Influence of Nutrient-Stress Conditions on Chlorella vulgaris Biomass Production and Lipid Content

Optimization of Cultivation Conditions of Native Microalga Scenedesmus quadricauda and Evaluation of Lipids for Enhanced Biodiesel Production

Biofuels are considered to be among the primary alternatives to the use of fossil fuels. These fuels, made from feedstock or waste raw materials, have the advantage of being renewable and contributing much less to global warming. Microalgae are a promising biodiesel source. Microalgae, unlike traditional crops that are now used to make commercialized biodiesel, may be grown on non-agricultural land and has a greater capacity for growth and yield. Cultivation has been considered as a critical stage in the generation of biofuels. The goal of the present study is to learn that Scenedesmus quadricauda has a potential for biodiesel production in the near future. Optimization studies revealed that BG-11 medium, temperature of 25 °C, pH 7.0, glucose and sucrose (as carbon sources), static condition (for lipid accumulation) & shaking condition (for biomass yield), cultivation days of 18, 21, and 24 day, NaNO3 dosing of 1.0 mM followed by 0.8 mM (on 5th day of cultivation), 3% yeast extract dosing, 3000 lx light intensity, photoperiod cycles of 24L/0D (for biomass yield) and 18L/6D (for lipid production) and 10 mM concentration of NaCl (salinity stress) can be regarded as best suited physio-biochemical parameters for efficient biomass and lipid yield from S. quadricauda. FTIR indicated presence of various stretching of carbohydrates and lipids that again is supporting biodiesel production capability of S. quadricauda. SEM showed that cells of S. quadricauda under stress conditions became fragmented separated from coenobium and were not so compactly arranged. Present optimization studies along with Nile red fluorescence, FTIR and SEM revealed that S. quadricauda could be a suitable candidate to produce good quality biofuel and that also in stress conditions.

Graphical Abstract

The Impact of Chlorella vulgaris Fortification on the Nutritional Composition and Quality Characteristics of Beef Burgers

Chlorella vulgaris (C.V) is known for its high protein and nutrient contents and has been touted as a potential functional ingredient in food products. For this study, beef burgers were formulated with varying levels of Chlorella vulgaris fortification (0%, 0.5%, 1%, and 1.5% by weight). The nutritional composition, including proximate analysis and mineral content, was determined for each treatment group. The quality characteristics evaluated included thiobarbituric acid (TBA), total volatile base nitrogen (TVBN), pH, and total acidity. The study included extracting the active substances from Chlorella vulgaris using three solvents, 50% ethanol, 95% ethanol, and water, to evaluate the effect on the antimicrobial and antioxidant activity. The results showed that the water extract had the highest total phenolic content (183.5 mg gallic acid equivalent per gram) and the highest flavonoid content (54 mg quercetin per gram). The aqueous extract had the highest content of total antioxidants, followed by the 95% ethanol and 50% ethanol extracts. Meanwhile, the 50% ethanol extract showed the best antimicrobial activity, while the aqueous extract had less of an effect on Gram-positive bacteria and no effect on E. coli. For the burger treatments, at the end of the storage period, it was observed that the microbial load of the treatments decreased compared to the control, and there was a high stability in the total volatile base nitrogen (TVBN) values for the treatments compared to the control, reaching a value of 22.4 at month 5, which is well above the acceptable limit, indicating spoilage. The pH values were higher for all of the treatments, with a lower total acidity for all of the treatments compared to the control. In conclusion, utilizing Chlorella vulgaris algae as a natural preservative to extend the freshness of burgers is a sustainable and innovative approach to food preservation. By harnessing the power of this green superfood, we not only enhance the shelf life of our food products but also contribute to a healthier and more environmentally friendly food industry.

Response of Chlorella vulgaris to exposure to CuO NPs: Contributions of particulate and dissolved metal forms as modulated by tannic acid and pH

A suspension of copper oxide nanoparticles (CuO NPs) is a mixture of dissolved and particulate Cu, the relative proportions of which highly depend on the water chemistry. However, the relationship between different proportions of particulate and dissolved Cu and the overall toxicity of CuO NPs is still unknown. This study investigated the response of Chlorella vulgaris to CuO NPs at varying solution pH and at different tannic acid (TA) additions, with a focus on exploring whether and how dissolved and particulate Cu contribute to the overall toxicity of CuO NPs. The results of the exposure experiments demonstrated the involvement of both dissolved and particulate Cu in inducing toxicity of CuO NPs, and the inhibition of CuO NPs on cell density of Chlorella vulgaris was found to be significantly (p < 0.05) alleviated with increased levels of TA and pH (< 8). Using the independent action model, the contribution to toxicity of particulate Cu was found to be enhanced with increasing pH values and TA concentrations. The toxic unit indicator better (R2 = 0.86, p < 0.001) explained impacts of CuO NPs on micro-algae cells than commonly used mass concentrations (R2 = 0.27-0.77, p < 0.05) across different levels of pH and TA. Overall, our study provides an additivity-based method to improve the accuracy of toxicity prediction through including contributions to toxicity of both dissolved and particulate Cu and through eliminating the uneven distribution of data due to large variations in total Cu, particulate Cu, dissolved Cu, Cu2+ activities, Cu-TA complexes and other Cu-complexes concentrations with varying water chemistry conditions.

Abiotic factors improving fatty acid profiling of freshwater indigenous microalgae isolated from Kumaun region of Uttarakhand, India

Microalgae have grabbed huge attention as a potential feedstock for biofuel production in response to the rise in energy consumption and the energy crisis. In the present study, indigenous microalgal strains were isolated from four freshwater lakes in the Kumaun region, Uttarakhand, India. Based on growth and lipid profiles, the four best-performing isolates were selected for further experiments. Initial identification of isolates was done by morphological observations, which were further validated by molecular identification using ITS sequencing. The screened cultures were subjected to abiotic stress conditions (varying concentrations of nitrogen and different temperatures) to monitor the biomass, lipid accumulation, and biochemical compositions (chlorophyll and carotenoids). The quantification of fatty acids was checked via gas chromatographic analysis. The strains were identified as KU_MA3 Chlamydopodium starrii, KU_MA4 Tetradesmus nygaardii, KU_MA5 Desmodesmus intermedius, and KU_MA6 Tetradesmus nygaardii. KU_MA3 Chlamydopodium starrii showed the best results in terms of growth and lipid production at 21 °C and 0.37 g/L NaNO2 concentration. The percentage of fatty acid methyl esters (FAMEs) attained >80% and met the standard for biodiesel properties. The strain has the potential to attain higher biomass and accumulate higher lipid content, and after some more studies, it can be used for upscaling processes and large-scale biodiesel production.

Effects of phytohormone on Chlorella vulgaris grown in wastewater-flue gas: C/N/S fixation, wastewater treatment and metabolome analysis

Chlorella vulgaris (C. vulgaris) can provide the means to fix CO2 from complicated flue gas, treat wastewater and reach a sustainable production of petrochemical substitutes simultaneously. However, a prerequisite to achieving this goal is to promote C. vulgaris growth and improve the CO2-to-fatty acids conversion efficiency under different conditions of flue gas and wastewater. Thus, the addition of indole-3-acetic acid (IAA) in C. vulgaris cultivation was proposed. Results showed that C. vulgaris were more easily inhibited by 100 ppm NO and 200 ppm SO2 under low nitrogen (N) condition. NO and SO2 decreased the carbon (C) fixation; but increased N and sulfur (S) fixation. IAA adjusted the content of superoxide dismutase (SOD) and malondialdehyde (MDA), improved the expression of psbA, rbcL, and accD, attenuated the toxicity of NO and SO2 on C. vulgaris, and ultimately improved cell growth (2014.64-2458.16 mgdw·L-1) and restored CO2 fixation rate (170.98-220.92 mg CO2·L-1·d-1). Moreover, wastewater was found to have a high treatment efficiency because C. vulgaris grew well in all treatments, and the maximal removal rates of both N and phosphorus (P) reached 100%. Metabonomic analysis showed that IAA, "NO and SO2" were involved in the down-regulated and up-regulated expression of multiple metabolites, such as fatty acids, amino acids, and carbohydrates. IAA was beneficial for improving lipid accumulation with 24584.21-27634.23 μg g-1, especially monounsaturated fatty acids (MUFAs) dominated by 16-18 C fatty acids, in C. vulgaris cells. It was concluded that IAA enhanced the CO2 fixation, fatty acids production of C. vulgaris and its nutrients removal rate.

Nitrogen and phosphorus stress as a tool to induce lipid production in microalgae

Microalgae, capable of accumulating large amounts of lipids, are of great value for biodiesel production. The high cost of such production stimulates the search for cultivation conditions that ensure their highest productivity. Reducing the content of nitrogen and phosphorus in the culture medium is widely used to change the content and productivity of lipids in microalgae. Achieving the right balance between maximum growth and maximum lipid content and productivity is the primary goal of many experimental works to ensure cost-effective biodiesel production from microalgae. The content of nitrogen and phosphorus in nutrient media for algal cultivation after converted to nitrogen (-N) and phosphorus (-P) lies in an extensive range: from 0.007 g L- 1 to 0.417 g L- 1 and from 0.0003 g L- 1 to 0.227 g L- 1 and N:P ratio from 0.12:1 to 823.33:1. When studying nutritional stress in microalgae, no single approach is used to determine the experimental concentrations of nitrogen and phosphorus. This precludes the possibility of correct interpretation of the data and may lead to erroneous conclusions. This work results from the systematisation of information on using nitrogen and phosphorus restriction to increase the lipid productivity of microalgae of different taxonomic and ecological groups to identify future research directions. The results of 301 experiments were included in the analysis using the principal components method. The investigation considered various divisions and classes: Cyanobacteria, Rhodophyta, Dinophyta, Haptophyta, Cryptophyta, Heterokontophyta/Ochrophyta (Bacillariophyceae, Eustigmatophyceae, Xanthophyceae), Chlorophyta, and also the ratio N:P, the time of the experiment, the light intensity during cultivation. Based on the concentrations of nitrogen and phosphorus existing in various nutrient media, a general scheme for designating the supply of nutrient media for nitrogen (as NO3- or NH4+, N g L- 1) and phosphorus (as РO4-, P g L- 1) has been proposed: replete -N (˃0.4 g L- 1), moderate -N (0.4-0.2), moderate N-limitation (0.19-0.1), strong N-limitation (˂0.1), without nitrogen (0), replete -Р (˃0.2), moderate -P (0.2-0.02), moderate P-limitation (0.019-0.01), strong P-limitation (˂0.01), without phosphorus (0).

Enhancement for the synthesis of bio-energy molecules (carbohydrates and lipids) in Desmodesmus subspicatus: experiments and optimization techniques

Microalgae are regarded as renewable resources of energy, foods and high-valued compounds using a biorefinery approach. In the present study, we explored isolated microalgae (Desmodesmus subspicatus) for the production of bio-energy molecules (carbohydrate and lipid). Optimizations of media (BG-11) components have been made using the Taguchi orthogonal array (TOA) technique to maximize biomass, carbohydrate and lipid production. Optimized results showed that biomass, carbohydrates and lipid productivity increased by 1.3 times at optimal combinations of media components than standard BG-11 media. Further, the influence of various carbon and nitrogen sources as nutritional supplement with optimum media composition under different light intensities was investigated for productivity of carbohydrate and lipid. Results demonstrated that 1.5 times higher productivity of carbohydrate and lipids were achieved in the presence optimum BG-11 under a broad range of light intensities (84-504 µmol m-2 s-1). Among different nitrogen sources, glycine was found to give higher productivity (1.5 times) followed by urea. Use of the cellulose as a carbon source in the media significantly increases biomass (2.4 times), carbohydrates (2.3 times) and lipids (2.3 times) productivity. Investigations revealed that cultivating Desmodesmus subspicatus under optimum culture conditions has the potential for large-scale bio-ethanol and bio-diesel production.

Nannochloris sp. Microalgae Strain for Treatment of Dairy Wastewaters

This paper focuses on a process for dairy wastewater treatment by mixotrophic cultivation of microalgae Nannochloris sp., using cheese whey obtained as a side flow from cheese production as an organic carbon source. The microalgae samples were prepared by adding to the standard growth medium increasing amounts of cheese whey, calculated to ensure a lactose concentration between 0 and 10 g/L. The samples were incubated at a constant temperature of 28 °C and 175 rpm stirring speed for a total time of seven days. Two LED (Light Emitting Diode) illumination schemes were applied in order to assess the effect of this parameter on microalgae development and bioactive compound accumulation: continuous illumination (light stress) versus alternative cycles of 12 h light-12 h dark (day-night cycle). The growth medium was analyzed before and after microalgae cultivation in order to determine the reduction of carbon, nitrogen, and phosphorus. The results obtained for this process, after a seven-day cultivation period, were as follows: reduction of 99-100% of lactose from the growth medium, up to 96% reduction in chemical oxygen demand, up to 91% reduction in nitrogen content, and up to 70% reduction in phosphorus content.

Carbon dioxide fixation and lipid storage of Scenedesmus sp. ASK22: A sustainable approach for biofuel production and waste remediation

In this study, an airlift reactor (ALR) has been employed to evaluate the carbon dioxide fixation rate (Rc) and lipid yield (LY) of unicellular green microalgae Scenedesmus sp. ASK22, using dairy effluent as a biofuel feedstock. Independent process parameters (PPs) such as light intensity, CO₂ concentration, and aeration rate and their effect on R_c and LY were revealed. The central composite design (CCD) was used to optimize the PPs. The best-operating conditions were measured as light intensity -6.24 Klux, CO₂ concentration -14.03% (v v^-1), and aeration rate -1.02 liter per minute (LPM). Under these conditions, LY and Rc were found to be 4.22 gL^-1 and 1.27 gL^-1d^-1 which were 2.24- and 1.94-fold higher than the value obtained in the control experiment (1.88 gL^-1 and 0.656 gL^-1d^-1) at the end of 12th day. The corresponding values for bioremediation of nitrate, phosphate, as well as chemical oxygen demand (COD), remained within 98-100%. The biochemical, CHN, thermogravimetric, and fatty acid analysis of Scenedesmus sp. ASK22 biomass and lipid confirmed their potential as a clean biofuel feedstock. Furthermore, a comprehensive analysis of lipid-extracted microalgae biomass (LEMB) was carried out suggesting that LEMB could be used as a high-quality cattle and fish feed, fertilizers, and a sustainable source for biogas, bioethanol, and bio-oils. In addition to improving the developed system's efficiency, a semi-continuous regime was implemented which resulted in biomass productivity of 1.89 gL^-1d^-1 which was 2.6-fold higher than the batch cultivation without hampering lipid productivity (0.377 gL^-1d^-1). The present results suggest that Scenedesmus sp. ASK22 is a potential candidate for CO₂ sequestration from atmosphere/flue gas, biofuel production (biodiesel, bioethanol, biogas, biobutanol, etc.), and waste remediation.

Cultivation of Pseudochlorella pringsheimii for biodiesel production in a scalable indoor photobioreactor: case studies from Egypt

BACKGROUND

Enhancement of lipid accumulation is the major strategy to improve the commercial feasibility of microalgae as a source for biodiesel production. Pseudochlorella pringsheimii (Formally was named as Chlorella ellipsoidea) green microalgae strain was chosen with respect to their ability as a potential source to produce high lipids content, could be used for the production of biofuel, which can be an alternative renewable energy source instead of fossil fuels.

RESULTS

Initially, the Pseudochlorella pringsheimii microalgae was evaluated on the basis of tested at Lab scales 2 L by applicable different nutrient individual of N, P, Fe conditions in BBM medium concentrations for choosing the best concentrations induce lipid contents and productivity to cultivate in large scale in the 2000 L PBR. The suitable concentrations of nutrients with highest lipid contents were obtained under deficient of nitrogen (1.25 gL^-1, limited N) and phosphorus (0.1 mg L^-1, limited P) coupled with high iron concentration (10 mg L, rich Fe) and CO₂ (6%). Therefore, their collective of nutrients was applied to culture of microalgae cells at large scale in 2000 L photobioreactor (PBR model), which, this techniques was used to quantify high lipid contents (25% w/w) and high lipid productivity (74.07 mgL^-1 day^-1). The inducted lipid conversion to biodiesel via transestrification process was 91.54 ± 1.43%. The fatty acid methyl esters (FAMEs profile by means of GC/MS resulted in C16:0, C18:1, C18:2, C18:3 as a main constituents. With regard to physical-chemical property (such as density, kinematic viscosity, gravity, and certain number), the Pseudochlorella pringsheimii biodiesel have biofuel properties, in accordance with appropriate biodiesel properties, as ASTM and EU standards, that thereby referring to high quality biodiesel.

CONCLUSIONS

Pseudochlorella pringsheimii cultured in large scale in photobioreactor under stress condition have a high potential of lipids production with high quality of FAMEs that can be used as a promising biodiesel fuel. It has also a potential to be applied for commercialization based on the techno-economic and environmental impacts.

Effect of biofertilizers on leaf yield, nitrate amount, mineral content and antioxidants of basil (Ocimum basilicum L.) in a floating culture

Hydroponics is one of the systems in agriculture which reinforce productivity by controlling environmental and growing conditions. In this study, we evaluated the effect of three bio-fertilizers, namely bacteria, micro-algae, and mycorrhiza, on basil leaf yield and quality (Ocimum basilicum L.) in a floating culture system. Soil has rich amounts of beneficial microorganisms, supporting plant nutrition, producing phytohormones, controlling phytopathogens, and improving soil structure. However, soilless culture usually contains no beneficial microorganisms if we do not include them in the system. This study aims to evaluate the response of three bio-fertilizers where mineral fertilizers are reduced by 50%. Considering the total harvest data, bacteria, mycorrhiza, and micro-algae treatments increased basil yield compared to 50% control by about 18.94%, 13.94%, and 5.72%, respectively. The maximum total yield and leaf area were recorded using bacteria with 2744 g m^-2 and 1528 cm² plant^-1. Plants with mycorrhiza achieved the highest number of leaves and branches, with 94.3 leaves plant^-1 and 24.50 branches plant^-1, respectively. It was observed that this bio-fertilizer increased the formation of lateral branches in the basil plant without thickening its stems. In addition, bacteria and mycorrhiza induced the highest percentage of dry matter and total soluble solids. The effect of bio-fertilizers on basil leaf EC and pH was insignificant for all the treatments at different harvest periods (p < 0.05). Using bio-fertilizers enhanced the intake of nutrients N (nitrogen), P (phosphorus), K (potassium), Ca (calcium), Mg (magnesium), Fe (iron), Mn (manganese), Zn (zinc), and Cu (copper). Using bio-fertilizers represents a promising and environmentally friendly approach to increasing crop yields and ameliorating quality and antioxidant compounds with fewer resources. An application of bio-fertilizers in hydroponic cultivation of basil cv. 'Dino' reduced the need for mineral fertilizers. At the same time, bio-fertilizers affected an increased plant yield and improved product quality. Furthermore, the bacteria had a pronounced enhancing effect on the increase of phenol and flavonoids in the leaves of basil plants.

Investigation of the chemical composition and physicochemical properties of Chlorella vulgaris biomass treated with pulsed discharges technology for potential use in the food industry

The use of chlorella as a dietary supplement has great prospects. Nevertheless, the processing of chlorella is associated with certain difficulties that limit its use on an industrial scale. Problems with the processing are primarily related to the thick and strong cell wall of chlorella (50-100 nm), which is poorly digested by most vertebrate species due to its complex multilayer structure. Our experiments have shown that discharge pulse treatment contributes to the destruction of the strong cell wall of chlorella. The results of atomic force microscopy and the determination of the antioxidant activity of the suspension confirm this. A study of the chemical composition of dried chlorella biomass showed a content of 56.8% protein and 12.6% fat, which causes a high nutritional value of chlorella. The study of the physicochemical properties of the prepared chlorella preparation showed pronounced hydrophilicity of proteins. Observation of gels with different contents of chlorella preparation, formed during heating and subsequent cooling and stored for seven days at +8 °C, showed that the gels do not emit a synergistic liquid. Total gels based on the chlorella preparation are characterized by high stability. Based on the results obtained, we concluded that the preparation based on disintegrated chlorella has a high potential for functional and technological application in food technologies

Production of microalgae with high lipid content and their potential as sources of nutraceuticals

In the current global scenario, the world is under a serious dilemma due to the increasing human population, industrialization, and urbanization. The ever-increasing need for fuels and increasing nutritional problems have made a serious concern on the demand for nutrients and renewable and eco-friendly fuel sources. Currently, the use of fossil fuels is creating ecological and economic problems. Microalgae have been considered as a promising candidate for high-value metabolites and alternative renewable energy sources. Microalgae offer several advantages such as rapid growth rate, efficient land utilization, carbon dioxide sequestration, ability to cultivate in wastewater, and most importantly, they do not participate in the food crop versus energy crop dilemma or debate. An efficient microalgal biorefinery system for the production of lipids and subsequent byproduct for nutraceutical applications could well satisfy the need. But, the current microalgal cultivation systems for the production of lipids and nutraceuticals do not offer techno-economic feasibility together with energy and environmental sustainability. This review article has its main focus on the production of lipids and nutraceuticals from microalgae, covering the current strategies used for lipid production and the major high-value metabolites from microalgae and their nutraceutical importance. This review also provides insights on the future strategies for enhanced microalgal lipid production and subsequent utilization of microalgal biomass.

GRAPHICAL ABSTRACT

Fatty Acid Profile of Microalgal Oils as a Criterion for Selection of the Best Feedstock for Biodiesel Production

Microalgae are considered to be potentially attractive feedstocks for biodiesel production, mainly due to their fast growth rate and high oil content accumulated in their cells. In this study, the suitability for biofuel production was tested for Chlorella vulgaris, Chlorella fusca, Oocystis submarina, and Monoraphidium strain. The effect of nutrient limitation on microalgae biomass growth, lipid accumulation, ash content, fatty acid profile, and selected physico-chemical parameters of algal biodiesel were analysed. The study was carried out in vertical tubular photobioreactors of 100 L capacity. The highest biomass content at 100% medium dose was found for Monoraphidium 525 ± 29 mg·L−1. A 50% reduction of nutrients in the culture medium decreased the biomass content by 23% for O. submarina, 19% for Monoraphidium, 13% for C. vulgaris and 9% for C. fusca strain. Nutrient limitation increased lipid production and reduced ash content in microalgal cells. The highest values were observed for Oocystis submarina, with a 90% increase in lipids and a 45% decrease in ash content in the biomass under stress conditions. The fatty acid profile of particular microalgae strains was dominated by palmitic, oleic, linoleic, and linoleic acids. Nutrient stress increased the amount of saturated and unsaturated fatty acids affecting the quality of biodiesel, but this was determined by the type of strain.