• 상하수도학회지
• /
• 제29권4호
• /
• pp.459-468
• /
• 2015

Deposits discharged through the cleaning mainly were cement mortar, bitumen paintings and rust pieces, and fragments of perforation, stones and gravels. Deposits were more removed through swabbing pig cleaning rather than air scouring cleaning on the whole. However, air scouring cleaning were not influenced by the constraint conditions such as a change in the diameter or the presence of the valve in water mains compare to swabbing pig cleaning. So, it was thought that air scouring cleaning might be more favorable to water distribution network cleaning in the future. After the cleaning, water quality including residual chlorine and turbidity also was improved because of the removal of a significant amount of the deposits. Therefore, if the cleaning is continuously and regularly implemented in water mains, it is expected that it will help to recover the reliability and to preserve the health of water quality.

• 상하수도학회지
• /
• 제33권5호
• /
• pp.353-366
• /
• 2019

This research proposes an optimal flushing operation technique in an effort to prevent secondary water pollutions and accidents in aged pipes, and to improve the cleaning effect of unidirectional flushing. Water flow directions were analyzed using EPANET 2.0, while flushing and air scouring experiments in forward and reverse directions were performed in the field. In 42 experiments, average residual chlorine concentration and turbidity were improved after cleaning compared to before cleaning. It was found that even when the same cleaning method was used, further improvement of cleaning effect was possible by applying air injection and reverse direction cleaning techniques. By means of one-way ANOVA(Analysis of variance), it was also possible to statistically verify the need of actively utilizing air injection and reverse direction cleaning. Based on correlation between turbidity and TSS, the total amount of suspended solids removal was estimated for 874 flushing operations and 194 air scouring operations. The result showed that air scouring used more discharge water than flushing by an average of $4.9m^3$ yet with larger amounts of suspended solids removal by an average of 145.9 g. The result of analysis on turbidity values from 887 flushing operations showed low cleaning effect of unidirectional flushing for the pipes with diameters over 300 mm. In addition, the turbidity values measured during cleaning showed an increasing tendency as pipe age increased. The methodology and results of this research are expected to contribute to the efficient maintenance and improvement of water quality in water distribution networks. Follow-up research involving the measurement of water quality at regular time intervals during cleaning would allow a more accurate comparison of discharge water quality characteristics and cleaning effects between different cleaning methods. To this end, it is considered necessary to develop a standardized manual that can be used in the field and to provide relevant trainings.

• 상하수도학회지
• /
• 제29권2호
• /
• pp.251-259
• /
• 2015

The main objective of this research is to study feasibility for applying metal membrane to remove particles from air scouring membrane backwash water. Also, the research was conducted to investigate the influence of polyamine coagulation on floc growth in membrane backwash water as pretreatment for removal particles. From the results of experiments for evaluating the influence of polyamine coagulation on floc growth, it was investigated that particles in the rage of $2{\sim}50{\mu}m$ grew up to $30{\sim}5,000{\mu}m$. In addition, all six metal membranes showed lower removal efficiency, which was 0.87~13.89%, in the case of no polyamine coagulant. On the other hand, in the case of injecting polyamine coagulant, those did extremely high efficiency in 56~92%. From the SEM(Scanning Electron Microscope) images of filtered wiremesh and metal foam membrane, sieve effects were predominant for liquid solid separation in wiremesh and adsorption and diffusion capture effects were predominant in metal foam membrane.

• Membrane and Water Treatment
• /
• 제15권2호
• /
• pp.59-66
• /
• 2024

This study evaluated the performance of a membrane aerated biofilm reactor (MABR) for nitrogen removal from a high-strength ammonia nitrogen-containing wastewater. The experimental setup consisted of four compartments that are sequentially anaerobic and aerobic to achieve complete nitrogen removal. The last compartment of the reactor setup contained a membrane bioreactor (MBR) to reduce sludge production in the system and to obtain a better-quality effluent. Continuous experiment over a period of 47 days showed that MABR exhibited excellent NH₄⁺-N removal efficiency (99.5%) compared to the control setup without MABR (56.5%). The final effluent NH₄⁺-N concentration obtained in the MABR was 2.99±1.56 mg/L. In contrast to NH₄⁺-N removal, comparable TOC removal values in the MABR and the control reactor (99.2% and 99.3%, respectively) showed that air supply through MABR is much more critical for denitrification than for organic removal. Further study to understand the effect of air supply rate and holding pressure on NH₄⁺-N removal in MABR revealed that an increase in both these parameters positively impacted reactor performance. These parameters are related to oxygen supply to the biofilm formed over the membrane surface, which in turn influenced NH₄⁺-N removal in MABR. Among the two different strategies to control biofilm over the membrane surface, results showed that scouring for a duration of 10 min on a weekly basis, along with mixing air supply, could be an effective method.

• 대한환경공학회지
• /
• 제30권9호
• /
• pp.948-954
• /
• 2008

침지형 MBR 공정에서 막 오염과 플럭스 감소의 주요 원인인 케이크층에 의한 저항을 저감하기 위하여 분리막 모듈의 외부에 원통형 관을 도입하였다. 도입된 원통형관 안에 노즐과 산기관을 적용하여 공기 주입량에 따른 공기와 액체의 2상흐름(Two phase flow)중 slug 흐름을 유도하여 공기 방울에 의한 막세정의 효과를 비교 분석하였다. 실험결과 동일한 유량의 공기를 공급할 경우 노즐에서 발생한 공기방울이 원통형관으로 유입되면서 효율적인 slug 흐름을 형성으로 산기관을 사용한 공급 방식보다는 막오염 방지에 효과적이었음을 알 수 있었다. 그러나 노즐로 공급되는 공기의 유량을 최적화하지 않는다면 원통형 관의 벽 부분부터 활성슬러지 혼합액이 퇴적하게 되거나 막간에 슬러지가 퇴적되어 관 내부의 급격한 막힘 현상이 발생하여 일정시간이 경과하면, 오히려 산기관보다 급격한 막오염 현상을 나타냄을 알 수 있었다. 또한 원통형 관 내부에 침지된 분리막의 면적의 최적 비율, A$_m$/A$_t$가 비율이 존재하는 것을 확인할 수 있었다. 산기관의 경우에는 A$_m$/A$_t$ 비율이 0.27일 때 최소화된 막오염이 관찰된 반면에, 노즐의 경우에는 A$_m$/A$_t$ 비율이 0.55일 때 막오염이 최소값을 보였다. 따라서 상승하는 공기방울에 의한 막오염 저감효과는 관 내부의 중공사막이 차지하고 있는 비율, A$_m$/A$_t$에 크게 의존하고 있으며, 산기관과 노즐의 경우 그 최적비율은 각각 다름을 알 수 있었다.

• 한국염색가공학회지
• /
• 제26권3호
• /
• pp.230-236
• /
• 2014

The kapok fibers which are the functional fiber materials having natural hollows are environment friendly materials the demand and interest of which are increasing. The kapok fibers are environment friendly and natural hollow fibers which are 5-8 times lighter than cottons and have excellent performances in thermo keeping property, air permeability, bulkiness and resilience. In this study, the pretreatment according to the dyeing behaviors of kapok fibers were studied. Pretreatment(scouring, bleaching) were a variety of conditions. Scouring and bleaching, images of changed surfaces and cross-sections and dyeing behaviors of the dye-o-meter according to the concentration measured in meters and compared. Although the final exhaustion ratio of the kapok fibers scoured with a high concentration recipe was almost as same as that of the kapok fibers bleached with a high concentration recipe, the initial absorption speed of the kapok fibers scoured with the high concentration recipe was faster than that of the kapok fibers bleached with the high concentration recipe.

• 상하수도학회지
• /
• 제34권4호
• /
• pp.267-276
• /
• 2020

In this study, air scouring cleaning was selected and applied among 5 small blocks (S1~S5) in domestic S cities to analyze the cleaning effect of particles causing discoloration. In order to identify the cleaning effect, 10 locations were selected as water quality investigation point, such as the stagnant or water mains ends. Removal of solids, variation of particle components, weight and concentration were analyzed. And the level of the cleanness of the surface inside water mains using endoscope was investigated. As a result of analysis, the solids discharged after cleaning were mainly sand and gravel, pieces related to pipe materials, and corrosion products. As a result of analyzing the concentrated particles of the filter before and after cleaning, it was found that the change in discoloration on the filter was large. In addition, as a result of comparing the weight and the concentration of the particles, it was found that the particles causing discoloration were significantly removed after cleaning. From the results of the endoscopy, it was confirmed that most of the precipitated and accumulated dark yellow discoloration matters inside water mains were removed through cleaning. Therefore, it seems that the particles causing discoloration in water decreased after cleaning. Therefore, it is expected that, if properly cleaning was applied, matters that cause discoloration can be removed from the water mains, and customer's complaints can also be reduced through water quality improvement.

• 상하수도학회지
• /
• 제34권2호
• /
• pp.115-125
• /
• 2020

This study was aimed to examine inorganic fouling and fouling reduction method in direct contact membrane distillation(DCMD) process. Synthetic seawater of NaCl solution with CaCO₃ and CaSO₄ was used for this purpose. It was found in this study that both CaCO₃ and CaSO₄ precipitates formed at the membrane surface. More fouling was observed with CaSO₄(anhydrite) and CaSO₄·0.5H₂O(bassanite) than CaSO₄·2H₂O(gypsum). CaCO₃ and gypsum were detected at the membrane surface when concentrates of SWRO(seawater reverse osmosis) were treated by the DCMD process, while gypsum was found with MED(multi effect distillation) concentrates. Air backwash(inside to out) was found more effective in fouling reduction than air scouring.

• 상하수도학회지
• /
• 제30권6호
• /
• pp.645-652
• /
• 2016

A membrane module including grid was designed and introduced to MBR (membrane bio-reactor) for the purpose of better control of membrane fouling. It could be anticipated that the grid enhances the shear force of fluid-air mixture into the membrane surface by even-distributing the fluid-air to the membrane module. As MLSS concentration, packing density which is expressed in the ratio of the housing and the cross-sectional area of membrane fibers ($A_m/A_t$) and air-flow rate were changed, membrane foulings were checked by monitoring fouling resistances. The total fouling resistance ($R_c+R_f$) without grid installation (i.e., control) was $2.13{\times}10^{12}m^{-1}$, whereas it was reduced to $1.69{\times}10^{12}m^{-1}$ after the grid was installed. Regardless of the grid installation, the $R_c+R_f$ increased as the packing density increased from 0.09 to 0.28, however, the increment of resistance for the grid installation was less than that of the control. Increase in the air flow rate did not always guarantee the reduction of fouling resistance, indicating that the higher air flow rate can partially de-flocculate the activated sludge flocs, which led to severer membrane fouling. Consequently, installation of grids inside the housing have brought a beneficial effect on membrane fouling and optimum air flow rate is important to keep the membrane lowering fouling.

• 대한환경공학회지
• /
• 제38권6호
• /
• pp.323-328
• /
• 2016

공기주입형 가압식 MBR 공정은 일반적인 침지식 MBR 공정과 마찬가지로 정상 운전조건에서 막 오염에 대한 제어 및 관리 기술뿐만 아니라 저유량, 저부하 조건과 같은 비정상 운전조건에서도 시설의 운영에 지장이 없도록 막 오염에 대한 제어 대책이 필요하다. $85m^3$/일 규모의 공기주입형 가압식 MBR 실증시설 운영을 통해 공기주입에 의한 분리막 오염 저감효과와 비상 시 운전조건에서 미생물에 의해 나타날 수 있는 막 오염 문제를 고찰하였다. 가압식 분리막에서 공기의 주입은 분리막 표면에서 공기방울에 의한 scouring 효과에 의해 TMP 상승 기간을 연장시키고 처리의 안정성과 높은 효율의 플럭스($40L/m^2{\cdot}h$ 이상)를 장시간 유지할 수 있는 것으로 분석되었다. 비정상 운전조건에서는 생물반응조에 PACl (53 mg/L as Al)을 주입한 경우 19%의 TMP 상승 감소효과가 있었으나 MBR 공정의 비정상 운전조건 지속에 따른 반복적인 PACl의 주입은 질산화 미생물의 활성도에 영향을 미치게 되어 궁극적으로 질소 처리효율이 악화될 수 있음을 회분식 배양 실험을 통해 확인하였다. 생물반응조에 PAC (0.6 g/L)을 주입한 경우에서는 연속운전 5일 동안 TMP 상승 없이 운전 초기 TMP인 $0.2kg/cm^2$을 유지하여 안정적으로 운전이 가능하였다. 이것은 미생물의 성장 저해조건에서 막 오염 원인물질을 유발하는 EPS와 같은 고분자 물질의 흡착에 따른 것으로 판단된다.