오정우Jung Woo Oh, 김주환Ju Hwan Kim

DOI: Vol.14(No.4) 455-462, 1998

In this study, THM formation in a water distribution system is predicted by statistical analysis and neural network with variables of AWWA model. The THM formation equation by statistical analysis is determined by multiple exponential regression (Model I) and multiple linear regression (Model II). The prediction of THM formation by neural network analysis (Model III and Model IV) is determined by including organic compounds such as TOC, DOC and UV254. The result shows that THM concentration increases by 30% or less in the C-distribution system as the distance from water treatment plant increases. It is shown that the correlation coefficients of THM prediction by statistical analysis are 0.917 and 0.937 for Model I and Model II , respectively. And, the correlation coefficients of THM prediction by neural network analysis show 0.986 and 0.977 for Model III and Model IV, respectively.) From the results, it is presented that the proposed methods are reflected well the characteristics of observed THM formation. Also, it is concluded that the neural network approaches of this research can be applied effectively to the prediction of THM formation in a water distribution system.

장윤영Yoon Young Chang, 최승희Seung Hee Choe, 신정엽Jung Yup Shin, 황경엽Kyung Yub Hwang

DOI: Vol.14(No.4) 463-468, 1998

In recent years considerable efforts for the removal of nitrate have been made in the development of nitrate removal techniques. One of the conventional treatment methods of nitrate is biological denitrification. However, this process needs other carbon sources for microbial activities and a long period of time to reduce the nitrate level in polluted water. In this study nitrate reduction using synthesized zero-valent iron powder(Fe˚) with nanoscale was proposed in situ or above-ground treatment of nitrate-polluted water at room temperatures and pressures. Nanoscale iron removed 50, 100, 200, and 400㎎/l of nitrate within 30min with little intermediates. Compared with commercial iron powders(15∼75㎛), the synthesized iron powder(1∼100㎚) showed high removal efficiencies(10∼100times) in a short time period with low metal to solution ratio(4∼10g/100㎖). The approach presented offers unique opportunities for both fundamental research and technological applications of zero-valent metals to nitrate-polluted water. For example, iron can be used to construct a reactive barrier in the path of a contaminated groundwater plume to remove NO_(3-).

심무준Moo Joon Shim, 김은수Eun Soo Kim, 김경태Kyung Tae Kim, 이기복Gi Bok Lee, 강화성Hwa Seong Kang, 이광우Kwang Woo Lee

DOI: Vol.14(No.4) 469-482, 1998

Shihwa Lake is a brackish lake with high organic productivity and anoxic bottom waters. The high biological activity in surface waters along with limited vertical mixing has resulted in the development of an oxic-anoxic interface at the 3∼4m water depth. And anoxic bottom waters are enriched with PO₄, NH₃ and H₂S. Three sediment cores were collected from Shihwa Lake near the Banweol Industrial Complex in October, 1997 and were analysed for organic matters, S/C ratios, δ ^(13)C and heavy metals. The average S/C ratio was about 0.30 in the sediment cores, which is lower than 0.36, the characteristic ratio of marine sediments. Sediments appeared to be depleted in sulfur relative to organic carbon, and the total reduced sulfur showed high correlation with organic carbon. The δ ^(13)C ratios in the upper layer were slightly lower than those in the deeper layer. Heavy metals of Cr, Co, Ni, Zn and Cu showed high correlation with organic matters and with each other. Those metals have similar geochemical behavior. On the other hand, Mn, As, Cd and Pb showed low correlation with organic matters, showing that these metals may have different pathways and geochemical behavior from the former groups of metals. Heavy metal contents in the surface sediment of Shiwha Lake is also relatively high in comparison with obtained from inshore and offshore sediments of Korea.

유춘만Chun Man Yu, 주현수Hyun Soo Joo, 박지인Ji In Park, 위인선In Sun Wui, 이종빈Jong Bin Lee

DOI: Vol.14(No.4) 483-489, 1998

This survey was carried out to evaluate offshore water quality to Western sea in Korea by bioassay using early development system of Asterias amurensis. Despite of the inflows of several river systems, most West coast maintained the grade Ⅱ water quality because embryo development of Asterias amurensis was moderately inhibited. This is thought to be due to the decrease in pollutant input resulting from the purification of inflow rivers (e. g., the control of waste water discharge and the construction of sewage treatment facilities), and the dilution of pollutants by a strong tidal mixing with a large difference between the ebb and flood tides. However, the water quality of Asan, Hampu˘ng and Choˇnsu Bays, where circulations of water are relatively poor, and Kunsan and Mokpo harbors which are influenced by pollutants from neighboring cities have shown the grade III because embryo development of Asterias amurensis was strongly inhibited.

이영식Young Sik Lee, 향정철웅Tetsuo Mukai, 용본화인Kazuto Takimoto, 강전광정Mitsumasa Okada

DOI: Vol.14(No.4) 383-392, 1998

심인식In Sick Sim, 임재호Jae Ho Lim, 박수영Soo Young Park, 조광명Kwang Myeung Cho

DOI: Vol.14(No.4) 393-398, 1998

This study was performed to investigate the applicability of ultrasonic irradiation for improvement of the efficiency of Fenton oxidation for treatment of biologically -treated dyeing wastewater. Ultrasonic irradiation at a frequency of 28㎑ with a maximum vibration output of 200W increased the water temperature in the reactor at an average rate of 0.37℃/min-L. The H₂O₂ concentration in the reactor reached a maximum value of 24.5㎎/L by ultrasonic irradiation for 30min at pH 5. The COD_(Mn) removal efficiency and transmittance improved as the pH decreased, and the optimal pH for ultrasonicated Fenton oxidation reaction was 3.5. At a condition of FeCl₂ dosage of 900㎎/L, a pH of 3.5 and no H₂O₂ addition, ultrasonicated Fenton oxidation was superior to non-sonicated Fenton oxidation in COD_(Mn) removal and transmittance improvement. In conclusion, the results of this research suggest that ultrasonicated Fenton oxidation can be effective for treatment of dyeing wastewater.

나기환G . H . Na, 남정배J . B . Nam, 박경대K . D . Park, 이진애J . A . Lee

DOI: Vol.14(No.4) 399-404, 1998

With increasing the insolation in summer, the blue-green algal blooms occurred periodically in the stagnant reservoirs and rivers in tropical and temperate regions. For mitigation, we employed the loess suspension techniques which have been used for the red tide control of Cochlodinium polykrikoides in the industrial scale in southern coast of Korea. Before applying this technique in situ, we tested the elimination effect of causing organisms, Microcystis sp., by loess suspension in 1 ℓ mass cylinder column test with different grain sizes and concentrations. As the grain sizes, the finer, the better; indifferent according to its origin but the applicable concentration was above 2,000ppm.

이의상Eui Sang Lee, 김상채Sang Chai Kim, 강희만Hee Man Kang

DOI: Vol.14(No.4) 405-411, 1998

Most of the existing sewage treatment plants in the highway service areas are experiencing many problems in their operation and maintenance because they have been adopted indiscreetly without relevent examination about treatment processes and designed without evaluation of design factors. To solve these problems, design factors were determined by the analysis of sewage generation rate and its characteristics (BOD, SS, T-N, T-P etc.). From the results of this study, influent loadings fluctuated widely with and without restaurants and septic tanks. Sewage generation rates in weekends and high-demand seasons were higher than those in the other days. The fluctuation range of sewage generation rates and influent loadings of sewage treatment plants in the highway service areas was larger than that of the municipal wastewater and the agricultural sewage. Average influent concentration were BOD 324㎎/ℓ, SS 229㎎/ℓ , T-N 96㎎/ℓ and T-P 10㎎/ℓ, respectively. Nitrogen and phosphorus concentrations were about 3∼7times greater than those of the municipal wastewater and the agricultural sewage. All the findings might be considered when we design sewage treatment plants in the highway service areas in the future.

윤제용Je Yong Yoon, 변석종Seok Jong Byun, 이상덕Sang Deok Lee, 석관수Kwan Su Seok

DOI: Vol.14(No.4) 413-423, 1998

Disinfection process in water treatment plants is one of the most important step in order to inactivate waterborne disease. However, what is the necessary disinfection which has to be achieved in water plants was not properly established in Korea. In this study, we introduced the concept of CT values and evaluated CT in several water treatment plants to propose reasonable guidelines of necessary disinfection capabilities. The concept of CT was referred to the SWTR(Surface Water Treatment Rule) which is current US-EPA regulation. The necessary disinfection capability is expressed by CT which may be variable depending on the type of disinfectant, temperature, and pH etc. C is the concentration of disinfectant in the effluent of clearwell and T(=T-10) is the detention time at which 90% of the water passing through the unit is retained within the basin. Total of 8 water treatment plants(CJ, SS, BS, KG, BW, YC, KC, YJ) were intended to investigate the necessary disinfection capability in clearwell. For two of them, tracer study to find out T_(10) was not possible due to the unavailability of the port of chemical addition in the clearwell. It was found that T-10/T were varied widely from 0.2 to 0.5 even though all the clearwell in water treatment plants investigated were not baffled. For reference, T_(10)/T of 0.1 were given for unbaffled clearwell in terms of US-EPA recommendation. Considering the operation condition of plants and water quality characteristics at the time of study, 6 of water treatment plants successfully met the necessary disinfection capability based on 90% giardia removal. However, under the scenario of worst case which can be anticipated year round, nearly all the water treatment plants failed to meet CT requirements. Therefore, the necessities for adjusting disinfection process to the condition of various water quality were raised.

신응배Eung Bai Shin, 윤현식Hyun Sik Yoon

DOI: Vol.14(No.4) 425-432, 1998

Combined sewer overflows (CSOs) have been considered as a major cause of water quality deterioration of water-courses in the vicinity of the heavily urbanized areas. It is important to know exact properties of pollutants contained in CSOs to address water quality impacts that are caused by CSOs inputs to the receiving waters. Recently, research has shown that a settling process is an efficient treatment for the removal of pollutants from CSOs. Therefore, the settling velocity of the pollutants in the CSOs to be treated has an important influence on performance and should be considered in developing design details. Results of settling velocity distributions for diverse pollutant sources (including CSOs, street-runoff, dry-weather flow) are presented with COD_(Cr), SS, TKN, T-P. The observed results in settling characteristics for pollutant sources showed widely different and exponential decay curve was well fitted to settling velocity profiles produced during the test.

김해숙Hae Suk Kim, 강성환Sung Hwan Kang, 이찬기Chan Ki Lee

DOI: Vol.14(No.4) 433-439, 1998

Biological nutrient removal process such as SBR was influenced by carbon to nitrogen ratio(C/N) in the influent wastewater, which was related with organic matter removal, nitrification and denitrification. This study was performed to investigate the effects of C/N ratio on the treatment of the mixed liquor, nightsoil and piggery wastewater, by SBR process. In summary, the results are follows; i) In order to obtain organic matter removal rate more than 90 percents, the C/N ratio should be maintained less than 12. ii) In the aerobic condition, the laboratory SBR operated with C/N ratio of 6, 9, 12 and 15, respectively, showed the nitrification rates of 1.27, 1.07, 0.97, and 1.26㎎NH₃^+-N/gMv·hr, respectively, and the alkalinity consumption rates of 6.7, 5.5, 5.9 and 3.4㎎Alk.(as CaCO₃)/㎎NH₃^+-N, respectively. iii) The optimum C/N ratio was 12 in consideration of total nitrogen removal efficiency. iv) In the C/N ratio of 6, 9, 12 and 15, the denitrification rates were 0.27, 0.53, 0.74 and 0.94㎎NO₃^--N/gMv·hr, respectively, and the alkalinity production rates were 2.1, 3.0, 3.3 and 3.4㎎Alk.(as CaCO₃)/㎎NH₃^+-N, respectively.

김영철Young Chul Kim, 김완중Wan Joong Kim

DOI: Vol.14(No.4) 441-453, 1998

This paper presents a comparative study of two experimental systems, high-rate algal ponds(HRAP) treating sewage; i.e., one without paddle-wheel mixing (nm-HRAP) to eliminate the use of mechanical elements, the other with a night aeration system(na-HRAP) for preventing HRAP from undergoing possible lower dissolved oxygen or completely anaerobic state in the absence of photosynthetic activities during the night. Although the nm-HRAP did not provide normal levels of pH and dissolved oxygen characterized by HR,AP with paddle-wheel mixers, they did not drop to low levels at night to affect its performance. The nm-HRAP system was poor for reducing COD but gave similar nutrients removal efficiencies as obtained from slowly mixed-HRAP. Aerating HRAP at night was not helpful at all in keeping the pH and DO from decreasing but rather, it resulted in lower reductions of COD and nutrients. It could be concluded that the nm-HRAP was reliable and efficient as the normal mixed-HRAP and could be easily built and operated without much of the excavation and maintenance works.

임연택Yeon Taek Rim, 서정범Jeong Beom Seo, 김용석Yong Seok Kim, 권오상Oh Sang Kwon, 한기봉Gee Bong Han, 유재근Jae Keun Ryu

DOI: Vol.14(No.4) 491-499, 1998

This study was focused on survey of sewage characteristics and investigation of operational efficiencies in terms of BOD, SS, TN and TP for treatment facility built on on-site apartment building. The oxidation ditch process of 40㎥/day capacity was applied for sewage treatment system. The results of the research showed that earth household had 3.2 dwellers with a sewage flow rate of 242Lpcd in average. The sewage flow rate was particulary low on Saturday and Sunday. The average sewage concentration of BOD, SS, TN and TP were 145㎎/L, 101㎎/L, 33.3㎎/L and 2.8㎎/L, respectively. BOD removal was observed to be 91.7% on average while SS removal to be 77.0% on average. Denitrification/nitrification were accomplished during intermittently aerated processes and removal rate of nitrogen was 50.0% in terms of total nitrogen. Removal efficiency of phosphorus was 47.7% in terms of total phosphorus. The average effluent concentration of BOD, SS, TN and TP were 12.0㎎/L, 19.5㎎/L, 17.0㎎/L and 1.5㎎/L, respectively. Observed microbial yield coefficient was 0.16gMLSS/gBOD. This experiment may prove that intermittently aerated oxidation ditch process can be employed to treat organic matter as well as nutrients in sewage that are generated from such sources as apartment building and community area.

이현동Hyun Dong Lee, 조영무Young Moo Cho, 정원식Won Sik Chung

DOI: Vol.14(No.4) 501-509, 1998

This research was to evaluate the characteristics of organic material, nitrogen removal, and settling with HRT and to find the proper ratio of aeration and deaeration time for intermittent aeration process on nitrogen removal in the intrachannel oxidation ditch which was modified oxidation ditch and designed the capacity of 2 ㎥/day. The results were showed that the removal efficiencies of BOD, COD_(Mn), SS and N were about 90%, 90%, 93% and 50%, respectively. The major characteristics of settling and removal efficiency were not showed by the changes of HRT and intrachannel type. In case nitrogen removal, the rate of nitrification showed more than 93%, and denitrification rate was 30∼60%. But the efficiencies of settling and organic removal are equal to or higher than thouse of conventional oxidation ditch. Therefore, the most advantages of intrachannel oxidation ditch are lower construction cost which caused from the reduction of area and feasibility of O&M Management than the conventional oxidation ditch.

윤재흥 Jae Heung Yoon

DOI: Vol.14(No.4) 511-520, 1998

The characteristics of optimization methods are inspected by applying those to groundwater in situ bioremediation. The methods used in the comparison are Evolutionary Algorithms (Binary-Coded Genetic Algorithm (BIGA), Real-Coded Genetic Algorithm (RGA), Derandomized Evolution Strategy (DES)), Direct Search Methods (Nelder-Mead Simplex (NSLX), Modified Simplex (MSLX), Parallel Directive Search (PDS), and Derivative-Based Methods (Implicit Filtering for Constrained Optimization (IFFCO), Successive Approximation Linear Quadratic Regulator (SALQR)). For time-invariant control (9 decision variables), MSLX, IFFCO, DES and SALQR show preciseness in solutions. In case of time-varying control (54 and 72 decision variables), all the directive search methods and IFFCO converge to local optima, and produce inaccurate solutions. SALQR, an optimal control algorithm, shows high efficiency, but also converges to local optima to yield uns table solutions for some cases of time-varying control problems. RGA is more efficient and accurate than BIGA, and more robust than the deterministic search methods. Among the methods, DES is a promising method to be easily applied to other system problems because of its efficiency and accuracy.

윤제용Je Yong Yoon, 변석종Seok Jong Byun, 이상덕Sang Duk Lee

DOI: Vol.14(No.4) 521-528, 1998

Chlorine is currently being used for the disinfection process in nearly all domestic water treatment plants. Trihalomethanes(THMs) and a lot of chlorinated disinfection byproducts(DBPs) are inevitably produced as a result of chlorine use. The chlorinated DBPs other than THMs are hard to measure and regulate individually. Total organic halides(TOXs) which indicate the sum of chlorinated DBPs may be used as a process control variable for the control of DBPs. In this study, the formation characteristics of THMs and TOXs as a function of the ratio of Cl₂ to NH₃-N in two types of raw water which have the different characteristics of ammonia concentration were investigated. The breakpoint chlorination of the drinking water treatment plants was simulated to represent the characteristics of DBPs formation. Breakpoint chlorination curves with naturally occurring ammonia were not significantly different, when compared to those with chemical ammonia. The breakpoint was observed at Cl₂/NH₃-N ratio of 7.0∼7.7. When Cl₂/NH₃-N ratio was below 5, where chloraminations were practiced, THMs & TOXs formation were low, becoming up to 8㎍/L and 78㎍/L respectively. Below Cl₂/NH₃-N ratio of 5, THMs formation was almost identical regardless of water quality presumed and the source of ammonia, while TOXs formation slightly reflected water quality. On the other hand, when the ratio of Cl₂to NH₃-N was above 7.5, the level of THMs & TOXs formation increased significantly, becoming up to 36㎍/L and 259㎍/L respectively. It was found that the overall level of THMs and TOXs formation was not high, considering the organic content and the high chlorine dose applied. The implication of this DBPs formation characteristics could be enormous for the regulation policy of DBPs. THMs that is only the regulated DBPs explained about 8∼14% of TOXs.

황규대Gye Dae Whang, 김민호Min Ho Kim, 조철휘Chul Hwi Cho

DOI: Vol.14(No.4) 529-537, 1998

The objective of this study was to examine the effect of solids concentration of influent and biological nitrification on the removal efficiency of organic matter and biological kinetic coefficients. Three sets of reactors were operated to investigate the effects of influent TSS concentration and nitrification on the COD removal efficiency and excess sludge production. Each set of reactor consists of three bench scale activated sludge reactors were operated under different SRT to determine the biological kinetic coefficients and the optimum operating conditions for COD removal and nitrification. In activated sludge reactors operated with 1.5day of HRT, with the organic loading ranging 0.80∼1.75㎏TCODc_r/㎥·day and TSS loading ranging 306∼1889㎎/ℓ, the removal efficiencies of TCODc_r and SCODc_r were about 71∼90% and 61∼78%, respectively. Influent TSS concentration affect the removal efficiency of organic matter and biological kinetic coefficients. However, SRT does not affect the COD removal efficiency and sludge settling characteristic. In operated with the loading rate of 0.51㎏NH₄^+·N/㎥·day, nitrification efficiency was over 91%. The optimum operating conditions for COD removal and nitrification was l0days of SRT. Yt and Kd Values of reactor set #1 which received influent of low TSS concentration and operated without nitrification were 0.2776㎎MLVSS/㎎SCODc_r and 0.036day^(-1), respectively. These coefficient increased to 1.9693㎎MLVSS/㎎ SCODc_r, and 0.187day^(-1) for activated sludge reactor set #2 received influent of high TSS concentration and operated without nitrification. Nitrified activated sludge reactor set #3 received influent of high TSS concentration produced Yt of 2.1769㎎MLVSS/㎎SCODc_r and Kd of 0.204day^(-1).