Tertiary amine as an efficient CO2 switchable solvent for extracting lipids from hypersaline microalgae

CO2-responsive switchable hydrophilic solvent as a novel extractant for selective extraction and separation of natural bioactive ingredients: A comprehensive review

When conventional solvents such as water, methanol, ethanol, hexane, petroleum ether, etc., are used to extract active ingredients from natural resources, an evaporation process is required to remove solvent from active ingredients, which not only consumes huge amounts of energy, but also causes harm to human health and the environment. The CO2-responsive switchable hydrophilic solvent (SHS) based on amines and water is an emerging, green and recyclable solvent, which not only has high extraction efficiency of active ingredients, but also can remove solvent from active ingredients without evaporation process. This paper reviews the research progress of amine-based SHS in the extraction of bioactive ingredients from natural resources. The process flow, extraction mechanism, critical influencing factors, recovery of amines and latest applications have been summarized. On this basis, some shortcomings of amine-based SHS are also pointed out. Finally, the improvement directions of amine-based SHS extraction in the future is prospected.

Cohesive phycoremediation of pyrene by freshwater microalgae Selenastrum sp. and biodiesel production and its assessment

In this study, the freshwater microalgae Selenastrum sp. was assessed for the effective degradation of pyrene and simultaneous production of biodiesel from pyrene-tolerant biomass. The growth of algae was determined based on the cell dry weight, cell density, chlorophyll content, and biomass productivity under different pyrene concentrations. Further, lipids from pyrene tolerant culture were converted into biodiesel by acid-catalyzed transesterification, which was characterized for the total fatty acid profile by gas chromatography. Increased pyrene concentration revealed less biomass yield and productivity after 20 days of treatment, indicating potent pyrene biodegradation by Selenastrum sp. Biomass yield was unaffected till the 20 mg/L pyrene. A 95% of pyrene bioremediation was observed at 20 days of culturing. Lipid accumulation of 22.14%, as evident from the estimation of the total lipid content, indicated a marginal increase in corroborating pyrene stress in the culture. Fatty acid methyl esters yield of 63.06% (% per 100 g lipids) was noticed from the pyrene tolerant culture. Moreover, fatty acid profile analysis of biodiesel produced under 10 mg/L and 20 mg/L pyrene condition showed escalated levels of desirable fatty acids in Selenastrum sp., compared to the control. Further, Selenastrum sp. and other freshwater microalgae are catalogued for sustainable development goals attainment by 2030, as per the UNSDG (United Nations Sustainable Development Goals) agenda. Critical applications for the Selenastrum sp. in bioremediation of pyrene, along with biodiesel production, are enumerated for sustainable and renewable energy production and resource management.

Bubble column photobioreactor (BCPR) for cultivating microalgae and microalgal consortium (Co-CC) with additional CO2 supply for enhancing biomass, lipid, and preferable fatty acids production

The present study has designed and developed a 5 L bubble column photobioreactor (BCPR) to investigate two microalgal strains Chlorella sp. S-01, Chlorella sp. S-02 and their consortium Co-CC (Chlorella sp. S-01 + Chlorella sp. S-02) at 0.03, 5, and 10% CO2 supply for biomass and lipid production. The dry cell weight of Chlorella sp. S-01, Chlorella sp. S-02 and Co-CC were, respectively about 1.41, 1.32, and 1.39 g/L on the 20th day without CO2 supply, while it was 1.76, 1.61, and 1.87 g/L, respectively at 10% CO2 supply and similarly, chlorophyll-a content was higher in 10% CO2 supplied condition over control. Interestingly, Co-CC grown at all the CO2 concentrations showed similar lipid content between 19.30 and 1F9.41%. As an integrated refinery approach, de-oiled biomass of Co-CC was subjected to carbohydrates and protein estimation and found that 46.2% and 30.80% in 10% CO2 supply condition in BCPR. Lipid extracted from the Co-CC grown under 0.03, 5, and 10% CO2 supply in 5L BCPR was converted to biodiesel, and the biodiesel yield was estimated to be 62.78%. Further, the fatty acid profile of Co-CC grown at 10% CO2 showed higher levels of C16:0, C16:1, C18:1, and monounsaturated fatty acids contents over other CO2 supplied conditions. Biodiesel of Co-CC showed favourable fuel properties such as density, higher heating value, oxidative stability, CFPP, viscosity, degree of unsaturation, saponification value, and cetane number, which were also in accordance with ASTM, and EN, biodiesel standards.

Extraction methods of algae oils for the production of third generation biofuels - A review

Microalgae are the main source of third-generation biofuels because they have a lipid content of 20-70%, can be abundantly produced and do not compete in the food market besides other benefits. Biofuel production from microalgae is a promising option to contribute for the resolution of the eminent crisis of fossil energy and environmental pollution specially in the transporting sector. The choice of lipid extraction method is of relevance and associated to the algae morphology (i.e., rigid cells). Therefore, it is essential to develop suitable extraction technologies for economically viable and environment-friendly lipid recovery processes with the aim of achieving a commercial production of biofuels from this biomass. This review presents an exhaustive analysis and discussion of different methods and processes of lipid extraction from microalgae for the subsequent conversion to biodiesel. Physical methods based on the use of supercritical fluids, ultrasound and microwaves were reviewed. Chemical methods using solvents with different polarities, aside from mechanical techniques such as mechanical pressure and enzymatic methods, were also analyzed. The advantages, drawbacks, challenges and future prospects of lipid extraction methods from microalgae have been summarized to provide a wide panorama of this relevant topic for the production of economic and sustainable energy worldwide.

Multifarious extraction methodologies for ameliorating lipid recovery from algae

Amongst the current alternatives, algae were proven to be a promising source of biofuel, which is renewable and capable of meeting world demand for transportation fuels. However, a suitable lipid extraction method that efficiently releases the lipids from different algal strains remains a bottleneck. The multifarious pretreatment methods are prevalent in this field of lipid extraction, and therefore, this article has critically reviewed the various lipid extraction methods for ameliorating the lipid yield from algae, irrespective of the strains/species. Physical, mechanical, and chemical are the different types of pretreatment methods. In this review, methodologies such as homogenization, sonication, Soxhlet extraction, microwave treatment, and bead-beating, have been studied in detail and are the most commonly used methods for lipid extraction. Specific advanced/emerging processes such as supercritical CO₂ extraction, ionic liquid, and CO₂ switchable solvent-based algal lipid extraction are yet to be demonstrated at pilot-scale, though promising. The extraction of lipids has to be financially conducive, environmentally sustainable, and industrially applicable for further conversion into biodiesel. Hence, this paper discusses variable pretreatment for lipid extraction and imparts a comparative analysis to elect an efficient, economically sound lipid extraction method for pilot-scale biodiesel production.

Metabolic transformation of cyanobacteria for biofuel production

World-wide, an emerging demand is moving towards the biofuels to replace the fossil fuels. In alternative biofuel production strategies, cyanobacteria have unique characteristic of accumulating glycogen, lipid, and fuel molecules through natural mechanisms. Moreover, the cyanobacteria can be easily engineered to synthesis a plenty of fuel molecules from CO₂. To obtain the fuel molecule from cyanobacteria, various techniques were invented in which the metabolic engineering is found to be a prerequisite to develop an economically feasible process. The expression of indigenous or heterologous pathways plays an important role in developing successful production process. In addition, the engineering of photosynthetic apparatus, destruction of competitive pathways and improvement of tolerance were also proven to improve the product specific synthesis. Although various metabolic engineering approaches have been developed, there are certain obstacles when it comes to implementation for the production. In this review, the important biosynthetic pathways for biofuels, alteration of other genes to improve the actual pathway and possibilities of developing cyanobacterial fuel production have been elaborated.

Design and fabrication of box-type passive solar dryer (BTPSD) with thermal insulation material for valorizing biomass and neutral lipids of marine Chlorella vulgaris for biodiesel application

The staggering rate of population growth has augmented the reliance on fossil fuel utilization, and it kindled the society to explore alternative and sustainable sources of energy. In this regard, biodiesel from microalgae came to the limelight; but crucial energy-consuming and expensive processes like cultivation, harvesting, and drying make the microalgal biodiesel unsustainable and economically unfeasible. To surpass these impediments, in this research work, a low-cost box-type passive solar dryer (BTPSD) is designed and fabricated with zero energy consumption mode and compared with conventional hot air oven for drying the biomass, neutral lipids of the marine microalga Chlorella vulgaris for biodiesel application. The onset of the work, BTPSD with 2 cm thickness of glass wool as TIM (thermal insulation material), 4 cm TIM thickness and no TIM was simulated for thermal storage behaviour using ANSYS FLUENT 19.2 Computational Fluid Dynamics tool and based on the results, 4 cm TIM thickness was chosen for experimentation. The time taken by BTPSD and hot air oven to remove the moisture from algal biomass is 3 and 2 h, respectively, whereas for neutral lipids drying, it was 4 and 3.5 h, respectively. Though there is a little difference in drying time, neutral lipid and FAME content from both drying systems are tantamount, i.e., ~ 12% neutral lipid and 95% FAME. Further, the percentage of vital fatty acids identified from BTPSD and hot air oven methods are almost similar, i.e., C16:0 (23.4%), C18:1 (14.3%), C18:3 (11.42%), C18:1 (9.22%). Though the time taken for valorizing biomass and neutral lipids of C. vulgaris by BTPSD is slightly longer than hot air oven, low energy consumption and cost-effectiveness make the BTPSD a promising system to scale down the microalgal biodiesel production cost significantly.