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Cake layer characteristics in long time ceramic MF filtration for surface water treatment

Mingyang LiMaster defence presentation

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Contents

• Background • Research objective• Experiments• Results• Conclusions• Recommendations & Futre work

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Background

• Good & stable water quality• Low energy use (low pressurized)• Easily operated

Ceramic microfiltrationMicrofiltration

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Background

Compared to conventional polymeric membranes:• Low fouling tendency• Higher permeability• Resistance to pH, heat and chemical conditions• Price becoming cheaper

Ceramic membranes

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Background

Membrane Fouling

Alternative solutions:• Pretreatment used: Pre-coagulation

Solid wastes• Frequent backwash used Low recovery High maintenance costHigh energy consumption

Ceramic Microfiltration problem

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Research objective

Increase the filtration time in ceramic microfiltration with in-line coagulation

Highlights:• In-line coagulation, no flocs removed• Long filtration time, TMP increase controlled

Practical Support: • MBR installations• Sludge layer on surface• effective fouling control

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ExperimentsCake layer importance

• Important cause for TMP increase (constant flux)• 80% resistance percentage in total resistance (PACl)

• Controlled by coagulation mechanisms (pH, dosage)

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ExperimentsCoagulation mechanisms

Figure 1 Coagulation zones• Three zones divided by pH and dosage• Cake layer formations membrane

performances

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ExperimentsFlow scheme

Figure 2 Experimental scheme• pH=4, 6 and 8,Dosage=8 and 16mg/L• Flux 60 L/(m2*h)

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ExperimentsExperimental setup

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ExperimentsExperimental setup

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Results

Figure 3 TMP curve with BW and without BW

• Recorded by data logger (Dataq, DI710)• Constant flux 60 (L/m2*h)• Slow TMP increase in cake filtration

TMP

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Results

Figure 4 TMP curve under coagulant dosage of 8 and 16 mg/L

• In cake filtration, TMP increased differently• pH=4 leads to slow TMP increase (Restabilization

coagulation)• pH=6 leads to rapid TMP increase (Adsorption

coagulation)

TMP

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Results

• Blank membrane filtered by demi-water Rm

• Recorded data of final TMP Rtot

• Frozen cake layer removed, membrane filtered by demi-water Rm+Rp

• Rc, Rp can be calculated from the above components

Resistance

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Results

Table 1 Resistance components

• Rc is the largest resistance component• pH=4 leads to the smallest resistance• pH=6 leads to largest resistance

Resistance

R (1012m-

1)

Fe3+=8mg/L Fe3+=16mg/L

Rm Rp Rc Rm Rp Rc

pH=4 0.48

0.48

1.37

0.54

0.42

1.61

pH=6 0.54

0.72

3.7

0.48

0.78

3.15

pH=8 0.54

0.60

2.15

0.54

0.42

1.91

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ResultsCake layer density & water content

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Results

Table 2 Cake layer density

Table3 Cake layer water content

• pH=4 leads to smallest density, but largest water content

• pH=6 leads to largest density, but smallest water content

Cake layer density & water content

Density (kg/m3*103)

Fe3+=8mg/L Fe3+=16mg/L

pH=4 1.025 1.018

pH=6 1.070 1.083

pH=8 1.045 1.050

Water content Fe3+=8mg/L Fe3+=16mg/L

pH=4 0.973 0.967

pH=6 0.921 0.928

pH=8 0.937 0.937

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Results

Cake layer thickness

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Results

Table 4 Cake layer thickness

• Higher chemical dosage, higher the cake layer• pH=4 leads to largest cake thickness, pH=6 leads to

the smallest cake thickness

Cake layer height

Thickness (mm)

Fe3+=8mg/L Fe3+=16mg/L

pH=4 0.35 0.56

pH=6 0.11 0.24

pH=8 0.15 0.28

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Results

Kozeny-Carmen equation for cake filtration:

Cake layer thickness

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Results

Table 5 Cake layer particle size

• pH=4 leads to largest cake particles• pH=6 leads to the smallest cake particles

Cake layer particle size

Particle size (m)

Fe3+=8mg/L Fe3+=16mg/L

pH=4 0.41 0.37

pH=6 0.10 0.13

pH=8 0.16 0.20

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Results

Empirical equation:

• The membrane and cake layer filtered by demi-water at 20, 30 and 45 L/(m2*h)

Cake layer compressibility

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Results

Table 6 Cake layer compressibility factor

• pH=4 leads to large compressibility factor, loose structure

• pH=6 leads to the small compressibility factor, dense structure

Cake layer compressibility

Compressibility factor

Fe3+=8mg/L Fe3+=16mg/L

pH=4 0.57 0.70

pH=6 0.33 0.48

pH=8 0.52 0.60

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Results

Table 7 DOC removal efficiency

• Higher chemical dosing, higher removal efficiency (first stage)

• DOC remove shows no clear tendency with pH

DOC removal

Fe3+=8mg/L Fe3+=16mg/L

S1 S2 Total

S1 S2 Total

pH=4 40%

17%

58%

42%

8% 50%

pH=6 25%

7% 32%

37%

15%

52%

pH=8 4% 15%

20%

10%

31%

41%

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Conclusions

• Membrane performance can be controlled by various pre-coagulation zones

• It is possible to achieve a long filtration time by applying cake filtration

• Cake layer plays an important role in fouling control process

• pH=4 leads to loose cake structure, shown as slow TMP increase, low cake layer density, high cake layer water content, thickness, particle size and compressibility

• pH=6 leads to dense cake structure, shown as rapid TMP increase, high cake layer density, low cake layer water content, thickness, particle size and compressibility

• DOC remove shows no clear tendency with pH

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Recommendations & Future work

• pH=4, Dos=8 is good pre-coagulation condition in ceramic microfiltration

• More experiments about the explanations between coagulation mechanisms and cake layer structure

Mechanism cake layer structure phenomenon

• More experiments about low chemical, for instance Dos=4mg/L