The crisis of energy producing molecules (fuels) is expected to increase in future, which is currently produced from crude mineral oil. Biodiesel is most reliable, non-toxic, biocompatible liquid fuel that can replace the existing unsustainable sources of energy. Among all the known sources, microalgae display high potential for the production of biodiesel owing to their numerous benefits like higher biomass productivities than plants, no agricultural land requirement, cultivation in waste water and accumulation of 20-50% triacylglycerols. Microalgae biomass and lipid content plays an important role in commercial production of biodiesel. The present work was carried out to develop an axenic culture of a potential microalga Chlorella sp. for high biomass and enhanced lipid accumulation. The important growth parameters like pH, light colour, light intensity and photoperiod were studied for better production of Chlorella biomass. The effect of salinity on cell growth was also studied and compared with normal Fogg's medium grown cells. The main biomolecules like carbohydrate, protein, lipid and chlorophyll content were also estimated with the help of standard biochemical methods in salt supplemented and without salt Fogg's medium. The cellular lipid content was increased by growing the cells under different salt concentrations. The micro algal strain showed highest growth of 0.822 g L −1 and 1.021g L −1 in Fogg's medium and under 0.2 M NaCl supplemented medium respectively. However, the maximum lipid production of 0.1842 g L −1 was estimated by growing the cells in Fogg's medium including 0.5 M NaCl with slight compromise in cell growth (0.858 g L −1 ). The lipid content of Chlorella sp. was found to be 26.84% as compared to 14% obtained under normal culture condition. Thus, growing Chlorella sp. under salt supplemented medium and optimizing light requirement will produce high biomass and oil for biodiesel production.

The benefits of the complex microscopic and industrially important group of microalgae such as diatoms is not hidden and have lately surprised the scientific community with their industrial potential. The ability to survive in harsh conditions and the presence of different pore structures and defined cell walls have made diatoms ideal cell machinery to produce a variety of industrial products. The prospect of using a diatom cell for industrial application has increased significantly in synch with the advances in microscopy, metabarcoding, analytical and genetic tools. Furthermore, it is well noted that the approach of industry and academia to the use of genetic tools has changed significantly, resulting in a well-defined characterization of various molecular components of diatoms. It is possible to conduct the primary culturing, harvesting, and further downstream processing of diatom culture in a cost-effective manner. Diatoms hold all the qualities to become the alternative raw material for pharmaceutical, nanotechnology, and energy sources leading to a sustainable economy. In this review, an attempt has been made to gather important progress in the different industrial applications of diatoms such as biotechnology, biomedical, nanotechnology, and environmental technologies.

Marine water diatom Phaeodactylum tricornutum is a photosynthetic organism that is known to respond to the changing light environment and adapt to different temperatures to prevent photoinhibition and maintain its metabolic functions. The objective of the present study was to test whether light shift variations in different growth phases impact the growth and lipid metabolism of P. tricornutum. Thus, we investigated R exposure in different growth phases to find the most effective light shift condition. The results showed that substituting white light (W) by red light (R) under autotrophic conditions, a condition called red shift (RS), increased biomass and lipid content compared to levels found under continuous W or R exposure alone. We observed an increase by 2-fold biomass and 2.3-fold lipid content in RS as compared to W. No significant change was observed in the morphology of lipid droplets, but the fatty acid (FA) composition was altered. Specifically, polyunsaturated FAs were increased, whereas monounsaturated FAs decreased in P. tricornutum grown in RS compared to W control. Therefore, we propose that a light shift during the beginning of the stationary phase is a low-cost cultivation strategy to boost the total biomass and lipids in P. tricornutum.Appl. Sci. 2020, 10, 2531 2 of 18 for the high production of desired bioactive molecules. Therefore, light should be provided with specific spectral components, intensity, and duration. Multiple ecophysiological studies have been published reporting on the distinct behaviors of different diatoms and algae in response to variations in light [4,5]. It has been shown that light quality has an impact on chloroplast migration and on the light acclimation reactions of photosynthesis [6,7]. Red light has been linked to stimulating growth, ethylene production [8], lipid accumulation [7], and increasing thylakoid stacking [6]. have suggested the involvement of phytochromes in increasing the intracellular nitrate content on exposure to red light for short periods altering the overall cellular nitrate content. Recent discoveries in genomics have revealed exciting information on phytochromes, blue-light sensing cryptochromes, and aureochromes [10]. In a study by Jungandreas et al. [11], it has been reported that P. tricornutum cells acclimated to both red and blue light have comparable metabolite profiles, but drastic changes in metabolites and carbon partitioning was observed under red to blue light shift. In addition, various interdisciplinary studies have shown that light perceived by the red-light receptor (phytochromes) can regulate nutrient metabolism, cellular events, and signaling cascades [12]. These discoveries are still in progress and much remains unknown, but these studies can be explored for application-based diatom experiments such as developing low-cost cultivation technology or efficient bioreactors.In both culture medium and natural water bodies, light (intensity, distribution, photoperiod) may vary and will not behave similar to the dissolved salts or nu...

Municipal wastewater (WW), if not properly remediated, poses a threat to the environment and human health by carrying significant loads of nutrients and pathogens. These contaminants pollute rivers, lakes and natural reservoirs where they cause eutrophication and pathogenmediated diseases. However, the high nutrient content of WW makes it an ideal environment for remediation with microalgae that require high nutrient concentrations for growth and are not susceptible to toxins and pathogens. Given that an appropriate algal strain is used for remediation, the incurred biomass can be refined for the production of biofuel. Four microalgal species (Chlamydomonas reinhardtii, Chlorella sp., Parachlorella kessleri-I and Nannochloropsis gaditana) were screened for efficient phycoremediation of municipal WW and potential use for biodiesel production. Among the four strains tested, P. kessleri-I showed the highest growth rate and biomass production in 100% WW. It efficiently removed all major nutrients with a removal rate of up to 98% for phosphate after ten days of growth in 100% ACCEPTED MANUSCRIPT ACCEPTED MANUSCRIPT 2 municipal WW collected from Delhi. The growth of P. kessleri-I in WW resulted in a 50% increase of biomass and a 115% increase of lipid content in comparison to growth in control media. The FAME and fuel properties of lipids isolated from cells grown in WW complied with international standards. The present study provides evidence that the green alga P. kessleri-I effectively remediates municipal WW and can be used to produce biodiesel.

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