**4. MF application to increase biomass and carbohydrate production**

New strategies of culture technologies with high yield of biomass concentration are necessary to enable biofuel production by microalgae [40]. Thus, MF application has been considered a new low-cost technological approach to stimulate cell growth and increased carbohydrate content in microalgal biomass. These outcomes may be achieved by the complex biochemical system in microalga cells, which may cause changes in their defense mechanism and activate proteins, some enzymatic systems and free radicals [21, 41].

Small et al. [42] evaluated the cultivation of *Chlorella kessleri* in a raceway bioreactor with Blue-Green Medium (BG-11) with static MF from 5 to 15 mT, generated by a water-cooled solenoid for 13 d. Cultivation with 10 mT had significant increase of 50% in biomass production while the carbohydrate content reached 42.2% at the end of cultivation. Bauer et al. [16] investigated the influence of 30 mT on *Chlorella kessleri* cultivation in BG-11 medium for 10 d. In relation to the control assay (without MF application), biomass concentration increased 23.5%; its carbohydrate content reached 21.4% with MF applied throughout cultivation (**Table 1**).


#### **Table 1.**

*Magnetic effect on biomass and carbohydrate contents of different species of microalga.*

Deamici et al. [43] investigated physiological changes in *Spirulina* sp. cultivated in Zarrouk medium under the influence of 30 mT in different periods of MF application (24 h d−1 and 1 h d−1) for 15 d. When the microalga was exposed to the permanent condition, biomass concentration increased 40% and reached the highest carbohydrate content of 30.3%, it was 133.2% higher than the one of the control. Shao et al. [44] evaluated enhancement of *Spirulina platensis* biomass with the application of 30 mT for 22 d. Different exposures times (3, 6 and 12 h d−1) were evaluated and the highest biomass concentration was reached when MF were applied for 6 h d−1, increasing 30.4% in relation to the control assay, with carbohydrate content of 12.8%.

#### **5. MF application to increase biomass and lipid production**

Cultivation strategies have been studied to increase biomass production and lipid synthesis by microalgae [23]. MF application affected the composition and production of biomass, fundamental parameters in biofuel production [21].

According to Albuquerque et al. [45], MF are capable of regulating metabolic pathways of microorganisms, gene expression and chemical reactions. The authors also commented that the influence of MF on cell metabolism and on the growth of biomass depends on the interaction between the intracellular and extracellular environment, such as the type of cell, characteristics of the culture medium and the existence of biomolecules which are susceptible to MF.

MF can affect the growth and metabolism of microorganisms positively and negatively, depending on its intensity, frequency, pulse shape, type of modulation and exposure time [9]. MF have been shown to be efficient to increase biomass and lipids, since their action can cause oxidative stress in cells of microorganisms, change energy levels and orientation of free radicals and affect enzymatic activity of cells [46–48].

Changes promoted by the MF are responses of the interaction between them and microorganisms, i. e., alteration in permeability of membranes and, consequently, in their cellular metabolism [49]. MF application is considered a low cost and promising tool to overcome some limitations of microalgae, such as lipid productivity [50]. **Table 2** shows the effects of MF on biomass concentration and lipid content.

**423**

cultivation.

**6. Conclusion**

to be cost-effective.

and 135.1% (39.5 mg L−1 d−1), respectively.

*Magnetic Field Application to Increase Yield of Microalgal Biomass in Biofuel Production*

10 mT for 0.3 h d−1 Increased

60 mT for 24 h d−1 Inhibition

50 mT for 1 h d−1 Increased

15 mT for 1 h d−1 Increased

*Influence of the MF on the synthesis of biomass and lipids in different species of microalga.*

**Lipid content (%w w−1)**

47%

23.2%

12.9%

22.4%

60 mT for 1 h d−1 Null effect Increased

30 mT for 24 h d−1 — Increased

50 mT for 3 h d−1 — Increased

**Biomass concentration (g L−1)**

12.8%

Increased 43%

Increased 20.5%

95.1%

30%

Increased 8.2%

Inhibition 33%

**References**

[51]

[42]

[17]

[43]

[19]

[52]

[18]

**exposure time MF**

Studies have shown that lipid content and productivity can be increased when there is an association between nitrogen reduction and MF application. Bauer et al. [16] identified that, when *Chlorella kessleri* was cultured in BG 11 medium and exposed to 60 mT for 1 h d−1, there was an increase in biomass concentration of 15% and 13.7% in lipid synthesis by comparison with the control. Chu et al. [28] evaluated the influence of MF application on *Nannochloropsis oculate* culture with modified Walne's medium. The highest lipid productivity (30.9 mg L−1 d−1) and lipid content (42.4%) were obtained when 20 mT was applied during 7 days of

*Nannochloropsis oculate* was exposed to different intensities of MF (5, 10 and 15 mT) to evaluate the influence its biochemical composition and cell growth. Cultivation under influence of 10 mT increased biomass productivity (45%) and lipid productivity (57%) by comparison with the control [53]. Costa et al. [18] reported that the *Chlorella homosphaera* cultivated in the Bristol's Modified Medium (BMM) with 50% reduction in the nitrogen source associated with exposure to 30 mT and 60 mT for 1 h d−1, increased lipid productivity in 108.4% (35 mg L−1 d−1)

This chapter reported the potential of microalgal cultivation with MF application for biofuel production. The use of microalgae as raw material is an attractive alternative that can reduce the use of fossil sources and CO2 emissions, and consequent pollution in the environment. Studies have suggested that MF application may be the most commercial production due to increased production of carbohydrates and lipids. For best results, in the case of every microalga species, parameters, such as MF intensity, exposure time, application period during cultivation and devices used to apply MF, should be evaluated. However, largescale production of biofuels derived from microalgae has yet to be achieved if it is

*DOI: http://dx.doi.org/10.5772/intechopen.94576*

**Microalga species Intensity and** 

*Chlorella pyrenoidosa* FACHB-9

*Chlorella kessleri* UTEX 398

*Chlorella fusca* LEB 111

*Spirulina* sp. LEB 18

*Chlorella minutissima* sp

*Chlorella homosphaera* sp

**Table 2.**

*Chlorella pyrenoidosa* FACHB-9

*Magnetic Field Application to Increase Yield of Microalgal Biomass in Biofuel Production DOI: http://dx.doi.org/10.5772/intechopen.94576*


#### **Table 2.**

*Biotechnological Applications of Biomass*

**Microalga species Intensity** 

*Chlorella kessleri* UTEX 398

*Chlorella fusca* LEB 111

*Chlorella kessleri* LEB 113

*Spirulina platensis* sp

*Chlorella minutissima* sp

**Table 1.**

**(mT)**

carbohydrate content of 12.8%.

Deamici et al. [43] investigated physiological changes in *Spirulina* sp. cultivated

*Spirulina* sp. LEB 18 30 24 40 30.3 [43]

in Zarrouk medium under the influence of 30 mT in different periods of MF application (24 h d−1 and 1 h d−1) for 15 d. When the microalga was exposed to the permanent condition, biomass concentration increased 40% and reached the highest carbohydrate content of 30.3%, it was 133.2% higher than the one of the control. Shao et al. [44] evaluated enhancement of *Spirulina platensis* biomass with the application of 30 mT for 22 d. Different exposures times (3, 6 and 12 h d−1) were evaluated and the highest biomass concentration was reached when MF were applied for 6 h d−1, increasing 30.4% in relation to the control assay, with

*Magnetic effect on biomass and carbohydrate contents of different species of microalga.*

**Time of exposure (h d−1)**

**Increased biomass content (%)**

10 0.3 50 42.2 [42]

60 24 21.4 31.4 [17]

30 24 23.5 21.4 [16]

30 6 30.4 12.8 [44]

30 24 30 60.5 [19]

**Carbohydrate content (%)**

**References**

**5. MF application to increase biomass and lipid production**

existence of biomolecules which are susceptible to MF.

Cultivation strategies have been studied to increase biomass production and lipid synthesis by microalgae [23]. MF application affected the composition and production of biomass, fundamental parameters in biofuel production [21].

According to Albuquerque et al. [45], MF are capable of regulating metabolic pathways of microorganisms, gene expression and chemical reactions. The authors also commented that the influence of MF on cell metabolism and on the growth of biomass depends on the interaction between the intracellular and extracellular environment, such as the type of cell, characteristics of the culture medium and the

MF can affect the growth and metabolism of microorganisms positively and negatively, depending on its intensity, frequency, pulse shape, type of modulation and exposure time [9]. MF have been shown to be efficient to increase biomass and lipids, since their action can cause oxidative stress in cells of microorganisms, change energy levels and orientation of free radicals and affect enzymatic activity

Changes promoted by the MF are responses of the interaction between them and microorganisms, i. e., alteration in permeability of membranes and, consequently, in their cellular metabolism [49]. MF application is considered a low cost and promising tool to overcome some limitations of microalgae, such as lipid productivity [50].

**Table 2** shows the effects of MF on biomass concentration and lipid content.

**422**

of cells [46–48].

*Influence of the MF on the synthesis of biomass and lipids in different species of microalga.*

Studies have shown that lipid content and productivity can be increased when there is an association between nitrogen reduction and MF application. Bauer et al. [16] identified that, when *Chlorella kessleri* was cultured in BG 11 medium and exposed to 60 mT for 1 h d−1, there was an increase in biomass concentration of 15% and 13.7% in lipid synthesis by comparison with the control. Chu et al. [28] evaluated the influence of MF application on *Nannochloropsis oculate* culture with modified Walne's medium. The highest lipid productivity (30.9 mg L−1 d−1) and lipid content (42.4%) were obtained when 20 mT was applied during 7 days of cultivation.

*Nannochloropsis oculate* was exposed to different intensities of MF (5, 10 and 15 mT) to evaluate the influence its biochemical composition and cell growth. Cultivation under influence of 10 mT increased biomass productivity (45%) and lipid productivity (57%) by comparison with the control [53]. Costa et al. [18] reported that the *Chlorella homosphaera* cultivated in the Bristol's Modified Medium (BMM) with 50% reduction in the nitrogen source associated with exposure to 30 mT and 60 mT for 1 h d−1, increased lipid productivity in 108.4% (35 mg L−1 d−1) and 135.1% (39.5 mg L−1 d−1), respectively.

#### **6. Conclusion**

This chapter reported the potential of microalgal cultivation with MF application for biofuel production. The use of microalgae as raw material is an attractive alternative that can reduce the use of fossil sources and CO2 emissions, and consequent pollution in the environment. Studies have suggested that MF application may be the most commercial production due to increased production of carbohydrates and lipids. For best results, in the case of every microalga species, parameters, such as MF intensity, exposure time, application period during cultivation and devices used to apply MF, should be evaluated. However, largescale production of biofuels derived from microalgae has yet to be achieved if it is to be cost-effective.
