Algae as green energy reserve: Technological outlook on biofuel production.

Depletion of fossil fuel sources and their emissions have triggered a vigorous research in finding alternative and renewable energy sources. In this regard, algae are being exploited as a third generation feedstock for the production of biofuels such as bioethanol, biodiesel, biogas, and biohydrogen. However, algal based biofuel does not reach successful peak due to the higher cost issues in cultivation, harvesting and extraction steps. Therefore, this review presents an extensive detail of deriving biofuels from algal biomass starting from various algae cultivation systems like raceway pond and photobioreactors and its bottlenecks. Evolution of biofuel feedstocks from edible oils to algae have been addressed in the initial section of the manuscript to provide insights on the different generation of biofuel. Different configuration of photobioreactor systems used to reduce contamination risk and improve biomass productivity were extensively discussed. Photobioreactor performance greatly relies on the conditions under which it is operated. Hence, the importance of such conditions alike temperature, light intensity, inoculum size, CO2, nutrient concentration, and mixing in bioreactor performance have been described. As the lipid is the main component in biodiesel production, several pretreatment methods such as physical, chemical and biological for disrupting cell membrane to extract lipid were comprehensively reviewed and presented. This review article had put forth the recent advancement in the pretreatment methods like hydrothermal processing of algal biomasses using acid or alkali. Eventually, challenges and future dimensions in algal cultivation and pretreatment process were discussed in detail for making an economically viable algal biofuel.

Progress on the development of floating photobioreactor for microalgae cultivation and its application potential.

Microalgae present great potential to replace land crops for the efficient production of large volumes of biomass for food, feed, fuels, and chemicals, as well as to treat wastewater and capture carbon. However, the commercialization of these technologies for bulk commodities requires a great reduction in the current microalgal biomass production cost. The bioreactor is the core of bioprocess engineering and is the premise for the commercial application of certain types of biotechnology. The challenges of phototrophic cultivation are completely different from those of heterotrophic processes because the efficiency of phototrophic cultivation is limited by the energy density of the input sunlight and the inorganic carbon supply. Thus, the development of microalgae cultivation technologies with low manufacturing and operating costs is key to addressing this problem, and floating photobioreactors (PBRs) are a promising solution. PBRs are deployed on the water surface without any land requirements, and wave energy provides free mixing energy. Additionally, the surrounding water can be used to control the culture temperature and to supply nutrients for microalgae growth. In this mini-review, the development of floating PBRs and their recent progress are presented. The effect of the carbon supply approach on the mixing and scaling-up of floating PBRs are critically discussed. The limitations and challenges in commercial applications of floating PBRs are analysed, and the need for future research is proposed. Finally, it is noted that microalgae farming on the ocean is a promising solution for human society to address the challenge of land space exhaustion due to the global population boom.

Industrial potential of carotenoid pigments from microalgae: Current trends and future prospects.

Microalgae are rich source of various bioactive molecules such as carotenoids, lipids, fatty acids, hydrocarbons, proteins, carbohydrates, amino acids, etc. and in recent Years carotenoids from algae gained commercial recognition in the global market for food and cosmeceutical applications. However, the production of carotenoids from algae is not yet fully cost effective to compete with synthetic ones. In this context the present review examines the technologies/methods in relation to mass production of algae, cell harvesting for extraction of carotenoids, optimizing extraction methods etc. Research studies from different microalgal species such as Spirulina platensis, Haematococcus pluvialis, Dunaliella salina, Chlorella sps., Nannochloropsis sps., Scenedesmus sps., Chlorococcum sps., Botryococcus braunii and Diatoms in relation to carotenoid content, chemical structure, extraction and processing of carotenoids are discussed. Further these carotenoid pigments, are useful in various health applications and their use in food, feed, nutraceutical, pharmaceutical and cosmeceutical industries was briefly touched upon. The commercial value of algal carotenoids has also been discussed in this review. Possible recommendations for future research studies are proposed.

Biology and Industrial Applications of Chlorella: Advances and Prospects.

Chlorella represents a group of eukaryotic green microalgae that has been receiving increasing scientific and commercial interest. It possesses high photosynthetic ability and is capable of growing robustly under mixotrophic and heterotrophic conditions as well. Chlorella has long been considered as a source of protein and is now industrially produced for human food and animal feed. Chlorella is also rich in oil, an ideal feedstock for biofuels. The exploration of biofuel production by Chlorella is underway. Chlorella has the ability to fix carbon dioxide efficiently and to remove nutrients of nitrogen and phosphorous, making it a good candidate for greenhouse gas biomitigation and wastewater bioremediation. In addition, Chlorella shows potential as an alternative expression host for recombinant protein production, though challenges remain to be addressed. Currently, omics analyses of certain Chlorella strains are being performed, which will help to unravel the biological implications of Chlorella and facilitate the future exploration of industrial applications.