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[Display omitted] • Two-stage fermentation process proposed for efficient bioconversion. • Engineered Y. lipolytica could convert syngas into β-carotene and lipids. • Tolerance up to 20 g/L acetic acid seen in the yeast strain. • Optimal lipid and β-carotene production were found at pH 6.0 in bioreactors. • The dominant lipid identified was C18:1, which is suited for biodiesel production. An engineered Yarrowia lipolytica strain was successfully employed to produce β-carotene and lipids from acetic acid, a product of syngas fermentation by Clostridium aceticum. The strain showed acetic acid tolerance up to concentrations of 20 g/L. Flask experiments yielded a peak lipid content of 33.7 % and β-carotene concentration of 13.6 mg/g under specific nutrient conditions. The study also investigated pH effects on production in bioreactors, revealing optimal lipid and β-carotene contents at pH 6.0, reaching 22.9 % and 44 mg/g, respectively. Lipid profiles were consistent across experiments, with C18:1 being the dominant compound at approximately 50 %. This research underscores a green revolution in bioprocessing, showing how biocatalysts can convert syngas, a potentially polluting byproduct, into valuable β-carotene and lipids with a Y. lipolytica strain. [ABSTRACT FROM AUTHOR]

[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]

• Bioremediation with flue gas CO 2 utilization potential of Chlorella was tested. • Wastewater cocktail based biodiesel and lutein production in open raceway ponds. • 100% nitrogenous substance with 85–91% carbon-phosphorus remediation were obtained. • Biomass and lutein productivity of 6.21 ± 0.16, 1.2 ± 0.08 g m−2 day−1 was achieved. • Two-fold increase in lipid content and 80.74 ± 0.07 mg L−1 day−1 CO 2 was utilized. We evaluated wastewater remediation and CO 2 utilization potential of Chlorella minutissima from flue gas in a raceway pond, while synthesizing lutein and lipid for potential healthcare and biofuel application. A mix of 20% kitchen waste, 10 g L−1 of poultry litter waste and 5% flue gas was maintained while cultivating the microalga. Complete removal of nitrate, nitrite and ammonium, 85% carbon and 91% phosphorus was observed. An average areal biomass productivity of 4.06 ± 0.12 g m−2 day−1 with a specific growth rate of 0.34 ± 0.03 day−1 was observed within 9 days. Biomass productivity of 6.21 ± 0.16 g m−2 day−1 with a specific growth rate of 0.34 ± 0.03 day−1 was achieved during winter. Furthermore, lipid content with appropriate fatty acid composition 1.04:1 (saturation:unsaturation) increased from 25% to 58%. Additionally, lutein productivity of 1.2 ± 0.08 mgL−1 day−1, while utilizing 80.74 ± 0.07 mg L−1 day−1 of CO 2 from 5% flue gas was obtained. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The monoethanolamine increased the amount of dissolved carbon by up to 500%. • The fed-batch culture with monoethanolamine had increased carbon during cultivation. • Fed-batch culture with MEA had increased proteins and lipids of the Chlorella biomass. Abstract The aim of this study was to evaluate the interaction between the periodic addition of monoethanolamine (MEA) and CO 2 during the cultivation of Chlorella fusca LEB 111. For this purpose, MEA has been added in abiotic assays, followed by fed-batch cultures with that green alga and the absorbent. BG-11 medium shown a higher potential of CO 2 absorption with MEA addition, and the bicarbonate was the chemical species of carbon prevailing in the chemical equilibrium. The periodic addition of MEA did not reduce the kinetics of growth, promoted a higher accumulation of DIC (81.4 mg L−1) in the medium and protein (44.0% w w−1) and lipid (30.8% w w−1) concentrations in the biomass of C. fusca LEB 111. Therefore, it was demonstrated that fed-batch culture with MEA increased CO 2 fixation and the biomolecule synthesis as proteins and lipids. [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]

This study investigates the year-round production potential and quality of biodiesel from wastewater treatment high rate algal pond (WWT HRAP) biomass and how it is affected by CO 2 addition to the culture. The mean monthly pond biomass and lipid productivities varied between 2.0 ± 0.3 and 11.1 ± 2.5 g VSS/m 2 /d, and between 0.5 ± 0.1 and 2.6 ± 1.1 g/m 2 /d, respectively. The biomass fatty acid methyl esters were highly complex which led to produce low-quality biodiesel so that it cannot be used directly as a transportation fuel. Overall, 0.9 ± 0.1 g/m 2 /d (3.2 ± 0.5 ton/ha/year) low-quality biodiesel could be produced from WWT HRAP biomass which could be further increased to 1.1 ± 0.1 g/m 2 /d (4.0 ton/ha/year) by lowering culture pH to 6–7 during warm summer months. CO 2 addition, had little effect on both the biomass lipid content and profile and consequently did not change the quality of biodiesel. [ABSTRACT FROM AUTHOR]

Oleaginous microalgae Nannochloropsis sp. was selected as potential strain for CO 2 mitigation into lipids and pigments. The synergistic effects of light intensity and photoperiod were evaluated to provide the adequate light energy for this strain. The saturation light intensity was 60 μmol·photon·m −2 s −1 . With full illumination, the biomass obtained was 0.850 ± 0.16 g·L −1 with a lipid content of 44.7 ± 1.2%. The pigments content increased with increasing light energy supply. Three main operating factors including initial cell concentration, CO 2 content and gas flow rate were optimized through Response Surface Methodology. The feedings with low CO 2 content at high gas flow rate gave the maximum biomass but with low lipid content. After optimization, the biomass and lipid production were increased up to 1.30 ± 0.103 g·L −1 and 0.515 ± 0.010 g·L −1 , respectively. The CO 2 fixation rate was as high as 0.729 ± 0.04 g·L −1 d −1 . The fatty acids of Nannochloropsis sp. lipids were mainly C16-C18 indicating its potential use as biodiesel feedstocks. [ABSTRACT FROM AUTHOR]

Filamentous microalgae Tribonema is promising for biodiesel production in terms of high lipid content, easy harvesting and good contamination tolerance. As high lipid productivity is a key basis, several methods including different culture medium, phosphorus, iron and CO 2 inductions were tested to enhance lipid productivity in Tribonema minus . T. minus subjected to BG11-freshwater medium achieved a favorable lipid productivity of 216.18 mg L −1 d −1 , much higher than those in other culture medium (BG11-S, Kuhl, f/2, f, 2f, BBM, ASW and ES). Secondly, the optimal phosphorus, iron and CO 2 concentrations for high lipid productivity of T. minus were obtained, respectively. Finally, the cells of T. minus grown in optimized BG11 medium containing 80 mg L −1 KH 2 PO 4 and 6 mg L −1 FeC 6 H 5 O 7 ·NH 4 OH with 2% CO 2 achieved a lipid productivity of 384.67 mg L −1 d −1 , representing a 1.56-fold increase from the control. Therefore, the strategy to enhance lipid productivity of T. minus was successfully proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lipid synthesis by oleaginous yeasts is a promising alternative to vegetable oils. • Y. lipolytica can bioconvert mixed C 2 -C 6 VFAs from gas fermentation into lipids. • Yarrowia lipolytica shows preference for acetic acid over butyric and caproic acids. • Y. lipolytica used the VFA mixture at a rate of 0.664 g/L·h with lipid accumulation. • The lipid profile obtained shows its high suitability for biodiesel production. Volatile fatty acids (VFAs) can be considered as low-cost carbon substrates for lipid accumulation by oleaginous yeasts. This study demonstrates that a common mixture of VFAs, typically obtained from the anaerobic fermentation of C1-gases by some acetogenic bacteria, can be used in a second aerobic fermentation with the yeast Yarrowia lipolytica to obtain lipids as precursors of biodiesel. In the batch experiments, the preference of Yarrowia lipolytica W29 for acetic acid over butyric and caproic acids was demonstrated, with the highest consumption rate reaching 0.664 g/L·h. In the bioreactor experiments, the amount initial biomass inoculated, as well as the initial acid concentration, were found to have a significant influence on the process. Though the lipid content was relatively low, it can be optimized and further improved. Oleic, linoleic and palmitic acids accounted for about 80 % of the fatty acids in the lipids, which makes them suitable for biodiesel. [ABSTRACT FROM AUTHOR]

Highlights: [•] Biomass and lipid yields achieved a theoretical model of 1+1>2 by mixed culture. [•] A double system bubble column photo-bioreactor was designed for mixing cultivation. [•] Growth curves of yeast and alga were confirmed in mixing cultivation system. [•] Real-time online detection of off-gas showed synergistic effects on O2/CO2 balance. [•] Analysis of metabolite variations proved synergistic effects on substance exchange. [Copyright &y& Elsevier]

Highlights: [•] Chlamydomonas sp. JSC4 was isolated from southern Taiwan sea coast. [•] Lipid productivity was assayed after cultivation under different CO2 concentrations. [•] Lipid productivity was 169.1mg/L/d as the best in most of the previous reports. [•] Result showed a potential to develop the system of microalga-based lipid production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Microalgae metabolic engineering for lipid and isoprenoid production is reviewed. • Comprehensive metabolic maps with metabolic engineering strategies are presented. • Challenges and perspectives of microalgae metabolic engineering are discussed. Microalgae are promising sustainable resources because of their ability to convert CO 2 into biofuels and chemicals directly. However, the industrial production and economic feasibility of microalgal bioproducts are still limited. As such, metabolic engineering approaches have been undertaken to enhance the productivities of microalgal bioproducts. In the last decade, impressive advances in microalgae metabolic engineering have been made by developing genetic engineering tools and multi-omics analysis. This review presents comprehensive microalgal metabolic pathways and metabolic engineering strategies for producing lipids, long chain-polyunsaturated fatty acids, terpenoids, and carotenoids. Additionally, promising metabolic engineering approaches specific to target products are summarized. Finally, this review discusses current challenges and provides future perspectives for the effective production of chemicals and fuels via microalgal metabolic engineering. [ABSTRACT FROM AUTHOR]

Highlights: [•] Isochrysis galbana was grown in batch, intermittent fed-batch and semi-continuous mode. [•] Increased biomass productivity was observed for CO2 enriched medium. [•] The intermittent fed-batch mode was proved to be useful for lipid accumulation. [•] Irradiance, C:N ratio and replacement time exhibit greatest impact on productivity. [•] The semi-continuous mode showed superior productivities of biomass and lipids. [Copyright &y& Elsevier]

Abstract: Over 100 green-colored colonies were isolated from environmental samples when cultivating on a BG11 agar medium, and 4 strains showing different morphologies were selected based on light microscopic observation. Among these strains, the microalgal species with the highest growth rate under 10% CO2 was identified as Ettlia sp. YC001 using an 18S rDNA-based phylogenetic analysis and morphological comparison. The highest cell density of 3.10g/L (based on dry cell weight) and biomass productivity of 0.19g/L/d were obtained under 5% CO2 after 16days. The lipid content and productivity were also up to 42% of the dry cell weight and 80.0mg/L/d, respectively. The color of the Ettlia sp. YC001 culture changed from green to red after a month due to the accumulation of certain carotenoids. Therefore, it would seem that Ettlia sp. YC001 is appropriate for mitigating CO2 due to its high biomass productivity, and a suitable candidate for producing biodiesel and high-value products. [Copyright &y& Elsevier]

Abstract: The effects of cultivation of Scenedesmus obliquus in nutrient medium supplemented with 0.03%, 3, 9% and 12% CO2 or 2.5–20mgL−1 of Fe3+ on dry weight of biomass (DW), total lipid accumulation (TL contents) and total lipid productivity (TLP) were evaluated under indoor conditions. The accumulation of TL and TLP showed an increasing trend with increasing of CO2 or Fe3+ levels. In cultures with 12% CO2 or 20mg/L Fe3+, maximum TL contents of 33.14% and 28.12%, respectively were obtained. These lipids displayed a fatty acid profile which is suitable for biodiesel production as the most abundant compounds were oleic (32.19–34.44%), palmitic (29.54–25.12%) and stearic (12.26–16.58% of total FAMEs) acids. The properties of biodiesel obtained from S. obliquus, were the same with those specification for biodiesel standards including ASTM D 6751 (American Society for Testing Material) and the European Standard En 14214. Thus, S. obliquus biomass could be used as suitable feedstock for biodiesel production. [Copyright &y& Elsevier]

Abstract: This study focuses on the cell growth and the neutral lipid production modeling of Chlamydomonas reinhardtii in terms of different ammonium concentrations. Autotrophy was maintained during growth in a double walled bioreactor, using Tris Phosphate (TP medium) with only CO2 and NH4Cl as sole sources of carbon and nitrogen, respectively. Nitrogen depletion results in an increase in neutral lipid production with an indirect effect on the growth of algal cells. Modified Baranyi–Roberts and logistic equations were used to describe the cell growth whereas Luedeking–Piret equation was used for neutral lipid production kinetics. Sensitivity analysis shows that the model equations satisfactorily predict the cell growth and lipid production. Based on the mathematical model predictions, growing algal cells in higher ammonium containing medium initially and switching to low ammonium containing medium in a later stage may result in elevated amounts of lipid production, which may be used for scale up and commercialization. [Copyright &y& Elsevier]

Abstract: In this study, the effects of different carbon sources on cell growth and lipid accumulation of Scenedesmus quadricauda were investigated. Results showed that S. quadricauda could grow on photoautotrophic, heterotrophic and mixotrophic modes. The lipid yield of S. quadricauda was much lower in the culture containing NaHCO3 as only carbon source, while CO2 and glucose concentration significantly influenced cell yield and lipid accumulation in photoautotrophic and heterotrophic culture, respectively. Furthermore, lipid content of S. quadricauda in mixotrophic culture (33.1% of cell dry weight) was much higher than that in photoautotrophic and heterotrophic cultivation (14–28%). Therefore, upon comparing these three trophic modes, present results revealed mixotrophy was the optimal culture method for S. quadricauda to produce lipid. Besides, it was a feasible and promising strategy to culture S. quadricauda using starch wastewater as raw material, which could reduce chemical oxygen demand (COD) of wastewater and the cost of biodiesel production. [Copyright &y& Elsevier]

Abstract: An approach based on energy gain was utilized to optimize algal cultivation in bubble columns. Net energy gain was estimated considering the energy input for mixing and providing carbon dioxide, and the energy that can be generated from the lipids extracted from the algal biomass. Energy input for sparging was minimized based on the gas-to-culture volume ratio and energy output from lipid production was maximized based on nitrate and CO2 levels. Sparging at a gas-to-culture volume ratio of 0.18min−1 with CO2-enrichment of 0.5% and initial nitrate concentration of 1mM was optimal for improving net energy gain with Nannochloropsis salina. Sparging with CO2-enriched air of 0.5% along with nitrogen starvation resulted in 50% more lipid productivity than sparging with ambient air. [Copyright &y& Elsevier]

Abstract: Filtration-based separation of Chlorella vulgaris, a species with excellent potential for CO2 capture and lipid production, was investigated using a surface-modified hydrophilic polytetrafluoroethylene (PTFE) membrane. Coagulation using polyaluminum chloride (PACl) attained maximum turbidity removal at 200mgL−1 as Al2O3. The membrane filtration flux at 1bar increased as the PACl dose increased, regardless of overdosing in the coagulation stage. The filtered cake at the end of filtration tests peaked in solid content at 10mgL−1 as Al2O3, reaching 34% w/w, roughly two times that of the original suspension. Differential scanning calorimetry (DSC) tests demonstrate that the cake with minimum water–solid binding strength produced the driest filter cake. Coagulation using 10mgL−1 PACl as Al2O3, followed by PTFE membrane filtration at 1bar, is an effective process for harvesting C. vulgaris from algal froth. [Copyright &y& Elsevier]

Abstract: Despite claims that microalgal biofuels are environmentally friendlier alternatives to conventional fuels, debate surrounding its ecological benefits or drawbacks still exists. LCA is used to analyze various biofuel production technologies from ‘cradle to gate’. Energy and CO2 balances are carried out for a hypothetical integrated PBR-raceway microalgae-to-biodiesel production in Singapore. Based on a functional unit of 1MJ biofuel, the total energy demands are 4.44MJ with 13% from biomass production, 85% from lipid extraction, and 2% from biodiesel production. Sensitivity analysis was carried out for adjustments in energy requirements, percentage lipid contents, and lower/higher heating product value. An ‘Optimistic Case’ was projected with estimates of: 45% lipid content; reduced energy needs for lipid extraction (1.3MJ per MJ biodiesel); and heating value of biodiesel (42MJ/kg). The life cycle energy requirements dropped significantly by about 60%. The results are compared with other published case studies from other countries. [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: This study examines the performance of supercritical carbon dioxide (SCCO2) extraction and hexane extraction of lipids from marine Chlorococcum sp. for lab-scale biodiesel production. Even though the strain of Chlorococcum sp. used in this study had a low maximum lipid yield (7.1 wt% to dry biomass), the extracted lipid displayed a suitable fatty acid profile for biodiesel [C18:1 (∼63 wt%), C16:0 (∼19 wt%), C18:2 (∼4 wt%), C16:1 (∼4 wt%), and C18:0 (∼3 wt%)]. For SCCO2 extraction, decreasing temperature and increasing pressure resulted in increased lipid yields. The mass transfer coefficient (k) for lipid extraction under supercritical conditions was found to increase with fluid dielectric constant as well as fluid density. For hexane extraction, continuous operation with a Soxhlet apparatus and inclusion of isopropanol as a co-solvent enhanced lipid yields. Hexane extraction from either dried microalgal powder or wet microalgal paste obtained comparable lipid yields. [ABSTRACT FROM AUTHOR]

Abstract: The Scenedesmus obliquus FSP-3, a species with excellent potential for CO2 capture and lipid production, was harvested using dispersed ozone flotation. While air aeration does not, ozone produces effective solid–liquid separation through flotation. Ozone dose applied for sufficient algal flotation is similar to those used in practical drinking waterworks. The algae removal rate, surface charge, and hydrophobicity of algal cells, and fluorescence characteristics and proteins and polysaccharides contents of algogenic organic matter (AOM) were determined during ozonation. Proteins released from tightly bound AOM are essential to modifying the hydrophobicity of bubble surfaces for easy cell attachment and to forming a top froth layer for collecting floating cells. Humic substances in the suspension scavenge dosed ozone that adversely affects ozone flotation efficiency of algal cells. [ABSTRACT FROM AUTHOR]

Abstract: Microalgae have the ability to mitigate CO2 emission and produce oil with a high productivity, thereby having the potential for applications in producing the third-generation of biofuels. The key technologies for producing microalgal biofuels include identification of preferable culture conditions for high oil productivity, development of effective and economical microalgae cultivation systems, as well as separation and harvesting of microalgal biomass and oil. This review presents recent advances in microalgal cultivation, photobioreactor design, and harvesting technologies with a focus on microalgal oil (mainly triglycerides) production. The effects of different microalgal metabolisms (i.e., phototrophic, heterotrophic, mixotrophic, and photoheterotrophic growth), cultivation systems (emphasizing the effect of light sources), and biomass harvesting methods (chemical/physical methods) on microalgal biomass and oil production are compared and critically discussed. This review aims to provide useful information to help future development of efficient and commercially viable technology for microalgae-based biodiesel production. [ABSTRACT FROM AUTHOR]

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]

Abstract: Pavlova sp. was employed to evaluate the efficiency of different lipid extraction methods. The microalgal crude lipids content determined using the mixed solvent with ultrasonic method was 44.7wt.%. The triglyceride content obtained by the mixed solvent method was 15.6wt.%. The extraction yield was the FAME yield divided by the maximum FAME (15.9wt.%). The extraction yield was improved by cell disruption prior to extraction, and the highest triglyceride extraction yield of 98.7% was observed using the supercritical fluid extraction (SFE) method with bead-beating. The results indicate that the SFE method is effective and provides higher selectivity for triglyceride extraction though the total lipid extracted was less than that using solvent extraction. [Copyright &y& Elsevier]

• Algae were grown in walnut shell extracts (WSE) supplemented with carbon dioxide. • CO 2 significantly boosted the biomass and lipid productivities of algae under WSE cultivation. • A combined strategy was developed for WSE utilization and biofuel production. Microalgae are a promising biofuel resource, but their high cost and low productivity hinder their commercial applications. In the present study, Monoraphidium sp. QLZ-3 was cultivated in walnut shell extracts (WSE) supplemented with carbon dioxide (CO 2). Biomass was enhanced from 0.40 g L−1 to 1.18 g L−1, and lipid content reached 49.54% in WSE-12% CO 2 media. Biomass and lipid productivity reached 196.88 and 97.52 mg L−1 d−1, which were 1.33- and 1.57-fold higher than those of the control, respectively. The amount of carbohydrates increased, but the protein contents decreased. Furthermore, the application of CO 2 promoted nutrient and polyphenol absorption and upregulated the expression levels of lipid biosynthetic genes of this WSE-cultivated alga. These results indicated that coupling WSE and CO 2 could be an efficient strategy to enhance biofuel production by microalgae. [ABSTRACT FROM AUTHOR]