• 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.

• 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 Environmental Science International
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• v.13 no.7
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• pp.675-680
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• 2004

This study was conducted to remove organics and nutrients using 2 stage intermittent aeration reactor. First reactor, using suspended microbial growth in intermittent aeration instead of anaerobic reactor in the typical BNR process, used minimum carbon source to release P, and it was possible to reduce ammonia loading going to second reactor. In the second reactor, using moving media intermittent aeration, it was effective to reduce nitrate in non-aeration time by attached microorganisms having long retention time. In aeration time, nitrification and P uptake were taken place simultaneously. From the experiment, two major results were as follows. First, the removal of organics was more than 90%, and optimum aeration/non-aeration time ratio for organic removal was corresponded with aeration/non-aeration time ratio for nitrogen removal. Second, in the first reactor, optimum aeration/non-aeration time ratio was 15/75 (min.) because it was necessary to maintain 75 min. of non-aeration time to suppress of impediment of return nitrate and to lead release of phosphate. In the second reactor, optimum aeration/non-aeration time ratio was 45/90 (min.).

• Journal of Environmental Science International
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• v.12 no.1
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• pp.55-61
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• 2003

This study was carried out to obtain the operating characteristics of SMMIAR process for biological nitrogenㆍphosphorus removal. SMMIAR was operated at HLR(Hydraulic loading rate) of 39.6, 52.8, 63.4 and 79.2 $\ell$/$m^2$/d respectively and the operating parameters such as intermittent aeration time ratio of aerobic/anoxic, DO and microorganism concentration were changed to confirm the optimum operating condition. The concentrations of the wastewater BOD, TN(Total nitrogen) and TP(Total phosphorus) were 150, 30 and 7.5mg/$\ell$ respectively. Achieving better removal efficiencies of BOD, TN and TP up to 90, 85.4 and 95.4% respectively, we must keep in operation condition of SMMIAR by 0.75 of time ratio of aerobic/anoxic and by minimum 45 minutes of oxic period simultaneously.

• Journal of Environmental Health Sciences
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• v.26 no.3
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• pp.98-102
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• 2000

The aim of this study was to evaluate on the removal effect of total nitrogen in municipal wastewater by decreasing hydraulic retention time(HRT) from 6 hour to 4 hour on CNR process. CNR-A(Cilia Nutrient Removal) is the process combining A2/O process with cilium media of H2L corporation. The removal efficiencies for T-N were 63.1% in A-1 reactor, and 73.5% in A-2 reactor and 77.0% in A-3 reactor. The specific nitrification(g-NH3-N/g-MLVSS.d) of Oxic in CNR-A process was 0.07-0.32. The specific denitrification in Anoxic and the specific nitrification inOxic was higher in HRT 4 hour because of optimum F/M ratio.

• Applied Chemistry for Engineering
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• v.17 no.5
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• pp.521-526
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• 2006

A membrane bioreactor (MBR) is an effective tool for wastewater treatment with recycling. MBR process has several advantages over conventional activated sludge process (ASP); reliability, compactness, and quality of treated water. The resulting high-quality and disinfected effluents suggest that MBR process can be suitable for the reused and recycling of wastewater. An anoxic/oxic (A/O) type MBR was applied to simultaneous removal of organics and nutrients in sewage. At first, the efficiency of submerged MBR process was investigated using a hollow fiber microfiltration membrane with a constant flux of $10.2L/m^2{\cdot}h$ at each solids retention time (SRT). Results showed that protein/carbohydrate (P/C) ratio increased and total extracellular polymeric substances (EPS) remained constant with SRT increased. Secondly, A/O type MBR with a reverse osmosis (RO) membrane was employed to treat the municipal wastewater. The performance of A/O type MBR-RO process is better for the treatment of organics and nutrients than ASP-MF-RO process in terms of consistent effluents quality.

• Journal of Korean Society on Water Environment
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• v.25 no.5
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• pp.713-719
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• 2009

A natural wetland in the Nakdong River basin which effectively removes non-point source pollutants was investigated for 2 years to understand wetland topography, vegetation types, and water quality characteristics. The water depth of the natural wetland was in the range of 0.5~1.9 m which is suitable for the growth of non-emergent hydrophytes. The wetland has a high length to width ratio (3.3:1) and a relatively large wetland to watershed area ratio (0.057). A broad-crested weir at the outlet increases the retention time of the wetland whose hydrology is mainly dependent on storm events. The concentrations of dissolved oxygen in the growing season and the winter season showed anoxic and oxic conditions, respectively. Diurnal variations of DO and pH in the growing season were also observed due to weather change and submerged plants. COD and TP concentrations were low in the winter season due to low inflow rate and increased retention time. Increased TP concentrations in the spring season were caused by degradation of dead wetland plants. Nitrogen in the wetland was mostly in organic nitrogen form (>75%). During the growing season, ammonium concentration was high but nitrate nitrogen concentration was low, possibly due to anoxic and low pH conditions which are adverse conditions for ammonificaiton and nitrification. The results of this study can be used as preliminary data for design, operation, monitoring and management of a constructed wetland which is designed to treat diffuse pollutants in the Nakdong river watershed.

• Journal of Environmental Health Sciences
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• v.38 no.6
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• pp.568-574
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• 2012

Objectives: The purpose of this experiment is to understand the phosphorus removal ratio effects of iron plates per unit of surface area through the iron electrolysis system, which consists of an anoxic basin, aerobic basin, and iron precipitation apparatus. Methods: Iron electrolysis, which uses an iron precipitation reactor in anoxic and oxic basins, consisted of iron plates with total areas of 400 $cm^2$, 300 $cm^2$ and 200 $cm^2$ respectively. The FNR process was operated with a hydraulic retention time and a sludge retention time of 12 hours and three days, respectively. Wastewater used in the experiments was prepared by dissolving $KH_2PO_4$ in influent water. Results: The iron plates 400 $cm^2$ (16.6 $mA/cm^2$), 300 $cm^2$ (13.3 $mA/cm^2$) and 200 $cm^2$ (7.3 $mA/cm^2$) in surface area in the phosphorus reactor had respective phosphorus of 2.4 mg/l, 2.7 mg/l and 3.2 mg/l in the effluent and phosphorus removal respective efficiencies of 90.3%, 89.1% and 87.1%. The effluent in the reactor, where the iron plate was not used, had relatively very low phosphorus removal efficiency showing phosphorus concentration of 15.3 mg/l and a phosphorus removal efficiency about 38.3%. Phosphorus removal per ferrous was 0.472 mgP/mgFe in the iron electrolysis system where the surface area of iron was low. Phosphorus pollution load per active surface area and the phosphorus removal efficiency had an interrelation of RE = -0.27LS + 89.0 (r = 0.85). Conclusion: With larger iron plate surface area, the elution of iron concentration and phosphorus removal efficiency was higher. The removal efficiency of phosphorus has decreased by increasing the initial phosphate concentration in the iron electrodes. This shows a tendency of decreasing phosphorus removal efficiency because of decreasing of iron deposition as the phosphorus pollution load per active surface area increases.

• Journal of Environmental Impact Assessment
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• v.21 no.5
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• pp.707-713
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• 2012

There are a lot of parameters affecting microbial acclimation/cultivation characteristics such as dynamic conditions, F/M ratio and substrate affinity. From the process control point of view, the effect of high salinity on the removal efficiencies of BOD and SS have been documented by few researchers. In this research, lab-scale CAS(Conventional Activated Sludge) process and modified $A_2O$(Anaerobic/Anoxic/Oxic) process were operated and monitored to evaluate the characteristics of microbial acclimation and cultivation under high salinity wastewater during the period of three weeks. As a result of acute microbial activity test(6hr) at various $Cl^-$ concentration, the appropriate $Cl^-$ concentration for microbial growth and acclimation ranged under 3,100 mg/l. As a result of acclimation/cultivation test, the trend of COD removal efficiency reduced gradually as time elapsed. It is considered that $NH_4$-N removal phenomenon of the conventional pollutants removal mechanisms gave little effect to the microbial acclimation/cultivation under high salinity wastewater.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.9 no.2
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• pp.64-72
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• 2004

We measured the vertical profiles of $O_2$, H$_2$S, and pH in sediment pore water beneath marine cage fish farms using a microsensor with a 25 ${\mu}{\textrm}{m}$ sensor tip size. The sediments are characterized by high organic material load. The oxygen consumption, hydrogen sulfide oxidation, and sulfate reduction rates in the microzonations (derived from the vertical distribution of chemical species concentration) were estimated by adapting a simple one-dimensional diffusion-reaction model. The oxygen penetration depth was 0.75 mm. The oxic microzonations were divided into upper and lower layers. Due to hydrogen sulfide oxidation within the oxic zone, the oxygen consumption rate was higher in the lower layer. The total oxygen consumption rate integrated with reaction zone depth was estimated to be 0.092 $\mu$mol $O_2$cm$^{-2}$ hr$^{-1}$ . The total hydrogen sulfide oxidation rate occurring within 0.7 mm thickness was estimated to be 0.030 $\mu$mo1 H$_2$S cm$^{-2}$ hr$^{-1}$ , and its turnover time in the oxic sediment layer was estimated to be about 2 minutes. This suggests that hydrogen sulfide was oxidized by both chemical and microbial processes in this zone. The molar consumption ratio, calculated to be 0.84, indicates that either other electron accepters exit on hydrogen sulfide oxidation, or elemental sulfur precipitation occurs near the $O_2$- H$_2$S interface. Total sulfate reduction flux was estimated to be 0.029 $\mu$mol cm$^{-2}$ hr$^{-1}$ , which accounted for more than 60% of total $O_2$ consumption flux. This result implied that the degradation of organic matter in the anoxic layer was larger than in the oxic layer.