• Journal of Korean Society of Water and Wastewater
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• v.12 no.4
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• pp.86-96
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• 1998

In this study, an intermittently aerated activated sludge process, modified process from conventional activated sludge process, was developed to treat high strength swine wastewater, which has been blamed as major pollutant for stream pollution. Therefore, the optimum cycle for oxic and anoxic period, SRT, and OLR were studied as design parameters. The effects of different time interval for oxic and anoxic period on nitrification and denitrification were examined by operating two reactors with 60/60min and 60/90min as oxic/anoxic period. Although the reactor with 60/60min showed complete denitrification of $NO_x-N$ generated during oxic period, the reactor with 60/90min showed incomplete nitrification due to the inactivity of nitrifier by accumulated $NH_3-N$ toxicity during anoxic period. Therefore, it is recommended to operate same interval for oxic and anoxic period. In order to determine the optimum cycle for oxic/anoxic period, four different reactors with 30/30, 60/60, 90/90 and 120/120min were examined. The reactor operation with 90/90min was optimum to get the most stable results in this study. However, the optimum cycle for oxic and anoxic period should be changed with characteristics of influent wastewater and operating conditions. According to lie operation results of three reactors with SRT of 15, 20 and 30days. The reactor with 2Odays SRT showed best removal efficiency of T-N. The optimum OLR would be $2.5Kg\;COD/m^3/day$ which showed the most stable nitrification and denitrification. Since characteristics of influent wastewater in the real system has a severe fluctuation, so it is very difficult to determine each interval for oxic and anoxic period. Therefore, ORP curves, describing the change of oxidation/reduction potential in reactor, can be used as a control parameter for automatic control of oxic and anoxic period. In other words, bending point (Nitrate Knee) of ORP curve during anoxic period could be used as a starting point of oxic period.

• Journal of Environmental Health Sciences
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• v.34 no.3
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• pp.233-239
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• 2008

In order to improve reactor performance of existing sewage treatment plants, the feasibility of enhancing reactor performance by bioaugmentation using EM as bioaugmentation agent and the effects of anoxic: oxic time ratio on reactor performance were investigated. Continuous and intermittent aeration modes were compared under the 6 hr of HRT. Three different types of intermittent aeration modes, that is, 15 min, of anoxic:45 min of oxic, 30 min of anoxic: 30 min of oxic, and 45 min of anoxic: 15 min oxic respectively were chosen as test modes to study the effects of anoxic : oxic time ratios on reactor performance. The optimum anoxic: oxic time ratio was 30 min:30 min when considering simultaneous removal of organic, nitrogen and phosphorus. When applying EM into a continuously aerated reactor under the varying dosing rates of 50-200 ppm, reactor performance in terms of organic and nitrogen removal efficiencies was not improved at all. Nitrogen removal efficiency was increase when the EM dosing rate was increased. However the degree of improvement was slight when the EM was injected above 100 ppm. However optimum phosphorus removal was found at the EM dosing of 200 ppm. Thus it was found that optimum injection concentration of EM is 200 ppm. It is apparent that putting EM into a sewage treatment plant significantly affects the T-N removal efficiency of the reactor by enhancing denitrification efficiency especially in operational conditions of relatively long anoxic periods. To achieve reciprocal condition in a reactor with intermittent aeration it is necessary to enhance the reactor performance by EM injection. In the case of modifying existing continuously aerated reactors into intermittent aerated reactors, it is obvious that operating costs of aeration would be reduced by reducing aeration time when compared with existing conventional sewage treatment plants.

• Environmental Engineering Research
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• v.10 no.5
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• pp.257-263
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• 2005

A batch and a continuous type experiments were conducted to test the conditions for simultaneous phosphorus release and uptake, and denitrification, taking place in one process. The bacteria able to denitrify as well as to remove phosphorus were evaluated for the application to biological nutrient removal(BNR) process. In the batch-type experiment, simultaneous reactions of phosphorus release and uptake, and also denitrification were observed under anoxic condition with high organic and nitrate loading. However the rate and the degree of P release were lower than that occurred under anaerobic condition. BNR processes composed of anaerobic-anoxic-oxic(AXO), anoxic-anaerobic-oxic(XAO) and anoxic-oxic(XO) were operated in continuous condition. The anoxic reactors in each process received nitrate loading. In the AXO process, P release in anaerobic reactor and the luxury uptake in oxic reactor proceeded actively regardless to nitrate loading. However in XAO and XO processes, P release and luxury uptake occurred only with the nitrate loading less than $0.07\;kg{NO_3}^--N$/kgMLSS-d. With higher nitrate load, P release increased and the luxury uptake decreased. Therefore, it appeared that the application of denitrifying phosphorus-removing bacteria (DPB) to BNR process must first resolve the problem with decrease of luxury uptake of phosphorus in oxic reactor.

• Journal of the Korean Applied Science and Technology
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• v.25 no.3
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• pp.355-362
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• 2008

One of the popular domestic sewage treatment process (called step feed oxic-anoxic-oxic process) for nitrogen removal was analyzed in this study by theoretical analysis based on the nitrification and denitrification reaction. Total nitrogen removal efficiency was suggested by considering influent qualities(i.e., ammonia, nitrite, nitrate, alkalinity, and COD). Total nitrogen removal efficiency depends on r (influent allocation ratio). In the case that all influent components are enough, the total nitrogen removal follows equation 100-b/(1+b), when r is 1/(1+b). Finally, it can be concluded that step feed oxic-anoxic-oxic process could be effective for nitrogen removal.

• Journal of Environmental Health Sciences
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• v.26 no.3
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• pp.69-75
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• 2000

This study was carried out to investigate the removal of nitrogen and phosphorus in municipal sewage according to the variation of volumetric ratio in the reactor. It also was performed to provide basic data necessary to the development and improvement of the process which is Anaerobic-Anoxic-Oxic(A2O). In the removal of BOD and COD, the best efficiency of the process showed in the condition of using the media, 1Q of internal recycle rate and 1:3:2 of the volumetric ratio in Anaerobic-Anoxic-Oxic process. In most cases, nitrogen and phosphorus removal efficiency of the process using the cilia media was superior to that of the process which didn't use the media. In the removal of T-N and T-P, the best efficiency of the process showed in the condition of using the media, 1Q of internal recycle rate and 1:3:2 of the volumetric ratio in Anaerobic-Anoxic-Oxic process.

• Membrane Journal
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• v.15 no.1
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• pp.70-83
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• 2005

By supplying air intermittently in various mode, the effects of oxic/anoxic time ratio and air scrubbing in aeration condition on the membrane flux and permeability were investigated. When suction pump stops, vacuum pressure remains inside the suction pump. Therefore, the effect of remaining vacuum pressure in the suction pump on fouling of membrane was investigated. The effect of EPS (Extra cellular Polymeric Substance) which is generated due to the long SRT and high concentration of MLSS and the dose of coagulant on the membrane were also investigated. The suitable oxic/anoxic time ratio for the best removal efficiency of organic matter and nitrogenous matter was 40 minutes (Oxic) : 20 minutes (Anoxic). At this time ratio, alum was dosed into the aeration tank. The result of dosing alum was that the concentration of alum solution might affect nitrification and denitrification. To remove 1 mg/L of phosphorus in MBR process, it needs 0.75 mg/L of alum solution.

• Journal of Korean Society of Water and Wastewater
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• v.16 no.6
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• pp.679-685
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• 2002

The objective of this study was investigated for the microbial community structure and treatment performance of domestic wastewater in lab-scale submerged membrane bioreactor operated with anoxic-oxic cycles. Respiratory quinone profiles were applied as tools for identifying different bacterial populations. The cycle time program of bioreactor was control under anoxic/oxic of 60/90 minutes with an hydraulic retention time of 8.4 hrs. The average $COD_{Cr}$ removal efficiency of domestic wastewater was as high as 93%. The results showed complete nitrification of $NH_4^+$-N generated during oxic period and up to 50% of the total nitrogen could be denitrified. The dominant quinone types of suspended microorganisms in bioreactor were ubiquinone (UQ)-8, -10, followed by menaquinone (MK)-6, and MK-7 for anoxic period, but those for oxic period were UQ-8, MK-6, followed by UQ-10 and MK-7. The microbial diversities of bioreactor at anoxic and oxic periods, calculated based on the composition of all quinones were 10.4 and 12.2-11.8, respectively. The experimental results showed that the microbial community structure in the submerged membrane bioreactor treating domestic wastewater was slightly affected by intermittent aeration.

• Journal of Environmental Science International
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• v.11 no.12
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• pp.1261-1265
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• 2002

This study was focused on the investigation of the characteristics of organics and nitrogen removal with the recycle ratio in anoxic/oxic(A/O) packed bed process that consisted of the anoxic reactor and the aerobic reactor. As increasing the recycle ratio by 0.5, 1.0, 2.0, the COD removal efficiency increased by 94.0%, 98.5%, 98.8% respectively. The aerobic reactor showed the perfect nitrification efficiency by 98.5%, 99.2%, 98.0% respectively. The T-N removal efficiency with the recycle ratio, increased by 56%, 67%, 70% respectively. As increasing the recycle ratio by 0.5, 1.0, 2.0, T-P removal efficiency decreased by 62.1%, 57.4%, 51.3% respectively. The process by releasing the stored phosphorus in the anoxic reactor and uptaking the excess phosphorus in the aerobic reactor, occurred well comparatively when recycle ratio is 0.5. But this process did not occur when the recycle ratio is 1.0 and 2.0. And optimum pH of nitrification was about 6~7 and alkalinity decreased as nitrification rate increased. As increasing the recycle ratio in the anoxic reactor, DO concentration and ORP increased.

• Journal of the Korean GEO-environmental Society
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• v.10 no.1
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• pp.43-48
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• 2009

This study was performed to investigate the characteristics of nutrient removal by Sequencing Batch Reactor (SBR) system, which could achieve high removal efficiencies of nitrogen and phosphorus and make it possible convenient management and operation. In this study, dissolved oxygen (DO), chemical oxygen demand (COD), nitrogen, and phosphorus in SBR system were examined by variation of anoxic-oxic phase repetition in order to optimize an operational method. The 1~4 times of anoxic-oxic phases (Run 1~4) were repeated during 1 cycle operation period. As the repetition frequency increased, it was more difficult to maintain DO condition enough for denitrification. The SBR system showed high COD removal efficiency more than 91% regardless of operational condition. About 68% of nitrogen removal rate was obtained in conditions of 2 or 3 times repetition of anoxic phases, in which NOx-N among discharged total nitrogen account for more than 99%. Approximately 40% of phosphorus was eliminated in the conditions of 1~3 times of anoxic phase repetition.

• Journal of Environmental Health Sciences
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• v.36 no.6
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• pp.502-509
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• 2010

In this study, the (phosphorous removal) the characteristics of phosphorous removal due to (the iron compound precipitated) iron compound precipitation by iron electrolysis in (the anoxic. oxic process) anoxic and oxic processes (equipped with the) in an iron precipitation device were analyzed. During the device operation period, the average concentration of BOD, T-N, and T-P were 219.9 mg/l, 54.6 mg/l and 6.71 mg/l, respectively. The BOD/$COD_{Cr}$ ratio was 0.74, and the BOD/T-N and BOD/T-P ratios were 4.0 and 32.8, respectively. The removal rate of (the organic matters) organic matter (BOD and $COD_{Cr}$) was very high at 91.6% or higher, and that of nitrogen was 80.5%. The phosphorous concentration (of the final) in the treated water was 0.43 mg/l (0.05-0.74 mg/l) on average, and the removal efficiency was high at 90.8%. The soluble T-P concentrations in (an) the anoxic reactor, oxic reactor (II) and final treated water were 1.99 mg/l, 0.79 mg/l and 0.43 mg/l, respectively, which indicated that the phosphorous concentration in the treated water was very low. Regardless of the changes in the concentrations of (organic matters) organic matter, nitrogen and phosphorous in the influent, the quality of the treated water was relatively stable and high. The removal rate of T-P somewhat increased with the increase in the F/M ratio in the influent, and it also linearly increased in proportion to the T-P loading rate in the influent. In the treatment process used in this study, phosphorous was removed (using) by the precipitated iron oxide. Therefore, the consumption of organic (matters) matter for biological phosphorus removal was minimized and (most of the organic matters were) was mostly used as the organic carbon source for the denitrification in the anoxic reactor. This (can be an economic) treatment process (without the need for the supply of additional organic matters) is economic and does not require the supply of additional organic matter.