Gijung Pak

Comparison of Antibiotic Resistance Removal Efficiencies Using Ozone Disinfection under Different pH and Suspended Solids and Humic Substance Concentrations

This study mainly evaluated the effectiveness of ozonation toward the enhancement of the removal efficiencies of antibiotic-resistant bacteria (ARB), pB10 plasmid transfer, and pB10 plasmids under different pH and suspended solids (SS) and humic acid concentrations. First, chlorination was tested as a reference disinfection process. Chlorination at a very high dose concentration of Cl2 (75 mg L(-1)) and a long contact time (10 min) were required to achieve approximately 90% ARB and pB10 plasmid transfer removal efficiencies. However, even these stringent conditions only resulted in a 78.8% reduction of pB10 plasmid concentrations. In case of ozonation, the estimated CT (concentration × contact time) value (at C0 = 7 mg L(-1)) for achieving 4-log pB10 plasmid removal efficiency was 127.15 mg·min L(-1), which was 1.04- and 1.25-fold higher than those required for ARB (122.73 mg·min L(-1)) and a model nonantibiotic resistant bacterial strain, E. coli K-12, (101.4 mg·min L(-1)), respectively. In preventing pB10 plasmid transfer, ozonation achieved better performance under conditions of higher concentrations of humic acid and lower pH. Our study results demonstrated that the applicability of CT concept in practice, conventionally used for disinfection, might not be appropriate for antibiotic resistance control in the wastewater treatment process. Further studies should be conducted in wastewater engineering on how to implement multiple barriers including disinfection to prevent ARB and ARG discharge into the environment.

Effects of land use change and water reuse options on urban water cycle

The aim of this article was to study the effects of land use change and water reuse options on an urban water cycle. A water cycle analysis was performed on the Goonja drainage basin, located in metropolitan Seoul, using the Aquacycle model. The chronological effects of urbanization were first assessed for the land uses of the Goonja drainage basin from 1975 to 2005, where the ratio of impervious areas ranged from 43% to 84%. Progressive urbanization was identified as leading to a decrease in evapotranspiration (29%), an increase in surface runoff (41%) and a decrease in groundwater recharge (74%), indicating a serious distortion of the water cycle. From a subsequent analysis of the water reuse options, such as rainwater use and wastewater reuse, it is concluded that wastewater reuse seemed to have an advantage over rainwater use for providing a consistent water supply throughout the year for a country like Korea, where the rainy season is concentrated during the summer monsoon.

Evaluation of overland flow model for a hillslope using laboratory flume data.

Comprehensive modelling of overland flow requires models for both rill and interrill area overland flow. Evaluation of a physically based mathematical model for simulating overland flow generated on rill and interrill areas of hillslope was done using a data set gathered from a laboratory experimental setup. A rainfall simulator has been constructed together with a 6.50 m × 1.36 m erosion flume that can be given adjustable slopes in both longitudinal and lateral directions. The model was calibrated and validated using the experimental results from the setup of the flume having 5% lateral and 10% longitudinal slopes where rainfall intensities of 105 and 45 mm/hr were induced with the use of nozzles. Results show that for the given slope combination, the model was capable of simulating the flow coming from the rill and interrill areas for the two different rainfall intensities. It was found that significantly more of the flow occurred in the form of the rill flow. The model studied here can be used for the better prediction of overland flow and can also be used as a building block for an associated erosion and sediment transport model.

Laboratory experiments of sediment transport from bare soil with a rill

Abstract Mathematical models developed for quantification of sediment transport in hydrological watersheds require data collected through field or laboratory experiments, but these are still very rare in the literature. This study aims to collect such data at the laboratory scale. To this end, a rainfall simulator equipped with nozzles to spray rainfall was constructed, together with an erosion flume that can be given longitudinal and lateral slopes. Eighty experiments were performed, considering microtopographical features by pre-forming a rill on the soil surface before the start of each experiment. Medium and fine sands were used as soil, and four rainfall intensities (45, 65, 85 and 105 mm h-1) were applied in the experiments. Rainfall characteristics such as uniformity, granulometry, drop velocity and kinetic energy were evaluated; flow and sediment discharge data were collected and analysed. The analysis shows that the sediment transport rate is directly proportional to rainfall intensity and slope. In contrast, the volumetric sediment concentration stays constant and does not change with rainfall intensity unless the slope changes. These conclusions are restricted to the conditions of experiments performed under rainfall intensities between and 105 mm h-1 for medium and fine sands in a 136-cm-wide, 650-cm-long and 17-cm-deep erosion flume with longitudinal and lateral slopes varying between 5 and 20%. Editor Z.W. Kundzewicz; Associate editor G. Mahé Citation Aksoy, H., Unal, N.E., Cokgor, S., Gedikli, A., Yoon, J., Koca, K., Inci, S.B., Eris, E., and Pak, G., 2013. Laboratory experiments of sediment transport from bare soil with a rill. Hydrological Sciences Journal, 58 (7), 1505–1518.

Analysis of effects of climate change on runoff in an urban drainage system: a case study from Seoul, Korea

Both water quantity and quality are impacted by climate change. In addition, rapid urbanization has also brought an immeasurable loss of life and property resulting from floods. Hence, there is a need to predict changes in rainfall events to effectively design stormwater infrastructure to protect urban areas from disaster. This study develops a framework for predicting future short duration rainfall intensity and examining the effects of climate change on urban runoff in the Gunja Drainage Basin. Non-stationarities in rainfall records are first analysed using trend analysis to extrapolate future climate change scenarios. The US Environmental Protection Agency Storm Water Management Model (SWMM) was used for single event simulation of runoff quantity from the study area. For the 1-hour and 24-hour durations, statistically significant upward trends were observed. Although the 10-minute duration was only nearly significant at the 90% level, the steepest slope was observed for this short duration. Moreover, it was observed that the simulated peak discharge from SWMM increases as the short duration rainfall intensity increases. The proposed framework is thought to provide a means to review the current design of stormwater infrastructures to determine their capacity, along with consideration of climate change impact.

Evaluation of an erosion-sediment transport model for a hillslope using laboratory flume data

Climate change can escalate rainfall intensity and cause further increase in sediment transport in arid lands which in turn can adversely affect water quality. Hence, there is a strong need to predict the fate of sediments in order to provide measures for sound erosion control and water quality management. The presence of microtopography on hillslopes influences processes of runoff generation and erosion, which should be taken into account to achieve more accurate modelling results. This study presents a physically based mathematical model for erosion and sediment transport coupled to one-dimensional overland flow equations that simulate rainfall-runoff generation on the rill and interrill areas of a bare hillslope. Modelling effort at such a fine resolution considering the flow connection between interrill areas and rills is rarely verified. The developed model was applied on a set of data gathered from an experimental setup where a 650 cm×136 cm erosion flume was pre-formed with a longitudinal rill and interrill having a plane geometry and was equipped with a rainfall simulator that reproduces natural rainfall characteristics. The flume can be given both longitudinal and lateral slope directions. For calibration and validation, the model was applied on the experimental results obtained from the setup of the flume having 5% lateral and 10% longitudinal slope directions under rainfall intensities of 105 and 45 mm/h, respectively. Calibration showed that the model was able to produce good results based on the R2 (0.84) and NSE (0.80) values. The model performance was further tested through validation which also produced good statistics (R2=0.83, NSE=0.72). Results in terms of the sedigraphs, cumulative mass curves and performance statistics suggest that the model can be a useful and an important step towards verifying and improving mathematical models of erosion and sediment transport.

The Removal of Nutrients and Heavy Metals Using Household Rain garden

In Korea, most rainfall events occur during summer which then leads to an increasing concern regarding high influx of non-point source pollutants since the pollutant loadings from these non-point sources are very significant. In particular, the first flush of roof-harvested rainfall is said to contain the most highest concentration of nutrients and heavy metals. Accordingly, it is important to develope the possible water quality management options in treating the contaminants and considering reclaimed water reuse. The rain garden could be one of suitable alternatives in addressing this issue. In this study, the development of an effective adsorption media and its application to a lab-scale rain garden was tested to evaluate the removal rate of various nutrient and organic matter (TN, TP, CODcr), and heavy metals (Cu, Cd, Pb). Results showed that carbonized peatmoss produced at higher temperature have better adsorption capacity as compared to the one produced at a lower temperature. When the carbonized peatmoss was applied as rain garden media, the highest removal of TN, TP, and CODcr was observed compared to no carbonized peatmoss applied rain garden. Therefore, this study showed that the carbonized peatmoss would be effectively applied to the rain garden for removing nutrients and heavy metals from roof-harvested rainwater.

Assessment of porous pavement effectiveness on runoff reduction under climate change scenarios

AbstractClimate change has affected both water quantity and quality by increased rainfall, runoff, and associated pollutant loading in urban areas. Stormwater Best Management Practices (BMPs) are now being popularly considered for the reduction of increased runoff due to urbanization. Most research has been conducted on the analysis of BMP effectiveness under current conditions. However, there is no extensive literature on BMP effectiveness studies considering climate change. In this study, the effectiveness of BMP, porous pavement in particular, has been assessed under climate change scenarios. Climate change scenarios were generated by trend analysis of the historical rainfall data. The 2-year and 100-year design storms having 24-h durations were determined for three scenarios: current conditions, 2020, and 2050 using frequency analysis. Storm Water Management Model was then calibrated and used to evaluate the impact of climate change and the effect of incorporating porous pavement on runoff. Geographic...

Characteristics of hydrochemical variations and contaminant load during rainfall in an acid mine drainage-impacted watershed, Korea

AbstractAcid mine drainage (AMD) refers to the outflow of acidic water from usually abandoned metal mines. Since AMD is closely related to the rainfall–runoff process, it is important to monitor rainfall events for its characterization. This work aims to study the characteristics of hydrochemical variations of metals during rainfall in the Geopung Mine Watershed, Korea. Eleven dry-weather and five rainfall event monitorings were conducted in 2010 at two locations (GP-1 and GP-2). At GP-1, concentrations significantly increased during the fifth event, which was the largest one (As from 0.0003 to 0.0046 mg/l; Cd from 0.0114 to 0.2188 mg/l; Cu from 0.0206 to 3.1512 mg/l; Pb from 0.0006 to 0.1857 mg/l; Zn from 0.5823 to 15.9194 mg/l; Ni from 0.0011 to 0.0294 mg/l). Similar though less-marked trend of increase in metal concentration was found at GP-2 during the fifth rainfall event. As for the load, as much as 62–97% of the annual metal loads were accounted for by rainfall at GP-1 and GP-2. This pattern implie...

Modelling of suspended sediment in a weir reach using EFDC model

Construction of hydraulic structures often leads to alteration of river dynamics and water quality. Suspended solids entering the upstream of the weir cause adverse effects to the hydroecological system and, therefore, it is necessary to build a modelling system to predict the changes in the river characteristics for proper water quality management. In this study, the discharges and total suspended solids upstream and downstream of the Baekje Weir installed in Geum River, Korea, was modelled using the environmental fluid dynamics code (EFDC) model. The resulting trend of four rainfall events shows that as rainfall increases, the total suspended solids (TSS) concentration increases as well. For the two larger events, at the upstream of the weir, TSS was observed to decrease or remain constant after the rainfall event depending on the lowering of the open gate. At the downstream, TSS supply was controlled by the weir during and after the rainfall event resulting in decline in the TSS concentration. The modelling produced good results for discharge based on %Diff. (4.37-6.35), Nash-Sutcliffe efficiency (NSE) (0.94-0.99) and correlation coefficient (r) (0.97-0.99) values as well as for TSS with acceptable values for %Diff. (12.08-14.11), NSE (0.75-0.81) and r (0.88-0.91), suggesting good applicability of the model for the weir reach of the river in the study site.