• Membrane Journal
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• v.23 no.4
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• pp.267-277
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• 2013

The effect of water back-flushing period (FT) and water back-flushing time (BT) was compared with the previous study of nitrogen back-flushing in viewpoints of resistance of membrane fouling ($R_f$), permeate flux (J), and total permeate volume ($V_T$) in hybrid process of tubular ceramic microfiltration and PES (polyethersulfone) beads loaded $TiO_2$ photocatalyst for advanced drinking water treatment. As FT decreasing, Rf decreased, but J and $V_T$ increased. Turdity treatment efficiency was the maximum at NBF (no back-flushing) and increased a little as FT decreasing in both water and nitrogen back-flushing. Organic matter treatment efficiency was the maximum at FT 4 min in water back-flushing, but increased as FT decreasing in nitrogen back-flushing. As BT increasing, Rf and resistance of reversible membrane fouling ($R_{rf}$) decreased, but J and $V_T$ increased. The turdity treatment efficiency was almost constant beyond 98% in water back-flushing, but increased as BT increasing except NBF in nitrogen. The organic matter treatment efficiency was the maximum at BT 6 sec in water back-flushing, but increased as BT increasing except NBF in nitrogen. The $V_T$ was the maximum at BT 30 and FT 2 min, and optimal condition was BT 30 sec per FT 2 min in this experimental range.

• Membrane Journal
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• v.24 no.2
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• pp.123-135
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• 2014

The effects of pH, saturated oxygen, and back-flushing media were investigated in hybrid process of tubular ceramic microfiltration and $TiO_2$ photocatalyst-loaded PES (polyethersulfone) beads for advanced drinking water treatment, and compared results of water, nitrogen, or oxygen back-flushing in the viewpoints of membrane fouling resistance ($R_f$), permeate flux (J) and total treated water ($V_T$). $R_f$ decreased, and J and $V_T$ increased as decreasing pH. Turbidity treatment efficiencies were similar at water or nitrogen back-flushing independent of pH, but DOM (dissolved organic matter) treatment efficiency did not have a trend at water back-flushing. $R_f$ at NBF (no back-flushing) with SO (saturated oxygen) was the lower than that at NBF without SO. Also, the DOM treatment efficiency at NBF with SO was the lower than that at NBF without SO. It happened because OH radicals produced by reaction of SO and photocatalyst could dilute with water inside the module. The DOM treatment efficiency of gas back-flushing showed the larger than that of water back-flushing at back-flushig period 10 min. It proved that the adsorption or photo-oxidation of PES beads could be activated by the more effective bead-cleaning of gas back-flushing than water back-flushing.

• Membrane Journal
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• v.21 no.2
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• pp.127-140
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• 2011

The effects of $TiO_2$ photocatalyst coating bead concentration, water-back-flushing period (FT), and back-flushing time (BT) were investigated in hybrid process of ceramic ultrafiltration and photocatalyst for advanced drinking water treatment in this study. Photocatalyst coating bead concentration was changed in the range of 10~40 g/L, FT in 2~10 min and BT in 6~30 sec. Then, we observed the effects on resistance of membrane fouling $(R_f)$, permeate flux (J) and total permeate volume $(V_{\Upsilon})$ during total filtration time of 180 min. As decreasing photocatalyst coating bead concentration, $R_f$ increased and J decreased. $V_{\Upsilon}$ was the highest value of 8.85 L at 40 g/L of photocatalyst coating bead concentration. At FT change experiment, $R_f$ decreased and J increased as decreasing FT. Then $R_f$ decreased and J increased according to increasing BT at BT change experiment. Because at NBF (no back-flushing) dramatic membrane fouling reduced membrane pore size, turbid and dissolved organic matters ($UV_{254}$ absorbance) could be removed efficiently. Therefore, treatment efficiencies of turbidity and dissolved organic matters were the highest at NBF. Then by cleaning effect of photocatalyst coating bead, the treatment efficiencies of turbidity and dissolved organic matters increased as decreasing FT and increasing BT.

• Membrane Journal
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• v.21 no.2
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• pp.201-211
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• 2011

The effects of humic acid (HA), photo-oxidation and adsorption were investigated in hybrid process of ceramic ultrafiltration and photocatalyst for drinking water treatment. UF, photocatalyst, and UV radiation processes were investigated in viewpoints of membrane fouling resistance $(R_f)$, permeate flux (J), and total penneate volume $(V_{\Upsilon})$ at 2 and 4 mg/L of HA respectively. As decreasing HA, $R_f$ decreased dramatically and J increased, and finally $V_{\Upsilon}$ was the highest at 2 mg/L HA. Average treatment efficiencies of turbidity decreased as increasing HA, but treatment efficiency of HA was the highest at 4 mg/L HA. It was because most of HA was removed by membrane and some HA passing through the membrane was adsorbed or photo-oxidized by photocatalyst at low HA, and therefore treated water quality was almost same at 2 and 4 mg/L HA, but feed water quality was higher at 4 mg/L. At effect experiment of photo-oxidation and adsorption, J of UF + $TiO_2$ + UV process was maintained at the highest, and ultimately $(V_{\Upsilon})$ after 180 minutes' operation was the highest. As results of comparing the treatment efficiencies of turbidity and HA, photocatalyst adsorption had more important role than photo-oxidation when HA increased from 2 to 4 mg/L.

• Membrane Journal
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• v.26 no.4
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• pp.301-309
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• 2016

The effects of water back-flushing time (BT) and photocatalyst-coated polypropylene (PP) beads were investigated in hybrid water treatment process of alumina microfiltration and the PP beads in this study, and compared with the previous study with alumina ultrafiltration membrane and the same PP beads. The BT was changed in the range of 6~30 s with fixed 10 min of back-flushing period (FT). Then, the BT effects on resistance of membrane fouling ($R_f$), permeate flux (J) and total permeate volume ($V_T$) were observed during total filtration time of 180 min. As longer BT, $R_f$ decreased and J increased dramatically; however, $V_T$ was the maximum at BT 10 s. The treatment efficiency of turbidity was high beyond 99.0%, and the BT effect was not shown. The treatment efficiency of organic matters was the highest value of 89.0% at no back-flushing (NBF), and increased as longer BT. The optimum input concentration of the PP beads was 20 g/L in the viewpoint of membrane fouling; however, the optimum PP beads of the previous study was 40 g/L. The treatment efficiency of turbidity and organic matters were the maximum at 30 g/L of the PP beads; however, those of the previous study with alumina ultrafiltration membrane and the same PP beads were the highest at 40 g/L.

• Membrane Journal
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• v.23 no.3
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• pp.226-236
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• 2013

The effect of $N_2$ back-flushing period (FT) and time (BT) was compared with the previous result used PES (polyethersulfone) beads loaded with titanium dioxide photocatalyst in hybrid process of alumina microfiltration and PP (polypropylene) beads coated with photocatalyst in viewpoints of membrane fouling resistance ($R_f$), permeate flux (J), and total permeate volume ($V_T$). The reason of nitrogen back-washing instead of the general air back-washing method is to minimize the possible effect of oxygen included in air on water quality analysis. As decreasing FT, $R_f$ decreased and J and $V_T$ increased. Treatment efficiency of dissolved organic matters (DOM) was 82.0%, which was the higher than 78.0% of the PES beads result. This means that PP beads coated with photocatalyst was the more effective than PES beads loaded with photo-catalyst in the DOM removal. As increasing BT, the final $R_f$ decreased and the final J increased, but $V_T$ was the maximum at BT 15 sec. The average treatment efficiency of turbidity did not have any trend as changing BT. As BT increasing from 6 sec to 30 sec, the treatment efficiency of DOM increased 11.8%, which was a little higher than the result of PES beads.

• Membrane Journal
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• v.23 no.1
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• pp.70-79
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• 2013

The $N_2$ back-flushing period (FT) and time (BT) were investigated in hybrid process of ceramic microfiltration and PES (polyethersulfone) beads loaded with titanium dioxide ($TiO_2$) photocatalyst for advanced drinking water treatment in viewpoints of membrane fouling resistance ($R_f$), permeate flux (J), and total permeate volume ($V_T$). As decreasing FT and increasing BT, $R_f$ decreased and J increased, and finally the maximum $V_T$ could be acquired at FT 10 min and BT 30 sec. In FT effect experiment, treatment efficiencies of turbidity and dissolved organic matters (DOM) were the highest at no back-flushing (NBF) because of dramatic membrane fouling. As result of BT effect, the treatment efficiencies were the maximum at BT 30 sec, which was different with the FT result. Because the photocatalyst beads could be cleaned effectively as decreasing FT and increasing BT, turbidity treatment efficiency increased a little from 95.4% to 97.5% as decreasing FT, and from 95.9% to 98.5% as increasing BT. Also DOM treatment efficiency increased from 70.8% to 80.6% as decreasing FT, and from 75.1% to 85.8% as increasing BT. The optimal condition, where the treatment efficiencies and $V_T$ were the maximum, should be FT 10 min and BT 30 sec in our experimental range.

• Membrane Journal
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• v.22 no.3
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• pp.171-177
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• 2012

Effect of humic acid (HA), photo-oxidation and adsorption with periodic $N_2$ back-flushing was investigated in hybrid process of ceramic ultrafiltration and photocatalyst for drinking water treatment. It was compared and investigated with the previous result at water back-flushing in viewpoints of membrane fouling resistance ($R_f$), permeate flux (J), and total permeate volume ($V_T$). As decreasing HA, $R_f$ decreased dramatically and J increased, and finally $V_T$ was the highest at HA 2 mg/L. As HA concentration increased from 2 to 10 mg/L, the membrane fouling resistance after 180 mins' operation ($R_{f,180}$) improved 0.8 times more than that of water back-flushing. Therefore, HA concentration should affect on the membrane fouling at $N_2$ back-flushing than water back-flushing. Turbidity treatment efficiencies were almost constant independent of HA concentration, but HA treatment efficiency was the maximum at HA 2 mg/L. This means that adsorption and photo-oxidation of photocatalyst beads could removed HA at HA 2 mg/L, but it was not enough at 4 mg/L. Beyond HA 6 mg/L, UF could effectively treat HA by thick cake layer on membrane surface and severe inner membrane fouling.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.02a
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• pp.183-184
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• 2013

Two main MBE growth techniques have been used: plasma-assisted MBE (PA-MBE), which utilizes a rf plasma to supply active nitrogen, and ammonia MBE, in which nitrogen is supplied by pyrolysis of NH3 on the sample surface during growth. PA-MBE is typically performed under metal-rich growth conditions, which results in the formation of gallium droplets on the sample surface and a narrow range of conditions for optimal growth. In contrast, high-quality GaN films can be grown by ammonia MBE under an excess nitrogen flux, which in principle should result in improved device uniformity due to the elimination of droplets and wider range of stable growth conditions. A drawback of ammonia MBE, on the other hand, is a serious memory effect of NH3 condensed on the cryo-panels and the vicinity of heaters, which ruins the control of critical growth stages, i.e. the native oxide desorption and the surface reconstruction, and the accurate control of V/III ratio, especially in the initial stage of seed layer growth. In this paper, we demonstrate that the reliable and reproducible growth of GaN on Si (110) substrates is successfully achieved by combining two MBE growth technologies using rf plasma and ammonia and setting a proper growth protocol. Samples were grown in a MBE system equipped with both a nitrogen rf plasma source (SVT) and an ammonia source. The ammonia gas purity was ＞99.9999% and further purified by using a getter filter. The custom-made injector designed to focus the ammonia flux onto the substrate was used for the gas delivery, while aluminum and gallium were provided via conventional effusion cells. The growth sequence to minimize the residual ammonia and subsequent memory effects is the following: (1) Native oxides are desorbed at $750^{\circ}C$ (Fig. (a) for [$1^-10$] and [001] azimuth) (2) 40 nm thick AlN is first grown using nitrogen rf plasma source at $900^{\circ}C$ nder the optimized condition to maintain the layer by layer growth of AlN buffer layer and slightly Al-rich condition. (Fig. (b)) (3) After switching to ammonia source, GaN growth is initiated with different V/III ratio and temperature conditions. A streaky RHEED pattern with an appearance of a weak ($2{\times}2$) reconstruction characteristic of Ga-polarity is observed all along the growth of subsequent GaN layer under optimized conditions. (Fig. (c)) The structural properties as well as dislocation densities as a function of growth conditions have been investigated using symmetrical and asymmetrical x-ray rocking curves. The electrical characteristics as a function of buffer and GaN layer growth conditions as well as the growth sequence will be also discussed. Figure: (a) RHEED pattern after oxide desorption (b) after 40 nm thick AlN growth using nitrogen rf plasma source and (c) after 600 nm thick GaN growth using ammonia source for (upper) [110] and (lower) [001] azimuth.

• Membrane Journal
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• v.19 no.3
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• pp.183-188
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• 2009

After membrane fouling factors in acrylic wastewater were minimized by pretreatment process accompanied with $TiO_2$, it was utilized in MF/UF/RO process. After composing of ultrafiltration/reverse osmosis or microfiltration/reverseosmosiss module set according to types and kinds of membrane, the separation characteristics were examined with the variation temperature and pressure using pretreated acrylic wastewater by membrane module sets. The permeate of ultrafiltration or microfiltration module was sent to reverse osmosis module. It was found that final permeate flux of reverse osmosis module in module set 2 (MWCO 200,000 UF+RO) was excellent. It was shown that the removal efficiency of TDS, T-N and COD was very low and was not dependent on the variation of temperature and pressure in UF and MF modules. From the above result, the removal efficiency of TDS, T-N and COD was very excellent in RO module. The removal efficiency of turbidity in UF and MF module was very high (> 99% removal efficiency). Final water quality of acrylic wastewater treated by the membrane module set was satisfied with effluent allowances limit and membrane module sets were ascertained to reuse wastewater.