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[Display omitted] • 20 K-lux light/3x-nutrients exhibited max. astaxanthin 54.4 mg/L by C. zofingiensis. • 4–8 K-lux successive light increase and 5% CO 2 exhibited the best biomass yield. • The maximum lipid 37% accumulation was obtained at 5% CO 2 and 20 k-lux light. • 20 K-lux light/3x-nutrients exhibited max. astaxanthin content 16.7 mg/g DCW. • Two-stage designed bioprocess boosts astaxanthin yield of C. zofingiensis. Microalgal astaxanthin possesses numerous bioactivities and has several health applications. The current research focuses on designing and optimizing the two-stage mixotrophic bioprocess by Chlorella zofingiensis for astaxanthin production. Gradual increase in light intensity (4-8k-lux) and 3x micronutrient concentration were the key parameters for maximizing biomass yield of 2.5 g/L during 15 days of stage I. Furthermore, stress conditions (excessive CO 2, light, salinity, etc.) enhanced astaxanthin yield at stage II. 20k lux light, 3x nutrients, and 5% CO 2 were the best ranges for maximum astaxanthin production. Maximum biomass yield and astaxanthin content were 3.3 g/L and 16.7 mg/g, respectively, after 29 days of bioprocess. Astaxanthin biosynthesis was also affected by salinity, but less than other parameters. Astaxanthin bioprocess resulted in enhanced lipid yields of 35–37%, which could be used for biodiesel. This study shows promising scale-up potential with attractive sustainability features of Chlorella zofingiensis model for commercial astaxanthin-lipid biorefinery. [ABSTRACT FROM AUTHOR]

[Display omitted] • Magnesium aminoclay (MgA) induces CO 2 absorption and oxidative stress. • The effect of MgA on growth and lipid accumulation is Chlorella strain-dependent. • MgA improved the total lipid content and hexane extractability of Chlorella KR-1. • MgA promoted triacylglycerol biosynthesis but reduced cell wall thickness. Magnesium aminoclay nanoparticles (MgANs) exert opposing effects on photosynthetic microalgae by promoting carbon dioxide (CO 2) uptake and inducing oxidative stress. This study explored the potential application of MgAN in the production of algal lipids under high CO 2 concentrations. The impact of MgAN (0.05–1.0 g/L) on cell growth, lipid accumulation, and solvent extractability varied among three tested oleaginous Chlorella strains (N113, KR-1, and M082). Among them, only KR-1 exhibited significant improvement in both total lipid content (379.4 mg/g cell) and hexane lipid extraction efficiency (54.5%) in the presence of MgAN compared to those of controls (320.3 mg/g cell and 46.1%, respectively). This improvement was attributed to the increased biosynthesis of triacylglycerols and a thinner cell wall based on thin-layer chromatography and electronic microscopy, respectively. These findings suggest that using MgAN with robust algal strains can enhance the efficiency of cost-intensive extraction processes while simultaneously increasing the algal lipid content. [ABSTRACT FROM AUTHOR]

Highlights • A mixotrophic microalgae Chlorella sp. G-9 was separated from a WWTP. • Increasing TOC/TN ratio of wastewater promoted algal growth and nutrient removal. • Growth rate of microalgae did not increase as TOC/TN ratio increased from 24 to 30. • 99.58% and 99.61% nitrogen was removed in the wastewaters with TOC/TN of 24 and 30. • The highest lipid content of 36.5% was achieved in wastewater with TOC/TN of 30. Abstract This study investigated the biomass/lipid production, nutrient removal and fatty acid composition of an isolated mixotrophic microalga (Chlorella sp. G-9) cultured in simulated wastewater with different TOC/TN ratio. As the TOC/TN ratio of wastewater increased from 0 to 24, the growth rate of Chlorella sp. G-9 increased gradually, but did not increase further at 30. Nutrient removal was related to microalgae growth. In the wastewater with TOC/TN ratio of 24 and 30, 99.58% and 99.61% nitrogen was removed, respectively. In conditions of initial TOC/TN ratios of 24 and 30, Chlorella sp. G-9 could accumulate lipid as high as 35.3% and 36.5%, respectively. The corresponding lipid productivities were 34.2 and 32.6 mg L−1 d−1, respectively, which were 13.7 and 13.0 times higher than those in photoautotrophic condition. Increasing the initial TOC/TN ratio of the wastewater could slightly increase the saturated degree in fatty acid, thereby improving the stability of biodiesel. [ABSTRACT FROM AUTHOR]

In this work, the removal of the Cephalexin by Chlorella sp., nonliving modified by extraction of lipids was evaluated. First, the microalga was grown to completing 20 days and later, the biomass of crop was centrifuged and the extraction of lipids was performed. Two adsorption experiments were performed: (1) with nonliving Chlorella sp. (control), and (2) the obtained biomass after lipid extraction. The high antibiotic removal, 71.19% and 82.77% (control), were obtained at the lowest initial concentration. The contact time between the biosorbent and the antibiotic was 2 h. The adsorption isotherm follows the Freundlich model and the obtained maximum absorption capacity was 63.29 mg of antibiotic/g of biosorbent for lipid-extracted biomass, while the control follows best to the Langmuir model with 129.87 mg/g in maximum absorption capacity. In summary, this biosorbent provides a potential alternative in the removal of Cephalexin. [ABSTRACT FROM AUTHOR]

The larger-scale generation of piggery and winery wastewaters and consequent eutrophication are quite alarming, necessitating the use of a cost-effective treatment. This study attempted to remediate wastewaters from piggery and winery mixed in the ratios of 20:80, 50:50, 80:20, 100:0 and 0:100, in terms of nutrient removal and subsequent lipid accumulation by soil microalga, Chlorella sp. MM3. The per cent removal of total nitrogen and phosphates by the alga from mixed wastewaters within 10-days ranged between 51 and 89 and 26–49, respectively. As determined by FTIR spectroscopy, the lipid accumulation in the microalgal cells grown in wastewater mixtures ranged between 29 and 51%. Our results suggest that Chlorella sp. MM3 could be a potential candidate for bioremediation of wastewaters derived from piggery farm and winery industry, and that mixing of these wastewaters in 20:80 ratio would be an efficient approach for phycoremediation of mineral-rich effluents and subsequent yield of fairly good amounts of biofuel. [ABSTRACT FROM AUTHOR]

The present study aims to investigate the biofuel production ability and potential of heavy metal remediation of Chlorella sp. ISTLA1 isolated from a landfill site. The strain was cultured in Bold’s Basal medium at different concentration of NaHCO 3 and pH. Response surface methodology was employed for the optimization of nutrient sources for higher lipid production. Under the optimized conditions, the yield of lipid and biomass was 365.42 and 833.14 mg L −1 respectively. GC–MS analysis of lipid indicated the presence of C 8 to C 31 organic compounds consisting mainly of palmitic acid (C16:0), stearic acid (C18:0) and oleic acid (C18:1). Additionally, remediation of heavy metals like Zn, Cu, Mn and Fe from waste water was observed by AAS and EDX. The removal efficiency was 82.6% for Zn, 56.5% for Cu, 79.8% for Mn and 40% for Fe. The study revealed simultaneous biodiesel production and waste water treatment by Chlorella sp. ISTLA1. [ABSTRACT FROM AUTHOR]

The influence of N-replenishment on cell growth, chlorophyll content, nitrogen uptake, and accumulation of starch and lipid was studied in Chlorella sp. N-starved algal cells were fully recovered within 2 days after N-replenishment. Stored starch in N-deficient culture was degraded immediately during recovery process. However, lipid response had a period of delay when suffered from long starvation. During the recovery process, neutral lipid was reduced accompanied by an increase in membrane lipid. It was speculated that starch served as a source of carbon and energy catabolized to support quick recovery of the culture, while lipid preferred to play a structural role that specific fatty acid species were released from storage lipid and as building blocks for quick synthesis of membrane lipid. In light of rapid growth recovery and no net degradation in total fatty acids, a semi-continuous cultivation process might be a potential way to enhance lipid productivity. [ABSTRACT FROM AUTHOR]

The study examined the effect of varying concentrations of iron in the form of ethylene diamine tetra-acetic acid ferric sodium salt (Fe-EDTA) for cultivation of Chlorella sp. under mixotrophic condition to evaluate biomass growth and metabolites production. The experimental data depicted enhanced biomass production along with lipids, carbohydrates and proteins at an optimal iron concentration (8 mg/L). Relatively higher biomass production (5.4 g/L; 96 h) with simultaneous total chlorophyll (5 mg/mL ( Chl a/b: 3.7/1.3 mg/mL)), carbohydrates (105 mg/g) and proteins (593 mg/g) was observed with 8 mg/L Fe-EDTA. Total and neutral lipid content of 38% and 15.6% was observed under nutrient deprived conditions. The presence of iron showed distinct influence on the saturated fraction of FAME and increment in oleic acid (omega fatty acids; edible oil). Higher concentrations of Fe-EDTA (10/12 mg/L) depicted incremental fraction of oleic acid. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ultrasound (US) effects during P. marina and C. zofingiensis growth were evaluated. • For P. marina , US treatment did not result in an increase of cell proliferation. • For C. zofingiensis , discontinuous US increased biomass concentration in 64 %. • Distinct behaviors may be related to differences in microalgae cell wall structures. • Carotenoid, chlorophyll, lipid, and protein contents were affected by US treatment. The present work evaluated the ultrasound (US) effects on the growth of Pseudoneochloris marina and Chlorella zofingiensis. For P. marina , US treatment did not increase cell proliferation and reduced cell density when used for 60 min (exponential phase, for 5 days), indicating a possible occurrence of cell damage. For C. zofingiensis , the application of discontinuous US for 10 min resulted in an increase of 65 % in biomass concentration compared to the control. These distinct behaviors indicate that microalgae species react differently to physical stimuli. After US treatment, a reduction of carotenoid, chlorophyll, lipid and protein concentrations was observed, which may be related to changes in the metabolic pathways to produce these compounds. Overall, the results of the present study show the potential of discontinuous US to enhance microalgae cell proliferation. [ABSTRACT FROM AUTHOR]

Cultivation of microalgae Chlorella sp. with livestock waste compost as an alternative nutrient source was investigated in this present study. Five culture media with different nutrient concentrations were prepared. The characteristics of algal growth and lipid production were examined. The results showed that the specific growth rate together with biomass and lipid productivities was different among all the cultures. As the initial nutrient concentration decreased, the lipid content of Chlorella sp. increased. The variations in lipid productivity of Chlorella sp. among all the cultures were mainly due to the deviations in biomass productivity. The livestock waste compost medium with 2000 mg L −1 COD provided an optimal nutrient concentration for Chlorella sp. cultivation, where the highest productivities of biomass (288.84 mg L −1 day −1 ) and lipid (104.89 mg L −1 day −1 ) were presented. [ABSTRACT FROM AUTHOR]

The present study investigates the effect of spent media of acetogenic dark fermentation for mixotrophic algal cultivation for biodiesel production. Mixotrophic growth conditions were optimized in culture flask (250 mL) using Chlorella sp. MJ 11/11. Maximum lipid accumulation (58% w/w) was observed under light intensity, pH, nitrate and phosphate concentration of 100 μmol m −2 s −1 , 7, 2.7 mM and 1.8 mM, respectively. Air lift (1.4 L) and flat panel (1.4 L) reactors were considered for algal cultivation. Air lift showed significant improvement in biomass and lipid production as compared to flat panel reactor. The results could help in development of sustainable technology involving acetogenic hydrogen production integrated with sequential mitigation of spent media by algal cultivation for improved energy recovery. [ABSTRACT FROM AUTHOR]

Cultivation modes of autotrophic microalgae for biodiesel production utilizing open raceway pond were analyzed in this study. Five before screened good microalgae were tested their lipid productivity and biodiesel quality again in outdoor 1000 L ORP. Then, Chlorella sp. L1 and Monoraphidium dybowskii Y2 were selected due to their stronger environmental adaptability, higher lipid productivity and better biodiesel properties. Further scale up cultivation for two species with batch and semi-continuous culture was conducted. In 40,000 L ORP, higher lipid productivity (5.15 versus 4.06 g m −2 d −1 for Chlorella sp. L1, 5.35 versus 3.00 g m −2 d −1 for M . dybowskii Y2) was achieved in semi-continuous mode. Moreover, the financial costs of 14.18 $ gal −1 and 13.31 $ gal −1 for crude biodiesel in two microalgae with semi-continuous mode were more economically feasible for commercial production on large scale outdoors. [ABSTRACT FROM AUTHOR]

[Display omitted] • Chlorella is an excellent lipid resource for biofuels and biorefineries. • Recent advances in cell disruption and lipid extraction methods updated. • Synergistic combination of physicochemical and biological methods is promising. • One-pot multiproduct extraction using green chemicals at low energy is required. Chlorella is a promising microalga for CO 2 -neutral biorefinery that co-produces drop-in biofuels and multiple biochemicals. Cell disruption and selective lipid extraction steps are major technical bottlenecks in biorefinement because of the inherent robustness and complexity of algal cell walls. This review focuses on the state-of-the-art achievements in cell disruption and lipid extraction methods for Chlorella species within the last five years. Various chemical, physical, and biological approaches have been detailed theoretically, compared, and discussed in terms of the degree of cell wall disruption, lipid extractability, chemical toxicity, cost-effectiveness, energy use, scalability, customer preferences, environment friendliness, and synergistic combinations of different methods. Future challenges and prospects of environmental-friendly and efficient extraction technologies are also outlined for practical applications in sustainable Chlorella biorefineries. Given the diverse industrial applications of Chlorella , this review may provide useful information for downstream processing of the advanced biorefineries of other algae genera. [ABSTRACT FROM AUTHOR]

Chlorella protothecoides is a valuable source of lipids that may be used for biodiesel production. The present work shows analysis of the potential of photoheterotrophic cultivation of C. protothecoides under various light intensities aiming to identify the conditions with maximal biomass and lipid content. An increase in light intensity was associated with an increased specific growth rate and a shortened doubling time. Also, the relative total lipid content increased from 24.8% to 37.5% with increase of light intensity. The composition of fatty acid methyl esters was affected by light intensity with the C16–18 fatty acids increased from 76.97% to 90.24% of total fatty acids. However, the content of linolenic acids decreased with the increase of the culture irradiance. These studies indicate that cultures irradiated with high light intensities achieve the minimal specifications for biodiesel quality on linolenic acids and thus are suitable for biodiesel production. [ABSTRACT FROM AUTHOR]

The development of a culture system for Chlorella sp. GD to efficiently produce biomass and oil for biodiesel production was investigated. Chlorella sp. GD was cultivated with 0%, 25%, 50%, 75% and 100% piggery wastewater (diluted by medium) at 300 μmol m −2 s −1 , a 2% CO 2 aeration rate of 0.2 vvm and 26 ± 1 °C; after a 10-day culture in batch cultures, the maximum specific growth rate and biomass productivity of the microalga obtained in 100% piggery wastewater were 0.839 d −1 and 0.681 g L −1 d −1 , respectively. The highest lipid content and lipid productivity were 29.3% and 0.155 g L −1 d −1 at 25% wastewater, respectively. In semi-continuous cultures, the biomass and lipid productivities with 25–75% wastewater ratios were greater than 0.852 and 0.128 g L −1 d −1 , respectively. These results show that Chlorella sp. GD grows efficiently in piggery wastewater, and that a stable growth performance was achieved for long-term microalgal cultivation in a semi-continuous culture. [ABSTRACT FROM AUTHOR]

Chlorella vulgaris , a marine microalgae strain adaptable to 0–50 g L −1 of salinity, was selected for studying the coupling system of saline wastewater treatment and lipid accumulation. The effect of total nitrogen (TN) concentration was investigated on algal growth, nutrients removal as well as lipid accumulation. The removal efficiencies of TN and total phosphorus (TP) were found to be 92.2–96.6% and over 99%, respectively, after a batch cultivation of 20 days. To illustrate the response of lipid accumulation to nutrients removal, C. vulgaris was further cultivated in the recycling experiment of tidal saline water within the photobioreactor. The lipid accumulation was triggered upon the almost depletion of nitrate (<5 mg L −1 ), till the final highest lipid content of 40%. The nitrogen conversion in the sequence of nitrate, nitrite, and then to ammonium in the effluents was finally integrated with previous discussions on metabolic pathways of algal cell under nitrogen deficiency. [ABSTRACT FROM AUTHOR]

In this work, neutral lipids (NLs) extraction capacity and selectivity of six solvents were firstly compared. In addition, an eco-friendly solvent combination of ethyl acetate and ethanol (EA/E) was proposed and tested for lipid extraction from Chlorella sp. cultivated in outdoor raceway ponds and effect of extraction variables on lipid yield were intensively studied. Results indicated that lipid extraction yield was increased with solvent to biomass ratio but did not vary significantly when the value exceeded 20:1. Lipid yield was found to be strongly dependent on extraction temperature and time. Finally, fatty acid profiles of lipid were determined and results indicated that the major components were octadecanoic acid, palmitic acid, linoleic acid and linolenic acid, demonstrating that the lipid extracted from the Chlorella sp. cultivated in outdoor raceway ponds by EA/E was suitable feedstock for biodiesel production. [ABSTRACT FROM AUTHOR]

In this study, different light intensities (80, 160, 240 and 320 μmol/m 2 s) and various mediums including control medium (CM), N/P rich medium (NPM), N rich medium (NM), and P rich medium (PM) were applied for cultivation of Chlorella sp. It was revealed that cultivation of Chlorella sp. in CM under the light intensity of 320 μmol/m 2 s led to a lipid content up to 30% enhancement, which was higher than the results of other cases. A rather high unsaturated fatty acid (UFA) content of 7.5% and unsaturated fatty acid/total fatty acid (UFA/TFA) ratio of 0.73 were obtained under 320 μmol/m 2 s in CM, indicating that the CM-320 system was applicable for the generation of UFA. Moreover, Chlorella sp. cultivated in PM under 320 μmol/m 2 s provided higher TFA content (7.3%), which was appropriate for biofuel production. [ABSTRACT FROM AUTHOR]

[Display omitted] • A potential lutein-producing isolate identified as Chlorella sorokiniana Kh12. • A 2X-HT-9 k condition offered the maximum lutein yield (47.36 mg l−1) under mixotrophy. • It has yielded maximum lutein 13.69 mg g−1, one of the best yields reported so far. • Bead milling was most effective to disrupt algal cell wall and lutein extraction. • Seven minutes bead milling was most efficient for maximum lutein extraction. A bioprospecting study was conducted from Seawater samples collected at Kaohsiung Seacoast, Taiwan. The current research was aimed to isolate potential lutein-producing strain, evaluate and optimize the best cultivation mode, lutein accumulation stage, lutein-extraction method, and condition to recover maximum lutein (main product) and lipid (byproduct). Biorefinery is the latest approach worldwide to extract multi-products for cost-effectiveness. Selected isolate among several isolates, identified as Chlorella sorokiniana Kh12 and exploited under biorefinery concept for lutein and lipid extraction. Kh12 cultivated under mixotrophy: 2X-(HT)-9k yielded maximum biomass (3.46 g L−1) and lutein (13.69 mg g−1) which is among the higher yields reported so far. Among various tested solvents, methanol was the best extractor. Bead milling was most effective to disrupt algal cell walls, seven minutes of milling was best for maximum lutein (7.56 mg g−1) extraction. Kh12 could be a promising candidate for commercial lutein and lipid co-production based on the outcome. [ABSTRACT FROM AUTHOR]

Microalgae have attracted growing attention due to their potential in biofuel feedstock production. However, current understanding of the regulatory mechanisms for lipid biosynthesis and storage in microalgae is still limited. This study revealed that the microalga Chlorella sorokiniana showed sequential accumulation of starch and lipids. When nitrogen was replete and/or depleted over a short period, starch was the predominant carbon storage form with basal levels of lipid accumulation. After prolonged nitrogen depletion, lipid accumulation increased considerably, which was partially due to starch degradation, as well as the turnover of primary metabolites. Lipid accumulation is also strongly dependent on the linear electron flow of photosynthesis, peaking at lower light intensities. Collectively, this study reveals a relatively clear regulation pattern of starch and lipid accumulation that is basically controlled by nitrogen levels. The mixotrophic growth of C. sorokiniana shows promise for biofuel production in terms of lipid accumulation in the final biomass. [ABSTRACT FROM AUTHOR]

Industrial CO 2 -rich flue-gases, owing to their eco-toxicity, have yet to be practically exploited for microalgal biomass and lipid production. In this study, various autotrophic and mixotrophic culture modes for an oleaginous microalga, Chlorella sp. KR-1 were compared for the use in actual coal-fired flue-gas. Among the mixotrophic conditions tested, the fed-batch feedings of glucose and the supply of air in dark cycles showed the highest biomass (561 mg/L d) and fatty-acid methyl-ester (168 mg/L d) productivities. This growth condition also resulted in the maximal population of microalgae and the minimal population and types of KR-1-associated-bacterial species as confirmed by particle-volume-distribution and denaturing-gradient-gel-electrophoresis (DGGE) analyses. Furthermore, microalgal lipid produced was assessed, based on its fatty acid profile, to meet key biodiesel standards such as saponification, iodine, and cetane numbers. [ABSTRACT FROM AUTHOR]

[Display omitted] • BGW can be used as a culture medium for Spirulina (BGWS) and Chlorella (BGWC). • BGWS/BGWC is an innovative cultivation strategy for Spirulina and Chlorella growth. • BGWS condition resulted in higher Spirulina carbohydrate productivity. • BGWC condition resulted in higher Chlorella lipid productivity. Brackish groundwater is promising for the cultivation of economically important microalgae; however, its effects have been evaluated only after nutrient supplementation. In this study, 100% brackish groundwater was evaluated as a culture medium for Spirulina sp. (BGWS) and Chlorella fusca (BGWC). In addition, the effects of supplementation with 25% of the nutrients from Zarrouk (BGWS25) and BG-11 (BGWC25) culture media were evaluated. BGWS and BGWC increased the concentration (68.1% w w−1) and productivity of carbohydrate (35.3 mg L−1 d−1) in Spirulina sp. and increased the concentration (56.4% w w−1) and productivity (13.5 mg L−1 d−1) of lipids in C. fusca biomass, when compared to that in the respective controls. The use of brackish groundwater as the sole culture medium is an innovative alternative for the economic production of biomass rich in carbohydrates and lipids. This has potential applications for biofuel production. [ABSTRACT FROM AUTHOR]

Highlights: [•] Chlorella pyrenoidosa XQ-20044 is able to accumulate lipids in growing cells. [•] One step production of algal lipid was achieved in chemostat culture. [•] Proper SNI was the key for simultaneous algal growth and lipid accumulation. [•] Lipid productivity was significantly enhanced by continuous culture. [Copyright &y& Elsevier]

Highlights: [•] Better results were obtained in the factors selection stage by GA. [•] RSM allowed obtaining reliable models that could fit the responses. [•] The composition of a medium to maximize lipid storage in Chlorella sp. was defined. [•] Enzymatic hydrolysate improved lipid storage in Chlorella sp. [•] Culture in an air-lift bioreactor is viable. [ABSTRACT FROM AUTHOR]

Highlights: [•] High-light-intensity is effective in improving the productivity of Chlorella. [•] Chlorella shows more stable growth in the 12:12-h light–dark cycle conditions. [•] The starch and lipids yields more increase in the continuous light conditions. [•] Long-chain fatty acids accumulate in Chlorella grown in sulfur-deficient medium. [•] Accumulation of starch and lipids vary in eight strains of six Chlorella species. [ABSTRACT FROM AUTHOR]

Highlights: [•] Environmental factors were proved to be helpful to lipid accumulation. [•] NaCl, Fe3+ and nitrogen starvation together made lipid content increase to 2.5 times. [•] Both high and low temperature could promote lipid accumulation. [•] UTEX 2341 was proved to be a potential species for high-quality biodiesel production. [ABSTRACT FROM AUTHOR]

Highlights: [•] TPP was used for concentrating microalgae cells from broth for the first time. [•] TPP efficiently concentrated microalgae biomass to the interlayer of the system. [•] Ethanol/DKP ratio, initial concentration and temperature were crucial to efficiency. [•] TPP enhanced lipid extraction while lipid quality was not disturbed. [•] Low energy consumption and non-toxic chemicals input are additional advantages. [ABSTRACT FROM AUTHOR]

Harvest water recycling for Chlorella zofingiensis re-cultivation under nutrient limitation was investigated. Using 100% harvest water, four cultures were prepared: Full medium, P-limited medium, N-limited medium and N- and P-limited medium, while another full medium was also prepared using 50% harvest water. The results showed that the specific growth rate and biomass productivity ranged from 0.289 to 0.403 day −1 and 86.30 to 266.66 mg L −1 day −1 , respectively. Nutrient-limited cultures witnessed much higher lipid content (41.21–46.21% of dry weight) than nutrient-full cultures (26% of dry weight). The N- and P-limited medium observed the highest FAME yield at 10.95% of dry weight, while the N-limited culture and P-limited culture shared the highest biodiesel productivity at 20.66 and 19.91 mg L −1 day −1 , respectively. The experiment on harvest water recycling times demonstrated that 100% of the harvest water could be recycled twice with the addition of sufficient nutrients. [ABSTRACT FROM AUTHOR]

The oleaginous alga Chlorella protothecoides accumulates lipid in its biomass when grown in nitrogen-restricted conditions. To assess the relationship between nitrogen provision and lipid accumulation and to determine the contribution of photosynthesis in mixotrophic growth, C. protothecoides was grown in mixo- and heterotrophic nitrogen-limited continuous flow cultures. Lipid content increased with decreasing C/N, while biomass yield on glucose was not affected. Continuous production of high lipid levels (57% of biomass) was possible at high C/N (87–94). However, the lipid production rate (2.48 g L −1 d −1 ) was higher at D = 0.84 d −1 with C/N 37 than at D = 0.44 d −1 and C/N 87 even though the lipid content of the biomass was lower (38%). Photosynthesis contributed to biomass and lipid production in mixotrophic conditions, resulting in 13–38% reduction in CO 2 production compared with heterotrophic cultures, demonstrating that photo- and heterotrophic growth occurred simultaneously in the same population. [ABSTRACT FROM AUTHOR]

Abstract: Microalga Chlorella protothecoides can accumulate high proportion of lipids during the heterotrophic growth with glucose as the carbon source. However, its commercial application is restricted due to the high cost of the carbon source. In this study, the wasted activated sludge (WAS) was hydrolyzed after ultrasonic pre-treatment and the hydrolyzate obtained was used as an alternative carbon source for algal biomass and biodiesel production. The results indicate that C. protothecoides can proliferate in the WAS hydrolyzate and accumulate biolipid. The final lipid content of the culture fed with the hydrolyzate was 21.5±1.44% (weight percent) after 156h cultivation in flasks and the maximum biomass obtained was 0.5gL−1. Acetic acid and isovaleric acid were favorable carbon sources for cell growth. The soluble microbial products (SMP) presents in the hydrolyzate can also be used as a carbon source for cell growth. [Copyright &y& Elsevier]

Highlights: [•] Chlorella sp. (FACHB-1748) could utilize urea as nitrogen source. [•] Chlorella sp. could be cultured in 70L bioreactor with natural sunlight under outdoor conditions. [•] The lipid productivity could be improved under the condition of sodium chloride or acetate. [•] The quality properties of the biodiesel met the standard of National Petroleum Agency (ANP255). [ABSTRACT FROM AUTHOR]

Highlights: [•] Comparison of lipid extractions for Chlorella sp. with low- and high-lipid content. [•] Lipid extractions of wet microalgae biomasses by four organic-nanoclays. [•] ∼100% conversion of the extracted lipid’s fatty acids to biodiesel. [•] One of most effective lipid extraction in wet microalgal biomass. [ABSTRACT FROM AUTHOR]

Abstract: A cultivation system in the two-stage photoautotrophic–photoheterotrophic/mixotrophic mode was adapted to maximize lipid productivity of two freshwater strains of Chlorella sp. grown in brewery wastewater (BWW). The endogenous Chlorella sp. isolated from BWW had a higher growth rate than wild-type Chlorella vulgaris (UTEX-265) while C. vulgaris (UTEX-265) had a higher maximal biomass and lipid contents than that of endogenous Chlorella sp., resulting in more than 90% of the inorganic nutrients in both total nitrogen (TN) and phosphorus (TP) was removed during the first stage in the two-stage photoautotrophic–photoheterotrophic mode in each Chlorella sp. The maximal biomass and lipid contents of C. vulgaris (UTEX-265) for single stage photoautotrophic cultivation were 1.5g/L and 18%, respectively. Importantly, during two-stage photoautotrophic–photoheterotrophic cultivation for C. vulgaris (UTEX-265), the biomass was increased to 3.5g/L, and the lipid productivity was increased from 31.1 to 108.0mg/Lday. [Copyright &y& Elsevier]

Abstract: Microalgae-derived lipids are an alternative to vegetable and fossil oils, but lipid content and quality vary among microalgae strains. Selection of a suitable strain for lipid production is therefore of paramount importance. Based on published results for 96 species, nine strains were selected to study their biomass, total fatty acid, and triacylglycerol (TAG) production under nitrogen-sufficient and deficient cultivation conditions. Under nitrogen-deficient conditions, Chlorella vulgaris, Chlorella zofingiensis, Neochloris oleoabundans, and Scenedesmus obliquus, accumulated more than 35% of their dry weight as TAGs. Palmitic and oleic acid were the major fatty acids produced. The main difference between these strains was the amount of biomass that was produced (3.0–7.8-fold increase in dry weight) and the duration that the biomass productivity was retained (2–7days) after nitrogen depletion. S. obliquus (UTEX 393) and C. zofingiensis (UTEX B32) showed the highest average TAG productivity (322 and 243mgl−1 day−1). [Copyright &y& Elsevier]

Abstract: For overcoming the long period of seed cultured photoautotrophically and inadequate cell supply for the inoculation of microalgae photoautotrophic cultivation, a model for the photoautotrophic culture of three Chlorella species with heterotrophic cells as seed was investigated. The model can not only take advantages of rapid cell growth in heterotrophic process for preparation of cells as seed but also increase the biomass and lipid productivities of the microalgae cultivated photoautotrophically. The results showed that biomass productivities of Chlorella pyrenoidosa, Chlorella ellipsoidea and Chlorella vulgaris cultured by heterotrophy were 20.9, 26.9 and 25.2 times higher than those by photoautotrophy in seed culturing period. In the subsequent photoautotrophic culture, the biomass and lipid productivities of C. pyrenoidosa, C. ellipsoidea and C. vulgaris with heterotrophic seed were 1.91, 1.51, 1.48 and 1.66, 1.37, 1.42 times higher than those with photoautotrophic seed. Furthermore, the culture model was also carried out successfully outdoor. [Copyright &y& Elsevier]

Abstract: The oleaginous microalga Chlorella sp. LAM-H screened from freshwater was proven to be a prospective feedstock for oil production according to its fatty acid composition. In order to enhance lipid production, response surface methodology (RSM) was used with central composite design (CCD) to optimize the heterotrophic cultivation of microalgae. The experiment results showed that a satisfactory second-order polynomial regression equation was achieved with a high coefficient of determination (R 2 =0.9911) in analysis of variance. The effects of individual factors and their interactions on lipid productivity were successfully revealed. The greatest lipid productivity reached 247.16mgl−1 d−1 under the optimal conditions of glucose concentration 26.2gl−1, sodium nitrate concentration 2.06gl−1 and temperature 28.18°C. Moreover, validation tests were performed and the results were very close to the predicted values. It was demonstrated that the obtained model was effective for predicting lipid productivity of the isolated microalga. [Copyright &y& Elsevier]

Abstract: Lipids obtained from Chlorella protothecoides in heterotrophic cultivation are considered a suitable feedstock for biodiesel production. In this study, glucose fed-batch fermentation was performed to increase final biomass and lipid production. The biomass productivity and lipid productivity were 6.28 and 2.06g/L day, respectively. Biomass/glucose conversion and the lipid/glucose conversion were 43.3% and 14.2%, respectively. Extraction of lipids from algae has been identified as a key bottleneck in bioprocessing operations. Supercritical carbon dioxide (SC-CO2) was applied for neutral lipids extraction and the SC-CO2 kinetics was investigated by the Goto et al. model. The modeling showed a good fit with experimental data. Additionally, neutral lipids extracted by SC-CO2 displayed a suitable fatty acid profile for biodiesel [mainly C18:1 (60.0%), C18:2 (18.7%) and C16:0 (11.5%)]. Our study demonstrated the ability to produce high levels of neutral lipids through heterotrophic algal culture and subsequent extraction of lipids with SC-CO2 method developed. [Copyright &y& Elsevier]

Abstract: A novel cultivation strategy called “sequential heterotrophy–dilution–photoinduction” was developed for efficient algal biomass and lipid production. Three Chlorella species were first cultivated heterotrophically to achieve high cell density, then the broth was diluted to suitable concentration (2–5g/L) and transferred to light environment for photoinduction. With this strategy, the Chlorella intracellular protein and chlorophyll increased rapidly to 50.87% and 32.97mg/g by a 12-h illumination, which were close to the level of cells cultivated photoautotrophically. Moreover, the lipid contents were increased by 84.57%, 70.65% and 121.59% within 24-h photoinduction for C. vulgaris, C. pyrenoidosa and C. ellipsoidea, respectively. Maximum lipid content as 26.11% of biomass and maximum lipid productivity of 89.89mg/L/d was both accomplished by C. pyrenoidosa. Further outdoor experiments showed consistent patterns. Therefore, the proposed strategy provided an effective approach for microalgal biomass production to meet the urgent need for both health food and biodiesel. [Copyright &y& Elsevier]

Abstract: The green microalga strain, Botryococcus braunii KMITL 2, was isolated from a freshwater reservoir in central Thailand, and the effects of light, nitrogen, phosphorus, iron, cultivation time and salinity on lipid production were studied by varying parameters one at a time. When cultured in Chlorella medium containing 222mgL−1 phosphorus () under continuous illumination of 200μEm−2 s−1 with a salinity of 0psu, a maximum lipid content of 54.69±3.13% was obtained. Its high lipid content makes strain KMITL 2 a potential source for biodiesel production in tropical regions. [Copyright &y& Elsevier]

Abstract: Culturing microalgae using natural sunlight is an effective way to reduce the cost of microalgae-based biodiesel production. In order to evaluate the feasibility of culturing Chlorella zofingiensis outdoors for biodiesel production, effects of nitrogen limitation and initial cell concentration on growth and lipid accumulation of this alga were investigated in 60L flat plate photobioreactors outdoors. The highest μ max and biomass productivity obtained was 0.994day−1 and 58.4mgL−1 day−1, respectively. The lipid content was much higher (54.5% of dry weight) under nitrogen limiting condition than under nitrogen sufficient condition (27.3%). With the increasing initial cell concentrations, the lipid contents declined, while lipid concentrations and productivities increased. The highest lipid content, lipid concentration, and lipid productivity obtained was 54.5%, 536mgL−1 and 22.3mgL−1 day−1, respectively. This study demonstrated that it was possible to culture C. zofingiensis under outdoor conditions for producing biodiesel feedstock. [Copyright &y& Elsevier]

Abstract: Mass cultivation of microalgae for biofuel production depends heavily on the performance of the microalgae strains used. In this study, 60 algae-like microorganisms collected from different sampling sites in Minnesota were examined using multi-step screening and acclimation procedures to select high-lipid producing facultative heterotrophic microalgae strains capable of growing on concentrated municipal wastewater (CMW) for simultaneous energy crop production and wastewater treatment. Twenty-seven facultative heterotrophic microalgae strains were found, among which 17 strains were proved to be tolerant to CMW. These 17 top-performing strains were identified through morphological observation and DNA sequencing as Chlorella sp., Heynigia sp., Hindakia sp., Micractinium sp., and Scenedesmus sp. Five strains were chosen for other studies because of their ability to adapt to CMW, high growth rates (0.455–0.498d−1) and higher lipid productivities (74.5–77.8mgL−1 d−1). These strains are considered highly promising compared with other strains reported in the literature. [Copyright &y& Elsevier]

Abstract: To reduce the cost of algal biomass production, mathematical model was developed for the first time to describe microalgae growth, lipid production and glycerin consumption under photoheterotrophic conditions based on logistic, Luedeking–Piret and Luedeking–Piret-like equations. All experiments were conducted in a 2L batch reactor without considering CO2 effect on algae’s growth and lipid production. Biomass and lipid production increased with glycerin as carbon source and were well described by the logistic and Luedeking–Piret equations respectively. Model predictions were in satisfactory agreement with measured data and the mode of lipid production was growth-associated. Sensitivity analysis was applied to examine the effects of certain important parameters on model performance. Results showed that S0, the initial concentration of glycerin, was the most significant factor for algae growth and lipid production. This model is applicable for prediction of other single cell algal species but model testing is recommended before scaling up the fermentation of process. [ABSTRACT FROM AUTHOR]

Abstract: We describe a methodology to investigate the potential of given microalgae species for biodiesel production by characterizing their productivity in terms of both biomass and lipids. A multi-step approach was used: determination of biological needs for macronutrients (nitrate, phosphate and sulphate), determination of maximum biomass productivity (the “light-limited” regime), scaling-up of biomass production in photobioreactors, including a theoretical framework to predict corresponding productivities, and investigation of how nitrate starvation protocol affects cell biochemical composition and triggers triacylglycerol (TAG) accumulation. The methodology was applied to two freshwater strains, Chlorella vulgaris and Neochloris oleoabundans, and one seawater diatom strain, Cylindrotheca closterium. The highest total lipid content was achieved with N. oleoabundans (25–37% of DW), while the highest TAG content was found in C. vulgaris (11–14% of DW). These two species showed similar TAG productivities. [ABSTRACT FROM AUTHOR]

Abstract: Chlorella vulgaris was used to study algal lipid production with wastewater treatment. Artificial wastewater was used to cultivate C. vulgaris in a column aeration photobioreactor (CAP) under batch and semi-continuous cultivation with various daily culture replacements (0.5l–1.5l per 2l reactor). The cell density was decreased from 0.89g/l with the daily replacement of 0.5l to 0.28g/l with 1.5l replacement. However, C. vulgaris culture achieved the highest lipid content (42%, average value of the phase) and the lipid productivity (147mg/ld−1) with daily replacement of 1.0l. And then the nutrient removal efficiency were 86% (COD), 97% () and 96% (TP), respectively. Analyses of energy efficiency showed that the net energy ratio (NER) for lipid production with daily replacement of 1.0l (1.25) was higher than the other volume replacement protocols. And cost analyses showed that the algal biomass can be competitive with petroleum at US$ 63.97 per barrel with the potential credit for wastewater treatment. According to the above results, it is concluded that the present research will lead to an economical technology of algal lipid production. [ABSTRACT FROM AUTHOR]

Abstract: To increase the lipid productivity and thus to reduce the production cost of microalgal biodiesel, effects of cultivation conditions including KNO3-level, CO2 concentration and irradiance on the cell growth, chlorophyll a content and lipid accumulation of Chlorella vulgaris were systematically investigated in a membrane sparged photobioreactor. The biochemical compositions including carbohydrates, proteins and lipids were analyzed simultaneously by the FT-IR spectroscopy. The results showed that the largest biomass productivity and the highest lipid content were obtained at different cultivation conditions. The algae should be harvested at a point that optimized the biomass productivity and lipid content. When the cultivation conditions were controlled at 1.0mM KNO3, 1.0% CO2 and 60μmol photons m−2 s−1 at 25°C, the highest lipid productivity obtained was 40mgL−1 d−1, which was about 2.5-fold that had been reported by . The influences of cultivation conditions on the cell growth, lipid accumulation, and other biochemical compositions of cells were further discussed and illustrated by a schematic which was also useful for other microalgal species. [Copyright &y& Elsevier]

Abstract: The present study aimed at investigating the carbon metabolism in terms of carbon dioxide fixation and its destination in microalgae cultivations. To this purpose, analysis of growth parameters, media of cultivation, biomass composition and productivity and nutrients balance were performed. Four microalgae suitable for mass cultivation were evaluated: Dunaliella tertiolecta SAD-13.86, Chlorella vulgaris LEB-104, Spirulina platensis LEB-52 and Botryococcus braunii SAG-30.81. Global rates of carbon dioxide and oxygen were determinated by a system developed in our laboratory. B. braunii presented the highest CO2 fixation rate, followed by S. platensis, D. tertiolecta and C. vulgaris (496.98, 318.61, 272.4 and 251.64mgL−1 day−1, respectively). Carbon dioxide fixated was mainly used for microalgal biomass production. Nitrogen, phosphorus (calcium for D. tertiolecta), potassium and magnesium consumption rates (mg gX−1) were evaluated for the four microalgae. Biomass composition presented a predominance of proteins but also a high amount of lipids, especially in D. tertiolecta and B. braunii. [Copyright &y& Elsevier]

The microalgae, Chlorella sp., were cultivated in various culture modes to assess biomass and lipid productivity in this study. In the batch mode, the biomass concentrations and lipid content of Chlorella sp. cultivated in a medium containing 0.025–0.200gL−1 urea were 0.464–2.027gL−1 and 0.661–0.326gg−1, respectively. The maximum lipid productivity of 0.124gd−1 L−1 occurred in a medium containing 0.100gL−1 urea. In the fed-batch cultivation, the highest lipid content was obtained by feeding 0.025gL−1 of urea during the stationary phase, but the lipid productivity was not significantly increased. However, a semi-continuous process was carried out by harvesting the culture and renewing urea at 0.025gL−1 each time when the cultivation achieved the early stationary phase. The maximum lipid productivity of 0.139gd−1 L−1 in the semi-continuous culture was highest in comparison with those in the batch and fed-batch cultivations. [Copyright &y& Elsevier]

• Electric field strength (E) and the specific energy input are the decisive factors. • PEF treatment increased the lipid extraction yield by up to 166.67% • An excessively high E decrease the extracted biodiesel's quality. • The liquid yields and the cell disintegration of Chlorella are controllable. • The leakage of cell contents reveals the mechanism of PEF treatment. In order to solve the increasingly serious problems of energy and environment, microalgae are used as a raw material for extracting lipids to produce biodiesel. Prior to the extraction of lipids, microalgae were treated with high-voltage pulsed electric field (PEF) to break the cell membrane. It was found that the lipid extraction yield depends on the electric field strength (E) and the specific energy input (Wsp), and has a certain relationship with the cell disintegration rate of Chlorella. The perforation degree of the Chlorella's cell membrane by PEF treatment is controllable, moderate perforation can be ensured by controlling the power parameters. PEF treatment significantly improved the extraction yield of lipids. Compared with the test samples without PEF treatment, PEF treatment increased the lipid extraction yields by up to 166.67%. However, an excessively high voltage will cause the quality of the extracted biodiesel to decrease. [ABSTRACT FROM AUTHOR]

• Chlorella vulgaris, Scenedesmus sp. and Synechococcus sp. were used in this study. • Higher biomass yield of 0.54 gL−1 was obtained in Chlorella vulgaris. • High lipid content 36% was obtained in Scenedesmus sp. over other strains. • Neutral lipids in C. vulgaris , and Scenedesmus sp. was 57 and 54% respectively. • High SFAs and low PUFAs were observed in C. vulgaris , and Scenedesmus sp. Selection of indigenous and potential algal strain with high lipid content is paramount challenge in the avenues of microalgal biodiesel production. Particularly, hyper lipid producing algae with maximal triacyglycerols (TAGs) content and preferable fatty acid composition is of interest for sustainable biodiesel. Hence, the present study on comparative assessment of Chlorella vulgaris, Scenedesmus sp. and Synechococcus sp. was done in terms of cell density, lipid, TAGs and fatty acid. Higher biomass yield was obtained in Chlorella vulgaris (0.54 gL−1) on 13th day while maximal lipid content of 36% was observed in Scenedesmus sp. followed by Chlorella vulgaris (33%). Lipidomic analysis revealed higher non-polar lipids in Chlorella vulgaris (57%) and Scenedesmus sp. (54%), whereas in Synechococcus sp. 69% polar lipids were present. In fatty acid profile, C24:0 (22.11%) was predominant in Chlorella vulgaris, while C20:0 (31.72%) and C18:2 (22.26%) was prevalent in Scenedesmus sp. and Synechococcus sp. respectively. [ABSTRACT FROM AUTHOR]

• The nitrogen sources and concentrations for the growth of the alga was optimized. • The lipid content of algal cells reached 53.5% when the light path was 5 cm. • The maximal lipid productivity obtained was 66.7 mg L−1 day−1 in FPPs outdoors. • More than 90% of the total fatty acids of this microalga were C16/C18. • Chlorella sp. GN1 was a promising microalgal species for biofuel production. To assess the potential of Chlorella sp. GN1 for producing biodiesel raw materials in flat plate photobioreactors (FPPs) outdoors, we optimized the nitrogen sources and concentrations for the growth of the algae. The effects of different light paths of FPPs on the growth, lipid accumulation, and fatty acids of Chlorella sp. GN1 were also studied. As the light path of the FPPs was reduced, the alga could accumulate lipids rapidly, achieving high lipid content and lipid productivity outdoors. The highest lipid content obtained was 53.5%, when the light path was 5 cm. In addition, the lipid productivity was 66.7 mg L−1 day−1. The main fatty acids were C16/C18, accounting more than 90% of the total fatty acids. Results showed that Chlorella sp. GN1 had the ability to accumulate large quantities of lipids in FPPs outdoors and was a promising microalgal species for biofuel production. [ABSTRACT FROM AUTHOR]