Biofixation of CO by microalgae has been recognized as an attractive approach to CO mitigation. The main objective of this work was to maximize the rate of CO fixation ( ) by the green microalga P12 cultivated photoautotrophically in bubble column photobioreactors under different CO concentrations (ranging from 2% to 10%) and aeration rates (ranging from 0.1 to 0.7 vvm). Results showed that the maximum (2.22 g L d ) was obtained by using 6.5% CO and 0.5 vvm after 7 days of cultivation at 30 °C. Although final biomass concentration and maximum biomass productivity of microalgae were affected by the different cultivation conditions, no significant differences were obtained in the biochemical composition of microalgal cells for the evaluated levels of aeration and CO . The present study demonstrated that optimization of microalgal cultivation conditions can be considered a useful strategy for maximizing CO bio-mitigation by .
The economic feasibility of algal mass culture for biodiesel production is enhanced by the increase in biomass productivity and storage lipids. Effect of iron on growth and lipid accumulation in marine microalgae were investigated. In experiment I, supplementing the growth media with chelated FeCl in the late growth phase increased the final cell density but did not induce lipid accumulation in cells. In experiment II, cells in the late-exponential growth phase were collected by centrifugation and re-inoculated into new media supplemented with five levels of Fe concentration. Total lipid content in cultures supplemented with 1.2 × 10 mol L FeCl was up to 56.6% biomass by dry weight and was 3–7-fold that in other media supplemented with lower iron concentration. Moreover, a simple and rapid method determining the lipid accumulation in with spectrofluorimetry was developed.
Freshwater microalga and marine microalga were used to investigate toxic effects induced by 50 nm silver nanoparticles (AgNPs). To induce AgNPs effect, we exposed and for 24 h to 0–10 mg/L. We showed that growth media had different effects in AgNPs agglomerates' formation. Cellular viability, reactive oxygen species (ROS) formation and lipids peroxidation were employed to assess the toxic effects of AgNPs. AgNPs were able to interact directly with the cells surface and large aggregates were observed. AgNPs have a negative effect on and , as manifested by a strong decrease in chlorophyll content, viable algal cells, increased ROS formation and lipids peroxidation. The variability in sensitivity of both algae towards AgNPs was observed. We conclude that AgNPs have a negative effect on aquatic algae and these alterations might have serious consequences on structure and function of aquatic plant communities. ► Two green algae were used to investigate silver nanoparticles' (AgNPs) effects. ► Growth media has an effect in aggregates' formation of AgNPs. ► Algae species vary in their response to AgNPs. ► AgNPs induced strong ROS induction and lipids peroxidation.
► Cheese whey was used as carbon source for growth. ► Mixotrophic microalgae grew faster than photoautotrophic cells. ► Maximum starch productivity was achieved under mixotrophic conditions. ► Highest pigment content (0.74%) was obtained in the photoautotrophic culture. Growth parameters and biochemical composition of the green microalga cultivated under different mixotrophic conditions were determined and compared to those obtained from a photoautotrophic control culture. Mixotrophic microalgae showed higher specific growth rate, final biomass concentration and productivities of lipids, starch and proteins than microalgae cultivated under photoautotrophic conditions. Moreover, supplementation of the inorganic culture medium with hydrolyzed cheese whey powder solution led to a significant improvement in microalgal biomass production and carbohydrate utilization when compared with the culture enriched with a mixture of pure glucose and galactose, due to the presence of growth promoting nutrients in cheese whey. Mixotrophic cultivation of using the main dairy industry by-product could be considered a feasible alternative to reduce the costs of microalgal biomass production, since it does not require the addition of expensive carbohydrates to the culture medium.
► A two-staged process was used to produce lipids from . ► The 1st stage is for a fast and high density cell growth under nutrient-rich conditions. ► The 2nd stage is for lipid production under limitations of nitrate and controlled conditions. ► About 53% of dry cell weight accumulated as lipids after 24 h at an optimal 2nd stage conditions. A two-stage process, composed of growth under nutrient-rich conditions followed by cultivation under nitrogen starvation and controlled conditions of phosphate, light intensity, aeration, and carbon sources was applied for lipid production by the green alga . Using conditions without addition of nitrogen, 2 mg/L PO -P, light intensity of 100 μmol/m /s and 0.25 vvm of air, about 43% of dry cell weight accumulated as lipids after 12 h, which equates to a lipid productivity of 77.8 mg/L/d. In a medium containing 5 mg/L NO -N and 2 mg/L PO -P, and at a light intensity of 100 μmol/m /s and 0.25 vvm of 2% CO , about 53% of dry cell weight consisted of lipids after 24 h, representing a lipid productivity of 77.1 mg/L/d. The low amount of nutrients, moderate aeration and light intensity were helpful for increasing lipid productivity.
A promising method of Carbon dioxide (CO ) valorization is to use green microalgae photosynthesis to process biofuel. Two Phase Partitioning Bioreactors (TPPBR) offer the possibility to use non-aqueous phase liquids (NAPL) to enhance CO solubility; thus making CO available to maximize algae growth. This requires relatively less toxic hydrophobic Ionic Liquids (ILs) that comprise a new class of ionic compounds with remarkable physicochemical properties and thus qualifies them as NAPL candidates. This paper concerns the synthesis of ILs with octyl and butyl chains as well as different cations containing aromatic (imidazolium, pyridinium) and non-aromatic (piperidinum, pyrrolidinium) rings for CO absorption studies. The authors measured their respective toxicity levels on microalgae species, specifically, , and . Results revealed that octyl-based ILs were more toxic than butyl-based analogues. Such was the case for bmim-PF6 at double saturation with an absorbance of 0.11, compared to Omim-PF6 at 0.17, bmim-NTf2 at 0.02, and Omim-NTf2 at 0.14, respectively. CO uptake results for ILs bearing octyl-based chains compared to the butyl analog were 54% (nCO /nIL) (i.e., moles of CO moles of IL) and 38% (nCO /nIL), respectively. Conclusively, 1-butyl-1-methylpiperidinium absorbed 13% (nCO /nIL) and appeared the least toxic, having an absorbance of 0.25 at 688 nm (double saturation at 7 d) compared to 1-butyl-3-methylimidazolium, which showed the highest toxicity with zero absorbance. Accordingly, these findings suggest that 1-butyl-1-methylpiperidinium is capable of transporting CO to a system containing green microalgae without causing significant harm; thus allowing its use in TPPBR technology.
The microalga is a potential feedstock for bioenergy due to its rapid growth, carbon dioxide fixation efficiency, and high accumulation of lipids and carbohydrates. In particular, the carbohydrates in microalgae make them a candidate for bioethanol feedstock. In this study, nutrient stress cultivation was employed to enhance the carbohydrate content of . Nitrogen limitation increased the carbohydrate content to 22.4% from the normal content of 16.0% on dry weight basis. In addition, several pretreatment methods and enzymes were investigated to increase saccharification yields. Bead-beating pretreatment increased hydrolysis by 25% compared with the processes lacking pretreatment. In the enzymatic hydrolysis process, the pectinase enzyme group was superior for releasing fermentable sugars from carbohydrates in microalgae. In particular, pectinase from displayed a 79% saccharification yield after 72 h at 50 °C. Using continuous immobilized yeast fermentation, microalgal hydrolysate was converted into ethanol at a yield of 89%.
► A sugar-rich FSP-E strain was used as feedstock for ethanol production. ► Enzymatic and acidic hydrolyses can efficiently saccharify the microalgae biomass. ► SHF & SSF processes produced ethanol from the microalgae biomass with high yield. ► SSF process gave better ethanol production performance with a 92% theoretical yield. This study aimed to evaluate the potential of using a carbohydrate-rich microalga FSP-E as feedstock for bioethanol production via various hydrolysis strategies and fermentation processes. Enzymatic hydrolysis of FSP-E biomass (containing 51% carbohydrate per dry weight) gave a glucose yield of 90.4% (or 0.461 g (g biomass) ). The SHF and SSF processes converted the enzymatic microalgae hydrolysate into ethanol with a 79.9% and 92.3% theoretical yield, respectively. Dilute acidic hydrolysis with 1% sulfuric acid was also very effective in saccharifying FSP-E biomass, achieving a glucose yield of nearly 93.6% from the microalgal carbohydrates at a starting biomass concentration of 50 g L . Using the acidic hydrolysate of FSP-E biomass as feedstock, the SHF process produced ethanol at a concentration of 11.7 g L and an 87.6% theoretical yield. These findings indicate the feasibility of using carbohydrate-producing microalgae as feedstock for fermentative bioethanol production.
The present study was undertaken to test the influence of exogenously applied phytohormones: auxins (IAA, IBA, NAA, PAA), cytokinins (BA, CPPU, DPU, 2iP, Kin, TDZ, ), gibberellin (GA ), jasmonic acid (JA) as well as polyamine - spermidine (Spd) upon the growth and metabolism of green microalga (Chlorophyceae) exposed to heavy metal (Cd, Cu, Pb) stress. The inhibitory effect of heavy metals on algal growth, metabolite accumulation and enzymatic as well as non-enzymatic antioxidant system was arranged in the following order: Cd > Pb > Cu. Exogenously applied phytohormones modify the phytotoxicity of heavy metals. Auxins, cytokinins, gibberellin and spermidine (Spd) can alleviate stress symptoms by inhibiting heavy metal biosorption, restoring algal growth and primary metabolite level. Moreover, these phytohormones and polyamine stimulate antioxidant enzymes’ (superoxide dismutase, ascorbate peroxidase, catalase) activities and ascorbate as well as glutathione accumulation by producing increased antioxidant capacity in cells growing under abiotic stress. Increased activity of antioxidant enzymes reduced oxidative stress expressed by lipid peroxidation and hydrogen peroxide level. In contrast JA enhanced heavy metal toxicity leading to increase in metal biosorption and ROS generation. The decrease in cell number, chlorophylls, carotenoids, monosaccharides, soluble proteins, ascorbate and glutathione content as well as antioxidant enzyme activity was also obtained in response to JA and heavy metals. Determining the stress markers (lipid peroxidation, hydrogen peroxide) and antioxidants’ level as well as antioxidant enzyme activity in cells is important for understanding the metal-specific mechanisms of toxicity and that these associated novel endpoints may be useful metrics for accurately predicting toxicity. The data suggest that phytohormones and polyamine play an important role in the responding to abiotic stressor and algal adaptation ability to metal contamination of aquatic environment. Auxins, cytokinins, gibberellin, jasmonic acid and spermidine can regulate heavy metal (Cd, Cu, Pb) biosorption and modify their toxic effect on growth, primary metabolite level and antioxidant system. ► Heavy metals toxicity in was arranged in the following order: Cd>Pb>Cu. ► Auxins, cytokinins, gibberellin and polyamine can alleviate heavy metals stress. ► Jasmonic acid enhanced harmful effect of heavy metals on algal cells.