Chapter 4: Results and Discussions
4.4 Analysis of membrane fouling
4.4.3 Distribution of fouling compositions in cake layer
From the CLSM images, protein, α-D-glucopyranose polysaccharides, of β-D-glucopyranose polysaccharides and DNA were represented by green color, cyan color, blue color and red color as shown in Figures 4.24~27. Figures 4.24~25 showed the presence of membrane fouling compositions on HPI and HPO membrane operated under 60% of critical flux in MBR-2. While for Figure 4.26~27, those compositions on HPI membranes operated under 80% of critical flux in MBR-2 and MBR-1 were given, respectively. In particular in Figure 4.24, images (a), (b), (c) and (d) show the presence of protein, α-D-glucopyranose polysaccharides, β-D-glucopyranose polysaccharides and DNA in membrane fouling on membrane surface, respectively. Image (e) shows the overlap image of membrane fouling. In general, it can be visibly seen that protein with green color are predominant compared to other substances for Figures 4.24~27. That means protein is the main constituent contributed to the fouling formation of membrane.
Polysaccharides (α-polysaccharides and β-polysaccharides) also contribute to the formation of membrane even thought polysaccharides play a smaller role than protein.
By this CLSM tests, the thickness of cake layers were measured with 95.77 µm and 62.4 µm for HPI membranes operated in MBR-1 and MBR-2, respectively, under the same fluxes. For HPI and HPO membrane operated under 80% of critical flux in MBR-2, it was 101.51 and 76.93 µm, respectively.
The vertical distribution of membrane fouling compositions in cake layer was also observed. Figures 4.28~31 show the vertical distribution of protein, α-polysaccharides, β-polysaccharides and DNA. The changes of these substances were observed from the cake layer surface to the membrane surface corresponding from 0% to 100% of X axis. All substances were lower at membrane surface and higher at cake layer surface. However, the highest peaks lie between 40% and 80% of the depth of the cake layer. That means all the substances tend to be deposited at the middle of the cake layer. Especially, in case of membrane fouling on HPI membrane operated under 60% of critical flux in MBR-2, all the fouling compositions at cake layer surface are lower than that at membrane surface excepting the case of DNA
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Figure 4.24 CLSM images of membrane fouling on HPI membrane operated under 60% critical flux in MBR-1 (a) CLSM image of protein (FITC); (b) CLSM image of α-D-glucopyranose polysaccharides (ConA); (c) CLSM image of β-D-glucopyranose polysaccharides (Calcoflour white); (d) CLSM image of DNA (SYTO 63); (e) CLSM overlap image
Figure 4.25 CLSM images of membrane fouling on HPO membrane operated under 80% critical flux in MBR-2 (a) CLSM image of protein (FITC); (b) CLSM image of α-D-glucopyranose polysaccharides (ConA); (c) CLSM image of β-D-glucopyranose polysaccharides (Calcoflour white); (d) CLSM image of DNA (SYTO 63); (e) CLSM overlap image
(a) (b)
(c) (d)
(e)
50 µm 50 µm
50 µm 50 µm
50 µm
(a) (b)
(c) (d)
50 µm 50 µm (e)
50 µm 50 µm
50 µm
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Figure 4.26 CLSM images of membrane fouling on HPI membrane operated under 80% critical flux in MBR-2 (a) CLSM image of protein (FITC); (b) CLSM image of α-D-glucopyranose polysaccharides (ConA); (c) CLSM image of β-D-glucopyranose polysaccharides (Calcoflour white); (d) CLSM image of DNA (SYTO 63); (e) CLSM overlap image
Figure 4.27 CLSM images of membrane fouling on HPI membrane operated under 60% critical flux in MBR-2 (a) CLSM image of protein (FITC); (b) CLSM image of α-D-glucopyranose polysaccharides (ConA); (c) CLSM image of β-D-glucopyranose polysaccharides (Calcoflour white); (d) CLSM image of DNA (SYTO 63) (e) CLSM overlap image
(a) (b)
(c) (d)
(e)
50 µm 50 µm
50 µm 50 µm
50 µm
50 µm 50 µm
50 µm 50 µm
50 µm
(a) (b) (e)
(c) (d)
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Relative distance from fouling surface
Intensity
Relative distance from fouling surface
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Relative distance from fouling surface
Intensity
Relative distance from fouling surface
(a) Protein (b) α-Polysaccharide
(c) β-Polysaccharide (d) DNA
Figure 4.28 Vertical distribution of EPS in membrane fouling on HPI membrane operated under 60% critical flux in MBR-1
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Relative distance from fouling surface Relative distance from fouling surface
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% Relative distance from fouling surface
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Relative distance from fouling surface
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
(a) Protein (b) α-Polysaccharide
(c) β-Polysaccharide (d) DNA
Figure 4.29 Vertical distribution of EPS in membrane fouling on HPO membrane operated under 80% critical flux in MBR-2
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Figure 4.30 Vertical distribution of EPS in membrane fouling on HPI membrane operated under 80% critical flux in MBR-2
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Relative distance from fouling surface
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Relative distance from fouling surface
Intensity
Relative distance from fouling surface
Intensity
Relative distance from fouling surface
(a) Protein (b) α-Polysaccharide
(c) β-Polysaccharide (d) DNA
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Relative distance from fouling surface
Intensity
Relative distance from fouling surface
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Relative distance from fouling surface
0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100%
Relative distance from fouling surface
Intensity
(a) Protein (b) α-Polysaccharide
(c) β-Polysaccharide (d) DNA
Figure 4.31 Vertical distribution of EPS in membrane fouling on HPI membrane operated under 60% critical flux in MBR-2
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Chapter 5:
Conclusions and Recommendations
5.1 Conclusions
(1) Critical flux for HPI membrane operated with activated sludge of 7,000 – 7,500 mg/l, HPI and HPO membranes under 6,000 – 6,500 mg/l were found at 18, 33 and 30lm-2h-1, respectively.
(2) With the same membrane material, operation in a reactor with higher sludge concentration would cause a higher propensity of membrane fouling.
(3) HPO membrane could be easier fouled than HPI membrane in not only the short-term operation but also in the long-term operation.
(4) The higher the flux imposed, the faster the TMP jumped.
(5) The small particle size contributes to the fouling propensity.
(6) FTIR analysis shows the presence of proteins and polysaccharides in membrane foulants.
(7) EEM results show the presence of proteins in fouling as tyrosine-like aromatic protein and soluble microbial by-product-like protein. In which, operated in higher AS concentration caused the higher proteins concentration in both cake layer and membrane pore inside were. Otherwise, the higher flux imposed, the higher proteins in cake layer and membrane pore inside were also observed. Proteins in HPI membrane are higher than in HPO membrane.
(8) CLSM images show the presence of proteins, polysaccharides (α-polysaccharides and β-polysaccharides) and DNA. The thickness of cake layer were also measured with 95.77, 62.4 for HPI membranes operated under 60% of critical flux in MBR-1 and MBR-2. While for HPI and HPO membrane operated under 80% of critical flux in MBR-2, it was 101.51 and 76.93 µm, respectively.
(9) Vertical distribution analysis shows that the concentration of all substances on membrane surface is lower than on cake layer surface. They are mainly distributed at from 40% to 80% of the depth of cake layer.
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5.2 Recommendations
(1) Further studies on membrane fouling under sub-critical flux operation is required.
(2) More investigation about the distribution of membrane fouling along the depth of cake layer should be concerned for understanding the fouling behavior.
(3) The effect of flux to the membrane fouling should be researched to analyze and solve economic problems in using MBR system.
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Appendix 1
Polysaccharide concentration in cake layer and in inside of membrane pore
In cake layer Inside of membrane pore
Membrane Bioreactor Percentage of critical flux (%)
Soluble (mg/l as glucose)
Bound
(mg/g MLSS as glucose)
Soluble (mg/l as glucose)
Bound
(mg/g MLSS as glucose) HPI
HPI HPI HPO
MBR-1 MBR-2 MBR-2 MBR-2
60 60 80 80
274.1 ± 30.03 31.34 ± 5.88 101.34 ± 44.31
12.96 ± 0.26
34.43 ± 1.78 35.14 ± 0.19 27.83 ± 5.46 61.21 ± 1.9
20.74 ± 1.78 4.36 ± 0.15 10.39 ± 2.1 3.8 ± 0.33
13.66 ± 0.1 4.89 ± 0.0 12.67 ± 0.66 11.42 ± 1.67
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Appendix 2
Protein concentration in cake layer and in inside of membrane pore
In cake layer Inside of membrane pore Membrane Bioreactor Percentage of
critical flux (%)
Soluble (mg/l as BSA)
Bound
(mg/g MLSS as BSA)
Soluble (mg/l as BSA)
Bound
(mg/g MLSS as BSA) HPI
HPI HPI HPO
MBR-1 MBR-2 MBR-2 MBR-2
60 60 80 80
89.35 ± 4.31 9.54 ± 0.19 36.25 ± 6.29
8.81 ± 1.51
25.59 ± 2.42 92.14 ± 12.71
21.09 ± 1.27 262.26 ± 3.52
2.75 ± 0.07 1.16 ± 0.46 1.71 ± 0.04 2.76 ± 0.56
106.72 ± 79.18 475.81 ± 14.11
34.4 ± 4.5 1131.13 ± 16.38
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Appendix 3
Polysaccharide and protein concentration in sludge and in the permeate of MBR-1 and MBR-2
Glucose Protein
Bioreactor Soluble
(mg/l as glucose)
Bound
(mg/g MLSS as glucose)
Soluble (mg/l as BSA)
Bound
(mg/g MLSS as BSA) MBR-1
MBR-2 MBR-1 MBR-2
Sludge Sludge Permeate Permeate
6.72 ± 0.48 5.39 ± 0.13 3.47 ± 2.78 3.3 ± 1.7
32.58 ± 0.16 28.95 ± 3.39
- -
13.05 ± 0.35 4.2 ± 0.04 1.66 ± 0.18 4.35 ± 0.78
26.12 ± 2.4 24.92 ± 0.57
- -