If present in the feed water, TEP reduce the deposition of suspended solid non-sticky particles (polysterene and carboxyl group coated polystyrene) in cross-flow filtration membranes. TEP causes aggregation of these particles. Large aggregates have bigger backtransport velocity that prevent them from reaching the membrane surface. At points farther from the membrane surface, the cross flow velocity is always higher due to the lower effect of wall friction. This higher flow captures the aggregated flocks, leading to lateral migration of particles all the way to the concentrate effluent. The TEP that have already deposited on the membrane have no effect on the particle aggregation but rather enhance the deposition of suspended particles to the membrane. Only the free-floating TEP can promote the gathering of the particles into the flocks.
The short term bacterial deposition experiments that have been performed solely with the E.coli cells, and the long term biofouling experiments that have been performed with natural sea water verify that the TEP enhance bacterial attachment to the membrane.
Bacterial properties assist them to use the TEP as a sticky matrix. The consumption of the TEP may or may not be responsible for the biological fouling, but the physical properties of the TEP certainly assist the deposition of microbes.
In order to minimise biological fouling in RO membranes enhanced by TEP, the use of UF pre-treatment proves to be a very effective approach.
Membrane fouling simulator is a useful device for studying particulate fouling. It has a glass for real-time observation and the pressure sensor connected to MFS reflects the particles deposition rate. Nevertheless, due to its very limited length and the lack of the permeate flow it does not reflect the long term biofouling in real spiral wound membranes. The long hollow fiber membranes with permeate flow are much more beneficial for biofouling tests.
The TEP can be possibly applied for commercial purposes. By aggregating solid particles the TEP can promote the sedimentation in still-standing waters. There is a huge room for studying the potential TEP application as a natural biological coagulant.
70
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73
List of figures
Figure 1. A piece of industrial membrane ... 111
Figure 2. A magnified surface of a clean industrial membrane ... 111
Figure 3. Filtration scale [10] ... 12
Figure 4. A bunch of hollow fiber membranes ... 13
Figure 5. The way hollow fiber membranes are arranged for big scale operation. The pipe is filled with hollow fibers ... 13
Figure 7. Spiral-wound membrane water purification plant ... 14
Figure 6. Hydrodynamics of spiral-wound membrane ... 14
Figure 8. Severe form of biofouling [37] ... 15
Figure 9. Severe form of chemical scaling [37] ... 15
Figure 10. Two identical plastic tubes with the two hollow fiber membranes inside each. ... 27
Figure 11. The scheme of laboratory UF installation.. ... 28
Figure 12. Scheme of the MFS installation. [34] ... 29
Figure 13. Particular (colloidal) fouling experimental plan in UF cross-flow filtration setup... 30
Figure 14. Particular (colloidal) fouling experimental plan in RO MFS ... 30
Figure 15. Experimental plan of initial biofouling in UF cross-flow filtration setup ... 31
Figure 17. Experimental plan of laboratory prepared water biofouling in RO MFS ... 32
Figure 16. Experimental plan of laboratory prepared water biofouling in UF cross-flow filtration setup ... 30
Figure 19. Experimental plan of sea water biofouling in RO MFS ... 33
Figure 18. Experimental plan of sea water biofouling in UF cross-flow filtration setup ... 333
Figure 20. The flows in the membrane unit ... 35
Figure 21. Physical meaning of particle deposition factor. Modified from [36] ... 40
Figure 22. Polystyrene microspheres concentration and ASW turbidity dependancy ... 44
Figure 23. Polystyrene deposition factor with and without TEP ... 45
74
Figure 24. Feed channel pressure drop. ... 46
Figure 25. The change in relative membrane permeability.. ... 46
Figure 26. Polystyrene particle deposition on a clean and on a pre-foules membrane ... 47
Figure 27. Polystyrene microspheres concentration and ASW turbidity dependancy ... 48
Figure 28. Polystyrene deposition factor with, without TEP and on a TEP pre-fouled membrane ... 48
Figure 29. E. coli ATCC 25922 deposition factor with, without TEP and on a TEP pre-fouled membrane ... 49
Figure 30. The change in relative membrane permeability of the long-term biofouling experiments ... 51
Figure 31. The change in feed channel pressure drop of the long-term biofouling experiments ... 54
Figure 32. Total organic carbon (TOC) per membrane area test of the long term biofouling experiments ... 55
Figure 33. Adenosine triphosphate (ATP) per membrane area test of the long term biofouling experiments ... 56
Figure 34. schematic illustration of the different forces imposed on particles in cross flow filtration systems ... 58
Figure 35. effect of cross flow velocity and particle diameter on backtransport velocity [11] ... 59
Figure 36. The polystyrene microspheres in ASW with the presence of the TEP under the light microscope ... 59
Figure 37. The polystyrene microspheres in ASW under the light microscope ... 59
Figure 38. the change in relative particle concentration in MFS in time ... 63
Figure 39. change of feed channel pressure drop in MFS ... 63
Figure 40. The spacer view of the experiment without TEP (top) and with TEP (bottom) after 10 hours. .... 62
Figure 41. The feed channel pressure drop - 5 um filtered raw sea water in MFS ... 65
Figure 42. The feed channel pressure drop - UF filtered sea water in MFS ... 65
Figure 43. The feed channel pressure drop - 5 um and UF filtered raw sea water in MFS ... 66
Figure 44. Feed channel pressure drop - long term biofouling experiments in MFS ... 66
Figure 45. The spacer view at the end of the experiments C+P+N (top) and TEP+C+P+N at the end of experient ... 67
Figure 46. The effect on membrane permeability filtering algal bloom impacted water and UF treated algal bloom imacted water ... 68
Figure 47. Abiotic formation of TEP in aquatic systems...19
75
Annexes
Annex 1. The salt recepie of the artificial sea water (ASW)
Component Name Reagent mg/L for 1 L for 5 L for 10 L for 20 L 1 Sodium Carbonate Na2CO3 2 0,002 0,010 0,019 0,04 2 Potassium Bromide KBr 8 0,008 0,041 0,082 0,16 3 Sodium Hydrogen Carbonate NaHCO3 213 0,21 1,07 2,13 4,27 4 Potassium Chloride KCl 739 0,74 3,69 7,39 14,77 5 Calcium Chloride dihydrate CaCl2.2H2O 1.540 1,54 7,70 15,40 30,81 6 Sodium Sulfate Na2SO4 3.993 3,99 19,97 39,93 79,86 7 Magnesium Chloride hexahydrate MgCl2.6H2O 10.873 10,87 54,36 108,73 217,46
8 Sodium Chloride NaCl 23.668 23,67 118,34 236,68 473,36
Mass (g)
Annex 2. Components of the media used in cultured TEP
Compound Amount (per 1L of MQ) Compound Amount (per 1L of MQ)
1 NaCl 24.55g 10 Na2 EDTA 4.16g
2 MgCl2.6H2O 9.82g 11 FeCl3.6H2O 3.15g
3 CaCl2.2H2O 0.53g 12 CuSO4.5H2O 0.01g
4 Na2SO4 3.21g 13 ZnSO4.7H2O 0.022g
5 K2SO4 0.85g 14 CoCl2.6H2O 0.01g
6 NaHCO3 50.4g 15 MnCl2.4H2O 0.18g
7 AlCl3.6H2O 0.0241g 16 Na2Mo4.2H2O 0.006g
8 Vitamin B1 0.1g 17 Vitamin B12 0.0005g
9 Biotin 0.0005g 18 Na2SiO3.9H2O 30g
Annex 3. Example of LC-OCD measurement for cultured TEP stock
Annex 4. The coliform agar composition
ChromoCult® Coliform Agar (Cat.No. 1.10426.0500) was used for the growing of the E.coli collonies. The recepie in grams per litre is:
Peptones 3.0; sodium chloride 5.0; sodium dihydrogen phosphate 2.2; disodium hydrogen
phosphate 2.7; sodium pyruvate 1.0; tryptophan 1.0; Agar-agar 10.0; Sorbitol 1.0; Tergitol®7 0.15;
chromogenic mixture 0.4.
Annex 5. The zeta potential measurement results (autotitration)
78 The meaning of zeta potential values [40]:
Zeta potential [mV] Stability behavior of the colloid
from 0 to ±5 Rapid coagulation or flocculation from ±10 to ±30 Incipient instability
from ±30 to ±40 Moderate stability from ±40 to ±60 Good stability more than ±61 Excellent stability
79 Annex 6. The values of E.coli concentration
The table above illustrates the real E.coli concentrations thorought the experiments that have been described in this report (in the feed, in the concentrate waters and their changes in time).
The data is based on a collony forming units.
80 Annex 7. The “4 X UF” setup empowering simultaneous run of 4 filtration experiments
81 Annex 8. The factors determing backtransport velocity