• Membrane Journal
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• v.16 no.3
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• pp.188-195
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• 2006

The purpose of this study was to investigate the effect of an intermittent aeration mode to reduce the membrane fouling in a submerged membrane process using the specifically devised module (YEF 750D-2). The fluid velocity on the module increased with increasing the supplied air volume, and decreased with the increment of MLSS in the biological reactor. The reduction rate of the fluid velocity was found to be $3\times10^{-4}m{\cdot}min/sec{\cdot}L$ per 1,000 mg MLSS/L increased. In the operation of the intermittent aeration, the intermitted stop of the aeration provoked the formation of a cake layer on the gel layer which was previously formed during the aeration, resulting in the highly increased TMP level. However, the TMP level could be significantly lowered by the subsequent backwashing and aeration that effectively removed the cake along with the gel layer on the membrane surface. In this study, the optimum condition for the intermittent aeration was determined to be aeration for 20 sec and pause for 20 sec.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.2
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• pp.161-170
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• 2014

It is essential to decrease energy consumption and excess sludge to economically operate sewage treatment plant. This becomes more important along with a ban on sea dumping and exhaustion of resource. Therefore, many researchers have been study on energy consumption reduction and strategies for minimization of excess sludge production from the activated sludge process. The aeration cost account for a high proportion of maintenance cost because sufficient air is necessary to keep nitrifying bacteria activity of which the oxygen affinity is inferior to that of heterotrophic bacteria. Also, additional costs are incurred to stabilize excess sludge and decrease the volume of sludge. There were anoxic, aerobic, membrane, deairation and concentration zone in this MBR process. Continuous aeration was provided to prevent membrane fouling in membrane zone and intermittent aeration was provided in aerobic zone through ammonia sensor. So, there was the minimum oxygen to remove $NH_4-N$ below limited quantity that could be eliminated in membrane zone. As the result of this control, energy consumption of aeration system declined by between 10.4 % and 19.1 %. Besides, we could maintain high MLSS concentration in concentration zone and this induced the microorganisms to be in starved condition. Consequentially, the amount of excess sludge decrease by about 15 %.

• Membrane Journal
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• v.19 no.4
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• pp.285-290
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• 2009

The permeation experiments were carried out for the nominal pore size $0.1\;{\mu}m$ and 5 mm inner diameter microfiltration tubular membrane equipped with self-designed discharging rod in order to determine the effect of fouling reduction. Dioctyl tinoxide (DOTO) latex particle was used to prepare up to 0.5 wt% concentration of feed solution, and the experiments were operated within 1.6 bar. The permeation flux effect on the discharged rod was measured as a result of flux comparison between the cases of equipped and non-equipped discharge rod modules for every experiment. The permeation flux for the case using the discharged rod was enhanced to 20% at 1.6 bar operating pressure. The improvement on permeation flux for using the discharged rod was greater as the concentration of feed increased, and reached up to 43% under 0.5 wt% concentration of feed solution.

• Journal of Korean Society of Environmental Engineers
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• v.30 no.11
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• pp.1139-1145
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• 2008

The objectives of this research are to investigate the mechanism of coagulation affecting UF and find out the optimum conditions of the combined of coagulation with UF membrane filtration for NOM removal. During the mixing period, substantial changes in particle size distribution occurred under rapid and slow mixing condition due to the simultaneous formation of microflocs and NOM precipitates. Therefore, combined pretreatment using coagulation (both rapid mixing and slow mixing) improved dissolved removal efficiency. Also, for combined coagulation to membrane process, flux reduction rate showed lower than only UF process. The rate of flux decline for the hydrophobic membrane was considerably greater than for the hydrophilic membrane. Applying coagulation process before membrane filtration showed not only reducing membrane fouling, but also improving the removal of dissolved organic materials that might otherwise not be removed by the membrane.

• Membrane Journal
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• v.32 no.4
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• pp.209-217
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• 2022

Ion exchange membrane (IEM) is an important class of membrane applied in batteries, fuel cells, chloride-alkali processes, etc to separate various mono and multivalent ions. The membrane process is based on the electrically driven force, green separation method, which is an emerging area in desalination of seawater and water treatment. Electrodialysis (ED) is a technique in which cations and anions move selectively along the IEM. Anion exchange membrane (AEM) is one of the important components of the ED process which is critical to enhancing the process efficiency. The introduction of cross-linking in the IEM improves the ion-selective separation performance due to the reduction of free volume. During the desalination of seawater by reverse osmosis (RO) process, there is a lot of dissolved salt present in the concentrate of RO. So, the ED process consisting of a monovalent cation-selective membrane reduces fouling and improves membrane flux. This review is divided into three sections such as electrodialysis (ED), anion exchange membrane (AEM), and cation exchange membrane (CEM).

• Journal of Korean Society on Water Environment
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• v.27 no.2
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• pp.235-241
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• 2011

This study was performed to investigate the characteristics of nutrient removal of municipal wastewater in the submerged membrane bioreactor by addition of alum directly into aerobic tank. Membrane bioreactor consists of three reactors such as two intermittent anaerobic tanks and the aerobic tank with hollow fiber membrane. The removal efficiencies of $COD_{cr}$, BOD, SS, TN and TP on the membrane bioreactor were 94.0%, 99.1%, 99.9%, 66.9%, and 58.9%, respectively. In addition, The removal efficiencies of $COD_{cr}$, BOD, SS, TN and TP on the membrane bioreactor with alum addition were 93.4%, 99.0%, 99.9%, 63.2%, and 96.8%, respectively. There was little difference between them on the nutrient removal efficiencies except phophorus removal. The estimated sludge production, specific denitrification rate, specific nitrification rate and phosphorus removal content on the membrane bioreactor were 1.76 kgTSS/d, $0.055mgNO_3-N/mgVSS{\cdot}d$, $0.031mgNH_4-N/mgVSS{\cdot}d$, and 0.095 kgP/d, respectively. And The estimated sludge production, specific denitrification rate, specific nitrification rate and phosphorus removal content on the membrane bioreactor with alum addition were 2.90 kgTSS/d, $0.049mgNO_3-N/mgVSS{\cdot}d$, $0.030mgNH_4-N/mgVSS{\cdot}d$, and 0.160 kgP/d, respectively. The alum content added was 1.7 molAl/molP on an average. The increasing ratio of tran-membrane pressure on the membrane bioreactor was $0.0056kgf/cm^2{\cdot}compared$ to $0.0033kgf/cm^2{\cdot}d$ on the membrane bioreactor with alum addition. There was a slightly reduction effect on membrane fouling by alum addition.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.26 no.2
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• pp.120-132
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• 1993

A continuous hollow fiber membrane reactor(CHFMR) was developed and optimized for the production of yellowfin sole(Limanda aspera) skin gelatin hydrolysates using trypsin. The results were summerized as follows: The $K_m$ value of the CHFMR was 2.4 times higher than that of the batch reactor, indicating reduced enzyme affinity for the substrate. The $K_2$ value of the CHFMR was 8.5 times lower than that of the batch process, showing a significant reduction in trypsin activity in the CHFMR. The optimum operating conditions for the CHFMR process were $55^{\circ}C$, pH 9.0, flux 7.79 ml/min, residence time 77min, and trypsin to substrate ratio, 0.01(w/w) After operating for 60min under the above conditions, $79\%$ of the total amount of initial gelatin was hydrolysed. Enzyme leakage was observed through the 10,000 MWCO membrane after the 20min of reactor operation, while none occurred after 5hr. Total enzyme leakage was about $12.95\%$ at $55^{\circ}C$ for 5hrs. However, there was no apparent correlation between enzyme leakage and substrate hydrolysis. The membrane has a significant effect on trypsin activity loss for 60min of the CHFMR operation. The CHFMR operating with the membrane lost $34\%$ of the initial activity versus a $23\%$ loss of activity after 3hr in the continuous reactor lacking the hollow fiber membrane. The measurement of fouling property showed that relative flux reduction was $91\%$ and flux recover rate was $92\%$ at $10\%$ substrate solution. The productivity(378.85mg product/mg enzyme) of the CHFMR was more than 4 times higher than that of the batch reactor at $55^{\circ}C$.

• Microbiology and Biotechnology Letters
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• v.40 no.2
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• pp.83-91
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• 2012

Quorum sensing (QS) is a cell-to-cell communication system, which is used by many bacteria to regulate diverse gene expression in response to changes in population density. Bacteria recognize the differences in cell density by sensing the concentration of signal molecules such as N-acyl-homoserine lactones (AHL) and autoinducer-2 (AI-2). In particular, QS plays a key role in biofilm formation, which is a specific bacterial group behavior. Biofilms are dense aggregates of packed microbial communities that grow on surfaces, and are embedded in a self-produced matrix of extracellular polymeric substances (EPS). QS regulates biofilm dispersal as well as the production of EPS. In some bacteria, biofilm formations are regulated by c-di-GMP-mediated signaling as well as QS, thus the two signaling systems are mutually connected. Biofilms are one of the major virulence factors in pathogenic bacteria. In addition, they cause numerous problems in industrial fields, such as the biofouling of pipes, tanks and membrane bioreactors (MBR). Therefore, the interference of QS, referred to as quorum quenching (QQ) has received a great deal of attention. To inhibit biofilm formation, several strategies to disrupt bacterial QS have been reported, and many enzymes which can degrade or modify the signal molecule AHL have been studied. QQ enzymes, such as AHL-lactonase, AHL-acylase, and oxidoreductases may offer great potential for the effective control of biofilm formation and membrane biofouling in the future. This review describes the process of bacterial QS, biofilm formation, and the close relationship between them. Finally, QQ enzymes and their applications for the reduction of biofouling are also discussed.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.4
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• pp.87-97
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• 2000

A steady state performance simulation and diagnostics program for the turboprop engine (PT6A-62), which is the power plant of the first developed military basic trainer KT-1 in Republic of Korea, was developed. The developed steady state performance analysis program was evaluated with the performance data provided by the engine manufacturer and with analysis results of GASTURB program, which is well known for the performance simulation of gas turbines. Performance parameters were discussed to evaluate validity of the developed program at various cases such as altitude, flight velocity and part load variation. GPA(Gas Pass Analysis) allows engine performance deterioration to be identified at the module level in terms of reduction in component efficiencies and changes in mass flow. In order to find optimal instrument set to detect the physical faults such as fouling, erosion and corrosion, a gas path analysis approach is utilized. This study was performed in two cases for selection of optimal measurement parameters. One case was considered with the effect of instrument number by changing independent parameter number. The other case was performed with selection of independent parameter set. According to the analysis results, the optimal measurement parameters selected were eight dependent variables such as shaft horsepower, fuel flow rate, compressor exit pressure and temperature, compressor turbine inlet pressure and temperature and power turbine inlet pressure and temperature.

• Clean Technology
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• v.24 no.4
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• pp.339-347
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• 2018

In order to cope with environmental problems and climate change caused by fossil fuels, renewable energy supply is increasing year by year. Currently, waste energy accounts for 60% of renewable energy production. However, waste has a lower calorific value than fossil fuels and contains various harmful substances, which causes serious problems when applied to power generation boilers. In particular, the chlorine in the waste fuel increases slagging and fouling of boiler heat exchangers, leading to a reduction in thermal efficiency and the main cause of high temperature corrosion, lowering facility operation rate and increasing operating cost. In this study, the high temperature corrosion experiments of superheater materials (ASME SA213/ASTM A213 T2, T12 and T22 alloy steel) by alkali chlorides were conducted, and their corrosion characteristics were analyzed by the weight loss method and SEM-EDS. Experiments show that the higher the temperature and chloride content, the more corrosion occurs, and KCl further corrodes the materials compared to NaCl under the same condition. In addition, the higher the chromium content of the material, the better the corrosion resistance to the alkali chlorides.