공학석사학위논문 수중유기물에대한세라믹막의 수처리특성 Water Treatment Characteristics of Ceramic Membrane for Aqueous Organic Matter 2016 년 2 월 서울대학교대학원 생태조경 지역시스템공학부 지역시스템공학전

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1 저작자표시 - 비영리 - 변경금지 2.0 대한민국 이용자는아래의조건을따르는경우에한하여자유롭게 이저작물을복제, 배포, 전송, 전시, 공연및방송할수있습니다. 다음과같은조건을따라야합니다 : 저작자표시. 귀하는원저작자를표시하여야합니다. 비영리. 귀하는이저작물을영리목적으로이용할수없습니다. 변경금지. 귀하는이저작물을개작, 변형또는가공할수없습니다. 귀하는, 이저작물의재이용이나배포의경우, 이저작물에적용된이용허락조건을명확하게나타내어야합니다. 저작권자로부터별도의허가를받으면이러한조건들은적용되지않습니다. 저작권법에따른이용자의권리는위의내용에의하여영향을받지않습니다. 이것은이용허락규약 (Legal Code) 을이해하기쉽게요약한것입니다. Disclaimer

2 공학석사학위논문 수중유기물에대한세라믹막의 수처리특성 Water Treatment Characteristics of Ceramic Membrane for Aqueous Organic Matter 2016 년 2 월 서울대학교대학원 생태조경 지역시스템공학부 지역시스템공학전공 손정우

3 국문초록 최근양질의수자원의안정적인공급에대한요구가확대되면서공정이간단하고양질의수자원을확보할수있는막공정이주목을받고있다. 그중에서도세라믹막은물리화학적강도와투과성이우수하여다양한분야에의적용이기대되고있다. 한편, 막공정에서필연적으로발생하는막오염은막공정의효율을떨어뜨리고막의수명을단축시키게되므로제어할필요가있으며, 수처리공정에있어서막오염을유발하는주요한물질은수중에존재하는유기물이다. 또한, 막오염은막공정의운전인자인막간압력차에큰영향을받는것으로알려져있다. 본연구에서는세라믹막을이용하여수중에존재하는유기물을제거하는경우의여과특성과막오염기작및특성을살펴보았다. 실험은십자류여과방식을이용하여일정한십자류유량과온도조건에서막간압력차를변화시켜여과수가 2 L가될때까지진행하였다. 유입수는증류수 (D.W.), 모사수인 Humic acid 용액 (HA10, HA20) 과현장수 (HR, SN) 를대상으로하였다. 유입수, 여과수, 농축수에대하여정성분석인 F-EEM, 정량분석인 DOC, UVA 254, SUVA를통하여수질분석을수행하였다. 여과실험에앞서세라믹막의성능을평가하기위하여증류수를이용하여투과실험을진행하였다. 실험에사용한세라믹막의투과성능 (Permeability) 은 10, 25, 40 로온도가증가함에따라각각 ± 2.92, ± 5.07, ± 4.50 LMH로증가하였으며, 이는온도가올라감에따라물의점성이낮아져 flux가증가하였기때문이다. 유입수를대상으로여과실험을수행한결과, 막간압력차가증가할수록 flux의감소가크게일어나고여과시간은단축되는경향을보였으며, 모사수보다현장수의 flux 감소가크게나타났다. 유입수, 여과수, 농축수 - i -

4 의수질특성을분석한결과, 모사수인 HA10과 HA20은소수성고분자물질로, 현장수인 HR과 SN은친수성저분자물질로주로이루어진것으로나타났다. 이러한유입수의특성으로인하여여과과정에서소수성을가지는모사수는농축이일어나면서막오염이적게발생하였으나, 친수성을가지는현장수는농축이되기보다는막표면에막오염을유발하는것으로나타났다. 여과실험의결과를바탕으로 Hermia 모델을이용하여막오염의기작을해석한결과, 전체적으로 Cake formation 모델이실험값을가장잘모사하는것으로나타났다. 여과실험후단계적인세척으로회복된 flux와직렬저항모델을이용하여막오염특성을평가하였다. 막간압력차가증가할수록총막오염은증가하였으며, 물리적세척으로회복이불가능한비가역적막오염의비율또한증가하는것으로확인하였다. 또한, 모사수인 HA10과 HA20보다현장수인 HR과 SN 의막오염이크게발생하였다. 주요어 : 세라믹막, 수중유기물, 막오염, 수처리학번 : ii -

5 목 차 초록 ⅰ 목차 ⅲ List of Tables ⅴ List of Figures ⅵ 제 1 장서론 연구의배경 막공정 분리막 세라믹막 막오염 수중유기물 연구의목적 연구의방법 8 제 2 장선행문헌연구 운전조건과유입수의특성에따른막오염의영향 수중유기물처리에대한세라믹막의적용 15 제 3 장재료및방법 유입수 세라믹막및세라믹막장치 실험방법및실험조건 실험방법 실험조건 28 - iii -

6 3.4 수질분석 정성분석 정량분석 모델분석 Hermia 모델 직렬저항모델 36 제 4 장결과및고찰 세라믹막의투과특성 Flux에영향을미치는요인 Permeability 및막자체의저항 세라믹막의수처리특성 여과특성 수질특성 정성분석 정량분석 모델분석 Hermia 모델 : 기작분석 직렬저항모델 : 막오염분석 59 제 5 장결론 62 참고문헌 63 Abstract 72 - iv -

7 List of Tables Table 1 Characteristics of different pressure-driven membrane 3 Table 2 Effects of operating condition and characteristics of feed water for ceramic membrane fouling 10 Table 3 Types of feed water for application of ceramic membrane 16 Table 4 Characteristics of feed water 22 Table 5 Characteristics of ceramic membrane 24 Table 6 Operating conditions 29 Table 7 Permeability of ceramic membrane 42 Table 8 Flux declines and filtration times 45 Table 9 Water quality analysis 52 Table 10 Hermia model parameters obtained by fitting models to experimental data 56 - v -

8 List of Figures Figure 1 Filtration type: (a) Dead-end filtration; (b) Cross-flow filtration 4 Figure 2 Principle fouling mechanism of membrane filtrationtion 6 Figure 3 Digital images: (a) Ceramic membrane; (b) Ceramic membrane system 25 Figure 4 Schematic system flow chart of the ceramic membrane system 26 Figure 5 Digital images: (a) TOC analyzer; (b) UV/Vis spectrophotometer; (c) Fluorescence-spectrometer 31 Figure 6 Location of F-EEM peaks (symbols) based on literature reports and operationally defined excitation and emission wavelength boundaries (dashed lines) for five F-EEM regions 32 Figure 7 Flux test of ceramic membrane: (a) 10 ; (b) 25 ; (c) Figure 8 Flux test of ceramic membrane 40 Figure 9 Flux decline of filtration test: (a) 1 bar (vs. volume); (b) 1 bar (vs. Time); (c) 2 bar (vs. volume); (d) 2 bar (vs. Time); (e) 3 bar (vs. volume); (f) 3 bar (vs. Time) 44 Figure 10 F-EEM analysis (HA10, HA20, HR, SN) 48 Figure 11 F-EEM analysis (HR, SN) 49 - vi -

9 Figure 12 Value of DOC: (a) HA10; (b) HA20; (c) HR; (d) SN 53 Figure 13 Removal of DOC 54 Figure 14 Hermia model analyses: HA10, HA20 57 Figure 15 Hermia model analyses: HR, SN 58 Figure 16 Value of resistance: (a) Membrane and fouling; (b) Reversible and irreversible fouling 61 - vii -

10 제 1 장서 론 1.1 연구의배경 수처리공정은화학약품을사용하여오염물질을응집하여침전시키는 1세대의물리화학적공정, 호기성또는혐기성미생물을이용하여오염물질을분해하는 2세대의생물학적공정을거쳐분리막을이용하여오염물질을여과하는 3세대의막분리공정으로발전해왔다. 막분리공정은다량의슬러지가발생하는물리화학적공정과난분해성물질의제거가불가능한생물학적공정의단점을극복할수있고, 조작과설비가간단하며안정적이고우수한수질개선효과를가지고있어, 높은초기투자비용과유지관리비용에도불구하고최근주목을받고있다. 막공정의핵심인분리막은크게유기막과무기막으로나눌수있으며, 무기막중에서세라믹막은높은물리화학적강도로인해다양한분야의적용성이높아지고있다. 한편, 수중에존재하는유기물은분리막의단점인막오염을일으키는지배적인물질로알려져있기때문에, 막공정의수처리적용시에수중에존재하는유기물의여과특성을파악하는것이중요하다 막공정막공정은대상원수의오염정도와요구되는처리수의수질에따라공극의크기를선정할수있어서다양한적용이가능하며, 공극과막의형태에따라서입자성물질뿐만아니라수중의용존물질까지도제거가가능하다. 막공정의주요한수처리기작은오염물질의크기에따른체거름으로, 막의공극크기보다큰오염물질을확실하게배제할수있기때문에안정적인수질을확보할수있다. 막은공극의크기에따라정밀여과 (Microfiltration, MF), 한외여과 - 1 -

11 (Ultrfiltration, UF), 나노여과 (Nanofiltration, NF), 역삼투 (Revers osmosis, RO) 로구분할수있으며, 분류에따라적용되는압력이상이하며, 제거할수있는물질의종류가상이해지게된다 (Kim and Dempsey, 2013). 일반적으로수처리에서는 MF 막과 UF 막이적용이되며, 해수담수화에는 RO 막이사용된다 (Table 1). 막공정은운전방식에따라전량여과방식 (Dead-end filtration) 과십자류여과방식 (Cross-flow filtration) 으로대별된다. 전량여과방식은유입수의흐름과여과수의흐름이같은방향으로이루어지며, 십자류여과방식은유입수의흐름과여과수의흐름이직각방향이된다 (Figure 1). 이로인해서십자류여과방식은막면에전단류를형성하여막표면에형성되는막오염을저감하는효과를나타낸다 분리막 세라믹막막은소재에따라유기고분자막과무기막으로대별할수있다. cellulose acetate (CA), polysulfon (PS), polyacrylonitrile (PAN), polyethylene (PE), Polypropylene (PP) 등과같은유기고분자로제조되는기존의유기막은제조가용이하고가격이낮다는장점이있었지만, 강도와내화학성이약하여다양한분야에대한적용에제한되었다. 한편, 무기질로이루어지는무기막중의세라믹막은주로 Alumina, Silica, Zirconia, Titania로이루어져있으며, 내화학성, 내압성, 내열성등의장점을가지고있다. 세라믹막은유기막에비하여물리적, 화학적강도가우수하여극한조건에서의운전이가능하여다양한분야에적용할수있다 (Lee and Cho, 2004). 세라믹막은이러한장점에도불구하고높은가격으로인하여유기고분자막에비하여아직까지는그적용이더딘상황이다. 하지만유기고분자막에비하여많은장점을가지고있어개발이활성화되고있으며, 이로인하여가격경쟁력이크게향상되고있다

12 Table 1 Characteristics of different pressure-driven membranes Membrane process Applied pressure (bar) Pore size Rejection / Application MF 0.1 ~ ~ 3 μm Particle, Turbidity, Bacteria, Algae, Protozoa UF 0.1 ~ ~ 0.1 μm, >1,000Dalton Small colloids, Macromolecule, Viruses NF 3 ~ ~ 400 Dalton RO 5 ~ ~ 400 Dalton Dissolved organic matter, Multivalent ions Monovalent ions, Desalination - 3 -

13 Figure 1 Filtration type: (a) Dead-end filtration; (b) Cross-flow filtration - 4 -

14 1.1.3 막오염한편 MF막과 UF막은체거름을주요한제거기작으로하며, 이에따라막의표면또는막의공극내분에부착되는오염물질에의한막오염 (fouling) 이막공정의가장큰제한요소이다. 막오염은공극크기와오염물질의크기에따라서다음과같이 (Figure 2) 크게 3가지의원리로분류할수있다 (Hashino et al., 2011). 1 공극이오염물질보다큰경우 (d pore >> d particle ) : 흡착 2 공극이오염물질과비슷한경우 (d pore = d particle ) : 공극막힘 3 공극이오염물질보다작은경우 (d pore << d particle ) : Cake 층형성 막에서일어나는막오염은공극막힘과 Cake 층의형성과같은크기배제에의한것뿐만아니라흡착에의한부분도발생하게되는데, 이는막표면과오염물질간의물리화학적인작용에기인한것이다. 한편, 일반적인유입수는다양한크기의오염물질들이혼재되어있기때문에막오염은한가지의원리만으로일어나기보다는복합적으로발생한다고할수있다. 일반적으로 Cake 층은이미막표면에부착되어있거나공극막힘을형성하고있는오염물질위에다시오염물질이누적되어형성되는것을의미하는데결과적으로막오염은 Cake 층의형성으로귀결되게된다. 한편이러한막오염은막공정의수처리능력을저하시키고막의수명또한단축되므로, 여과과정에서막오염을저감시키고세척과정을통하여막을회복시키는것이중요하다 (Reissmann and Uhl, 2006; Qin et al., 2010). 막오염은막공정에있어서여과수의여과속도인 flux를결정하는주요한요소중하나인막간압력차 (Transmembrane pressure, TMP) 에영향을받는것으로알려져있다 (Alpatova et al., 2014)

15 Figure 2 Principle fouling mechanism of membrane filtration - 6 -

16 1.1.4 수중유기물수처리에있어서막오염을유발하는물질은지표수, 지하수, 하수등에다량으로존재하는자연유기물 (Natural organic matter, NOM) 의영향이지배적이다 (Huang et al., 2007; Lee et al., 2008). NOM은자연적으로발생한유기화학물질을말한다. 수중에존재하는 NOM은동식물의사체가분해되어유래된유기화합물이많으며, 방향족및지방족물질, 아미노산, 탄수화물, 변형물질이포함되어정확한구조의파악이힘들다. 이에따라작용기의형태, 친수성 (hydrophilic), 소수성 (hydrophobic) 등과같은제한된특성을통해해석한다 ( 박종율, 2004). NOM은크게소수성을띄는휴믹 (humic) 물질과친수성을띄는비휴믹 (non-humic) 물질로나누어진다. 휴믹물질은동식물의사체등이자연부패하여형성된물질이해당하며, 비휴믹물질은아미노산, 단백질등과같이생분해가가능한물질이다. 휴믹물질은다시펄빅산 (fulvic acid), 휴믹산 (humic acid), 휴민 (humin) 으로분류된다 ( 박상혁, 2008). 한편, NOM은유기탄소 (Organic carbon) 의농도로측정하는것이일반적이며, 총유기탄소 (Total organic carbon, TOC) 는 0.45 μm 이상의입자를가지는입자성유기탄소 (Particulate organic carbon, POC) 과 0.45 μm 미만의용존유기탄소 (Dissolved organic carbon, DOC) 으로분류한다. 막오염의주원인이되는유기물은 DOC이며 NOM 중에는휴믹산, 단백질, 탄수화물, 탄닌등이해당한다. 이들은종래의모래여과또는침전등의처리로는제거가어려운물질로알려져있다 ( 정재현, 2011)

17 1.2 연구의목적 따라서본연구에서는세라믹막을이용하여수중에존재하는유기물을여과하여그여과특성을파악하고, 막오염의형태를분석하고자한다. 이때, Humic Acid 용액으로제조한모사수와다양한현장수를대상으로하여막간압력차가막오염에미치는영향을파악하고, 각각의유입수의수질특성에따른세라믹막의수처리특성을알아보고자한다. 1.3 연구의방법 수질특성분석은유입수, 여과수, 농축수에대하여수행하였으며, ph, EC, DOC, UVA 254, SUVA, Fluorescence excitation-emission matrix (F-EEM) 를이용하여비교분석하였다. 증류수를이용한온도, 막간압력차, 십자류유량등의다양한조건에서의투과실험을통하여세라믹막고유의투과특성을평가하였으며, 모사수와현장수의여과실험을통하여여과유량과여과시간에따른 flux의감소를살펴보았다. 여과실험은동일한조건에서의수처리특성을평가하기위하여모든조건에서여과수의유량이 2 L가될때까지수행하였다. 여과실험이종료한뒤에는 flux 감소곡선과 Hermia 모델을이용하여막오염의기작을해석하고, 단계적인세척과정과직렬저항모델 (Resistance-in-series) 을이용하여막오염특성을분석하였다

18 제 2 장선행문헌연구 2.1 운전조건과유입수의특성에따른막오염의영향 선행연구자들에의하여세라믹막의운전조건과유입수의특성이막오염에미치는영향이연구되어왔다 (Table 2). 세라믹막의막오염에대한운전조건의영향은막간압력차와십자류속도에관한것이다. Gomes et al. (2011), Xia et al. (2013), Gulrgls et al. (2015) 등은막간압력차가세라믹막의막오염에미치는영향을연구하였으며, 막간압력차가커질수록막오염이증대되는것을확인하였다. Agana et al. (2011) 과 Majewska-Nowak (2011) 은십자류속도의변화에따른막오염에대한연구를수행한바있으며, Abadi et al. (2011) 은막간압력차와십자류속도를모두변화시켜막오염을평가하는연구를수행하였다. 유입수의특성에따른연구로는유입수의 ph와온도에따른영향과유입수에존재하는염의영향에대한내용이진행되어왔다. Lee et al. (2013) 은유입수의온도에따른영향을하수를대상으로연구한바있으며, Zhang et al. (2013) 은염의존재에따른여과특성에대한실험을수행하였다. Barredo-Damas et al. (2011) 과 Shang et al. (2014) 는유입수의 ph에따른영향을살펴보았다

19 Table 2 Effects of operating condition and characteristics of feed water for ceramic membrane fouling Author Title Operating parameters Feed water Summary Effects of operating parameters such as Abadi et al. (2011) Ceramic membrane performance in microfiltration of oily wastewater TMP, CFV Oily wastewater transmembrane, cross flow velocity and temperature on permeate flux, TOC removal efficiency and fouling resistance were investigated. The recommended operating conditions are TMP of 1.25 bar, CFV of 2.25 m/s and temperature of 32.5 C. Optimization of the Agana et al. (2011) operational parameters for a 50 nm ZrO 2 ceramic membrane as applied to the ultrafiltration of post-electrode position rinse CFV Post-electro deposition rinse wastewater The influence on filtration performance of operating parameters such as crossflow velocity and transmembrane pressure was investigated. Results show a combination of high CFV and low TMP to be beneficial - typified by a CFV of 3.2 m s 1 and TMP of 100 kpa. wastewater

20 Effec of ph and The effect of both ph and molecular weight Barredo-Damas et al. (2011) MWCO on textile effl uents ultrafiltration by tubular ceramic ph Textile effluents cut-off (MWCO) on membrane performance was determined while working on concentration mode. Results showed a noticeable influence of both membranes ph and MWCO on process performance. Microfiltration runs were performed in batch mode Biodiesel production using a 0.2 um ceramic membrane at 1.0, 2.0, and from degummed 3.0 bar transmembrane pressures. The results Gomes et al. (2011) soybean oil and glycerol removal TMP Degummed soybean oil showed that the water concentration added to the mixture plays an important role in glycerol using ceramic separation, as well as in the permeate flux, membrane according to the proposed glycerol separation mechanism using ceramic membrane. The study is aimed at investigating the suitability of ceramic membranes to the decolourization of Majewska-Now ak and Kawiecka-Sko wron (2011) Ceramic membrane behaviour in anionic dye removal by ultrafiltration CFV Anionic dye organic dye solutions. Transport and separation properties of the membranes towards dye solutions were investigated at varied linear velocity in the modules (1.5; 2.9; 4.4; 5.9, and 6.9 m/s). Seven anionic organic dyes of molecular weight ranging from 327 to 1,084 Da were used in the tests

21 Two ceramic nanofiltration membranes with a Sentana et al. (2011) Reduction of chlorination byproducts in surface water using ceramic nanofiltration membranes TMP, Conductivity, ph Surface water molecular weight cutoff of 450 Da (NF450) and 1000 Da (NF1000) were used to reduce the concentration of organic matter (OM) in natural water, and the effect on the formation of disinfection by-products (DBPs) was evaluated. The effects of pressure, conductivity and ph were studied. The formation of trihalomethanes, haloacetic acids, haloacetonitriles and haloketones was evaluated. Ebrahimi et al. (2013) Dynamic cross-flow filtration of oilfield produced water by rotating ceramic filter discs membrane rotational speed, Oilfield produced water The purpose is to assess the effects of the process parameters membrane rotational speed (1,200, 1,500 and 1,800 rpm), volume concentration factor (VCF) and feed characteristics - in terms of oil and total organic carbon (TOC) separation capability, permeability and permeate quality. Lee et al. (2013) Effects of water temperature on fouling and flux of ceramic membranes for wastewater reuse Temperature Wastewater High water temperature caused initial flux rise the flux became similar to that of low temperature water after 2 h of operation. High temperature of water can increase irreversible fouling of ceramic membrane probably caused by inorganic scale formation in the membrane pores

22 The flux evolution and retention performance of a tubular ceramic membrane with nominal pore size of 0.01 lm was systematically investigated. Filtration Ultrafiltration of experiments were carried out on a pilot-scale Xia et al. (2013) humic acid and surface water with tubular TMP Humic acid, surface water crossflow unit using humic acid (HA) solution and surface water as feed by varying transmembrane pressure (TMP). Measurements such as total ceramic membrane organic carbon (TOC), ultraviolet absorbance at 254nm (UV254), fluorescence excitation emission matrices (EEMs), ph, and conductivity were made on both raw water and the permeate. Ceramic membranes with different membrane pore Application of ceramic sizes were studied for their use in produced water Zhang et al. (2013) membranes in the treatment of Salts Oilfield-pro duced water treatment. The effects of the NaCl concentrations and the PAM concentrations on the filtration oilfield-produced water performance were investigated. Interactions between PAM, NaCl and membrane fouling were discussed. Modeling water flux The water and ion transport through a mesoporous γ Farsi et al. (2014) and salt rejection of mesoporous γ-alumina and microporous organo Conductivity Modeling water -alumina membrane and a microporous organo silica membrane was simulated using the extended Nernst Planck equation combined with models for Donnan, silica membranes steric and dielectric interfacial exclusion mechanisms

23 Shang et al. (2014) Tight ceramic UF membrane as RO pre-treatment: The role of electrostatic interactions on phosphate rejection ph Model solution This paper focuses on electrostatic interactions during tight UF filtration. The increase of ph from 6 to 8.5 led to a substantial increase in phosphate rejection by both membranes due to increased electrostatic repulsion. Ceramic membranes in tubular configurations with Treatment of pore sizes of 20 kda, 50 nm and 100 nm were Guirgis et al. (2015) produced water streams in SAGD processes using tubular ceramic TMP Produced water streams investigated for the removal of solids and dissolved organics from boiler feed water (BFW). The original BFW sample contained 125, 1300 and 20mg/L of oil and grease (O&G), membranes naphthenic acids (NAs) and total suspended solids (TSS), respectively

24 2.2 수중유기물처리에대한세라믹막의적용 세라믹막의여과과정에서발생하는막오염을일으키는물질중유입수내에포함되어있는용존유기물에대한연구가선행연구자들에의하여진행되어왔다 (Table 3). 연구가진행된유입수의종류는하천수, 호소수, 하수, 미생물에의해유래된유기물, 염료등으로분류할수있다. Li et al. (2011), Xia et al. (2013), Zhang et al. (2013) 등은실제하천수를대상으로실험을진행하여수중에존재하는자연유기물에의한세라믹막의막오염에대한연구를수행하였으며, Li et al. (2010) 은호소수에대한연구도선행한바있었다. 하수에대해서는 Barredo-Damas (2011), Zhu et al. (2012), Yin et al. (2013), Lee et al. (2014), Chen et al. (2015), Fujioka and Nghiem (2015) 등많은연구자들에의하여수행되었다. 이는세라믹막이극한조건에서적용이가능하다는장점을가지고있기때문에하천수와호소수보다용존유기물의농도가높은하수에대한연구가많이진행되고있는추세이다. 한편, Zhang et al. (2013; 2014) 은 Microcystis aeruginosa에의해유래되는수중유기물에대한연구를진행한바있다. 한편, 대부분의연구자들은이러한수중유기물을 COD, TOC, DOC, UVA 254 등을통하여분석하였으며, 추가적으로 SS와 Turbidity를분석한연구도존재한다

25 Table 3 Types of feed water for application of ceramic membrane Author Title Feed water Coagulation-microfil tration for lake Li et al. water purification (2010) using ceramic lake water membranes Effect of ph and MWCO on textile Barredo-Da effluents textile mas et al. ultrafiltration by effluents (2011) tubular ceramic membranes Treatment of river water by a hybrid Li et al. coagulation and (2011) ceramic membrane River water process Analysis parameter TOC, UVA 254 COD, TOC, SS, Turbidity DOC, UVA 254 Summary A microfiltration process coupled with online coagulation using honeycomb ceramic membranes was used to purify lake water. The turbidity of feed lake water was from 13 to 30 NTU and the suitable dose of the coagulant was mg L 1 by the jar test. The effect of both ph and molecular weight cut-off (MWCO) on membrane performance was determined while working on concentration mode. Results showed a noticeable influence of both ph and MWCO on process performance. Effects of coagulant dosages and hydraulic retention times (HRTs) on the system performance were examined in a hybrid coagulation and ceramic membrane system. The system performance was evaluated by measuring dissolved organic carbon (DOC), ultraviolet absorbance at 254 nm (UV 254 ), particle counts, and membrane permeate flux

26 The study is aimed at investigating the suitability Majewska-N owak and Kawiecka-Sk owron (2011) Ceramic membrane behaviour in anionic dye removal by ultrafiltration anionic dye UV absorbance of ceramic membranes to the decolourization of organic dye solutions. Transport and separation properties of the membranes towards dye solutions were investigated at varied linear velocity in the modules (1.5; 2.9; 4.4; 5.9, and 6.9 m/s). Seven anionic organic dyes of molecular weight ranging from 327 to 1,084 Da were used in the tests. This paper assesses the performance of three Operation and ceramic membranes in the treatment of the press Perez-Galve z et al. (2011) cleaning of ceramic membranes for the filtration of fish fish press liquor COD liquor resulting from a compaction operation of sardine byproducts. The cleaning efficiency of the membranes was assessed by the COD press liquor reduction in the permeate streams, related to that of the raw press liquor. In this study, pilot-scale ceramic microfiltration Characterization of equipment was used to treat real secondary Zhu et al. (2012) membrane fouling in a microfiltration ceramic membrane system treating secondary effluent COD, TOC, UVA 254 effluents from a wastewater treatment plant. Reversible fouling and irreversible fouling, which are defined based on backwashing, were characterized, and the effects of coagulation and secondary effluent membrane pore sizes on fouling evolution, as well as the composition of foulants, were also studied

27 Filtration experiments were carried out on a Xia et al. (2013) Ultrafiltration of humic acid and surface water with tubular ceramic membrane humic acid, surface water TOC, UVA 254 pilot-scale crossflow unit using humic acid (HA) solution and surface water as feed by varying transmembrane pressure (TMP). Measurements such as total organic carbon (TOC), ultraviolet absorbance at 254nm (UV 254 ), fluorescence excitation emission matrices (EEMs), ph, and conductivity were made on both raw water and the permeate. Yin et al. (2013) Ceramic membrane fouling and cleaning in ultrafiltration of desulfurization wastewater desulfurization wastewater COD, SS Foundation of ceramic UF membrane in the treatment of desulfurization wastewater. Fouling causes were sulfur and tar oil deposition on the membrane surface. Fouling mechanism was completion of pore blocking, and then cake layer formation. In situ ozonation was combined with In situ ozonation to coagulation/ceramic filtration process. Membrane Zhang et al. (2013) control ceramic membrane fouling in drinking water river water, polluted water TOC, UVA 254, Turbidity fouling was alleviated by in situ ozonation with low ozone dosage. Ozonation inside membrane pores changed the molecular structures of treatment organics. Organics with molecular weights of 1100 ~ 1500 Da in HPI fouled membrane most

28 Zhang et al. (2013) Understanding the fouling of a ceramic microfiltration membrane caused by algal organic matter released from Microcystis aeruginosa Effects of algal organic matter DOC Algal organic matter (AOM) released from Microcystis aeruginosa has high potential to cause fouling of water treatment membranes. The role of AOM components in the fouling of a commercial tubular ceramic microfiltration (MF) membrane (ZrO2 TiO2, 0.1mm) was investigated. A tubular ZnO3/TiO2 ceramic membrane with a transmembrane molecular weight cutoff of 300kD was used for Lee et al. (2014) pressure and ozonation on the reduction of ceramic membrane fouling secondary effluents TOC, UVA 254, Turbidity filtration tests at different TMPs of 1, 2, and 3 bar. Pre-ozonation at 3, 6, and 9mg/L O3 followed by membrane filtration at 1 bar were also conducted to assess the effect of ozonation on the during water reduction of membrane fouling and the Zhang et al. (2014) reclamation Feedwater coagulation to mitigate the fouling of a ceramic MF membrane caused by soluble algal organic matter AOM in drinking water DOC, UVA 254 improvements of water qualities. The effect of feed water coagulation using alum, aluminium, ACH, ferric sulphate and ferric chloride for reducing the fouling of a commercial ceramic MF membrane (ZrO 2 TiO 2 ) caused by the AOM released from Microcystis aeruginosa was investigated. The hydrophobic compounds in the AOM solution were more susceptible to the coagulation treatment than the hydrophilic and transphilic compounds

29 Cleaning ceramic Analyze fouling mechanism of ceramic membrane Chen et al. (2015) membranes used in treating desizing wastewater with a complex-surfactant treating desizing wastewater COD, TOC used in treating desizing wastewater. Develop a cleaning strategy by studying interaction mechanism between cleaning agents and foulants. Both hydrolysis of NaOH and solubilization of SDBS SDBS-assisted method micelles play a significant role in cleaning process. Fujioka and Nghiem (2015) Fouling control of a ceramic microfiltration membrane for direct sewer mining by backwashing with ozonated water Municipal wastewater TOC, Turbidity Backwashing using ozonated water was investigated to control fouling during direct sewer mining using a ceramic microfiltration (MF) membrane. Results reported here suggest that backwashing using ozonated water has the ability to remove most foulants deposited on the membrane surface and can be used for sewer mining, where severe cake formation occurs

30 제 3 장재료및방법 3.1 유입수 본연구에서는증류수, 모사수인 Humic acid 용액 (10 or 20 mgha/l), 현장수등에대하여투과및여과실험을진행하였다. 증류수는세라믹막의투과성능을파악하기위하여사용되었으며, Millipore 社의초순수기 (Direct-Q) 를이용하였다. Humic acid 용액은 Sigma Aldrich 社에서구매한 Humic acid를 1 L의증류수에 24시간용해시켜 1 gha/l의 stock solution을제조한뒤, 이를 10 또는 20 mgha/l (HA10 or HA20) 로희석하였다. 현장수는서울특별시에소재하는한강의하천수 (HR) 와서남물재생센터의하수 2차처리수 (SN) 를이용하였다. 증류수를제외한모든 Feed water는 4 이하에서보관하였으며, 0.45 μm의 Cellulose membrane에전량여과한뒤실험에이용하였다. 모든실험은항온유지장치를이용하여일정한온도를맞추어진행하였으며, 실험에사용한 Feed water의수질특성은 Table 4와같다

31 Table 4 Characteristics of feed water ph EC (us) DOC (mg/l) UVA 254 DW HA HA HR SN

32 3.2 세라믹막및세라믹막장치 본연구에서는 TAMI industry 社 (France) 의 INSIDE CeERAM TM 세라믹막을사용하여실험을진행하였다 (Figure 3). 이세라믹막은관형으로서공극크기가 300 kd이며 7채널로이루어져있다. Support layer는 Alumina, Titania, Zirconia로구성되어있으며, active layer 는 Titania로이루어져있다. 상세한제원은 Table 5과같다. 세라믹막장치는유입수조 (Feed tank), 원심펌프, 세라믹막을포함하는세라믹막모듈, 압력계, 밸브, 스테인리스배관등으로구성되어있다 (Figure 3). 컨트롤패널을통하여제어가되는원심펌프와밸브를제어하여세라믹막으로유입되는유입수의십자류유량과막간압력차를조절할수있다. 항온유지장치 (RW-2025G, JEIO tech, Korea) 를원수탱크에연결하여세라믹막에유입되는원수의온도를일정하게유지하였으며, 여과수의유량은전자저울 (Explorer, OHAUS, USA) 을이용하여일정한시간간격으로수집하였다 (Figure 4)

33 Table 5 Characteristics of ceramic membrane Pore size (kd) No. of channel Surface area (cm 2 ) Diameter (mm) Length (mm) Operating pressure (bar) Operating ph Operating temperature ( ) < 10 0 ~ 14 <

34 Figure 3 Digital images: (a) Ceramic membrane; (b) Ceramic membrane system

35 Figure 4 Schematic system flow chart of the ceramic membrane system

36 3.3 실험방법및실험조건 실험방법 본연구에사용한세라믹막의성능을파악하기위하여증류수를이용한세라믹막특성실험을선행하였다. 일정한온도의증류수를펌프와밸브를조절하여일정한막간압력차와십자류유량에서여과수의 flux를측정하였다. 세라믹막특성실험의결과를바탕으로모사수인 Humic acid 용액과세가지의현장수를대상으로여과실험을수행하였다. 여과실험은여과수가 2 L가될때까지일정한온도, 막간압력차, 십자류유량에서이루어졌다. 여과실험이끝난뒤에는여과수와농축수를샘플링하여수질분석을실시하였다. 여과실험이끝난세라믹막은직렬저항모델을통한막오염특성을분석하기위하여단계적인세척과정을거쳤다. 우선물리적세척과정은다음과같은단계를거쳤다. 농도분극에의한막오염을제거하기위하여증류수 3 L를 0.5 bar의막간압력차에서 10분간운전하였다. 다음으로세라믹막표면에약하게형성된 Cake 층에의한막오염을제거하기위하여증류수 3L를 300 L/h의십자류유량으로실시한여과실험의막간압력차조건에서 10분간운전하였다. 물리적세척의마지막단계로 5 bar의막간압력차조건에서여과방향과반대방향으로증류수를 10분동안운전하였다. 각단계가끝난뒤에는증류수를이용하여실시한여과실험조건에서증류수의 flux를측정하였다. 화학적세척은 85 의 20 g/l의 NaOH 용액에세라믹막을 30분동안침지시킨후증류수를이용하여충분히세척하였다. 다음으로 50 의 1 ml/l의 H 3 PO 4 용액에세라믹막을 15분동안침지시킨후증류수를이용하여충분히세척하

37 였다. 각세척과정이끝난후에는증류수를이용하여실시한여과실험조건에서의회복된 flux를각각측정하였다 실험조건세라믹막의투과특성을확인하기위한투과실험은증류수를이용하여온도, 막간압력차, 십자류유량을달리하여수행하였다. HA10, HA20, HR, SN에대한모사수및현장수에대한여과실험은일정한온도와십자류유량에서막간압력차를달리하여수행하였다. 상세한운전조건은 Table 6와같다

38 Table 6 Operating conditions Feed water Q cross flow (L/h) TMP (bar) Temperature ( ) Volume of Feed water (ml) Volume of permeate (ml) D.W. 0 / 50 / 100 / / 2 / 3 / 4 10 / 25 / HA10 HA20 HR / 2 / ,000 2,000 SN

39 3.4 수질분석 정성분석 수중에존재하는유기물의특성및구성성분을정성적으로분석하기위하여 Fluorescence excitation-emission matrix (F-EEM, FluoroMate FS-2, scinco, Korea) 를이용하였다. F-EEM은수중에존재하는유기물이포함하고있는형광물질을흡광도를이용하여 3차원으로측정하는방법으로서, 유기물이고유하게흡수, 방출하는파장역역을측정하여수중에존재하는유기물의성상을파악할수있다. 분석한샘플의 F-EEM은선행연구를통하여확립된다양한유기물의방출파장 (Emission wavelength) 과여기파장 (Excitation wavelength) 에따른 peak를정리한 reference F-EEM (Figure 6) 과상호비교하여샘플에존재하는유기물을정성적으로파악할수있다. 수중유기물에대한 F-EEM은파장대별로 Aromatic protein Ⅰ (Region Ⅰ), Aromatic Protein Ⅱ (Region Ⅱ), Fulvic acid-like (Region Ⅲ), Soluble microbial by-product-like (Region Ⅳ), Humic acid-like (Region Ⅴ) 으로크게 5 부분으로구분할수있다 (Chen et al., 2003). 본연구에서의 F-EEM 분석은유입수, 여과수, 농축수에대하여방출파장스펙트럼의범위는 280 ~ 550 nm, 여기파장스펙트럼의범위는 200 ~ 400 nm에서동일한조건으로수행하였다

40 Figure 5 Digital images: (a) TOC analyzer; (b) UV/Vis spectrophotometer; (c)fluorescence-spectrometer

41 Figure 6 Location of F-EEM peaks (symbols) based on literature reports and operationally defined excitation and emission wavelength boundaries (dashed lines) for five F-EEM regions

42 3.4.2 정량분석실험전후의수질의변화를파악하기위하여유입수, 여과수, 농축수에대하여특성분석을진행하였다. 기본적인수질정보를파악하기위하여 ph (ph meter, Thermo scientific 420A, USA) 와 EC (TRANS instruments HC3010, USA) 를측정하였다. 또한, 용존유기물을측정하기위하여 DOC (Total organic carbon analyzer, Sievers 5310C, USA) 와수중유기물질의지표인 UVA 254 (Thermo scientific GENESYS 10S UV/Vis spectrometer) 를측정하였다. 세라믹막여과과정에따른수중유기물의제거율은 DOC와 UVA 254 를이용하여다음과같은식으로각각계산하였다. Removal of DOC (%) = (1) Removal of UVA 254 (%) = (2) 여기에서,,, 는각각유입수와여과수의 DOC와 UVA 254 값이다. 한편, DOC와 UVA 254 값과식 (3) 을이용하여친수성과소수성의경향을파악하는값인 SUVA (Specifec ultraviolet absorbance) 를산정하였다. SUVA ( ) = (3)

43 3.5 모델분석 Hermia 모델 Hermia 모델은정압전량여과의공극막힘에의한막오염기작을해석하기위한식으로개발되었으며 (Hermia, 1982), 식 (4) 와같다. (4) 여기에서 t는여과시간, V는여과량, k는상수이며, n은 blocking 인자로서 n에따라서막오염기작을분류할수있다. n = 2인경우에는 Complete pore blocking 모델로서, 입자가다른입자위에쌓임이없이막공극을막는경우이다. 일반적으로막의공극보다여과되는입자의크기가큰경우이다. n = 1인경우는 Intermediate pore blocking 모델로서, Complete pore blocking 모델과유사하지만입자가막공극뿐만아니라다른입자위에쌓이는경우이다. n = 1.5는 Internal pore blocking 모델로서, 공극보다작은입자가공극내에부착되면서공극이좁아지면서 flux 가감소하는경우이다. n = 0은 Cake formation 모델로서최종적으로이루어지는막오염형태로막표면에입자들이쌓이는경우이다. Hermia 모델은정압전량여과를위해서개발되었지만, 십자류여과방식에도적용하여막오염기작을해석하는연구가진행되어왔다 (Zhou et al., 2015; Vela et al., 2009). 식 (4) 는비선형식으로나타나게되므로해석에어려움이존재하기때문에선형변환을통하여접근하며, n에따른선형식은다음과같다

44 Complete pore blocking (n = 2) : ln (5) Intermediate pore blocking (n = 1) : (6) Internal pore blocking (n = 1.5) : (7) Cake formation (n = 0) : (8) SAE = (9) 식 (5) 에서 (8) 을각각실험데이터에적용하였으며, SAE (Sum of absolute error) 가최소가되는기울기와절편을구하였다. 여기에서 J calc 는식 (5) ~ (8) 을이용하여구한 flux이며, J meas 는실험을통하여얻은 flux이다

45 3.5.2 직렬저항모델직렬저항모델 (Resistance-in-series model) 은 Darcy s law를기초로하여형성된것으로, flux에대한막자체에의한영향과막오염에의한영향등을직렬로연결된저항으로표현할수있다 (Fillaudeau and Lalande, 1998; Bessiere et al., 2005). (10) J는여과수의 flux, A는막면적, V는여과수의부피, t는시간, ΔP 는막간압력차, μ는유입수의점성계수, R T 는총막저항을의미한다. 총막저항 R T 는막자체에의한저항 R M 과막오염에의한저항 R F 로구분할수있다. 막자체에의한저항 R M 은막오염을일으킬수있는물질이존재하지않는증류수를이용하여측정할수있다. 막오염에의한저항 R F 는구분방법에따라다시물리적세척으로회복이가능한가역적막오염저항 R RF 와화학적세척으로회복이가능한비가역적막오염저항 R IRF 로구분할수있다. 따라서식 (10) 은다음과같은식으로표현할수있다. (11) (12) 이러한세분화된막오염저항은단계적인세척과정을통하여구한회 복된 flux 를이용하여계산할수있으며, 각각의막오염저항은대상이

46 되는원수의특징과운전조건에따라추가되거나제외될수있다. 우선, 막자체에의한막저항 R M 은증류수를이용하여구한초기 flux인 J 0 를이용하여구할수있으며, 총막오염저항은모든여과가종료된후의최종 flux (J t ) 를이용하여구할수있다. 이를식으로표현하면다음과같다. (13) (14) 모든여과가종료된후에형성된막오염을분류하기위해서는각각의막오염을제거할수있는세척과정이필요하다. 본연구에서는식 (10) 을기준으로하여세척과정을통하여얻은회복된 flux를이용하여각각의막오염저항을아래와같은식으로계산하였다. (15) (16) 여기에서 J PC 는물리적세척을통하여막표면에형성된 cake 층에 의한저항이제거된후의회복된 flux, J CC 는화학적세척을통하여비 가역적인막오염이제거된후의회복된 flux 를나타낸다

47 제 4장결과및고찰 4.1 세라믹막의투과특성 Flux에영향을미치는요인실험에사용한세라믹막의투과성능을평가하기위하여증류수를이용하여막간압력차, 십자류유량, 온도를각각달리하여실험을수행하였다. 우선운전조건에대한영향을알아보기위하여증류수의온도를 25 로고정하여, 막간압력차를 1, 2, 3, 4 bar, 십자류유량을 0, 50, 100, 150 L/h 의조건에서실험을수행하였다. 실험결과, 동일한막간압력차에서는십자류유량이증가함에따라 flux가감소하는경향을보였지만십자류유량이 0 L/h일때의 3.00 ~ 4.17 % 범위에불과하였다. 반면, 동일한십자류유량조건에서막간압력차가증가할수록실험조건범위에서선형적으로 flux가증가하는것을확인할수있었다 (Figure 7). 온도에따른영향을알아보기위하여증류수의온도를 10, 25, 40 의조건에서실험을수행하였다. 25 의 flux를기준으로 10 에서의 flux는 ~ % 감소하였고, 40 에서의 flux는 ~ % 증가하였다 (Figure 8)

48 Figure 7 Flux test of ceramic membrane: (a) 10 ; (b) 25 ; (c)

49 Figure 8 Flux test of ceramic membrane

50 4.1.2 Permeability 및막자체의저항실험결과를토대로단위면적당단위시간당단위막간압력차에대한여과부피인 Permeability [L/m 2 h bar, LMH] 를계산하여실험에사용한세라믹막의성능을평가하고자하였다. 동일한십자류유량에서막간압력차에따른증류수의 flux 변화는선형적으로증가하기때문에 (Figure 8), 그기울기를 이용하여온도와십자류유량에따른 Permeability를계산하였다. 온도별 Permeability는 10, 25, 40 에서각각 ± 2.92, ± 5.07, ± 4.50 LMH이었다. 실험을통하여얻은값과식 (10) 을이용하여막자체의저항을산정하였다. 증류수의온도가 10, 25, 40 일때의증류수의점성은각각 , , Pa s이며, 이를통하여얻은막자체의저항 RM은각각 1.23.E+11 ± 1.61.E+11, 1.26.E+11 ± 2.00.E+11, 1.39.E+11 ± 1.58.E+11 m -1 이었다. 막자체의저항은온도가증가함에따라최대 % 증가하였는데, 이는증류수의점성이높아지면서막표면과의마찰이증가하였기때문이라고판단된다

51 Table 7 Permeability of ceramic membrane Temperature ( ) Q crossflow (L/h) Slope R 2 Permeability (L/m 2 h) R m (m -1 ) E E E E E E E E E E E E E E E

52 4.2 세라믹막의수처리특성 여과특성 D.W., HA10, HA20, HR, SN에대하여 1, 2, 3 bar의막간압력차 (TMP) 에서여과수가 2 L가될때까지여과실험을진행하였으며, 그결과는 Figure 9과같다. 각각의유입수에대한 Flux (J) 는초기 flux (J 0 ) 로나누어표준화하여모든데이터를비교하였다. 용존유기물이존재하지않는 D.W. 는 flux의감소가보이지않았으며, 막간압력차가 1 ~ 3 bar로증가함에따라여과수가 2 L가될때까지걸리는시간 ( 이하여과시간 ) 이 분에서 9.67 분으로단축되었다. 이는유입수가 D.W. 인경우에는식 (1) 에따라 J 0 는막간압력차에비례하기때문이다. 용존유기물이존재하는 HA10, HA20, HR, SN에대한 flux 감소는 SN > HR > HA20 > HA10 순으로크게나타났다. 이는모든막간압력차조건에서동일한결과를보였다. 또한여과시간역시같은경향을나타내었다. 한편, Humic acid 용액인 HA10과 HA20은 flux의감소가 9.66 ~ % 의범위로나타났지만, 현장수인 HR, SN은 ~ % 의범위를나타내어 Humic acid 용액과현장수의여과특성에차이가있음을확인할수있었다. 또한, HA10과 HA20는여과과정에서 flux가선형에가깝게감소하는경향을보이는반면에, HR, SN은여과초기에가파르게감소하다가선형적으로감소하는경향을보인다. 가파르게감소하는경향은막간압력차가높아질수록여과초기에일어나는것을확인할수있다

53 Figure 9 Flux decline of filtration test: (a) 1 bar (vs. volume); (b) 1 bar (vs. Time); (c) 2 bar (vs. volume); (d) 2 bar (vs. Time); (e) 3 bar (vs. volume); (f) 3 bar (vs. Time)

54 Table 8 Flux declines and filtration times TMP (bar) D.W. HA10 HA20 HR SN Flux decline (%) Filtration time (min)

55 4.2.2 수질특성정성분석인 F-EEM 분석과정량분석인 DOC, UVA 254 를이용하여유입수, 여과수, 농축수의수질변화를확인하였다. F-EEM 분석은 5가지로구분되는영역의 Intensity의상대적비교를통하여여과특성을파악하였으며, DOC와 UVA 254 값은식 (1) 과식 (2) 를이용하여제거율을계산하였으며, SUVA 값을산정하는데이용하였다 정성분석유입수, 여과수, 농축수에대한 F-EEM 분석결과는 Figure 10과같다. 제일상단부터아래로각각 HA10, HA20, HR, SN의순서이다. HA10과 HA20의경우에는유입수, 여과수, 농축수의뚜렷한변화를확인할수있었지만 HR, SN은큰변화가없었다. HA10과 HA20의경우에는유입수가 Region Ⅴ에속하여 Humic acid-like 물질을포함하고있으며, 농도의차이로인하여 HA20이 HA10보다 Intensity가높게나타나는것을확인할수있다. 여과수는유입수에비하여 Region Ⅴ의상단부분의 Intensity가낮아진것을확인할수있다. 해당부분은소수성을띄는고분자물질들이존재하는범위로서, 여과과정을통하여친수성물질보다는소수성고분자물질이여과되었음을확인할수있다. 반면, 농축수의경우에는유입수보다 Region Ⅴ의상단부분의 Intensity가높아진것을확인할수있으며, 이는유입수보다농축이된것으로판단할수있다. 한편, 자연수인 HR과 SN의유입수의경우에는 Region Ⅳ와 Region Ⅴ에서존재가확인되었으며, 이는 HR과 SN은 Humic acid-like 물질뿐만아니라 Soluble microbial by-product-like 물질을포함하고있다고판단할수있다. Soluble microbial by-product-like 물질은

56 Humic acid-like 물질이소수성고분자물질을나타내는것과달리친수성저분자물질을나타낸다. 여과수와농축수의경우에는전범위의 Intensity에서는큰변화를관찰할수없었기때문에 Intensity의범위를한정하여살펴보았다 (Figure 11). 범위를한정한 F-EEM에서는비교적작은차이이지만 HR과 SN에서유입수보다여과수와농축수의 Intensity가낮은것을확인할수있다. 특히, 여과수에서는 Region Ⅴ 의상단부분의 Intensity가낮아졌으며, 이는 HA10과 HA20의결과와동일하다. 반면에, HR과 SN의농축수는 Region Ⅴ의상단부분의 Intensity가여과수와마찬가지로낮아졌는데, 이는 HA10과 HA20과상반된결과이다. 농축수의 Intensity가유입수보다낮아졌다는것은수중에존재하는유기물이농축이되기보다는막표면에부착되었음을나타내고, 이는막오염을유발하였음을시사한다. 이결과는 4.2.3에서모사수 (HA10, HA20) 와현장수 (HR, SN) 의막오염정도를통하여다시확인할수있다. 한편, 모사수와현장수의농축수결과의차이는수중에존재하는유기물의특성의차이에기인하다. 앞서살펴본바와같이모사수는 Region Ⅴ의소수성의경향을보이는물질로이루어져있으며, 현장수는친수성경향을보이는 Region Ⅳ와소수성경향을보이는 Region Ⅴ의물질이혼재하기때문이다. 이결과는 의 SUVA 분석을통하여재확인할수있다

57 Feed Permeate Retentate HA10 HA20 HR SN Figure 10 F-EEM analysis (HA10, HA20, HR, SN)

58 Feed Permeate Retentate HR SN Figure 11 F-EEM analysis (HR, SN)

59 정량분석유입수, 여과수, 농축수에대한 ph, EC, DOC, UVA 254, SUVA 값은 Table 9과같다. 정량분석을통해서앞선정성분석인 F-EEM 분석과같은결과를확인할수있었다. HA10, HA20, HR, SN의유입수 DOC는각각 3.7, 8.5, 3.4, 7.9 mg/l이며, HA10과 HR, HA20과 SN이유사한 DOC 값을나타내고있기때문에모사수와현장수의상호비교가가능하다. 여과수는모사수와현장수모두에서 DOC 값이감소하였으나, 농축수의경우에는모사수는증가하였고, 현장수는감소하였다 (Figure 12). 식 (1) 을이용하여 DOC의제거율을산정한결과는 Figure 13와같다. HA10, HA20, HR, SN의여과수는각각 76.6 ~ 85.6, 19.6 ~ 87.5, 62.7 ~ 64.7, 50.2 ~ 55.3 % 의 DOC 제거율을보였다. 모사수와현장수모두에서막간압력차가증가함에따라제거율이감소되는경향을보였으며, 현장수보다모사수의 DOC 제거율이상대적으로높은것을확인할수있었다. 유사한 DOC 범위를나타내는 HA10과 HR은최대 20.9 %, HA20과 SN은최대 32.4 % 의차이를보였다. 농축수의경우에는모사수인 HA10과 HA20은유입수에비하여 DOC 농도가증가하였으며, 현장수인 HR과 SN은감소하였다. 모사수와현장수의경향성의차이는 1 수중에존재하는유기물의수질특성과 2 세라믹막의특성에기인한다. 우선소수성과친수성의경향성을파악할수있는 SUVA 값을비교하면, HA10과 HA20의유입수는각각 6.35, 5.55이며, HR과 SN의유입수는각각 1.21, 1.37이다. SUVA 값은 2보다작은경우에는대부분낮은소수성과낮은분자량을나타내며, 2 ~ 4의범위에서는소수성물질과친수성자연유기물이혼합된형태, 4보다큰경우에는대부분 Humic 물질로구성되어높은소수성과높은분

60 자량을나타낸다 (Ghernaout, 2004). HA10과 HA20은 SUVA 값이 6 이상의높은값을나타내고있어소수성이며고분자물질로이루어져있는경향을알수있으며, HR과 SN은 2 이하의값을나타내므로친수성이며저분자물질로이루어져있음을확인할수있다. 이는앞선 F-EEM 결과와도일치한다. 한편, 실험에사용한세라믹막은접촉각이 42 로친수성을나타낸다 (Ha, 2013). 따라서소수성경향을띄는모사수인 HA10과 HA20은막표면에부착되기보다는농축이되는결과를나타내어여과수의높은유기물제거율과농축수의높은농축율을나타낸다. 반면에, 친수성경향을띄는현장수인 HR과 SN은막표면과의친화력으로인하여수중유기물이막표면에부착되거나막을통과하게되어상대적으로낮은유기물제거율을나타내는것으로판단할수있다

61 Table 9 Water quality analysis ph EC (μs) DOC (mg/l) UVA 254 (m -1 ) SUVA (L/mg m) D.W Feed HA Permeate Retentate Permeate Retentate Permeate Retentate Feed Permeate Retentate HA20 2 Permeate Retentate Permeate Retentate Feed Permeate Retentate HR 2 Permeate Retentate Permeate Retentate Feed SN Permeate Retentate Permeate Retentate Permeate Retentate

62 Figure 12 Value of DOC: (a) HA10; (b) HA20; (c) HR; (d) SN

63 Figure 13 Removal of DOC

64 4.2.3 모델분석 Hermia 모델 : 기작분석 Hermia 모델은 flux가감소하는현상을여러가지공극막힘기작으로해석하는모델이며, 막오염초기에는 Complete pore blocking, Intermediate pore blocking, Internal pore blocking이이루어지다가막오염이증가하면서 Cake formation이형성되는것으로알려져있다. 한편막표면에서발생하는 Complete pore blocking과 Intermediate pore blocking은 Complete pore blocking이발생한후에 Intermediate pore blocking이일어나게되며, 최종적으로 Cake formation으로귀결된다. Hermia 모델을이용하여실험값을분석한결과는 Table 13과같으며, 해석된인자를이용하여구한 flux와실험값은 Figure 14과 Figure 15와같다. 전체적으로 Cake formation 모델이가장낮은 SAE를나타내어실험값을가장잘모사하는것으로나타났으며, 모사수인 HA10과 HA20은 1 bar에서 Complete pore blocking 모델이, HR과 SN은 3 bar에서 Intermediate pore blocking 모델이가장적합하였다. HA10과 HA20이 1 bar에서 2, 3 bar와달리 Complete pore blocking 모델이더적합하게해석된이유는낮은막간압력차에의해막오염이적게발생하여 Cake 층이형성되기보다는막오염초기단계인 Complete pore blocking 모델이적합하게된것으로판단된다

65 Table 10 Hermia model parameters obtained by fitting models to experimental data HA10 HA20 HR SN Complete pore blocking Internal pore blocking Intermediate pore blocking Cake formation a b SAE a 2.01.E E E E E E E E E E E E-03 b 1.18.E E E E E E E E E E E E-02 SAE a 4.88.E E E E E E E E E E E E-04 b 1.40.E E E E E E E E E E E E-03 SAE a 1.43.E E E E E E E E E E E E-05 b 1.95.E E E E E E E E E E E E-05 SAE

66 1 bar 2 bar 3 bar HA10 HA20 Figure 14 Hermia model analyses: HA10, HA

67 1 bar 2 bar 3 bar HR SN Figure 15 Hermia model analyses: HR, SN

68 직렬저항모델 : 막오염분석세척과정을통하여회복된 flux와직렬저항모델을이용하여각각의실험조건에따른막저항을산정하였다 (Figure 16). 실험에따른초기 flux (J 0 ) 의차이로인하여막자체의저항 R M 은 1.17.E+11 ~ 1.40.E+11 m -1 의범위에서평균 1.29.E+11 ± 6.94.E+11 m -1 을나타내었다. 총막저항 R T 는 D.W. 을제외한모든유입수에대하여막간압력차가증가함에따라증가하는경향을보였다. R T 에서 R M 을제외한막오염에의한저항 R F 는모든유입수에서 R M 이큰차이를보이고있지않기때문에 R F 역시막간압력차가증가함에따라증가하는경향을보인다. 이는 R T 의증가는 R F 의증가로인한것이라고판단할수있다. R F 는 HA10은 1.33.E+10 ~ 5.56.E+10, HA20은 1.83.E+10 ~ 6.88.E+10, HR은 3.50.E+10 ~ 1.65.E+11, SN은 1.69.E+11 ~ 2.79.E+11 m -1 의범위를나타내었다. HA10, HA20은 HR, SN에비하여낮은 R F 값을나타내어, 모사수가자연수보다상대적으로막오염이적게발생했음을확인할수있었다. 이는앞서살펴본바와같이모사수와자연수의수중유기물의특성과세라믹막의특성에기인한것이다. 소수성경향을띄는모사수의유기물질은친수성을띄는세라믹막표면에부착되기보다는농축이되어막오염을적게발생시키며유기물의제거율이높은반면, 친수성경향을띄는자연수의유기물질은세라믹막표면에부착되어막오염을크게발생시켰으며막의공극을통하여유기물질이빠져나와유기물의제거율이상대적으로낮음을확인할수있다. R F 는 R RF 와 R IRF 의합으로이루어진다. R RF 는물리적세척으로회복이된 flux를이용하여계산된값이며, R IRF 는물리적세척후화학적세척

69 을통하여회복이된 flux 에의하여계산되었다. R IRF 가 차지하는비율 은 HA10은 1.04 ~ 54.22, HA20은 0.00 ~ 56.00, HR은 0.00 ~ 45.93, SN은 ~ % 의범위를나타내었다. 비가역적인막오염인 R IRF 는 D.W. 을제외한모든유입수에대하여막간압력차가증가함에따라증가하였다. 이는막간압력차가증가함에따라막을통과하는여과량이증가하며, 막표면에형성되는 Cake 층이압착되기때문이다. 낮은막간압력차에서는비가역적인막오염이거의발생하지않았으므로, 주기적인물리적인세척만으로 flux를유지할수있다

70 Figure 16 Value of resistance: (a) Membrane and fouling; (b) Reversible and irreversible fouling

71 제 5 장결론 본연구에서는세라믹막을이용하여수중에존재하는유기물을제거하는경우의여과특성과막오염기작및특성을살펴보았다. 실험은증류수 (D.W.), 모사수인 Humic acid 용액 (HA10, HA20) 과현장수 (HR, SN) 를유입수로하여십자류여과방식을이용하여일정한십자류유량과온도조건에서막간압력차를변화시켜여과수가 2 L가될때까지진행하였다. 실험에사용한세라믹막의투과성능 (Permeability) 은 10, 25, 40 로온도가증가함에따라각각 ± 2.92, ± 5.07, ± 4.50 LMH로증가하였으며, 이는온도가올라감에따라물의점성이낮아져 flux가증가하였기때문이다. 유입수를대상으로여과실험을수행한결과, 막간압력차가증가할수록 flux의감소가크게일어나고여과시간은단축되는경향을보였으며, 모사수보다현장수의 flux 감소가크게나타났다. 유입수, 여과수, 농축수의수질특성을분석한결과, 모사수인 HA10과 HA20은소수성고분자물질로, 현장수인 HR과 SN은친수성저분자물질로주로이루어진것으로나타났다. 이러한유입수의특성으로인하여여과과정에서소수성을가지는모사수는농축이일어나면서막오염이적게발생하였으나, 친수성을가지는현장수는농축이되기보다는막표면에막오염을유발하는것으로나타났다. 여과실험의결과를바탕으로 Hermia 모델을이용하여막오염의기작을해석한결과, 전체적으로 Cake formation 모델이실험값을가장잘모사하는것으로나타났다. 여과실험후단계적인세척으로회복된 flux 와직렬저항모델을이용하여막오염특성을평가하였다. 막간압력차가

72 증가할수록총막오염은증가하였으며, 물리적세척으로회복이불가능한비가역적막오염의비율또한증가하는것으로확인하였다. 또한, 모사수인 HA10과 HA20보다현장수인 HR과 SN의막오염이크게발생하였다

73 참고문헌 Abadi SRH, Sebzari MR, Hemati M, Rekabdar F, Mohammadi T Ceramic membrane performance in microfiltration of oily wastewater. Desalination 265: Agana BA, Reeve D, Orbell JD Optimization of the operational parameters for a 50 nm ZrO 2 ceramic membrane as applied to the ultrafiltration of post-electrode position rinse wastewater. Desalination 278: Agana BA, Reeve D, Orbell JD Performance optimization of a 5 nm TiO 2 ceramic membrane with respect to beverage production wastewater.desalination 311: Alpatova AL, Davies SH, Masten SJ Hybrid ozonation-ceramic membrane filtration of surface waters: The effect of water characteristics on permeate flux and the removal of DBP precursors, dicloxacillin and ceftazidime. Separation and Purification Technology 107: Amarsanaa B, Park JY, Figoli A, Drioli E Optimum operating conditions in hybrid water treatment process of multi-channel ceramic MF and polyethersulfone beads loaded with photocatalyst. Desalination and Water Treatment 51: Amarsanaa B, Park JY Effect of water back-flushing and PP beads in hybrid water treatment of multi-channel alumina MF and photocatalyst-coated PP beads. Desalination and Water Treatment 54: Angelis LD, Cortalezzi MMFD Ceramic membrane filtration of organic compounds: Effect of concentration, ph, and mixtures interactions on fouling. Separation and Purification Technology 118:

74 Barredo-Damas S, Alcaina-Miranda MI, Iborra-Clar MI, Mendoza-Roca A, Gemma M Effect of ph and MWCO on textile effluents ultrafiltration by tubular ceramic membranes. Desalination and Water Treatment 27: Blanpain-Avet P, Faille C, Delaplace G, Benezech T Cell adhesion and related fouling mechanism on a tubular ceramic microfiltration membrane using Bacillus cereus spores. Journal of Membrane Science 385: Buekenhoudt A, Bisignano F, Luca GD, Vandezande P, Wouters M, Verhulst K Unravelling the solvent flux behaviour of ceramic nanofiltration and ultrafiltration membranes. Journal of Membrane Science 439: Chen D, Columbia M Enzymatic control of alginate fouling of dead-end MF and UF ceramic membranes. Journal of Membrane Science 381: Chen P, Znong Z, Liu F, Xing W Cleaning ceramic membranes used in treating desizing wastewater with a complex-surfactant SDBS-assisted method. Desalination 365: Cui Z, Xing W, Fan Y, Xu N Pilot study on the ceramic membrane pre-treatment for seawater desalination with reverse osmosis in Tianjin Bohai Bay. Desalination 279: de-la-ruvia A, Rodriguez M, Prats D ph, Ionic strength and flow velocity effects on the NOM filtration with TiO 2 /ZrO 2 membranes.separation and Purification Technology 52:

75 Ebrahimi M, Schmitz O, Kerker S, Liebermann F, Czermak P Dynamic cross-flow filtration of oilfield produced water by rotating ceramic filter discs. Desalination and Water Treatment 51: Farsi A, Boffa V, Qureshi HF, Nijmeijer A, Winnubst L, Christensen ML Modeling water flux and salt rejection of mesoporous -alumina and microporous organosilica membranes. Journal of Membrane Science 470: Fujioka T, Khan SJ, McDonald JA, Nghiem LD Nanofiltration of trace organic chemicals: A comparison between ceramic and polymeric membranes. Separation and Purification Technology 136: Fujioka T, Nghiem LD Fouling control of a ceramic microfiltration membrane for direct sewer mining by backwashing with ozonated water. Separation and Purification Technology 142: Gomes MCS, Arroyo PA, Pereira NC Biodiesel production from degummed soybean oil and glycerol removal using ceramic membrane. Journal of Membrane Science 378: Guirgis A, Gay-de-Montella R, Faiz R Treatment of produced water streams in SAGD processes using tubular ceramic membranes. Desalination 358: Gyeong GM, Park JY Role of photo-oxidation and adsorption at water back-flushing in hybrid water treatment of multi-channels alumina MF and PP beads coated with photocatalyst. Desalination and Water Treatment 54: Hashino, M., Katagiri, T., Kubota, N., Ohmukai, Y., Maruyama, T. and Matsuyama, H Effect of membrane surface morphology on membrane

76 fouling with sodium alginate. Journal of Membrane Science 366(1 2): Hermia J Constant pressure blocking filtration laws-application to power-law non-newtonian fluids. Chemical Engineering Research and Design 60a: Huang, H., Lee, N., Young, T., Gary, A., Lozier, J.C. and Jacangelo, J.G Natural organic matter fouling of low-pressure, hollow-fiber membranes: Effects of NOM source and hydrodynamic conditions. Water Research 41(17): Karnik BS, Davies SH, Baumann MJ, Masten SJ The effects of combined ozonation and filtration on disinfection by-product formation. Water Research 39: Kim, H.-C. and Dempsey, B.A Membrane fouling due to alginate, SMP, EfOM, humic acid, and NOM. Journal of Membrane Science 428(0): Konieczny K, Bodzek M, Rajca M A coagulation MF system for water treatment using ceramic membranes. Desalination 198: Lee, E.K., Chen, V. and Fane, A.G Natural organic matter (NOM) fouling in low pressure membrane filtration -- effect of membranes and operation modes. Desalination 218(1-3): Lee HW, Kim SG, Choi JS, Kim SK, Oh HJ, Lee WT Effects of water temperature on fouling and flux of ceramic membranes for wastewater reuse. Desalination and Water Treatment 51:

77 Lee SJ, Dilaver M, Park PK, Kim JH Comparative analysis of fouling characteristics of ceramic and polymeric microfiltration membranes using filtration models. Journal of Membrane Science 432: Lee SJ, Dilaver M, Park PK, Kim JH Comparative analysis of fouling characteristics of ceramic and polymeric microfiltration membranes using filtration models. Journal of Membrane Science 432: Lee, S. and Cho, J Comparison of ceramic and polymeric membranes for natural organic matter (NOM) removal. Desalination 160(3): Lee W, Lee HW, Choi JS, Oh HJ Effects of transmembrane pressure and ozonation on the reduction of ceramic membrane fouling during water reclamation. Desalination and Water Treatment 52: Li M, Wu G, Guan Y, Zhang X. Treatment of river water by a hybrid coagulation and ceramic membrane process. Desalination 280: Li W, Zhou L, Xing W, Xu N Coagulation-microfiltration for lake water purification using ceramic membranes. Desalination and Water Treatment 18: Lim GT, Jeong HG, Hwang IS, Kim DH, Park NE, Cho JW Fabrication of a silica ceramic membrane using the aerosol flame deposition method for pretreatment focusing on particle control during desalination. Desalination 238: Majewska-Nowak K, Kawiecka-Skowron J Ceramic membrane behaviour in anionic dye removal by ultrafiltration. Desalination and Water Treatment 34:

78 Marchetti P, Butte A, Livingston AG An improved phenomenological model for prediction of solvent permeation through ceramic NF and UF membranes. Journal of Membrane Science : Mori M, Sugita T, Mase A, Funatogawa T, Kikuchi M, Aizawa K, Kato S, Saito Y, Ito T, Itabashi H Photodecomposition of humic acid and natural organic matter in swamp water using a TiO 2 -coatedceramicfoamfilter:potentialfortheformationofdisinfectionbyproducts.c hemosphere 90: Oulton R, Hasse JP, Kaalberg S, Redmond CT, Nalbandian MJ, Cwiertny DM Hydroxyl radical formation during ozonation of multiwalled carbon nanotubes: Performance optimization and demonstration of a reactive CNT filter. Environmental Science and Technology 49: Park HS, Kim YH, An BR, Choi HC Characterization of natural organic matter treated by iron oxide nanoparticle incorporated ceramic membrane-ozonation process. Water Research 46: Perez-Galvez R, Guadix EM, Berge JP, Guadix A Operation and cleaning of ceramic membranes for the filtration of fish press liquor. Journal of Membrane Science 384: Ruohomaki K, Nystrom M Fouling of ceramic capillary filters in vacuum filtration of humic acid. Filtration and Separation 37: Schlichter B, Mavrov V, Chmiel H Study of a hybrid process combining ozonation and membrane filtration - filtration of model solutions. Desalination 156: Sentana I, Puche RDS, Sentana E, Prats D Reduction of chlorination byproducts in surface water using ceramic nanofiltration membranes. Desalination 277:

79 Shang R, Verliefde ARD, Hu J, Zeng Z, Lu J, Kemperman AJB, Deng H, Nijmeijer K, Heijman SGJ, Rietveld LC Tight ceramic UF membrane as RO pre-treatment: The role of electrostatic interactions on phosphate rejection. Water Research 48: Sklari SD, Szymanska K, Pagana AE, Samaras P, Zaspalis VT, Zouboulis AI NanoMembraneWater: development of innovative hybrid processes for contaminated water treatment using nanoporous membranes. Desalination and Water Treatment 51: Stylianou SK, Sklari SD, Zamboulis D, Zaspalis VT, Zouboulis AI Development of bubble-less ozonation and membrane filtration process for the treatment of contaminated water. Journal of Membrane Science 492: Sutzkover-Gutman I, Hasson D, Semiat R Humic substances fouling in ultrafiltration processes. Desalination 261: Szymaneka K, Zouboulis AI, Zamboulis D Hybrid ozonation microfiltration system for the treatment of surface water using ceramic membrane. Journal of Membrane Science 468: Vela M, Blanco S, Garcia J, Rodriguez E Analysis of membrane pore blocking models adapted to crossflow ultrafiltration in the ultrafiltration of PEG. Chemical Engineering Journal 149: Xia S, Zhou Y, Ma R, Xie Y, Chen J Ultrafiltration of humic acid and surface water with tubular ceramic membrane. Desalination and Water Treatment 51: Xia S, Zhou Y, Ma R, Xie Y, Chen J Ultrafiltration of humic acid and surface water with tubular ceramic membrane. Desalination and Water Treatment 51: