Recent Advancements in Microalgae-Biofuel Generation Employing Nano-Additives

Introduction

Photosynthetic microorganisms like green microalgae, diatoms, and cyanobacteria offer significant advantages over terrestrial plants providing an abundance of various biomolecules to be used for food, feed, and fuel applications. Microalgae or microphytes are microscopic algae. They are naturally found in freshwater bodies and oceans. Microalgae are unicellular species that can exist individually or in chains or groups. Microalgae can vary in size depending on the species, from a few micrometers (μm) to a few hundred micrometers. Microalgae are efficient photosynthesizers and are crucial for life on earth producing around half of the atmospheric oxygen it also performs its role as a photoautotroph consuming greenhouse gases like carbon dioxide to grow. Forming the base of the food web Microalgae and bacteria provide energy for all the trophic levels above them (Peter et al., 2021). There exists a rich biodiversity of microalgae which represents an abundant, almost untapped resource. There are about 200,000-800,000 species in different genera of microalgae of which about 50,000 species are characterized and described. More than 15,000 novel compounds originating from algal biomass have been identified including carotenoids, antioxidants, fatty acids, enzymes, polymers, peptides, toxins, and sterols.

Microalgae form an abundance of carbon-rich biomass, that can be tapped for the production of biofuels, cosmetics, health supplements, and pharmaceuticals. They also have numerous applications in wastewater treatment and sequestration of atmospheric CO2. A wide range of bioproducts, including polysaccharides, lipids, pigments, bioactive compounds, proteins, vitamins, and antioxidants are also derived from microalgae. There is a rapidly growing interest in the use of microalgae as a renewable and sustainable feedstock for biofuels production fueling new research in the field of biorefinery using microalgae. The cultivation of microalgae on an industrial scale to produce biofuels and bioproducts has increased radically in the last couple of decades (Low et al., 2021).

Figure 1.

Different biofuels from microalgae and conversion processes

(Hossain et al, 2009)

Microalgae As A Biofuel

The increasing global demand for fuel energy, the intensive use of fossil fuels worldwide leads to its depletion and economic crises and global tension around the control of fossil fuels heralds the need for alternative, environment-friendly and sustainable fuel sources. Thus, biofuels are increasingly viewed as an alternative to fossil fuels. Some developed countries have already started the mass production of biofuels. Biofuels such as biodiesel and bioethanol are superb alternative fuels and can be produced from a number of sources of biomass, including garbage, food crops, crop wastes or fruits, woody parts of plants, and algae (Harun, Danquah and Forde, 2010; Ho, Chen and Chang, 2010). The advantages of the use of biofuels from biomass are renewability and a significantly smaller contribution to environmental pollution and global warming. The release of CO2 from the burning of fossil fuels is one of the main causes of global warming. 29 gigatons/year of CO2 is released with a total of 35.3 billion tons of CO2 released to date from the burning of fossil fuel (Paul et al., 2014). Biofuels like algal fuels have oxygen levels of 10–45% and negligible levels of sulphur emission while petroleum-based fuels have no oxygen levels and considerable sulphur emission. Microalgae fuels are known for being environment-friendly, non-toxic, and capable of fixing global CO2. Gendy et al., 2013 reported that 1 kg of algal biomass is capable of fixing 1.83 kg of CO2 additionally certain species are known to utilize and remove SOx and NOx along with CO2.