Lipid Content Of Microalgae Research Articles

Lipid monitoring of Chlorella vulgaris using non-invasive near-infrared spectral imaging

AbstractMicroalgal lipids are molecules of biotechnological interest for their application in sustainable food and energy production. However, lipid production is challenged by the time-consuming and laborious monitoring of lipid content in microalgae. This study aimed to predict the lipid content of Chlorella vulgaris cultivations based on non-invasively collected near-infrared (NIR) range hyperspectral data. A gravimetric analysis of total lipids was used as reference data (between 2 and 22% per dry weight) to compare three different models to determining the lipid content. A one-dimensional convolutional neural network and partial least squares models performed at a similar level. Both models could predict the lipid content of Chlorella dry weight with an error of 4%pt (root mean squared error). The index-based linear regression model performed the weakest of the three models, with the error of the prediction being 6%pt. Nile Red staining was used to visualise lipids on a microscope and lipid class analysis to resolve the lipid classes that explained most of the increase in lipids in Chlorella. A SHAP algorithm (SHapley Additive exPlanations) was used to analyse the wavebands of NIR spectra that were important for predicting the total lipid content. The results show that spectral data, when combined with an adequate algorithm, could be used to monitor microalgae lipids non-invasively in a closed system, in a way that has not previously been demonstrated with an imaging system.

Improving microalgal growth and nitrogen, and phosphorus removal by electric field in municipal wastewater

The promoting effect of electric fields on the growth and lipid production of microalga provides a new research direction for biorefining. However, researchers have rarely applied this technology to the treatment of actual wastewater. In this study, the dry weight and lipid content of microalgae increased by 47.45 % and 28.28 %, respectively, when optimized for light, growth phase and energization time. By optimizing the initial microalgal concentration and the ratio of nitrogen and phosphorus, the removal of total nitrogen (TN) and ammonia nitrogen (NH4+) increased by 18.5 % and 10.9 %, respectively. Compared to peroxidase (POD), significant changes in the relative activities of catalase (CAT) and total superoxide dismutase (T-SOD) were observed after the application of an electric field to the microalgae. Along with the cultivation, the relative activities of T-SOD and CAT showed a tendency of an increase and then a decrease compared with the control. This was mainly due to the increased internal secretion of T-SOD and CAT by the microalgae in response to the oxidative stress of the electric field on the microalgae, while the lack of nutrients at the later stages of cultivation also led to the increase of the content of the two enzymes in the control.

Theoretical Models Constructed by Artificial Intelligence Algorithms for Enhanced Lipid Production: Decision Support Tools

Theoretical models that predict the lipid content of microalgae are an important tool for increasing lipid productivity. In this study, response surface methodology (RSM), RSM combined with artificial neural network (ANN), and RSM combined with ensemble learning algorithms (ELA) for regression were used to calculate the maximum lipid percentage (%) from Chlorella minutissima (C. minutissima). We defined one set of rules to achieve the highest lipid content and used trees.RandomTree (tRT) to simulate the process parameters under various conditions. Among the various models, results showed the optimum values of the root mean squared error (0.2156), mean absolute error (0.1167), and correlation coefficient (0.9961) in the tRT model. RSM combined with tRT estimated that the lipid percentage was 30.3% in wastewater (< 35%), lysozyme (≥ 3.5 U/mL), and chitinase (< 15 U/mL) concentrations, achieving the best model based on experimental data. The optimal values of wastewater concentration, chitinase, and lysozyme were 20% (v/v), 5 U/mL, and 10 U/mL, respectively. Also, the if-then rules obtained from tRT were also used to test the process parameters. The tRT model served as a powerful tool to obtain maximum lipid content. The final rankings of the performance of various algorithms were determined. Furthermore, the models developed can be used by the fuel industry to achieve cost-effective, large-scale production of lipid content and biodiesel.

Microalgae Lipids Detection and Quantification Method Towards Online Real-Time Monitoring: A Review

Bioprospecting toward biofuel has appeared as a sustainable and alternative energy option as fossil fuels are finite and causing a large number of environmental problems such as global warming by the greenhouse effect, leading the development of alternative substantial energy has attracted more and more attention. Hence, microalgae are potential candidates as third generation biofuel producers to tackle this problem. Under stress-condition, microalgae can produce an abundance of value-added products such as triacylglycerols which is an energy-rich fatty acid. This review highlights various quantification and detection methods of microalgae lipids, ranging from conventional methods like gravimetric and chromatographic techniques to non-conventional methods like fluorescent staining, Raman scattering, and dielectric insulation. While conventional methods require a series of procedures, including biomass dehydration and lipid extraction, non-conventional methods provide advantages such as rapidity, low cost, and smaller sample sizes needed. Future prospects revealed that real-time monitoring and online measurement of lipid content in microalgae is required to quantify the intracellular lipid level of microalgae in controlling and rapidly adjusting the growing conditions for cultivation. These real-time results, combined with the Internet of Things (IoT) technology, can be further processed using machine learning to maximize the productivity of microalgae as an alternative biofuel producer.

Biostimulation of green microalgae Chlorella sorokiniana using nanoparticles of MgO, Ca10(PO4)6(OH)2, and ZnO for increasing biodiesel production

Microalgae have the potential to become the primary source of biodiesel, catering to a wide range of essential applications such as transportation. This would allow for a significant reduction in dependence on conventional petroleum diesel. This study investigates the effect of biostimulation techniques utilizing nanoparticles of Magnesium oxide MgO, Calcium hydroxyapatite Ca10(PO4)6(OH)2, and Zinc oxide ZnO to enhance the biodiesel production of Chlorella sorokiniana. By enhancing cell activity, these nanoparticles have demonstrated the ability to improve oil production and subsequently increase biodiesel production. Experimentally, each nanomaterial was introduced at a concentration of 15 mg L−1. The results have shown that MgO nanoparticles yielded the highest biodiesel production, with a recorded yield of 61.5 mg L−1. Hydroxyapatite nanoparticles, on the other hand, facilitated lipid accumulation. ZnO nanoparticles showcased a multifaceted advantage by enhancing both growth and lipid content. Thus, it is suggested that these nanoparticles can be used effectively to increase the lipid content of microalgae. These findings highlight the potential of biostimulation strategies utilizing MgO, hydroxyapatite, and zinc oxide nanoparticles to bolster biodiesel production.

Efficient coupling of sulfadiazine removal with microalgae lipid production in a membrane photobioreactor

This study explored the feasibility of a coupled system for antibiotic removal and biofuel production through microalgae cultivation. Initial, batch culture experiments demonstrated that sulfadiazine (SDZ) had an inhibitory effect on Chlorella sp. G-9, and 100.0 mg L-1 SDZ completely inhibited its growth. In order to improve SDZ removal efficiency by microalgae, three membrane photobioreactors (MPBRs) with different hydraulic retention times (HRTs) were established for continuous microalgae cultivation. The efficient coupling of SDZ removal and microalgal lipid production was achieved through the gradual increment of influent SDZ concentration from 0 to 100.0 mg L-1. The reduction in SDZ ranged between 57.8 and 89.7%, 54.7–91.7%, and 54.6–93.5% for the MPBRs with HRT of 4 d, 2 d, and 1 d, respectively. Chlorella sp. Was found to tolerate higher concentrations of SDZ in the MPBR system, and the resulting stress from high concentrations of SDZ effectively increased the lipid content of microalgae for potential biodiesel production. With the increase of influent SDZ concentration from 0 to 100.0 mg L-1, the lipid content of microalgae increased by 43.5%. Chlorophyll content, superoxide dismutase activity, and malondialdehyde content of microalgae were also evaluated to explore the mechanism of microalgae tolerance to SDZ stress in MPBR.

In-situ transesterification of microalgae using carbon-based catalyst under pulsed microwave irradiation

In the production of biofuels, microalgae represent an emerging class of renewable feedstock that can address the problems associated with the use of the traditional land-based lignocellulosic biomass. The high lipid content of microalgae makes them ideal in producing fatty acid methyl esters (FAME), the main components of biodiesel. In this study, the transesterification of the lipids in Chlorella vulgaris with methanol was performed in-situ using graphene oxide (GO) under microwave irradiation. From FTIR measurements and titration experiments, GO was shown to possess oxygen functional groups that can serve as catalysts in transesterification. Moreover, the catalytic performance of GO in terms of FAME yield was found to be better than conventional metal-based catalysts. Microwave irradiation, on the other hand, was found to offer a more efficient heating than conventional methods by taking advantage of the excellent microwave absorptivity of methanol and the local heating induced on the surface of GO. Furthermore, irradiation of microwave in pulses rather than in a continuous mode was shown to be more cost-effective. It is proposed that the high energy introduced into the biomass at short time intervals facilitated the release of more lipids by more effectively disrupting the algal cell wall. Lastly, operating with a methanol reflux allowed the microwave-irradiated system to be operated at the boiling point of methanol (Tb = 64.7 °C) while providing a higher FAME yield than an operation at 160 °C without reflux. This study presents graphene oxide under microwave irradiation as a green, carbon-based, and sustainable catalyst in the production of biodiesel from microalgae.

Influence of exogenous phytohormone supplementation on the pigment and fatty acid content of three marine diatoms.

Diatoms are ubiquitous photosynthetic microorganisms with great potential for biotechnological applications. However, their commercialisation is hampered by production costs, requiring hence optimisation of cultivation methods. Phytohormones are plant growth regulators which may be used to influence physiological processes in microalgae, including diatoms. In this study, the model species Phaeodactylum tricornutum (Phaeodactylaceae) and two Irish isolates of Stauroneis sp. (Stauroneidaceae) and Nitzschia sp. (Bacillariaceae) were grown with varying amounts of the phytohormones indoleacetic acid (IAA), gibberellic acid (GA3), methyl jasmonate (MJ), abscisic acid (ABA) or salicylic acid (SA), and their influence on pigment and fatty acid profiles was monitored. The application of GA3 (200mg/l) stimulated the growth of P. tricornutum which accumulated 52% more dry biomass compared to the control and concomitantly returned the highest eicosapentaenoic acid (EPA) yield (0.6mg/l). The highest fucoxanthin yield (0.18mg/l) was obtained for P. tricornutum cultivated with GA3 (2mg/l) supplementation. In Stauroneis sp., SA (1mg/l) had the most positive effect on EPA, the content of which was enhanced up to 45.7μg/mg (4.6% of total dry weight). The SA (1mg/l) treatment also boosted carotenogenesis in Nitzschia sp., leading to 1.7- and 14-fold increases in fucoxanthin and β-carotene compared to the control, respectively. Of note, MJ (0.5mg/l) increased the EPA content of all diatom species compared to their controls. These results indicate that phytohormone-based treatments can be used to alter the pigment and lipid content of microalgae, which tend to respond in dose- and species-specific manners to individual compounds.Key points• Response to phytohormones was investigated in diatoms from distinct families.• MJ (0.5mg/l) caused an increase in EPA cellular content in all three diatoms.• Phytohormones mostly caused dose-dependent and species-specific responses.

An increase in the membrane lipids recycling by PDAT overexpression stimulates the accumulation of triacylglycerol in Nannochloropsis gaditana

Oleaginous microalgae represent potential feedstocks for the sustainable production of lipids thanks to their ability to accumulate triacylglycerols (TAGs). TAG accumulation in several algal species is strongly induced under specific conditions such as nutrient deprivation and high light which, however, also negatively impact growth. Genetic modification of lipogenic pathways can potentially enhance TAG accumulation without negatively affecting growth, avoiding the trade-off between biomass and lipid productivity.In this study, the phospholipid: diacylglycerol acyltransferase (PDAT), an enzyme involved in membrane lipid recycling, was overexpressed in the seawater alga Nannochloropsis gaditana. PDAT overexpression induced increased TAG content in actively growing algae cultures while no effects were observed in conditions naturally stimulating strong lipid accumulation such as high light and nitrogen starvation. The increase of TAG content was confirmed also in a strain cultivated in industrially relevant conditions even though PDAT overexpression, if too strong, the gene overexpression becomes detrimental for growth in the longer term. Results overall suggest that genetic modulation of the PDAT gene represents a promising strategy to increase microalgae lipid content by minimizing negative effects on biomass productivity.

High-efficiency biofuel production by mixing seawater and domestic sewage to culture freshwater microalgae

Although microalgae biofuel has many advantages, its production is faced with difficulties regarding algal cell harvesting and low lipid content. In this experiment, mixtures of seawater and domestic sewage were prepared for the cultivation of freshwater microalgae. The results showed that the proportion of seawater had an important effect on the precipitation and biofuel production of the microalgae. The increasing proportion of seawater in the mixed wastewater improved the sedimentation performance and lipid content of microalgae, but the growth of microalgae was greatly inhibited under 80% seawater stress. Therefore, the highest algal lipid productivity of 10.74 mg L-1 d-1 was achieved in the wastewater containing 60% seawater, which was 2.15-fold higher than that of the control. Furthermore, the fatty acid saturation and the C16-C18 fatty acid proportion of the microalgae cultured in wastewater containing 60% seawater were relatively ideal, which was beneficial for improving the quality of biodiesel. Therefore, wastewater containing 60% seawater was the most favourable for the cultivation of biofuel-producing microalgae. The mechanism by which seawater improved the precipitation performance of freshwater microalgae was also investigated. The addition of seawater to the sewage increased the cell diameter of the microalgae, reduced the zeta potential of microalgal colloids, and promoted the synthesis of extracellular polymeric substances by the microalgal cells. Thus, the precipitation performance of the microalgae cells was effectively improved. The pigment contents and antioxidant enzyme activities of the microalgae were also determined, and it was found that the glutathione peroxidase activity of microalgae increased under certain seawater stress, indicating that glutathione peroxidase played an indispensable role in the removal of reactive oxygen species produced by seawater stress.

Ca2+ participates in the regulation of microalgae triacylglycerol metabolism under heat stress

Microalgae are the largest CO2 fixer and O2 producer on the earth and occupy an increasingly important position in human life and production. Various environmental factors have a significant impact on the growth and metabolism of microalgae. As global warming intensifies, heat stress has become a crucial factor affecting the microalgae industry. However, till now, it has not been clear how microalgae sensed the temperature stress, transmitted stress signals and adjusted in intracellular metabolic pathways. In this study, the growth of microalgae Auxenochlorella protothecoides UTEX2341 was inhibited at 32 °C, but the single cell dry weight increased. The cell component analyses showed that both the carbohydrate and total protein content decreased significantly, while the lipid content increased by 158%. Meanwhile, the intracellular Ca2+ concentration increased continuously, with a maximum increase of 1.65 times. According to the transcriptome analyses, the up-regulation of Ca2+ influx channel protein mid1-complementing activity 1 (MCA1) gene and the down-regulation of efflux channel protein cation exchanger 1(CAX) and autoinhibited Ca2+-ATPase 1 (ACA1) genes in cytoplasmic membrane jointly facilitated the increase of Ca2+ in the cytoplasm. Coexpression network analysis indicated that the fluctuation of Ca2+ in the cytoplasm could activate the expression of transcription factors MYB3 and AP2-4 through calmodulin (CAM) and calcium-dependent protein kinase (CDPK), and then regulate glycerol-3-phosphate acyltransferases (GPAT) at the beginning of TAG synthesis and diacylglycerol acyltransferase (DGAT)/phospholipid: diacylglycerol acyltransferase (PDAT) in the last step of TAG synthesis. Furthermore, the addition of Ca2+ specific chelator BAPTA-AM inhibited the expression of GPAT, which was consistent with the decrease in microalgae lipid content. The results proved that Ca2+ participated in the regulation of microalgae TAG synthesis under heat stress, which provided a new view for the understanding of the microalgae lipid accumulation mechanism.

Improving sedimentation and lipid production of microalgae in the photobioreactor using saline wastewater

Saline wastewater was used in this study to culture freshwater microalgae Chlorella pyrenoidosa in sequencing batch photobioreactor to improve the sedimentation and lipid production of algal cells. Influent salinity of 0.5% or above effectively promoted the sedimentation of microalgae in the settling stage of photobioreactor, and greatly reduced the algal biomass in effluent. The mechanism of the saline wastewater in improving the sedimentation of microalgae included decreasing zeta potential, increasing cell particle size and promoting extracellular polymeric substances synthesis, which varied with influent salinity. Saline wastewater also promoted the lipid accumulation in microalgae. Lipid content of microalgae increased with increasing influent salinity. However, the growth of microalgae was greatly inhibited at the influent salinity of 2.0% and 3.0%. Therefore, the PBR with influent salinity of 1.0% achieved the highest productivity of microalgae lipid. The saturation of fatty acids of microalgae gradually increased with increasing influent salinity.

Microalgae as a multipotential role in commercial applications: Current scenario and future perspectives

Microalgal feedstocks have gained tremendous potential for sustainable biofuel production in recent years. For biofuel processing, thermochemical, biochemical, and transesterification processes are used. Many researchers have recently become interested in the hydrothermal liquefaction of microalgae. Renewable biofuel production from microalgae, as well as a broad range of value-added co-products, describe its potential as a biorefinery feedstock from this perspective. Microalgae convert solar energy into carbon storage compounds, such as TAG (triacylglycerols), which can then be converted into biodiesel, bioethanol, and bio-methanol. Microalgae are considered to be the most attractive source of biofuel production for all the organisms used. This review explored the percentage of oil content, chemical composition, and lipid content of microalgae. This analysis depicts the various aspects of microalgal species for biofuel conversion. Also, other bioenergy and value-added items are discussed briefly.

Statistical study of growth kinetics and lipid content of microalgae grown in brackish waters for bioenergetic purposes

This study aimed to statistically prove the influence of salinity on growth kinetics and intracellular lipid accumulation in microalgae. The species Chlorella sp., Scenedesmus acuminatus, Nannochloropsis sp., Monoraphidium contortum and Pediastrum tetras were studied, which were isolated in the Brazilian semi-arid region and cultivated in synthetic media with the addition of NaCl. From the crops, growth kinetics, dry biomass production and lipid content were analyzed, using the experimental planning for one factor as a tool, with the NaCl concentration as an independent variable. The kinetic parameters maximum growth speed (µmax) and generation time (tg), as well as lipid concentration were the response variables studied. The results showed that, in the species Scenedesmus acuminatus, Nannochloropsis sp. and Pediastrum tetras, salt stress contributed to the increase in µmax and the consequent decrease in tg. The highest levels of lipid accumulation were obtained in Nannochloropsis sp. (62.04%), in the medium with the highest salinity and Pediastrum tetras (54.04%) in the lowest. Dry biomass production was higher in Scenedesmus acuminatus (1,941.37 mg.L-1) and Nannochloropsis sp. (1237.05 mg.L-1), both at a concentration of 4.0 g.L-1. Therefore, saline stress acted directly on the cell growth and lipid content of the species, which can be used as a device to enhance lipid production for the purpose of producing biofuels.

Cultivation of Scenedesmus obliquus and Chlorella pyrenoidosa in Municipal Wastewater Using Monochromatic and White LED as Light Sources

In this study, the red LED with wavelength range of 625 ~ 627.5 nm and the blue LED with wavelength range of 464 ~ 467 nm are chosen as the light source in order to increase the lipid content of microalgae as well as to reduce the energy consumption. The highest lipid weight of Scenedesmus obliquus is achievedwith 5000lux light intensity, 12L:12D of photoperiod and blue continuous LED light which consuming 53.4 times less energy in term of the total lipid content per unit than that of tricolor energy-saving lamp. In addition, the highest biomass and lipid weight of Chlorella pyrenoidosa are achieved with 5000lux of light intensity, 8L:16D of photoperiod and red continuous LED light, which is 0.73 g/L and 0.552 g/L respectively. And it consumes 29.4 times less energy consumption for units of the total lipid content than that of tricolor energy-saving lamp. Furthermore, continuous LED light improves effect of municipal wastewater treatment as the better light source for Scenedesmus obliquus and Chlorella pyrenoidosa comparing with intermittent LED light.

Chlorella vulgaris growth on anaerobically digested sugarcane vinasse: influence of turbidity

This paper shows the influence of turbidity (in Nephelometric Turbidity Units - NTU), chemical oxygen demand (COD) and aeration (CO2 supply) on the productivity and growth rate and lipid content of microalgae (a mixed culture predominantly composed of Chlorella vulgaris), using anaerobically digested vinasse as a culture medium. The microalgae can be cultivated in anaerobically digested vinasse, at turbidity and chemical oxygen demand of 690 NTU and 2.5 gCOD L -1, respectively, according to the modified Gompertz model, and removal of turbidity by filtration did not influence the microalgae productivity (≈ 77 mg L1 d1). Furthermore, aeration increased the productivity up to 139 mg L1 d1, with a biomass dry weight of 2.7 g L-1. Finally, a maximum lipid content of 265 mg L -1 was obtained, while a nitrogen removal of 98% was recorded for all conditions. Thus, the combination of anaerobic digestion followed by the use of the digestate for the cultivation of microalgae may be an efficient way to treat large quantities of this residue, in turn yielding large amounts of microalgae biomass, which can be transformed into fertilizer and biofuel.

Decolourization of chicken compost derived liquid fertilizer via synergic ultraviolet (UV) irradiation and ozonation for enhanced microalgae cultivation

Compost-derived liquid fertilizers are uncostly and nutrient-enriched; however, its dark brown appearance limits light uptake of microalgae during autotrophic cultivation. Here, integrated UV irradiation/ozonation pretreatment was employed to decolourize the compost solution prior to microalgae cultivation. Aforesaid pretreatment could accomplish 16.52 % (8 h) or 40.88 % (24 h) decolorization efficiency by using optimal parameters (initial pH of 12, ozone concentration of 30 mg/L, and ozone flow rate of 3 L/min. Compared to untreated compost solution, microalgae Chlorella vulgaris grew better in the medium supplemented with decolourized compost solution (after 24 h UV irradiation/ozonation). For the autotrophic cultivation of C. vulgaris with 10 vol.% compost solution, UV irradiation/ozonation pretreatment eventually increases the microalgae dry weight, specific growth rate, and biomass productivity from 0.58 g/L, 0.14 d-1, and 0.040 g/(L·d) to 0.88 g/L, 0.19 d-1, and 0.065 g/(L·d), respectively. Furthermore, the lipid content of microalgae has been increased by 33.33% with pretreatment of compost solution.

Biosynthesis of Silver Nanoparticles from Synechocystis sp to be Used as a Flocculant Agent with Different Microalgae Strains

Background: Biofuels produced from trans-esterification of high lipid content in microalgae represent a promising alternative renewable source of energy to the limited and depleted global fossil fuel reservoir. The most critical step in such a process is the harvesting of algal cells. Objective: We aimed to improve the current methodology for microalgae harvesting via utilizing biosynthesized silver nanoparticles (AgNPs) from Synechocystis sp. ElfSCS31 as an eco-friendly, stable, and affordable flocculant agent. Methods: AgNPs were prepared by the green synthesis method using the alcoholic extract of Synechocystis sp. ElfSCS31. The synthesized nanoparticles were characterized by Zeta sizer, X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FT-IR), and UV-Vis Spectroscopy. Biosynthesised AgNPs were applied for harvesting 20 microalgae strains, and then, harvesting efficiency was determined by UV Spectrophotometry. Results: Our results revealed an average size of polydispersed nanoparticles ranging from 10 to 100 nm for prepared AgNPs and the potential of 1.78 mV, with an average crystallite size of 22 nm. Biosynthesised AgNPs exhibited harvesting efficiency towards different strains of microalgae, which reached 97% in some strains as in Chlorella lobophora and Chlorococcum oleofaciens. Conclusion: The presented study introduces a feasible strategy using biosynthesized AgNPs as a flocculant agent to harvest different strains of microalgae at normal growth conditions of light and temperature. Our developed method could replace the classical high-cost step of harvesting that leads to unravelling the full potential of microalgae as a promising and fascinating source for biofuels production.

Lipids monitoring in Scenedesmus obliquus based on terahertz technology

BackgroundMicroalgae are considered as a source of low pollution and renewable fuel due to their ability to synthesize an abundance of lipids. Conventional methods for lipid quantification are time-consuming and chemically contaminated, while spectroscopic method combined with mathematical model is much more attractive due to its ability of qualitative and quantitative analysis of material composition, in this sense, terahertz technology provides not only timely and non-destructive testing without chemical pollution, but also provides information on the functional group vibration mode and structure of the measured components. Therefore, terahertz technology is utilized in our investigation and proposed for microalgae metabolism detection.ResultsThe aim of this study was to use terahertz spectroscopy to observe lipid content in Scenedesmus obliquus (S. obliquus). We collected the THz spectra of S. obliquus which were cultivated under nitrogen stress and terahertz spectroscopy was used to analyze changes in substance components (lipids, proteins, carbohydrates and β-carotene). The PLS algorithm was used to model the terahertz data to distinguish the different lipid content of S. obliquus under nitrogen stress. The correlation coefficient of the prediction results of the lipid characteristic band modeling was above 0.991, and the root mean square error was less than 0.132. It indicated that terahertz technology can be used to discriminate S. obliquus cells under different nitrogen stress effectively. The correlation between the terahertz characteristic peak (9.3 THz) and the total lipid content determined by gravimetry reaches 0.960. The final results were compared with the commonly used spectroscopic methods for lipid observation (Raman spectroscopy).ConclusionsIn this article, we demonstrated the effectiveness of terahertz spectroscopy to monitor changes in microalgae lipid content under nitrogen stress. Terahertz spectroscopy is more suitable for industrial production or ordinary laboratories which require intermediate result with low-frequency screening. When quantifying microalgae lipids, the constraint of terahertz spectroscopy is far less than that of Raman spectroscopy, and it is easier for operator to accurately quantify microalgae lipid. In addition, it is still in early stage for the study of microalgae using terahertz spectroscopy technology, there is still much potential for us to explore.

Application of Heterogeneous Catalysts for Biodiesel Production from Microalgal Oil—A Review

The depletion of fossil fuel reserves and increased environmental concerns related to fossil fuel production and combustion has forced the global communities to search for renewable fuels. In this regard, microalgae-based biodiesel has been considered as one of the interesting alternatives. Biodiesel production from the cultivation of microalgae is eco-friendly and sustainable. Moreover, microalgae have several advantages over other bioenergy sources, including their good photosynthetic capacity and faster growth rates. The productivity of microalgae per unit land area is also significantly higher than that of terrestrial plants. The produced microalgae biomass is rich with high quality lipids, which can be converted into biodiesel by transesterification reactions. Generally, the transesterification reactions are carried out in the presence of a homogeneous or heterogeneous catalyst. The homogeneous catalysts have many disadvantages, including their single use, slow reaction rate and saponification issues due to the presence of fatty acids in the feedstock. The acidic nature of the homogeneous catalysts also causes equipment corrosion. On the other hand, the heterogeneous catalysts offer several advantages, including their reusability, higher reaction rate and selectivity, easy product/catalyst separation and low cost. Due to these facts, the development of solid phase transesterification catalysts have been receiving growing interest. The present review is focused on the use of heterogeneous catalysts for biodiesel production from microalgal oil as a reliable feedstock with a comparison to other available feedstocks. It also highlights optimal reaction conditions for maximum biodiesel yields, reusability of the solid catalysts, cost, and environmental impact. The superior lipid content of microalgae and the efficient concurrent esterification and transesterification of the solid acid−base catalysts can offer new advancements in biodiesel production.