Sep-2024

Microalgae’s role in sustainable biofuel production (RI 2024)

Major fossil fuels such as coal, natural gas, and oil are depleting and emit high levels of CO₂ and nitrogen oxides when used for energy generation.

Diksha Singh and Sreevidya RV
Research & Development Centre, Engineers India Limited

Article Summary

The diminishing reserves of readily recoverable fuels, concern over global climate change, and increasing fuel prices demand the development and use of alternate fuels for energy independence and security of a country.

Recently, there has been an increased shift towards using biomass-based energy to reduce carbon footprints. Bioenergy includes a suite of biomass-based energy sources, including biofuels such as bioethanol, biodiesel, biogas, Bio-CNG, and Bio-ATF. Currently, biofuels like bioethanol and biodiesel are partially replacing gasoline and diesel, respectively, in the transportation sector.

Biorefineries are also gaining momentum for converting biomass into value-added products such as biofuels, biochemicals, and bioenergy/biopower. For biorefineries to operate on a continuous basis, large-scale biomass production and harvesting are required. Growing dedicated crops specifically for biofuel production may reduce the land available for food crop production. Hence, sustainable practices must be followed for large-scale biomass production and harvesting.

The various biomass feedstocks for bioenergy production are starch/sugar-based feedstocks such as corn, sweet potato, and cassava; oil seed-based feedstocks such as soybean, rapeseed, and coconut (first generation, 1G); ligno cellulose-based feedstocks such as rice and wheat straw (second generation, 2G); and algae-based feedstock such as micro and macroalgae.

The major drawback of 1G fuel sources is that the production of raw materials competes with the food and fodder supply for land and requires a huge amount of water. 2G fuel technologies are cost intensive. This can be resolved by 3G fuels, specifically biofuel produced from microalgae.

Microalgae are photosynthetic organisms that convert sunlight, water, and carbon dioxide from macromolecules such as lipids [triacylglycerols (TAGs)] into sugars. These lipids TAGs are promising and stable for biofuel feedstock.

Microalgae are mainly composed of carbohydrates (11-56%), lipids, proteins (30-80%), pigments, and vitamins. The content of lipids in microalgae is usually 30-70% of the cell dry weight and can be as high as 90% under stressful environmental conditions. Through various biochemicals, thermochemical, nano-catalytic transformations, and genetic engineering, microalgae can be used to produce biofuels, including biodiesel, bio-syngas, bio-oil, bioethanol, and bio-hydrogen. They also produce value-added byproducts like phycocyanin, β-carotene, antioxidant, and vitamins. The lipid component from microalgae can be transesterified into biodiesel, and the left-over biomass, mainly composed of carbohydrate, can be fermented into bioethanol.

The unique advantages of microalgae as a renewable and sustainable energy source include their high photosynthetic efficiency and ability to grow in non-arable land, saline water, and wastewater. When compared to crop feedstocks like palm, corn, soybean, sunflower, rapeseed, canola, and jatropha, which produce 68.13 L/acre to 2,404 L/acre oil, microalgae has a 19,000 L/acre to 57,000 L/acre oil yield.

Preliminary literature and laboratory studies have been carried out to identify robust microalgae species for biofuel production. The study identified spirulina platensis for further focusing on its characterisation and analysing its lipid content and fatty acid profiling.

The spirulina platensis used in this study was procured from one of the national repositories for microorganisms. The selected strains were cultivated in a Zarrouk nutrient medium suitable for their growth. Microalgal strains were cultivated in different capacities of Erlenmeyer flasks in a orbital shaking incubator and fermentor.

The growth parameters pH and temperature were kept constant based on the requirement of the strain. The cultivated strains were then harvested by filtration/centrifugation and dried. The cultivation of desired samples were then confirmed microscopically.

Proximate analysis was carried out as per the ASTM standards (ASTM E-1755-E1757). Total solids were obtained in the range of 6.7- 12%, ash content was 12.98-45%, and moisture was achieved in the range of 70-90%. The calorific value obtained for the microalgae biomass was 2039.65 Cal/g.

To analyse the fatty acid profile, the lipids were extracted from the biomass and GC-MS analysis was performed. In our study, a lipid content of 48.4% has been obtained. The composition of the fatty acids includes palmitic acid, erucic acid, stearic acid, oleic acid, and linoleic acid. The lipid accumulation in microalgae demonstrates the potential of spirulina platensis as an effective feedstock for biofuel production.

The high value-added products obtained as byproducts during the cultivation of these microalgae can make biofuel production feasible. Microalgae are also involved in carbon sequestration. These biological advantages make microalgae a potential contributor to helping India achieve its net-zero target.

This short article originally appeared in the 2024 Refining India Newspaper, which you can VIEW HERE