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The current study examines the phycoremediation potential cum biomass productivity and biomass quality of hitherto uninvestigated five algae in Bold's Basal Medium (BBM) of varying nitrogen (½ to 4 × N), phosphorus (½ to 4 × P), and both together (½ to 2 × NP) with varying N:P. All five algae displayed unique responses in biomass productivity, lipid yield and productivity, and nitrogen (N) and phosphorous (P) removal efficiency. Chlorolobion braunii exhibited the highest biomass productivity (107 to 109.23 mg/L/ day) in N-rich media (3 to 4 × N in BBM), and Monoraphidium contortum exhibited the highest biomass productivity (103.66 mg/L/day) in P-rich media (2 to 4 × P in BBM). All the algae exhibited a higher lipid yield and productivity in BBM with a reduced ratio of N:P (0.85 to 1.47) from a lesser addition of N (½ × N or NP in BBM). Monoraphidium contortum exhibited significantly higher lipid yield (44.38%) and productivity (35.94 mg/L/day) than other species. The lipid content of four species demonstrated high-quality biofuel properties. Halochlorella rubescens exhibited the maximum nitrogen removal efficiency of 96% (in BBM), and Monoraphidium contortum exhibited the maximum phosphorus removal efficiency of 94.4% (2 × NP in BBM). Overall, the experiments stand as a model for understanding the influence of variations in N and P concerning N:P on biomass productivity, lipid content, lipid productivity, and N and P removal rate and efficiency of algae for initial standardization of the culture protocols for further industrial trials. [ABSTRACT FROM AUTHOR]

Algal bioprospecting in ecosystems leads to exploring native microalgae and the competency evaluation of economically producing lipids as biofuel or nutritional applications. In this study, ten microalgae species were screened from the saline water lake. Chlorella vulgaris, Chlorella sorokiniana, Chlamydomonas raudensis, Chlamydomonas hedleyi, Dunaliella salina, Picochlorum bazangan sp. nov., Tetraselmis bazangan sp. nov., Haematococcus lacustris, Nannochloropsis oceanic, and Scenedesmus rubescens were isolated and identified using 18SrDNA and tufA markers. Biodiesel potentials were assayed by the determination of biomass productivity, biochemical components, fatty acid profile, and biodiesel properties. The results showed that the maximum biomass yield (1.22 g/L) belonged to C. vulgaris. The highest protein, carbohydrate, chlorophyll, and carotenoid content were recorded in C. vulgaris, C. raudensis, C. sorokiniana, and D. salina, respectively. N. oceanica accumulated high lipid content and omega-3 fractions (31.09%). However, C. hedleyi had the highest lipid productivity (11.64 g/L/day) compared to other microalgae. The best species for biodiesel production was C. vulgaris, with a specific growth rate of 0.36 day−1, lipid productivity of 7.45 g/L/day, and C16-C18 fatty acid profile of 78.3%. The microalgae C. vulgaris had appropriate biodiesel properties of low viscosity (4.49), high cetane number (55.38), and relatively low cloud point (4.98). Another choice was N. oceanic, with high lipid productivity, cetane number (59.79), oxidative stability (56.43), and low iodine value (47.11). Microalgae T. bazangan sp. nov. had a cetane number (55.24), low cloud point (4.71), and C16-C18 fatty acid profile of 82.34%. Accordingly, C. vulgaris, T. bazangan sp. nov., and N. oceanic can be considered potential species for biodiesel. [ABSTRACT FROM AUTHOR]

Microalgae are lipid-rich microscopic eukaryotic algae that can be used aiming for more sustainable biodiesel production by employing environmentally sound processes. The present work evaluates biodiesel production using a biocatalyst and two microalgae species as oil feedstock (Chlorella vulgaris and Aurantiochytrium sp.). Lipid extraction was performed using different techniques, namely, Soxhlet extractions (8 h — both species) with different solvents (hexane; hexane:ethanol (1:1 v/v); and chloroform) and room temperature hexane extraction (72 h — Aurantiochytrium sp.). Transesterification occurred for 24 h (150 rpm), using 30 % lipase loading. The results showed that high extraction temperatures cause microalgae oil degradation, focused on unsaturated fatty acids, leading to a lower biodiesel conversion yield. Using Aurantiochytrium sp. oil, it was possible to obtain around 55 %wt. of biodiesel conversion yield using oil extracted at room temperature (6:1 methanol:oil molar ratio), whereas for the oil extracted in the Soxhlet apparatus, the biodiesel conversion yield was around 30 %wt.. The low lipid content (1.0 %wt.) and biodiesel conversion yield (up to 25 %wt.) obtained using C. vulgaris show that the biomass used in the current study has low potential for biodiesel production. However, enzymatic biodiesel production from microalgae represents a promising avenue for sustainable energy generation, offering a renewable and environmentally responsible solution to the world's energy needs. For that purpose, further studies, such as the optimisation of the extraction and transesterification of Aurantiochytrium sp. oil, should be carried out. [ABSTRACT FROM AUTHOR]

Cold climate ecosystems hint the researchers to discover economically native cold-adapted strains, which can tolerate temperature fluctuations in outdoor large-scale cultivation for producing lipids as biofuel or for nutritional applications. Cheshmeh-Sabz Lake (Iran) was screened in winter. The lake water was sampled at 5 °C and three strains of Scenedesmus sp. (dominant in BG-11), Ankistrodesmus sp. (dominant in WC), and Chlorella sp. (dominant in BBM) were identified using molecular methods. Strains' growth parameters, lipid content, and lipid productivity were also investigated at 8 and 25 °C. Scenedesmus sp. had the most biomass productivity (~ 0.54 ± 0.001 g/L*d) with no significant difference at 8 and 25 °C and demonstrated the highest amount of lipid productivity at 25 °C (9.43 ± 1.05 g/L*d). Scenedesmus sp. produced the highest percentage of α-linolenic acid at 15 and 25 °C (10.96 ± 1.5% and 11.07 ± 0.31%, respectively) among the strains. There was no significant difference for palmitic acid content at 8, 15, and 25 °C (41.05 ± 5.2, 38.48 ± 4.25, and 39.82 ± 1.58% respectively). Biomass productivity decreased in Ankistrodesmus sp. and Chlorella sp. at 8 °C in comparison to that of 25 °C (~ 86% and ~ 34% decrease, respectively). Ankistrodesmus sp. produced the highest proportion of α-linolenic acid at 8 °C (9.98 ± 0.10%). The highest percentage of palmitic acid was observed in Chlorella at 25 °C (44.41 ± 7.56%). Based on the results, Scenedesmus sp. is the proper choice for outdoor cultivation at different seasons due to its relatively high biomass productivity and the specific growth rate in low and high temperatures (8 and 25 °C). [ABSTRACT FROM AUTHOR]

The microalga, Dunaliella salina, is a treasure of fine chemicals, carotenoids, and lipids of industrial importance. The present investigation focused on the maximization of lipid content in the context of biofuel. Mixotrophic cultures growing in different combinations of sodium bicarbonate (NaHCO3) and glucose (Glu) or sodium acetate (Na-Ace) were monitored for essential growth parameters such as photosynthesis, dry biomass, and Chl a content. The maximum photosynthetic quantum yield (Fv/Fm) of all the screened mixotrophic cultures along with control ranged between 0.63 and 0.72, indicating the cells were in a good physiological state. The highest biomass productivity (33.46 ± 0.58 mg/L/d) was recorded in 1.0 mM NaHCO3 + 1.0 mM Glu-containing cultures. However, the highest lipid content (56% DCW) was recorded in 1.0 mM NaHCO3 + 0.5 mM Na-Ace-containing cultures. Interestingly, a 1.7-fold higher starch content (72.3 μg/mL) was recorded in 0.25 mM NaHCO3 + 0.5 mM Na-Ace over 1.0 mM NaHCO3 + 0.5 mM Na-Ace-containing cultures. Thus, data indicated that the higher concentration of NaHCO3 along with Na-Ace favoured lipid biosynthesis, while the lower concentration of NaHCO3 with Na-Ace favoured starch synthesis. Thus, substrate provision determined the desired products. Lipids obtained from D. salina at stage II (nitrogen-deficient condition) possessed ideal fuel properties according to international standards of EN 14214 and ASTM D6751. Therefore, the present work explored the threshold level of bicarbonate along with Na-Ace which was able to maintain good physiological status and produced higher lipids with better biodiesel properties. [ABSTRACT FROM AUTHOR]

Microalgal-biofilm culture has the advantages of less water requirement and higher lipid productivity. For efficient lipid production in an aerial phase condition, it is ideal to simultaneously induce microalgal biofilm growth and lipid accumulation. Biomass production and lipid accumulation in the aerial microalga Coccomyxa subellipsoidea KGU-D001 were investigated in the logarithmic growth phase. Initially, the alga was cultured in three different conditions: in liquid phase using Bold's basal medium (BBM), and in the aerial phase in the presence or absence of BBM. In aerial phase conditions with nutrients (i.e., BBM), biomass production was prioritized over cell proliferation until approximately the 7th day of culture. In the liquid phase conditions, the ratio of total organic carbon to total nitrogen (C/N) in cells was almost constant during the culture period. However, in both aerial phase conditions, the C/N ratio increased during the culture period, more so in the absence of nutrients. The total fatty acid content also increased throughout the culture period. Then, algal cells were cultured for a 17-day culture; there would be a growth period of 10 days followed by a lipid accumulation period of 7 days. In such cultures in the presence of BBM, the biomass and lipid productivities (388 and 94.2 mg/m2/day) were both significantly higher in the aerial phase than in the liquid phase during the lipid production period. C. subellipsoidea can produce lipids even during growth if the CO2 supply is efficient and the C/N ratio is high. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate biomass generation and determine the total lipid content of a microalgae isolated from a lagoon of the Ecuadorian Amazon. The morphological identification of the isolated microalgae was done through bibliographic comparisons and molecular identification by PCR followed by DNA sequencing and phylogenetic analysis. A 10-day batch culture was operated in 1-L glass bottles, and nutrient removal was determined daily. After harvesting, biomass was centrifuged to remove most of the water content. Half of the obtained biomass was kept wet and the other half was dried for further analysis. Cell growth, optical density, and dry weight were measured during cultivation time. In addition, total lipid and free fatty acid (FFA) percentages were evaluated. Removal of chemical oxygen demand (COD), nitrates (NO3−), and phosphates (PO43−) was 33.12%, 67.77%, and 76.73%, respectively. The biomass concentration was 2.19 ± 0.12 g/L with a productivity of 0.22 g/L per day. The best extraction percentages of total lipids and FFA were 18.43% and 61.46%, respectively. Although the results of lipids and FFA do not reach the required limits, the productivity of biomass and lipids is comparable with species that are cultivated for biodiesel production. [ABSTRACT FROM AUTHOR]

Microalgae are a sustainable source for many bioproduct syntheses. This study shows how different cultivation systems and nutrient concentrations affect Chlorella sp. development. The cultivation was performed in open and closed lab-scale systems. A Tukey test was used to evaluate the significant differences between the microalgae growth and composition under the two systems analyzed. The effect of nitrogen and phosphorus concentration was analyzed with a 22 full factorial design. Lipids, carbohydrates, proteins, and pigments were extracted and quantified. The highest specific growth rate (0.52 1/day) was obtained in the open pond, with a cell density of 5.06 × 107 cells/mL and a biomass concentration of 1.30 mg/mL. In this condition, the higher concentration of pigments was obtained: 13 μg/mg of chlorophyll-a, 15 μg/mg of chlorophyll-b, and 2 μg/mg of carotenoids. An expressive increase in the lipid (from 17 to 35%) was obtained in low nitrogen and high phosphorus. Protein percentage increases with both nutrients at a higher level, reaching up to 60%. The percentage of carbohydrates decreases from 32 to 13% with phosphorus reduction. Thus, this study points out the conditions that benefit the accumulation of each Chlorella sp. metabolite, contributing to the decision-making for the cultivation and applications of this microalgae. [ABSTRACT FROM AUTHOR]

The study aimed to apply gamma radiation as a cell pretreatment method for lipid extraction and for obtaining astaxanthin from residual biomass of Haematococcus pluvialis. Factor 1 of the two-factor experimental design was represented by cell pretreatment methods: biomass with chloroform:methanol under ultrasound (BCMU), biomass with chloroform:methanol under γ radiation (BCMR), dry biomass under γ radiation (DBR), and control (without pretreatment). Factor 2 considered the vegetative and cystic phases. Cultivation was performed in a mixotrophic system, and biomass was collected in both phases, centrifuged, lyophilized, and submitted to cell pretreatment and lipid extraction. Lipid content and FAMEs were evaluated comparing pretreatment methods and life cycle phases. Total lipid content was higher with the BCMR method in the vegetative (18% DW) and cystic (14% DW) phases. Gamma radiation combined with organic solvent was more efficient for increasing lipid yield, and DBR had a lipid yield similar to BCMU. FAME content differed between phases and pretreatments for most fatty acids, mainly C16:0, C16:1, C18:1n9c, C18:2n6c, C18:2n6t, and C18:3n3. The predominance of saturated or low unsaturated fatty acids makes H. pluvialis, in both phases, suitable for biofuel production. The preservation of astaxanthin from residual cystic biomass was observed when submitted to the DBR method, with a concentration similar to the raw biomass (1.5% DW). Gamma radiation in dry biomass has an antioxidant effect. Therefore, the lipid extraction method preceded by gamma irradiation was efficient for vegetative and cystic cells of H. pluvialis and contributed to the preservation of astaxanthin from residual cystic biomass. [ABSTRACT FROM AUTHOR]

The effect of sugarcane molasses on lipid content and fatty acids methyl ester (FAME) profile by Chromochloris zofingiensis is investigated in this work. For this purpose, the strain has been cultivated under mixotrophic conditions in a medium amended with specific concentrations of molasses (0.5 g/L, 1 g/L, and 2 g/L) able to sustain microalgae growth. Better biomass concentration, lipid content, and lipid productivity (1.6 g/L, 38% wt, and 286 mg/L/day) than the control (1.32 g/L, 16% wt, and 139 mg/L/day) were obtained with 2 g/L of molasses. The highest value of the total lipid content (42% wt) was reached with 1 g/L of molasses. FAME profile revealed a 97% composition in C16-C18 with no statistically meaningful differences among the three concentrations of molasses tested. The most represented fatty acids were C18:1 oleic (> 38% wt), C18:2 linoleic (> 21% wt), and C16:0 palmitic (> 14% wt). When using 2 g/L of molasses unsaturated fatty acids reached the highest portion (77%) than the control (61%). Specifically, all FAMEs have been quantitatively and qualitatively analyzed in order to improve biodiesel properties. The main characteristics of biodiesel obtainable from the algal lipids appeared in compliance with ASTM standards for unblended biodiesel and fulfilled European regulations (EN 14,214 and EN 590) for the quality of biodiesel. Owing the compliance of the corresponding biodiesel characteristics with international standards, a profitable biodiesel can be obtained under mixotrophic conditions triggered by the use of a food industry waste. Highlights: Sugarcane molasses can be used by Chromochloris zofingiensis to produce lipids. Molasses enhanced better cell growth than control medium. Molasses triggered biomass and lipid productivity better than control medium. Internal cell metabolism was modified by molasses to improve lipid production. Saturation and unsaturation levels in FAMEs were directly influenced by molasses. [ABSTRACT FROM AUTHOR]

Rhodosporidium toruloides have been considered as a potential feedstock for lipid accumulation. Several studies have been conducted to enhance lipid productivity; however, studies on the effects of trace metals on R. toruloides-1588 are limited. In this sense, the present study investigates the effect of five trace metal salts on the lipid accumulation of R. toruloides-1588. Trace metal salts such as iron and manganese resulted in the highest cell mass production of 17.5 and 17 g/L, respectively, while magnesium and copper lead to the maximum lipid yield of 40 and 36.7% (w/w), respectively. The maximum lipid accumulation was observed in magnesium-supplemented media and was twice the amount observed in control hydrolysate. Additionally, supplementation of trace metal salts led to the maximum production of linoleic acid of 31.27% along with the production of several long-chain unsaturated fatty acids such as docosahexaenoic acid and eicosatrienoic acid, which will strengthen the potential of R. toruloides-1588 as a feedstock not only for biofuel industries but also for pharmaceutical as well as food industries. [ABSTRACT FROM AUTHOR]

The irradiance level used in the microalgae cultures can modify the growth and proximate composition; however, this response is specie specific. The dinoflagellate group has the potential to be used as a source of biofuel production. This study evaluated the effect of five irradiance levels (50, 100, 150, 200, and 250 µmol photon m−2 s−1) on the growth rate, proximal composition, pigment content, and photosynthesis of Amphidinium carterae. The highest cell concentration was for the cultures at 150 µmol photon m−2 s−1 (130 × 103 cells mL−1) and the lowest value for 50 µmol photon m−2 s−1 (49 × 103 cells mL−1). The cultures maintained under the lowest irradiance had the highest values of organic dry weight (ODW) and inorganic dry weight (IDW). The protein and carbohydrate content changes significantly concerning the irradiance level, with the higher values (1599.46 pg cell−1 and 557.24 pg cell−1, respectively) at an irradiance of 200 µmol photon m−2 s−1. Lipid content was modified by the effect of irradiance, with the highest values (6920.89 pg cell−1) at the lowest irradiance used. As a general trend, the high irradiances increased the photosynthesis rates. These findings demonstrate that the strain of A. carterae used in this work can grow in high irradiances (100 to 250 µmol photon m−2 s−1) and significantly increase the lipid content at low irradiance used. [ABSTRACT FROM AUTHOR]

Starch and lipids are two major carbon storage compounds in algal cells. Theoretically, switching the carbon flow from starch to lipid synthesis may be a promising approach to realize the overproduction of microalgae-derived biodiesel. However, the results in previous studies vary across algal strains. To test the hypothesis, Monoraphidium sp. mutants were generated using ethyl methane sulfonate (EMS) as a random chemical mutagen. Among the 10% survival cells after exposure to EMS (4 mM) for 30 min, 23 low-starch mutants were selected, of which only 9 strains exhibited enhanced relative fluorescence unit (RFU) compared to wild type, implying the complexity in metabolic steps underlying the re-allocation of starch and lipid in Monoraphidium. Amid these mutants, EM25 showed increased lipid content (25.1%) and moderate biomass productivity (71 mg L−1 day−1), resulting in a higher lipid productivity (17.8 mg L−1 day−1) than that of wild type. The alteration of carbon storage compounds in the mutant was attributed to changes in the activities of enzymes (AGPase, ACCase, PEPC, DGAT) related to starch and lipid synthesis. Additionally, the fatty acid composition of the mutant complied with most of the parameters defined by ASTM D6751 and EN 14,214, with a sharp decrease in cloud point compared to wild type, suggesting its application in wide geographic area and the potential to be developed as a promising candidate for biodiesel production. [ABSTRACT FROM AUTHOR]

Microalgae can synthesize and accumulate high neutral lipids under abiotic stress such as nutrient starvation or limitation. In the present study, an indigenous microalgae Chlorella sp. T4 was cultivated under both nitrogen (N)- and phosphorus (P)-limiting and N- and P-replete conditions to produce lipid and biodiesel consequently. Highest biomass productivity of 36.48 ± 0.64 and 37.52 ± 0.53 mg L−1d−1 was obtained under N- and P-replete media, respectively, and relative expression of rbcL gene was noted (p < 0.05). However, high lipid productivity of 15.54 ± 0.27 mg L−1 d−1 and expression of accD gene were observed under N-limiting medium which was significantly higher than the control (BG-11) and other treatments (p < 0.05). Nutrient-limiting conditions produced fatty acid methyl ester that is suitable for biodiesel production compared to the nutrient sufficient medium. The variation in the expression of desaturase gene (KAS-1, ω-6 FAD, and ω-3 FAD) was triggered by different N and P treatments. These results would provide an insight into the physiological response and gene expression level under different nutrient levels, which could be harnessed for future genetic engineering of Chlorella sp. T4 for improved lipid production. [ABSTRACT FROM AUTHOR]

The reuse of the culture media after biomass growth can be a cost-effective strategy for large-scale microalgae production, especially when the target product is biofuel. Therefore, this study aimed to investigate the effect of recycling the microalgae Tetradesmus obliquus culture medium, focusing on the improved production of biomass and lipids, biodiesel properties, and cost reduction. The experiments were carried out in duplicate and three sequential steps with successive recycling (50% of the clarified medium and 50% of the standard). It was found that cells from recycled cultures had a similar overall performance as those from the fresh medium (standard). From this verification, the main findings of this research pointed out that (i) the consumption of the nutrients was efficient, with values in the order of 99% nitrate, 20% phosphate, 64% total iron, and 9% potassium; (ii) the average contents of biomass and lipids in the recycled medium increased around 20% to 24%, respectively, concerning the standard; (iii) the polyunsaturated fatty acids pool present in the microalgal oil dropped from 20.71 to 9.78% in the recycled culture, which represents a high-quality feedstock for biofuel; and (iv) the biodiesel properties evaluated, including iodine and saponification values, were 48 g I2 100 g−1 and 254 mg KOH/goil−1, respectively. Finally, this recyclability bioprocess can reduce overall costs by about 34%, thus improving the economic viability of microalgae production. [ABSTRACT FROM AUTHOR]

Biodiesel production from the microalgal oil of the estuarine diatom Halamphora coffeaeformis has proven to be technically viable. However, a fuller understanding of the environmental factors that regulate its tolerance and neutral lipid accumulation is required for improved mass cultivation in seawater-based outdoor raceway ponds. Meteorological conditions and evaporation processes can significantly influence factors such as the salt levels, water temperature and nutrient and light availability in these systems. Laboratory experiments with H. coffeaeformis growing in f/2 medium were therefore carried out in order to evaluate the effect of temperature and salinity on its growth and tolerance ranges and the effect of salinity on its total lipid and lipid fraction content and fatty acid methyl ester profile. Results indicate that the temperature and salinity ranges of the species were 5 °C to 30 °C and 5‰ to 95‰, respectively. The optimum temperature was between 20 and 25 °C, and the optimum salinity was 20‰. Neutral lipid accumulation increased in cells adapted at 45‰ with respect to those growing at 20‰. Total lipid composition at 45 ‰ was characterized by 85.5% neutral lipids, 2.5% phospholipids and a high percentage of C16.1 (36.4% of total fatty acids). These properties are important for an adequate quality of biodiesel. The eurytolerant behaviour of H. coffeaeformis and the effect of salinity stress on its growth and neutral lipid accumulation are demonstrated. The findings indicate the beneficial attributes of this strain for the development and feasibility of seawater-based outdoor raceway ponds for biodiesel production. [ABSTRACT FROM AUTHOR]

Freshwater deficiency and growing requests for renewable energy have led to increased concern about water and energy security. Therefore, the present study attempted to evaluate the feasibility of using wastewater (WW) as a culture medium for microalgal cultivation with the aim of nutrient removal and biodiesel production. The green microalga Asterarcys quadricellulare (Chlorophyta) was isolated from a wastewater treatment plant in Menoufia, Egypt, and grown for 24 days in Bold's Basal Medium as a control and at different concentrations of secondary treated WW in distilled water (25%, 50%, 75%, and 100%). The results of 75% WW treatment recorded 96.6%, 98.4%, and 89.9% removal efficiency for nitrate, ammonia, and total phosphorus, respectively. Also, it revealed high biomass yield and biomass productivity (1.44 g L−1 and 69.0 mg L−1 day−1, respectively). In addition, it showed higher lipid production (360.6 mg L−1) and lipid productivity (17.2 mg L−1 day−1). Asterarcys quadricellulare fatty acid profile estimation revealed elevated proportions of oleic (54.92%), palmitic (20.54%), and linoleic acids (13.9%). Most of the properties of biodiesel derived from the studied microalga are consistent with those recommended by the international standards. The current study concluded that A. quadricellulare could be used for wastewater bioremediation and biomass production with high potential as biodiesel feedstock. [ABSTRACT FROM AUTHOR]

Oleaginous microorganisms and the thermal decomposition of their recovered lipids are new attractive research fields for the sustainable production of biofuels from actual biomass. In this work, the thermal decomposition of lipids from C. vulgaris and from L. starkeyi was investigated using a thermogravimetric analyzer coupled to a mass spectrometer (TGA-MS) under non-isothermal conditions. Thermal decomposition was examined using the one-step reaction model. Integral, differential, and advanced isoconversional methods were implemented to analyze the conversion-dependent activation energy. The Friedman method resulted in an accurate and reliable estimation of the kinetic parameters. The activation energy showed a strong dependence on conversion from 123.5 to 246 kJ mol-1 for lipids from C. vulgaris and from 80.3 to 299.9 kJ mol-1 for lipids from L. starkeyi. The generalized master plot approach evidenced that the thermal decomposition of lipids from C. vulgaris proceeds via three-dimensional diffusion (D3—Jander's equation). Also, the kinetic analysis indicated that Valensi's equation (D2), controlled by a two-dimensional diffusion model, is the most likely mechanism for the thermal decomposition of lipids from L. starkeyi. The rate parameters were evaluated via a kinetic compensation plot. Ion temperature evolution was investigated by TGA-MS revealing many of the functional groups evolved in the range of 350–500 °C as C1–C7 aliphatic hydrocarbons, aromatic hydrocarbons, aldehydes, carboxylic acids, and furan derivatives. All these aspects favor the lipid biosynthesis from microbial biomass to potential lipid-based building blocks. [ABSTRACT FROM AUTHOR]

Microalgal biodiesel is technically viable to power diesel engines. This third-generation biofuel has great performance of combustion and can reduce emission of greenhouse gases into the atmosphere. However, its production is currently very expensive, relative to petrochemical diesel. Development and implementation of strategies to optimize productivity and quality of biomass and thus ensure this future-proof biofuel is economically feasible to fabricate and competitive with diesel oil on an industrial scale is challenging. This meta-analytic overview documents the diversity of fastest-growing, oil-accumulating microalgae; performance of cultures and systems; strategies for inducing lipids; and quality and economics of microalgal biodiesel. The microalgae, Neochloris oleoabundans, Scenedesmus obliquus, Desmodesmus sp., and Micractinium sp., are hyperaccumulators of lipids. The genre, Micractinium sp., is a thermophile, and thus it can resist hydrothermal streams. Complementarily, it is the fastest to grow and the most productive in both biomass and biodiesel. This should be of great importance to roll-out sustainable, high-performance algal systems in marginal lands in tropical zones, where the heat often makes the planning and management of projects difficult and expensive. Heat shock, nutritional starvation, and photoperiod are the most effective algae-specific strategies for inducing mechanisms for lipogenesis in Ankistrodesmus dimorphus, Chlorella vulgaris and Leptolyngbya sp., Cylindrotheca closterium and N. oleoabundans, and Amphora subtropica and Dunaliella sp., respectively. Rhodococcus sp. produces a significant amount of biomass at very low cost, relative to diesel oil. The concept of synergistically co-culturing microalgae with this photosynthetically active bacterium may be an option to save the producer the expenditures and uncertainties of third-generation biodiesel. [ABSTRACT FROM AUTHOR]

For transforming the massive amounts of extensive wasted glycerol from the procedure of biodiesels production, oleaginous yeasts were isolated from an activated sludge tank located at a biodiesel manufacturing factory in this study. One of the isolated oleaginous yeast proved with the most lipid production potential was identified as Rhodotorula mucilaginosa LP-2 by 18S rDNA sequencing. The optimal conditions for lipid production among strain R. mucilaginosa LP-2 were investigated. The optimum temperature for maximum lipid productivity was 33 °C. The most suitable carbon and nitrogen sources for strain R. mucilaginosa LP-2 to accumulate lipids were pure glycerol and yeast extract, respectively. C/N ratio was also demonstrated to be the significant factor for intracellular lipid accumulation. Cell growth and lipid production were both inhibited when the C/N ratio was higher than 85. The highest lipid yield was observed at C/N ratio of 65 due to a significant impact on the degree of fatty acid desaturation of this strain. [ABSTRACT FROM AUTHOR]

The initial biomass density had a significant effect on the growth behaviour of Leptolyngbya foveolarum HNBGU-001 in the batch culture. The test organism produced substantial amounts of biomass and lipids when allowed to grow at 40 °C and pH 8.0. The Placket-Burman design appropriately indicated the positive and negative influences of the tested nutrient factors on biomass and lipid productivities of L. foveolarum. Employing the Box-Behnken design of response surface methodology, the elevated concentrations of sulphate-S (300 mg/L) and carbonate-C (45.39 mg/L) but relatively low levels of phosphate-P (10 mg/L) and nitrate-N (375 mg/L) were identified as the optimal nutritional requirements of the test organism for the maximum lipid productivity (49.60 ± 0.70 mg/L/day) along with high lipid content (32.10 ± 0.40% dry cell weight) and biomass productivity (154.80 ± 3.60 mg/L/day). These maximized responses of biomass productivity, lipid content, and lipid productivity were respectively 2.8-, 2.4-, and 6.8-fold higher than their corresponding values under the unoptimized conditions. FAME analysis of lipids obtained from the test organism revealed some promising features for their use as algal biodiesel feedstock. Nonetheless, the test organism seems to have better potential than several other microalgae for use in biofuel production as it can give a high output of biomass as also lipids at elevated temperature prevalent in outdoor conditions of subtropical and tropical regions. [ABSTRACT FROM AUTHOR]

This study was designed to isolate microalgal species which can tolerate severe environmental stresses and can be used for wastewater treatment and biofuel generation. Three different microalgal strains (including Chlorella sorokiniana GEEL-01, Parachlorella kessleri GEEL-02, and Parachlorella kessleri GEEL-03) were isolated from a wastewater treatment plant and Waterwheel Park. The highest growth rate (1.61 OD680nm) was observed for C. sorokiniana GEEL-01 with highest removal of total nitrogen (1.5 mg L−1 day−1) and total phosphorus (1.82 mg L−1 day−1). The biocomponents of the isolated species ranged from 19.47–29.64%, 39.39–52.51%, and 15.08–22.75% for carbohydrate, protein, and lipid, respectively, based on the dry cell weight (DCW). The function groups in microalgal biocompounds were also confirmed by Fourier-transform infrared radiation (FT-IR) spectra, indicated their ability for biofuel generation. Ultimate and proximate analyses of C. sorokiniana GEEL-01 showed high carbon (54.24% DCW) and volatile content (92.69% DCW), compare to other strains. Moreover, it exhibited a significant accumulation of lipid with an increase in the fractions of saturated fatty acids (64.5%), and the major fatty acids were palmitic acid (11.17%), stearic acid (33.86%), oleic acid (9.84%), and linoleic acid (11.56%). Biodiesel derived from the major fatty acids had optimum engine efficiency properties including iodine value (77.34 g I2/100 g oil) and cetane number (54.83). Cultivation of C. sorokiniana GEEL-01 can serve as a dual function of biodiesel feedstock generation and nutrients removal. [ABSTRACT FROM AUTHOR]

Mucor circinelloides is a filamentous fungus capable of producing mycelium-bound lipase and lipids and able to assimilate a wide array of substrates, like agricultural wastes and industrial effluents. A biotechnological valorization of cheese whey is described herein, in which simultaneous reduction of the organic loading and conversion of the various compounds of the by-product into added-value microbial metabolites is obtained. M. circinelloides URM 4182 was tested for the ability of producing biomass containing lipids and mycelium-bound lipase using raw cheese whey as culture medium. The fungal cultivation assays were performed in non-supplemented cheese whey at pH 4.5, 26 °C, 250 rpm for 120 h providing biomass concentration of 4.7 g L−1 containing lipids (22.5% of dry biomass weight) and lipolytic activities up to 160 U g−1. The mycelium-bound lipase was characterized in terms of its biochemical and kinetic parameters and tested on biogas production assays of cheese whey as a way to enhance the lipid hydrolysis, the limiting step in anaerobic digestion. Results demonstrate that the addition of M. circinelloides lipase on cheese whey reduced the lag phase of anaerobic digestion up to 43.7%, and the biogas production was increased by up to ninefold when compared with the control experiments. [ABSTRACT FROM AUTHOR]

Lipid productivity of microalgae depends considerably on the method of its cultivation. In the present study, a two-stage culture strategy was conducted to cultivate Chlorella vulgaris to enhance lipid productivity. In the first stage, C. vulgaris was grown in the synthetic medium to obtain maximum biomass concentration. Wastewater is used as a medium for growing microalgae to have commercial and environmental aptitudes for biomass production. The nutrient removal efficiencies were 80.5% (COD), 70% (TN), and 78% (TP). In the second stage, the synergistic effects of nitrogen and NaCl concentration on the lipid productivity was investigated by response surface methodology (RSM) for 2 days. The optimum conditions for relatively high lipid productivity (up to 80 mg L−1 day−1) were 2.6 mg L−1 of nitrogen, 6.3 g L−1 of NaCl, and 4.9 g L−1 of biomass concentration. The value which was predicted by model was in good agreement with the experimental value, as it was determined by the validation experiments. Saturated fatty acid composition was increased by 27.3% under optimized medium compared with synthetic medium, which is very suitable for biodiesel production. According to the above results, it is concluded that the combination of multiple stress conditions can lead to a cost-effective technology of microalgae lipid production. [ABSTRACT FROM AUTHOR]

Developing effective, energy-efficient methods to extract lipids from microalgae remains a challenge in bioenergy. This study assesses electric pulse (EP) pretreatments to enhance lipid extraction from Chlorella protothecoides. In tandem with solvent extraction, we applied 10, 50, 100, 200, and 300 60 kV/cm, 60 ns duration EPs or 3, 17, 33, 67, and 100 60 kV/cm, 300 ns duration EPs to match the energy density u applied to the sample for each EP duration. Lipid recovery increased with increasing u for each EP duration until reaching a maximum for 17 300 ns EPs (the second lowest u) and 100 60 ns EPs (the third lowest u) to achieve a 13.3% and 16.1% increase in lipid extraction, respectively. Lipid extraction declined at higher u due to increased cell lysis. The largest net energy released calculated from the difference between the energy available from the extracted lipids and the applied energy of the EPs occurred at the lowest u for each EP duration. Applying trains of 100 μs EPs induced qualitatively similar behavior. These results suggest that a more detailed parametric study may optimize EP parameters for net energy release for specific microalgae and solvents. [ABSTRACT FROM AUTHOR]

The large-scale culture of microalgae has become a focus of interest for the biorefinery industry, combining the production of biofuels with that of other value-added bioproducts and thus increasing the profitability of the process. In order to evaluate its potential as biodiesel feedstock under a biorefinery approach, the biomass, pigment, nutrient, total lipid and lipid fraction kinetics of the Argentinian Nannochloropsis oceanica CCALA 978 strain were analysed. The species was first cultivated under optimal conditions (f/2 medium) and then transferred to nutritional stress conditions (N-deprivation or P-deprivation media). Under complete f/2 medium, N. oceanica presented maximum growth rate (μ) and chlorophyll-a values and minimum values for lipid and carotenoid content. The high nutrient consumption rate (N or P) in this exponential phase was associated with increasing cell density. Under both nitrate and phosphate deprivation, μ was drastically reduced but biomass production reached its highest values, indicating a phase of metabolite accumulation. Maximum values of total lipids (ca. 39% dw) and carotenoids (1100 × 10−3 ± 15 μg mL−1) were obtained under nitrate deprivation. In addition, total lipid composition was characterized by 92% neutral lipids, 0.7% phospholipids, a high percentage of C16:1 (ca. 37% of total fatty acids) and minimum values of PUFA (5.9% of total fatty acids). Biodiesel properties inferred from the fatty acid methyl ester profile of neutral lipids meet the standards established by EN 14214 and ASTMD 6751-08. Although N and P deficiency both produced an increase in neutral lipids in the studied strain, under a biorefinery approach, nitrate deprivation is considered to be a better method of stress induction than phosphate deprivation for the purpose of co-producing neutral lipids for biodiesel and value-added pigments. [ABSTRACT FROM AUTHOR]

In the present study, the effect of trace metal nutrients on biomass and lipid productivity of Scenedesmus obliquus cultured in municipal wastewater was evaluated. Lipid productivity of S. obliquus significantly increased by 18.63%, 19.21%, and 27.95% by adding trace metals of Mo, Mn, and Fe, respectively, with the highest lipid productivity of 24.69 mg/(L·d) in case of Fe (3.00 mg/L FeSO4·7H2O). GC analysis of the lipids showed that the control (WW) and ferrous sulfate–treated cultures had very similar compositions, and both of them contained considerable proportions C16-18, showing their suitability for biodiesel production. Moreover, using FeSO4·7H2O enhanced the removal rates of total phosphorus, ammonia nitrogen, and total nitrogen in municipal wastewater, which attained 94.7%, 99.2%, and 95.8%, respectively. [ABSTRACT FROM AUTHOR]

Discovery of high-yielding microalgae rich in valuable lipids, proteins, pigments, or carbohydrates is essential to the growth of nutraceutical and biofuel industries. Therefore, bioprospecting of microalgae from diverse environmental conditions has become highly significant to meet the demand of such bioresources globally. In this context, bioprospecting of three species of microalgae isolated from bloomed freshwaters of Kerala, India, was carried out; morphological and molecular characterizations revealed two of the algae as new species to science and named accordingly. The industrial potentials of these algae (Fasciculochloris boldii (MH992105.1), Sphaerocystis antoni-kadavilaii Ray & Prasanth sp. nov. (MK005299.1), and Chlorella zachariaii Ray & Prasanth sp. nov. (MH930447.1)) were assessed in terms of biomass yield and biochemical profile. The alga Sphaerocystis antoni-kadavilaii with a biomass yield of 176.8 ± 2.0% increase L−1 day−1, lipid productivity of 4.4 ± 0.3 mg L−1 day−1, the protein content of 46.1%, is found promising, in comparison with the known species such as Spirulina sp. and Chlorella sp. It is high in chlorophyll a, and total carotenoid content as well. The alga Fasciculochloris boldii showed high lipid content of 26.8 ± 1.1% and the alga Chlorella zachariaii showed 30.1% of omega-3 fractions in its total fatty acids. The Fourier transform infrared spectroscopy confirmed biodiesel feasibility of lipids from all these algae. However, the alga Fasciculochloris boldii with high proportions of saturated fatty acids in its lipid (71.2%) can be considered as a potential species for biodiesel as the biodiesel from the same also shows the required cetane number (63.3) and low iodine value (38.9). [ABSTRACT FROM AUTHOR]

Lipid extraction from microalgal biomass faces some challenges such as the selection of a suitable biomass type and its quality, lipid yield (LY), and process energy consumption. This study aimed to develop optimized processing conditions using response surface methodology, for the ultrasonic extraction (UE) of lipids from wet and dried marine Chlorella sp. Integrated process approaches with different extraction and solvent recovery steps were developed for the evaluation of the lipid recovery and process energy consumption. The effects of other processing factors, such as the biomass-to-solvent ratio, solvent type, and solvent-to-solvent ratio were investigated. The biomass and lipids extracted were characterized by scanning electron microscopy-energy-dispersive X-ray (SEM-EDX) and gas chromatography-flame ionization detection (GC-FID) analysis, respectively. With a single extraction and single-solvent recovery (1-1 cycle) process, the LYs from fresh and stored paste were 11.7% and 6%, respectively, while freeze-dried biomass produced an 18.5% LY. The energy consumption was 6000 MJ/kg lipid for the wet route and 8200 MJ/kg lipid for the dry route in the 1-1-cycle process. Dried biomass was selected for further investigation due to its longer storage-period capability and higher LY. The LY of the 2-1-cycle process using methanol/hexane (2/1 v/v) with a biomass-to-solvent ratio of 1/20 g/mL was 31% and was considered as a base case scenario of this study, which is 40.3% and 9.7% greater than those of the 1-1 cycle and 2-2 cycle, respectively. The lipids obtained from the 2-1 cycle at the optimum condition were mainly saturated fatty acids which are suitable for a biodiesel feedstock. [ABSTRACT FROM AUTHOR]

The aquatic fern Azolla is one of the fastest-growing nitrogen-fixing plants on Earth and therefore considered as a potential source of biomass for bioenergy production. The lipid fraction from Azolla filiculoides was analyzed to investigate whether it suited biodiesel production. Since the productivity of Azolla is further increased at higher CO concentrations, A. filiculoides biomass was produced at 800 ppm CO mimicking a cultivation system utilizing CO waste from industry. The harvested biomass contained 7.92 ± 0.14 % dry weight (dw) crude lipids. Drying conditions did not significantly affect lipid composition or yields, indicating that drying conditions may be energetically optimized without the risk of product loss. Total lipid extracts contained 4.2 ± 0.38 % free fatty acids. Of the crude lipid fraction, 41 ± 13 % consisted of fatty acids that were converted into fatty acid methyl esters upon saponification in methanol. Unique mid-chain (di)hydroxy compounds constituted 7.2 ± 2.8 % of the crude lipids. Based on the fatty acid profile, it was estimated that Azolla biodiesel meets requirements set by the EN14214 standard on fuel density, cetane number, and iodine value. The cold filter plugging point (CFPP), however, is expected to be too high due to relatively high concentrations of lignoceric acid and the presence of the mid-chain (di)hydroxy compounds. To produce high-quality biodiesel from Azolla lipids, therefore, a fractionation step will be required removing these compounds. As an advantage, the long-chain alcohols and (di)hydroxy fatty acids obtained after fractionation may provide a valuable secondary product stream with applications to chemical industry and nutrition. [ABSTRACT FROM AUTHOR]

We illustrate a detailed compositional characterization of hydrothermal liquefaction (HTL) oils derived from two biochemically distinct microalgae, Nannochloropsis gaditana and Chlorella sp. (DOE 1412), for a range of reaction temperature as observed by high-resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS). The unique capability to unequivocally derive molecular formulae directly from FT-ICR MS-measured mass-to-charge ratio (for several thousand compounds in each oil) shows that lipids are completely reacted/converted for any reaction temperature above 200 °C and reveals the formation of nonlipid reaction products with increasing temperature. Specifically, lipid-rich oil is obtained at low reaction temperature (<225 °C) for both microalgal strains. For positive ion mode, the major lipid components in Chlorella sp. and N. gaditana HTL oils are betaine lipids and acylglycerols, respectively. Acidic species in the HTL oils (observed by negative ion mode) are dominated by free fatty acids (FFA) regardless of reaction temperature. HTL oils obtained at higher temperatures (≥225 °C) are composed of a variety of basic nitrogen- and oxygen-containing compounds that originate from protein and carbohydrate degradation at elevated temperature. Similar structural features are observed for the abundant nitrogen heterocyclics between the two strains with slightly lower carbon number for Chlorella sp., overall. [ABSTRACT FROM AUTHOR]

Rapid induction of lipid accumulation in microalgae is an important prerequisite towards the use of microalgae as a feedstock for biodiesel production. In this study, we present a novel approach to induce lipids in Chlorella sp. within 24 h by short-term UV-C radiation (UVR) stress at different energy intensities ranging from 0 to 1000 mJ/cm. Increase in the lipid fluorescence was measured by Nile red staining and fluorescence-activated cell sorting analysis followed by gas chromatography-mass spectrometry. Lipid fluorescence was significantly increased in cultures radiated at or above 250 mJ/cm compared to the mock-treated control cultures. Lower dosages at 100 and 250 mJ/cm led to a near doubling of total fatty acids, with a significant increase in unsaturated fatty acids and also most saturated fatty acids. This study provides a protocol for rapid lipid induction of microalgal cells by UV-C and the possible impact of UV-C radiation on fatty acid metabolism. [ABSTRACT FROM AUTHOR]

Enzymatic hydrolysis of complex wastes is a critical step for efficient biogas production in anaerobic digesters. Inhibition of this hydrolytic step was studied by addition of humic acid-like (HAL) and fulvic acid-like (FAL) substances, extracted from maize silage and fresh cow manure, to batch tests with cellulose and cellulases from Aspergillus niger and tributyrin and lipases from Candida rugosa. To confirm the inhibition results, microbially catalysed hydrolysis trials were performed, where Fibrobacter succinogenes was grown exclusively on cellulose. Hydrolysis products, as glucose, glycerol and butyric acid, were measured to determine the hydrolysis efficiency and its rate. Cellulose hydrolysis was inhibited by 0.5 to 5.0 g l of HAL and FAL substances extracted from maize and cow manure, which are relevant concentrations for manure and maize digestion. Tributyrin hydrolysis, on the other hand, was only inhibited by 0.5 to 5.0 g l of HAL substances extracted from maize and cow manure and not by FAL substances. [ABSTRACT FROM AUTHOR]

Economically feasible and sustainable energy production from microalgae requires optimization of algal growth, maximization of lipid content, and enhancement of biomass conversion into energy. An innovative, mixed trophic state process with high productivity was implemented to generate microalgae with high lipid content for generating biodiesel and biogas. Auxenochlorella protothecoides, a unicellular green alga, was grown phototrophically to 0.28 dry weight per L (gdw/L) then concentrated to 36 gdw/L for use as an inoculum for a subsequent heterotrophic cultivation to a final density of nearly 120 gdw/L. Simultaneous nitrogen deprivation and glucose supplementation during the heterotrophic stage increased the total lipid content from 16 to 57 % while the triacylglycerol (TAG) fraction of total lipids advanced from 2 to 79 %. Productivity peaked at 4.9 g of biomass/L-h and 1.7 g TAGs/L-h. The extracted lipids, including high levels of oleic, linoleic, and palmitic acids, were converted into biodiesel with a predicted cetane number of 56.4 and low concentrations of long-chain saturated and polyunsaturated fatty acid methyl esters. Both intact microalgal biomass and lipid-extracted algal residues (LEA) were good substrates for anaerobic digestion (AD) with methane yields of 0.6 and 0.4 L/g volatile solids (VS), respectively. These yields represented nearly 80 % of theoretical methane potential. LEA, with a favorable carbon to nitrogen ratio (C:N) of approximately 19:1, is an appropriate substrate for anaerobic microorganisms, most likely because it contains essential nutrients required for microbial digestion. The biochemical composition of the biomass, especially its lipid content, is the major contributor for energy output. As a result, coupling biodiesel production with AD of LEA to generate methane can increase the overall process' energy output up to 40 %. [ABSTRACT FROM AUTHOR]

The original version of this article unfortunately contained incorrect data in Fig. 2 caption. [ABSTRACT FROM AUTHOR]