• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.1
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• pp.21-29
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• 2015

A steady-state controllable M/G/1 queueing model operating under the {T:Min(T,N)} policy is considered where the {T:Min(T,N)} policy is defined as the next busy period will be initiated either after T time units elapsed from the end of the previous busy period if at least one customer arrives at the system during that time period, or after T time units elapsed without a customer' arrival, the time instant when Nth customer arrives at the system or T time units elapsed with at least one customer arrives at the system whichever comes first. After deriving the necessary system characteristics including the expected number of customers in the system, the expected length of busy period and so on, the total expected cost function per unit time for the system operation is constructed to determine the optimal operating policy. To do so, the cost elements associated with such system characteristics including the customers' waiting cost in the system and the server's removal and activating cost are defined. Then, procedures to determine the optimal values of the decision variables included in the operating policy are provided based on minimizing the total expected cost function per unit time to operate the queueing system under considerations.

• Journal of Korean Society of Water and Wastewater
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• v.21 no.5
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• pp.589-599
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• 2007

This study was conducted to investigated the removal efficiency of BOD and nutrient for the treatment of low strength municipal wastewater by a biological nutrient removal system. In this experiment, the effect of operating parameter including HRT of 7.0hr, BOD/TN ratios of 2.62~4.08, internal recycle of 50~300%, and return sludge of 50~100%, were studied during winter season. Efficiencies of organic matter and T-P removal and denitrification were not significantly affected by the change of temperature in winter season. However, the specific nitrification rate and nitrification efficiency decreased at low temperature. Besides, denitrification efficiencies increased with increasing BOD/TN ratios. It was also found that the internal recycle and return sludge ratio below 50% is required for the effective denitrification of low strength municipal wastewater. With operating mode 4 of the optimum, the effluent BOD, T-N and T-P concentration were obtained to average 5.8, 14.6, and 0.84 mg/L, respectively. The temperature-activity coefficient (${\theta}$) of specific nitrification rate, specific denitrification rate and specific phosphorus uptake rate were obtained 1.044, 1.017, 1.028, respectively.

• Korean Journal of Soil Science and Fertilizer
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• v.44 no.5
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• pp.929-936
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• 2011

To treat non-point source pollution in Dongbok lake, removal efficiencies of pollutants were investigated in Dongbokcheon constructed wetlands (CWs) at different treatment time and wastewater loading. The wetlands consisted of forebay, wetlands ($1^{st}$, $2^{nd}$, $3^{rd}$, $4^{th}$, $5^{th}$, $6^{th}$, $7^{th}$, and $8^{th}$ wetlands) and sedimentation pond. The concentrations of BOD, SS, T-N, and T-P in inflow ranged $0.85{\sim}3.14mg\;L^{-1}$, $3.33{\sim}9.70mg\;L^{-1}$, $0.64{\sim}5.33mg\;L^{-1}$, and $0.03{\sim}0.10mg\;L^{-1}$ from April to October in 2008, respectively. The removal rates of BOD, SS, T-N, and T-P in Dongbokcheon CWs were 34%, 5%, 31%, and 13%, respectively. The removal rates of BOD and T-N were higher than those for SS and T-P. The amounts of pollutant removal in Dongbokcheon CWs were higher in the order of forebay > wetlands > sedimentation pond for BOD, sedimentation pond > wetlands > forebay for SS, sedimentation pond > forebay > wetlands for T-N. The amount of T-P removal in wetlands was higher than forebay and sedimentation pond.

• Journal of Environmental Science International
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• v.16 no.6
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• pp.707-714
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• 2007

A laboratory experiment was performed to investigate nitrogen removal by the soil column. The addition of 20% waste oyster shell to the soil accelerated nitrification in soil column. The $NO_3^--N$ concentration in the effluent decreased with the decrease of HRT(Hydraulic Retention Time). When methanol and glucose added as carbon sources, the average removal rates of T-N(Total Nitrogen) were 82% and 77.9%, respectively. The $NO_3^--N$ removal by methanol supplementation in soil column can likely be attributed to denitrification. In continuous removal of nitrogen using the soil column, the COD(Chemical Oxygen Demand) and $NH_4^+-N$ removed simultaneously in organic matter decomposing column. The greater part of $NH_4^+-N$ was nitrified by the percolated through nitrification column, and the little $NH_4^+-N$ was found in the effluent. The T-N of 87.4% removed at HRT of 36 hrs in denitrfication column. Because of nitrified effluents from nitrification column are low in carbonaceous matter, an external source of carbon is required.

• 한국생물공학회:학술대회논문집
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• 2000.04a
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• pp.414-417
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• 2000

BACC(Biological Activated Carbon Cartridge)process is a newly developed biological process to remove organic compounds, nitrogen, and phosphorus with activated carbon granules in iron fixed-frame cartridge type. The largest defect of previous BACC process was denitrification inefficiency. The removal efficiencies of nitrogen and phosphorous with external recycle ratios $100{\sim}200%$ for synthetic wastewater were $69.8{\sim}90.1%$ and $62.18{\sim}91%$, respectively, since the modified BACC process with external recycle overcame the defect of BACC process. When external recycle ratio was increased more than 300%, T-N removal efficiencies were decreased. In the treatment of a real sewage using modified BACC process, $COD_{Cr}$, removal efficiencies were $96.3{\sim}97.5%$ which was similar to those of the previous BACC process. while T-N removal efficiencies was $88.3{\sim}95.7%$ which were superior to those of the previous BACC process.

• Journal of Environmental Health Sciences
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• v.34 no.5
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• pp.374-381
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• 2008

In this study, the factors affecting biological N and P removal using SND (simultaneous nitrification and denitrification) process were investigated and evaluated to examine the possibility of treating N and P through SND with NADH by surveying N and P traces in an aeration tank. Variations of $NH_4^+$-N+$NO_3^-$-N concentration were used to estimate the degree of SND in each point (P2, P3, P4, P5) of the aeration tank and these variations showed that denitrification efficiency in P2 (front zone), nitrification and denitrification efficiencies in P4 (middle zone) were 67%, 86% and 39%, respectively. When $PO_4^{-3}$-P concentration was analyzed in each point of the aeration tank, it was shown that $PO_4^{-3}$-P concentration coming into P2 was 1.25 mg/L, which increased to 2.22 mg/L by P release in P2 zone and then decreased to 0.74 mg/L by P uptake in P4. Consequently, we were able to estimate which high P removal efficiency observed in this study was caused by biological phosphorus removal. To determine the operating factors affecting effluent T-N, we analyzed the correlation among FN/M ratio, C/N ratio, Temp., SRT etc and these results showed that the correlation among FN/M ratio, C/N ratio and Temp was not high. However, the relationship of SRT and other parameters (effluent $NH_4^+$-N and effluent BOD) and the short SRT could have an affect on effluent $NH_4^+$-N and so effluent BOD could be increased. Thus, SRT operation should be controlled over 10 days. The results for analyzing the correlation between SRT and influent $NO_3^-$-N in order to investigate the operating factors affecting effluent T-P showed that T-P or $PO_4^{-3}$-P was not highly correlation with SRT, whereas $PO_4^{-3}$-P concentration increased along with increasing $NO_3^-$-N concentration into P2. Based on these results, we concluded, using regression analysis (R2=0.97), that effluent $PO_4^{-3}$-P concentration depends on $NO_3^-$-N concentration into P2.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.9 no.2
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• pp.23-32
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• 2006

Total suspended solids (TSS), five-day biochemical oxygen demand ($BOD_5$), total nitrogen (T-N), and total phosphorous (T-P) concentrations around and under a floating island were examined from October 2002 to September 2003. The island was installed in July 2002 on the surface of an agricultural irrigation reservoir located in the southern part of the Korean Peninsula. It was composed of six polyethylene panels. Each panel was 2 m (length) ${\times}$ 1 m (width) ${\times}$ 0.02 m (thick) and had about thirty-two holes each with a diameter of eight centimeters, through which plant roots grew down into the water. Coconut fibers of nine-centimeters in height were placed on the panel, which sustained plants rhizomes and roots. Both the fibers and the panel were raped with polyethylene wire mashes. About thirty irises (Iris pseudoacorus) were planted into the fibers of each panel. The concentrations of TSS, $BOD_5$, T-N and T-P below the island during the iris-growing season averaged 9.70, 2.59, 3.61 and 0.14 mg/L, respectively and those around it averaged 9.99, 2.83, 4.07 and 0.16 mg/L, respectively. The average concentrations of TSS, $BOD_5$, T-N and T-P below it during the iris non-growing season were 8.68, 2.37, 3.25 and 0.14 mg/L, respectively and those near it were 8.76, 2.43, 3.34 and 0.15 mg/L, respectively. At a significance level of ${\alpha}$=0.05, $BOD_5$, T-N and T-P concentrations under the island during the iris-growing season were significantly low when compared with those around it except TSS. No differences in TSS, $BOD_5$, T-N and T-P concentrations between around and near it were found at a significance level of ${\alpha}$=0.05 during the iris non-growing season. The removal of $BOD_5$, T-N, and T-P during the growing season were significantly high when compared with those during the non-growing season. TSS abatement of the floating island was very low during both the growing and non-growing seasons. The island's reductions of $BOD_5$, T-N and T-P were good during the growing season, especially T-N and T-P, which have been considered as primary pollutant sources causing the water quality degradation of reservoirs. The removal of T-N and T-P was primarily attributed to the absorption of nitrogen and phosphorous by the irises during the growing season.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.14 no.1
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• pp.121-132
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• 2011

Removal rates of $NO_3$-N and TN in the free-water surface wetland system during winter; December, January, February and March, spring and fall; April, May, October and November, and summer; Jun, July, August and September were investigated. The system was established on floodplain in the downstream reach of the Gwangju Stream in 2008. It measures 50 meters in length and 5.5 meters in width. Iris pseudacorus L. grown in pots for about two years were planted in the system. The water stream was funneled in by gravity and its effluent was discharged back in. Volumes and water quality of inflow and outflow were analyzed from December 2008 to November 2010. The inflow was averaged approximately 350 $m^3/day$ and hydraulic residence time was about 3 hours. Average influent and effluent $NO_3$-N concentration was 3.75 and 3.35 mg/L, respectively and $NO_3$-N retention was amounted to 10.6%. Influent and effluent TN concentration were averaged 4.93 and 4.30 mg/L, respectively and TN abatement reached to 12.9%. One-way ANOVA statistics claimed that the average removal rates of $NO_3$-N and TN during winter, spring and fall, and summer were not always the same (p<0.001). The t-Tests of three pairs among $NO_3$-N removal rates of winter, spring and fall, and summer illustrated that the removal rates of winter ($5.04{\pm}1.94$), spring and fall ($10.53{\pm}2.24$), and summer ($18.61{\pm}2.26$) were significantly different each others (p<0.001). Among TN removal rates, the three pairs of t-Tests of three seasons showed that the removal rates of winter ($5.21{\pm}2.51$), spring and fall ($11.71{\pm}3.12$), and summer ($21.53{\pm}4.86$) were significantly different from each others (p<0.001).

• Korean Journal of Environmental Agriculture
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• v.27 no.1
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• pp.27-34
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• 2008

To effectively treat the domestic sewage that was produced on a small-scale in farming and fishing village in order to encourage an ecologically friendly environment, a small-scale sewage treatment apparatus using natural purification methods that consisted of an aerobic and an anaerobic plots were constructed. The efficiency of sewage treatment according to the sewage loading was investigated to obtain the optimum sewage loading in small-scale sewage treatment apparatus. Removal rate of pollutants according to the sewage loading were in the order of $150\;Lm^{-2}day^{-1}{\fallingdotseq}300\;Lm^{-2}day^{-1}>600\;Lm^{-2}day^{-1}$. Therefore, the optimum sewage loading was 300 L m-2 day-1. Under the optimum sewage loading, removal rate of BOD, $COD_{Mn}$, turbidity, T-N and T-P were 99, 94, 99, 49 and 89%, respectively. However, to satisfy the water quality standard in effluent in small-sclae sewage treatment apparatus for domestic sewage treatment, the low removal efficiency of T-N and T-P must be improved. So to improve the removal rate of T-N and T-P, the efficiency of sewage treatment according to the improved sewage treatment process such as, re-treatment at aerobic plot, anaerobic condition of aerobic plot, changing the filter media sizes and the depths in anaerobic plot, and also addition of oyster shells to filter media at anaerobic plot were investigated. In case of 150 cm depth in anaerobic plot with filter medium A (effectivity particle size 1.50 mm) and addition of oyster shells to filter media at anaerobic plot, removal rate of T-N and T-P in both plots were increased by 10 and 3%, and 14 and 7% in comparison with 100 cm depth in anaerobic plot with filter medium B(effectivity particle size 0.95 mm), respectively. The optimum improved sewage treatment process in small-scale sewage treatment apparatus were 150 cm depth in anaerobic plot with filter medium A and addition of oyster shells to filter media at anaerobic plot.

• Proceedings of the Membrane Society of Korea Conference
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• 2004.05a
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• pp.117-120
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• 2004

The separation characteristics were investigated with the variations of pressure and temperature using ultrafiltration and reverse osmosis membrane module sets composed of different membrane types and materials. TDS, T-N and COD removal efficiencies were not affected and low with the change of temperature and pressure in case of using UF modules contained in module set 1, 2, 3. TDS, T-N and COD removal efficiencies were very high in RO modules. The final water quality of acrylic wastewater was satisfied within the discharge limit value of plant wastewater. It was known that membrane module sets could be used for the reuse of wastewater.