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As the increase of carbon dioxide in atmospheric accelerates climate change, various efforts have been performed to reduce carbon worldwide. Recently, as the concept of green carbon stored and sequestrated through photosynthesis by land plants has been emphasized to reduce carbon content from environments, the importance of carbon absorption survey for plant groups analysis of terrestrial ecosystems such as forests and river wetlands is increasing. Carbon absorption sources in terrestrial ecosystems exist in various forms of plant, soil, and topography, and represent various carbon absorption through physical, chemical and biological reactions between each other depending on the location and height of the plant groups. In this study, an industrial RTK drone capable of taking high-resolution images was used for efficient carbon absorption survey in Damyang stream wetland. Based on the global navigation satellite system by RTK, the location could be corrected in real time, and ecosystem surveys could be conducted on the height of the terrain with RTK drone. The point cloud technique of the high-density surface model was used to analyze the three-dimensional topography of areas that are difficult to access. Using the photo survey function of the RTK drone, it is expected to play an important role in understanding the total amount of green carbon of terrestrial ecosystems and carbon circulation of the land ecosystem by enabling the creation of topographic maps of stream wetlands, and riparian vegetation with complex terrain.

Objectives : This paper summarizes effective waste management and disposal methods for plastic and medical wastes during the prolonged COVID-19 pandemic.Methods : We reviewed the literatures reporting and identifying the current status and characteristics of wastes related to COVID-19, and the management and treatment guidelines for those wastes. We also investigated various technologies for waste treatment and disposal, and assessed the current status and future direction of the technologies in Korea.Results and Discussion : In the first half of 2020 in Korea, the amount of plastic waste produced had increased by 15.6% year-on-year, and medical waste production also increased significantly from 0.6 ton in January 2020 to 2,928 ton in August 2021. All of the infectious wastes are currently being incinerated in Korea, but there are concerns on air pollutant emissions and insufficient treatment facilities. Municipal solid waste also suffers from a lack of landfill capacity and low price competitiveness in the recycling industry.Conclusions : Policy and system need to be improved to reduce the infectious waste generation from the sources, and treatment and disposal technologies for produced wastes also need to be developed. Furthermore, hospitals and health care facilities should establish their own waste reducing systems which may include chemical treatment and sterilization units.

The abundant growth in cyanobacterial blooms poses severe ecological threats with a high risk to aquatic organisms and global public health. Control of cyanobacterial blooms involves spraying cyanobacteria removal materials, including coagulants. However, little is known about the fate of the coagulated-cyanobacteria-laden water. Here, we examined long-term changes in water quality following treatment with various coagulants and minerals for cyanobacterial removal when the coagulated cyanobacterial cells were not removed from the water. An experiment in a controlled water system tested the effects of six different compounds, one conventional coagulant, two natural inorganic coagulants, and three minerals. All tested coagulants and minerals exhibited >75% of cyanobacterial removal efficiency. However, compared to the control, higher concentrations of nitrogen were observed from some samples treated during the experimental period. After 20 months, the final total phosphorus concentration of the raw water increased 20-fold compared to the initial concentration to 11.82 mg/L, indicating significant nutrient release over time. Moreover, we observed that the decomposition of sedimented cyanobacterial cells caused the release of intracellular contents into the supernatant, increasing phosphorous concentration over time. Therefore, cyanobacterial cells should be removed from water after treatment to prevent eutrophication and maintain water quality.

Objectives:We analyzed the occurrence of blue-green algae at Algae Alert System and Water Quality Forecast System sites in Daegu and Gyeonsangbuk-do between 2012 and 2019.Methods:Data from 17 sites in Daegu and Gyeonsangbuk-do were collected and reclassified to 8 Nakdong river (ND) sites and 9 water source (WS) sites. Influencing factors on the occurrence of blue-green algae were investigated.Results and Discussion:At the ND sites, blue-green algae were observed in the range of 0-495,360 cells/mL. Between 2012 and 2019, the average number of blue-green algae increased as the sites go downstream from ND-1 (Sangju weir) to ND-8 (Dalseong weir), while the number of blue-green algae was lower at the site in-between weirs than the site adjacent to weir. At the WS sites, blue-green algae were observed in the range of 0-112,000 cells/mL. The average numbers of blue-green algae in 2014, 2015 and 2017 were higher than those of other years. The dominant species of blue-green algae was Microcystis at all the sites during the summer when the water temperature was high; when the water temperature was low Aphanizomenon had higher rates of dominance. Water temperature was positively correlated with the number of blue-green algae grown, while the dissolved oxygen concentration was found to have a negative correlation with it. pH and chlorophyll-a were less correlated.Conclusions:In Daegu and Gyeongsangbuk-do, the main stream of the Nakdong river showed higher blue-green algae occurrence than the water source sites. In most cases, Microcystis was dominant species. In the main stream of Nakdong river, blue-green algae tended to occur more downstream, and the number of blue-green algae was higher at sites close to weir than sites in-between weirs. The occurrence of blue-green algae was highly related to water temperature.

We developed a three-dimensional unstructured grid coastal and estuarine circulation model, named the General Ocean Model (GOM). Combining the finite volume and finite difference methods, GOM achieved both the exact conservation and computational efficiency. The propagation term was implemented by a semi-implicit numerical scheme, the so-called scheme, and the time-explicit Eulerian&ndash, Lagrangian method was used to discretize the nonlinear advection term to remove the major limitation of the time step, which appears when solving shallow water equations, by the Courant&ndash, Friedrichs&ndash, Lewy stability condition. Because the GOM uses orthogonal unstructured computational grids, allowing both triangular and quadrilateral grids, considerable flexibility to resolve complex coastal boundaries is allowed without any transformation of governing equations. The GOM was successfully verified with five analytical solutions, and it was also validated when applied to the Texas coast, showing an overall skill value of 0.951. The verification results showed that the algorithm used in GOM was correctly coded, and it is efficient and robust.

Replication of natural mixing through artificial water circulation techniques, such as convectional water circulation systems (CWCS), can break thermal stratification in stagnant water and suppress algal blooms. Here, the field performance of a novel CWCS was evaluated in a eutrophic reservoir (Shingal reservoir, South Korea) for three seasons between September 2016 and September 2018. The CWCS was deployed in a corner of stagnated water in the reservoir. The changes in water temperature and dissolved oxygen (DO) concentrations at different water depths were examined at the deployment site and two control sites within the stagnant area during the 2016 and 2017 seasons. In 2018, the performance of the CWCS in replicating natural mixing was assessed by monitoring water temperature changes at different depths at the CWCS unit deployment site and a comparison site with natural water flow. The differences in water temperature and DO concentrations between the epilimnion and the hypolimnion were significantly smaller at the deployment site than at the control sites, demonstrating the effectiveness of the CWCS in vertical and horizontal mixing as well as in oxygen transfer. The findings of the field study revealed that the CWCS effectively induced natural-like mixing without disturbing the hypolimnion.

The purpose of this study was to develop a two-dimensional shallow water flow model using the finite volume method on a combined unstructured triangular and quadrilateral grid system to simulate coastal, estuarine and river flows. The intercell numerical fluxes were calculated using the classical Osher-Solomon's approximate Riemann solver for the governing conservation laws to be able to handle wetting and drying processes and to capture a tidal bore like phenomenon. The developed model was validated with several benchmark test problems including the two-dimensional dam-break problem. The model results were well agreed with results of other models and experimental results in literature. The unstructured triangular and quadrilateral combined grid system was successfully implemented in the model, thus the developed model would be more flexible when applying in an estuarine system, which includes narrow channels. Then, the model was tested in Mobile Bay, Alabama, USA. The developed model reproduced water surface elevation well as having overall Predictive Skill of 0.98. We found that the primary inlet, Main Pass, only covered 35% of the fresh water exchange while it covered 89% of the total water exchange between the ocean and Mobile Bay. There were also discharge phase difference between MP and the secondary inlet, Pass aux Herons, and this phase difference in flows would act as a critical role in substances’ exchange between the eastern Mississippi Sound and the northern Gulf of Mexico through Main Pass and Pass aux Herons in Mobile Bay.

The algae bloom in river has been issued in Korea. In order to alleviate treatment load of water treatment plant and to meet water treatment capacity of the plant, a high-speed algae pretreatment methods connected with water intake pipe are required. In this study, a pilot-scale of pretreatment system was tested. It was consisted of coagulation and electro flotation processes. The algae pretreatment efficiency by the comparisons of chlorophyll-a, nutrients (total nitrogen, total phosphorous), and chemical oxygen demand (COD) concentration was evaluated. As a result, the system showed about 45% of removal efficiency by the only flotation separation without coagulation judged by chlorophyll-a concentration. On the other hand, the removal efficiency was improved with increase of coagulant dosage and electric power. It was improved to about 80% of chlorophyll-a concentration. The system could treat algae containing solution within a few minutes on the basis of residence time of flotation tank. Consequently, this study suggests that the system could be used as an algae pretreatment step in water treatment process.

This research was conducted to investigate the magnitude and nature of the emission of runoff pollutants with the goal of quantifying stormwater pollutant concentrations from driveways site. A statistical summary for concentration characteristics of driveway runoff is provided based on the various analysis techniques. Runoff water qualities in temporal variation were generally higher in wet season than in dry season with a high degree of variability. The 95 % confidence intervals of washed-off pollutant concentration are ranged to 82.4-141.4 mgL -1 for TSS, 53.3-87.6 mgL -1 for Turbidity, 19.0-38.7 mgL -1 for BOD, 34.0-59.2 mgL -1 for COD, 16.4-27.4 mgL -1 for DOC, 4.3-5.6 mgL -1 for TN and 0.25-0.34 mgL -1 for TP, showing the high values based on the surface or lake quality standards in Korea. The first flush effect is mostly occurred within initial 30 min of storm duration. Concentrations of water quality constituents in urban stormwater are often expressed in probabilistic terms using statistics such as the mean and standard deviation and selected quintiles. Three probability distributions, weibull in TSS and Turbidity, lognormal in BOD and COD and gamma in DOC, TN and TP were fitted and the goodness-of-fit was assessed using the Anderson-Darling test. The correlation matrix of all water quality variables shows significant relationships between all parameters (P

The high-speed algae pretreatment system consisted of coagulation and electro coagulation process was tested. This study examined algae removal efficiency by the comparison of chlorophyll-a concentration before and after treatment. As a result, the system showed about 45% of removal efficiency by the only flotation separation without coagulation. As increase of electric power and coagulant dosage, the removal efficiency was improved to about 80%. The system could treat algae containing solution with a few minutes on the basis of residence time of flotation tank. Consequently, this study suggests that the system could be used as a pretreatment step in water treatment process.

In this study, the generation characteristics of the Combined Sewer Overflows (CSOs) that occur in urban areas were investigated. In addition, performance evaluation of the CSO treatment efficiency was conducted through the field application of a high-speed filtering apparatus using a fibrous filter medium for the treatment of the CSOs that occurred in an urban area. The study site, a city located in Seoul, South Korea, was one that included the typical residential and commercial districts. The daily average flow rate of the Eungbong drainage area, which was the study site, was 92.5 m 3 /hr during the dry season, and the daily average flow rate ranged from 70.2 to 129.2 m 3 /hr, indicating a wide daily-average-flow-rate range. The highest flow rate was shown at around 9 a.m. on weekdays and at around 11 a.m. on weekends. The average influent concentrations that occurred during the dry season were 19.0 mg/L (BOD), 15.9 mg/L (COD), 10.9 mg/L (SS), 33.9 mg/L (TN), and 0.5mg/L (TP), and the hourly concentration ranges turned out to be 4.1~43.5 mg/L (BOD), 9.5~26.8 mg/L (COD), 3.6~33.0 mg/L (SS), 25.5~52.2 mg/L (TN), and 0.4~0.9 mg/L (TP). The results of the field application of a high-speed filtering apparatus using a fibrous filter medium showed that the average treatment efficiency of SS was 63.7% during the dry season. The average treatment efficiency of SS during rainfall was 84.2% (1 st ), 88.0% (2 nd ), 87.5% (3 rd ), 85.8% (4 th ), 75.8% (5 th ), 75.5% (6 th ), and 90.3% (7 th ), and exhibiting more than 80% treatment efficiency. In the case of organic contaminants like BOD, however, low treatment efficiency (less than 30%) appeared. Judging from the above results, it is difficult to expect a treatment effect if the influent concentration is less than 30 mg/L in the case of an organic material when the high-speed filtering apparatus is applied to the site, and even in the case of an influent concentration of more than 30 mg/L, the treatment efficiency is about 30% on average. The treatment effect of the particulate material (SS) remained quite high, however, without significant restrictions on the filtering liner velocity and influent concentration. The results of the analysis of the characteristics of the CSOs in urban areas and of the application of a highspeed filtering apparatus using a fibrous filter medium are expected to be utilized as basic data for management alternatives to reduce rainfall runoff loads with respect to overflows that occur during rainfall.