• 한국환경과학회지
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• 제6권3호
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• pp.219-224
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• 1997

The cloging phenomenon in the fixed film reactor Is shown when biomass growth Is excessive for long operating time. In addition, effluent water Quality gets worse because of detachment of biomass. In this study, we conducted air-backwashing to sustain biomass In reactor to complement these defects. The results of experimental are showed In the following conclusion. The detachment rate was 19.5 - 38.0% when the organic loading rate was 0.40 - 1.32 kg COD/$m^3$/day, the k - backwashing Intensity was 2 L/min(6.7 $m^3$/$m^2$/hrl and the backwashing time was 15 - 19 seconds. And the detachment rate was 32.2 - 58.6 % when the organic loading rate was 1.37 - 2.27 kg COD/$m^2$/day, the backwashing time was 1 - 12 minutes. As orgnic loading rate and backwashing time ale Increased, detachment of fixed biomass Is Increased. The detachment equation with detachment rate(DR, %), backwashing time(BWT, min), fixed biomass concentration(FB. mg/L), and organic leading rate(OLR, kg COD/ms/day) through multiple linear regession was given by the following equation: DR : 17.964 $BWT^{0.1407} FB^{0.0597} OLR^{0.1946}$

• 한국물환경학회지
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• 제22권6호
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• pp.1082-1087
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• 2006

BAC backwashing process in ozone-BAC advanced water treatment process was experimentally studied. The operation and performance of backwashing were evaluated by measuring the effects of water temperature and water input rate on the backwashing interval and duration, and also the change of the amounts of biofilm and HPC in treated water before and after backwashing. The experiments were carried out with the pilot scale test module built in a existing water treatment plant, and the following results were obtained. Longer backwashing time than that of design operating condition was needed for satisfying the suitable turbidity of washing water effluent. Depending on water temperature, 7 days of backwashing cycle was recommended for the period lower than $15^{\circ}C$, and 10 days for the period higher than $15^{\circ}C$. After backwashing, the amounts of biofilm and HPC decreased to 1/10 and 80%, respectively.

• 상하수도학회지
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• 제25권3호
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• pp.335-342
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• 2011

Secondary effluent contains particle compounds which are comprised of microorganisms that occurs membrane fouling when the water is reused. This study evaluates the characteristics of membrane fouling of secondary effluent reuse. Effects of chemical backwashing are analyzed to reduce membrane fouling by regular chemical backwashing. As the result, major membrane foulants are verified EPS materials which include protein and polysaccharide that cause biofilm cake layer on the membrane. Also, sodium hypochlorite is applied to chemical backwashing. The backwashing improves recover rate when injected chemical concentration is increased and chemical backwashing cycle is amplified. Chemical backwashing cycle affects more than injected chemical concentration yet idle time does not noticeably influence on reducing membrane fouling.

• 한국물환경학회지
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• 제22권2호
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• pp.250-257
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• 2006

The objective of this study is to propose an alternative process for the small sewage treatment plants in rural communities. A biofilter has been used for biological wastewater treatment, which is becoming the alternative to the conventional activated sludge system. The proposed process used in this study, which is packed with floating media (i.e. expanded polystylene), has advantages of biofilter system and alternative flow system and they are incorporated into one process. Pilot and bench scale studies were performed using domestic wastewater. In the results of pilot plant study, it was observed that the stable effluent water quality was achieved and it met the present effluent criteria of suspended solid (SS), organic matters, T-N and T-P. In the study for determination of the cycle of backwashing, it was observed that the cycle of backwashing depended on BOD loading rates of influents. In the BOD loading rates of $0.5kg\;BOD/m^3{\cdot}day$ and $1.0kg\;BOD/m^3{\cdot}day$, the backwashing cycle of 28 hour and 16 hour were needed, respectively. The optimum backwashing time was 120~80 seconds at the media expansion rate of 50%. In the removal of SS, organic matters, T-N and T-P, SS removal was rather achieved by physical filtration than biological mechanism and the removal of organic matters except for SS, T-N and T-P were mainly rather achieved by biological mechanism than physical filtration. In bench-scale study, the effects of recirculation rate was investigated on removal of SS, TCOD, T-N and T-P. It was observed that the recirculation made removal efficiencies of SS, TCOD, T-N and T-P increased. Especially, in T-N removal, the increase of T-N removal efficiency of 40% was observed in the reicirculation rate of 1Q compared with 0Q.

• 상하수도학회지
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• 제25권6호
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• pp.981-987
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• 2011

Biologically treated water contains a large quantity of organic matters and microorganisms which can cause various problems to membrane. The membrane fouling occurred by these reasons is hard to control by single physical cleaning. This study analyzes the efficiency of aeration with chemical backwashing and foulants removal during chemical backwashing. The cleaning efficiency improves when the chemical concentration is high and the contact time of chemical is long. Chemical backwashing with aeration shows exceptional cleaning efficiency which leads the physical cleaning is required during chemical backwashing since it forms flow inside the membrane submerged tank. From the foulants removal analysis, the particles such as turbidity and TOC removal rate increase when the aeration is applied. Dissolved matter of DOC and UV254 removal is dependent on higher chemical concentration. According to FTIR analysis, one of major foulants, the polysaccharide is controlled by the chemical backwashing with aeration condition.

• 상하수도학회지
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• 제13권3호
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• pp.61-72
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• 1999

To obtain the experimental data for design and operation of actual filtration processes, a sand filter and three kinds of dual media filters in pilot-plant scale were operated in this study. We analyzed the effect of filter medium composition on the filter performance and the effects of backwash water flow rates, length of stream line and air flow rate on the filter backwash efficiency. We also compared the efficiencies of the combined air-water backwashing and the water backwashing in dual media filters. As the backwash water flow rates or the length of stream line increased, the final turbidity of backwash water was decreased and the filtration duration time after backwash was increased. In the case of the combined air-water backwashing, the backwash water quantity needed for backwashing the dual media filters could be decreased. The total volume of filtered water for the dual media filters during filter run was over three times larger than that for the sand filter. The dual media filters could be operated at a high filtration rate of 360 m/day.

• 한국물환경학회지
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• 제37권6호
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• pp.433-441
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• 2021

The aim of this study was to optimize the ozonation and ceramic membrane integrated process for greywater reclamation. The integrated process is a repeated sequential process of filtration and backwash with the same ceramic membrane. Also, this study used ozone and oxygen gas for the backwashing process to compare backwashing efficiency. The study results revealed that the optimum filtration and backwash time for the process was 10 minutes each when comparing the filtrate flow and membrane recovery rate. The integrated process was operated at three different operating conditions with i) 10 minutes for filtration and 10 minutes for ozonation, ii) 10 minutes for filtration and 10 minute for oxygen aeration, and iii) continuous filtration without any aeration for synthetic greywater. The integrated process with ozone backwashing could produce 0.55 L/min of filtrate with an average of 18.42% permeability recovery, while the oxygen backwashing produced 0.47 L/min and 6.26%, respectively. And without any backwashing, the integrated process could produce 0.29 L/min. This shows that the ozone backwash process is capable of periodically recovering from membrane fouling. The resistance of the fouled membrane was approximately 34.4% for the process with ozone backwashing, whereas the resistance was restored by 10.8% for the process with oxygen backwashing. Despite the periodical ozone backwashing and chemical cleaning, irreversible fouling gradually increased approximately 3 to 4%. Approximately 97.6% and 15% turbidity and TOC were removed by ceramic membrane filtration, respectively. Therefore, the integrated process with ozonation and ceramic membrane filtration is a potential greywater treatment process.

• 한국물환경학회지
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• 제18권2호
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• pp.113-122
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• 2002

A bench-scale anoxic membrane bioreactor (MBR) system, consisting of a bioreactor coupled to a ceramic crossflow ultrafiltration module, was evaluated to treat a synthetic wastewater containing alkaline hydrolysis byproducts (hydrolysates) of RDX, The wastewater was formulated the same as RDX hydrolysates, and consisted of acetate, formate, formaldehyde as carbon sources and nitrite, nitrate as electron accepters. The MBR system removed 80 to 90% of these carbon sources, and approximately 90% of the stoichiometric amount of nitrate, 60% of nitrite. The reactor was also operated over a range of transmembrane pressures, temperatures, suspended solids concentration, and organic loading rate in order to maximize treatment efficiency and permeate flux. Increasing transmembrane pressure and temperature did not improve membrane flux significantly. Increasing biomass concentration in the bioreactor decreased the permeate flux significantly. The maximum volumetric organic loading rate was $0.72kg\;COD/m^3/day$, and the maximum F/M ratio was 0.50 kg N/kg MLSS/day and 1.82 kg COD/kg MLSS/day. Membrane permeate was clear and essentially free of bacteria, as indicated by heterotrophic plate count. Permeate flux ranged between 0.15 and $2.0m^3/m^2/day$ and was maintained by routine backwashing every 3 to 4 day. Backwashing with 2% NaOCl solution every fourth or fifth backwashing cycle was able to restore membrane flux to its original value.

• 한국물환경학회지
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• 제23권6호
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• pp.920-926
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• 2007

The upflow Biobead$^{(R)}$ process, one of biological aerated filters (BAF), which was used commercially, invented for removal of organic materials and nitrification. This process was modified to enhance the ability of denitrification through the induction of pre-anoxic tank. In this research, we investigated the effects of hydraulic retention time (HRT) and backwashing period in aerobic tank. The characteristics of nitrifying bacteria, which are composed of ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB), also investigated using fluorescence in situ hybridization (FISH). Even though the HRT was shortened, the efficiency of nitrification was not decreased when the organic loading rate and ammonium-nitrogen loading rate were $2.10kg/m^3/day$ and $0.25kg/m^3/day$, respectively. And then the distribution ratios of AOB and NOB showed the similar patterns. However, when the backwashing period was lengthened from 12 hours to 24 hours in aerobic 1 tank, the nitrification efficiency was decreased to 63.9% from 89.2%. The results of FISH explained that this decrease of nitrification efficiency was caused by the decrease of distribution ratio of AOB in aerobic 1 tank. The nitrification efficiencies of aerobic 1 and aerobic 2 tank were increased when the backwashing period was lengthened because of relative high distribution ratios of nitrifying bacteria.

• 한국수자원학회논문집
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• 제35권2호
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• pp.213-220
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• 2002

하수 처리수의 재이용을 위하여 표준활성슬러지법에 의한 생물학적 처리 후 최종침전지 유출수를 급속여과공정으로 처리하기 위한 Pilot Plant 실험연구가 수행되었다. 또한, 활성슬러지와 연계된 급속여과공정과 포기조 후단에 응집제를 주입하는 활성슬러지 이후 급속여과 처리하는 공정과의 비교 실험도 행해졌다. 최종침전지 유출수를 급속여과공정으로 처리한 경우 여과속도는 100m/day, 여과지속시간은 40시간 이하로 운전하는 것이 타당한 것으로 나타났으며, 여과지의 역세척 주기는 여과속도 100m/day일 때 40시간에 1회 정도가 되었다. 여과지 역세척 시 역세척 방법은 공세 1분, 공세+수세 30초, 수세 1분, 공세·수세 2분, 수세 3분, 안정 30초, 배수 10분의 순으로 행하는 것이 효과적이었으며, 수세속도는 10LPM으로 전체 여과수량의 2%정도였다. 표준활성슬러지 시스템에 의한 2차 처리수를 잡용수로 재이용 하기 위해서는 폭기조 후단에 응집제를 첨가하여 여과 공정을 후속공정으로 하는 시스템으로 유용하게 사용할 수 있을 것으로 판단된다.