서연태Youn Tae Seo,정동환Dong Hwan Chung,임성균Seong Kyun Lim,박규홍Kyoo Hoon Park

DOI: Vol.17(No.3) 283-297, 2001

In order to estimate the cost of microfiltration(MF), ultrafiltration(UF), nanofiltration(NF), and reverse osmosis(RO) membrane processes, the operating data obtained from the existing water supplying facilities were collected and analyzed. The effect of flux, recovery, the frequency of flushing, and design capacity was investigated on the cost of membrane processes for drinking water supply. One of the best ways of maintaining the economic membrane processes is to maximize the efficiency of membrane operation. The highest flux and maximized cleaning intervals should be maintained within the range of mass transport limit, recovery must be increased in general. In the existing MF, UF, and NF plants. cost was calculated to increase quickly as the design capacity decreased below 12,000㎥/d. Above 40,000㎥/d of design capacity, the predicted decreasing rate of cost was flattened. At 40,000㎥/d, the cost of MF, UF, and NF was $0.08/㎥, $0.12/㎥, $0.23/㎥, respectively. Permeate quality for NF would be about the same as for RO, but it was much improved compared with MF and UF. Although cost of NF was twice as much as UF cost, it was only half of that in conventional ozone-GAC process with design capacity of up to 19,000㎥/d. When cost and permeate quality of NF was considered. NF seemed very competitive or less expensive than the other processes for drinking water supply.

신은성Eun Sung Shin,최지용Ji Yong Choi,이동훈Dong Hoon Lee

DOI: Vol.17(No.3) 299-311, 2001

The principal non-point sources of water pollution from agriculture has been known as nutrients, organic matters, sediments, fertilizer and toxic chemicals. Among all of these pollutants, nutrients give a significant impact on water quality, such as eutrophication. For issues of integrated water quality management, a thorough investigation on both point source and non-point source of pollution loaded from streamlets to rivers should be conducted. Therefore, it is necessary to investigate the relationship between land use, pollutant discharge from non-point sources, and the unit load and its contribution to total pollution loadings. The objectives of this study is to investigate the surface runoff characteristics of agricultural pollutants from non-point sources by land use in order to promote effective management of the non-point source of pollution in rural areas. The watershed under investigation consists of eleven basins(smaller than 500ha)located in Chunchon city in Kangwon Province. Flow and quality parameters, such as biochemical oxygen demand(BOD), chemical oxygen demand(COD), suspended solids(SS), total nitrogen(T-N), and total phosphorous are summarized below : 1. Slower runoff flow was observed in rural areas than areas of built-up(urban areas). Peak SS and T-P concentrations were observed prior to the flow. T-N was decreased as flow increased due to high ratio of NO₃-N. 2. The concentration graph of SS and T-P, and flow was appeared to be a clock-wise hook-shape curve. The maximum concentration was observed on the point of maximum flow. However, the concentration of T-N showed on opposite curve to the graph above.

이현동Hyun Dong Lee,안재환Jae Hwan Ahn,배철호Chul Ho Bae,김운지Woon Ji Kim

DOI: Vol.17(No.3) 313-326, 2001

In the study, unit loading and total loading on landuse types in Paldang watershed were estimated by using runoff loading of nonpoint source on nonurban(Forest/Resort and Rice/Crops area) areas and urban areas. Those areas were selected as river basins that have similar landuse types that could be represented as unit landuse types. Although it was difficult to compare directly unit loading proposed in this study with that used conventionally because of the difference of field investigation. But the results showed that unit loading on landuse types may be included in the range of conventional unit loading. The results also showed that total loading of BOD was 29,085 ton/year in Paldang watershed. The contribution ratio of South Han River in Paldang watershed was about 69%. Among total BOD loading generated of 18,097 ton/year (62%) attributed to loading from urban areas and 5,703 ton/year derived in forest/resort areas. While 5,285 ton/year was loaded in rice/crops areas. In addition, the contribution ratio of total nitrogen (T-N) in urban areas was also higher than other landuse types. On the other hand, the ratio of total phosphorous (T-P) was lower than in all areas. In case of considering total loading generated of point source, the contribution ratios of nonpoint source pollutants such as BOD. T-N, and T-P were 37.8%. 38.4% and 18.5% respectively. Among those pollutants. the contribution ratio T-N was higher than other pollutants.

윤제용Je Yong Yoon,변석종Seok Jong Byun,최유식Yu Sik Choi

DOI: Vol.17(No.3) 327-337, 2001

Disinfection is one of the most important processes in water treatment plants since it protects consumers from waterborne diseases. In Korea, chlorine which is most frequently used as a disinfectant is generally applied in two ways: prechlorination and postchlorination. Postchlorination is to supply chlorine to the influent of a clearwell. While, prechlorination is to add chlorine to rapid mixing chamber or water intake in plants. Major disinfection reaction occurs in the step of post chlorination. Therefore, frequently, prechlorination is not counted on in evaluating disinfection credit. This study was conducted to evaluate the importance of prechlorination and the existence of baffling wall in clearwell with the United States disinfection requirement(Surface Water Treatment Rule). Eight water plants were considered. Yoon`s classification(1997) was selected in classifying the prechlorination practice in water treatment plant. It was found that most of the prechlorination practices performed in water plants(three out of four types) were not important in gaining any significant disinfection credit. One prechlorination practice conducted to remove ammonia in raw water became significant in meeting the disinfection requirement. Despite the existence of baffling walls of clearwell, T_(10)/T varied considerably in the range of 0.3-0.6, indicating that the existence of baffling wall itself does not guarantee the goodness of plug flow characteristics. For some plants, T_(10)/T were lower than that of US-EPA conservative recommendation which is considered when tracer test could not be performed.

이광현Kwang Hyun Lee

DOI: Vol.17(No.3) 339-346, 2001

Total volume flux and reject coefficient with the variation of pressure and feed concentration were compared and determined using reverse osmosis plate and frame single-stage and multi-stage. Reverse osmosis process for NaCl separation was highly effective from the result of 96-98% rejection coefficient of low concentration and 93-96% of high concentration with single-stage, 95-96% rejection coefficient of low concentration and 87-95% of high concentration with multi-stage at 20㎏_f/c㎡ applied pressure and 25℃ temperature. The experimental results followed Pusch`s linear model which predicts the linear relationship between inverse of rejection coefficient and inverse of total volume flux. Degree of concentration was increased with the decrease of feed concentration and the increase of applied pressure at 25℃ temperature.

전항배Hang Bae Jun,이영주Young Ju Lee,이병두Byung Doo Lee,이종대Jong Dae Lee

DOI: Vol.17(No.3) 347-355, 2001

The effects of prechlorination on diatoms coagulation were investigated. The dominant diatom that caused filter clogging in both Han river and Daecheong lake water sources was Synedra acus. The optimum alum dose for coagulation of Synedra spp. was 1.62 ㎎-Al/L, which was 50% higher than that for optimum turbidity removal. The coagulation pH was above 6.8 and alum dose was above 1.6 ㎎-Al/L(30 ppm), that actually coincided with optimum sweep coagulation zone. As chlorine dose increased, the removal efficiency of slender type diatoms, such as Synedra spp. and Asterionella spp. remained constant or decreased a little. However, the removal efficiency of short cylinder type diatom, such as Aulacoseira spp. and Stephanodiscus spp. increased. The removal efficiencies of Synedra spp. in Daecheong lake water were 32% at chlorine dose of 1.0 ㎎-Cl₂/L, and 72% at 1.2 ㎎-Cl₂/L, respectively. which showed lower than 88% without chlorine. From the Jar-test result using Han river water, the removal efficiency of Synedra spp. was lower up to chlorine dose of 1.5 ㎎-Cl₂/L than that without chlorine, however, it increased at chlorine dose above 3.0 ㎎-Cl₂/L. With SEM`s images after 10 minutes chlorine contact, diatoms cell wall was partly destroyed. The accumulated sludge on the surface of sand filter was sticky lump of alum floc with numerous broken Synedra cells. The broken Synedra cells in sticky lump of alum floc could be formed by both long chlorine contact at low chlorine concentration and hydraulic shear stress exerted during surface and back washing.

황규대Gye Dae Whang,황선진Sun Jin Hwang,이지웅Ji Woong Lee

DOI: Vol.17(No.3) 357-367, 2001

Effects of light intensity, catalyst loading, DO, pH and initial dye concentration in treating a dye wastewater were examined, taking Acid Red 337 as a specific dye for analysis. The results of light intensity indicated no significant changes on color density and TOC removal when two or more lamps were used. 1.0g/L of TiO₂ had been added, the rate of reaction was not affected by further addition, also with increasing DO, the degradation rates increased. The maximum color and TOC removal rate was observed at pH 6.0. The effects of initial substrate concentration in the photocatalytic degradation were observed and reaction rate increased with respect to increasing concentration of dye below 0.lg/L. Color and TOC removals were explained well with first and zero-order kinetics during the photoreaction. The amount of dye adsorption of TiO₂ was influenced by a initial solution pH.

A . R . Khan , Kyung Sok Min , Yong Jun Jung

DOI: Vol.17(No.3) 369-381, 2001

In continuation of our pervious work, a foam forming species, Rhodococcus rubra, and the biological samples from actual wastewater treatment plants with the history of foaming were investigated. The hydrophobicity and foaming potential of the samples were measured. Laboratory scale control measures were studied by using an antifoaming agent (dimethyl siloxane, DMS) and a surface modifying chemical (polyethylene glycol, PEG). Although, higher hydrophobicity is implicated with stable foam formation, yet no clear-cut relationship was found in the existing studies, however further work would be needed to confirm this fact. A relationship between hydrophobicity and foaming was found which too was not strictly followed. Nostocoida-dominated foam samples were although more hydrophobic compared to Gordona (formerly Nocardia) dominated samples, yet there were marked differences in their foam stabilities, Gordona-dominated being more stable compared to Nostocoida. These studies have indicated that the stability of foams dominated by the causative species was found in the order: Rhodococcus 〉 Gordona 〉 Microthrix 〉 Nostocoida. The studies related to the control measures of foams indicated that dimethyl siloxane was more effective antifoaming agent compared to polyethylene glycol. However, the optimum dose of this antifoam required to disrupt stable foams was so high that can not be used during foaming in actual treatment plants due to higher risk of the oxygen transfer.

정팔진Paul Gene Chung,권지영Ji Young Kwon,김민정Min Jeong Kim

DOI: Vol.17(No.3) 383-394, 2001

This study was conducted to remove COD_(Cr) and nutrients by using ionized gas from non-thermal plasma generator and bromide ion as fundamental physicochemical experiment for municipal wastewater treatment. Removal efficiencies of COD_(Cr). SS were not related to bromide ion concentration. The removal efficiency of SS was 90% over under all variations of bromide ion dosage. The higher bromide ion concentration, the higher removal efficiency of total nitrogen was obtained. The optimal pH for the removal of COD_(Cr). SS and T-N was at neutral pH, but that of T-P was under the alkali conditions. The optimal ionized gas flow rate for the removal of COD_(Cr) was at 7.5L/min. that of SS and T-P was almost similar under all conditions. The removal efficiency of T-N was best at ionized gas flow 2.5L/min. Therefore the influent ionized gas flow rate to remove COD_(Cr) and nutrients was suitable at 5.0L/min. Reaction time to remove COD_(Cr) and nutrients was suitable 90 to 120 minutes. Municipal wastewater treatment using ionized gas from non-thermal plasma generator and bromide ion could be considered as an effective method for organic matter and nutrients.

신응배Eung Bai Shin,윤은경Eung Kyung Youn,이두진Doo Jin Lee,주봉현Bong Hyun Joo

DOI: Vol.17(No.3) 395-406, 2001

This study investigated the occurrence and the behavior of Denitrifying Phosphate Accumulating Organisms (DePAOs). These organisms are capable of phosphorus removal and denitrification simultaneously under anoxic conditions. The experiment was conducted in two parts: The phosphorus removal efficiency was evaluated in an anaerobic-intermittent aeration process which was designed to be an Enhanced Biological Phosphorus Removal(EBPR) process: Then, several batch tests were carried out in order to elucidate how the DePAOs responds in an anaerobic-intermittent aeration process under varying conditions. In the first part of the experiment, the results show that the overall phosphorus removal efficiency is as high as 93.3% in a continuous flow system and hence the anaerobic-intermittent aeration process is in fact an EBPR process. In the batch tests, the presence of DePAOs under different anoxic conditions was observed with a limited amount of substrate. Several batch tests were run under anoxic conditions. The test samples were spiked with different nitrate concentrations of 5, 10 and 20 ㎎NO₃^- -N/L respectively. The tests revealed that both phosphorus uptake rate and denitrification rate were proportional in the first 30 min and phosphate uptake rate was 17.78∼24.89 ㎎PO₄^(-3) -P/gVSS/d and denitrification rate was 37.33∼53.33 ㎎NO₃^- -N/gVSS/d. The rate of phosphate uptake under anoxic conditions is 15.8∼26.3% slower than under aerobic conditions. With the available organic substrate, phosphates are released in anoxic condition. Results of these experiments cleary indicate that DePAOs exist under anoxic conditions in the EBPR process and that the phosphorus release and uptake under anoxic conditions depends on the presence of available organic substrate and the concentration of nitrate.

조만재M . J . Cho,신응배E . B . Shin,김연권Y . K . Kim,배우근W . K . Bae

DOI: Vol.17(No.3) 407-415, 2001

The sewer sediment vary widely in character and composition: some are essentially inorganic, while others have significant organic content. The objective of this study is to estimate the effect of the solids and to analyse such characteristics as concentration and particle size distribution of the pollutants emanating from sediments in the combined sewer network in the study area. The concentrations observed are 3 to 25 times higher than those of dry weather conditions. The concentrations of the pollutant from the sediments are similar to those of the combined sewer overflows(CSOs) in an initial phase. The particle size observation has shown that more pollutant load is likely from the smaller particles of the sediment than from the larger particles. This is generally expected since small the particle more chances for resuspension and more organics are in the smaller particle range.

윤제용Je Yong Yoon,변석종Seok Jong Byun,조순행Soon Haing Cho

DOI: Vol.17(No.3) 417-428, 2001

In a nationwide scale, we investigated the characteristics of disinfection facilities & operation practices of the water treatment plants. Disinfection requirement based on the SWTR (Surface Water Treatment Rule) of the U.S. (0.5-log and 1-log Giardia removal) was applied in estimating the compliance, considering only postdisinfection process in clearwells. All of the water treatment plants mainly used the chlorine as a disinfectant and 43 % of those adopted predisinfection. 55∼81% of the water treatment plants failed to satisfy CT value required for the removal of 0.5-log Giardia., depending upon the retention time based on design or operation. The plants showing the high non-compliance rate were largely than 50,000 ㎥/day. One of the main reasons was that the effective residence time was not achieved due to the lack of baffle wall in clearwells. Seventy plants, which failed to comply with the CT requirement for 2-log virus inactivation, were found.