Microalgae dewatering is a major obstruction to industrial-scale processing of microalgae for biofuel prodn. The dil. nature of harvested microalgal cultures creates a huge operational cost during dewatering, thereby, rendering algae-based fuels less economically attractive. Currently there is no superior method of dewatering microalgae. A technique that may result in a greater algal biomass may have drawbacks such as a high capital cost or high energy consumption. The choice of which harvesting technique to apply will depend on the species of microalgae and the final product desired. Algal properties such as a large cell size and the capability of the microalgae to autoflocculate can simplify the dewatering process. This article reviews and addresses the various technologies currently used for dewatering microalgal cultures along with a comparative study of the performances of the different technologies.

Dewatering of microalgal cultures : a major bottleneck to algae-based fuels

The excessive demand for fossil fuels has caused severe environmental impacts, such as GHG-related effects and widespread pollution. Firstly, it is essential to identify the main problems arising from fossil fuel production and consumption, which will enable the search and implementation of technological, sustainable, and economical alternatives to mitigate the current issue. With the modern technological advances in this specific area, the use of biofuels has expanded, given their high potential of production from diverse classes of biomass. Producing biodiesel from microalgae oil specifically, as a way of obtaining clean and renewable energy, can play a significant role in this context, and the process is of high interest to the energy sector. Biodiesels are produced through mixtures of ethyl esters or fatty acid methyl esters, which are generated by the synthesis of oil with alcohol in the presence of the enzyme alcohol lipase. There are clear challenges linked to the new technologies employed to obtain biofuels from microalgae, and there also are strong prospects to these approaches, since they are very energy-efficient and environmentally friendly. Thus being, the present review describes the main aspects associated with biodiesel production from microalgae, highlighting the fundamentals of the technique, the immobilization processes followed, the use of solvents to optimize reaction media, bioreactor systems, as well as the performance optimization of microalgae biodiesel-based engines, while considering important economic and environmental aspects. Future trends in the biofuel scientific research and industry are also included, aiming at fostering discussions on the development of other significant advances in the use of microalgae lipase and oil technology for biodiesel production. 

Biodiesel production from microalgae using lipase-based catalysts: Current challenges and prospects

Microorganisms capable of accumulating lipids in high percentages, known as oleaginous microorganisms, have been widely studied as an alternative for producing oleochemicals and biofuels. Microbial lipid, so-called Single Cell Oil (SCO), production depends on several growth parameters, including the nature of the carbon substrate, which must be efficiently taken up and converted into storage lipid. On the other hand, substrates considered for large scale applications must be abundant and of low acquisition cost. Among others, lignocellulosic biomass is a promising renewable substrate containing high percentages of assimilable sugars (hexoses and pentoses). However, it is also highly recalcitrant, and therefore it requires specific pretreatments in order to release its assimilable components. The main drawback of lignocellulose pretreatment is the generation of several by-products that can inhibit the microbial metabolism. In this review, we discuss the main aspects related to the cultivation of oleaginous microorganisms using lignocellulosic biomass as substrate, hoping to contribute to the development of a sustainable process for SCO production in the near future.

https://www.mdpi.com/2076-3417/10/21/7698/pdf

Lignocellulosic Biomass as a Substrate for Oleaginous Microorganisms: A Review

Recent advances in functional foods and nutraceuticals have emphasized the beneficial impact of bioactive molecules on human health and longevity. The omega-3 (ω-3) long-chain polyunsaturated fatty acids (LC-PUFAs), namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), have been shown to exert numerous positive effects on cardiovascular events, inflammatory disease, some cancers, and neurological disorders. The primary sources of ω-3 LC-PUFAs for human consumption are cold-water fish and seafood; however, these are harvested currently beyond a sustainable capacity. Therefore, new sources of ω-3 LC-PUFAs such as oleaginous microalgae are regarded as promising alternatives to fish and seafood. In this context, the aim of the present review is to summarize the recent biotechnological progress made regarding the production, purification, and concentration of ω-3 LC-PUFAs from marine microalgae.

Microalgae as sources of omega-3 polyunsaturated fatty acids: Biotechnological aspects

Over the last three decades, consumption of total and saturated fat has steadily declined in Western diets as a proportion of calories intake. At the same time, omega (ω)-6 fatty acid intake has risen at the expense of ω-3 fatty acids, resulting in an ω-6/ω-3 ratio of 20:1 or higher. The observed changes in fatty acids ratio coincide with a significantly increased prevalence of coronary heart disease, hypertension, cancer, diabetes, obesity, rheumatoid arthritis, and autoimmune or neurodegenerative disorders. The low intake of ω-3 fatty acids may be attributed to their absence from the diet or lack of awareness about suitable dietary sources. A sustainable and cost-effective way of reaching a large population with essential ω-3 fatty acids is fortification of staple foods. A variety of food items enriched with ω-3 have entered the market in recent years, including beef, fish, dairy products, cereals, cereal bars, and infant formula. The present review discusses the role of ω-3 and ω-6 fatty acids, as well as their ratio, on human health. Additionally, it focuses on the latest developments regarding dietary sources, innovative technologies, and challenges of food fortification with ω-3 fatty acids. 

Futuristic food fortification with a balanced ratio of dietary ω-3/ω-6 omega fatty acids for the prevention of lifestyle diseases

Microorganisms are known to be natural oil producers in their cellular compartments. Microorganisms that accumulate more than 20% w/w of lipids on a cell dry weight basis are considered as oleaginous microorganisms. These are capable of synthesizing vast majority of fatty acids from short hydrocarbonated chain (C6) to long hydrocarbonated chain (C36), which may be saturated (SFA), monounsaturated (MUFA), or polyunsaturated fatty acids (PUFA), depending on the presence and number of double bonds in hydrocarbonated chains. Depending on the fatty acid profile, the oils obtained from oleaginous microorganisms are utilized as feedstock for either biodiesel production or as nutraceuticals. Mainly microalgae, bacteria, and yeasts are involved in the production of biodiesel, whereas thraustochytrids, fungi, and some of the microalgae are well known to be producers of very long-chain PUFA (omega-3 fatty acids). In this review article, the type of oleaginous microorganisms and their expertise in the field of biodiesel or omega-3 fatty acids, advances in metabolic engineering tools for enhanced lipid accumulation, upstream and downstream processing of lipids, including purification of biodiesel and concentration of omega-3 fatty acids are reviewed.

/pdf/an-overview-of-potential-oleaginous-microorganisms-and-their-55mm6lbq3m.pdf

Emma Rova

Papers

An Overview of Potential Oleaginous Microorganisms and Their Role in Biodiesel and Omega-3 Fatty Acid-Based Industries.