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Despite the vast interest in microalgae as feedstock for biodiesel production, relatively few studies examined their response to diurnal temperature fluctuation. Here, we describe biomass and lipid productivities and fatty acid profiles of thermo-resistant Micractinium sp. and Scenedesmus sp. grown in batch cultures in a laboratory set-up that mimics a typically warm summer day in Central Anatolia with a 16-h light temperature of 30 °C and 8-h dark temperature of 16 °C (30 °C (day)/16 °C (night)). Both strains can survive a temperature range of 10–50 °C. We found the lipid productivities of Micractinium sp. and Scenedesmus sp. as 30/21 mg L −1 d −1 and 6/7 mg L −1 d −1 , respectively during the 30 °C (day)/16 °C (night) cycle. Saturated fatty acid content increased with increasing temperature. Additionally, we cultured Micractinium sp. under Nitrogen (N) and Phosphorus (P) limiting conditions. Highest lipid productivity of 85.4 ± 2 mg L −1 d −1 was obtained under P-depletion during exponential growth phase. Oleic acid amount also increased eight fold during P-deplete. [ABSTRACT FROM AUTHOR]

Two fresh water microalgae, Coelastrella sp. M-60 and Micractinium sp. M-13 were investigated in this study for their potential of biodiesel production. For increasing biomass and lipid production, these microalgae were subjected to nutrient starvation (nitrogen, phosphorous, iron), salinity stress and nutrient supplementation with sugarcane industry effluent, citric acid, glucose and vitamin B 12 . The lipid productivity obtained from the isolates Coelastrella sp. M-60 (13.9 ± 0.4 mg/L/day) and Micractinium sp. M-13 (11.1 ± 0.2 mg/L/day) was maximum in salinity stress. The media supplemented with all the four nutrients yielded higher lipid productivity than the control. The response surface methodology (RSM) was employed to evaluate the effect of sugarcane industry effluent and citric acid on growth and lipid yield. Fatty acid profile of Coelastrella sp. M-60 and Micractinium sp. M-13 were composed of C-14, C-16:0, C-18:0, C-18:1 and C-18:2 and their fuel properties were also in accordance with international standards. [ABSTRACT FROM AUTHOR]

Nannochloropsis has emerged as a promising alga for biodiesel production. However, the genus consists of 6 species and hundreds of strains making strain selection a challenge. Furthermore, oil productivity is instrumental to economic viability of any algal strain for industrial production, which is dependent on growth rate and oil content. In most cases, these two parameters have been studied independently. Thus, the goal of this study is to provide a combined method for evaluating strain performance in specially designed photobioreactors together with an in-depth lipidomic analyses. The nine strains of Nannochloropsis tested showed considerable variations in productivity and lipidomics highlighting the importance of strain selection. Finally, Nannochloropsis gaditana CCMP527 and Nannochloropsis salina CCMP537 emerged as the two most promising strains, with an oil content of 37 and 27 dry wt% after 11-day nitrogen starvation, respectively, resulting in TAG productivity of 13 × 10 −3 and 18 × 10 −3 kg m −3 d −1 , respectively. [ABSTRACT FROM AUTHOR]

The study explores on upstream and downstream process in Microcystis aeruginosa for biodiesel production. The alga was isolated from temple tank, acclimatized and successfully mass cultivated in open raceway pond at semi-continuous mode. A two step combined process was designed and harvested 99.3% of biomass, the daily dry biomass productivity was recorded up to 28 g m –2 day −1 . The lipid extraction was optimized and achieved 21.3%; physicochemical properties were characterized and found 11.7% of FFA, iodine value 72% and 99.2% of ester content. The lipid was transesterified by a two step simultaneous process and produced 90.1% of biodiesel; the calorific value of the biodiesel was 38.8 MJ/kg. Further, the physicochemical properties of biodiesel was characterized and found to be within the limits of American ASTM D6751. Based on the areal and volumetric biomass productivity estimation, M. aeruginosa can yield 84.1 tons of dry biomass ha −1 year −1 . [ABSTRACT FROM AUTHOR]

In this study, Scenedesmus obtusus XJ-15 was firstly selected from seven strains microalgae (Chlorophyta, Scenedesmaceae ) and then cultivated using a two-stage strategy, which composed of fast cell growth in stage I and followed by lipid induction in stage II in 5-L flasks outdoors. In stage I, the biomass productivity was increased from 139.4 to 212.1 mg L −1 d −1 . In stage II, lipid content was increased from 26.1% to 47.7% by adding NaCl into the culture. This two-stage process was also realized in an 140-L photobioreactor outdoors, with a biomass productivity of 86.5 mg L −1 d −1 and CO 2 fixation rate of 170.0 mg L −1 d −1 in the first stage, and high lipid content of 42.1% in the second stage. With such a culture strategy, the overall lipid productivity was improved and better biodiesel quality was obtained. These results suggested the photoautotrophic two-stage system was not only feasible but also effective. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heavy ion irradiation mutagenesis was firstly applied in microalgae breeding. [•] The mutant HP-1 showed higher biomass production than the wild type Nannochloropsis. [•] Its lipid productivity was increased by 28% compared to the wild type. [•] The reason caused its higher biomass accumulation and lipid productivity was studied. [•] Further, its TAG content was higher and polar lipid was lower than the wild type. [Copyright &y& Elsevier]

Highlights: [•] Microalgae base oil production was analyzed as a potential biodiesel feedstock. [•] Different harvesting and solvent lipid extraction pathways were evaluated. [•] It is of capital importance to reduce the investment of the cultivation process. [•] Biomass production (cultivation/harvesting) is responsible of 65% of the total cost. [•] The required biodiesel price must be around $6000 per MT to have a feasible process. [Copyright &y& Elsevier]

Abstract: To address the large energy consumption of microalgae dewatering and to simplify the conventional two-step method (cellular lipid extraction and lipid transesterification) for biodiesel production, a novel process for the direct conversion of wet microalgae biomass into biodiesel by microwave irradiation is proposed. The influences of conventional thermal heating and microwave irradiation on biodiesel production from wet microalgae biomass were investigated. The effects of using the one-step (simultaneous lipid extraction and transesterification) and two-step methods were also studied. Approximately 77.5% of the wet microalgal cell walls were disrupted under microwave irradiation. The biodiesel production rate and yield from wet microalgae biomass obtained through the one-step process using microwave irradiation were 6-fold and 1.3-fold higher than those from wet microalgae obtained through the two-step process using conventional heating. [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: High-cost downstream process is a major bottleneck for producing microalgal biodiesel at reasonable price. Conventional lipid extraction process necessitates biomass drying process, which requires substantial amount of energy. In this regard, lipid extraction from wet biomass must be an attractive solution. However, it is almost impossible to recover lipid directly from wet microalgae with current technology. In this study, we conceived osmotic shock treatment as a novel method to extract lipid efficiently. Osmotic shock treatment was applied directly to wet Chlamydomonas reinhardtii biomass with water content >99%, along with both polar and non-polar organic solvents. Our results demonstrated that osmotic shock could increase lipid recovery approximately 2 times. We also investigated whether the presence of cell wall or different cell stages could have any impact on lipid recovery. Cell wall-less mutant stains and senescent cell phase could display significantly increased lipid recovery. Taken together, our results suggested that osmotic shock is a promising technique for wet lipid extraction from microalgal biomass and successfully determined that specific manipulation of biomass in certain cell phase could enhance lipid recovery further. [Copyright &y& Elsevier]

Abstract: The myxomycetes are a group of primitive phagotrophic eukaryotes characterized by a distinctive plasmodial stage that is well known for its rapid growth rate. In the present study, biomass and lipid production of several different species of myxomycetes were investigated. Physarum polycephalum was found to produce the highest amounts of both dry biomass (1.30g), and lipid (0.143g) per 20mL medium (equal to 65.0g biomass and 7.15g lipid per one liter of medium). Analysis of P. polycephalum lipids by thin layer chromatography (TLC) and fatty acid methyl esters (FAMES) by gas chromatography–mass spectrometry (GC–MS) techniques showed that the major lipid type is triglyceride (95.5%), followed by phospholipids (2.6%); diglyceride (0.92%) and monoglyceride (0.92%). Myxomycete lipids consist of three dominant fatty acids: oleic (20%), linoleic (33%), and palmitoleic (17%). These results suggest that P. polycephalum has considerable potential as a source of lipids for biodiesel production. [Copyright &y& Elsevier]

Abstract: In order to develop feasible production processes for microalgal biodiesel, the isolation of high neutral lipid producing microalgae is crucial. Since the established Nile Red (NR) method for detection of intracellular lipids has been successful only for some microalgae, a more broadly applicable detection method would be desirable. Therefore, BODIPY 505/515, a lipophilic bright green fluorescent dye was tested for detection of intracellular lipids in Chlorella vulgaris, Dunaliella primolecta and Chaetoceros calcitrans. An optimum concentration of 0.067μgml−1 was determined for lipid staining in the microalgae. Compared to NR, BODIPY 505/515 was more effective in staining microalgae and showed resistance to photobleaching, maintaining its fluorescence longer than 30min. [Copyright &y& Elsevier]

Abstract: Bio-sequestration of CO2 through microalgae cultivation is considered as a viable option for biofuel production as well as CO2 mitigation. Influence of CO2 sparging period and interval was evaluated on the growth and lipid accumulation of microalgae cultivated in domestic wastewater under mixotrophic microenvironment. Process performance was assessed in two phases viz., growth (GP) and starvation phases (SP) each with 8days of retention time. Experimental variations depicted marked influence on biomass growth and lipid accumulation of microalgae with the function of harvesting period. Sparging period of 120s documented maximum biomass growth (GP, 3.4mg/ml) and lipid productivity (SP, 27.3%) while in intervals, 4h (120s) condition showed maximum biomass (3.2mg/ml) and lipid productivity (27.8%). Total chlorophyll components documented higher concentrations of Chl b supporting the observed higher lipid productivity. Fatty acid composition varied with the experimental variations and represented higher degree of saturation indicating their utility as biodiesel. [Copyright &y& Elsevier]

Abstract: This study investigated the possibility of utilizing detoxified sugarcane bagasse hydrolysate (DSCBH) as an alternative carbon source to culture Yarrowia lipolytica Po1g for microbial oil and biodiesel production. Sugarcane bagasse hydrolysis with 2.5% HCl resulted in maximum total sugar concentration (21.38g/L) in which 13.59g/L is xylose, 3.98g/L is glucose, and 2.78g/L is arabinose. Detoxification of SCBH by Ca(OH)2 neutralization reduced the concentration of 5-hydroxymethylfurfural and furfural by 21.31% and 24.84%, respectively. Growth of Y. lipolytica Po1g in DSCBH with peptone as the nitrogen source gave maximum biomass concentration (11.42g/L) compared to NH4NO3 (6.49g/L). With peptone as the nitrogen source, DSCBH resulted in better biomass concentration than d-glucose (10.19g/L), d-xylose (9.89g/L) and NDSCBH (5.88g/L). The maximum lipid content, lipid yield and lipid productivity of Y. lipolytica Po1g grown in DSCBH and peptone was 58.5%, 6.68g/L and 1.76g/L-day, respectively. [Copyright &y& Elsevier]

Abstract: A 1.2kW, 2450MHz resonant continuous microwave processing system was designed and optimized for oil extraction from green algae (Scenedesmus obliquus). Algae-water suspension (1:1 w/w) was heated to 80 and 95°C, and subjected to extraction for up to 30min. Maximum oil yield was achieved at 95°C and 30min. The microwave system extracted 76–77% of total recoverable oil at 20–30min and 95°C, compared to only 43–47% for water bath control. Extraction time and temperature had significant influence (p <0.0001) on extraction yield. Oil analysis indicated that microwaves extracted oil containing higher percentages of unsaturated and essential fatty acids (indicating higher quality). This study validates for the first time the efficiency of a continuous microwave system for extraction of lipids from algae. Higher oil yields, faster extraction rates and superior oil quality demonstrate this system’s feasibility for oil extraction from a variety of feedstock. [ABSTRACT FROM AUTHOR]

Abstract: The fresh water microalga Neochloris oleoabundans was investigated for its ability to accumulate lipids and especially triacylglycerols (TAG). A systematic study was conducted, from the determination of the growth medium to its characterization in an airlift photobioreactor. Without nutrient limitation, a maximal biomass areal productivity of 16.5gm−2 day−1 was found. Effects of nitrogen starvation to induce lipids accumulation was next investigated. Due to initial N. oleoabundans total lipids high content (23% of dry weight), highest productivity was obtained without mineral limitation with a maximal total lipids productivity of 3.8gm−2 day−1. Regarding TAG, an almost similar productivity was found whatever the protocol was: continuous production without mineral limitation (0.5gm−2 day−1) or batch production with either sudden or progressive nitrogen deprivation (0.7gm−2 day−1). The decrease in growth rate reduces the benefit of the important lipids and TAG accumulation as obtained in nitrogen starvation (37% and 18% of dry weight, respectively). [Copyright &y& Elsevier]

• Report the highest accumulated lipids content (≥40%) microalgal species till 2019. • Wild microalgal strains exhibit high accumulative lipid content. • Advanced abiotic stress induced the microalgal growth and lipid content. • High lipid content microalgae supported the advanced wastewater treatment. • Lipidomics direct suitable engineered microalgal strain for high lipid content. Microalgal lipids consist of non-polar and polar lipids. Triacyleglyceride (TAG), a non-polar lipid, is convertible to biodiesel, whereas glycolipids and phospholipids are polar and not convertible to biodiesel owing to their high degree of unsaturation (polyunsaturated fatty acids), which makes the production process insufficient and expensive. In this review, microalgal species that contain the highest lipid content (≥40%) in the literature till 2019 are highlighted. The differentiation between non-polar and polar lipids and the limitations in the conversion of polar lipids to biodiesel are reported. The basic and advanced factors contributing to the accumulation of lipids convertible to biodiesel is discussed. Microalgal species including Scenedesmus obliquus , Ourococcus multisporus , Chlamydomonas pitschmannii , Micractinium reisseri , and Botryococcus braunii with high lipid content are potential candidates for biomass/biodiesel production and nutrient removal from wastewater. Application of lipidomics and transcriptomics to manipulate the lipid associated gene acetyl-CoA synthetase in microalgae improves the accumulative lipid content. [ABSTRACT FROM AUTHOR]