No-Suk Park

This study applied a Bayesian Network (BN) model to identify the causal factors influencing the formation of trihalomethanes (THMs) during the chlorination process in water treatment plants. While conventional multiple linear regression (MLR) explains THMs concentrations based on linear correlations among variables, it is limited in representing probabilistic dependencies and directional relationships. In contrast, the BN approach allows probabilistic representation of dependencies and directional relationships through structural and parametric learning. Using twenty years (2003–2022) of operational data from the A Water Treatment Plant in the Han River basin, four structure learning algorithms—Hill-Climbing, Tabu Search, Grow–Shrink, and Max–Min Hill-Climbing (MMHC)—were compared. Tabu and MMHC yielded the best model fit (BIC=–1914.059). A consensus network combining common arcs across algorithms was constructed, and 500 bootstraps were performed to assess structural robustness. Edges satisfying strength ≥ 0.7 and direction ≥ 0.7 were retained, resulting in a double-robust causal network. The final DAG(Directed Acyclic Graph) identified O_IV (iodine number), O_Pre_CL (pre-chlorination dose rate), R_TEMP (temperature), T_pH(final treated water pH), and T_RCL (residual chlorine) as variables directly associated with THMs, while ammonia nitrogen of raw water(R_NH3) and COD of raw water(R_COD) acted as indirect (grandparent) nodes through O_Pre_CL and T_pH, respectively. Standardized coefficients (β) showed negative effects for O_IV (–0.449) and T_pH (–0.164), and positive effects for R_TEMP (+0.398), T_RCL (+0.153), and O_Pre_CL (+0.011). These results indicate that THMs formation is primarily governed by operational factors such as chlorine dosage, temperature, pH, and residual chlorine. The BN thus serves as a probabilistic causal model with both predictive accuracy and explanatory power, providing a theoretical foundation for data-driven decision-making in disinfection by-product control and process optimization in water treatment systems.

Nxumerous studies have investigated the formation mechanisms, influencing factors, and removal strategies of DBPs. However, most previous studies were based on laboratory-scale experiments or short-term data, which limited their ability to reflect actual water treatment plant (WTP) operating conditions and water quality variations, and thus failed to assess long-term effects. To address these limitations, this study analyzed 20 years of operational data from a full-scale WTP to evaluate the long-term impact of an advanced water treatment process (AWTP) on DBPs formation and removal Characteristics. Multiple linear regression (MLR) and interrupted time series (ITS) analyses were conducted to examine changes before and after AWTP implementation. Evaluation of individual unit processes revealed that the average removal efficiency of trihalomethanes (THMs) by granular activated carbon (GAC) was 17.2%, but it decreased sharply after 5-6 months due to breakthrough, while ozonation showed less than 5% removal efficiency under real operating conditions. The average THMs concentration decreased by approximately 28% (from 0.029mg/L to 0.021mg/L, p<0.001), indicating a statistically significant reduction. Furthermore, Hedges' g, MLR, and ITS analyses identified residual chlorine concentration and iodine number (an indicator of adsorption performance) as the most influential variables directly affected by AWTP implementation. These findings indicate that although the introduction of ozonation and GAC adsorption units significantly reduced THMs concentrations, the effect is largely attributable to the removal of THMs precursors (TOC) by GAC and the reduction of residual chlorine concentration—rather than direct THMs removal by ozonation or sustained adsorption performance of GAC.

The purpose of this study were to examine the safety and appropriateness of water pipe repair construction methods and to suggest these methodology as a standard. In this study, the flow field force applied to nine pipe wall segments was calculated using the Computational Fluid Dynamics (CFD) technique for a case of repairing a water pipe breaks. In addition, the temporal change in pressure head at key points (K_tank junction, D_junction, S_tank junction) on the connecting pipeline was simulated through water hammer analysis. The CFD simulation results showed that the pressure inside the bend was lower, and the pressure outside the bend was relatively higher than that in other parts. This can be explained by the phenomenon of dynamic effects transfer due to the flow velocity in the pipe. The water hammer analysis results showed that when the valve closing time was 30 sec, the pressure head at the branch point adjacent to the closed valve increased by up to 150 m. In conclusion, in the case of the water pipe under study, a water hammer phenomenon may occur due to the sudden closure of the S_water tank inlet valve. If the current valve operation status does not allow for control of the valve opening over time, it is necessary to examine a method of controlling the valve closing time by installing an actuator.

There is a possibility that Chironomidae Larva may appear in sand and activated carbon filters during drinking water treatment. This study was conducted to determine whether the presence or absence of larva that may appear in filters through image data analysis. Image data were created for cases with and without larva background with interference materials such as sand and activated carbon granules used in the actual water treatment process. We used ResNet, one of the image classification deep learning models, and verified and evaluated its accuracy. Among the 12 models, the top three models with high TPR were ResNet50 No-pretrained LR=0.1, ResNet18 No-pretrained LR=0.001, and ResNet18 No-pretrained LR=0.01. Models trained by only obtaining the structure of the ResNet model without pre-training showed higher accuracy and superior performance. Among the models with the highest accuracy, ResNet50 No-pretrained LR=0.1 had a large TPR value. However, FPR also showed a large value. Therefore, it could not be suitable for judging the presence or absence of larva in the water treatment process.When comparing ResNet18 No-pretrained LR=0.001 and ResNet18 No-pretrained LR=0.01, which had the second and third highest TPRs, the ResNet18 No-pretrained LR=0.01 model had the highest Accuracy and F1 Score.

Objectives:The objective of this research is to evaluate how the COVID-19 pandemic spread and prevention actions are affecting the inflow patterns of wastewater treatment plants(WWTP) in the domestic small-medium sized city. Also, the main contribution is the assessment of water consumption during a pandemic, proving information for management of wastewater collection and treatment system in order to be resilient in challenging situation for the community.Methods:In this study, data on the inflow rates of 6 WWTPs (5 in J_City, 1 in J_Myeon) from January 1, 2018 to December 31, 2023 water consumption data during the same period was investigated. Results and Discussion:As a result of investigating the inflow of WWTPs in J_City and J_Myeon, the subject of this study (data from January 2018 to December 2023), the amounts of flowing into the WWTPs during the 5th and 6th pandemic showed a relative decrease compared to the 2018 data. The reason for the decrease in flow into WWTP was analyzed to be the relatively small amount of precipitation compared to the base year, rather than the change in water consumption.Conclusion:As a result of correlation analysis between the annual precipitation and the WWTP inflow in J_City and J_Myeon, the correlation coefficients were 0.58 and 0.59, respectively, showing a clear positive linear correlation. Accordingly, in these area using combined sewer pipe system, the inflow into WWTP was found to be more dependent on changes in annual precipitation than on changes in water consumption pattern.

Objectives:The purpose of this study was to improve the previously developed Eulerian path-based water pipe network operation program.Methods:Dynamic programming, integer programming, genetic algorithms, and harmonic search methods were reviewed to overcome memory limitations for program execution. However, it was found that the application of existing optimization techniques has limitations. Therefore, as an alternative method, a minimum hydraulic gradient method based on physical theory was introduced to establish a sequential pipes removal algorithm.Results and Discussion:The excellence and the effectiveness of this program were proven through the existing pipe network and optimal path analysis using the EPANET2 input file of the test-bed Y_area. According to the results of the optimal path analysis, in the case of the Y_ area pipe network, 66 pipes and 6,465 m pipe length were analyzed to be possible for removal or maintenance, which was found to be 18.3% of the total pipe length.Conclusion:According to the results of the optimal pipe network analysis derived by the minimum hydraulic gradient method, there was little change in the minimum pressure head, and it was evaluated that there was no effect on water supply from a hydraulic perspective. In particular, in terms of water quality, the minimum residual chlorine concentration was found to increase by 0.011 mg/L due to a decrease in residence time and pipe length, which was analyzed to improve water quality.

Objectives : The purpose of this study was to investigate the treatment efficiency according to the oxidant types for dissolved manganese in the inflow of raw water into the water treatment plant in Korea.Methods : Three types of oxidant were selected: chlorine, ozone, and potassium permanganate. Experimental factors influencing manganese removal efficiency were determined as dissolved manganese concentration in raw water, dose, water temperature, pH, and contact time. In addition, total experimental schemes were designed according to the design of experiments method. According to the designed analysis method, the mentioned factors were used as multi variables on which evaluate the manganese removal efficiency.Results and Discussion : When using chlorine, the effect of pH was the greatest, followed by dose, water temperature, and contact time in order to have a significant effect on removal efficiency. In the case of using ozone, the pH effect was relatively large at low concentration of dissolved manganese, and the dose effect was found to be greater as the concentration was increased. Also, when potassium permanganate was used, the effect of pH, contact time and temperature was insignificant, while the effect of dose was the greatest for manganese removal.Conclusion : The optimum dose of chlorine is about three times to secure a removal rate of about 40 to 80%. The optimum dose of ozone was 1.0 to 1.6 mg/L, and it was found that a removal rate of at least 40% or more could be secured. Also, the optimum dose of potassium permanganate is 1.7 to 2.5 times of the dissolved manganese concentration, and it is possible to secure a removal rate of at least 60%.

Objectives : In this study, the concept of the Eulerian path, which has already been proposed as a solution to the problem of head loss and residual chlorine reduction caused by complexity of nodes and pipelines, and the non-Euerian path proposed in this study were compared and their feasibility were examined.Methods : The concepts of ‘removal of odd nodes’, ‘removal of 3-intersection nodes’, and ‘removal of zero demand nodes’ were applied to the virtual water supply networks, and the number of cases were analyzed and evaluated from the viewpoint of configuration complexity and hydraulic efficiency. For Euler graph and non-Euler graph water supply networks, each total pipe length, number of removal pipes, pressure head and flow rate were simulated with EPANET2 program.Results and Discussion : As a result of simplifying and designing new output networks for virtual Euler and non-Euler graph, it was revealed that the concept of ‘removing a 3-intersection nodes’ could be the most efficient by removing more pipes. However, in terms of configuring the output network as an Euler graph, the concept of ‘removing odd nodes’ can be considered more reasonable.Conclusion : It is difficult to configuring watersupply network as a perfect Euler graph. Therefore, the application of the concept of removing odd nodes suggested in this study can promote efficient simplification of the network. In addition, it can be thought that the application of this concept can expect efficiency in terms of hydraulics and water quality.

Objectives : The objectives of this study are to assess the degree of uniformity of the flow rate flowing into four grit chamber for actual waste water treatment and to to improve hydraulic structure of the existing distribution channel.Methods : Mobile ultrasonic flow meter was used to measure each flow rate flowing into four grit chambers, and the CFD technique was used to suggest several hydraulic structure improvements for enhancing flow rate evenness.Results and Discussion : From the results of the actual measurement using ultrasonic flowmeter and CFD simulation, The flow rates distributed to four grit chamber through the existing complicated open channels (four outlets) showed a severe unevenness. It was revealed that the flow rate passing through the outlets 1 and 4 at both right anf left ends showed a difference of more than 20% compared to those through outlets 2 and 3 installed in the center.Conclusion : As a result of examining the data of the water level, flow rate, and distribution percentages passing through the 4 distribution channels using the CFD simulation, it was found that case 4 (the case to install the orifice walls on both sides) had the most even flow rate distribution effect. However, as a result of comparing the water levels in case 4 and case 6, the case installing both orifice walls make relatively higher head loss.

Objectives : This study was conducted to suggest field operating conditions that can minimize disinfection by-products for three types of sodium hypochlorite.Methods : In this study, changes in free available chlorine, chlorate and bromate were analyzed according to storage temperature, storage time and presence or absence of sunlight for three types of sodium hypochlorite(two types of bleach and one type of sodium hypochlorite made on-site hypochlorite generator).Results and Discussion : In the case of bleach with 12% free available chlorine, when operating with a target of 10% of more of free available chlorine, the storage time for each storage temperature was 3 days at 40℃, 13 days at 30℃, 27 days at 20℃, 85 days at 10℃, and 200 days at 5℃. In the case of bleach with 5% free available chlorine, when operating with a target of 4% of more of free available chlorine, the storage time for each storage temperature was 37 days at 35℃, 255 days at 20℃, 1,343 days at 10℃, and 4,821 days at 4℃. In the case of sodium hypochlorite with 0.8% free available chlorine made on-site hypochlorite generator, when operating with a target of 0.7% of more of free available chlorine, the storage time for each storage temperature was 10 days at 3 5℃, 42 days at 20℃, 470 days at 10℃, and 1,770 days at 4°C. As a result of evaluating the quality change according to the presence or absence of UV protection, the free available chlorine decreased rapidly when exposed to sunlight, whereas the free available chlorine decreased slowly in the case of indoor storage.Conclusion : Bleach with 12% free available chlorine can be stored for about 60 days at 15℃, and bleach with 5% free available chlorine can be used within about 6 months at 15℃. And sodium hypochlorite with 0.8% free available chlorine can be used within 10 days at room temperature. In addition, when storing sodium hypochlorite, it is suggested that it be stored indoors protected from sunlight.