Use of solvent mixtures for total lipid extraction of Chlorella vulgaris and gas chromatography FAME analysis

Sequential two-stage cultivation system using novel microalga consortia for treatment of municipal wastewater and simultaneous biomass production: Sustainable environmental management

Monoculture-based microalgae cultivation systems to treat wastewater are well-reported. Despite that, this method has some limitations in terms of nutrient removal potential, environment adaptation, and low biomass productivity. Conversely, microalgae co-cultivation and a two-stage sequential cultivation system (TSSCS) recently emerged as a promising approach to improve the treatment process and biomass productivity through better adaptation to the environment. However, no outdoor large-scale experiments were reported using this approach which hinders the viability of the process. Thus, in the present study, a sequential two-stage large-scale outdoor novel microalgae consortia experiment was developed. In first stage consortia-assisted sequential cultivation, two ratios of Tetraselmis indica (TS) and one ratio of Picochlorum sp. (PC) (2 TS:1 PC) were cultivated in a 1000-L pond containing 75%-municipal wastewater (MWW) + 25%-ASN-III, while in the second stage, 2 PC:1 TS was cultivated in two different ponds, and each containing 375-L 2 TS:1 PC-treated water + 375-L ASN-III. Outdoor parameters and nutrient removal efficiency (NRE), biomass, and biomolecule productivity such as lipid, photosynthetic pigments, astaxanthin, and β-carotene were quantified, and cost analysis was performed. At the end of the first and second stages, 2 TS:1 PC and 2 PC:1 TS showed maximum NRE of COD (68.71 and 86.40%), TN (66.98 and 94.73%), and TP (82.70 and 94.36%), respectively. Moreover, 2 TS:1 PC and 2 PC:1 TS Pond 1 and 2 produced maximum dry biomass production; 2.41 and ∼2.54 g/L contained lipid content; 36.89 and 34.90% that have 86.50 and 55.79% FAME content respectively. Similarly, 2 TS:1 PC and 2 PC:1 TS biomass exhibited valuable pigments production of astaxanthin i.e., 0.56 and 0.35 mg/g, and β-carotene; 4.65 and 2.82 mg/g, respectively. The cost analysis suggested that only microalgal-based MWW treatment was unfeasible, while valorization of produced biomass into co-products could offset the operation costs and could allow the option for the microalgal-based sustainable approach for the treatment of MWW and recovery of valuable resources.

A Comprehensive Study of Techniques to Optimize the Extraction of Lipids from the Autotrophic Strain of the Microalgae Chlorella vulgaris

Microalgae represent a promising source of triglycerides and free fatty acids, synthesized in the form of lipids, for use in renewable fuels and chemicals. One challenge is the ability to efficiently recover the lipids from within the microalgae cell. Although various techniques have been studied individually, a comprehensive study of extraction techniques using consistent experimental and analytical methodology is missing. This study aims to provide this unifying comparison using the common microalgae strain Chlorella vulgaris. The factors that were surveyed and then optimized to achieve maximum extraction efficiency included the solvent type; mechanical pre-treatment using a ball mill at a variety of grinding speeds; microalgae-to-solvent ratio; extraction facilitated by microwave; extraction facilitated by sonication; extraction facilitated using increased temperature; and extraction facilitated by in situ transesterification to convert the lipids into esters prior to extraction. The optimum conditions determined during these studies were utilizing methanol as the solvent, with ball mill pretreatment at a grinding speed of 500 rpm, and a 1:9 microalgae to solvent ratio. When used in combination with microwave-assisted extraction at a temperature of 140 °C, approximately 24 wt% of the initial lipids were recovered. Recoveries of over 70 wt% were obtained without a microwave at extraction temperatures of over 200 °C.

Cell disruption and lipid extraction from Chlorella species for biorefinery applications: Recent advances

Chlorella is a promising microalga for CO₂-neutral biorefinery that co-produces drop-in biofuels and multiple biochemicals. Cell disruption and selective lipid extraction steps are major technical bottlenecks in biorefinement because of the inherent robustness and complexity of algal cell walls. This review focuses on the state-of-the-art achievements in cell disruption and lipid extraction methods for Chlorella species within the last five years. Various chemical, physical, and biological approaches have been detailed theoretically, compared, and discussed in terms of the degree of cell wall disruption, lipid extractability, chemical toxicity, cost-effectiveness, energy use, scalability, customer preferences, environment friendliness, and synergistic combinations of different methods. Future challenges and prospects of environmental-friendly and efficient extraction technologies are also outlined for practical applications in sustainable Chlorella biorefineries. Given the diverse industrial applications of Chlorella, this review may provide useful information for downstream processing of the advanced biorefineries of other algae genera.

Integrated analytical approaches for the characterization of Spirulina and Chlorella microalgae

Microalgae are well-known for their content of bioactive molecules such as pigments, proteins, fatty acids, polysaccharides, vitamins and antioxidants, all of which are of great interest in the preparation of a wide range of products such as food, cosmetics and nutraceuticals. The purpose of this project was the analytical characterization of commercial dry microalgal biomass: four samples of Chlorella and five of Spirulina were analysed in order to highlight their content in terms of micro/macro nutrients. The research was oriented towards the development and validation of accurate, fast and reproducible methods for the nutritional assessment of algal biomasses, aiming to provide a guiding methodology. The lipid profiles of algal matrixes were analysed for the content of saturated, unsaturated and polyunsaturated fatty acids. The process was divided into two phases: firstly, the extraction and determination of the total lipids and pigment content; secondly, the trans-esterification of the extracted lipid-pigment portion in order to analyse fatty acid methyl esters (FAMEs) with a GC-MS method. A fingerprinting of MUFAs and PUFAs was obtained regarding microalgae species. The determination of total carotenoids and chlorophylls content in the lipid extracts was evaluated through a fast UV-Vis spectrophotometric analysis, which was validated by a new HPLC-DAD analysis. Furthermore, the total antioxidant activity of each lipid extract was determined along with the determination of the microalgae protein content. Then, with the aid of the principal component analysis (PCA) plots, the two microalgae were clustered in terms of their micro/macro nutrients, for differentiating their properties. Spirulina, resulting to have a greater antioxidant activity, supposedly due to a higher content in pigments and higher protein concentration, could be suggested for an appropriate diet for sporting people. Chlorella, instead, showed a more balanced profile of PUFAs and MUFAs and its use could be suggested for cosmetics and vegan diets. This paper puts forward an overall analytical approach, sustained by a multivariate analysis, for emphasising content differences and activity of two different microalgae strains, in order to underline specific claims for each class, addressed to defined final users.

Advanced Extraction of Lipids with DHA from Isochrysis galbana with Enzymatic Pre-Treatment Combined with Pressurized Liquids and Ultrasound Assisted Extractions

Microalgal biomass is a sustainable and valuable source of lipids with omega-3 fatty acids. The efficient extraction of lipids from microalgae requires fast and alternative extraction methods, frequently combined with biomass pre-treatment by different procedures. In this work, Pressurized liquid extraction (PLE) was optimized and compared with traditional lipid extraction methods, Folch and Bligh and Dyer, and with a new Ultrasound Assisted Extraction (UAE) method for lipids from microalgae Isochrysis galbana. To further optimize PLE and UAE, enzymatic pre-treatment of microalga Isochrysis galbana was studied with commercial enzymes Viscozyme and Celluclast. No significant differences were found for lipid yields among different extraction techniques used. However, advanced extraction techniques with or without pre-treatment are a green, fast, and toxic solvent free alternative to traditional techniques. Lipid composition of Isochrysis was determined by HPLC-ELSD and included neutral and polar lipids, showing that each fraction comprised different contents in omega-3 polyunsaturated fatty acids (PUFA). The highest polar lipids content was achieved with UAE (50 °C and 15 min) and PLE (100 °C) techniques. Moreover, the highest omega-3 PUFA (33.2%), eicosapentaenoic acid (EPA) (3.3%) and docosahexaenoic acid (DHA) (12.0%) contents were achieved with the advanced technique UAE, showing the optimized method as a practical alternative to produce valuable lipids for food and nutraceutical applications.

Emerging techniques for cell disruption and extraction of valuable bio-molecules of microalgae Nannochloropsis sp

Microalgae of Nannochloropsis sp. present valuable source of bio-molecules (pigments, lipids, proteins) that have nutritional potential for the prevention and treatment of human diseases. Moreover, some species of Nannochloropsis are the promising sources of biofuels and excellent candidates for the replacement of classical biofuel crops. This review describes and compares the efficiency of different conventional and novel techniques that can be used for cell disruption and recovery of bio-molecules from Nannochloropsis sp. Classification of different extraction techniques includes chemical, enzymatic, mechanical and other physical methods. The detailed analysis of extraction efficiency assisted by pressure and temperature (subcritical and supercritical fluids, hydrothermal liquefaction), ultrasound, microwaves, and pulsed electric energy (pulsed electric fields and high voltage electrical discharges) is presented. The general discussion includes comparison between techniques, their effectiveness for cell disruption and selectivity of bio-molecules extraction from Nannochloropsis sp. The cost-effectiveness, benefits and limitations of different techniques are also analyzed.

Simultaneous cell disruption and lipid extraction of wet aurantiochytrium sp. KRS101 using a high shear mixer

Microalgae are regarded as a promising source of biofuels, and the concept of a microalgae-based biorefinery has attracted increasing attention in recent years. From an economic perspective, however, the process remains far from competitive with fossil fuels. This is particularly true of lipid extraction, due in part to the energy-intensive drying step. As a result, wet extraction methods have been studied as an economic alternative. In the present study, a novel extraction approach which utilizes high shear stress mixing was adopted and demonstrated for simultaneous lipid extraction and cell disruption to enable the retrieval of lipids directly from concentrated wet biomass. When a high shear mixer (HSM) was used to extract lipid from a dense biomass (> 350 g/L) of the oleaginous algae Aurantiochytrium sp., it exhibited a yield of esterifiable lipids which exceeded 80% in 10 min at 15,000 rpm with various solvent types. The HSM was found to improve the lipid yields substantially with solvents less miscible with either lipids or water, such that the range of Hansen solubility parameters for the usable solvents became 3.3 times wider (14.9-26.5 MPa^1/2). The HSM, which appeared effectively to loosen the water barrier that prevents solvent molecules from penetrating through the cell envelope, was found to be more efficient with hexane, hexane/isopropanol, and ethanol, all of which showed nearly identical lipid yields compared to the dry extraction process. The HSM can, indeed, offer a powerful mechanical means of lipid extraction with non-polar and less toxic solvents from wet biomass.