176
I. A. Sanusi et al.
3 Nanoparticles as Immobilization Matrix for Biofuel
Production
Common immobilization approaches (cells or enzymes) employ materials with sizes
above the nanometre (10
–9 ) range (Nikzad et al. 2015; Wiboon et al. 2012; Charlimagne et al. 2015; Martins et al. 2013; Zhaohui et al. 2016). Nevertheless, nanoparticles have been well established as an immobilization matrix and have desirable
biotechnological advantages. These advantages include large surface to volume ratio,
high loading of the specific molecules targeted, easy separation from the reaction
using an external magnetic field and strong adsorption ability (Han et al. 2011).
In addition, multivalent nanoparticles bearing multiple targeting groups can give
stronger anchoring for cells and enzymes (Willner et al. 2006; Han et al. 2011;
Ansari and Husain 2012). Nanoparticles can also play a vital role for the improvement of thermal and pH stability of microbial cells and enzymes (Pandurangan and
Kim 2015). For instance, magnetic nanoparticles are suitable for lipase immobilization, due to their ability to form nanocrystals. This phenomenon increases thermal
stability and reusability of the enzyme. Furthermore, the formation of nanocrystals
tends to clump together, increasing the biocatalyst surface area.
The incorporation of nano-immobilized enzymes/microbes is beneficial for
bioprocessing, since they enhance process costs, conversion efficiency and the overall
process performance (Sekoai et al. 2019). Limited studies exist on the application of
nanoparticles as an immobilization matrix in biofuel production (Table 5).
The study by Tran et al. (2012) immobilized lipase on magnetic nanoparticles
(Fe 3 O 4 ) coated with silica (Fe 3 O 4 –SiO 2 ) and demonstrated an increased tolerance to
high methanol to oil ratio (67:93) in an in-situ transesterification of Chlorella vulgaris
lipid. Furthermore, the immobilized lipase could withstand high water content of
71% with a biodiesel conversion value of 97.3 wt% oil (Tran et al. 2012). Likewise,
Ivanova et al. (2011) assessed the effect of immobilized S. cerevisiae on bioethanol
productivity. The immobilized cells substantially enhanced bioethanol productivity.
Moreover, the entrapped cells were employed successfully over 42 days without
a significant loss of bioethanol productivity. Similarly, the study by Cherian et al.
(2015) reported on cellulase immobilized on MnO 2 nanoparticles and found the
immobilized enzyme to be more thermostable at 70 °C. Also, the reusability (after
five cycles, retained 60% activity) of cellulase was significantly increased after immobilization. Studies showing the influence of various nanoparticles as immobilization
agents for biofuel production are summarized in Table 5.
4 Present Challenges and Future Perspectives on Biofuel
Production
Fermentative production of biofuel is achieved by the bioconversion fermentable
sugars contained in organic waste through pre-treatment and fermentation. However,
I. A. Sanusi et al.
3 Nanoparticles as Immobilization Matrix for Biofuel
Production
Common immobilization approaches (cells or enzymes) employ materials with sizes
above the nanometre (10
–9 ) range (Nikzad et al. 2015; Wiboon et al. 2012; Charlimagne et al. 2015; Martins et al. 2013; Zhaohui et al. 2016). Nevertheless, nanoparticles have been well established as an immobilization matrix and have desirable
biotechnological advantages. These advantages include large surface to volume ratio,
high loading of the specific molecules targeted, easy separation from the reaction
using an external magnetic field and strong adsorption ability (Han et al. 2011).
In addition, multivalent nanoparticles bearing multiple targeting groups can give
stronger anchoring for cells and enzymes (Willner et al. 2006; Han et al. 2011;
Ansari and Husain 2012). Nanoparticles can also play a vital role for the improvement of thermal and pH stability of microbial cells and enzymes (Pandurangan and
Kim 2015). For instance, magnetic nanoparticles are suitable for lipase immobilization, due to their ability to form nanocrystals. This phenomenon increases thermal
stability and reusability of the enzyme. Furthermore, the formation of nanocrystals
tends to clump together, increasing the biocatalyst surface area.
The incorporation of nano-immobilized enzymes/microbes is beneficial for
bioprocessing, since they enhance process costs, conversion efficiency and the overall
process performance (Sekoai et al. 2019). Limited studies exist on the application of
nanoparticles as an immobilization matrix in biofuel production (Table 5).
The study by Tran et al. (2012) immobilized lipase on magnetic nanoparticles
(Fe 3 O 4 ) coated with silica (Fe 3 O 4 –SiO 2 ) and demonstrated an increased tolerance to
high methanol to oil ratio (67:93) in an in-situ transesterification of Chlorella vulgaris
lipid. Furthermore, the immobilized lipase could withstand high water content of
71% with a biodiesel conversion value of 97.3 wt% oil (Tran et al. 2012). Likewise,
Ivanova et al. (2011) assessed the effect of immobilized S. cerevisiae on bioethanol
productivity. The immobilized cells substantially enhanced bioethanol productivity.
Moreover, the entrapped cells were employed successfully over 42 days without
a significant loss of bioethanol productivity. Similarly, the study by Cherian et al.
(2015) reported on cellulase immobilized on MnO 2 nanoparticles and found the
immobilized enzyme to be more thermostable at 70 °C. Also, the reusability (after
five cycles, retained 60% activity) of cellulase was significantly increased after immobilization. Studies showing the influence of various nanoparticles as immobilization
agents for biofuel production are summarized in Table 5.
4 Present Challenges and Future Perspectives on Biofuel
Production
Fermentative production of biofuel is achieved by the bioconversion fermentable
sugars contained in organic waste through pre-treatment and fermentation. However,