Progress and Challenges in Microalgal Biodiesel Production

Abstract

The last decade has witnessed a tremendous impetus on biofuel research due to the irreversible diminution of fossil fuel reserves for enormous demands of transportation vis-a-vis escalating emissions of green house gasses (GHGs) into the atmosphere. With an imperative need of CO2 reduction and considering the declining status of crude oil, governments in various countries have not only diverted substantial funds for biofuel projects but also have introduced incentives to vendors that produce biofuels. Currently, biodiesel production from microalgal biomass has drawn an immense importance with the potential to exclude high-quality agricultural land use and food safe-keeping issues. Moreover, microalgae can grow in seawater or wastewater and microalgal oil can exceed 50–60% (dry cell weight) as compared with some best agricultural oil crops of only 5–10% oil content. Globally, microalgae are the highest biomass producers and neutral lipid accumulators contending any other terrestrial oil crops. However, there remain many hurdles in each and every step, starting from strain selection and lipid accumulation/yield, algae mass cultivation followed by the downstream processes such as harvesting, drying, oil extraction, and biodiesel conversion (transesterification), and overall, the cost of production. Isolation and screening of oleaginous microalgae is one pivotal important upstream factor which should be addressed according to the need of freshwater or marine algae with a consideration that wild-type indigenous isolate can be the best suited for the laboratory to large scale exploitation. Nowadays, a large number of literature on microalgal biodiesel production are available, but none of those illustrate a detailed step-wise description with the pros and cons of the upstream and downstream processes of biodiesel production from microalgae. Specifically, harvesting and drying constitute more than 50% of the total production costs; however, there are quite a less number of detailed study reports available. In this review, a pragmatic and critical analysis was tried to put forward with the on-going researches on isolation and screening of oleaginous microalgae, microalgal large scale cultivation, biomass harvesting, drying, lipid extraction and finally biodiesel production.

Applications of microalga Chlorella vulgaris in aquaculture

“…Integrating microalgal production with biogas generation is another option employed to reduce the cost incurred in outsourcing the energy (Bagnoud-Vel asquez et al 2015). Other solutions are sourcing the CO 2 from thermal power stations or flue gas, integrating the microalgal cultivation with wastewater treatment (secondary and tertiary wastewater could provide for the microalgal nutrient requirements) and the use of cheaper sources of nutrient like urea (Mallick et al 2016). In order to mitigate the microbial contamination of wastewater, post-chlorinated water is used and an alternative is the use of detergents or phenols to lower the bacterial contamination (da & Reis 2015).…”

Screening of fungal strains with potentiality to hydrolyze microalgal biomass by Fourier Transform Infrared Spectroscopy (FTIR)

“…After lipid extraction, the lipid content obtained in the separation of biomass through electroflotation was 6.07% for D. subspicatus and 4.72% for Chlorella sp. Mallick, Bagchi, Koley, and Singh (2016), indicate that microalgae lipids can exceed 50-60% of dry cell weight. On the other hand, Silva and Bertucco (2016) describes levels in a range of 8-15%.…”

Overexpression of acetyl-CoA synthetase (ACS) enhances the biosynthesis of neutral lipids and starch in the green microalga Chlamydomonas reinhardtii

“…In the last decades there has been an in creas ing in ter est in ex ploit ing mi croal gae for the pro duc tion of bio fuel pre cur sors, such as tri a cyl glyc erol (TAG) and starch, which can be trans formed into biodiesel and bioethanol, re spec tively [1][2][3][4][5]. How ever, un til now the com mer cially vi able pro duc tion of these com pounds has been re stricted by the high cost of pro duc ing al gal bio mass at large scale and by the fact that these com pounds are usu ally ac cu mu lated un der stress con di tions, such as ni tro gen star va tion, which lim its al gal growth and there fore re duces their over all yield [6].…”