윤선주Sun Ju Yoon,오경두Kyung Doo Oh,이태호Tae Ho Lee,김현용Hyun Yong Kim,이홍근Hong Keun Lee

DOI: Vol.15(No.2) 141-151, 1999

The objective of this study is to develop the expert systems for helping field workers to determine effective drinking-water treatments and management strategies of small water supply system. The results of this study are summarized as follows: 1. Developed system is composed of 4 modules; 1) calculation of planning water volume, 2) determination of suitable treatment methods for clean drinking-water, 3) causes and countermeasures for electric accidents and pump disorders, 4) management for safe water. 2. Graphic user interface is developed with Microsoft Visual Basic program. 3. Knowledge base modules are expressed with smart elements by using production rule, and developed prototype system is operated successfully. So, this system win help many field workers and will be good advisor to non-experts so as to operate lots of small water supply systems efficiently. 4. This expert system will perform more accurate inference, if rules in the knowledge base are modified and why and how functions to give confidence to users are developed.

김순래Soon Rae Kim,김성석Sung Seok Kim,최규열Gyu Yeol Choi,정의호Eui Ho Jeong

DOI: Vol.15(No.2) 153-159, 1999

To establish the efficient removal scheme of anion surfactants from car washing wastewater, the optimal conditions of aeration rate, duration of aeration and temperature were estimated. Anion surfactants in car washing wastewater was removed about 60% by the simple aeration(1.6ℓair/min for 7ℓ of wastewater), and the higher aeration rate was required at low temperature to get the similar removal rate. Considering the in situ temperature(10∼20℃), the aeration must be kept for 5∼6 hrs. Combining the biological method to the conventional method, the high removal rate more than 80% of anion surfactants could be achieved.

강호Ho Kang,왕창근Chang Keun Wang,이진흥Jin Hong Lee,진창숙Chang Suk Jin,김은희Eun Hee Kim

DOI: Vol.15(No.2) 161-173, 1999

Biodegradability test for several hazardous chemicals found in the watershed of Daechung reservoir was investigated by using TOC-HANDAI method that is a combined technology of River Die-away test and HANDAI method. Aniline and phenol were easily mineralized by natural water microcosm and their initial degradation rates of samples from Daechung reservoir were much faster than those from the main streams of Kum rivers. This was probably due to the numbers and the activities of participated microorganisms during their respective degradation. It is obvious that the metabolic pathways of both chemicals were different, showing that phenol started degradation immediately without any adaptation period. Bispenol A(BPA) at each sampling points was appeared to be mineralized 68∼89% of initial TOC concentration by natural water microcosm. BPA seems more recalcitrant against biodegradation than simple aromatic compounds such as aniline and phenol in natural water environments. Moreover, the remaining TOC components in BPA biodegradation considered to be refractory metabolites of BPA. Consequently it is likely that BPA showed semi-recalcitrant while aniline and phenol were biodegradable compounds in the watershed of Daechung reservoir.

한무영Moo Young Han,독고석Seok Dockko,박중현Chung Hyun Park

DOI: Vol.15(No.2) 175-184, 1999

Biodegradability test for several hazardous chemicals found in the watershed of Daechung reservoir was investigated by using TOC-HANDAI method that is a combined technology of River Die-away test and HANDAI method. Aniline and phenol were easily mineralized by natural water microcosm and their initial degradation rates of samples from Daechung reservoir were much faster than those from the main streams of Kum rivers. This was probably due to the numbers and the activities of participated microorganisms during their respective degradation. It is obvious that the metabolic pathways of both chemicals were different, showing that phenol started degradation immediately without any adaptation period. Bispenol A(BPA) at each sampling points was appeared to be mineralized 68∼89% of initial TOC concentration by natural water microcosm. BPA seems more recalcitrant against biodegradation than simple aromatic compounds such as aniline and phenol in natural water environments. Moreover, the remaining TOC components in BPA biodegradation considered to be refractory metabolites of BPA. Consequently it is likely that BPA showed semi-recalcitrant while aniline and phenol were biodegradable compounds in the watershed of Daechung reservoir.

독고석Seok Dockko,한무영Moo Young Han,박중현Chung Hyun Park,남기진Ki Jin Nam

DOI: Vol.15(No.2) 185-192, 1999

In this research, the theoretical modeling of DAF which was obtained by trajectory analysis has been verified. Especially, the effects of electrostatic nature and particle size of bubble and particle (floc) was focused. To measure the electrostatic nature of bubble, zeta potential measuring setup was made in a well controlled laboratory. The effects of several operational parameters in DAF process are investigated on a system composed of batch DAF reactor, microscope and video system. The effect of pH on the removal efficiency of DAF is presented. The effect of mixing time is presented. The effect of zeta potential of floc and bubbles with the addition of coagulant is presented. It is found that all the phenomena can be explained primarily from the electrostatic nature of bubble and particle and secondarily from the effect of particle size. The findings from this research are compared and verified with the results of DAF modeling by α_(bp). This research will be helpful to understand and explain the process better and possibly can be used to modify and improve the DAF process.

윤조희Cho Hee Yoon,이상훈Sang Hoon Lee

DOI: Vol.15(No.2) 193-201, 1999

In this study, the characteristics of organics and nitrogen removal from wastewater with various HRT in fixed biofilm system using anaerobic/anoxic/oxic (A₂/O) process was investigated. Two types of laboratory experimental systems packed with different media, which composed of polyvinylidene chloride fiber and ceramic ball, were used. These systems were operated with HRT of 8hrs through 48hrs at C/N ratio of 4, internal recycle of 200% and 20±2℃. The results were obtained as follows; TOC removal efficiency was showed over 90% of TOC with internal recycle in both reactors while HRT was 8hrs through 24hrs. And the maximum removal efficiency(93%) was obtained at HRT of 24hrs. The removal efficiencies for NH₄-N were 35.1% (reactor1) and 44.9% (reactor2) at HRT of 8hrs and 98.5% (reactor1) and 97.1 (reactor2) when HRT was over 12hrs. The removal efficiencies for TIN were 39.5% (reactor1) and 46.7% (reactor2) at HRT of 8hrs. In both reactors removed 75% of TIN with internal recycle while HRT was 12hrs through 24hrs. On the other hand, the reactor1 and reactor2 removed 46.8% and 51.4% of TIN without recycle at HRT of 48hrs. Of total removed TIN, 44.2% (reactor1) and 54.8% (reactor2) were consisted of denitrification in an oxic basin at the HRT of 12hrs through 24hrs.

윤주환Zu Whan Yun,김경희Kyung Hoe Kim

DOI: Vol.15(No.2) 203-215, 1999

A laboratory-scale 2-stage denitrifying filter plant was operated under the various dosage of methanol as an external carbon source. The methanol dosages were computed on the basis of emperical equation developed by McCarty et al. The imbalance of carbon usage for denitrification was noticed when the methanol supplied for the nitrate reduction for both 50% and 100%. Although it was primarily reasoned that the leaching of organics from the biofilm and solids trapped between the sand media, a further study is needed to confirm the findings. The organic contents in the effluent of 2-stage denitrifying filter operated with an excess methanol dosage was not as high as up to that of single stage configurations. It was probably due to the biological removal of excess organics in the second stage filter. The finding suggests that the 2-stage configuration could reduce the possible `COD-leak problem` which is an important consideration for design of the post-denitrification processes. The operating temperature has a pronounce impact on denitrification process. The nitrate reduction significantly decreased at 10℃ of operating temperature. It was also observed that the nitrous oxide(N₂O) gas was included in the denitrified gas under the normal operating conditions. The result suggested that the various nitrate reduction pathways could exist in the denitrifying filter in addition to the conventional denitrification pathway.

허남효Nam Hyo Heo,최광수Kwang Soo Choi,김창원Chang Won Kim,김병군Byong Goon Kim,강호Ho Kang

DOI: Vol.15(No.2) 217-227, 1999

Recently, various control strategies for the activated sludge process based on respirometry were introduced by the IAWQ Task Group on Respirometry in its Scientific and Technical Report (STR). Respirometry is the measurement of the oxygen consumption rate of activated sludge under well defined experimental conditions. Because oxygen consumption is directly associated with both growth and substrate removal, respirometry is a useful technique for controlling and operating of the activated sludge process. This paper is based on two different respiration rate, which can be measurement with the substrate-limiting and excess of substrate condition. The actual respiration rate of activated sludge is dependent on the substrate concentration and reflects the loading of the plant, and the maximum respiration rate is independent of the substrate concentration. Literature shows that measuring actual respiration rate and maximum respiration rate can be useful for loading control, toxicity dection, estimation of active biomass on the activated sludge. In this study, actual and maximum specific respiration rate were used as control parameter for stable sludge loading rate and detection of toxicity, respectively.

김종민Jong Min Kim,임도영Do Young Lim,고광백Kwang Baik Ko,정연규Youn Kyoo Choung

DOI: Vol.15(No.2) 229-239, 1999

Effects of various organic carbon sources on biological nutrient removal were investigated. Acclimated activated sludges were supplied in synthetic wastewater in a series of lab-scale sequencing batch reactors, which were operated in the 2 hour anoxic and 4 hour aerobic mode during a 12 hour period. The results show that phosphorus release and uptake occurred both in a culture fed with glucose and in one fed with sodium acetate. However, the rate of phosphorus release and uptake was higher in the culture fed with sodium acetate than in the culture fed with glucose. Variation of organic carbon sources in influent did not inhibit nitrification in any rector. Relatively significant denitrification was observed in all reactors in the beginning of aerobic phase since DO concentrations were rather low and organic content was relatively high during this period. As G bacteria might outnumber Poly-P bacteria in a culture fed with a mixture of glucose and sodium acetate. the rate of phosphorus release and uptake was lower in the culture than in a culture fed with sodium acetate only.

한지용Ji Yong Han,허목Mock Huh

DOI: Vol.15(No.2) 241-255, 1999

This study was performed to evaluate the effects of the ratio of aeration/mixing time, the fill tires and the repeat cycle of aeration/mixing, for the removal of organics, nitrogen and phosphorus in sewage by sequencing batch reactor process. The results of this study were summarized as follows; (1) As the ratio of aeration/mixing time was lower and the fill time was longer, the ORP showed a greater potential difference and the pH values was maintained in a more stable state on microbes because the consumption rate of alkalinity was deceased. (2) The organics removal efficiency was increased with increasing the ratio of aeration/mixing time, the fill time and the repeat cycle of aeration/mixing, and it was the highest when the repeat cycle of aeration/mixing was 6 times/cycle. (3) The TSS removal efficiency exceeded 93% and it was not affected by the ratio of aeration/mixing time, the fill time and the repeat cycle of aeration/mixing. (4) The T-N removal efficiency was increased as the ratio of aeration/mixing time was lower and the fill time was longer. Especially, the T-N removal efficiency was the highest when the repeat cycle of aeration/mixing was 6 times/cycle. (5) The T-P removal efficiency showed a great difference in each operating condition, it was influenced greatly by the ratio of aeration/mixing time and the repeat cycle of aeration/mixing among the operating conditions, and it was the highest in the run which the denitrification rate was the highest.

최승희Seung Hee Choe,김지형Jee Hyeong Khim,장윤영Yoon Young Chang,황경엽Kyung Yub Hwang

DOI: Vol.15(No.2) 257-264, 1999

For environmental remediation of a contaminated groundwater plume the use of zero-valent metal represents one of the latest innovative technologies. In this paper, the kinetics of denitrification by zero-valent iron (Fe°) has been studied for an analysis of factors effecting contaminant degradation rates. Batch studies demonstrated that synthesized nanoscale iron granular, characterized by high surface area to mass ratios(31.4㎡/g) and high reactivities can quickly remove nitrate from nitrate-polluted water within minutes. Compared the ability of nanoscale Fe° with that of microscale Fe° to destruct reductively nitrate at room temperature (23℃), the reactivity of Fe° with nitrate depends on its specific surface area and shows higher observed reaction rate constant k_(obs) with nanoscale iron powder. The reductive reaction of nitrate with nanoscale Fe° indicated that the degradation of nitrate appeared to be pseudo first-order with respect to nitrate concentration, with the observed reaction rate constant k_(obs) (0.1463 min^(-1)) appearing to be directly proportional to the specific surface area to volume ratio. The minimal effects of muting rate (rpm) on nitrate reduction rates suggest that the observed reaction rates were controlled by mass transfer of the nitrate to the metal surface in low mixing intensity.

이희자Hee Ja Lee,안승구Seoung Koo Ahn

DOI: Vol.15(No.2) 265-276, 1999

In this study, methane-oxidizing bacteria were isolated from a landfill cover soil and cultured in inorganic nutrient medium with methane as a carbon and energy source. The methane oxidation rate on O₂/CH₄ ratio and other important factors affecting the growth of methanotrophs were evaluated by batch cultures. Also, the possibility of aerobic denitrification by mixed culture of methanotrophs, NH₃ and NO₃^- removal rate on nitrogen concentration were investigated. The results of the study showed that methane-oxidizing bacteria were short rod and gram negative, and formed pink colonies. The settleability of the sludge was very good When O₂/CH₄ volume ratio were 1.8, 2.2 and 5.4, methane was oxidized in a first-order reaction with respect to the concentration of methane and rate coefficients of the reactions were 0.7, 0.9 and 1.1, methane was oxidized in a second-order reaction. Methanotrophs could tolerate pH fluctuations of influent, and the maximum denitrification rate and cell yield at pH 7.5 was 16.4㎎ NO₃^- -N/g VSS·hr and 12.2㎏ VSS/㎏ NO₃^- -N, respectively. The maximum specific growth rate of the methanotrophs was 0.3/day at 30℃, and the maximum denitrification rate was 35㎎ NO₃^- -N/g VSS·hr at 35℃. At a Cu variation of 0-30ppm, the growth rate of methanotrophs was highest at 1ppm. At an O₂/CH₄ volume ratio of 1.3, at which the growth rate was highest, and the maximum denitrification rate was 45㎎ NO₃^- -N/g VSS·hr. In the aerobic condition with DO concentration of 1.2㎎/L, denitrification rate was increased in porportion to nitrate concentration, Vmax and Ks were 3.5㎎ NO₃^- -N/g VSS·hr, 145㎎ NO₃-N/L, respectively.

김응호Eung Ho Kim,조진규Jin Kyu Cho,조태룡Tai Ryong Cho

DOI: Vol.15(No.2) 277-282, 1999

The objective of this study was to evaluate the applicability of solidified sewage sludge by converter slag as daily/intermediate cover materials in the viewpoint of geotechnical characteristics. For this purpose, some geotechnical properties such as specific gravity, grain size distribution, compaction characteristics, unconfined compressive strength and permeability were experimentally determined The results showed that solidified digested sewage sludge was suitable for daily/intermediate cover materials in that viewpoint.

Sang Ho Lee,Young Ran Kim,Myung Jin Yu

DOI: Vol.15(No.2) 283-289, 1999

The removal efficiencies of volatile organic chemicals, trichloroethylene (TCE), tetrachloroethylene (PCE) and 1,1,1-trichloroethane (TCA) of the aqueous phase in the simulated systems were compared by using granular activated carbon (GAC) columns and biological activated carbon (BAC) columns. Pre-oxidation systems used in this research were advanced oxidation processes (AOPs) by ozone alone and combination of ozone and hydrogen peroxide. The microbial consortium for this study were selected from the contaminated soil by the above three VOCs and identified as Pseudomonas aeroginosa, Pseudomonas maltophilia, Acinetobacter calcoceticus and Bacillus sphaericus. Removal efficiencies of VOCs were more enhanced in the BAC systems than in the GAC systems. Also, VOCs pre-oxidized by H₂O₂-O₃ were more removed than those pretreated by ozone alone.

정팔진Paul Gene Chung,원찬희Chan Hee Won,김명순Myoung Soon Kim,김보국Bo Guk Kim,최정윤Jeoung Youn Choi

DOI: Vol.15(No.2) 291-299, 1999

Biological fixation was studied to reduce the CO₂ emitted from thermal power plant. Euglena glacilis was used as a photosynthetic microorganism. In culture experiments, we investigated characteristics of Euglena growth and CO₂ fixation for the various conditions : influent CO₂ concentration, light intensity, pH, temperature, nitrogen and phosphorous concentration. Immobilized Euglena was also used to fix CO₂. The maximum growth of Euglena was obtained from the influent CO₂ concentration 5∼10%. But the growth of Euglena was partly inhibited above 10% CO₂. Therefore, it was suggested that Euglena glacilis was one of the suitable strain to fix CO₂ emitted from a LNG thermal power plant. Optimal light intensity for the growth of Euglena was considered between 4 and 7 klux. It required 19.28㎎ - N and 8.69㎎ - P to get lg of Euglena biomass. The maximum biological CO₂ fixation was obtained at pH 6 and 27℃. Immobilized Euglena had not the capability of fixing CO₂.