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Biotechnological Approaches for Biomass and Lipid Production Using Microalgae Chlorella and Its Future Perspectives
Division of Biotechnology, The Catholic University of Korea, Bucheon 14662, Republic of Korea
Correspondence to:J. Microbiol. Biotechnol. 2022; 32(11): 1357-1372
Published November 28, 2022 https://doi.org/10.4014/jmb.2209.09012
Copyright © The Korean Society for Microbiology and Biotechnology.
Abstract
Keywords
Graphical Abstract
Introduction
Microalgae have recently drawn considerable attention for their high potential to produce valuable compounds as well as their applications in biodiesel production, phycoremediation, and dietary supplements. As a source of bioenergy raw materials that can be used to produce biofuels, microalgae are a unique bioresource that has been proposed as a solution to combat energy shortages and alleviate problems associated with global warming [1, 2]. Compared to terrestrial plants, microalgae have tremendous potential as a bioresource with greater biomass productivity [3, 4]. Typically, 10-20% of the biomass derived from microalgae consists of fatty acids that can be used as raw materials for bioenergy [5]. However, there are some limitations to the industrial applications of microalgae bioenergy [6]. The biomass produced through microalgae cultivation is harvested using processes such as centrifugation and filtration [7, 8]. Significant losses and production costs are incurred during harvest [7, 8]. Therefore, solutions to reduce the losses and production costs associated with harvesting processes are essential [9].
For example, lipids accumulated by microalgae can be used as feedstock for biodiesel production, and microalgal oils can be used in the food industry [17, 18]. Many studies have shown the importance of cultivation conditions for microalgal growth and lipid accumulation. Nutrients [19, 20], high salinity [21, 22], metal ions [23], light intensity, temperature, pH, and abiotic/biotic treatments are regarded as critical parameters for microalgal growth and lipid accumulation. This review presents updated research on
Nutrients
Carbon Source for Cultivation of Chlorella
Photoautotrophic growth of microalgae requires inorganic carbon as a carbon source for growth, which relies on light as a sole energy source. The application of organic carbon sources can be divided into two types depending on light's presence (mixotrophic) or absence (heterotrophic).
Photoautotrophic Mode
In photoautotrophic cultivations, the only source of carbon for photosynthesis comes from the available atmospheric CO2 (Fig. 1). The photobioreactor system is capable of photoautotrophic cultivation of
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Table 1 .
Chlorella biomass and lipid productivity using different carbon sources.Mode Carbon source Carbon Strain Medium Culture volume Biomass Unit Lipid Unit Ref. Autotrophic CO2 Nitrogen depletion C. minutissima Guillard f/2 62.5 mg/L/d 5.72 mg/L/d [28] Amaral et al ., 2020Autotrophic CO2 Nitrogen depletion C. pyrenoidosa 2738Fog’s media 5 g/L/13d 410 mg/L/d [16] Nawkarkar et al ., 2019Autotrophic CO2 - C. sorokiniana AM-02BBM 2.4 L 3.45 g/L NA [30] Ziganshina et al ., 2020Heterotrophic Glucose 10 g/L glucose C. vulgaris AB MCCS 130BG11 2 L 265 mg/L/d 118 mg/L/d [32] Morowvat et al ., 2019Heterotrophic Glucose 10 g/L glucose Chlorella sp. HS2BG11 3 L 5370 mg/L/d 860 mg/L/d [33] Kim et al ., 2019Mixotrophic Glucose 15 g/L glucose C. vulgaris KNUA104BG11 2.98 mg/L/d 68.80% DCW [38] Yun et al ., 2021C. sorokiniana KNUA1224.73 40%* Heterotrophic C. vulgaris KNUA1041.72 30%* C. sorokiniana KNUA1223.64 40%* Mixotrophic Glucose 18.8 g/L glucose C. vulgaris strain UTEX 2714TAP 150 mL 6.1 g/L 383 mg/L/d [39] Ward et al ., 2019Mixotrophic Acetate 10 g/L acetic acid C. pyrenoidosa (FACHB-1216)BG11 800 mL 134 mg/L/d 42.04 mg/L/d [54] Li et al ., 2022Mixotrophic Acetate 100 mM acetic acid C. sorokiniana 211-32250 mL 1390 mg/L/d 193.37 mg/L/d [40] León-Vaz et al ., 2019Mixotrophic Acetate 10 g/L NaAc C. pyrenoidosa (FACHB-9)BG11 300 mL 40* mg/L/d 13.48 mg/L/d [41] Liu et al ., 2018Mixotrophic Glycerol 3 g/L glycerol (synthetic wastewater) C. pyrenoidosa - 3.5 L 1.28 g/L 30.76% DCW [45] Rana et al ., 2021Heterotrophic Glucose 20 g/L glucose C. vulgaris CCALA 256BBM 2 L NA 32.70% DCW [55] Canelli et al ., 2020Mixotrophic 24.20% Mixotrophic Wastewater 25% Sweet sorghum bagasse (SSB) C. vulgaris UTEX 395BBM 2 L 3.44 g/L 141 mg/L/d [80] Arora et al ., 2021Mixotrophic Wastewater Food waste extract (20 g/L glucose) Chlorella sp. GY-H4- 2 L 6.9 g/L 1.8 g/L [86] Wang et al ., 2020Mixotrophic Wastewater 30% Palm oil mill effluent (POME) C. sorokiniana CY-1- 7.02 L 409 mg/L/d 14.43% DCW [81] Cheah et al ., 2020Heterotrophic Wastewater Sugarcane bagasse (20 g/L sugar conc) C. protothecoides - 7 L 10.7 g/L 16.80% DCW [83] Chen et al ., 2019Heterotrophic Wastewater Forest biomass (C/N 60) C. sorokiniana SAG 211–8 k- 1.9 L 8.28 g/L 3.61 g/L [84] Vyas et al ., 2022Autotrophic Wastewater + CO2 Seafood processing wastewater (SPW) + 10% CO2 C. vulgaris NIOCCV- 4 L 264 mg/L/d 100.54 mg/L/d [85] Jain et al ., 2019Mixotrophic Wastewater Seafood processing wastewater (SPW) Chlorella sp.- 350 mL 77.7 mg/L/d 20.4 mg/L/d [86] Gao et al ., 2018Mixotrophic Wastewater Tannery effluent : sewage effluent = 20 : 80 C. vulgaris - 300 mL 3.25 g/L 25.40% DCW [87] Saranya et al ., 2019C. pyrenoidosa 2.84 9.30% Mixotrophic Wastewater OSCCW : Water = 50 : 50 C. vulgaris (NRMCF0128)- - 60.1 mg/L/d 20.8 mg/L/d [88] Azam et al ., 2022P. pringsheimii (VIT_SDSS)56.5 17.5 Mixotrophic Wastewater Butyric acid type effluent Chlorella sp. UJ-3- 200 mL NA 25.40% DCW [89] Huo et al ., 2018Autotrophic Wastewater + CO2 Real swine wastewater (RSW) + 3% CO2 C. vulgaris MBFJNU-1- 3000 L 478.5 mg/L/d 9.1 mg/L/d [90] Xie et al ., 2022Mixotrophic Wastewater 2000 mg/L COD Chlorella sp.- 225 mL 288.84 mg/L/d 104.89 mg/L/d [91] Zhu et al ., 2017Heterotrophic Sucrose + yeast 10 g/L sucrose C. pyrenoidosa BG11 100 mL 2290 mg/L/10d 124.3 mg/L/d [104] Kilian et al ., 1996Mixotrophic + Cryptococcus sp.2930 165.4 Heterotrophic Sucrose + yeast 1% sucrose C. pyrenoidosa FACHB-9BG11 100 mL 340 mg/L/d 29.70% DCW [103] Wang et al ., 2016+ Rhodotorula glutinis Detailed conditions of carbon treatments for the accumulation of lipids in
Chlorella .*indicates value estimated from figure images.
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Table 2 .
Chlorella biomass and lipid productivity using different nitrogen sources.Nitrogen Source Nitrogen Strain Medium Culture volume Growth rate Unint Biomass Unit Lipid Unit Protein Unit Ref Nitrite Nitrite 0% (Nitrite+Nitrate) C. vulgaris B3N 50 mL 1.3 day NA NA NA [64] Pozzobon et al ., 2021Nitrate+Nitrite Nitrite 20-100% (Nitrite+Nitrate) 0.82-0.97 Nitrate NA C. vulgaris Jaworsky 8 L NA day 0.18 g/L 12.29% DCW 50.80% DCW [66] Mutlu et al ., 2011Nitrate+Nitrite 0.12 13.04% 41.03% –Nitrogen 0.18 35.60% 13.01%% Nitrite 15 mg N/l Chlorella sp. HQmBG11 180 mL NA day 342.5 mg/L 38.75 mg/L NA [67] Zhan et al ., 2016Nitrate 357.5 19.99 Ammonium 102.5 5.86 Urea 270 12* Nitrite 200 umol/L Nitrite Chlorella sp. L38BG11 1 L NA day NA 3.05 mg/L/d 2.67 mg/L/d [65] Li et al ., 2020Nitrate+Nitrite 200 umol/L Nitrate+Nitrite 1.15 5.06 Nitrite 0.8 g N/L Chlorella sp. GN1BG11 1 L 0.947 day 216 mg/L/d NA NA [70] Feng et al ., 2020Urea 1.9 345 Ammonium 0.726 170 Urea 17.6 mM N Chlorella sp. HS2BG11 100 mL 0.765 day 301.4 mg/L/d 63.6 mg/L/d NA [70] Nayak et al ., 2019Sodium nitrate 0.751 274.3 37.7 Potassium nitrate 0.733 241.1 52.9 Ammonium nitrate 0.415 24.3 4.2 Ammonium chloride 0.387 21.4 3.4 Ammonium acetate 0.741 255.7 50.4 Ammonium sulfate 0.421 27.1 4.9 Ammonium bicarbonate 0.696 187.1 37.9 Ammonium ~215 mg/L Ammonium C. sorokiniana AM-02BBM 2.6 L 1.26 day NA NA NA [74] Wang et al ., 2019Nitrate ~730 mg/L Nitrate 1.07 Detailed conditions of nitrogen treatments for biomass, lipid and protein productions in
Chlorella .* indicates value estimated from figure images. Numbers discussed in the text are in bold.
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Fig. 1. Overview of the putative metabolic pathways for lipid biosynthesis under heterotrophic cultivation in
Chlorella . Uptake of glucose, acetate, and glycerol to produce lipids. Intermediate products and other metabolic biosynthesis pathways were omitted from this metabolic pathway.
Heterotrophic Mode
Although microalgae can utilize inorganic carbon sources for photosynthesis, the biomass productivity of microalgae is low and limited [31]. Biomass productivity can be improved under heterotrophic conditions compared to the basal photoautotrophic culture conditions. Morowvat
Mixotrophic Mode
In the mixotrophic mode, photoautotrophic metabolism is integrated with heterotrophic metabolism. Recent studies successfully increased the
Acetic acid is preferentially adsorbed by the microalgal cells and directly converted into acetyl-CoA, achieving higher efficiency of lipid production. León-Vaz
Chai
The question is which carbon source will provide the best lipid productivity. Glucose is first catabolized into glucose-6-phosphate and converted to pyruvate through an anaerobic glycolysis process. Furthermore, it is converted into acetyl-CoA, which is subsequently utilized in the TCA cycle for energy production or as a precursor for fatty acid synthesis (Fig. 1); therefore, both biomass and lipid production can be accelerated. On the other hand, acetate is a simple substrate necessitating only one or two activation steps at the expense of one ATP molecule to produce acetyl-CoA [47]. Perez-Garcia
Heterotrophic Mode vs. Mixotrophic Mode
Some researchers compared the effects of conditions in heterotrophic and mixotrophic cultivation modes for
It remains a question as to which trophic mode is best for growing
Nitrogen Source for Cultivation of Chlorella
Nitrogen is one of the essential nutrients for microalgal cultivation. Nitrogen can be delivered in various forms to the culture, such as nitrate NO3-, nitrite NO2-, ammonium NH4+, and urea CO(NH2)2. Although ammonium (NH4+) can be directly assimilated into amino acids via the GS/GOGAT cycle [58, 59], nitrate (NO3-) needs to be reduced to nitrite (NO2-) in the cytosol, after which it is immediately reduced to ammonium in chloroplasts or plastids [60] (Fig. 2). Thus, ammonium is more efficient than nitrate as a nitrogen source. However, ammonium can be toxic to many organisms, particularly plants and oxygenic photosynthetic microorganisms [61, 62]. Here, we mentioned recent trials to investigate the nitrogen sources that allow better cultivation and growth of
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Fig. 2. Overview of the putative metabolic pathways for nitrogen assimilation in
Chlorella . Uptake of nitrate, nitrite, ammonium, and urea to produce amino acids. Intermediate products and other metabolic biosynthesis pathways were omitted from this metabolic pathway. NR, nitrate reductase: NiR, nitrite reductase GS, glutamine synthetase; GOGAT; glutamine oxoglutarate aminotransferase.
Nitrate vs. Nitrite
Pozzobon
A few studies showed better lipid productivity using nitrite as a nitrogen source. Zhan
Urea
The consumption of either nitrate or ammonium by microalgae causes a change in medium pH as they grow. Davis
Ammonium
Ammonia nitrogen includes the ionized (ammonium, NH4+) and unionized form (ammonia, NH3, toxic to aquatic organisms). Unlike nitrate NO3-, when ammonium NH4+ is utilized, microalgae spend less energy on its assimilation, and ammonium is directly incorporated into amino acids [71]. However, excessive amounts of ammonium are toxic to algae due to the damaging effects on photosynthesis [61, 72]. This is because ammonium directly induces photodamage to PSII rather than affecting the repair of photodamaged PSII [73, 74].
In photosynthetic eukaryotes, nitrogen assimilation is performed by nitrate or nitrite transports. From the structural point of view, three families of proteins are involved in nitrate or nitrite transport in microalgae:
Phycoremediation: Wastewater as a Nutrient Source for Cultivation of Chlorella
Phycoremediation refers to remediation with the help of algae. Using wastewater to grow microalgae as a nutrient source would decrease the cultivation costs and purify polluted water. Food waste also represents a valuable carbon source for algal cultivation and can improve the production of microalgal biomass and valuable oleochemicals. Arora and Philippidis utilized 25% sweet sorghum bagasse (SSB) hydrolysate and achieved the highest biomass and lipid productivity (3.44 g/l and 120 mg/l/day, respectively) under mixotrophic conditions compared to heterotrophic and photoautotrophic conditions [80]. Wang
Using forest residues for biofuel production has attracted interest due to the generation of additional revenue and reduction of greenhouse gas emissions. Vyas
The commercial seafood processing industry generates large quantities of solids and wastewater. Seafood processing wastewater (SPW) usually contains high concentrations of nutrients, indicating that SPW could be an alternative nutrient source for microalgae cultivation. Jain
Sewage wastewater treatment with microalgae cultivation is an eco-friendly process. Saranya and Shanthakumar evaluated the remediation of combined sewage and tannery effluent under different dilutions. The maximum biomass yield was achieved at 20% tannery effluent and 80% sewage effluent (20% tannery effluent diluted with sewage), resulting in 3.25 g/l and 2.84 g/l in
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Fig. 3. Stress factors that induce lipid production in
Chlorella strains. (A) Diagram of the stress factors that induce lipid production inChlorella strains. (B) Microscopy images of the Nile Red-stained cells grown in TAP medium with nitrogen (+N) or without nitrogen (-N) for 72 h. Brightfield, Nile Red (lipid droplets), autofluorescence, and merged images with Nile Red and chlorophyll autofluorescence are shown. Scale bars, 10 μm.
Using livestock wastewater for microalgal cultivation seems to be another alternative solution.
It is worth mentioning that free ammonia in wastewater has been demonstrated as the primary stress factor suppressing microalgal activities. Gao
The contaminated biomass generated during phytoremediation poses a threat to our environment. Therefore, proper management is essential to dispose of the wastes to prevent them from further entering the food chain. The use and safe disposal of algal biomass after phytoremediation has been addressed by some researchers. For instance, the integration of algal bio-fertilizer production is recently gathering attention only when we use wastewater with a high level of safety to obtain pollutant-free biomass, such as wastewater from food or feed industries [95]. On the other hand, polluted water limits the application of the algae biomass produced [96]. In general, the microalgae biomass from contaminated waters can be used to produce alternative energies, including biodiesel, bioethanol, and biomethane. Additional experimentation and validation are required before the exploitation of such biomass for industrial or domestic use.
Co-Cultivation with Bacteria, Yeast, or Other Microalgae
Co-cultivation of algae and bacteria can enhance the efficiency of nutrient utilization in wastewater, and the growth rate of microalgal cells can be improved [97]. Since various microorganisms are present in wastewater, investigating the symbiotic systems existing between microalgae and bacterial communities is necessary for developing wastewater treatment technologies. Shen
Generally, the biomass produced through microalgae cultivation is harvested using processes such as centrifugation and filtration [8]. To reduce harvesting costs and remove nitrogen and phosphorous from wastewater, the floc formed by bacteria can be applied to microalgal biomass harvesting [100]. In the study by Kim
Disaccharides or polysaccharides, such as sucrose and lactose, are difficult to utilize for microalgae under heterotrophic conditions [35, 102]. Some yeasts extracellularly hydrolyze sucrose into monosaccharides. Since the sucrose hydrolysis rate is much higher than the monosaccharide uptake rate, the monosaccharide is accumulated in the culture [103, 104]. Wang
Hu
Using Nanoparticles for Chlorella Culture
Nanotechnology is currently a hot topic for its various applications and prospects for providing solutions to the various needs of many industries [108]. Nanoparticle application in microalgae for enhanced lipid production is an ongoing task that contributes to biodiesel production (reviewed in [109]). For example, magnesium, zinc, or lead nanoparticles induced a higher lipid content than non-metal exposed medium in
Various Stress Factors for Lipid Accumulation in Chlorella
Under favorable growth conditions,
Nutrient Starvation for Lipid Accumulation
Nitrogen is one of the essential nutrients for the growth of microalgae. Nitrogen deprivation in microalgae is widely studied during cultivation to induce lipid productions (Table 1 in [113]). Several studies have employed a frequently used approach for increased lipid production consisting of a combination of the biomass (favorable medium) and lipid induction phase (limited nutrient medium). A commonly used two-stage strategy has been adopted for lipid induction, in which the algal cultures are harvested by centrifugation after the biomass production phase, followed by incubation in a fresh nutrient-deficient medium for the lipid induction phase [70, 114]. Due to a time- and cost-consuming harvesting process before the lipid induction stage, recently, a single-stage strategy has been getting attention, wherein nitrogen concentration in the media is adjusted to improve the overall lipid productivity. Farooq
In addition to nitrogen starvation, various nutrient starvation methods also achieved lipid stimulation in
Various Stresses for Lipid Accumulation
Dong
Research in magnetic fields has significantly affected the growth and production of proteins, carbohydrates, and lipids in microalgae. The magnetic field has been shown to have significant effects on the growth and production of proteins, carbohydrates, and lipids with
Genetic Engineering of Chlorella for Better Lipid Production
As discussed in Yang
Potential Applications of Chlorella
According to a market report of the Research and Market, the
Valuable Compounds from Chlorella
Omega-3 and omega-6 fatty acids are essential to human health, and we must consume them through food; therefore, they are called essential fatty acids. Omega-3 polyunsaturated fatty acids (PUFAs) include a-linolenic acid (18:3; ALA), eicosapentaenoic acid (20:5; EPA), and docosahexaenoic acid (22:6; DHA), which are efficient at preventing cardiovascular diseases in humans, due to their characteristics that alter membrane fluidity and decrease triacylglycerols (TAGs) [144, 145]. In
Flavonoids, secondary metabolites of plants, are involved in defense against pathogens, photosynthesis, and growth [148]. Also, flavonoids are in many human foods because of their antioxidant capacity, which can prevent ROS formation in cells [149]. Yadavalli
The demand for natural colorants has significantly increased due to health and environmental issues [151]. Because of the fast growth rates and diversity of pigments, microalgae have attracted great interest as a natural colorant.
Carotenoids have two important functions in human health as antioxidants and a precursor of vitamin A. However, humans cannot synthesize carotenoids in the de novo pathway, so it is important to consume foods containing carotenoids [158]. Carotenoids are divided into two classes, carotenes and xanthophylls [157]. Many
Clinical Trial of Chlorella Nutritional Supplements
Based on the valuable compounds of
Bioplastic Production
Bioplastics are being actively studied to eliminate the dependency on fossil fuels to produce plastics and avoid endocrine disruptors [177], and some
Taste Aspect of Chlorella for Plant-Based Alternatives
Indeed, several companies have recently developed
Future Perspectives and Conclusion
The current severe bottleneck includes the high manufacturing cost of
Overall,
Acknowledgments
Y.Y. was supported by the NRF grant (2022R1C1C1008690 and 2022M3A9I3018121) funded by the Korean government (Ministry of Science and ICT) and the Catholic University of Korea, Research Fund, 2022. We thank Yuree Lee (School of Biological Sciences, Seoul National University, Korea) for kindly providing the fluorescence microscope to capture
Conflict of Interest
The authors have no financial conflicts of interest to declare.
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Related articles in JMB
Article
Review
J. Microbiol. Biotechnol. 2022; 32(11): 1357-1372
Published online November 28, 2022 https://doi.org/10.4014/jmb.2209.09012
Copyright © The Korean Society for Microbiology and Biotechnology.
Biotechnological Approaches for Biomass and Lipid Production Using Microalgae Chlorella and Its Future Perspectives
Sujeong Je and Yasuyo Yamaoka*
Division of Biotechnology, The Catholic University of Korea, Bucheon 14662, Republic of Korea
Correspondence to:Yasuyo Yamaoka, yasuyoyamaoka@gmail.com
Abstract
Heavy reliance on fossil fuels has been associated with increased climate disasters. As an alternative, microalgae have been proposed as an effective agent for biomass production. Several advantages of microalgae include faster growth, usage of non-arable land, recovery of nutrients from wastewater, efficient CO2 capture, and high amount of biomolecules that are valuable for humans. Microalgae Chlorella spp. are a large group of eukaryotic, photosynthetic, unicellular microorganisms with high adaptability to environmental variations. Over the past decades, Chlorella has been used for the large-scale production of biomass. In addition, Chlorella has been actively used in various food industries for improving human health because of its antioxidant, antidiabetic, and immunomodulatory functions. However, the major restrictions in microalgal biofuel technology are the cost-consuming cultivation, processing, and lipid extraction processes. Therefore, various trials have been performed to enhance the biomass productivity and the lipid contents of Chlorella cells. This study provides a comprehensive review of lipid enhancement strategies mainly published in the last five years and aimed at regulating carbon sources, nutrients, stresses, and expression of exogenous genes to improve biomass production and lipid synthesis.
Keywords: Chlorella, biotechnology, lipids, microalgae, biomass, phycoremediation
Introduction
Microalgae have recently drawn considerable attention for their high potential to produce valuable compounds as well as their applications in biodiesel production, phycoremediation, and dietary supplements. As a source of bioenergy raw materials that can be used to produce biofuels, microalgae are a unique bioresource that has been proposed as a solution to combat energy shortages and alleviate problems associated with global warming [1, 2]. Compared to terrestrial plants, microalgae have tremendous potential as a bioresource with greater biomass productivity [3, 4]. Typically, 10-20% of the biomass derived from microalgae consists of fatty acids that can be used as raw materials for bioenergy [5]. However, there are some limitations to the industrial applications of microalgae bioenergy [6]. The biomass produced through microalgae cultivation is harvested using processes such as centrifugation and filtration [7, 8]. Significant losses and production costs are incurred during harvest [7, 8]. Therefore, solutions to reduce the losses and production costs associated with harvesting processes are essential [9].
For example, lipids accumulated by microalgae can be used as feedstock for biodiesel production, and microalgal oils can be used in the food industry [17, 18]. Many studies have shown the importance of cultivation conditions for microalgal growth and lipid accumulation. Nutrients [19, 20], high salinity [21, 22], metal ions [23], light intensity, temperature, pH, and abiotic/biotic treatments are regarded as critical parameters for microalgal growth and lipid accumulation. This review presents updated research on
Nutrients
Carbon Source for Cultivation of Chlorella
Photoautotrophic growth of microalgae requires inorganic carbon as a carbon source for growth, which relies on light as a sole energy source. The application of organic carbon sources can be divided into two types depending on light's presence (mixotrophic) or absence (heterotrophic).
Photoautotrophic Mode
In photoautotrophic cultivations, the only source of carbon for photosynthesis comes from the available atmospheric CO2 (Fig. 1). The photobioreactor system is capable of photoautotrophic cultivation of
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Table 1 .
Chlorella biomass and lipid productivity using different carbon sources..Mode Carbon source Carbon Strain Medium Culture volume Biomass Unit Lipid Unit Ref. Autotrophic CO2 Nitrogen depletion C. minutissima Guillard f/2 62.5 mg/L/d 5.72 mg/L/d [28] Amaral et al ., 2020Autotrophic CO2 Nitrogen depletion C. pyrenoidosa 2738Fog’s media 5 g/L/13d 410 mg/L/d [16] Nawkarkar et al ., 2019Autotrophic CO2 - C. sorokiniana AM-02BBM 2.4 L 3.45 g/L NA [30] Ziganshina et al ., 2020Heterotrophic Glucose 10 g/L glucose C. vulgaris AB MCCS 130BG11 2 L 265 mg/L/d 118 mg/L/d [32] Morowvat et al ., 2019Heterotrophic Glucose 10 g/L glucose Chlorella sp. HS2BG11 3 L 5370 mg/L/d 860 mg/L/d [33] Kim et al ., 2019Mixotrophic Glucose 15 g/L glucose C. vulgaris KNUA104BG11 2.98 mg/L/d 68.80% DCW [38] Yun et al ., 2021C. sorokiniana KNUA1224.73 40%* Heterotrophic C. vulgaris KNUA1041.72 30%* C. sorokiniana KNUA1223.64 40%* Mixotrophic Glucose 18.8 g/L glucose C. vulgaris strain UTEX 2714TAP 150 mL 6.1 g/L 383 mg/L/d [39] Ward et al ., 2019Mixotrophic Acetate 10 g/L acetic acid C. pyrenoidosa (FACHB-1216)BG11 800 mL 134 mg/L/d 42.04 mg/L/d [54] Li et al ., 2022Mixotrophic Acetate 100 mM acetic acid C. sorokiniana 211-32250 mL 1390 mg/L/d 193.37 mg/L/d [40] León-Vaz et al ., 2019Mixotrophic Acetate 10 g/L NaAc C. pyrenoidosa (FACHB-9)BG11 300 mL 40* mg/L/d 13.48 mg/L/d [41] Liu et al ., 2018Mixotrophic Glycerol 3 g/L glycerol (synthetic wastewater) C. pyrenoidosa - 3.5 L 1.28 g/L 30.76% DCW [45] Rana et al ., 2021Heterotrophic Glucose 20 g/L glucose C. vulgaris CCALA 256BBM 2 L NA 32.70% DCW [55] Canelli et al ., 2020Mixotrophic 24.20% Mixotrophic Wastewater 25% Sweet sorghum bagasse (SSB) C. vulgaris UTEX 395BBM 2 L 3.44 g/L 141 mg/L/d [80] Arora et al ., 2021Mixotrophic Wastewater Food waste extract (20 g/L glucose) Chlorella sp. GY-H4- 2 L 6.9 g/L 1.8 g/L [86] Wang et al ., 2020Mixotrophic Wastewater 30% Palm oil mill effluent (POME) C. sorokiniana CY-1- 7.02 L 409 mg/L/d 14.43% DCW [81] Cheah et al ., 2020Heterotrophic Wastewater Sugarcane bagasse (20 g/L sugar conc) C. protothecoides - 7 L 10.7 g/L 16.80% DCW [83] Chen et al ., 2019Heterotrophic Wastewater Forest biomass (C/N 60) C. sorokiniana SAG 211–8 k- 1.9 L 8.28 g/L 3.61 g/L [84] Vyas et al ., 2022Autotrophic Wastewater + CO2 Seafood processing wastewater (SPW) + 10% CO2 C. vulgaris NIOCCV- 4 L 264 mg/L/d 100.54 mg/L/d [85] Jain et al ., 2019Mixotrophic Wastewater Seafood processing wastewater (SPW) Chlorella sp.- 350 mL 77.7 mg/L/d 20.4 mg/L/d [86] Gao et al ., 2018Mixotrophic Wastewater Tannery effluent : sewage effluent = 20 : 80 C. vulgaris - 300 mL 3.25 g/L 25.40% DCW [87] Saranya et al ., 2019C. pyrenoidosa 2.84 9.30% Mixotrophic Wastewater OSCCW : Water = 50 : 50 C. vulgaris (NRMCF0128)- - 60.1 mg/L/d 20.8 mg/L/d [88] Azam et al ., 2022P. pringsheimii (VIT_SDSS)56.5 17.5 Mixotrophic Wastewater Butyric acid type effluent Chlorella sp. UJ-3- 200 mL NA 25.40% DCW [89] Huo et al ., 2018Autotrophic Wastewater + CO2 Real swine wastewater (RSW) + 3% CO2 C. vulgaris MBFJNU-1- 3000 L 478.5 mg/L/d 9.1 mg/L/d [90] Xie et al ., 2022Mixotrophic Wastewater 2000 mg/L COD Chlorella sp.- 225 mL 288.84 mg/L/d 104.89 mg/L/d [91] Zhu et al ., 2017Heterotrophic Sucrose + yeast 10 g/L sucrose C. pyrenoidosa BG11 100 mL 2290 mg/L/10d 124.3 mg/L/d [104] Kilian et al ., 1996Mixotrophic + Cryptococcus sp.2930 165.4 Heterotrophic Sucrose + yeast 1% sucrose C. pyrenoidosa FACHB-9BG11 100 mL 340 mg/L/d 29.70% DCW [103] Wang et al ., 2016+ Rhodotorula glutinis Detailed conditions of carbon treatments for the accumulation of lipids in
Chlorella ..*indicates value estimated from figure images..
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Table 2 .
Chlorella biomass and lipid productivity using different nitrogen sources..Nitrogen Source Nitrogen Strain Medium Culture volume Growth rate Unint Biomass Unit Lipid Unit Protein Unit Ref Nitrite Nitrite 0% (Nitrite+Nitrate) C. vulgaris B3N 50 mL 1.3 day NA NA NA [64] Pozzobon et al ., 2021Nitrate+Nitrite Nitrite 20-100% (Nitrite+Nitrate) 0.82-0.97 Nitrate NA C. vulgaris Jaworsky 8 L NA day 0.18 g/L 12.29% DCW 50.80% DCW [66] Mutlu et al ., 2011Nitrate+Nitrite 0.12 13.04% 41.03% –Nitrogen 0.18 35.60% 13.01%% Nitrite 15 mg N/l Chlorella sp. HQmBG11 180 mL NA day 342.5 mg/L 38.75 mg/L NA [67] Zhan et al ., 2016Nitrate 357.5 19.99 Ammonium 102.5 5.86 Urea 270 12* Nitrite 200 umol/L Nitrite Chlorella sp. L38BG11 1 L NA day NA 3.05 mg/L/d 2.67 mg/L/d [65] Li et al ., 2020Nitrate+Nitrite 200 umol/L Nitrate+Nitrite 1.15 5.06 Nitrite 0.8 g N/L Chlorella sp. GN1BG11 1 L 0.947 day 216 mg/L/d NA NA [70] Feng et al ., 2020Urea 1.9 345 Ammonium 0.726 170 Urea 17.6 mM N Chlorella sp. HS2BG11 100 mL 0.765 day 301.4 mg/L/d 63.6 mg/L/d NA [70] Nayak et al ., 2019Sodium nitrate 0.751 274.3 37.7 Potassium nitrate 0.733 241.1 52.9 Ammonium nitrate 0.415 24.3 4.2 Ammonium chloride 0.387 21.4 3.4 Ammonium acetate 0.741 255.7 50.4 Ammonium sulfate 0.421 27.1 4.9 Ammonium bicarbonate 0.696 187.1 37.9 Ammonium ~215 mg/L Ammonium C. sorokiniana AM-02BBM 2.6 L 1.26 day NA NA NA [74] Wang et al ., 2019Nitrate ~730 mg/L Nitrate 1.07 Detailed conditions of nitrogen treatments for biomass, lipid and protein productions in
Chlorella ..* indicates value estimated from figure images. Numbers discussed in the text are in bold..
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Figure 1. Overview of the putative metabolic pathways for lipid biosynthesis under heterotrophic cultivation in
Chlorella . Uptake of glucose, acetate, and glycerol to produce lipids. Intermediate products and other metabolic biosynthesis pathways were omitted from this metabolic pathway.
Heterotrophic Mode
Although microalgae can utilize inorganic carbon sources for photosynthesis, the biomass productivity of microalgae is low and limited [31]. Biomass productivity can be improved under heterotrophic conditions compared to the basal photoautotrophic culture conditions. Morowvat
Mixotrophic Mode
In the mixotrophic mode, photoautotrophic metabolism is integrated with heterotrophic metabolism. Recent studies successfully increased the
Acetic acid is preferentially adsorbed by the microalgal cells and directly converted into acetyl-CoA, achieving higher efficiency of lipid production. León-Vaz
Chai
The question is which carbon source will provide the best lipid productivity. Glucose is first catabolized into glucose-6-phosphate and converted to pyruvate through an anaerobic glycolysis process. Furthermore, it is converted into acetyl-CoA, which is subsequently utilized in the TCA cycle for energy production or as a precursor for fatty acid synthesis (Fig. 1); therefore, both biomass and lipid production can be accelerated. On the other hand, acetate is a simple substrate necessitating only one or two activation steps at the expense of one ATP molecule to produce acetyl-CoA [47]. Perez-Garcia
Heterotrophic Mode vs. Mixotrophic Mode
Some researchers compared the effects of conditions in heterotrophic and mixotrophic cultivation modes for
It remains a question as to which trophic mode is best for growing
Nitrogen Source for Cultivation of Chlorella
Nitrogen is one of the essential nutrients for microalgal cultivation. Nitrogen can be delivered in various forms to the culture, such as nitrate NO3-, nitrite NO2-, ammonium NH4+, and urea CO(NH2)2. Although ammonium (NH4+) can be directly assimilated into amino acids via the GS/GOGAT cycle [58, 59], nitrate (NO3-) needs to be reduced to nitrite (NO2-) in the cytosol, after which it is immediately reduced to ammonium in chloroplasts or plastids [60] (Fig. 2). Thus, ammonium is more efficient than nitrate as a nitrogen source. However, ammonium can be toxic to many organisms, particularly plants and oxygenic photosynthetic microorganisms [61, 62]. Here, we mentioned recent trials to investigate the nitrogen sources that allow better cultivation and growth of
-
Figure 2. Overview of the putative metabolic pathways for nitrogen assimilation in
Chlorella . Uptake of nitrate, nitrite, ammonium, and urea to produce amino acids. Intermediate products and other metabolic biosynthesis pathways were omitted from this metabolic pathway. NR, nitrate reductase: NiR, nitrite reductase GS, glutamine synthetase; GOGAT; glutamine oxoglutarate aminotransferase.
Nitrate vs. Nitrite
Pozzobon
A few studies showed better lipid productivity using nitrite as a nitrogen source. Zhan
Urea
The consumption of either nitrate or ammonium by microalgae causes a change in medium pH as they grow. Davis
Ammonium
Ammonia nitrogen includes the ionized (ammonium, NH4+) and unionized form (ammonia, NH3, toxic to aquatic organisms). Unlike nitrate NO3-, when ammonium NH4+ is utilized, microalgae spend less energy on its assimilation, and ammonium is directly incorporated into amino acids [71]. However, excessive amounts of ammonium are toxic to algae due to the damaging effects on photosynthesis [61, 72]. This is because ammonium directly induces photodamage to PSII rather than affecting the repair of photodamaged PSII [73, 74].
In photosynthetic eukaryotes, nitrogen assimilation is performed by nitrate or nitrite transports. From the structural point of view, three families of proteins are involved in nitrate or nitrite transport in microalgae:
Phycoremediation: Wastewater as a Nutrient Source for Cultivation of Chlorella
Phycoremediation refers to remediation with the help of algae. Using wastewater to grow microalgae as a nutrient source would decrease the cultivation costs and purify polluted water. Food waste also represents a valuable carbon source for algal cultivation and can improve the production of microalgal biomass and valuable oleochemicals. Arora and Philippidis utilized 25% sweet sorghum bagasse (SSB) hydrolysate and achieved the highest biomass and lipid productivity (3.44 g/l and 120 mg/l/day, respectively) under mixotrophic conditions compared to heterotrophic and photoautotrophic conditions [80]. Wang
Using forest residues for biofuel production has attracted interest due to the generation of additional revenue and reduction of greenhouse gas emissions. Vyas
The commercial seafood processing industry generates large quantities of solids and wastewater. Seafood processing wastewater (SPW) usually contains high concentrations of nutrients, indicating that SPW could be an alternative nutrient source for microalgae cultivation. Jain
Sewage wastewater treatment with microalgae cultivation is an eco-friendly process. Saranya and Shanthakumar evaluated the remediation of combined sewage and tannery effluent under different dilutions. The maximum biomass yield was achieved at 20% tannery effluent and 80% sewage effluent (20% tannery effluent diluted with sewage), resulting in 3.25 g/l and 2.84 g/l in
-
Figure 3. Stress factors that induce lipid production in
Chlorella strains. (A) Diagram of the stress factors that induce lipid production inChlorella strains. (B) Microscopy images of the Nile Red-stained cells grown in TAP medium with nitrogen (+N) or without nitrogen (-N) for 72 h. Brightfield, Nile Red (lipid droplets), autofluorescence, and merged images with Nile Red and chlorophyll autofluorescence are shown. Scale bars, 10 μm.
Using livestock wastewater for microalgal cultivation seems to be another alternative solution.
It is worth mentioning that free ammonia in wastewater has been demonstrated as the primary stress factor suppressing microalgal activities. Gao
The contaminated biomass generated during phytoremediation poses a threat to our environment. Therefore, proper management is essential to dispose of the wastes to prevent them from further entering the food chain. The use and safe disposal of algal biomass after phytoremediation has been addressed by some researchers. For instance, the integration of algal bio-fertilizer production is recently gathering attention only when we use wastewater with a high level of safety to obtain pollutant-free biomass, such as wastewater from food or feed industries [95]. On the other hand, polluted water limits the application of the algae biomass produced [96]. In general, the microalgae biomass from contaminated waters can be used to produce alternative energies, including biodiesel, bioethanol, and biomethane. Additional experimentation and validation are required before the exploitation of such biomass for industrial or domestic use.
Co-Cultivation with Bacteria, Yeast, or Other Microalgae
Co-cultivation of algae and bacteria can enhance the efficiency of nutrient utilization in wastewater, and the growth rate of microalgal cells can be improved [97]. Since various microorganisms are present in wastewater, investigating the symbiotic systems existing between microalgae and bacterial communities is necessary for developing wastewater treatment technologies. Shen
Generally, the biomass produced through microalgae cultivation is harvested using processes such as centrifugation and filtration [8]. To reduce harvesting costs and remove nitrogen and phosphorous from wastewater, the floc formed by bacteria can be applied to microalgal biomass harvesting [100]. In the study by Kim
Disaccharides or polysaccharides, such as sucrose and lactose, are difficult to utilize for microalgae under heterotrophic conditions [35, 102]. Some yeasts extracellularly hydrolyze sucrose into monosaccharides. Since the sucrose hydrolysis rate is much higher than the monosaccharide uptake rate, the monosaccharide is accumulated in the culture [103, 104]. Wang
Hu
Using Nanoparticles for Chlorella Culture
Nanotechnology is currently a hot topic for its various applications and prospects for providing solutions to the various needs of many industries [108]. Nanoparticle application in microalgae for enhanced lipid production is an ongoing task that contributes to biodiesel production (reviewed in [109]). For example, magnesium, zinc, or lead nanoparticles induced a higher lipid content than non-metal exposed medium in
Various Stress Factors for Lipid Accumulation in Chlorella
Under favorable growth conditions,
Nutrient Starvation for Lipid Accumulation
Nitrogen is one of the essential nutrients for the growth of microalgae. Nitrogen deprivation in microalgae is widely studied during cultivation to induce lipid productions (Table 1 in [113]). Several studies have employed a frequently used approach for increased lipid production consisting of a combination of the biomass (favorable medium) and lipid induction phase (limited nutrient medium). A commonly used two-stage strategy has been adopted for lipid induction, in which the algal cultures are harvested by centrifugation after the biomass production phase, followed by incubation in a fresh nutrient-deficient medium for the lipid induction phase [70, 114]. Due to a time- and cost-consuming harvesting process before the lipid induction stage, recently, a single-stage strategy has been getting attention, wherein nitrogen concentration in the media is adjusted to improve the overall lipid productivity. Farooq
In addition to nitrogen starvation, various nutrient starvation methods also achieved lipid stimulation in
Various Stresses for Lipid Accumulation
Dong
Research in magnetic fields has significantly affected the growth and production of proteins, carbohydrates, and lipids in microalgae. The magnetic field has been shown to have significant effects on the growth and production of proteins, carbohydrates, and lipids with
Genetic Engineering of Chlorella for Better Lipid Production
As discussed in Yang
Potential Applications of Chlorella
According to a market report of the Research and Market, the
Valuable Compounds from Chlorella
Omega-3 and omega-6 fatty acids are essential to human health, and we must consume them through food; therefore, they are called essential fatty acids. Omega-3 polyunsaturated fatty acids (PUFAs) include a-linolenic acid (18:3; ALA), eicosapentaenoic acid (20:5; EPA), and docosahexaenoic acid (22:6; DHA), which are efficient at preventing cardiovascular diseases in humans, due to their characteristics that alter membrane fluidity and decrease triacylglycerols (TAGs) [144, 145]. In
Flavonoids, secondary metabolites of plants, are involved in defense against pathogens, photosynthesis, and growth [148]. Also, flavonoids are in many human foods because of their antioxidant capacity, which can prevent ROS formation in cells [149]. Yadavalli
The demand for natural colorants has significantly increased due to health and environmental issues [151]. Because of the fast growth rates and diversity of pigments, microalgae have attracted great interest as a natural colorant.
Carotenoids have two important functions in human health as antioxidants and a precursor of vitamin A. However, humans cannot synthesize carotenoids in the de novo pathway, so it is important to consume foods containing carotenoids [158]. Carotenoids are divided into two classes, carotenes and xanthophylls [157]. Many
Clinical Trial of Chlorella Nutritional Supplements
Based on the valuable compounds of
Bioplastic Production
Bioplastics are being actively studied to eliminate the dependency on fossil fuels to produce plastics and avoid endocrine disruptors [177], and some
Taste Aspect of Chlorella for Plant-Based Alternatives
Indeed, several companies have recently developed
Future Perspectives and Conclusion
The current severe bottleneck includes the high manufacturing cost of
Overall,
Acknowledgments
Y.Y. was supported by the NRF grant (2022R1C1C1008690 and 2022M3A9I3018121) funded by the Korean government (Ministry of Science and ICT) and the Catholic University of Korea, Research Fund, 2022. We thank Yuree Lee (School of Biological Sciences, Seoul National University, Korea) for kindly providing the fluorescence microscope to capture
Conflict of Interest
The authors have no financial conflicts of interest to declare.
- Abstract
- Introduction
- Nutrients
- Photoautotrophic Mode
- Heterotrophic Mode
- Mixotrophic Mode
- Heterotrophic Mode vs. Mixotrophic Mode
- Nitrogen Source for Cultivation of
Chlorella - Nitrate vs. Nitrite
- Urea
- Ammonium
- Phycoremediation: Wastewater as a Nutrient Source for Cultivation of
Chlorella - Co-Cultivation with Bacteria, Yeast, or Other Microalgae
- Using Nanoparticles for
Chlorella Culture - Various Stress Factors for Lipid Accumulation in
Chlorella - Nutrient Starvation for Lipid Accumulation
- Various Stresses for Lipid Accumulation
- Genetic Engineering of
Chlorella for Better Lipid Production - Potential Applications of
Chlorella - Valuable Compounds from
Chlorella - Clinical Trial of
Chlorella Nutritional Supplements - Bioplastic Production
- Taste Aspect of
Chlorella for Plant-Based Alternatives - Future Perspectives and Conclusion
- Acknowledgments
- Conflict of Interest
Fig 1.
Fig 2.
Fig 3.
-
Table 1 .
Chlorella biomass and lipid productivity using different carbon sources..Mode Carbon source Carbon Strain Medium Culture volume Biomass Unit Lipid Unit Ref. Autotrophic CO2 Nitrogen depletion C. minutissima Guillard f/2 62.5 mg/L/d 5.72 mg/L/d [28] Amaral et al ., 2020Autotrophic CO2 Nitrogen depletion C. pyrenoidosa 2738Fog’s media 5 g/L/13d 410 mg/L/d [16] Nawkarkar et al ., 2019Autotrophic CO2 - C. sorokiniana AM-02BBM 2.4 L 3.45 g/L NA [30] Ziganshina et al ., 2020Heterotrophic Glucose 10 g/L glucose C. vulgaris AB MCCS 130BG11 2 L 265 mg/L/d 118 mg/L/d [32] Morowvat et al ., 2019Heterotrophic Glucose 10 g/L glucose Chlorella sp. HS2BG11 3 L 5370 mg/L/d 860 mg/L/d [33] Kim et al ., 2019Mixotrophic Glucose 15 g/L glucose C. vulgaris KNUA104BG11 2.98 mg/L/d 68.80% DCW [38] Yun et al ., 2021C. sorokiniana KNUA1224.73 40%* Heterotrophic C. vulgaris KNUA1041.72 30%* C. sorokiniana KNUA1223.64 40%* Mixotrophic Glucose 18.8 g/L glucose C. vulgaris strain UTEX 2714TAP 150 mL 6.1 g/L 383 mg/L/d [39] Ward et al ., 2019Mixotrophic Acetate 10 g/L acetic acid C. pyrenoidosa (FACHB-1216)BG11 800 mL 134 mg/L/d 42.04 mg/L/d [54] Li et al ., 2022Mixotrophic Acetate 100 mM acetic acid C. sorokiniana 211-32250 mL 1390 mg/L/d 193.37 mg/L/d [40] León-Vaz et al ., 2019Mixotrophic Acetate 10 g/L NaAc C. pyrenoidosa (FACHB-9)BG11 300 mL 40* mg/L/d 13.48 mg/L/d [41] Liu et al ., 2018Mixotrophic Glycerol 3 g/L glycerol (synthetic wastewater) C. pyrenoidosa - 3.5 L 1.28 g/L 30.76% DCW [45] Rana et al ., 2021Heterotrophic Glucose 20 g/L glucose C. vulgaris CCALA 256BBM 2 L NA 32.70% DCW [55] Canelli et al ., 2020Mixotrophic 24.20% Mixotrophic Wastewater 25% Sweet sorghum bagasse (SSB) C. vulgaris UTEX 395BBM 2 L 3.44 g/L 141 mg/L/d [80] Arora et al ., 2021Mixotrophic Wastewater Food waste extract (20 g/L glucose) Chlorella sp. GY-H4- 2 L 6.9 g/L 1.8 g/L [86] Wang et al ., 2020Mixotrophic Wastewater 30% Palm oil mill effluent (POME) C. sorokiniana CY-1- 7.02 L 409 mg/L/d 14.43% DCW [81] Cheah et al ., 2020Heterotrophic Wastewater Sugarcane bagasse (20 g/L sugar conc) C. protothecoides - 7 L 10.7 g/L 16.80% DCW [83] Chen et al ., 2019Heterotrophic Wastewater Forest biomass (C/N 60) C. sorokiniana SAG 211–8 k- 1.9 L 8.28 g/L 3.61 g/L [84] Vyas et al ., 2022Autotrophic Wastewater + CO2 Seafood processing wastewater (SPW) + 10% CO2 C. vulgaris NIOCCV- 4 L 264 mg/L/d 100.54 mg/L/d [85] Jain et al ., 2019Mixotrophic Wastewater Seafood processing wastewater (SPW) Chlorella sp.- 350 mL 77.7 mg/L/d 20.4 mg/L/d [86] Gao et al ., 2018Mixotrophic Wastewater Tannery effluent : sewage effluent = 20 : 80 C. vulgaris - 300 mL 3.25 g/L 25.40% DCW [87] Saranya et al ., 2019C. pyrenoidosa 2.84 9.30% Mixotrophic Wastewater OSCCW : Water = 50 : 50 C. vulgaris (NRMCF0128)- - 60.1 mg/L/d 20.8 mg/L/d [88] Azam et al ., 2022P. pringsheimii (VIT_SDSS)56.5 17.5 Mixotrophic Wastewater Butyric acid type effluent Chlorella sp. UJ-3- 200 mL NA 25.40% DCW [89] Huo et al ., 2018Autotrophic Wastewater + CO2 Real swine wastewater (RSW) + 3% CO2 C. vulgaris MBFJNU-1- 3000 L 478.5 mg/L/d 9.1 mg/L/d [90] Xie et al ., 2022Mixotrophic Wastewater 2000 mg/L COD Chlorella sp.- 225 mL 288.84 mg/L/d 104.89 mg/L/d [91] Zhu et al ., 2017Heterotrophic Sucrose + yeast 10 g/L sucrose C. pyrenoidosa BG11 100 mL 2290 mg/L/10d 124.3 mg/L/d [104] Kilian et al ., 1996Mixotrophic + Cryptococcus sp.2930 165.4 Heterotrophic Sucrose + yeast 1% sucrose C. pyrenoidosa FACHB-9BG11 100 mL 340 mg/L/d 29.70% DCW [103] Wang et al ., 2016+ Rhodotorula glutinis Detailed conditions of carbon treatments for the accumulation of lipids in
Chlorella ..*indicates value estimated from figure images..
-
Table 2 .
Chlorella biomass and lipid productivity using different nitrogen sources..Nitrogen Source Nitrogen Strain Medium Culture volume Growth rate Unint Biomass Unit Lipid Unit Protein Unit Ref Nitrite Nitrite 0% (Nitrite+Nitrate) C. vulgaris B3N 50 mL 1.3 day NA NA NA [64] Pozzobon et al ., 2021Nitrate+Nitrite Nitrite 20-100% (Nitrite+Nitrate) 0.82-0.97 Nitrate NA C. vulgaris Jaworsky 8 L NA day 0.18 g/L 12.29% DCW 50.80% DCW [66] Mutlu et al ., 2011Nitrate+Nitrite 0.12 13.04% 41.03% –Nitrogen 0.18 35.60% 13.01%% Nitrite 15 mg N/l Chlorella sp. HQmBG11 180 mL NA day 342.5 mg/L 38.75 mg/L NA [67] Zhan et al ., 2016Nitrate 357.5 19.99 Ammonium 102.5 5.86 Urea 270 12* Nitrite 200 umol/L Nitrite Chlorella sp. L38BG11 1 L NA day NA 3.05 mg/L/d 2.67 mg/L/d [65] Li et al ., 2020Nitrate+Nitrite 200 umol/L Nitrate+Nitrite 1.15 5.06 Nitrite 0.8 g N/L Chlorella sp. GN1BG11 1 L 0.947 day 216 mg/L/d NA NA [70] Feng et al ., 2020Urea 1.9 345 Ammonium 0.726 170 Urea 17.6 mM N Chlorella sp. HS2BG11 100 mL 0.765 day 301.4 mg/L/d 63.6 mg/L/d NA [70] Nayak et al ., 2019Sodium nitrate 0.751 274.3 37.7 Potassium nitrate 0.733 241.1 52.9 Ammonium nitrate 0.415 24.3 4.2 Ammonium chloride 0.387 21.4 3.4 Ammonium acetate 0.741 255.7 50.4 Ammonium sulfate 0.421 27.1 4.9 Ammonium bicarbonate 0.696 187.1 37.9 Ammonium ~215 mg/L Ammonium C. sorokiniana AM-02BBM 2.6 L 1.26 day NA NA NA [74] Wang et al ., 2019Nitrate ~730 mg/L Nitrate 1.07 Detailed conditions of nitrogen treatments for biomass, lipid and protein productions in
Chlorella ..* indicates value estimated from figure images. Numbers discussed in the text are in bold..
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