Desalination 249 (2009) 1380–1384

Contents lists available at ScienceDirect

Desalination

j ourna l homepage: www.e lsev ie r.com/ locate /desa l

Experimental study of filterability behavior of model extracellular polymericsubstance solutions in dead-end membrane filtration

Zhan Wang a,⁎, Yin Song a, Mei Liu a, Jinmiao Yao a,b, Yuanyuan Wang a, Zhang Hu b, Zhaohui Li b

a Department of Chemistry and Chemical Engineering, College of Environment and Energy Engineering, Beijing University of Technology, Beijing, 100022, Chinab Beijing Fluid Filtration and Separation Technology Research Center, Beijing 101312, China

⁎ Corresponding author. Fax: +86 10 6739 1983.E-mail addresses: zhanwang3401@yahoo.com.cn (Z.

songyin1012@hotmail.com (Y. Song).

0011-9164/$ – see front matter © 2009 Published by Edoi:10.1016/j.desal.2008.06.028

a b s t r a c t

a r t i c l e i n f o

Article history:Accepted 30 June 2008Available online 3 October 2009

Keywords:EPSModel solutionCumulative filtrate volumeRejectionSpecific cake resistance

A series of model extracellular polymeric substance (EPS) solutions was prepared by using sodium alginate,humic acid and some proteins on the basis of the components of actual EPS extracted from sludge for laboratory-scale SBR by the formaldehyde–NaOHmethod. The dead-endmodel filter of these solutionswas carried outwith0.1 μm PVDFMFmembrane under a transmembrane pressure of 0.1 MPa and the filterability behaviors of thesesolutions were also investigated. The experimental results showed that the filterability behaviors of BSA, β-lactoglobulin and lysozyme model solutions with five times the protein concentration in the actual EPS weresimilarwith that of the actual EPS solution; in addition, the addition of sodium alginate and humic acid enhancedthe rejection of proteins, and the values ofαc ofmodel solutions increasedwith the addition of sodiumalginate orhumic acid, and especially the values ofαc of themodel solution greatly increasedwith the addition of humic acid,and the presence of protein in the mixed components model solutions caused the decrease of the αc values ofsodium alginate.

Wang),

lsevier B.V.

© 2009 Published by Elsevier B.V.

1. Introduction

It is known that the major obstacle of MBR is membrane fouling,which leads to a decline inmembrane flux and shortens the longevity ofmembrane module service in MBR. Therefore, it is very important toascertain themain substance that causesmembrane fouling inMBR andto investigate its filterability behavior.

Many researches take the macromolecular components, known asextracellular polymeric substances (EPS), that are composed ofpolysaccharide, protein, humic substances, uronic acid and deoxyribo-nucleic acids (DNA) [1–6], as amajor fouling component [7–10], and thecorrelation between EPS and membrane fouling is investigated deeply[11–15]. For instance, the impact of operating conditions on thefilterability of sludge has been investigated [11–13]; moreover, thecontribution of different components in EPS to membrane fouling isanother attractive branch inMBR research field [16–22]. Houghton [16]insists that proteins and polysaccharides play an important role insludgefilterability and thepolysaccharideshad the greatest influence onthe operation of MBR. Lesjean [17] found a correlation between thefiltration resistance and polysaccharide concentration. Tarnacki [18]believes that the permeateflux is inversely related to the polysaccharideconcentration in activated sludge. Because the extracted EPS hasvariability in composition, concentration, and complexity in real MBRsystems, many researchers use alginate [19,20], dextran [21], bovine

serum albumin (BSA) [19], β-lactoglobulin [22], lysozyme [21],myoglobin [21], cytochrome C [21] and BSA+alginate [19] to modelthe actual EPS solution inMBR. However, the present researches cannotprovide an alternative between the model solution and actual EPSsolution, therefore, how to choose the proper model solution to exactlydescribe the filterability behaviors of the actual EPS solution is verysignificant.

The aimof this paper is to compare the differentmodel EPS solutions(sodium alginate, BSA, β-lactoglobulin, lysozyme, humic acid and theircombination) with the actual EPS solution in its filterability behaviors(the cumulative filtrate volume (Vcumu), observed rejection of themembrane (Robs) and specific cake resistance (αc)) by using 0.1 μmPVDF membranes under 0.1 MPa TMP in order to get a model EPSsolution that can replace the actual EPS solution in filterability behavior.

2. Material and methods

2.1. Experimental equipment and operating conditions

In this paper, the EPS were extracted from two activated sludgesamples respectively producedby two sequencingbatch reactors (SBRs)(Fig. 1a) in our laboratory. One treated a synthetic wastewatercomprising of glucose, starch soluble and trace nutrients. This SBR wascalled SBR1. The other treated domestic wastewater, and was calledSBR2.

The components and concentrations of the syntheticwastewater areglucose 278 mg L−1, starch soluble 278 mg L−1, peptone 28 mg L−1,

Fig. 1. A diagram of an SBR system (a) and a diagram of a dead-end filtration system (b).(a): 1. air compressor, 2. valve, 3. rotameter, 4. air blower, 5. stirrer, 6. temperaturecontroller, 7. bioreactor; (b): 1. compressed air, 2. valve, 3. manometer, 4. manometerpressure reducer, 5. temperature humidity controller, 6. UF cell, 7. stirring rod,8. membrane, 9. measuring cylinder, 10. electronic scale.

1381Z. Wang et al. / Desalination 249 (2009) 1380–1384

NH4Cl 297 mg L−1, NaHCO3 111 mg L−1, CaC12 6 mg L−1, MgSO4·7H2O66 mg L−1, MnSO4·7H2O 6 mg L−1, FeSO4 0.3 mg L−1, and KH2PO4

52.8 mg L−1. The COD, NH3–N, and pH are 350–500 mg L−1, 65–80 mgL−1 and 7.0 respectively. The COD, NH3–N and pH of the domesticwastewater are 206–285 mg L−1, 49–63 mg L−1 and 7.5 respectively.

The working volume of SBR1 was 17 L and SBR2 had a workingvolume of 10 L. Theywere run atmixed liquor suspended solids (MLSS)of 3000 mg L−1, an organic loading of 0.25 kg COD/(kg MLSS d), ahydraulic retention time (HRT) of 13 h, a sludge retention time (SRT) of30 days and a dissolved oxygen concentration (DO) in a bioreactor of5.3 mgL−1. The temperaturewasmaintained at 25 °Cwith temperaturecontrollers. The pH was 7.0∼8.0. Both of them were operated at 6 h ofnitrification and 2 h of denitrification per day. The COD and NH3–Nremoval efficiencies of SBR1 were over 90% and 99% respectively. TheCOD and NH3–N removal efficiencies of SBR2 were over 91% and 98%respectively.

The dead-end filtration experiments were performed using thesetup represented in Fig. 1b.

Table 1Compositions of EPS extracted from activated sludge (mg L−1).

Activated sludge Polysaccharide Protein Hum

Sludge 1 (SBR1) 93.6±8.7 103.4±1 9.2Sludge 2 (SBR2) 60.7±4.2 157.3±2.4 22.4

Note: mean value (n=2)±S.D.

2.2. Membranes

Based on the membranes commonly used in MBR [13,23–26] and inthe research ofmembrane foulingmechanismof EPS [18–21,27], a 0.1 μmPVDF membrane was selected in this paper, which was purchased fromAndeMembraneSeparationTechnology andEngineering (Beijing, China).

2.3. Extraction of EPS

The EPS quantification strongly depends upon the extractionmethods [28], so the extraction method should be chosen carefully.Comparing with formaldehyde–ultrasonication, EDTA, cation ex-change resin and formaldehyde, Hong [29] reported that theformaldehyde–NaOH process extracted the highest amounts of EPSfrom all the sludges, and the formaldehyde could fix the cell andprevent cell lysis efficiently. Thus, the formaldehyde–NaOH extractionmethod was chosen in this paper. The sampled activated sludge wassettled for 1.5 h and then the supernatantwas decanted. The thickenedsludge was centrifuged at 2000g for 15 min at 4 °C. The sludge pelletswere resuspended to their original volume using a buffer consisting of2 mmol·L−1 Na3PO4, 4 mmol·L−1 NaH2PO4, 9 mmol·L−1 NaCl and1 mmol·L−1 KCl at pH=7. EPS extraction was performed as follows:formaldehyde was added to the above suspension for 1 h at 4 °C, andthen added 1 N NaOH for 3 h at 4 °C. The extracted EPS were harvestedby centrifugation of a sample of the formaldehyde/NaOH/sludgesuspension at 20,000g for 20 min, followed by 0.2 μm membranefiltration at 25 °C. Extractant residues in the solution were removed bythe dialysis membrane filtration (3500 Da; Pierce, USA) in thesubsequent treatment [1,29]. The comparisons of EPS compositionsextracted from the activated sludge from SBRs by the formaldehyde–NaOH are shown in Table 1.

As shown in Table 1, for the two extracted EPS solutions, the quantityof DNA was small, which indicated that the cells were not lysed duringthe extraction process. Their TOCvalueswere almost equal to the sumofthe concentrations of protein, polysaccharide and humic substance andthis confirmed that these substances are the major composition of EPS,and on the other hand, it indicated that the amount of EPS could beobtained bymeasuring the TOC value of the EPS solution. The quantitiesof the humic substance in EPS from sludge 1 were small because thesyntheticwastewater did not include the humic substance. The quantityof protein in the EPS from sludge 2 was more than that ofpolysaccharides, which is in accord with the results by Fang and Veiga[30,31]. In this experiment, theextractedEPS solution fromtheactivatedsludge 1 was chosen as the actual EPS solution.

2.4. Model EPS solutions

In this paper, sodium alginate (Sinopharm Chemical Reagent Co.,Ltd., China), BSA (Beijing ShuangxuanMicrobe CultureProducts Factory,China), β-lactoglobulin (Sigma, from bovine milk, approx. 90%),lysozyme (Sigma, Solarbio) and humic acid (Beijing Chemical ReagentCo., China)were chosen tomodel actual EPS solutions on the basis of theexperimental data of extracted EPS. The components ofmodel EPSwerethe same as or five times the concentration of protein, polysaccharideand humic acid in the EPS respectively, and the results were shown inTable 2.

ic substance DNA EPS TOC

±3.8 0 206.3 ±13.5 209.5±10.2±1.4 0 240.3±5.1 263.5±5.3

Fig. 2. Flux vs. time of themixed liquor 1 and actual EPS solution (0.1 MPa, 0.1 μmPVDF,T=25 °C, pH=7.5).

1382 Z. Wang et al. / Desalination 249 (2009) 1380–1384

2.5. Analytical methods

The protein and humic substance contents in EPSweremeasured bythemodified Lowrymethod [2], using bovine serumalbumin andhumicacid as the respective standards. The polysaccharide contents weremeasured by the anthrone method [32], using glucose as the standard.The DNA contents were measured using the diphenylamine DNAmeasurement kit (GMS20014, Genmed, China). The DNA was alsomeasured because the EPS normally contained small quantities of DNA,and a large quantity of DNA in the EPS could be an alarming indicationthat the cells were lysed during the harsh extraction process. Theviscosity was measured using a viscometer (ViscoTester 6L, Thermo-Haake, Germany). The total organic carbon (TOC)wasmeasured using aTOC analyzer (TOC-VCPH, Shimadzu, Japan). The pH was measuredusing a pH meter (pHS-3C, Leici, China).

3. Results and discussion

3.1. Comparison of the filtration characterization of the activated sludgemixed liquor and the actual EPS solution

The activated sludge mixed liquor 1 from SBR1 and the actual EPSsolution from activated sludge 1 were filtrated with 0.1 μm PVDFmembranes under the sameoperating conditions. The resultwas shownin Fig. 2. Flux decline caused by the actual EPS solution was bigger thanthatby themixed liquor 1. The specific cake resistanceof the sludge cakeis generally lower than that of macromolecules such as EPS [19]. Thusflux decrease caused by the EPS was more significant than that by themixed liquor. At different TMP ranging from 0.01 to 0.1 MPa, all theexperimental results were similar as shown in Table 3. The same as theconclusions reported by other papers [7–10], all of these resultsindicated that the EPSwas themajor fouling component in the activatedsludge mixed liquor.

3.2. Dead-end filtration of the different solutions

Dead-end filtrations of all the solutions in Table 2 were carried outunder 0.1 MPa, at 25 °C and pH=7.5 with 0.1 μm PVDF membrane for780 s. The results are shown in Figs. 3–5 respectively.

It can be seen from Fig. 3 that the filterability behaviors of modelsolutions are different. Except for solution 1 (BSA) and 2 (sodiumalginate), the model solution including single solute (solution 4–6) hasalmost the sameVcumu as the actual EPS solution, and their solution 4fits

Table 2Model EPS solutions.

Solutions Components Concentration

Solution 1 BSA The protein concentration is 103.4 mg L−1

Solution 2 Sodium alginate The polysaccharide concentration is 93.6 mg L−1

Solution 3 BSA+sodium alginate+humic acid

The concentrations of protein, polysaccharide andhumic acid are 103.4 mg L−1, 93.6 mg L−1 and9.2 mg L−1 respectively

Solution 4 BSA The protein concentration is 517.0 mg L−1

Solution5 β-lactoglobulin The protein concentration is 517.0 mg L−1

Solution 6 Lysozyme The protein concentration is 517.0 mg L−1

Solution 7 BSA+sodium alginate

The concentrations of protein and polysaccharideare 103.4 mg L−1 and 93.6 mg L−1 respectively

Solution 8 β-lactoglobulin+sodium alginate

The concentrations of protein and polysaccharideare 103.4 mg L−1 and 93.6 mg L−1 respectively

Solution 9 Lysozyme+sodium alginate

The concentrations of protein and polysaccharideare 103.4 mg L−1 and 93.6 mg L−1 respectively

Solution 10 β-lactoglobulin+sodium alginate+humic acid

The concentrations of protein , polysaccharide andhumic acid are 103.4 mg L−1, 93.6 mg L−1 and9.2 mg L−1 respectively

Solution 11 Lysozyme+sodium alginate+humic acid

The concentrations of protein, polysaccharide andhumic acid are 103.4 mg L−1, 93.6 mg L−1 and9.2 mg L−1 respectively

very well. On the contrary, Vcumu of the combination model (solution 3,7–11)was less than that of the actual EPS solution.When comparing themodel solutions 1, 7, and 3 with the actual EPS solution, or comparingthe model solutions 5, 8, and 10 with the actual EPS solution, orcomparing themodel solutions 6, 9, and 11with the actual EPS solution,it is easy to make the conclusion that the Vcumu of the combinationmodel solution including sodium alginate (solution 7, 8 and 9) orincluding sodium alginate and humic acid (solution 3, 10, 11) was lessthan that of the actual EPS solution due to the gelation of sodiumalginate [33]. Furthermore, the addition of humic acid would continu-ously decrease the filterability of these solutions.

Taking all of these factors into account, the β-lactoglobulin,lysozyme and BSA with five times the protein concentration of theactual EPS solution, can be chosen as the model solution for the actualEPS solution on the values of cumulative filtrate volume (Vcumu).

It can be seen from Fig. 4 that except for solution 6 (lysozyme), Robsof proteins in model solutions are all bigger than that in the actual EPSsolution. On the contrary, Robs of humic acid are all 100% for actual EPSsolution and model solutions, but the Robs of sodium alginate are all100% formodel solutions andhave anobvious differencewith the actualEPS solution.

If comparing themodel solution including single solute (solutions 1,4–6) with the combination model solution including sodium alginate(solutions 7, 8 and 9) or including sodium alginate and humic acid(solutions 3, 10, and 11), it was easy tomake the conclusion that theRobsof proteins in the combinationmodel solution including sodiumalginate(solutions 7, 8 and 9) or including sodium alginate and humic acid(solutions 3, 10, and 11) were more than that of the model solutionincluding the single solute. Based on the same reason as for thecumulative filtrate volume (Vcumu), the addition of sodium alginate orhumic acid would enhance the rejection of proteins.

As shown in Fig. 4, although the sequence of molecular weight andsize of protein was BSA (about 69,000 Da)>β-lactoglobulin (about18,000 Da)>lysozyme (about 14,400 Da), the configuration of theproteinmoleculewasdifferent, BSAwasaprolate ellipsoidalmoleculeofdimensions 14 nm× 4 nm×4 nm, and β-lactoglobulin was

Table 3Values of cumulative filtrate volume (Vcumu) of the mixed liquor 1 and actual EPSsolution for the first 780 s under different TMP (0.1 μm PVDF, T=25 °C, pH=7.5) (mL).

0.01 MPa 0.03 MPa 0.05 MPa 0.08 MPa 0.1 MPa

Vcumu/actual EPS solution 11.8 28.5 43.4 63.2 96.8Vcumu/mixed liquor 1 21.6 53.7 86.2 131.6 147.7

Fig. 3. The Vcumu values of different solutions under 0.1 MPa, at 25 °C and pH=7.5 with0.1 μm PVDF membrane for the first 780 s.

Fig. 5. Standard blocking model (a) and cake filtration model (b) of different solutionsfor 0.1 μm PVDF membrane, at 0.1 MPa, T=25 °C, pH=7.5.

1383Z. Wang et al. / Desalination 249 (2009) 1380–1384

approximately spherical, with a diameter of 3.6 nm [33]. Lysozymewasa prolate ellipsoidal molecule of dimensions 4.5 nm×3 nm×3 nm [34].So it is easy to make the conclusion that the Robs of β-lactoglobulin andBSA were bigger and the Robs of lysozyme was smaller.

It was obvious that the solutions 4, 5 and 6 would be chosen as themodel solution for the EPS solution on the values of the observedrejection of proteins.

3.3. Study of the membrane fouling mechanism

All the experimental filtration data were analyzed by using classicfiltration laws developed by Hermia [19]. The first part of the filtrationmet the standard blocking law described as t/V=at+b, and after thatthe cake filtration model described as t/V=aV+b could be applied upto the end of the run as shown as in Fig. 5.

The result in Fig. 5 showed that the timeof standard blockingperiodswas very short, and the maximum time of filtration met the cakefiltration model very well. This means that the “dummy cake” wasformed on the membrane surface by the BSA, β-lactoglobulin andlysozyme solutions.

The specific cake resistanceαc of different solutions canbe calculatedfrom Eq. (1) according to the cake filtration model [19]:

a =ηαcCb

2A2Δp: ð1Þ

where, η is the permeate dynamic viscosity, Pa s; αc is the specificcake resistance, m/kg; ΔP is transmembrane pressure, Pa; A is the

Fig. 4. The observed retention of the membrane (Robs) of different solutions under0.1 MPa, at 25 °C and pH=7.5 with 0.1 μm PVDF membrane for the first 780 s.

membrane surface area, m2; Cb is the concentration of the bulk g/l anda is the slope of the linear equation t/V=aV+b.

The calculating results were given in Fig. 6.It can be seen from Fig. 5 that except for solution 2, the model

solution including single solute (solutions 1, 4–6) has the values of αc

less than that of the actual closed EPS solution and solutions 1, 4, and 5are close to the values ofαc of the EPS solution. Except for solution 7, thevalues of αc of the combinationmodel solution (solutions 3, 8–11) havevalues of αc more than that of the actual EPS solution and solution 7 isclose to the values of αc of the EPS solution.

If comparing themodel solutions 1, 7 and 3 or themodel solutions 5,8 and 10 or the model solutions 6, 9 and 11, it was easy to make theconclusion that the values ofαc of themodel solution increasedwith the

Fig. 6. The values of specific cake resistance (αc×1015m/kg) for different solutionsunder 0.1 MPa, at 25 °C and pH=7.5 with 0.1 μm PVDF membrane for the first 780 s.

1384 Z. Wang et al. / Desalination 249 (2009) 1380–1384

addition of sodiumalginate or humic acid, and especially the addition ofhumic acid could greatly increase the values of αc of themodel solution.

If comparing the model solutions 2 and 7, it was easy to make theconclusion that the presence of protein in themixed component modelsolutions caused αc values of sodium alginate to decrease as reported inthe literature [19].

We can draw the conclusion from Sections 3.2 and 3.3 that, solution4 (BSA), solution 5 (β-lactoglobulin) and solution 6 (lysozyme) all havefive times the protein concentration of the actual EPS, and they aremoreapproximate to that of the actual EPS and can be chosen as the modelsolution for the actual EPS solution.

4. Conclusions

According to the analysis of all experimental data, the followingconclusions would be obtained.

(1) The present single simulated solution can't exactly describe thefilterability of the actual EPS solution. The filterability of modelsolutions was connected with different combinations on thecomponents of extracted EPS from sludge for laboratory-scaleSBR.

(2) The filterability behaviors (Vcumu, Robs and αc) of modelsolutions BSA, β-lactoglobulin and lysozyme which all havefive times the protein concentration of the actual EPS, weresimilar to that of the actual EPS solution, therefore, thesesolutions could be used to model EPS in the actual EPS foulingmechanism research.

(3) The addition of polysaccharide and humic acid enhanced therejection of proteins, but this effect of β-lactoglobulin on thefilterability behaviors was smaller than that of BSA andlysozyme. The presence of protein in the mixed componentsof model solutions caused the decrease of αc values of sodiumalginate.

Acknowledgements

We thank Qiong Wang Beijing Fluid Filtration and SeparationTechnology Research Center for editorial assistance.

The authors wish to thank the Beijing Municipal Natural ScienceFoundation (Project No. 8052006) and National Natural ScienceFoundation of China (Project No. 20276003) for the financial support ofthis study.

References

[1] B. FrØlund, R. Palmgren, et al., Extraction of extracellular polymers from activatedsludge using a cation exchange resin, Water Res. 30 (8) (1996) 1749–1758.

[2] B. Frølund, T. Griebe, P.H. Nielsen, Enzymatic activity in the activated-sludge flocmatrix, Appl. Microbiol. Biotechnol. 43 (1995) 755–761.

[3] M.F. Dignac, V. Urbain, et al., Chemical description of extracellular polymers:implication on activated sludge floc structure, Water Sci. Technol. 38 (8–9) (1998)45–53.

[4] X.Q. Zhang, P.L. Bishop, B.K. Kinkle, Comparisonof extractionmethods for quantifyingextracellular polymers in biofilms, Water Sci. Technol. 39 (7) (1999) 211–218.

[5] S. Tsuneda, S. Park, et al., Enhancement of nitrifying biofilm formation using selectedEPS produced by heterotrophic bacteria, Water Sci. Technol. 43 (6) (2001) 197–204.

[6] J.I. Houghton, T. Stephenson, Effect of influent organic content on digested sludgeextracellular polymer content and dewaterability, Water Res. 36 (2002) 3620–3628.

[7] I.S. Chang, S.O. Bag, C.H. Lee, Effects of membrane fouling on solute rejection duringmembrane filtration of activated sludge, Proc. Biochem. 36 (8–9) (2001) 855–860.

[8] J. Cho, K.H. Ahn, Y. Seo, et al., Modification of ASM no. 1 for a submerged membranebioreactor system: including the effects of SMP on membrane fouling, Water Sci.Technol. 47 (12) (2003) 177–181.

[9] J. Cho,K.H.Ahn, Y.H. Lee, et al., Investigationof biological and fouling characteristics ofsubmerged membrane bioreactor process for wastewater treatment by modelsensitivity analysis, Water Sci. Technol. 49 (2) (2004) 245–254.

[10] Y. Ye, P. Le Clech, V. Chen, A.G. Fane, Evolution of fouling during crossflow filtrationof model EPS solutions, J. Membr. Sci. 264 (2005) 190–199.

[11] H. Nagaoka, S. Ueda, et al., Influence of bacterial extracellular polymers on themembrane separation activated sludge process, Water Sci. Technol. 34 (9) (1996)165–172.

[12] I.S. Chang, C.H. Lee, Membrane filtration characteristics in membrane-coupledactivated sludge system — the effect of physiological states of activated sludge onmembrane fouling, Desalination 120 (3) (1998) 221–233.

[13] J.S. Kim, C.H. Lee, I.S. Chang, Effect of pump shear on the performance of acrossflow membrane bioreactor, Water Res. 35 (9) (2001) 2137–2144.

[14] P.H. Hodgson, G.L. Leslie, et al., Cake resistance and solute rejection in bacterialMF: the role of extracellular matrix, J. Membr. Sci. 79 (1) (1993) 35–53.

[15] B.D. Cho, A.G. Fane, Fouling transients in nominally sub-critical fluxoperation of amembrane bioreactor, J. Membr. Sci. 209 (2002) 391–403.

[16] J. Houghton, J. Quarmby, et al., Municipal wastewater sludge dewaterability and thepresenceofmicrobial extracellularpolymer,WaterSci. Technol. 44 (2–3) (2001)373.

[17] B. Lesjean, S. Rosenberger, C. Jekel, G. Amy, et al., Correlation between membranefouling and soluble/colloidal organic substances in membrane bioreactors formunicipalwastewater treatment, Proc.WEMT2004, Seoul, Vol. 2, 2004, pp. 525–532.

[18] K. Tarnacki, S. Lyko, T. Wintgens, et al., Impact of extra-cellular polymericsubstances on the filtration of activated sludge in membrane bioreactors forlandfill leachate, Extended Abstracts of the International Congress on Membranesand Membrane Processes, Seoul, Korea, 2005, pp. 1253–1254.

[19] Y. Ye, P. Le Clech, V. Chen, et al., Foulingmechanisms of alginate solutions as modelextracellular polymeric substances, Desalination 175 (2005) 7–20.

[20] Y. Ye, V. Chen, A.G. Fane, Modeling for the long-term sub-critical filtration ofmodel EPS solutions, Extended Abstracts of the International Congress onMembranes and Membrane Processes 2005, Seoul, Korea, 2005, pp. 251–252.

[21] H. Susanto, M. Ulbricht, Mechanisms for polysaccharide fouling of ultrafiltrationmembranes, Extended Abstracts of the International Congress on Membranes andMembrane Processes, Seoul, Korea, 2005, pp. 341–342.

[22] S. Ognier, C. Wisniewski, et al., Influence of macromolecule adsorption duringfiltration of a membrane bioreactor mixed liquor suspension, J. Membr. Sci. 209 (1)(2002) 27–37.

[23] I.T. Yeom, Y.M. Nah, K.H. Ahn, Treatment of household wastewater using anintermittently aerated membrane bioreactor, Desalination 124 (1999) 193–204.

[24] S. Rosenberger, U. Kruger, et al., Performance of a bioreactor with submergedmembranes for aerobic treatment of municipal wastewater, Water Res. 36 (2002)413–420.

[25] J.S. Park, K.M. Yeon, C.H. Lee, Hydrodynamics and microbial physiology affectingperformance of a new MBR, membrane-coupled high-performance compactreactor, Desalination 172 (2005) 181–188.

[26] A. Drews, M. Vock, et al., Influence of unsteady membrane bioreactor operation onEPS formation and filtration resistance, Extended Abstracts of the InternationalCongress onMembranes andMembrane Processes, Seoul, Korea, 2005, pp. 387–388.

[27] Mei Liu, Zhan Wang, Chong Zhou, Ting Wang, Fouling mechanism of flat sheetmembranes in wastewater reuse, Tech. Equip. Environ. Pollut. Control 8 (2006)124–132.

[28] J.Wingender, T.R. Neu, H.C. Flemming,Microbial Extracellular Polymeric Substances:Characterization, Structures and Function, Springer-Verlag, Berlin Heidelberg, 1999Chapter 3.

[29] Hong Liu, HerbertH.P. Fang, Extraction of extracellular polymeric substances (EPS)of sludges, J. Biotechnol. 95 (2002) 249–256.

[30] H. Fang, X. Jia, Extraction of extracellular polymers from anaerobic sludges,Biotechnol. Tech. 10 (1996) 803–808.

[31] M.C. Veiga, M.K. Jain, et al., Composition and role of extracellular polymers inmethanogenic granules, Appl. Environ. Microbiol. 63 (2) (1997) 403–407.

[32] K. Raunkjær, T Hvitved-Jacobsen, P.H. Nielsen, Measurement of pools of protein,carbohydrate and lipid in domestic wastewater, Water Res. 28 (2) (1994)251–262.

[33] Dong-bao He, Shi Yi, Hong-bo Liang, Dong-feng Zhan, Study on synergisticinteraction and gelation of chitosan and sodium alginate, J. Wuhan Univ. (Nat. Sci.Ed.) 2 (2002) 193–196.

[34] H. Shirahama, J. Lyklema, W. Norde, Comparative protein adsorption in modelsystems, J. Colloid Interface Sci. 139 (1990) 177–187.