• Environmental Engineering Research
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• v.15 no.1
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• pp.41-48
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• 2010

This paper describes the influence of nutrient salts eluted from the bottom of a closed water area where polluted sediment has been deposited by inflowing river water. The elution pattern was monitored at our experimental facility. Both the sediment pore water and water above the bottom were sampled using a dialyzer sampler (peeper). The pore water of the eutrophicated sediment contained a large amount of nutrient salts, and the effect of elution was confined to a limited area of the bottom surface. The nutrient concentration of the sediment pore water was closely related to both the water temperature and dissolved oxygen (DO) concentration. The eluted nutrients from the sediment provided a source for phytoplankton and algae growth. This experimental data indicated that the water quality of the surface was not directly connected to the eluted nutrient salts, while it was indirectly affected by the total ecosystem, including all the organisms within an area and their environment.

• Journal of Korean Society of Water and Wastewater
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• v.12 no.4
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• pp.59-69
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• 1998

Biological treatment systems generally can be divided into two main classes of a suspended sludge process and attached one like a fluidized bed reactor. These process are considered to bring remarkable change in species composition of microorganisms, due to difference of a state of biofilm, a concentration and diffusion velocity of dissolved oxygen, a concentration and diffusion velocity of substance or poisonous matter. The change of species composition bring different treatment result for influence factors like F/M ratio, DO concentration, pH or poisonous matter. This study is to investigate the reaction characteristics of both microorganisms, namely, a suspended sludge and attached sludge, through the changes of pH, temperature and substance concentration.

• Journal of Korean Society on Water Environment
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• v.27 no.2
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• pp.218-227
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• 2011

The objective approach for assessment of stream naturalness is an essential part of the stream restoration project. This study proposes the methodology for the assessment of stream naturalness considering physical, biological and chemical factors. Physical factors consists of riffle and pool, river bed material, bank protection, floodplain vegetation and levee materials; biological factors are benthic macroinvertebrate, KSI (Korean Saprobic Index), and IBI (Index of Biological Integrity) and chemical factors are pH, DO (dissolved oxygen), and TP (total phosphorus). This procedure is applied to the Mokgamcheon. As a result, the downstream of Mokgamcheon (zone I) needs the prompt improvement of stream naturalness, compared to the others (zone II and III). This evaluation technique will be an effective tool to quantify the stream naturalness and can be used to set the target of stream restoration project.

• Environmental Sciences Bulletin of The Korean Environmental Sciences Society
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• v.3 no.2
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• pp.113-119
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• 1999

The quality of the effluent from an activated sludge aeration tank can deteriorate when the substrate removal rate decreases due to an abrupt reduction in the DO concentration, which is affected by such operating conditions as the loading rate, temperature, wastewater composition, and so on. In this research, a DO control system that includes a PI (proportional-integral) controller/Hiraoka controller was developed and applied to a pilot-scale activated sludge process, then its acceptability was estimated. The applicability of the respiration rate to DO control was also estimated. The respiration rate indicated a variety of input organic loading rates, which is the main disturbance to the DO concentration in an aeration tank. When the influent concentration incrementally decreased and increased between CODcr 1,000 mg/l and 100 mg/l, the control system with a PI controller exhibited a good llperformance-the average DO concentrations were 2.00$\pm$0.14 mg/l and 1.88$\pm$0.15 mg/l (set value was 2.0 mg/l), respectively, and the settling time was just 10 minites. When the control system was operated for 4 days, the DO concentration was 1.99$\pm$0.18 mg/l and 32.6% of the air flowrate was saved. However, the fluctuations in the respiration rates and air flowrates were severe, which could be harmful to the stability of the biomass and mechanical stability of the blower. A possible approach to solve this problem may be the simultaneous control of the loading rate and DO concentration.

• Korean Journal of Ecology and Environment
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• v.43 no.2
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• pp.338-344
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• 2010

The automatic water quality monitoring system (AWQMS) have been installed to immediately response to any pollution incident. It also make it possible to conduct the task efficiently regarding water quality control. The purpose of this study is to enhance reliability by securing accuracy of automatic water quality data through quality assessment (QA) for temperature, pH, dissolved oxygen (DO), electric conductivity (EC), total organic carbon (TOC). The result of comparison between manual and automatic data, relative accuracy of general items (temperature, pH, EC, DO) and TOC were mostly satisfied with guideline (i.e. less than 20%). On the other hand, relative accuracy of DO between sampling site and housing site was somewhat against the guideline. The contamination by attaching algae and microorganism in the pipeline is considered as main cause. After backwashing the pipeline, DO concentration was increased up to 53%. Therefore, pipeline management is recognizable as important thing to secure reliability of water quality data.

• Corrosion Science and Technology
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• v.12 no.6
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• pp.280-287
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• 2013

Flow accelerated corrosion(FAC) of the carbon steel piping in pressurized water reactors(PWRs) has been major issue in nuclear industry. Severe accident at Surry Unit 2 in 1986 initiated the worldwide interest in this area. Major parameters influencing FAC are material composition, microstructure, water chemistry, and hydrodynamics. Qualitative behaviors of FAC have been well understood but quantitative data about FAC have not been published for proprietary reason. In order to minimize the FAC in PWRs, the optimal method is to control water chemistry factors. Chemistry factors influencing FAC such as pH, corrosion potential, and hydrazine contents were reviewed in this paper. FAC rate decreased with pH up to 10 because magnetite solubility decreased with pH. Corrosion potential is generally controlled dissolved oxygen (DO) and hydrazine in secondary water. DO increased corrosion potential. FAC rate decreased with DO by stabilizing magnetite at low DO concentration or by formation of hematite at high DO concentration. Even though hydrazine is generally used to remove DO, hydrazine itself thermally decomposed to ammonia, nitrogen, and hydrogen raising pH. Hydrazine could react with iron and increased FAC rate. Effect of hydrazine on FAC is rather complex and should be careful in FAC analysis. FAC could be managed by adequate combination of pH, corrosion potential, and hydrazine.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.5
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• pp.251-259
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• 2016

This study examined the DO concentration distribution and ORP distribution using microbubbles on pilot-scale aeration tanks. As a result of MLSS mixing and oxygen transfer phenomenon using microbubbles, different DO concentrations were observed depending on the circulation of the liquid with the microbubble supply location on the lateral of an aeration tank. The simulation results of CFD (computational fluid dynamics) program showed that MLSS mixed with a microbubble supply in the middle the reactor is much better than on the left side of the reactor. A single reactor containing an anaerobic, anoxic, and aerobic zone, was evaluated without partition according to the location of the microbubble supply based on the experiments and CFD analysis. MLSS was separated into solid-liquid by the microbubble supply in the aeration tank. Consequently, selecting the appropriate microbubble size is important for MLSS mixing and was maintained at the proper DO concentration for biological treatment.

• Journal of the Korean Society of Marine Environment & Safety
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• v.25 no.4
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• pp.457-467
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• 2019

To investigate the long-term variation characteristics of nutrients in the east coast of Korea, water temperature, salinity, dissolved oxygen, and nutrients were measured at three stations of Sokcho, Jukbyeon and Gampo coasts for five years from 2013 to 2017. For five years, the water temperature of the East Sea coast was in the range of $1.2{\sim}28.8^{\circ}C$, the salinity was in the range of 30.63~34.79 and the dissolved oxygen (DO) was in the range of 3.53~7.64 mL/L. Distribution and variation of the water environment factors in the study area were determined by the vertical stratification of water column and distribution of water temperature. The high DO concentration in Sokcho coast From 2015 to August 2016 is presumed to be the result of the southward inflow of North Korean Cold Water (NKCW). Concentrations of dissolved inorganic nitrogen (DIN, $NH_4-N+NO_2-N+NO_3-N$) ranged $0.11{\sim}24.19{\mu}M$, phosphate concentration ranged $0.01{\sim}1.75{\mu}M$, and silicate ranged $0.17{\sim}32.80{\mu}M$. The N:P ratio was in the range of 0.7~54.3 (mean 15.2) and the N:P slope was in the range of 11.67~13.75. The N:P ratios in this study were lower than the Redfield ratio (16), indicating that nitrate did act as a limiting factor in phytoplankton growth. The correlation ($R^2$) of total N:P ratio was as high as 0.95, indicating that the effect of the surrounding land or non-point sources was not significant. In conclusion, the spatial and temporal variation of nutrients in the east coast of Korea was determined by the vertical mixing of water mass with thermocline and mainly affected by physical factors such as influx of external water masses and coastal upwelling, and the influences from inflows from the land were minimal.

• Journal of Microbiology and Biotechnology
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• v.21 no.6
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• pp.604-612
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• 2011

Beauveria bassiana SFB-205 supernatant can effectively control cotton aphid populations, which is closely associated with its chitinase activity. The present work extends to optimizing a culture medium to produce more efficacious supernatant in flask conditions, followed by scale-up in 7 L, 300 L and 1.2 KL fermentors with the parameter of chitinase. In flask conditions, a combination of soluble starch and yeast extract produced the greatest amount of chitinase (5.1 units/ml) and its supernatant had the highest aphicidal activity. An optimal quantitative combination of the two substrates, estimated by a response surface method, enabled the supernatant to have 15.7 units/ml of chitinase activity and 3.7 ml/l of median lethal concentration ($LC_{50}$) of toxicity against cotton aphid adults in laboratory conditions. In the scale-up conditions, overall supernatant had 25-28 units/ml of chitinase activity. Decrease in pH and limitation of dissolved oxygen (DO) during cultures were significantly related to the yield of chitinase. These results suggest that the substrate-dependent chitinase production can be background information for optimizing a culture medium, and pH and DO are critical factors in maximizing the production in scale-up conditions.

• Journal of Korean Society of Water and Wastewater
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• v.19 no.1
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• pp.31-37
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• 2005

One of the major obstacles confronted in promoting the rainwater harvesting is the concerns of acid rain and heavy metals. Although there are many data concerning the quality of rainwater precipitation for the study of acid rain, the study on the quality of stored rainwater has been limited. In this study, we monitored the quality of stored rainwater at Galmoe middle school, where a rainwater harvesting system is installed and in use for more than two years. We measured water quality parameters such as pH, Electro Conductivity(EC), Dissolved Oxygen(DO), and some metals (aluminium (Al), chromium(Cr), manganese(Mn), zinc(Zn), copper(Cu), arsenic(As), cadmium(Cd), lead(Pb)). The monitoring period was during one year from September 9th 2003 to August 5th 2004. It was observed that the average pH of stored rainwater is neutral. DO is similar to tap water and EC is lower than tap water. Metal Concentrations are within the concentration specified in Drinking Water Quality Standard. Overall, the stored rainwater quality is good enough for sundry use and there's no threat of acid rain and air pollution, if the rainwater harvesting system is well designed and maintained.