Flocculation of Microalgal Biomass for Biofuels

Production by Flocculation using pH Adjustment

and Coagulant Addition

Rifka Aisyah1, Kuei-Ling Yeh1, Chun-Yen Chen1,2 and Jo-Shu Chang 1,2,3

1Department of Chemical Engineering, National Cheng Kung University, Tainan, Taiwan2Sustainable Environment Research Center, National Cheng Kung University, Tainan, Taiwan3Center for Biosciences and Biotechnology, National Cheng Kung University, Tainan, Taiwan

10th International Conference on Clean Energy (ICCE-2010)

Famagusta, N. Cyprus, September 15-17, 2010

1st University Road, National Cheng Kung University, Tainan, 701, Taiwan

Corresponding author: email: changjs@mail.ncku.edu.tw

INTRODUCTION

MICROALGAE AS A PROMISING SOURCE

FOR BIOFUELS PRODUCTION

Microalgal biomass is a promising source for biofuels production

The ability to produce lipid or

carbohydrate components

The ability to address some major limitations associated with the application of first and second generation of biofuels

Capability of all round year production

Be able to be cultivated in non-productive land

2

Lack of an economical and efficient method to harvest microalgae

Low cell densities and

small size of

microalgae

The cost required for

downstream processing can be

up to

Biofuels are low-value

products 3

INTRODUCTION

HARVESTING: A MAJOR BOTTLENECK TO

MICROALGAE-BASED BIOFUELS

HARVESTING IS

VERY CHALLENGING!

20-30% of the total

costs production

Harvesting should be

energy-efficient and relatively

inexpensive

4

INTRODUCTION

SOME MAJOR TECHNIQUES IN

MICROALGAL HARVESTING

MICROALGAL

FLOCCULATIONMicroalgal

Harvesting Methods

Flocculation

Centrifugation

Filtration

Flotation

Electrolytic process

Gravity sedimentation

o More appropriate process

than conventional

methods, such as

centrifugation and gravity sedimentation

o Allows rapid handling of

large quantities of

microalgal cultures

5

INTRODUCTION

MICROALGAL FLOCCULATION

METHODS

Microalgal Flocculation

Methods

pH adjustment

Hydrolyzing metals

addition

Polyelectrolyte addition

Bioflocculation

Focus

of our study!!

• AlCl3• Al2(SO4)3

• FeCl3• etc

THE OBJECTIVES OF STUDY

To compare the performance of two types of

flocculation methods, flocculation using pH

adjustment and flocculation using AlCl3 as

coagulant

To evaluate the influence of initial biomass

concentration and coagulant concentration on

flocculation performance

6

Species

Chlorella vulgaris ESP-31

Culture condition

7

METHODS

MICROALGAL STRAIN AND CULTIVATION

CONDITION

Criteria Basal medium

Working volume 5 L

Agitation rate (rpm) 300 rpm

Carbon source CO2

Carbon source

concentration

20% CO2; 0.02 vvm

Cultivation day 19 days

pH adjustment AlCl3 addition

8

METHODS

EXPERIMENTAL DESIGN

MICROALGAL FLOCCULATION

Effect of initial

biomass

concentration

Effect of final

pH value

Effect of initial

biomass

concentration

Effect of AlCl3concentration

• Initial pH = 7.00

• 0.67 g/l (OD688, initial = 3.36)

• 1.27 g/l (OD688, initial = 6.34)

• Final pH = 10.00 and

12.00, respectively

• Working volume = 250 ml

• Initial pH = 7.00

• 0.47 g/l (OD688, initial = 2.35)

• 1.55 g/l (OD688, initial = 7.76)

• 2.60 g/l (OD688, initial = 13.00)

• AlCl3 concentration = 0; 0.1;

0.3; 0.5; 0.7; 0.9; 1.5 g/l

• Working volume = 40 ml

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• Initial pH = 7.00

• 0.67 g/l (OD688, initial = 3.36)

• 1.27 g/l (OD688, initial = 6.34)

• Final pH = 10.00 and

12.00, respectively

• Working volume = 250 ml

• Initial pH = 7.00

• 0.47 g/l (OD688, initial = 2.35)

• 1.55 g/l (OD688, initial = 7.76)

• 2.60 g/l (OD688, initial = 13.00)

• AlCl3 concentration = 0; 0.1;

0.3; 0.5; 0.7; 0.9; 1.5 g/l

• Working volume = 40 ml

Parameter pH adjusment AlCl3 addition

Initial pH 7.00 7.00

Initial

biomass

concentration

0.67 g/l (OD688 =

3.36)

1.27 g/l (OD688 =

6.34)

0.47 g/l (OD688 = 2.35)

1.55 g/l (OD688 = 7.76)

2.60 g/l (OD688 = 13.00)

Final pH or

AlCl3

concentration

10.00 and 12.00

respectively

0;0.1 g/l; 0.3 g/l; 0.5 g/l; 0.7

g/l; 0.9 g/l; 1.5 g/l

Working

volume (ml)

250 20

10

90

110

130

150

170

190

30

50

70

210

230

250

Four-fifths

Three-fifths

One-fifths

pHinitial = 7.00

[Biomass initial] = 0.67 g/l and 1.27 g/l,

respectively

NaOH 1 N

Agitation: 200 rpm; 1 min

pH

mete

r

pHfinal = 10 and 12

respectively

Cell density

Measurement using UV

(Wavelength = 688 nm)

METHODS

FLOCCULATION USING PH ADJUSTMENT

Take thesamples at

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METHODS

FLOCCULATION USING AlCl3 AS COAGULANT

[Initial biomass] = 0.47 g/l

[Initial biomass] = 1.55 g/l

[Initial biomass] = 2.60 g/l

pH = 7.00

pH = 7.00

pH = 7.00

0.1 0.3 0.5 0.7 0.9 1.5

0.1 0.3 0.5 0.7 0.9 1.5

0.1 0.3 0.5 0.7 0.9 1.5

Add AlCl3 (g/l)

20 ml

Blank

Blank

Blank

2/3 from bottom of tube

1/2 from bottom of tube

Cell density

Measurement using UV

(Wavelength = 688 nm)

Take the samples at

Parameters to be evaluated:

o Flocculation efficiency

The flocculation efficiency was evaluated by comparing

the remaining cell density in several sampling points

with the cell density before treatment.

Ci = concentration of cell in the suspension before

treatment

Cf = concentration of cells in suspension

o The highest flocculation efficiency

o Specific flocculation rate

Specific flocculation rate was evaluated by taking the

highest slope of the graph which correlates the

flocculation efficiency and flocculation time.

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METHODS

FLOCCULATION PERFORMANCE

PARAMETERS

Flocculation/harvest efficiency = x 100i f

i

C C

C

Growth condition

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EXPERIMENTAL RESULTS

MICROALGAE GROWTH ON BASAL MEDIUM

Time (day)

0 4 8 12 16 20

Bio

mass c

oncentr

ation (

g/l)

0

1

2

3

4

pH

6.4

6.6

6.8

7.0

7.2

7.4

Biomass concentration (g/l)

pH

Strain Chlorella

vulgaris ESP-

31

Medium Basal

CO2

concentration

20%; 0.02

vvm

Working

volume

5L

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EXPERIMENTAL RESULTS

FLOCCULATION USING PH ADJUSMENT

(1)

Time (h)

0 15 30 45 60 75

Flo

ccula

tion e

ffic

iency (

%)

0

20

40

60

80

100

pH 10.0

pH 12.0

Time (h)

0 15 30 45 60 75

Flo

ccula

tion e

ffic

iency (

%)

0

20

40

60

80

100

pH 10.0

pH 12.0

[Initial biomass] = 0.67 g/l

[Initial biomass] = 1.27 g/l

Percent flocculation efficiency using pH adjustment method at

different final pH and different initial biomass concentration

At fixed initial biomass concentration, increasing in pH value resulted in increasing in flocculation efficiency

4

30.10%

60.95%

4

47.63%

75.71%

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FLOCCULATION USING PH ADJUSTMENT

(2)

Initial

OD688

Initial biomass

concentration

(g/l)

Final

pH

Specific

flocculation rate

(%/min)

Highest

flocculation

efficiency (%)

3.36 0.67 10.0 0.11 73.77

12.0 0.47 91.80

6.34 1.27 10.0 0.30 92.74

12.0 0.54 94.80

At fixed initial biomass concentration, increasing in pH led to increase in specific flocculation rate and highest flocculation efficiency

At the same pH value, the increase of initial biomass concentration led to increase in specific flocculation rate and the highest flocculation efficiency

Specific flocculation rate and the highest flocculation efficiency of Chlorella vulgaris ESP-31 at different initial biomass concentration

and final pH

Increase! Increase!

Increase! Increase!

Increasing the pH was a potential method to

recover oil-rich microalgal strain Chlorella vulgaris

ESP-31

Although this method has several advantages, such

as high biomass recovery, operational simplicity,

and cheap running cost, this method is very

slow To overcome this problem, flocculation

experiment using AlCl3 as coagulant was

conducted16

SUMMARY

FLOCCULATION USING PH ADJUSTMENT

Specific flocculation rate of Chlorella vulgaris ESP-31 at different

initial biomass and coagulant concentration

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EXPERIMENTAL RESULTS

FLOCCULATION USING AlCl3 AS COAGULANT

AlCl3concentration

(g/l)

Specific flocculation rate (%/min)

Initial

biomass

concentration

= 0.47 g/l

Initial biomass

concentration

= 1.55 g/l

Initial biomass

concentration

= 2.60 g/l

0 0.85 1.02 2.80

0.1 3.22 0.96 2.72

0.3 5.82 6.33 4.43

0.5 4.70 9.11 4.68

0.7 6.71 9.06 16.19

0.9 6.70 17.11 16.95

1.5 8.21 17.17 17.01

Data used in this experiment originated from the samples taken at two-

thirds from the bottom of tube

Incre

ase!

Incre

ase!

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AlCl3concentration

(g/l)

Highest flocculation efficiency (%)

Initial

biomass

concentration

= 0.47 g/l

Initial biomass

concentration

= 1.55 g/l

Initial biomass

concentration =

2.60 g/l

0 23.39 26.93 35.38

0.1 94.57 30.32 41.54

0.3 95.48 97.98 28.62

0.5 94.87 98.97 93.31

0.7 94.44 98.69 98.13

0.9 91.30 98.68 97.99

1.5 ~100 99.03 97.83

Highest flocculation efficiency of Chlorella vulgaris ESP-31 at different initial biomass concentration and coagulant concentration

EXPERIMENTAL RESULTS

FLOCCULATION USING AlCl3 AS COAGULANT (2)

The highest flocculation efficiency pertime was determined from

flocculation efficiency at 4 h of settling time

Incre

ase!

Incre

ase!

Comparison of flocculation performance at different

initial biomass concentration

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EXPERIMENTAL RESULTS

FLOCCULATION USING AlCl3 AS COAGULANT (3)

Initial

OD688

Initial

biomass

concentration

(g/l)

Dose of AlCl3 needed

to obtain at least

90% flocculation

efficiency (g/l)

Specific flocculation

rate needed to obtain at

least 90% flocculation

efficiency (%/min)

2.35 0.47 0.10 3.22

7.76 1.55 0.30 6.33

13.00 2.60 0.50 4.68

Increase! Increase! Much FASTER than

flocculation using

pH adjustment

method

Comparison of flocculation performance at different

initial biomass concentration

20

EXPERIMENTAL RESULTS

FLOCCULATION USING AlCl3 AS COAGULANT (3)

Initial

biomass

concentration

(g/l)

Dose of AlCl3 needed

to obtain at least

90% flocculation

efficiency (g/l)

Specific flocculation

rate needed to obtain at

least 90% flocculation

efficiency (%/min)

0.47 0.10 3.22

1.55 0.30 6.33

2.60 0.50 4.68

Increase! Increase! Much FASTER than

flocculation using

pH adjustment

method

CONCLUSION

Oil-rich microalgae strain Chlorella vulgaris ESP-31

can be harvested using flocculation by pH

adjustment and flocculation by coagulant

addition

Flocculation using AlCl3 as coagulant showed

much faster specific flocculation rate

For a fixed initial biomass concentration, increase in

dosage of AlCl3 tended to increase the flocculation

efficiency

Increasing in initial biomass concentration increase

the dosage of AlCl3 needed to obtain more than

90% of flocculation efficiency

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Thankyou for your attention !!

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