ultrafiltration process: Influence of cake layer on membrane fouling

Author’s Accepted Manuscript Application of Al species in coagulation/ultrafiltration process: Influence of cake layer on membrane fouling Wenyu Wang, Qinyan Yue, Kangying Guo, Fan Bu, Xue Shen, Baoyu Gao www.elsevier.com/locate/memsci

PII: DOI: Reference:

S0376-7388(18)31899-4 https://doi.org/10.1016/j.memsci.2018.11.014 MEMSCI16616

To appear in: Journal of Membrane Science Received date: 11 July 2018 Revised date: 19 September 2018 Accepted date: 6 November 2018 Cite this article as: Wenyu Wang, Qinyan Yue, Kangying Guo, Fan Bu, Xue Shen and Baoyu Gao, Application of Al species in coagulation/ultrafiltration process: Influence of cake layer on membrane fouling, Journal of Membrane Science, https://doi.org/10.1016/j.memsci.2018.11.014 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Application of Al species in coagulation/ultrafiltration process: Influence of cake layer on membrane fouling Wenyu Wang, Qinyan Yue*, Kangying Guo, Fan Bu, Xue Shen, Baoyu Gao* Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Qingdao 266000, China

E-mail addresses: [email protected] (Q. Yue), [email protected] (B. Gao).

*

Corresponding author.

Abstract The membrane fouling is a challenge for the application of ultrafiltration, one of 1

which the cake layer is the main influencing factor. However, the pros and cons of cake layer generated in the coagulation-ultrafiltration (C-UF) process needs to be explored. This study was carried out to investigate that the effect of a cake layer on the membrane fouling behavior with three Al species coagulants for different effluents. The results indicated that the fouling mechanisms of cake layer under different effluents conditions were diverse due to the particle characteristics. The Al hydrolysis that accompanied by the interaction between Al species coagulants and the – OH/-COOH functional groups of humic acid were conducted, and the effluents of Ala presented lighter membrane fouling. Meanwhile, the components mainly trapped by the membrane were soluble microbial products, protein, polypeptides and amino acid-like materials during C-UF process, because of the decrease in the proportion of fluorescence response. For the less/compact cake layer (system 2), the average of the external and internal membrane resistances were about 25×1010 m-1 and 21×1010 m-1, respectively, which caused severe membrane fouling. It was concluded that the poriferous/loose cake layer could effectively alleviate membrane fouling by re-adsorbing some organic matters.

2

Graphical abstract

Keywords: Coagulation-ultrafiltration; Al species; Cake layer; External and internal fouling

3

1. Introduction The reclaimed water from water treatment could be widely concerned as an alternative water resource, and most of them are used for agricultural irrigation due to its nutrient content [1]. The safety of the reclaimed water should be attached more attention, and the membrane technology has bright prospects to reduce pollution risk and protect human health. Moreover, ultrafiltration (UF) as a kind of membrane technology can almost entirely eliminate a widespread range of contaminants [2, 3] and purify protein solutions [4, 5]. However, the main contaminant in water is natural organic matter (NOM) and pathogenic microorganisms which causes membrane fouling, limiting the application of UF process [4, 6]. The membrane fouling affects by concentration polarization [7, 8], cake layer [9, 10] and membrane pore plugging [11, 12], which leads to the decline of membrane flux and the increase of filtration resistance. In general, the concentration polarization and cake layer, which also cause external fouling, is controlled by the tangential flow and shear force [13]. Some soluble matters plug the membrane pore and contribute to the internal membrane fouling [14], and some of them cannot be eliminated by backwashing and hydraulic cleaning, resulting in irreversible membrane fouling. In order to settle these problems, the removal of NOM should be concentrated on the effect of cake layer properties, membrane resistance and fluorescence intensity [9, 15]. The UF process operation and maintenance costs of per 1000 m3 water treatment are about 3 times higher than that of conventional treatment [16, 17], thus some measures need to be taken to reduce membrane fouling and save costs in water treatment. The coagulation as a pretreatment technology before UF process can control membrane fouling to reduce costs [18], which is known as a coagulation-ultrafiltration (C-UF) process. The suspended particles, colloids, protein and microorganisms could further remove effectively in C-UF process [19, 20]. The combination of organic matters and coagulants is deposited on the membrane surface to generate cake layer [21, 22]. The cake layer can increase filtration resistance, but much more NOM that has not been removed by coagulation is blocked by the cake layer. Indeed, the loose cake layer can 4

further adsorb particles to alleviate membrane fouling [14, 23, 24], thus the characteristics of cake layer are the main factor to control membrane fouling. The residual organic matters (protein, microbial products, fulvic acid and humic acid, etc.) can enter the membrane pore through the cake layer to result in irreversible fouling. However, the effect of cake layer for internal membrane resistance during C-UF process remains indistinct. Therefore, the advantages and disadvantages of the cake layer need to be further investigated. The coagulants with different coagulation mechanisms generates different cake layer. Aluminum salt is one of the most widely used coagulant in water treatment [25], which can hydrolyze to form polymers products, including Ala (the mononuclear species), Alb (the medium polymer species), and Alc (the higher polymers species) [26]. Moreover, Ala and Alb exerts strong charge neutralization, and a better bridging effects of Alc can be presented [27, 28]. Sun et al. has indicated that the flocs formed by aluminum salts with NOM are multi-scale fractal, and the irregularity and roughness aggregates influenced the structure of cake layer [29]. This implies that the structure of flocs and cake layer could be significantly affected by aluminum salts-NOM interaction. Indeed, the complexes of aluminum salts-NOM can play a pivotal role for the connection of membrane and NOM [30]. Xu et al. has suggested that the membrane fouling is affected by the interactions between the functional groups of NOM and aluminum salts [31]. This indicated that the membrane fouling is associated with the removal efficiency of NOM, cake layer properties, membrane flux, membrane resistance and fluorescence intensity. Although the membrane fouling and mechanisms has been investigated well, the effects of three aluminum species cake layer on membrane fouling remain unclear. Thus, the research of the relationship between three aluminum species coagulants in membrane fouling and cake layer is necessary. The objective of this research was to evaluate the effect of a cake layer on the membrane fouling with three aluminum species coagulants during C-UF process. Three system experiments with different effluents were designed to investigate the role of the cake layer. The membrane flux, size distribution, NOM removal efficiency, 5

fluorescence intensity and membrane resistances were elucidated to analyze the characteristics of cake layer, which were associated with the external and internal membrane fouling.

2. Material and methods 2.1 Water sample and coagulants The Kaolin clay (Sinopharm Chemical Reagent Co. Shanghai, China) and humic acid (HA) (Aladdin Industrial Corporation, Shanghai, China) were used as raw water sample, and the stock solution was composited according to our previous research [27]. Then, the concentration of HA stock solution was 1 g L-1. For a series of tests, the composite water sample was diluted with the tap water to a concentration of 10 mg HA L-1 [9]. The synthetic three aluminum species coagulants was applied in this research, and the concentration of Ala, Alb and Alc was 1, 3.375 and 3.375 g L-1, respectively. Furthermore, the solution with high concentration of Ala was prepared by dissolving AlCl3·6H2O in deionized water. Polyaluminum chloride (PACl) with the basicity of 2.4 was synthesized by micro alkaline titration method. Moreover, the high concentration of Alb (94.76%) was purified from the preformed PACl by an ethanol/acetone mixture, and the other PACl sample which contained high concentration of Alc (76.92%) was purified by a methanol/acetone mixture. 2.2 Ultrafiltration procedure In order to investigate the effect of cake layer, a series of ultrafiltration experiments were performed. Three aluminum species coagulants were applied to treat raw water, and the optimal coagulant dosage of 6 mg L-1 was selected to add in coagulation process. In ultrafiltration process, a polyether sulfones (PES) membrane (Millipore, USA) with a molecular weight (MW) cut-off of 100 kDa was used in this research, and a constant trans-membrane pressure of 0.06 MPa was provided by nitrogen gas. The electronic balance (MSU5201S-000-D0; SartoriusAG, Germany) was employed to record the membrane flux. In coagulation and ultrafiltration experiments, the detailed procedure and methods were listed in Supplementary information. 6

The ultrafiltration experiments (Supplementary Fig. S1) were conducted with different coagulation effluents. As shown in Fig. 1, the coagulation effluents (1 L) without sedimentation was filtrated for system 1. The effluents after sedimentation were divided into supernatant and sediment, and the supernatant was directly used as water sample for system 2. The sediment was compounded with deionized water to a volume of 1 L, which was filtrated in system 3. The characteristics of coagulation effluents with three aluminum species coagulants for three systems (System 1, 2 and 3) were investigated in Table 1. The external (Ref) and internal (Rif) membrane resistances were calculated by the difference of membrane flux

values

(Supplementary Table S1), which could investigate the severity of membrane fouling. Moreover, the Rif, including the reversible (Rif-r) and physically irreversible (Rirr) fouling resistances, were related to the long-term operation of the membrane. The equation of membrane resistances is shown in Eq. (1). P

R = μ△J

(1)

where R is the membrane resistance (m-1); P is the trans-membrane pressure (Pa); μ is the water viscosity (Pa·s); △J is the difference of membrane flux (m3/ (m2s)). 2.3 Analytical measurements The organic matter still remained in the membrane pore after back wash, and then the cross-section of membrane was observed by a scanning electron microscope (SEM) (Navo NanoSEM 450, FEI, USA). The characteristics of the effluents were measured (e.g. Turbidity, pH, UV254, DOC, size distribution, protein, humic acid and soluble microbial byproduct). The turbidity, UV254, DOC and size distribution was analyzed with a turbi-dimeter 2100P, UV-Vis spectrophotometry, Shimadzu TOC-VCPH analyzer and Zetasizer Nano ZS instrument, respectively. The component of protein, humic acid and soluble microbial byproduct was determined by excitation and emission

matrix

(EEM)

fluorescence

spectroscopy

analysis

(F-4500

FL

spectrophotometer, Hitachi, Japan). According to the emission spectra (EM) and the excitation wavelength (EX), the EEM spectra was divided into three regions, including Region I EX230-300/EM250-390 (proteins, microbial products, polypeptides, 7

amino acid-like), Region II EX230-300/EM390-550 (fulvic acid-like) and Region III EX300-480/EM340-550 (humic acid-like) [32]. The quantitative analysis of EEM spectra was determined by fluorescence regional integration (FRI) method. The EX and EM wavelength was divided to many 5 nm×5 nm areas, and then the fluorescence intensity of each area was achieved. The fluorescence response of each region was calculated as follows [33, 34]: Φ𝑖,𝑛 = 𝑀𝐹𝑖 ∫𝑒𝑥 ∫𝑒𝑚 𝐼(𝜆𝑒𝑥 𝜆𝑒𝑚 )𝑑𝜆𝑒𝑥 𝑑𝜆𝑒𝑚 𝑃𝑖,𝑛 =

Φ𝑖,𝑛 Φ𝑇,𝑛

(2)

× 100%

(3)

where Φi,n is the cumulative fluorescence response of organic matters at region i; I (λex λem) is the fluorescence intensity at each EX-EM wavelength; MFi is the ratio of total area to each EX-EM area; ΦT,n is the sum of Φi,n; Pi,

n

is the percent of

fluorescence response at region i.

3. Results and discussion 3.1 Membrane flux and SEM images The ultrafiltration experiments by different coagulation effluents were subjected to the effects of cake layer, and the normalized permeate fluxes (J/J0) changed with filtration time as shown in Fig. 2. The difference of normalized permeate fluxes (△J/J0) and the final value of J/J0 after backwash were demonstrated in the small figures of Fig. 2. The J/J0 values decreased from 1 to 0.2 for the un-treated water (Fig. 2d), and the membrane fouling was serious with the increase of filtration cycle. However, the values of △J/J0 (Table 2) were reduced as coagulants dosed, especially for system 3. This indicated that the interactions between coagulants and NOM could alleviate membrane fouling in C-UF process. Meanwhile, the system 3 taken less filtration time to filter the same volume of effluents, which was attributed to the porous cake layer on the membrane surface. The cake layer with pore structures could adsorb colloids and other pollutants and aggregate on the membrane surface, which could be removed or reduced by the applied shear force [35, 36]. The value of △J/J0 was smaller for Ala which caused lighter membrane fouling, that is, the concentration polarization of Ala was weak compared with Alb and Alc. From the small figures in Fig. 2, the final value 8

of J/J0 after backwash for system 3 was larger than that of system 1 and 2, which was lower decreased by comparing the J/J0 before backwash. This indicated that the membrane fouling was relieved for system 3 especially for irreversible fouling. The SEM images were taken for the membrane cross-section to investigate the cake layer and internal membrane fouling. As shown in Supplementary Fig. S2, the membrane pores of new membrane were arranged in order. The hydrophilic fraction of organics with MW below 100 KDa could plug membrane pore leading to the membrane flux decline, and then these colloids were difficult to remove by backwash and remained in the membrane pore (Fig. 3). The cake layer was less or lacking for system 2 that induced many aggregates to enter membrane pores (Fig. 3b). Comparatively, there were less flocs in the membrane pore for system 3 (Fig. 3c), and this led to lighter irreversible membrane fouling, which was consistent with the results of J/J0. Therefore, the cake layer formed by system 1 and 3 was more loose and porous than that of system 2, and then some smaller aggregates were adsorbed in the cake layer and hard to enter membrane pore. In addition, the SEM images of the membrane cross-section near the top layer and the membrane surface were investigated in Supplementary Fig. S3 and S4, respectively. There were less residual particles in the membrane surface of system 3, which demonstrated that the cake layer could alleviate the membrane fouling. 3.2 Characteristics of different effluents 3.2.1 Removal efficiency The ultra-filtered water samples should be pretreated by coagulation. From table 1, the removal efficiencies were increased especially for system 3, indicating that much more organic matters remained in supernatant. The remaining turbidity of system 1 and 3 was larger than that of raw water. Because the flocs without sedimentation floated in water, thereby leading to back-mixing [37]. The values of zeta potential were shown that Ala had better charge neutralization than that of Alb and Alc. Due to the removal of particles, the pH of coagulation effluents was decreased comparing with the initial pH. As mentioned in Section 2.3, the characteristics of the effluents for three systems and coagulants before and after ultrafiltration were investigated. The 9

removal efficiency of UV254 and DOC was shown in Fig. 4 to reflect the removal of NOM. The values of UV254 and DOC were increased after ultrafiltration process, indicating that the organic matters were further removed by membrane. The removal efficiency was associated with the membrane mechanisms (concentration polarization, cake layer and pore plugging) [10, 38]. Generally, the small and compact flocs with less cake layer contributed to serious membrane fouling. As a result, the promotion of removal efficiency after ultrafiltration was less obvious for system 2, because the less cake layer prevented organics from being adsorbed. For system 1 and 2, the UV254 and DOC removal efficiency after ultrafiltration process had close values, demonstrating that the compound of organic matters was similar after ultrafiltration. But the disparities were the case that, the NOM was adsorbed by cake layer and trapped by membrane for system 1, and the removal of NOM for system 2 was mainly dominated by the membrane. From Fig. 4, it could be seen that the system 3 presented better removal efficiency. Because most organics combined with coagulants to form aggregates which could deposit on the membrane surface to generate cake layer, causing that the effluents contained less organic matters and deionized water. Regardless of the impact of the system, the difference of removal efficiency for three coagulants was small, but the effluents coagulated/ultrafiltrated by Ala performed relatively better removal efficiency than that of Alb and Alc. The reason was that for Ala coagulant, the pH of coagulation effluents was weakly acidic (Table 1), thus Ala could rapidly hydrolyze to Al(OH)2+, Al(OH)2+, and Al(H2O)63+ that accelerated the combination of coagulants and the functional groups of NOM, leading to less residual organics in the coagulated effluents. 3.2.2 Size distribution The size distribution of effluents before and after ultrafiltration were analyzed to indirectly determine the nature of membrane fouling. The majority of flocs could deposit on the membrane surface, which was led to the development of a cake layer. And the partly particles plugged the membrane pores and filtered into the filtrate, separately. Fig. 5 shown that the size of different system was similar for the same 10

coagulant, and the floc size of coagulated effluents was larger than 1000 nm. Cho. et al. investigated that the small flocs could aggravate membrane fouling [39].Moreover, the effluents of system 2 was supernatant that much more aggregates were precipitated, leading to a large proportion of small particles and severe membrane fouling. Besides, the major peak of size after ultrafiltration shifted to the left of that before ultrafiltration, indicating that some of flocs trapped by membrane and then the intensity of small size were increased after ultrafiltration. According to the intensity percent, it was obvious that most of the particle size was less than 100 nm after ultrafiltration, and a small fraction of the size was concentrated around 1 nm due to the maldistribution of particles. The difference in size before and after ultrafiltration was large for system 3, indicating that much more organic matters were adsorbed in cake layer and remained in membrane pore. Regardless of the effect of the system, Ala also had the large difference in size, because the cake layer formed by Ala was porous to alleviate membrane fouling. 3.2.3 3D EEM spectra EEM fluorescence spectroscopy was implemented to analyze the effluents before and after ultrafiltration (Fig. 6). The EEM spectra was divided into three regions to express the specific components of NOM. It directly reflected the fluorescence intensity and proportion of different components. From Fig. 6, the fluorescence maxima of system 1 and 2 were apparently red-shifted along the EX compared with system 3. The red shift investigated that the effluents of system 1 and 2 contained much more organic matters. The fluorescence intensity of effluents were blue-shifted after ultrafiltration, indicating that the ultrafiltration could further remove NOM. As shown in Supplementary Fig. S5 and S6, Alb and Alc also had the same conclusion. The disparities of fluorescence response for three systems were quantified by FRI method, and the results were provided in Table 3. The total cumulative fluorescence intensities for three system were in the order of: system 1 > system 2 > system 3. The cumulative fluorescence intensity of system 1 was approximately 3 times higher than that of system 3. Moreover, the lowest total cumulative fluorescence intensities happened in system 3, which could reduce the accumulation of organic matter on the 11

membrane and then mitigate the membrane fouling. The effluents of Ala had the least fluorescence intensity compared with the effluents of Alb and Alc (Supplementary Table S2 and S3), indicating that there were low contents of organic matters in the effluents of Ala. In addition, the Region I with soluble microbial products, protein, polypeptides and amino acid-like materials exhibited the main fluorescent components, which occupied almost 45% of the ΦT,n. The fulvic acid-like compounds (Region II) contained the second highest values of Φi,n, according for greater than 20% of the ΦT,n. The percent of fluorescence response after ultrafiltration at Region I was decreased, but the proportion of the other two regions was increased. This indicated that the soluble microbial products, protein, polypeptides and amino acid-like materials were mainly removal components for ultrafiltration. 3.3 Membrane resistances The membrane resistances were divided into Ref and Rif. The loose and strong attached cake layer was induced the Ref, and Rif was concerned with the residual concentration and components of organic matters. The membrane resistances for three systems under different coagulants were shown in Fig. 7. Compared without coagulants, the hydroxyl groups and carboxyl groups of HA and coagulants were interacted as coagulants dosed, leading to the decrease of membrane resistances. The total membrane resistance for three system was in the order of: system 2 > system 1 > system 3, indicating that the loose cake layer formed by system 1 and 3 could control membrane fouling. The total membrane resistance of effluents generated by Ala was lower than that of Alb and Alc, due to the difference in coagulation mechanisms. Therefore, the components presented in NOM and the cake layer were associated with the serious of membrane fouling and membrane mechanisms. The aggregates deposited on the membrane surface to generate cake layer. The loose cake layer was reduced by applying higher shear force in micro-scale eddies, and then the strongly cake layer was wiped by a wet sponge. These loose cake layer was easier to remove/reduce than that of strong cake layer, which was benefit to alleviate external membrane fouling. Moreover, the better control of the cake layer could alleviate external membrane fouling. As shown in Fig. 7, the values of Ref were 12

smaller for system 3 due to the loose cake layer with large floc size, which was consistent with the results of Fig. 5. From Fig. 2, both the membrane flux of system 1 and 2 rapidly decreased firstly, and then the membrane flux of system 1 continued declined obviously because the loose cake layer could adsorb the particles constantly to prevent the filtration of effluents. Furthermore, the higher difference of membrane flux for system 1 was presented, but the external resistance of system 1 was less than that of system 2 with the difference of 1×1010 m-1. The reason was that the mainly external membrane fouling of system 1 and 2 was loose cake layer and strong cake layer, respectively. The significantly external membrane resistance reduction of system 3 could be attributed to the loose cake layer. In addition, the porous cake layer and the weaker concentration polarization of effluents formed by Ala caused the lightest external membrane fouling than that of Alb and Alc. Some soluble compounds which could not be trapped by cake layer were adsorbed in the membrane pores, of which the membrane reversible fouling could be eliminated by backwashing. As shown in Fig. 7, the effluents of supernatant caused serious reversible membrane resistance with about 6×1010 m-1, which impeded the recovery of the membrane and aggravated the irreversible fouling. The effluents coagulated by Ala presented light reversible fouling due to the large size with loose cake layer, which was consistent with the conclusions of Section 3.2.2. In addition, the membrane irreversible fouling could indirectly discuss the effect of cake layer. The irreversible resistance for three system was in the order of: system 2 > system 1 > system 3, and the resistance of system 1 was higher than that of system 3. Because some organic matters in effluents for system 1 were eliminated during system 2 to generate system 3, and the similar conclusion was obtained from the removal efficiency of UV254 and the analysis of EEM fluorescence spectroscopy. Moreover, the membrane irreversible resistance of system 2 was greater than 14×1010 m-1, and then much more soluble pollutants remained in the membrane pore as shown in Fig. 3. This could be attributed to the smaller particles with compact cake layer of system 2 that were difficult to intercept by cake layer. Therefore, the loose cake layer could effectively alleviate the irreversible and reversible membrane fouling. 13

4. Conclusion The membrane fouling mechanism of cake layer was related to the particle characteristics under different effluents conditions. Furthermore, the effects of cake layer on membrane fouling were analyzed by the membrane flux, size distribution, NOM removal efficiency, fluorescence intensity and membrane resistances. The Al hydrolysis and the interaction between Al salts and function groups of NOM was occurred simultaneously, and Ala presented better removal efficiency. Moreover, the membrane resistance of effluents generated by Ala was smaller than that of Alb and Alc. The EEM fluorescence results indicated that soluble microbial products, protein, polypeptides and amino acid-like materials were the most components entrapped by membrane. Meanwhile, the characteristics of cake layer were directly affected the degree of membrane fouling. Indeed, the sample treated by Alc in system 2 with less/compact cake layer could cause severe external membrane resistance of 26.7×1010 m-1, and the loose cake layer could adsorb the particles constantly to alleviate internal membrane fouling.

Acknowledgments This research was supported by the National Natural Science foundation of China (Nos. 21377071, 51678349) and the Tai Shan scholar Foundation (Nos. ts201511003). The kind suggestions from the anonymous reviewers are greatly acknowledged.

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Effect of ultraviolet (UV) irradiation and titanium dioxide photocatalysis on dissolve organic matter fractions, Chemical Engineering Journal, 303 (2016) 252-260. [33] Y. Meng, M. Wang, B. Guo, F. Zhu, Y. Wang, J. Lu, D. Ma, Y. Sun, B. Gao, Characterization and C-, N-disinfection byproduct formation of dissolved organic matter in MBR and anaerobic-anoxic-oxic (AAO) processes, Chemical Engineering Journal, 315 (2017) 243-250. [34] D. Ma, B. Gao, C. Xia, Y. Wang, Q. Yue, Q. Li, Effects of sludge retention times on reactivity of effluent dissolved organic matter for trihalomethane formation in hybrid powdered activated carbon membrane bioreactors, Bioresource technology, 166 (2014) 381-388. [35] M. Yao, J. Nan, T. Chen, D. Zhan, Q. Li, Z. Wang, H. Li, Influence of flocs breakage process on membrane fouling in coagulation/ultrafiltration process—Effect of additional coagulant of poly-aluminum chloride and polyacrylamide, Journal of Membrane Science, 491 (2015) 63-72. [36] M. Aslam, A. Charfi, G. Lesage, M. Heran, J. Kim, Membrane bioreactors for wastewater treatment: A review of mechanical cleaning by scouring agents to control membrane fouling, Chemical Engineering Journal, 307 (2017) 897-913. [37] J.-L. Lin, J.R. Pan, C. Huang, Enhanced particle destabilization and aggregation by flash-mixing coagulation for drinking water treatment, Separation and Purification Technology, 115 (2013) 145-151. [38] P.K. Park, C.H. Lee, S. Lee, Permeability of collapsed cakes formed by deposition of fractal aggregates upon membrane filtration, Environmental Science & Technology, 40 (2006) 2699-2705. [39] M.-H. Cho, C.-H. Lee, S. Lee, Effect of flocculation conditions on membrane permeability in coagulation–microfiltration, Desalination, 191 (2006) 386-396.

18

Fig. 1 Schematic diagram of ultrafiltration experiments with different effluents.

19

1.0

(a)

cycle 1

cycle 2

cycle 3

0.9 0.8 0.7 △ J/J0

0.6

J/J0

0.5 0.9

0.5

△ J/J0

0.3

0.8

0.3 0.2

0.7

0.2 0.1

0.1 0.0

0.0

△ J/J0

J/J0 (After backwash)

System 1

0

500

1000

Syetem 1 Syetem 2 Syetem 3

0.6

System 3

System 2

J/J0 (After backwash)

0.4

0.4

1500

2000

2500

3000

Time (s) 1.0

cycle 1

cycle 2

cycle 3

(b)

0.9 0.8 0.7 0.5

J/J0

0.6

0.9

0.5 0.4 △ J/J0

0.3

J/J0 (After backwash)

0.4

0.8

0.3

0.1 0.2

0.0

0

Syetem 1 Syetem 2 Syetem 3

0.7

0.2 △ J/J0

J/J0 (After backwash)

System 1

System 2

500

0.6

System 3

1000

1500

Time (s)

20

2000

2500

3000

1.0

cycle 1

cycle 2

cycle 3

(c)

0.9 0.8 0.7

J/J0

0.6 0.5

0.8

0.4

0.7

0.3

0.6

J/J0 (After backwash)

0.5

0.3 0.2

△ J/J0

0.4

0.1 0.2

0.0

△ J/J0 System 1

0

J/J0 (After backwash) System 2

500

System 3

1000

Syetem 1 Syetem 2 Syetem 3

0.5

1500

2000

2500

3000

Time (s) 1.5

1.0

1.0

(d) J/J0 (After backwash)

0.9 1.0

△ J/J0

0.8 0.7

0.5

0.5

J/J0

0.6 0.5 0.0

△ J/J0

J/J0 (After backwash)

0.0

0.4 0.3 cycle 1

cycle 2

0.2

cycle 3

0.1 HA-Kaolin 0.0

0

1000

2000

3000

4000

5000

6000

Time (s)

Fig. 2 The membrane flux of the coagulated effluents by (a) Ala; (b) Alb; (c) Alc and (d) HA-Kaolin raw water.

21

Fig. 3 The membrane cross-section SEM image of the coagulated-ultrafiltrated effluents (after backwash) by Ala (a) System 1; (b) System 2; (c) System 3 and (d) HA-Kaolin raw water.

22

100

(a)

95

90

90

85

85

80

80

75

75

70

70

65

65 System 1 System 2 System 3

60

System 1 System 2 System 3

55

Alb

Alc

100

100

(b)

90

80

80

70

70

60

60

50

50

40

40

30 20

DOC removal (After UF)

DOC removal (Before UF)

60 55

Ala

90

UV254 Removal (After UF)

UV254 Removal (Before UF)

95

100

30 System 1 System 2 System 3

Ala

System 1 System 2 System 3

Alb

20

Alc

Fig. 4 The NOM removal efficiency of the effluents before and after ultrafiltration: (a) UV254; (b) DOC.

23

100

System 1 (Before UF) System 2 (Before UF) System 3 (Before UF)

(a)

System 1 (After UF) System 2 (After UF) System 3 (After UF)

100

Intensity percent (%)

60

40

20

60

40

20

0 0.1

1

10

100

1000

0 0.1

10000

1

10

System 1 (Before UF) System 2 (Before UF) System 3 (Before UF)

(c)

System 1 (After UF) System 2 (After UF) System 3 (After UF)

50

1000

10000

HA-Kaolin (Before UF) HA-Kaolin (After UF)

(d)

40

Intensity percent (%)

Intensity percent (%)

80

60

40

30

20

10

20

0 0.1

100

Size (nm)

Size (nm)

100

System 1 (After UF) System 2 (After UF) System 3 (After UF)

80

80

Intensity percent (%)

System 1 (Before UF) System 2 (Before UF) System 3 (Before UF)

(b)

1

10

100

1000

10000

0 0.1

Size (nm)

1

10

100

1000

10000

Size (nm)

Fig. 5 The size distribution of the effluents before and after ultrafiltration: (a) Ala; (b) Alb; (c) Alc; (d) HA-Kaolin raw water.

24

270.0

450

210.0

450

240.0

180.0

210.0

400

Ⅲ

400

Ⅲ

150.0

150.0

350

EX (nm)

EX (nm)

180.0

120.0 90.00

300

90.00 300

60.00

Ⅰ

60.00

Ⅱ

Ⅰ

120.0 350

Ⅱ 30.00

30.00

250

250 0.000

0.000 250

300

350

400

450

500

550

250

300

350

400

EM (nm)

450

500

550

EM (nm)

210.0 210.0

450

450 180.0

180.0

400

150.0

Ⅲ

150.0

Ⅲ

120.0

120.0

EX (nm)

EX (nm)

400

350 90.00 300

Ⅱ

90.00

60.00

300

60.00

Ⅰ

350

Ⅱ

Ⅰ

30.00

250

30.00

250 0.000 250

300

350

400

450

500

0.000

550

250

300

350

EM (nm)

400

450

500

550

EM (nm)

270.0 450

210.0

450

240.0

180.0

210.0 400

180.0

Ⅲ

150.0 350 120.0

EX (nm)

EX (nm)

400

Ⅲ

150.0 120.0

350 90.00

90.00 300

300

60.00

60.00

Ⅱ

Ⅰ

Ⅱ

Ⅰ

30.00

30.00 250

250

0.000

0.000 250

300

350

400

450

500

250

550

300

350

400

450

500

550

EM (nm)

EM (nm)

Fig. 6 The EEM spectra of the effluents for Ala before (Ⅰ) and after (Ⅱ) ultrafiltration: (a) System 1; (b) System 2; (c) System 3.

25

Rirr Rif-r Ref

180

27.04

6.73

13.69

4.78

3.91

9.53

5.16

20

1

Sy

m Sy

3

3

6.01

9.85

14.95 5.3

17.09

5.97

10.45

3.31

23.72

18.94

24.46

25.6

22.32

140.17

3.56

2.96

22.54

ste

m

m 15.04

Sy

14.13

Sy

ste

12.84

Sy

ste

40

ste

ste m

m ste Sy

m

3

Sy

2 m

1 m

ste Sy

te

1

2

60

ste m

2

140

Sy s

Membrane resistance (*1010 m-1)

160

25.67

26.7 20.93

0

Ala

Alb

Alc

HA-Kaolin

Fig. 7 The membrane resistance for three systems under different coagulants.

26

Table 1. The characteristics of coagulation effluents with three aluminum species coagulants for three systems (System 1, 2 and 3).

Parameters

Turbidity (NTU)

pH

Zeta potential (mV) UV254 (cm-1) DOC (mg L-1)

Raw water 15.0 ± 0.5 8.12 ± 0.03 -19.06 ± 0.24 0.213 ± 0.0030 4.104 ± 0.043

Coagulation effluents (Ala)

Coagulation effluents (Alb)

Coagulation effluents (Alc)

System

System

System

System

System

System

System

System

System

1

2

3

1

2

3

1

2

3

16.3 ± 0.3 6.77 ± 0.05 -0.97 ± 0.09 0.071 ± 0.0015 2.620 ± 0.048

0.95 ± 0.05 6.94 ± 0.08 -1.96 ± 0.15 0.041 ± 0.0013 2.414 ± 0.035

16.0 ± 0.2 7.01 ± 0.02 4.38 ± 0.19 0.023 ± 0.0020 0.860 ± 0.055

16.5 ± 0.2 7.23 ± 0.03 -1.22 ± 0.14 0.068 ± 0.0007 2.833 ± 0.006

1.05 ± 0.05 7.42 ± 0.02 -2.57 ± 0.25 0.045 ± 0.0010 2.660 ± 0.060

16.2 ± 0.3 7.28 ± 0.04 4.62 ± 0.31 0.059 ± 0.0011 1.155 ± 0.047

16.9 ± 0.3 7.33 ± 0.02 -2.25 ± 0.06 0.071 ± 0.0015 2.777 ± 0.028

1.12 ± 0.03 7.54 ± 0.01 -2.64 ± 0.17 0.044 ± 0.0021 2.576 ± 0.068

16.7 ± 0.1 7.40 ± 0.03 4.98 ± 0.23 0.033 ± 0.0023 0.859 ± 0.038

27

Table 2 The membrane flux difference for three systems. System 1

△ J/J0

System 2

System 3

Ala

Alb

Alc

Ala

Alb

Alc

Ala

Alb

Alc

0.48

0.44

0.50

0.29

0.37

0.37

0.22

0.26

0.29

28

Table 3 FRI parameters for operationally defined EEM regions and EEM analysis of the effluents for Ala before (a) and after (b) ultrafiltration. (a) FRI parameters

EEM region

EEM analysis System1

Projected excitation-emission

MFi

2

area (nm )

Φi,n

System 2

Pi,n

Φi,n

(×10 )

(%)

6

6

System 3

Pi,n

Φi,n

(×10 )

(%)

6

Pi,n

(×10 ) (%)

I

9800

6.73

4.81

48.77

4.48

47.67

2.73 75.19

II

11,200

5.89

4.19

42.50

4.05

43.15

0.73 20.04

III

45,000

1.47

0.86

8.73

0.86

9.18

0.17 4.77

Summation

66,000

9.86

100

9.39

100

3.63

100

(b) FRI parameters

EEM region

EEM analysis System1

Projected excitation-emission

MFi

2

area (nm )

System 2

Φi,n

Pi,n

Φi,n

Pi,n

(×106)

(%)

(×106)

(%)

System 3 Φi,n

Pi,n

(×106) (%)

I

9800

6.73

4.25

46.59

3.93

45.52

1.73 74.92

II

11,200

5.89

4.03

44.20

3.87

44.88

0.44 19.21

III

45,000

1.47

0.84

9.21

0.83

9.60

0.14 5.87

Summation

66,000

9.12

100

8.62

100

2.30

29

100

Highlights  Hybrid coagulation before ultrafiltration (UF) alleviated membrane fouling.  The soluble microbial products and protein were mainly removed components during UF.  The effluents of Ala presented lighter membrane fouling.  The cake layer prevented serious external and internal fouling.

30