To meet the mounting regulations on per- and poly-fluoroalkyl substances (PFAS) in drinking water, ion exchange (IX) has become one of the most widely used technologies. However, the effects of resin characteristics and effects of common water matrix ions (sulfate) on the competitive uptake of PFAS of varying chain lengths and functionalities in multicomponent systems are not well understood. In this study, two commercial strong-base IX resins were tested for competitive removal of 10 PFAS. This study demonstrates that polystyrene matrix (IRA900) IX significantly outperforms polyacrylic matrix (A860) IX in the removal of PFAS due to both electrostatic and hydrophobic interactions. More effective removal in IX was found in longer-chain PFAS and perfluoroalkyl sulfonic acids (PFSAs) than in perfluoroalkyl carboxylic acids (PFCAs). PFAS removal was effective over a broad pH range of 4–8.5 except for short-chain PFCAs, which were competed with hydroxide ions. The uptake of IRA900 decreased with the increase in sulfate concentration and the decrease was profoundly in shorter-chain PFAS. In kinetic tests, the PFAS removal for IRA900 was ~85% without sulfate and ~80% with sulfate within 48 h. Moreover, it was confirmed that the presence of sulfate suppressed shorter-chain PFAS and PFCA homologues. IRA900 was regenerated using NaCl, methanol (CH3OH), and a combination. A decrease by 10.7–12.6% after first regeneration was attributed to PFCA.

Transformations of polystyrene-microplastic-derived dissolved organic matter (PS-DOM) in aquatic systems and the implications for the fates of nanosized polystyrene (PS) were investigated focusing on the roles of microbial activity and UV irradiation. PS-DOM, composed of oxygenated and hydrophobic products and nanosized PS, were found to undergo self-assembly and aggregation to form colloids and microparticles, meaning PS-DOM can act as a precursor for the formation of particulate organic matter. Microbial activity markedly enhanced both self-assembly and aggregation, causing marked increases in the particle size and molecular weight. UV irradiation promoted PS-DOM transformations through photo-oxidation and the generation of hydrophilic products, but prolonged UV exposure caused partial breakdown of the microparticles that formed. Nanosized PS actively participated in these transformation processes and underwent reversible hydrophilic-hydrophobic conversions under UV irradiation. After 21 d of incubation under dark/UV and biotic/abiotic conditions, nanosized PS supplied approximately 20% of the total organic carbon content, indicating that transformed PS-DOM gave a stable total organic carbon content. The results indicated that self-assembly and aggregation assisted by microbial processes and UV irradiation play critical roles controlling PS-DOM transport, persistence, and environmental behaviors.

Accurate forecasting of phytoplankton dynamics at drinking-water intake points is essential for proactive reservoir management because sudden biomass increases can directly impair filtration and increase backwashing demand. Using daily monitoring data collected at the Hoedong Reservoir intake depth from November 2012 to December 2021, we developed and evaluated a physics-informed Transformer (PITF) framework to predict the intake-point cell density of two operationally problematic genera (Microcystis and Stephanodiscus). Missing observations were addressed using a centered rolling-median interpolation, and a noise-perturbed dataset was additionally generated to assess robustness under realistic input uncertainty. All models performed were evaluated using R2 and RMSE. Intake point monitoring indicated risk patterns, with Microcystis peaking during mid-summer to autumn (up to 43,560 cells·mL-1) and Stephanodiscus peaking in winter (up to 5,120 cells·mL-1). PITF achieved strong validation performance for Microcystis (R2=0.711) and reasonable performance for Stephanodiscus (R2=0.505). Under noise-perturbed inputs, PITF showed slight performance degradation (e.g., Microcystis R2=0.701; RMSE=0.761), indicating robust forecasting skill under input uncertainty. A SHAP-based plausibility assessment identified ecologically consistent drivers, with water temperature and dissolved oxygen as dominant predictors for both taxa. Overall, PITF provides an interpretable and robust intake-focused forecasting approach that can support early-warning decision-making for drinking-water treatment operations.

This study evaluated the applicability of ferric chloride (FeCl3) as a coagulant for drinking water treatment using raw water from the lower Nakdong River and compared its performance with aluminum sulfate (alum). Jar-tests and pilot-scale experiments were conducted using raw water from the Maeri intake station. Water quality parameters including turbidity, total organic carbon (TOC), chlorophyll-a (Chl-a), color, alkalinity, and pH were monitored. Dissolved organic matter (DOM) fractions were characterized using LC-OCD, while disinfection by-product formation potentials (THMFP and HAAFP) were measured to assess the removal efficiency of organic precursors. The performance of a hybrid coagulant (alum mixed with FeCl3) was also investigated. Results showed that FeCl3 outperformed alum in removing turbidity, TOC, and Chl-a in both batch and continuous experiments. Notably, FeCl3 exhibited superior removal of humic substances (HS) and building blocks (BB) fractions, resulting in a more significant reduction in THMFP and HAAFP. Although the supernatant color increased initially with FeCl3 application, the filtered water color remained lower than that of alum, suggesting that residual color-causing agents were primarily particulate microflocs. Furthermore, FeCl3 effectively reduced the DOC load delivered to the subsequent granular activated carbon (GAC) process, enhancing overall treatment efficiency. FeCl3 is a promising alternative or supplement to alum for treating raw water with high organic and algal content, provided that alkalinity and pH are appropriately controlled during practical application.

Cyanobacterial blooms threaten aquatic ecosystems and human health, and their occurrence has been intensified by hydrological and weather variations associated with climate change. This study proposes an optimal weir operation framework by coupling Long Short-Term Memory (LSTM) models with a Soft Actor-Critic (SAC)-based deep reinforcement learning (DRL) agent for managing cyanobacterial blooms. The LSTM models simulated hydrological, nutrient, and cyanobacteria-related state variables that were input to the DRL environment to update continuous weir operation. The SAC-based DRL system was trained to determine the optimal weir overflow strategy to reduce cyanobacteria compared to the baseline LSTM simulation within operational storage constraints. Additional sensitivity analyses indicated that average operation metrics were relatively stable under cyanobacteria prediction perturbations and across SAC training seeds, while cyanobacterial reduction performance and peak-event responses remained sensitive to these uncertainties. On the validation set, the LSTM models achieved R2 values ranging from 0.75 to 0.89 for hydrological and nutrient variables and 0.76 for cyanobacteria regression, while the cyanobacteria occurrence classification yielded an accuracy of 92.22%. The DRL-based optimal weir operation reduced cyanobacteria concentrations by up to 13.01% and 8.39% during training and validation, respectively. Hydro-thermal scenarios revealed that higher inflow can partially mitigate thermal stress on cyanobacteria; however, the tested inflow range had limited capacity to reduce cyanobacterial concentrations under rising water temperature conditions. These results demonstrated the potential ability of the proposed LSTM-DRL framework to manage cyanobacterial blooms, though site-specific calibration and further uncertainty evaluation are required before operational application.

Per-and polyfluoroalkyl substances (PFAS) are persistent contaminants of increasing concern in aquatic environments, yet assessment remains challenging due to the diversity of target compounds and precursors. This study investigated PFAS occurrence, composition, and sources in industrial and municipal wastewater effluents and river waters from the Nakdong River basin, Republic of Korea, using an integrated framework bridging target analysis and total-fluorine screening through liquid chromatography-tandem mass spectrometry (LC-MS/MS), the total oxidizable precursor (TOP) assay, and combustion ion chromatography for adsorbable organofluorine (AOF). Method validation demonstrated that AOF preferentially recovers intermediate-and long-chain PFAS while excluding ultrashort-chain PFAS and inorganic fluorinated species. The application of sequential TOP oxidation (TOP-AOF) enhanced selectivity by eliminating interferences from non-PFAS organofluorines. Although the TOP-AOF method retains limitations regarding short-chain recovery, this trade-off demonstrates its potential as a robust, risk-oriented screening tool focused on the toxicologically significant fraction of adsorbable total PFAS. Distinct sector-specific fingerprints were observed. Dyeing, textile, and pulp and paper effluents exhibited the highest PFAS concentrations and precursor contributions, dominated by short-chain perfluoroalkyl carboxylic acids and perfluorobutane sulfonate. Electronics-related wastewater was enriched in short-chain PFAS, whereas metal-processing effluents showed perfluoroalkyl sulfonate-dominated profiles. Municipal effluents contained lower PFAS concentrations, but their large discharge volumes produced mass loads comparable to major industrial sources. Overall, TOP-AOF enables improved assessment of PFAS contamination by linking compound-specific LC-MS/MS with total-fluorine screening for source identification and mass-load assessment in industrialized watersheds.

Temperature and solid retention time (SRT) are major parameters influencing performance and removal of antibiotic resistance genes (ARGs) during anaerobic digestion (AD). Recuperative thickening (RT) has been applied to isolate the effect of SRT from hydraulic retention time; however, RT-AD remains less explored under thermophilic conditions. The current study investigated the effects of SRT alone on AD performance using RT under both mesophilic and thermophilic conditions, microbial communities, functional profiles, and ARG abundances. Four conditions were tested: Meso-C (mesophilic, SRT 20 d), Thermo-C (thermophilic, SRT 20 d), Meso-R (mesophilic, SRT 40 d), and Thermo-R (thermophilic, SRT 40 d). Thermophilic conditions and extended SRT enhanced biogas production by extending microbial retention times and removing inhibitory materials. As a result, Meso-C had a biogas yield of 304.5 mL/g-VSadded, while Thermo-C yielded 320.3 mL/g-VSadded. Extended SRT improved biogas yield by 9.3 % (Meso-R) and 43.9 % (Thermo-R) compared to their controls. Temperature had a stronger influence than SRT in shaping microbial composition and functional profiles. Bacteroidetes dominated under mesophilic conditions, utilizing carbohydrate and carboxylate degradation, whereas Coprothermobacterota dominated thermophilic conditions with proteogenic amino acid degradation. Temperature also affected ARG-host microorganisms, influencing ARG composition. Moreover, low microbial diversity was observed with extended SRT under mesophilic conditions, and short SRT under thermophilic conditions improved ARG removal efficiency, limiting ARG transfer potential. Consequently, ARG removal efficiencies were higher in Meso-R (57.0 %) and Thermo-C (68.5 %) compared to Meso-C (55.2 %) and Thermo-R (59.0 %), respectively. These results underscore the dominant role of temperature over SRT in AD performance and ARG removal.

Climate-induced changes in dissolved organic matter (DOM) and trace organic contaminants (TrOCs) present growing challenges for drinking water treatment, particularly in surface water-dependent regions. Bank filtration (BF), a natural subsurface treatment process, offers a sustainable solution, but its performance and scalability require further validation. This study simultaneously assesses the performance of laboratory-scale and full-scale BF systems using a horizontal collector well (HCW), both receiving the same source water and aquifer materials, to remove DOM and TrOCs, and to investigate changes in microbial communities under equivalent residence times (20 days). The full-scale HCW system achieved a 63.0 % DOM removal rate compared to 37.0 % in laboratory-scale columns, effectively reducing biopolymers and humic substances through soil passage. Microbial analysis revealed distinct shifts, with Proteobacteria comprising 80.1 % of the full-scale filtrate compared to 59.1 % in the laboratory-scale. Total cell counts and microbial activity decreased by 85.0 % and 90.4 % in the full-scale system, respectively. The removal efficiency for 60 selected TrOCs varied by their properties: hydrophobic ionic compounds achieved high removal (91.2 %), while hydrophilic and neutral compounds, including perfluoroalkyl substances (PFAS), showed lower removal rates (37.3 % and 24.5 %, respectively). Pharmaceuticals, steroid hormones, and pesticides were effectively removed, with some exceeding 99.9 %. This study is the first to directly compare full-scale HCW and laboratory-scale BF systems under controlled conditions. These findings highlight BF's effectiveness and the need for integrating complementary technologies to improve water quality and sustainability.

Organic micropollutants in drinking water can pose a public health risk. Chemical analysis alone cannot capture the full range of contaminants or assess their associated risks, promoting the growing use of bioanalytical tools as a complementary approach. This study assessed a drinking water treatment plant in the Nakdong River basin, Korea, using in vitro bioassays targeting nine endpoints. The highest estrogen receptor (ERα) activity was observed in the influent and significantly decreased throughout treatment. Bioactivities related to xenobiotic metabolism (PAH, PPARγ, and PXR) and oxidative stress response (Nrf2) initially increased during pre-oxidation but decreased in later treatment stages. An increase in p53 activity was also noted during treatment. Both season and treatment processes were found to affect the bioactivity variation for most endpoints, based on correlation analysis. The bioactivities observed were consistent with those reported for treated drinking waters in other countries. PAH, PPARγ, PXR, and Nrf2 activities in the final treated waters exceeded some effect-based trigger (EBT) values, indicating potential risks, although uncertainty remain regarding the EBT values for PPARγ and PXR. Additionally, the bioanalytical equivalent concentrations of volatile disinfection byproducts detected after pre- and post-chlorination were lower than the measured Nrf2 activities by factors of 7.5 and 5.5, respectively. This study highlights the importance of monitoring of bioactive chemicals to safeguard public health and ecosystems, underscoring the value of in vitro bioassays in water quality assessment.

This study investigated how the biodegradation rate constant (kbio) of 11 micropollutants (MPs) responded to changes in the concentrations of growth substrates and microbial activities while considering the predominant microbial degraders of MPs. Metformin, losartan, valsartan, and cimetidine (group A) were biodegraded predominantly by nitrifiers. MPs of group A showed a positive correlation with kbio and nitrifying activity, while a negative correlation was observed with the initial concentration of ammonium, possibly due to competitive inhibition. Atenolol, caffeine, and naproxen (group B) were biodegraded predominantly by heterotrophs, with kbio remaining stable despite changes in organic matter concentration or heterotrophic activity. Olmesartan, candesartan, diclofenac, and sulfamethoxazole (group C) showed low kbio regardless of growth substrate concentration and microbial activity, which could be attributed to their chemical structures. These findings suggest that the kbio of MPs in WWTPs could respond differently to growth substrate concentration and microbial activity depending on their predominant degraders.

This study evaluated the effects of alkaline pretreatment on solubilization, anaerobic digestion (AD), and microbial community dynamics of polylactic acid (PLA) and agricultural biocomposite products (ABPs). Pretreatment with 1, 5, and 10 M NaOH enhanced solubilization, with PLA exhibiting rapid and high chemical oxygen demand (COD) release, while ABPs showed slower, substrate-limited solubilization. Liquid chromatography-organic carbon detection (LC-OCD) and Fourier transform infrared spectroscopy (FTIR) analyses showed structural degradation of broken ester bonds in PLA, while ABPs displayed partial lignocellulosic breakdown and increased humic-like substances. AD of untreated PLA showed limited methane production due to structural recalcitrance. In contrast, pretreatment significantly improved PLA biodegradability, achieving methane yields close to theoretical potential. However, ABPs showed reduced methane yield after pretreatment, attributed to the formation of inhibitory compounds and reduced availability of readily degradable organics. Volatile fatty acids (VFAs) profiles supported these trends, indicating enhanced acidogenesis in pretreated PLA and suppressed VFAs production in pretreated ABPs. Microbial analysis revealed taxonomic and functional shifts driven by pretreatment and substrates, with fermentative and methanogenic taxa aligning with solubilized organics in multiple factor analysis (MFA). These findings underscore the importance of tailoring pretreatment strategies based on substrate type to optimize methane production and microbial function. Alkaline pretreatment of PLA enhanced its solubilization and biodegradability, enabling methane production close to its theoretical potential. In contrast, pretreatment of ABPs requires careful optimization to avoid inhibitory byproducts and reduced digestion efficiency.

Objectives : This study aims to evaluate the removal rates of nine cyanotoxins produced by cyanobacteria using a laboratory-scale simulated drinking water treatment process (DWTP), providing useful data for DWTP operations during algal blooms.Methods : A lab-scale simulated DWTP was used to evaluate the removal rates of nine cyanotoxins under typical operating conditions, including specific chemical dosages and contact times. The study employed chlorine and ozone, as well as powdered activated carbon (PAC) and biological activated carbon (BAC).Results and Discussion : According to the experimental results of removal efficiency for chlorination and ozonation, microcystin-LR (MC-LR), MC-RR, MC-LA, MC-LF, MC-LY, MC-YR, cylindrospermopsin (CYN), and nodularin (NOD) were effectively removed within the typical ranges of pre- and post-chlorine and pre- and post-ozone concentrations in the DWTP. However, anatoxin-a (ANA) exhibited a significantly lower removal efficiency. The evaluation of removal efficiency for PAC treatment indicated that MC-LA, MC-LF, and MC-LY had low removal rates. In contrast, the other six cyanotoxins achieved over 50% removal when PAC concentrations were above 25 mg/L and contact times exceeded 30 minutes. The evaluation of removal rate for BAC treatment showed that under conditions with an empty bed contact time (EBCT) of more than 5 minutes, over 70% of the nine cyanotoxins were removed. When the EBCT exceeded 2 minutes, removal rates reached between 95% and 100%. In the BAC process, the removal of MC-RR was primarily facilitated by the biodegradation, while the removal of CYN was mainly achieved through adsorption.Conclusion : Due to climate change, the bloom periods of various cyanobacteria in domestic water sources are gradually increasing, resulting in a rising trend in both the frequency and concentration of detected cyanotoxins. This study evaluated the removal efficiency of various cyanotoxins in DWTPs, focusing on chlorine/ozone treatment (oxidation), PAC treatment (adsorption), and BAC (adsorption and biodegradation). The different DWTPs at the facility act as multiple barriers, effectively removing cyanotoxins upon their introduction.

This research developed and optimized innovative, cost-effective methods to quantify extractable total per- and polyfluoroalkyl substances (PFAS) in water, overcoming limitations of existing techniques by integrating persulfate preoxidation with subsequent solid phase extraction (SPE), followed by chemical defluorination using sodium biphenyl (SBP assay) or ion-pair formation with methylene blue (MB assay). Persulfate preoxidation improved selectivity by oxidizing interfering organofluorines and anionic surfactants, while SPE concentrated PFAS and removed impurities such as inorganic fluoride. Both the SBP and MB assays exhibited high responses across various PFAS structures, except for some (ultra)short-chain PFAS. The refined assays, including SPE, achieved limits of detection of 0.016 mu gF/L for SBP and 0.2 mu gF/L for MB assay, with robust recoveries across various PFAS compounds in synthetic water matrices. Analyses of PFAS-contaminated real waters using the SBP assay revealed extractable total PFAS concentrations of 5.1 mu gF/L in industrial wastewater and 0.30 mu gF/L in river water, matching those by combustion ion chromatography (CIC), a current benchmark method. The MB assay, however, showed concentrations 1.9-3.1 times higher than the SBP and CIC assays. The extractable total PFAS concentrations in the real waters exceeded the sum of individual PFAS quantified by LC-MS, underscoring the necessity of identifying unknown PFAS.

Organic micropollutants present in effluents of wastewater treatment plants (WWTPs) can negatively affect the quality of receiving waters or drinking water sources. The present work monitored the concentration of bioactive chemicals using a battery of in vitro bioassays in 14 WWTP effluents, 2 effluent-dominant streams, and 5 river waters in the Nakdong River basin, Korea, for a two-year period. The WWTP effluents showed AR/ERα/TRβ (androgen/estrogen/thyroid hormone) activities at a few to tens ng/L, PAH/PPARγ/p53 (polycyclic-aromatic-hydrocarbon/lipid metabolism/genotoxicity) activities at hundreds ng/L, and PXR/Nrf2 (xenobiotic metabolism/oxidative stress) activities at tens to hundreds μg/L as bioanalytical equivalent concentrations. The concentration level and type of bioactivities were statistically not affected by the source, season, or treatment processes of WWTPs for most endpoints. The effluent-dominant streams showed similar levels of AR/ERα/PAH/PXR/Nrf2 activities compared to the upstream WWTP effluents. The river waters showed lower levels of AR/ERα activities (by factors of 6 or 7) but had only slightly lower PAH/PXR/Nrf2 activities (within factors of 2) than the WWTP effluents when compared based on median concentration. Cytotoxicity was below the quantification limit (0.3 μg/L) in most effluent and river samples. For ERα/PAH/PXR/Nrf2, the median bioactivity levels of the river waters were higher than at least one of the effect-based trigger (EBT) values proposed in the literature. Further monitoring work and reliable/realistic EBT derivation are needed to determine possible ecological risks posed by the observed bioactivities.

To predict the fate of micropollutants (MPs) in the anaerobic zone at the lab and full-scale levels, anaerobically biological removal (adsorption and biodegradation) of 40 MPs was performed. Among the 40 MPs in the full-scale anaerobic tank, estriol and acetaminophen showed the highest total removal efficiencies in the anaerobic zone (similar to 100 %). In batch tests, five MPs belonging to estrogens (estriol and 17b-estradiol), parabens (ethyl paraben and propyl paraben), and iopromide were completely removed within 12 h. Meanwhile, MPs belonging to perfluorinated compounds and nitrosamines were infrequently removed (<20 %) within 12 h. The obtained solid -water distribution coefficient (Kd) and biodegradation rate constants (Kbiol) values were used for predictive modeling of residual MPs' concentrations in the full-scale anaerobic zone and were compared with Kbiol obtained from the oxic zone. Most MPs had similar Kbiol values regardless of redox conditions (oxic or anaerobic); however, caffeine, ibuprofen, naproxen, trimethoprim, and iopromide showed different values depending on the redox conditions. Differences in the efficiencies of total MP' removal were noted between that predicted via modeling and actually observed (-37 % [iopromide] to 49 % [caffeine]) under altered conditions such as levels of dissolved oxygen (DO) and introduction of the primary or returned sludge. This implies that strictly anaerobic conditions are required for the degradation of specific MPs. The K-d and K-biol values obtained in this study could help predict changes in the concentration of MPs in the anaerobic zone.

Given the frequent association between freshwater plankton and water quality degradation, several predictive models have been devised to understand and estimate their dynamics. However, the significance of biotic and abiotic interactions has been overlooked. In this study, we aimed to address the importance of the interaction term in predicting plankton community dynamics by applying graph convolution embedded long short-term memory networks (GC-LSTM) models, which can incorporate interaction terms as graph signals. Temporal graph series comprising plankton genera or environmental drivers as node features and their relationships for edge features from two distinct water bodies, a reservoir and a river, were utilized to develop these models. To assess the predictability, the performances of the GC-LSTM models on community dynamics were compared those of LSTM and GCN models at various lead times. Moreover, GNNExplainer was used to examine the global and local importance of the nodes and edges for all predictions and specific predictions, respectively. The GC-LSTM models outperformed the LSTM models, consistently showing higher prediction accuracy. Although all the models exhibited performance degradation at longer lead times, the GC-LSTM models consistently demonstrated better performance regarding each graph signal and plankton genus. GNNExplainer yielded interpretable explanations for important genera and interaction pairs among communities, revealing consistent importance patterns across different lead times at both global and local scales. These findings underscore the potential of the proposed modeling approach for forecasting community dynamics and emphasize the critical role of graph signals with interaction terms in plankton communities.

Objectives Globally, the mass proliferation of phytoplankton driven by climate change has emerged as a significant societal issue. This study analyzes over two decades of long-term hydraulic, hydrological, and water quality data collected from the lower Nakdong River, along with changes in phytoplankton community biomass. The aim is to evaluate long-term trends in water quality and the ecological changes occurring in this region. Methods The monitoring site in the lower Nakdong River is Mulgeum, where samples were collected weekly from January 2000 to December 2021 for the analysis of physicochemical water quality characteristics, as well as phytoplankton abundance and species composition. The hydrological status was assessed using flow rate data from the Jin-dong (Haman) station of the Nakdong River, along with rainfall data from the Korea Meteorological Administration for eight regions influencing the lower Nakdong River. Results and Discussion Analysis of the annual average concentration changes of water quality parameters at the Mulgeum intake site in the lower Nakdong River found that water quality has generally improved since the construction period (2009-2012) of the weir. This improvement is attributed to the strengthening of T-P water quality standards for sewage treatment plant discharges in 2012, which resulted in enhanced phosphorus treatment at wastewater facilities in the river's middle and upper regions. Consequently, significant reductions were observed in the annual average concentrations of BOD, NO3-N, T-N, and T-P. Evaluating long-term changes in flow rate and rainfall, it was found that both annual average rainfall and flow rate decreased after the weir was installed, particularly from May to September when temperatures rise. Rainfall decreased by approximately 8% to 38%, while flow rate decreased by 46% to 62%. Long-term temperature changes indicated that summer temperatures increased by 0.9oC to 1.4oC, and winter temperatures rose by 1.6oC to 2.0oC, resulting in an overall annual average increase of about 1.3oC. An analysis of long-term changes in phytoplankton biomass and community composition revealed an increase in average biomass from 3,639 cells/mL before the weir was installed to 4,034 cells/mL afterward, representing an increase of about 11%. In winter, the dominance period and biomass of diatoms decreased, while in summer, the biomass and dominance period of cyanobacteria increased. Notably, in August, biomass increased approximately 7.5 times, rising from 2,009 cells/mL before the dam to 15,059 cells/mL afterward. This significant increase was identified as a key factor in the overall rise in phytoplankton biomass following the weir's installation. Conclusion Recent climate change impacts, such as rising average temperatures and shifting rainfall patterns, have become increasingly evident in South Korea. This study utilizes over 20 years of long-term data to demonstrate that, in the lower Nakdong River, there has been a gradual decline in both rainfall and flow rates, accompanied by an increase in average temperatures. Consequently, the dominance period and biomass of diatoms have decreased. In contrast, cyanobacteria, which thrive in warmer conditions, have experienced an extended dominance period into early spring and late autumn as a result of rising temperatures, leading to an overall increase in cyanobacterial biomass.

Objectives : This study developed a simple and automated analytical method using headspace-SPME (solid phase microextraction) and GC (gas chromatography)-MSD (mass selective detector) to simultaneously analyze ten odorous compounds (dimethyl trisulfide (DMTS), 3-hexenylacetate (HA), 2-isopropyl-3-methoxypyrazine (IPMP), 2-methylbenzofuran (MBF), 2-isobutyl-3-methoxypyrazine (IBMP), β-cyclocitral (CC), trans-2-decenal (DCNL), 2-trans-4-trans-decadienal (DENL) 2,4,6-trichloroanisole (TCA) 및 β-ionone (ION)), evaluating their distribution characteristics throughout the Nakdong River basin.Methods : To optimize the extraction efficiency of the headspace-SPME method for ten odorous compounds, we evaluated various SPME fiber materials, extraction temperatures, extraction times, desorption temperatures, desorption times and salt (NaCl) dosages. Additionally, using the optimized headspace-SPME, we investigated the detection concentrations at ten main stream sites and six tributary sites in the Nakdong River basin.Results and Discussion : The most suitable SPME fiber material for the pretreatment of ten odorous compounds was CAR/PDMS/DVB. The optimal SPME extraction temperature and time were 75°C and 60 minutes, respectively, and the optimal desorption temperature and time at the GC injection port were 250°C and 3 minutes. Additionally, the optimal salt (NaCl) dosage for a 10 mL water sample was 2 g. Using the optimized headspace-SPME pretreatment method for GC-MSD analysis, the detection limits and quantification limits for the ten odorous compounds ranged from 2 to 10 ng/L and 5 to 25 ng/L, respectively, with HA exhibiting the highest detection and quantification limits. The evaluation of the distribution characteristics of odorous compounds throughout the Nakdong River basin revealed that only three compounds—DMTS, CC and ION—were detected. Among these, DMTS was found at the highest concentration of 115.5 ng/L in the tributary Jincheon-cheon, while CC was detected at the highest concentration of 30.6 ng/L in the main river at Goryeong. In the case of the Nakdong River basin, there was no contamination by odorous compounds in the upstream area. In the middle reach, influenced by effluent of wastewater treatment plants, the detection concentrations of three odorous compounds increased, but they showed a decreasing trend as they moved downstream.Conclusion : Since odorous compounds can lead to distrust in water quality even at extremely low concentrations in the ng/L range in tap water, regular monitoring of water sources is necessary during algal bloom season, including the dry season. Furthermore, continuous research is needed on various odorous compounds beyond the 10 odorous compounds in this study, including the optimization of analytical methods and the detection characteristics in water sources.

Objectives This study aimed to evaluate the removal efficiency of trace organic contaminants (TrOCs) in UVbased advanced oxidation processes (AOPs) as an alternative to the post-ozonation process in a drinking water treatment plant (DWTP) in the downstream of Nakdong River. The results are expected to be utilized as basic data for modernizing aging water treatment facilities. Methods Eight organophosphorus flame retardants (OPFRs), known for their persistence and resistance to degradation, were selected as the target TrOCs for evaluating the efficiency of ozonation and UV-based AOPs. Experiments were conducted using sand-filtered water from a DWTP in the downstream of Nakdong River, with the OPFRs spiked into the sample matrix. Lab-scale experiments of ozonation and UV-based AOPs (UV, UV/H2O2, and UV/Cl2) were performed, and the concentrations of the OPFRs were analyzed using stir bar sorptive extraction (SBSE) system, followed by GC-MS/MS. Results and Discussion The second-order rate constants (kOH) for the reaction of OPFRs with OH radicals were estimated using the group contribution method and ranged from 1.4(±0.6)×109 to 1.8(±0.1)×1010 M⁻1 s⁻1, depending on their structural characteristics. In the ozonation process, the removal of Cl-containing aliphatic OPFRs was not effective, likely due to the electron-withdrawing effects of the -Cl groups, which inhibited their reactivity with both ozone and OH radicals. However, for non-Cl-containing aliphatic and aromatic OPFRs, more than 90% removal efficiency was achieved at a specific ozone dose of 1.5 mgO3/mgDOC. In the UV-based AOPs, the aliphatic OPFRs showed poor removal efficiency of 5~35% at a UV fluence of 1,000 mJ/cm2 under direct UV photolysis. However, in the presence of oxidants (H2O2 or free available chlorine), the UV/H2O2 process showed up to an 89% increase in removal efficiency, and the UV/Cl2 process exhibited up to a 49% increase. The difference in removal patterns between the UV/H2O2 and UV/Cl2 processes is likely attributed to the difference in reactivity between reactive chlorine species and aliphatic OPFRs. For aromatic OPFRs, direct UV photolysis achieved high enough removal efficiencies of 90~98% at a UV fluence of 1,000 mJ/cm2. These results demonstrate the potential of UV/H2O2 and UV/Cl2 processes for the effective removal of OPFRs, particularly for Cl-containing aliphatic OPFRs, which exhibited low removal efficiency in the ozonation process. Conclusion The comparative evaluation of removal efficiencies of OPFRs in ozone and UV-based AOPs confirmed the potential of UV processes for efficient removal of OPFRs. The UV/H2O2 and UV/Cl2 processes showed promise as alternative treatments to ozonation for the removal of OPFRs during drinking water treatment.