Abstract
Third-generation biofuels that are derived from microalgal biomass have gained momentum as a way forward in the sustainable production of biodiesel. Such efforts are propelled by the intention to reduce our dependence on fossil fuels as the primary source of energy. Accordingly, growing microalgal biomass in the form of suspended cultivation has been a conventional technique for the past few decades. To overcome the inevitable harvesting shortcomings arising from the excessive energy and time needed to separate the planktonic microalgal cells from water medium, researchers have started to explore attached microalgal cultivation systems. This cultivation mode permits the ease of harvesting mature microalgal biomass, circumventing the need to employ complex harvesting techniques to single out the cells, and is economically attractive. However, the main bottleneck associated with attached microalgal growth is low biomass production due to the difficulties the microalgal cells have in forming attachment and populating thereafter. In this regard, the current review encompasses the novel techniques adopted to promote attached microalgal growth. The physicochemical effects such as the pH of the culture medium, hydrophobicity, as well as the substratum surface properties and abiotic factors that can determine the fate of exponential growth of attached microalgal cells, are critically reviewed. This review aims to unveil the benefits of an attached microalgal cultivation system as a promising harvesting technique to produce sustainable biodiesel for lasting applications.
Highlights
Among the third-generation biofuels, microalgae-based biodiesel production has been more promising than others since it only requires a short period of time and low energy for harvesting attached growth microalgae, whilst producing a high yield of biomass with a good quality of neutral lipids for high-value biodiesel production [11]
In Rosli et al.’s [96] studies, petroleum ether had been used to harvest the non-polar lipid from microalgae and the results showed the lipid content increased in pH 2 to 6, but reduction occurred when the pH increased from 7 to 9
There is one study by Lin-Lan et al [40] reporting that the microalgae were best grown on a smooth substrate surface such as glass, since it was easy to harvest using the mechanical scrapping method
Summary
The methods that are often used for microalgae harvesting such as centrifugation and flocculants require more energy to perform and lead to cell damage [12] and contamination of the harvested biomass [13] This is where attached microalgal cultivation becomes the solution for all the issues associated with suspended cultivation to produce third-generation biofuels. Among the third-generation biofuels, microalgae-based biodiesel production has been more promising than others since it only requires a short period of time and low energy for harvesting attached growth microalgae, whilst producing a high yield of biomass with a good quality of neutral lipids for high-value biodiesel production [11]
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