Effects of Nitrogen Forms and Supply Mode on Lipid Production of Microalga Scenedesmus obliquus

Phycospheric Bacteria Alleviate the Stress of Erythromycin on Auxenochlorella pyrenoidosa by Regulating Nitrogen Metabolism

Macrolide pollution has attracted a great deal of attention because of its ecotoxic effects on microalgae, but the role of phycospheric bacteria under antibiotic stress remains unclear. This study explored the toxic effects of erythromycin (ERY) on the growth and nitrogen metabolism of Auxenochlorella pyrenoidosa; then, it analyzed and predicted the effects of the composition and ecological function of phycospheric bacteria on microalgae under ERY stress. We found that 0.1, 1.0, and 10 mg/L ERY inhibited the growth and chlorophyll of microalgae, but the microalgae gradually showed enhanced growth abilities over the course of 21 days. As the exposure time progressed, the nitrate reductase activities of the microalgae gradually increased, but remained significantly lower than that of the control group at 21 d. NO3- concentrations in all treatment groups decreased gradually and were consistent with microalgae growth. NO2- concentrations in the three treatment groups were lower than those in the control group during ERY exposure over 21 d. ERY changed the community composition and diversity of phycospheric bacteria. The relative abundance of bacteria, such as unclassified-f-Rhizobiaceae, Mesorhizobium, Sphingopyxis, Aquimonas, and Blastomonas, varied to different degrees. Metabolic functions, such ABC transporters, the microbial metabolism in diverse environments, and the biosynthesis of amino acids, were significantly upregulated in the treatments of higher concentrations (1.0 and 10 mg/L). Higher concentrations of ERY significantly inhibited nitrate denitrification, nitrous oxide denitrification, nitrite denitrification, and nitrite and nitrate respiration. The findings of this study suggest that phycospheric bacteria alleviate antibiotic stress and restore the growth of microalgae by regulating nitrogen metabolism in the exposure system.

Improving the biodiesel production in the marine diatom Thalassiosira pseudonana cultivated in nutrient deficiency and sewage water

The use of microalgae as a feedstock in biofuel production is highly encouraging. The marine diatom in this study, Thalassiosira pseudonana, was used as a test organism to evaluate the impact of nitrogen or phosphorus limitation and sewage water on improving biodiesel production. The growth rate is more affected in cultures without phosphorus by 41.8% lower than in control and the highest dry weight estimated in control. The cellular dry weight significantly increased in cultures treated with mix1 and mix2 wastewater compared to the control cultures. Chlorophyll a content decreased in the absence of nitrogen and phosphorous and in sewage water cultures. Lipid content in algal cultures without nitrogen or phosphorus and in sewage water accumulated nearly twice as much lipid content in synthetic medium. T. pseudonana showed high FAME contents; the two most abundant fatty acids, stearic acid (C18:0) and palmitoleic acid (C16:1), in the algal extracts revealed that T. pseudonana was predominantly composed of these fatty acids. T. pseudonana grown in nitrogen or phosphorus-deficient conditions exhibited an extreme percentage of saturated fatty acids (SFAs) by 87.38% and 85.47%, respectively, of the total fatty acids (TFAs). More importantly, the low polyunsaturated fatty acid content in oils indicates a high cetane number, low iodine value, and low corrosion for biodiesel quality indicators. Producing biodiesel that closely meets worldwide biodiesel requirements (ASTM D6751 and EN 14214) is the goal of this work, which shows that growing T. pseudonana under nutrient limitations leads to algal metabolism in that direction.

Microalgae as future food: Rich nutrients, safety, production costs and environmental effects

The improvement of food security and nutrition has attracted wide attention, and microalgae as the most promising food source are being further explored. This paper comprehensively introduces basic and functional nutrients rich in microalgae by elaborated tables incorporating a wide variety of studies and summarizes factors influencing their accumulation effects. Subsequently, multiple comparisons of nutrients were conducted, indicating that microalgae have a high protein content. Moreover, controllable production costs and environmental friendliness prompt microalgae into the list that contains more promising and reliable future food. However, microalgae and -based foods approved and sold are limited strictly, showing that safety is a key factor affecting dietary consideration. Notably, sensory profiles and ingredient clarity play an important role in improving the acceptance of microalgae-based foods. Finally, based on the bottleneck in the microalgae food industry, suggestions for its future development were discussed.

Native microalgal-bacterial consortia from the Ecuadorian Amazon region: an alternative to domestic wastewater treatment

In low-middle income countries (LMIC), wastewater treatment using native microalgal-bacterial consortia has emerged as a cost-effective and technologically-accessible remediation strategy. This study evaluated the effectiveness of six microalgal-bacterial consortia (MBC) from the Ecuadorian Amazon in removing organic matter and nutrients from non-sterilized domestic wastewater (NSWW) and sterilized domestic wastewater (SWW) samples. Microalgal-bacterial consortia growth, in NSWW was, on average, six times higher than in SWW. Removal rates (RR) for NH4 +- N and PO4 3--P were also higher in NSWW, averaging 8.04 ± 1.07 and 6.27 ± 0.66 mg L-1 d-1, respectively. However, the RR for NO3 - -N did not significantly differ between SWW and NSWW, and the RR for soluble COD slightly decreased under non-sterilized conditions (NSWW). Our results also show that NSWW and SWW samples were statistically different with respect to their nutrient concentration (NH4 +-N and PO4 3--P), organic matter content (total and soluble COD and BOD5), and physical-chemical parameters (pH, T, and EC). The enhanced growth performance of MBC in NSWW can be plausibly attributed to differences in nutrient and organic matter composition between NSWW and SWW. Additionally, a potential synergy between the autochthonous consortia present in NSWW and the native microalgal-bacterial consortia may contribute to this efficiency, contrasting with SWW where no active autochthonous consortia were observed. Finally, we also show that MBC from different localities exhibit clear differences in their ability to remove organic matter and nutrients from NSWW and SWW. Future research should focus on elucidating the taxonomic and functional profiles of microbial communities within the consortia, paving the way for a more comprehensive understanding of their potential applications in sustainable wastewater management.

Bioprospecting Microalgae from Sewage Water: Assessment of Biochemicals for Biomass Utilization

Microalgal species from sewage treatment plant were identified by 18S rRNA sequencing and were explored for total lipids, carbohydrate, and protein contents, to serve as a potential candidate for biorefinery. Seven unicellular microalgae were identified as Chlorella sorokiniana, Dictyosphaerium sp., Graesiella emersonii belonging to Chlorellaceae and Scenedesmus sp., Desmodesmus sp., Tetranephris brasiliensis, and Coelastrella sp. belonging to Scenedesmaceae family. Biochemical assessment of all isolates revealed total lipid content from 17.49 ± 1.41 to 47.35 ± 0.61% w/w, total carbohydrate content from 12.82 ± 0.19 to 64.29 ± 0.63% w/w, and total protein content from 8.55 ± 0.19 to 16.65 ± 0.20% w/w. FAME analysis of extracted lipid was found to be rich in Hexadecane (C16:0), Tetradecane (C17:0), Octadecane (C18:0), Eicosane (C20:0), Tetracosane (C24:0), Pentacosane (C25:0) fatty acids, the presence of which makes excellent candidate for biodiesel. Being rich in lipid, microalgae Chlorella sorokiniana, Coelastrella sp., and Scenedesmus sp. have high potential for biofuels. Due to the presence of high protein content, Scenedesmus sp. and Chlorella sorokiniana can serve as food or feed supplement, whereas the high carbohydrate content of Dictyosphaerium sp., Coelastrella sp., and Scenedesmus sp. makes them an ideal candidate for fermentative production of alcohol and organic acids. Chlorella sp. and Scenedesmus sp., being dominant microalgae across all seasons, demonstrate remarkable resilience for their cultivation in sewage water and utilization of biomass in biorefineries.

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).

Microalgae on distillery wastewater treatment for improved biodiesel production and cellulose nanofiber synthesis: A sustainable biorefinery approach

Sugarcane spent wash generates waste at a large scale that impacts the environment, hence the classic waste reuse technology needs to be implemented. An integrated approach of spent wash and microalgae cultivation to produce biodiesel has gained momentum in recent times. However, the microalgae technology lacks the functional utilization of de-oiled microalgae biomass (DOB). This study proposed the development of a microalgae-based advanced process for distillery spent wash treatment, biomass recovery for biodiesel and utilizing algal residue as a step towards waste management. A novel microalga Coelastrella sp KJ-04 grown in distillery spent wash represented with high biomass (4.61g/L) and lipid production (3.6 g/L). The significant reduction in Chemical Oxygen Demand (COD, 49.3%), Total Nitrogen (TN, 49.7%), Total Phosphorous (TP, 21.8%), Total Organic Carbon (TOC, 40.2%), Total Sulphur (S, 37.2%) and Potassium (K, 42.5%) were achieved in spent wash. The extracted lipids of Coelastrella sp KJ-04 were converted to Fatty acid methyl ester (FAME) and examined by Gas chromatography -mass spectrometry (GC-MS) to observe the suitability for biodiesel prospect. The de-oiled biomass (DOB) was utilized for the synthesis of Cellulose nanofibers (CNF), purified and estimated with a diameter ranging between 20 and 27 nm. The crystalline structure and functional group of CNF were analyzed by X-ray diffraction (XRD) and Fourier Transform infrared spectroscopy (FTIR). The unprecedented work demonstrated the microalgae biorefinery approach for spent wash remediation, biodiesel synthesis and simultaneous production of biodegradable CNF from algal residue to support waste-free technology. In future, CNF can be reinforced into material for concrete as it could be the smart alternative to replace synthetic cement plastics.

Biodiesel Production from Chlorella homosphaera by Two-Step Catalytic Conversion Using Waste Radish Leaves as a Source for Heterogeneous Catalyst

The economic viability of algal biodiesel can be improved by enhancing the microalgal lipid accumulation and using agricultural waste as a cheap and sustainable source of catalysts. In the current study, the effect of various nitrogen concentrations on the growth and lipid of Chlorella homosphaera were investigated. Furthermore, two-step catalytic conversion was applied to convert the oil of C. homosphaera with high free fatty acids (FFA) to biodiesel using waste radish leaves as a source of a heterogeneous base catalyst. The result revealed that the maximum lipid productivity of 25.0 mg L^-1 day^-1 and lipid content of 30.83% were obtained under nitrogen-depleted and limited nitrogen conditions, respectively. The FFA was reduced from 18.79 to 0.76%, and the acid value was decreased from 37.4 to 1.52 mg KOH g^-1 using a 15:1 methanol to oil molar ratio (MTOR), 1.5 wt.% H₂SO₄, at 60 °C for 150 min. Under the optimized conditions, i.e., MTOR of 10:1, 3 wt.% of catalyst ratio for 120 min at 60 °C, the highest oil conversion of 96.61% was obtained. The physicochemical properties of the produced biodiesel were in the range of the standard specification norms for biodiesel. Hence, the proposed two-step catalytic conversion using calcined radish leaves as a heterogeneous catalyst has thus exhibited good potential for biodiesel production using algal oil with high FFA.

Industry chain and challenges of microalgal food industry-a review

Currently, the whole world is facing hunger due to the increase in the global population and the rising level of food consumption. Unfortunately, the impact of environmental, climate, and political issues on agriculture has resulted in limited global food resources. Thus, it is important to develop new food sources that are environmentally friendly and not subject to climate or space limitations. Microalgae represent a potential source of nutrients and bioactive components for a wide range of high-value products. Advances in cultivation and genetic engineering techniques provide prospective approaches to widen their application for food. However, there are currently problems in the microalgae food industry in terms of assessing nutritional value, selecting processes for microalgae culture, obtaining suitable commercial strains of microalgae, etc. Additionally, the limitations of real data of market opportunities for microalgae make it difficult to assess their actual potential and to develop a better industrial chain. This review addresses the current status of the microalgae food industry, the process of commercializing microalgae food and breeding methods. Current research progress in addressing the limitations of microalgae industrialization and future prospects for developing microalgae food products are discussed.

Influence of Nutrient Manipulation on Growth and Biochemical Constituent in Anabaena variabilis and Nostoc muscorum to Enhance Biodiesel Production

The present study aims to improve biomass and biochemical constituents, especially lipid production of Anabaena variabilis and Nostoc muscorum by formulating an optimal growth condition using various concentrations of nutrients (NO3−, PO43− and CO32−) for biodiesel production. The supplementation of the three nutrients by +50% showed the maximum dry weight and biomass productivity, while the macromolecule contents were varied. The depletion of N-NO3− by 50% N-NO3− showed the maximum lipid yield (146.67 mg L−1) in A. variabilis and the maximum carbohydrate contents (285.33 mg L−1) in N. muscorum with an increase of 35% and 30% over control of the synthetic medium, respectively. However, variation in P-PO43− and C-CO32− showed insignificant improving results for all biochemical compositions in both cyanobacteria. A. variabilis was the superior species for lipid and protein accumulation; however, N. muscorum showed the maximum carbohydrate content. Accordingly, A. variabilis was selected for biodiesel production. In A. variabilis, −50% N-NO3− resulted in 35% higher lipid productivity compared to the control. Furthermore, the fatty acid profile and biodiesel quality-related parameters have improved under this condition. This study has revealed the strategies to improve A. variabilis lipid productivity for biodiesel production for small-scale in vitro application in terms of fuel quality under low nitrate levels.

Microalgae as Sustainable Bio-Factories of Healthy Lipids: Evaluating Fatty Acid Content and Antioxidant Activity

The demand for sustainable and environmentally friendly food sources and food ingredients is increasing, and microalgae are promoted as a sustainable source of essential and bioactive lipids, with high levels of omega-3 fatty acids (ω-3 FA), comparable to those of fish. However, most FA screening studies on algae are scattered or use different methodologies, preventing a true comparison of its content between microalgae. In this work, we used gas-chromatography mass-spectrometry (GC-MS) to characterize the FA profile of seven different commercial microalgae with biotechnological applications (Chlorella vulgaris, Chlorococcum amblystomatis, Scenedesmus obliquus, Tetraselmis chui, Phaeodactylum tricornutum, Spirulina sp., and Nannochloropsis oceanica). Screening for antioxidant activity was also performed to understand the relationship between FA profile and bioactivity. Microalgae exhibited specific FA profiles with a different composition, namely in the ω-3 FA profile, but with species of the same phylum showing similar tendencies. The different lipid extracts showed similar antioxidant activities, but with a low activity of the extracts of Nannochloropsis oceanica. Overall, this study provides a direct comparison of FA profiles between microalgae species, supporting the role of these species as alternative, sustainable, and healthy sources of essential lipids.

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

Microalgal biomass and its cellular components are used as substrates for the production of fuels. A valuable group among the components of microalgal biomass is lipids, which act as a precursor for the production of biodiesel in the transesterification process. Some methods, including the creation of stressful conditions, are applied to increase the accumulation of lipids. This study aimed to determine the effect of limited nutrient access on the growth and development of the microalga Chlorella vulgaris and the amount of lipids stored in its cells. Aquaculture wastewater (AWW) was used in the study as a source of nutrients at doses of 20%, 40%, 60%, 80% and 100%. The amount of microalgal biomass, optical density, lipid content after extraction of the biomass in Soxhlet apparatus and chlorophyll a content were determined. It was observed that the microalgae efficiently used the nutrients contained in the AWW. The largest amount of biomass was obtained in AWW80 (727 ± 19.64 mg·L−1). The OD680 (0.492 ± 0.00) determined under the same conditions was almost five times higher in AWW than in the synthetic medium. Under nutrient-stress conditions, the content of lipids in biomass ranged from 5.75% (AWW80) to 11.81% (AWW20). The highest content of chlorophyll a in microalgal cells was obtained in AWW20 (206 ± 11.33 mg∙m−3).

The Effect of Chromium on Photosynthesis and Lipid Accumulation in Two Chlorophyte Microalgae

Heavy metals have adverse effects on microalgae metabolism and growth. Photosynthesis and lipid profile are quite sensitive to heavy metal toxicity. The impact of hexavalent chromium—Cr(VI) on photosynthesis and lipid accumulation in Mucidosphaerium pulchellum and Micractinium pusillum exposed to different concentrations (0–500 μg L−1) was investigated for 11 days. A significant (p < 0.05) increase in lipid content was observed with increasing Cr(VI) concentration. However, growth was suppressed at higher concentrations exceeding 100 μg L−1. Addition of Cr(VI) in the cell culture medium showed a negative effect on quantum yield (Fv/Fm), and a photosynthetic inhibition of >65% was noted in both species at 500 μg L−1. However, the lipid gravimetric analysis presented inner cell lipid content up to 36% and 30% of dry weight biomass for M. pulchellum and M. pusillum, respectively. The fatty acids profiles of both microalgae species showed higher levels of hexadecenoic acid as well as ω3, ω6, and ω7 fatty acids. The effect of Cr(VI) on photosynthesis and lipid accumulation in both microalgae species was concentration and exposure time dependent. This shows that an appropriate concentration of Cr(VI) in culture medium could be beneficial for higher lipid accumulation in freshwater eukaryotic microalgae species.

Influence of Nitrogen and Phosphorus on Microalgal Growth, Biomass, Lipid, and Fatty Acid Production: An Overview

Microalgae can be used as a source of alternative food, animal feed, biofuel, fertilizer, cosmetics, nutraceuticals and for pharmaceutical purposes. The extraction of organic constituents from microalgae cultivated in the different nutrient compositions is influenced by microalgal growth rates, biomass yield and nutritional content in terms of lipid and fatty acid production. In this context, nutrient composition plays an important role in microalgae cultivation, and depletion and excessive sources of this nutrient might affect the quality of biomass. Investigation on the role of nitrogen and phosphorus, which are crucial for the growth of algae, has been addressed. However, there are challenges for enhancing nutrient utilization efficiently for large scale microalgae cultivation. Hence, this study aims to highlight the level of nitrogen and phosphorus required for microalgae cultivation and focuses on the benefits of nitrogen and phosphorus for increasing biomass productivity of microalgae for improved lipid and fatty acid quantities. Furthermore, the suitable extraction methods that can be used to utilize lipid and fatty acids from microalgae for biofuel have also been reviewed.

Effects of different phosphorus concentrations on growth and biochemical composition of Desmodesmus communis (E.Hegewald) E.Hegewald

The members of the family Scenedesmaceae has the most widely used microalgae species in algal biotechnology studies because of their fast growth rate, quality of nutrition content and lipid accumulation under nutrient-limiting conditions. However, the biochemical responses of the species under phosphorus (P) limiting conditions are still unknown. The growth and biochemical composition of Desmodesmus communis in response to different phosphorus concentrations were investigated in this research. Five different phosphorus conditions were used: control (BG11); excess treatments (50% P+, 75% P+) and limited treatments (50% P-, 75% P-The highest cell concentration was observed in 75% P+ (725.6 × 104 cells/mL), whereas the highest dry weight concentration (1.81 mg/L) was found in 50% P- medium. The highest total lipid (4.94%) accumulation was found in the 50% P + medium and the maximum protein (49.5%) content was detected in 50% P- medium. Fatty acid and amino acid compositions change according to P concentration. PUFAs concentrations are higher than SFAs and MUFAs. Therefore the microalgae biomass obtained from this study cannot be used for biodiesel production although it is more suitable for nutritional supplement productions.

Lignocellulosic Biomass as a Substrate for Oleaginous Microorganisms: A Review

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.

Evaluation of Scenedesmus rubescens for Lipid Production from Swine Wastewater Blended with Municipal Wastewater

This study examined the feasibility of using non-sterilized swine wastewater for lipid production by an isolated microalga, Scenedesmus rubescens. Different dilution ratios using municipal wastewater as a diluent were tested to determine the suitable levels of microalgal growth in the wastewaters, its nutrient removal, and its lipid production. The highest lipid productivity (8.37 mg/L/d) and NH4+ removal (76.49%) were achieved in swine wastewater that had been diluted to 30 times using municipal wastewater. Various bacteria coexisted in the wastewaters during the cultivation of S. rubescens. These results suggest the practical feasibility of a system to produce lipids from swine wastewater by using microalgae.

Recommended turbulent energy dissipation rate for biomass and lipid production of Scenedesmus obliquus in an aerated photosynthetic culture system

Effects of turbulent energy dissipation rate (increased from 1.28 × 10^-6 to 1.67 × 10^-5 m² s^-3) on Scenedesmus obliquus biomass and lipid accumulation at different aeration rates (0.3, 0.6, 0.9, 1.2, and 1.5 L min^-1) were investigated. The turbulent energy dissipation rate was calculated by CFD model simulation. When the turbulent energy dissipation rate increased to 7.30 × 10^-6 m² s^-3, the biomass and lipid productivity increased gradually, and finally reached their maximum values of 1.11 × 10⁷ cells mL^-1 and 16.0 mg L^-1 day^-1, respectively. When it exceeded 7.30 × 10^-6 m² s^-3, the biomass and lipid productivity showed a decreasing trend. Therefore, the most favorable turbulent energy dissipation rate for S. obliquus growth and lipid accumulation was 7.30 × 10^-6 m² s^-3.