정승현 Seung Hyun Jeong , 정병곤 Byung Gon Jeong

DOI: Vol.21(No.1) 1-6, 2005

The effect of ozone oxidation on biodegradability of leachate was studied. Ozone oxidation process was used as pre-treatment process to enhance performance of biological process in treating landfill leachate. Optimum ozone dosing rate and contact time in this experiment was 160 mg O₃/L hr and 45 minutes, respectively. Biodegradability was enhanced 5.08% by ozone oxidation. The ratio of ozone demand/DOC concentration was 0.049~0.091 mg O₃/mg DOC. The increase of biodegradability depending on ozone dosing rate(D) and contact time(T) can be expressed as follows ; ΔE=0.00479?D^(0.773)?T^(0.800) The biodegradation rate of DOC was increased proportionally with the increase of ozone dosing rate and contact time irrespective of landfill site age. The increase of biodegradability by ozone addition was not satisfactory. It is hard to expect significant increase in biodegradability by ozone treatment only. Thus, it is evaluated that ozone oxidation can not increase biodegradability significantly in concentrated wastewater composed of complex organic compound such as leachate.

Biodegradability, Leachate, Ozone oxidation, DOC

조민 Min Cho , 정현미 Hyen Mi Chung , 김이호 Ree Ho Kim , 손진식 Jin Sik Sohn , 박상정 Sang Jung Park , 윤제용 Je Yong Yoon

DOI: Vol.21(No.1) 7-13, 2005

With the appearance of pathogenic microorganisms, which were resistant to free chlorine, the significant attention to the necessity of powerful alternative disinfection methods such as ozone, chlorine dioxide, LTV irradiation to inactivating pathogens has been increased in water treatment. Among these alternative disinfection methods, ozone is well known as strong biocidal method and the usage of ozone is also increasing in Korea. However, in Korea, there has been no report on the quantitative study of Cryptosporidium parvum with ozone and its evaluation in advanced drinking water treatments. This study reports on the methodology for predicting the ozone inactivation of Cryptosporidium parvum by ozone disinfection in advanced drinking water treatment. The method is based on the fact that a specific inactivation level of microorganisms is achieved at a unique value of ozone exposures, independent of ozone dose and type of water, and quantitatively described by a delayed Chick-Watson model. The required values ^-CT for 2 log inactivation of Cryptosporidium parvum was 6.0 mg/L-min and 15.5 mg/L-min at 20℃ and 5℃, respectively. From this obtained Cryptosporidium parvum inactivation curves and calculated ^-CT values of advanced drinking water treatment water in Korea with FIA (Flow injection alaysis), we can predict that water treatment plant can achieve a 1.1~1.8 log inactivation and 0~0.4 log inactivation at 20℃ and 5℃, respectively. This methodology will be useful for drinking water treatment plants which intend to evaluate the disinfection efficiencies of their ozonation process without full scale test and direct experiments with Cryptosporidium parvum.

Ozone, Cryptosporidium parvum, Modified Delayed Chick-Watson model, Disinfection, CT

정동환 Dong Hwan Jeong , 박규홍 Kyoo Hong Park

DOI: Vol.21(No.1) 21-28, 2005

The training and prediction modeling using an artificial neural network was implemented to predict the turbidity of treated water as well as to estimate the optimized feed concentration of polyaluminium chloride (PACl) in a water treatment plant. The parameters used in the input layers were pH, temperature, turbidity and alkalinity, while those in output layers were PACl and turbidity of treated water. Levenberg-Marquadt method of feedforward back-propagation perceptron in the neural network toolbox of MATLAB program was used in this study. Correlation coefficients of the training data with the measured data were 0.9997 for PACl and 0.6850 for turbidity and those of the testing data with measured data were 0.9140 for PACl and 0.3828 for turbidity, when four parameters at input layer, 12-12 nodes each at both the first and the second hidden layers, and two parameters(PACl and turbidity) at output layer were used. Although the predictability of PACl was improved, compared to that of the previous studies to use the only coagulant dose as output layer, turbidity in treated water could not be predicted well. Acquisition of more data through several years obtained with the advanced on-line measuring system could make the artificial neural network useful and practical in actual water treatment plants.

Artificial neural network, Coagulant, Turbidity, Optimization, Rapid mixing

정용준 Yong Jun Jung , 권구호 Koo Ho Kwon , 민경석 Kyung Sok Min

DOI: Vol.21(No.1) 29-33, 2005

In order to recycle the waste material and to develop the thickening unit of waste activated sludge from wastewater treatment facilities, the filtration bio-reactor equipped with a shadow mask filter module was employed for this work from which the operating properties and parameters were drawn. The sludge thickening and filtration unit is made of cylindrical acryl tank(12㎝ i.d. X 58㎝ height: working volume of 6L), where the flat-sheet type of shadow mask filter module(pore size: 220~250um, opening area: 34.8~39.6%) was installed and the effluent was withdrawn from the effluent port at the lowest point of the reactor, and the filtration was performed only by the hydraulic pressure. For evaluating the operating performance of this reactor, some parameters such as the solid-liquid separation of different biomass concentrations, the water quality of filtrate, the aeration cleaning time and the cleaning effect were investigated. Depending on the MLSS concentrations, the different time to withdraw 3L of filtrate was required in which the longer filtration time was necessary for the higher MLSS concentrations caused by the thicker formation of cake layer: 40 minutes for 5,000 ㎎/L, 70 minutes for 10,000 ㎎/L and 100 minutes for 15,000 ㎎/L, where the concentrations of SS were 8.9, 6.7 and 6.5 ㎎/L, respectively. Under the same operating conditions (the intensity of aeration cleaning: 80 L/min, MLSS: 10,000 ㎎/L), the proper aeration cleaning time was revealed 30 seconds, and the stable formation of cake layer was in the range of 10 to 15 minutes. Therefore, the shadow mask considered as a waste material can be of use as a filter material for the sludge thickening system.

Shadow mask, Filter module, Waste activated sludge, Thickening, Solid-Liquid separation

배진연 Jin Yeon Bae , 민경석 Kyung Sok Min

DOI: Vol.21(No.1) 34-39, 2005

The performance of elutriated acid fermentation with slurry-type piggery waste was investigated, especially to evaluate the effects of temperature and pre-treatment. In the first phase, the acid elutriation reactor with piggery waste after centrifugation operated at both mesophilic and thermophilic conditions to evaluate the effect of temperature. Solubilization yield(gVFAs/gSCOD_(prod.)) and acidification rate(gVFAs/gSCOD_(prod.)) in the thermophilic digestion were 0.45 and 0.55, which were higher than those of the mesophilic digestion, 0.25 and 0.45. In addition, the acid elutriation reactor at thermophilic temperature is more effective in removing e-coli. In the second phase, the acid elutriation reactor was fed with piggery waste before centrifugation. With piggery wastes before centrifugation, the solubilization yield and the acidificaton rate were 0.40 and 0.80, respectively, which were higher than the rates using piggery waste after centrifugation at both mesophilic and thermophilic conditions. The higher sludge volume reduction of 80% benefits sludge management. Furthermore, economical advantages can be achieved by removing the pre-treatment process, such as centrifugation. Consequently, the treatment with piggery waste before centrifugation proved to be effective. Also, the optimum temperature condition was estimated at mesophilic or thermophilic conditions, considering solubilization yields and acidification rates, though the system should be heated.

Solubilization, Acidification, Piggery waste, Temperature, Pre-treatment

유명진 Myong Jin Yu , 김현철 Hyun Chul Kim , 류성호 Seong Ho Ryu

DOI: Vol.21(No.1) 40-45, 2005

Sedimentation is one of the most common and important units in conventional water treatment plant. Structure such as various baffle walls and inclined plate settler may be obstacles to the horizontal flow when it is poorly designed. Therefore, the effects of these structures on characteristics of hydraulic flow must be evaluated to improve the settling efficiency of the floc. The hydraulic characteristic of the two sedimentations at Y water treatment plant (YWTP), which have different deflector baffles inside the settling basin, were investigated by tracer (fluoride) test. The inclined plate settler installed inside settling basin caused an undesirable impact on horizontal flow and produced dead zone. Solid baffle wall under the plate settler could help to minimize the formation of density currents and flow short circuiting. NalE used as a tracer was recovered more than 90% at investigated all basins. Morill index (t_(90)/t_10)), Modal index (t_p/T-HRT) and short-circuiting index ([M-HRT-t_p]/M-HRT) were determined from tracer test results performed at YWTP. Those indices ranged 2.95~3.02, 0.40~0.53 and 0.32~0.46, respectively.

Inclined plate settler, Deflector baffle, Tracer test, Morill index, Modal index, Short-circuiting index

박영식 Young Seek Park

DOI: Vol.21(No.1) 46-51, 2005

The photocatalytic oxidation of Rhodamine B (RhB) was studied using immobilized TiO₂ and rotating disk photocatalytic reactor. Immobilized TiO₂ onto the surface of the aluminum plate was employed as the photocatalyst and two 20 W germicidal lamps and two 20 W UV-BLB lamps were used as the light source and the reactor volume was 1.0 L. The effects of parameters such as the number of rotating disk, rpm of rotating disk, the number of coating, H2O2 and photo-Fenton amounts, and the concentrations of anions and cations (NO₃^- , SO₄^(2-), C1^-, Ca^(2+), Zn^(2+), Na^+) were examined.

UV/TiO2, Dye, Rotating disk, Rpm

이현동 H. D. Lee , 배철호 C. H. Bae , 김정현 J. H. Kim , 황재운 J. W. Hwang , 홍성호 S. H. Hong

DOI: Vol.21(No.1) 52-58, 2005

The assessment on characteristics of hydraulic behavior and water quality variations of underground reservoirs of buildings were studied. Firstly, it was thought that underground reservoir capacities(m³) of buildings should be not determinated by the uniform and same methods but be estimated on the basis of the dwelling areas on dominated households and their residential characteristics, because these characteristics influence significantly on actual water usages and patterns of buildings. Secondly, it was likely that the average reduction rate of residual chlorine in underground reservoirs were affected from the their capacities, because the average reduction rate of residual chlorine in underground reservoirs under 1,000m³ was 43 percent, on the other hand, that rate of underground reservoirs over 1,000m³ was 60 percent. Thirdly, through the field investigation, the retention time of drinking water in underground reservoirs were in the range from 0.3 day to 3.9 day. In addition to, the average reduction rate of residual chlorine were depended largely on the retention time of drinking water. When the retention time was under 24 hours, the average reduction rate of residual chlorine was 45 percent, and in case of over 24 hours, was 49 percent. Fourth, water level in underground reservoirs was averagely varied in the range from 0.1 m to 2.65 m at the height of underground reservoirs. If considered actual height of underground reservoirs, 37.6 percent of the height of underground reservoirs was only used. Consequently, the frequency of the inflow and outflow of drinking water in underground reservoir were very increased, and had an effect on the reduction of residual chlorine. Lastly, the investigations on hydraulic structure characteristics of underground reservoirs inside showed the locations of inflow and outflow of drinking water almost were in the opposite direction. And some buildings had several baffles in the middle. Nevertheless, their installations had no beneficial for the improvement of water quality.

Underground reservoir, Hydraulic behavior, Residual chlorine, Retention time

김응호 Eung Ho Kim , 임수빈 Soo Bin Yim , 정호찬 Ho Chan Jung , 이억재 Eok Jae Lee , 조진규 Jin Kyu Cho

DOI: Vol.21(No.1) 59-65, 2005

A phosphate recovery system from artificial wastewater was developed using a completely mixed phosphorus crystallization reactor, in which powdered converter slag was used as a seeding crystal. In preliminary test, the optimal pH range for meta-stable hydroxyapatite crystallization for high phosphorus concentration was observed to be 6.0 to 7.0, which was different from the conventionally known pH range (8.0~9.5) for effective crystallization in relatively low phosphorus concentration less than 5 ㎎/L. The average phosphorus removal efficiency in a lab-scaled completely mixed crystallization system for artificial wastewater with about 100 ㎎/L of average PO₄-P concentration was shown to be 60.9% for 40 days of lapsed time. XRD analysis exhibited that crystalline of hydroxyapatite formed on the surface of seed crystal, which was also observed in SEM analysis. In EDS mapping analysis, composition mole ratio (=Ca/P) of the crystalline was found to be 1.78, indicating the crystalline on the surface of seed crystal is likely to be hydroxyapatite. Particle size distribution analysis showed that average size of seed crystal increased from 28μm up to 50μm, suggesting that phosphorus recycling from wastewater with high phosphorus concentration can be successfully obtained by using the phosphorus crystallization recovery system.

Powdered converter slag, Phosphate recovery, Phosphorus crystallization process, Seeding material, Hydroxyapatite crystallization

신인수 In Soo Shin , 최봉종 Bong Jong Choi , 이승목 Seung Mok Lee , 양재규 Jae Kyu Yang

DOI: Vol.21(No.1) 66-72, 2005

Effect of the pH, molar ratio of Cu(Ⅱ)/EDTA, concentration of Cu(Ⅱ)-EDTA and ionic strength on the photocatalytic oxidation(PCO) of Cu(Ⅱ)-EDTA in solar light was studied in this work. Experimental results in this work were compared with previous results obtained with UV-lamp. In the kinetics, Cu(Ⅱ)-EDTA decomposition was favorable below neutral pH. The removal of Cu(Ⅱ) and DOC was favorable as TiO₂ dosage increased. The initial rate for the decomplexation of Cu(Ⅱ)-EDTA linearly increased as the concentration of Cu(Ⅱ)-EDTA increased. The removal of Cu(Ⅱ) and DOC was not much affected by variation of ionic strength with NaC1O₄ as a background ion while much reduction was observed in the presence of background ions having higher formal charges. The removal trend of Cu(Ⅱ) and DOC with variation of ionic strength and concentration of Cu(Ⅱ)-EDTA in solar light was similar with that in UV light. Variation of the molar ratio of Cu(Ⅱ)/EDTA showed a negligible effect on the removal of both Cu(Ⅱ) and DOC. However, removal of both Cu(Ⅱ) and DOC was two-times greater than that previous results obtained with UV light.

Cu(2)-EDTA, Solar Light intensity, UV, Ionic strength, Photocatalysis

김응호 Eung Ho Kim , 조연제 Yeon Je Cho , 박성주 Seong Joo Park , 신광수 Kwang Soo Shin , 임수빈 Soo Bin Yim , 박현주 Hyun Ju Park

DOI: Vol.21(No.1) 73-78, 2005

This study was performed to examine the disinfection capability of a Rotating Activated Bacillus Contactor (RABC) system, in which the predominant species, Bacillus sp. was expected to have a removal or inactivation effect of total coliforms. In a settling test with mixtures of E. coli and Bacillus sp., a high removal of E. coli was observed at 20~40℃, while insignificant removal at 10℃. In a batch test, a 4.5% addition of Bacillus sp. to activated sludge considerably enhanced the removal effect of total coliforms, indicating Bacillus sp. played an important role in improving the settlability of the sludge and coliforms. In a pilot scale RABC system, the concentration of total colifroms reduced remarkably in the settling tank, suggesting that total coliforms in the RABC process were eliminated through coagulation and precipitation, probably due to extracellular polymeric substance (EPS) of Bacillus sp. The fraction of Bacillus sp. in the total cell count in the RABC process was in the range of 4.5%~6.3%. The majority (75%) of the Bacillus sp. in the RABC process was Bacillus subtilis which is known to enhance coagulation and precipitation by producing EPS. Hence, an adoption of a RABC process might be able to eliminate the disinfection unit process from a wastewater treatment system.

Rotating Activated Bacillus Contactor, RABC, process, Total coliform, Bacillus sp., Extracellular polymeric substance, Disinfection unit process

박배경 Bae Kyung Park , 박석순 Seok Soon Park

DOI: Vol.21(No.1) 79-83, 2005

Foraging behaviour of false dace, Pseudorasbora parva, was investigated in water flowing at various velocities with the existence of a cavity for rest. The pursuit comprised three succeeding processes such as, approaching, chasing and attacking. Angles between the fish body and the water flow direction and swimming speeds increased in the latter stages of approaching, chasing and attacking. All pursuit angles, swimming speeds and distances increased with flow velocity and peaked at the flow velocity of 7 ㎝/sec. At higher velocities, however, the fish avoided the use of much energy against the large drag force. The probability of capture and the feeding rate steadily decreased with increasing flow velocity. Under the fast flow, the fish adjusted their swimming speed to get the optimum velocity relative to the flowing water for the energetic budget. Fish spent more time in the cavity as flow velocity increased to avoid the energy expenditure necessitated by the high velocity.

Aquatic ecosystem, Flowing water environment, Focal velocity, Pseudorasbora parva, Saltatory searching

이승목 Seung Mok Lee

DOI: Vol.21(No.1) 84-91, 2005

TiO₂-catalyst suspensions work efficiently in Photocatalytic oxidation (PCO) for wastewater treatment. Nevertheless, once photocatalysis is completed, separation of the catalyst from solution becomes the main problem. The PCO of Cu(Ⅱ)-EDTA was studied to determine the reusability of the titanium dioxide catalyst. Aqueous solutions of 10^(-4)M Cu(Ⅱ)-EDTA were treated using illuminated TiO₂ particles at pH 6 in a circulating reactor. TiO₂ was reused in PCO system for treatment or Cu(Ⅱ)-EDTA comparing two procedures: reuse of water and TiO₂ and reuse of the entire suspension after PCO of Cu(Ⅱ)-EDTA. The results are as follows; (ⅰ) Photocatalytic efficiency worsens with successive runs when catalyst and water are reused without separation and filtration, whereas, when TiO₂ is separated from water, the reused TiO₂ is not deactivated. (ⅱ) The TiO₂ mean recovery (%) with reused TiO₂ was 86.4%(1.73g/L). Although the mean initial degradation rate of Cu(Ⅱ)-EDTA and Cu(Ⅱ) was lower than that using fresh TiO₂, there was no significant change in the rate during the course of the three-trial experiment. It is suggested that Cu(Ⅱ)-EDTA could be effectively treated using an recycling procedure of PCO and catalyst recovery. (ⅲ) However, without TiO₂ separation, the loss of efficiency of the PCO in the use of water and TiO₂ due to Cu(Ⅱ), DOC remained from previous degradation and Cu(Ⅱ)-EDTA added to the same suspension was observed after 2 trials, and resulted in the inhibition of the Cu(Ⅱ)-EDTA, Cu(Ⅱ) and DOC destruction.

Cu(2)-EDTA, Photocatalytic oxidation, PCO, TiO2, Reuse, Recovery

최철호 Chul Ho Choi , 이승목 Seung Mok Lee , 윤종화 Jong Hwa Yoon , 황필기 Pil Gi Hwang , 김정용 Jung Yong Kim

DOI: Vol.21(No.1) 92-98, 2005

Nutrients removal performance of a contact oxidation reactor covered with soil was investigated when basalt rubble was used as a contact medium under various operating conditions. The objective of the experiment was to determine the effectiveness of the system by measuring the removal efficiencies of nutrients from a technical and economical viewpoint. Under the ranges of HRT(20 and 40 hrs) in the experiment, the removal rates of organic matter were as high as 97.5% by showing an effluent BOD_5 of less than 10 ㎎/L. The test of nitrogen removal when the turf was planted on the top soil showed that the average removal rate increased as much as 25% as compared to that without planting. It was suggested that the construction and maintenance cost could be reduced over 20% when the HRT of the system was decreased from 72 to 40 hrs.

Contact oxidation system covered with soil, Contact media, Turf, Basalt rubble, Hydraulic retention time, HRT