

Dissolved organic nitrogen removal and its mechanisms during simulated soil aquifer treatment

Soil aquifer treatment systems are known to further remove contaminants in wastewater effluent when applied through infiltration into the ground. Dissolved organic nitrogen (DON) in the effluent, a precursor for nitrogenous disinfection by-products (DBPs) such as N-nitrosodimethylamine (NDMA), is of great concern upon subsequent use of the groundwater infiltered into the aquifer. In this study, the vadose zone of the soil aquifer treatment system was simulated using 1 m laboratory soil columns under unsaturated conditions representing the vadose zone. The final effluent of a water reclamation facility (WRF) was applied to these columns to investigate the removal of N species with a focus on DON, as well as NDMA precursors. DON removal achieved was up to 99 % with an average of 68 % and was accompanied by a 52 % nitrate increase suggesting the occurrence of ammonification and nitrification through the soil columns. Around 62 % of total DON removal was seen at <10 cm travel distance, which was in accordance with higher adenosine triphosphate (ATP) concentrations at the top of the column due to more oxygen and organic matter availability. Total Dissolved N removal was drastically lowered to 4.5 % in the same column without microbial growth, which highlights the importance of biodegradation. The columns were capable of removing 56 % of the fluorescent dissolved organic matter (FDOM). Soil columns could remove NDMA precursors up to 92 % through the column with the initial concentration of 89.5 ng/L, possibly due to the removal of DON fractions. The results demonstrate the capability of the vadose zone in further treatment of DON and other organic matter before reaching the groundwater through infiltration or indirect discharge to surface water. Differences in applied water quality and the site-specific oxic conditions in SAT systems could lead to variable removal efficiencies.

A tailored and rapid approach for ozonation catalyst design

Catalytic ozonation is widely employed in advanced wastewater treatment owing to its high mineralization of refractory organics. The key to high mineralization is the compatibility between catalyst formulation and wastewater quality. Machine learning can greatly improve experimental efficiency, while fluorescence data can provide additional wastewater quality information on the composition and concentration of organics, which is conducive to optimizing catalyst formulation. In this study, machine learning combined with fluorescence spectroscopy was applied to develop ozonation catalysts (Mn/γ-Al₂O₃ catalyst was used as an example). Based on the data collected from 52 different catalysts, a machine-learning model was established to predict catalyst performance. The correlation coefficient between the experimental and model-predicted values was 0.9659, demonstrating the robustness and good generalization ability of the model. The range of the catalyst formulations was preliminarily screened by fluorescence spectroscopy. When the wastewater was dominated by tryptophan-like and soluble microbial products, the impregnation concentration and time of Mn(NO₃)₂ were less than 0.3 mol L^-1 and 10 h, respectively. Furthermore, the optimized Mn/γ-Al₂O₃ formulation obtained by the model was impregnation with 0.155 mol L^-1 Mn(NO₃)₂ solution for 8.5 h and calcination at 600 °C for 3.5 h. The model-predicted and experimental values for total organic carbon removal were 54.48% and 53.96%, respectively. Finally, the improved catalytic performance was attributed to the synergistic effect of oxidation (•OH and ¹O₂) and the Mn/γ-Al₂O₃ catalyst. This study provides a rapid approach to catalyst design based on the characteristics of wastewater quality using machine learning combined with fluorescence spectroscopy.

FexO/FeNC modified activated carbon packing media for biological slow filtration to enhance the removal of dissolved organic matter in reused water

The biological slow filtration reactor (BSFR) process has been found to be moderately effective for the removal of refractory dissolved organic matter (DOM) in the treatment of reused water. In this study, bench scale experiments were conducted using a mixture of landscape water and concentrated landfill leachate as feed water, to compare a novel iron oxide (Fe_xO)/FeNC modified activated carbon (Fe_xO@AC) packed BSFR, with a conventional activated carbon packed BSFR (AC-BSFR), operated in parallel. The results showed that the Fe_xO@AC packed BSFR had a refractory DOM removal rate of 90%, operated at a hydraulic retention time (HRT) of 10 h at room temperature for 30 weeks, while under the same conditions the removal by the AC-BSFR was only 70%. As a consequence, the treatment by the Fe_xO@AC packed BSFR substantially reduced the formation potential of trihalomethanes, and to a less extent, haloacetic acids. The modification of Fe_xO/FeNC media raised the conductivity and the oxygen reduction reaction (ORR) efficiency of the AC media to accelerate the anaerobic digestion by consuming the electrons that are generated by anaerobic digestion itself, which lead to the marked improvement in refractory DOM removal.

Identification of key precursors contributing to the formation of CX3R-type disinfection by-products along the typical full-scale drinking water treatment processes

Identification and characterization of disinfection by-product (DBP) precursors could help optimize drinking water treatment processes and improve the quality of finished water. This study comprehensively investigated the characteristics of dissolved organic matter (DOM), the hydrophilicity and molecule weight (MW) of DBP precursor and DBP-associated toxicity along the typical full-scale treatment processes. The results showed that dissolved organic carbon and dissolved organic nitrogen content, the fluorescence intensity and the SUVA₂₅₄ value in raw water significantly decreased after the whole treatment processes. Conventional treatment processes were in favor of the removal of high-MW and hydrophobic DOM, which are important precursors of trihalomethane and haloacetic acid. Compared with conventional treatment processes, Ozone integrated with biological activated carbon (O₃-BAC) processes enhanced the removal efficiencies of DOM with different MW and hydrophobic fractions, leading to a further decrease in almost all DBP formation potential and DBP-associated toxicity. However, almost 50% of the detected DBP precursors in raw water has not been removed after the coagulation-sedimentation-filtration integrated with O₃-BAC advanced treatment processes. These remaining precursors were found to be mainly hydrophilic and low-MW (< 1.0 kDa) organics. Moreover, they would largely contribute to the formation of haloacetaldehydes and haloacetonitriles, which dominated the calculated cytotoxicity. Since current drinking water treatment process could not effectively control the highly toxic DBPs, the removal of hydrophilic and low-MW organics in drinking water treatment plants should be focused on in the future.

Viral lysing can alleviate microbial nutrient limitations and accumulate recalcitrant dissolved organic matter components in soil

Viruses are critical for regulating microbial communities and biogeochemical processes affecting carbon/nutrient cycling. However, the role of soil phages in controlling microbial physiological traits and intrinsic dissolved organic matter (DOM) properties remains largely unknown. Herein, microcosm experiments with different soil phage concentrates (including no-added phages, inactive phages, and three dilutions of active phages) at two temperatures (15 °C and 25 °C) were conducted to disclose the nutrient and DOM dynamics associated with viral lysing. Results demonstrated three different phases of viral impacts on CO₂ emission at both temperatures, and phages played a role in maintaining Q₁₀ within bounds. At both temperatures, microbial nutrient limitations (especially P limitation) were alleviated by viral lysing as determined by extracellular enzyme activity (decreased V_angle with active phages). Additionally, the re-utilization of lysate-derived DOM by surviving microbes stimulated an increase of microbial metabolic efficiency and recalcitrant DOM components (e.g., SUV254, SUV260 and HIX). This research provides direct experimental evidence that the "viral shuttle" exists in soils, whereby soil phages increase recalcitrant DOM components. Our findings advance the understanding of viral controls on soil biogeochemical processes, and provide a new perspective for assessing whether soil phages provide a net "carbon sink" vs. "carbon source" in soils.

The transformation of dissolved organic matter and formation of halogenated by-products during electrochemical advanced oxidation pretreatment for shale gas produced water

Electrochemical advanced oxidation processes (EAOPs) have shown great potential for the treatment of shale gas produced water (SGPW). In this study, we investigated the transformation of dissolved organic matter (DOM) during EAOPs of SGPW and the formation of toxic halogenated by-products at various current densities, using fluorescence spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry. We found that the priority of DOM removal was terrestrial humic-like > microbial humic-like > protein-like substances. Non-Halogenated organic compounds (non-HOCs) and HOCs were predominantly CHO, and CHOCl/CHOBr compounds in EAOP-treated SGPW, respectively. As applied current density and treatment time increased, the production of oxyhalides increased, with chlorate > bromate > perchlorate. Meanwhile, most DOM was mineralized, resulting in residual products with higher modified aromaticity index (AI_mod) and nominal oxidation state of carbon (NOSC). The resistants had lower mass-to-charge ratio (m/z), AI_mod, NOSC, and double bond equivalent minus oxygen per carbon ((DBE-O)/C). The dominant reactions were the addition of tri-oxygen and deallyl. Bromine addition dominated the reactions of halogenating addition, while chlorine addition took second place. Furthermore, the acute toxicity of SGPW was positively correlated with inorganic halogenated by-products. This study contributes to the understanding and improvement of EAOPs for the treatment of SGPW.

Molecular insights towards changing behaviors of organic matter in a full-scale water treatment plant using FTICR-MS

The changing behavior of organic matter in a full-scale water treatment process was characterized based on the three-dimensional excitation-emission matrix (3D-EEM) and Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS). Polyaluminum chloride (PAC) as a coagulant can help to effectively remove soluble microbial by-products-like and aromatic protein-like substances during coagulation and sedimentation, corresponding to tannin and coagulated aromatic regions. The leakage of soluble microbial products during sand filtration resulted in an increase in the intensity of biomass-like regions. Nitrogen-containing compounds have higher weighted average value of double bond equivalents (DBE_w) and the modified aromaticity index (AI_mod-w) than nitrogen-free compounds. Water treatment can preferentially remove unsaturated nitrogen-containing compounds with more O atoms and higher-oxidation-state carbon. The dissolved organic carbon (DOC) and UV₂₅₄ were not correlated well with changes in nitrogen-containing compounds due to the preferential removal of nitrogen-containing compounds. This study revealed the specificity of organic matter removal during water treatment, and it was helpful in optimizing treatment processes for various raw water to ensure water quality.

Characterization of Dissolved Organic Matter from Agricultural and Livestock Effluents: Implications for Water Quality Monitoring

There is growing concern about the impact of agricultural practices on water quality. The loss of nutrients such as nitrogen and phosphorous through agricultural runoff poses a potential risk of water quality degradation. However, it is unclear how dissolved organic matter (DOM) composition is associated with pollution levels in water bodies. To address this, we conducted a cross-year investigation to reveal the nature of DOM and its relationship to water quality in agricultural effluents (AEs) and livestock effluents (LEs). We discovered that DOM fluorescence components of AEs were mainly from autochthonous and terrestrial sources, while in LEs it was primarily from autochthonous sources. LEs showed a higher β:α and biological index (BIX) than AEs, indicating that LEs had higher biological activity. Compared to the LEs, DOM in AEs exhibited a higher humification index (HIX), illustrating that DOM was more humic and aromatic. Overall, our results suggest that the BIX and fluorescence index (FI) were best suited for the characterization of water bodies impacted by LEs and AEs. Excitation-emission matrix spectroscopy and parallel factor (EEMs-PARAFAC) analysis showed that DOM in AEs was mainly a humic-like material (~64%) and in LEs was mainly protein-like (~68%). Tryptophan-like compounds (C1) were made more abundant in AEs because of the breakdown of aquatic vegetation. The microbial activity enhanced protein-like substances (C1 and C2) in LEs. Our study revealed a positive correlation between five-day biochemical oxygen demand (BOD₅) concentrations and tyrosine-like substance components, suggesting that fluorescence peak B may be a good predictor of water quality affected by anthropogenic activities. For both LEs and AEs, our results suggest that peak D may be a reliable water quality surrogate for total phosphorus (TP).

Drinking water treatment and associated toxic byproducts: Concurrence and urgence

Reclaimed water is highly required for environmental sustainability and to meet sustainable development goals (SDGs). Chemical processes are frequently associated with highly hazardous and toxic by-products, like nitrosamines, trihalomethanes, haloaldehydes, haloketones, and haloacetic acids. In this context, we aim to summarize the formation of various commonly produced disinfection by-products (DBPs) during wastewater treatment and their treatment approaches. Owing to DBPs formation, we discussed permissible limits, concentrations in various water systems reported globally, and their consequences on humans. While most reviews focus on DBPs detection methods, this review discusses factors affecting DBPs formation and critically reviews various remediation approaches, such as adsorption, reverse osmosis, nano/micro-filtration, UV treatment, ozonation, and advanced oxidation process. However, research in the detection of hazardous DBPs and their removal is quite at an early and initial stage, and therefore, numerous advancements are required prior to scale-up at commercial level. DBPs abatement in wastewater treatment approach should be considered. This review provides the baseline for optimizing DBPs formation and advancements in the remediation process, efficiently reducing their production and providing safe, clean drinking water. Future studies should focus on a more efficient and rigorous understanding of DBPs properties and degradation of hazardous pollutants using low-cost techniques in wastewater treatment.

Properties of river organic carbon affected by wastewater treatment plants

Tracking the sources of organic carbon (OC) is critical not only for understanding riverine carbon dynamics but also for providing management options to improve water quality. We collected water samples from upland forest streams to the mainstream Geumho River (GHR) of South Korea, which included a variety of wastewater treatment plants (WWTP) effluents. We analyzed the concentrations, optical properties, and dual carbon isotope ratios of these samples to identify the sources of OC. Dissolved organic carbon (DOC) was the dominant form of OC in the GHR compared to particulate organic carbon (POC), as the former accounted for 87 % of OC. The concentrations of DOC and POC ranged from 1.2 to 11.2 mg L^-1 and from 0 and 3.6 mg L^-1, respectively, aside from the livestock WWTP effluent. Dominant fluorescence components were terrestrial humic substances in upper reaches whereas protein-like materials in lower reaches of the GHR whose watershed includes a large city with many WWTPs. Significantly lower Δ¹⁴C-DOC and Δ¹⁴C-POC were observed in industrial WWTP effluents than the other sites due to the contribution of fossil OC. Livestock WWTP effluents had higher δ¹³C-DOC and δ¹³C-POC than most of the sites, possibly due to the animal feed derived from C4 plants such as corn. Fossil OC contributed 29-52 % of [DOC] and 36-56 % of [POC] from industrial WWTP effluents, whereas C4-plants derived OC contributed about half of [DOC] and [POC] from a livestock WWTP effluent. The results suggest that anthropogenic sources of organic carbon could alter river carbon dynamics, and that caution is needed when we interpret isotope ratios of riverine organic carbon, particularly when the river passes through highly populated areas wherein WWTP effluents are large.

Stable isotope labeling for detection of ozonation byproducts in effluent organic matter with FT-ICR-MS

Despite effluent organic matter (EfOM) being a major consumer of ozone during wastewater treatment, little is known about ozonation byproducts (OBPs) produced from EfOM. To unambiguously identify OBPs, heavy ozone was used to ozonate EfOM, resulting in ¹⁸O labeled and unlabeled OBPs. Labeled OBPs mostly represent a single ¹⁸O transfer and were classified as either direct or indirect OBPs based on the ¹⁸O/¹⁶O intensity ratios of the isotopologues. Of the 929 labeled OBPs, 84 were unequivocally classified as direct OBPs. The remainder suggest a major contribution by indirect, hydroxyl radical induced formation of OBPs in EfOM. Overall, labelled OBPs possess a low degree of unsaturation and contributed most to OBP peak intensity - marking them as potential end products. A few direct and indirect OBPs with high peak intensity containing ¹⁸O and heteroatoms (N, S) were fragmented with CID FT-ICR-MS/MS and screened for indicative neutral losses carrying heavy oxygen. The neutral loss screening was used to detect the ¹⁸O location on the OBP and indicate the original functional group in EfOM based on known reaction mechanisms. We identified sulfoxide and sulfonic acid functional groups in selected OBPs - implying the presence of reduced sulfur in EfOM molecules - while no evidence for nitrogen containing functional groups reacting with ozone was found.

Sources, characteristics, and in situ degradation of dissolved organic matters: A case study of a drinking water reservoir located in a cold-temperate forest

Dissolved organic matter (DOM) plays a pivotal role in the biogeochemical cycles of elements and the regulation of forest ecosystem functions. However, studies on the regional and seasonal characteristics of DOM in cold-temperate montane forests are still not comprehensive. In this study, samples of water, soil, and sediment from different sites in the forest drainage basin were collected, and their DOM was characterized by an excitation-emission matrix and parallel factor analysis (EEM-PARAFAC). The results showed that terrestrial-sourced humic-like substances were the dominant DOM in the studied reservoir and inflowing rivers. The quality and quantity of DOM exhibited spatiotemporal variations with the influence of terrain and monsoonal precipitation. The average concentration of dissolved organic carbon (DOC) in the wet season was 11.62 mg/L, which was higher than that in the dry season (8.18 mg/L). Higher humification index (HIX) values were observed in the wet season and upstream water than in the dry season and reservoir water. Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) was used to further develop a molecular-level understanding of the in situ degradation process of DOM. The results indicated that photodegradation rather than biodegradation may play a dominant role in the in situ degradation of terrestrial-sourced humic-like substances under natural conditions. The biodegradability of DOM was enhanced after the in situ degradation process. Additionally, a significant decrease in the precursors of disinfectant byproducts in DOM was observed after in situ degradation. To our knowledge, this is the first study of the sources, characteristics, and in situ degradation of DOM in a reservoir in a cold-temperate forest. These findings help better understand the quality, quantity, and biogeochemical process of DOM in the studied reservoir and may contribute to the selection of drinking water treatment technologies for water supply.

Decomposition of Total Organic Halogen Formed during Chlorination: The Iceberg of Halogenated Disinfection Byproducts Was Previously Underestimated

Total organic halogen (TOX) is widely used as a surrogate bulk parameter to measure the overall exposure of halogenated disinfection byproducts (DBPs) in drinking water. In this study, we surprisingly found that the level of TOX in chlorinated waters had been significantly underestimated under common analytical conditions. After the addition of quenching agent sodium thiosulfate, total organic chlorine and total organic bromine exhibited a two-phase decomposition pattern with increasing contact time, and a significant decomposition was observed for different types of quenching agents, quenching doses, and pH conditions. More importantly, the decomposed TOX closely correlated with the acute toxicity of quenched water against luminous bacteria, implying that the DBPs responsible for TOX decomposition could be of important toxicological significance. Based on nontarget analysis by using high-resolution mass spectrometry, molecular formulas for the decomposed TOX were determined. After re-examining the mass balance of TOX in the context of unintentional decomposition, it was found that both the level and percentage of unknown TOX in chlorinated waters were considerably higher than historically thought. Overall, this study brings new insights into the knowledge of TOX formed during chlorination, providing important clues on the identification of toxicity driver in drinking water.

Optical and molecular indices of dissolved organic matter for estimating biodegradability and resulting carbon dioxide production in inland waters: A review

Biodegradable dissolved organic carbon (BDOC) constitutes the most labile fraction of dissolved organic matter (DOM), which also functions as a source of CO₂ emissions from inland waters. However, no systematic review is available on DOM indicators of BDOC and CO₂ production potential. Optical and molecular indices can be used to track small changes in DOM composition during biodegradation. In this review, we identified four different methods for measuring BDOC together with their strengths and limitations. In addition, we discuss the potential of using documented optical indices based on absorption and fluorescence spectroscopy and molecular indices based on Fourier transform ion cyclotron mass spectrometry as proxies for estimating BDOC and biodegradation-induced CO₂ production based on previously reported relationships in the literature. Many absorbance- and fluorescence-based indices showed inconsistent relationships with BDOC depending on watershed characteristics, hydrology, and anthropogenic impacts. Nevertheless, several indices, including specific UV absorbance at 254 nm (SUVA₂₅₄), humification index (HIX), and terrestrial humic-like fluorescent DOM (FDOM) components, tended to have negative relationships with BDOC in tropical and temperate watersheds under baseflow or drought periods. Protein-like FDOM exhibited the strongest correlation with BDOC in different systems, except during storms and flood events. Despite the limited number of studies, DOM molecular indices exhibited consistent relationships with BDOC, suggesting that the relative abundance of aliphatic formulas and the molecular lability index could act as reliable proxies. The DOM optical indices explain up to 96% and 78% variability in BDOC and CO₂, respectively; nonetheless, there were limited studies on molecular indices, which explain up to 74% variability in BDOC. Based on literature survey, we recommend several sensitive indices such as SUVA₂₅₄, HIX, and terrestrial humic- and protein-like FDOM, which could be useful indicators of BDOC and dissolved CO₂ in inland water. Future research should incorporate a wider range of geographic regions with various land use, hydrology, and anthropogenic disturbances to develop system- or condition-specific DOM optical or molecular proxies for better prediction of BDOC and CO₂ emissions.

Removal and toxic forecast of microplastics treated by electrocoagulation: Influence of dissolved organic matter

In recent years, the break of COVID-19 makes the large use of disposable products, which causes the removal of microplastics become an imperative problem. Electrocoagulation is one of the effective removal technologies, but there is hardly research concentrating on the effect of substrate in the actual water on the microplastics removal with electrocoagulation. As an important role of water bodies, dissolved organic matter (DOM) has a vital and inevitable effect on the efficiency of electrocoagulation. In this study, the effect of DOM in tailwater on microplastics during electrocoagulation is elucidated by comparing the electrocoagulation treatment results between simulated wastewater and tailwater, using parallel factor analysis (PARAFAC), Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectrometer (FTIR) and zeta potential analyzer. Three kinds of microplastic particles (i.e. polypropylene, polyethylene, and polymethyl methacrylate) were added into each of the two kinds of wastewaters to form six electrocoagulation systems. Results show that DOM in tailwater promotes the production of flocs and free radicals during electrocoagulation process. Fe²⁺ and Fe³⁺ are adsorbed on the surface of DOM molecules and combined with •OH form flocs. Although DOM accelerates the production of free radicals and thus promotes the aging of microplastics, flocs with DOM as crystal nucleus can prevent toxic substances and small-sized microplastics from leaching into water again. Therefore, electrocoagulation is preferred to removal microplastics in water with high concentration of DOM. This study provides a significant reference for microplastics removal by electrocoagulation in actual water, and promote the practical application of electrocoagulation for microplastics removal in water treatment.

Charting the landscape of the environmental exposome

The exposome depicts the total exposures in the lifetime of an organism. Human exposome comprises exposures from environmental and humanistic sources. Biological, chemical, and physical environmental exposures pose potential health threats, especially to susceptible populations. Although still in its nascent stage, we are beginning to recognize the vast and dynamic nature of the exposome. In this review, we systematically summarize the biological and chemical environmental exposomes in three broad environmental matrices-air, soil, and water; each contains several distinct subcategories, along with a brief introduction to the physical exposome. Disease-related environmental exposures are highlighted, and humans are also a major source of disease-related biological exposures. We further discuss the interactions between biological, chemical, and physical exposomes. Finally, we propose a list of outstanding challenges under the exposome research framework that need to be addressed to move the field forward. Taken together, we present a detailed landscape of environmental exposome to prime researchers to join this exciting new field.