정연곤 Yeon-gon Jung , 고준일 Joon-il Ko , 정선용 Seon-yong Chung

DOI:10.15681/KSWE.2019.35.3.201 JKWST Vol.35(No.3) 201-208, 2019

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In this study, we analyzed composition of the bioflocculant, which strain YG-02 produces. First, supernatant and suspension from centrifugation of culture fluid of the strain, were used in the flocculation experiment. As a result, the SVI(sludge volume index) added with the suspension, was 182 mL/g, same as the control group with no additive, and the SVI added with supernatant, was 164 mL/g. So, the result above showed that flocculation capacity of the bioflocculant, was dependent on the substance which strain YG-02 produces, not on factors such as the body of germs. As a result of the thermostability test on substances that cause flocculation, the flocculation effect was significantly reduced, compared to the result of the flocculation test, before applying heat to the culture fluid, and it was able to assume that the substance that causes flocculation, was damaged by heat. Additionally, to understand the component of the bioflocculant, analyzation of sugar composition and fatty acid, was conducted. As a result, sugar composition was the polysaccharide consisting of glucose: lactose with molar ratio of 90.75:9.25. Fatty acid content was detected, as 0.0012 g/100g, showing that it contained glycolipid in the bioflocculant. Such results show that the bioflocculant which strain YG-02 produces, is the new bioflocculant, different from bioflocculantstudiedto date.

김홍수 Hongsu Kim , 조병욱 Byunguk Cho , 박상현 Sanghyun Park , 이무규 Mukyu Lee , 김창기 Changgi Kim , 최정호 Jeongho Choi

DOI:10.15681/KSWE.2019.35.3.209 JKWST Vol.35(No.3) 209-223, 2019

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Broadly speaking, in order to analyze the water quality improvement effects of the implementation of the Total Water Pollutant Management System in the Sapgy-Lake waterways, a reference was made to the [Plans for implementation of the Total Maximum Daily Load(TMDL)] in 3 cities (Cheonan, Asan, Dangjin). The results of the investigation into the plans to reduce the pollutant load show in that region show that there are plans to reduce pollution for a total of 16 reduction facilities. As for the result of the computation of the reduction in the load, these measurements were computed at the Gokgyo-stream basin and Namwon-stream basin, with BOD and T-P at the Gokgyo-stream basin reduced by 13.9 % and 13.3 %, respectively, while BOD and T-P at the Namwon-stream were reduced by 3.7 % and 3.3 %, respectively. In this way, thus using the results of the water quality forecast of Sapgyo-Lake in measures for the improvement of water quality (in accordance with the implementation of the TMDL), and using the QUAL-MEV model and EFDC model, it is noted that BOD will be improved by 26.4 % from 6.1 mg/L to 4.5 mg/L 0.0 %, T-P by 36.7 % from 0.168 mg/L to 0.107 mg/L and TOC by 26.4 % from 7.7 mg/L to 5.6 mg/L. However, it is forecasted that the targeted standards for the medium influence area will not be achieved. Evidently, Gokgyo-stream and Namwon-stream have been implementing the Total Water Pollutant Management System for the BOD items since January 1, 2019, but the Sapgyo-stream and Muhan-stream were excluded from being designated as subject regions. As such, it is noted now that it is necessary to implement the TMDL for the entire Sapgyo-Lake water systems including Sapgyo-stream and Muhan-stream in order to improve the water quality of Sapgyo-Lake, and likewise the T-P should be designated as the substance subjected to management in addition to BOD.

김미숙 Mi-sug Kim , 곽동희 Dong-heui Kwak

DOI:10.15681/KSWE.2019.35.3.224 JKWST Vol.35(No.3) 224-233, 2019

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Nitrogen components in liquid manure can reduce safety and quality of environment harmfully. To minimize the environmental risks of manure, understanding fate of manure in environment is necessary. This study aimed at investigating applicability of a simplified Level Ⅲ fugacity model for simulating NH₃-N component to analyze environmental fate and transport of NH₃-N in liquid manure and to provide basis for improving management of N in the liquid manure system and for minimizing the environmental impacts of N. The model simulation conducted for four environmental compartments (air, water, soil, and rice plants) during rice-cropping to trace NH₃-N component and provided applicability of the Level Ⅲ fugacity model in studying the environmental fate of NH₃-N in manure. Most of NH₃-N was found in water body and in rice plants depending upon the physicochemical properties and proper removal processes. For more precise model results, the model is needed to modify with the detailed removal processes in each compartment and to collect proper and accurate information for input parameters. Further study should be about simulations of various N-typed fertilizers to compare with the liquid manure based on a modified and relatively simplified Level Ⅲ fugacity model.

윤여정 Yeojeong Yun , 박형석 Hyungseok Park , 정세웅 Sewoong Chung

DOI:10.15681/KSWE.2019.35.3.234 JKWST Vol.35(No.3) 234-247, 2019

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In a deep lake and reservoir, thermal stratification is of great importance for characteristics of hydrodynamic mixing of the waterbody, and thereby influencesvertical distribution of dissolved oxygen, substances, nutrients, and the phytoplankton community. The purpose of this study, was to project the effect of a future climate change scenario on water temperature, stratification strength, and thermal stability in the Soyanggang Reservoir in the Han River basin of South Korea, using a suite of mathematical models; SWAT, HEC-ResSim, and CE-QUAL-W2(W2). W2 was calibrated with historical data observed 2005-2015. Using climate data generated by HadGEM2-AO with the RCP 4.5 scenario, SWAT predicted daily reservoir inflow 2016-2070, and HEC-ResSim simulated changes in reservoir discharge and water level, based on inflow and reservoir operation rules. Then, W2 was applied, to predict long-term continuous changes of water temperature, in the reservoir. As a result, the upper layer (5 m below water surface) and lower layer (5 m above bottom) water temperatures, were projected to rise 0.0191 ℃/year(p<0.05) and 0.008 ℃/year (p<0.05), respectively, in response to projected atmospheric temperature rise rate of 0.0279 ℃/year(p<0.05). Additionally, with increase of future temperature, stratification strength of the reservoir is projected to be stronger, and the number of the days when temperature difference of the upper layer and the lower layer becomes greater than 5 ℃, also increase. Increase of water temperature on the surface of the reservoir, affected seasonal growth rate of the algae community. In particular, the growth rate of cyanobacteria increased in spring, and early summer.

공동수 Dongsoo Kong , 김범철 Bomchul Kim

DOI:10.15681/KSWE.2019.35.3.248 JKWST Vol.35(No.3) 248-256, 2019

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Most of the lakes in Korea are artificial, and their limnological characteristics are significantly different from those of natural lakes in other countries. In this study, the relationship between trophic state parameters was investigated, based on summer average data of the upper layer, in 81 lakes in Korea , 2013-2017. Compared with trends of foreign natural lakes, chlorophyll α (Chl.α) concentration was slightly lower at the same total phosphorus (TP) concentration, and transparency (Secchi depth, SD) was noticeably lower at the same Chl.α concentration. This is because of excessive allochthonous loading of non-algal material during the monsoon period, and the reduction in phosphorus availability to algal growth, by light limitation and short hydraulic residence time. Considering these characteristics, we suggested site-specific thresholds of trophic state classification for Chl.α, TP and SD, based on annual average data at the upper layer of lakes (3-10 μg L^-1 of Chl.α measured by UNESCO method; 13-33 μg L^-1 of TP; 1.6-3.2 m of SD for mesotrophic state class, respectively). The threshold value of TP for each trophic state class, corresponded to the upper value of previously reported range, and that of SD was out of the range. We suggested applying only TP and Chl.α in assessment of trophic state of lakes in Korea, excluding SD.

김성진 Sung-jin Kim , 정세웅 Se-woong Chung , 박형석 Hyung-seok Park , 조영철 Young-cheol Cho , 이희숙 Hee-suk Lee , 박연정 Yeon-jeong Park

DOI:10.15681/KSWE.2019.35.3.257 JKWST Vol.35(No.3) 257-270, 2019

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Followingthe Four Rivers Project, cyanobacterial blooms have been frequently observed in the upstream of the installed weirs. The aim of this study was to characterize the major environmental factors that are associated with the cyanobacteria dominance in Baekje Weir (Geum River) and Juksan Weir (Youngsan River) based on intensive experiments and systematic data mining methods. The factors related to the cyanobacteria dominance include7-days cumulative rainfall (APRCP7), 7-days averaged flow (Q7day), water temperature (Temp), stratification strength (Δ T), electronic conductivity (EC), DO, pH, NO₃-N, NH₃-N, TN, TP, PO₄-P, Chl-a, Fe, BOD, COD, TOC, and SiO₂. The most highly correlatedfactors to the dominant cyanobacteria were found to be EC, Temp, Q7day, PO4-P in theBaekje Weir. On the other hand, those dominant in the Juksan Weir were △T, TOC, Temp, EC and TN. The EC showed a strong correlation with cyanobacteria dominance in both weirs because a high EC represents a persisted low flow condition. The cyanobacteria dominance was as high as 56 % when the EC was equal or greater than 418 μS/cm in Baekje Weir. It was as high as 63% when the ΔT ≥ 2.1℃ in the Juksan Weir. However, nutrients showed a minor correlation with cyanobacteria dominance in both weirs. The results suggest that the cyanobacteria dominate in astate where the water flow rate is low, water temperature is high and thermal stratification is strengthened. Therefore, the improvement of flow regimes is the most important to prevent persistent thermal stratification and formation of cyanobacteria bloom in theBaekje and JuksanWeirs.

김범철 Bomchul Kim , 공동수 Dongsoo Kong

DOI:10.15681/KSWE.2019.35.3.271 JKWST Vol.35(No.3) 271-277, 2019

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Korean Trophic State Index (TSIKO) was developed in 2006, and was composed of COD (COD_Mn based on permanganate method), Chlorophyll α (Chl.α) and total phosphorus (TP). However, COD_Mn usually represents only 50-60% of total organic matter in stream or lake water due to low oxidizing power of permanganate. This study investigated the relationship between TOC and COD_Mn based on the average data for the whole layer in 81 lakes in Korea, during the period 2013-2017. As a result, COD_Mn was found to be 1.54 times more than TOC in 66 of the freshwater lakes and 3 brackish lakes (TOC measured using thermo-oxidation method). TOC was about a quarter of COD_Mn in 8 coastal lakes (TOC measured using UV-persulfate oxidation method), and it appeared to be underestimated due to chloride interference. Using the data of 69 lakes with exception of 12 brackish lakes, TSI_KO(TOC) was developed based on the correlation between TOC and COD_Mn, while TSI_KO(COD) was replaced with TSI_KO(TOC). However, for trophic state assessment of brackish lakes, the TSI_KO(TOC) can only be utilized in case that TOC is measured through thermo-oxidation method. The determination coefficient of TSI_KO(Chl) to TSI_KO(COD) in 66 freshwater lakes and 3 brackish lakes was 0.83, while that to TSI_KO(TOC) was 0.68. This difference could be attributed to the recalcitrant organic part of TOC.