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Graphical abstract Highlights • Two strains of non-acidophilic microalgae (NAM) were acclimated to pH 3.0. • Flow cytometry analysis indicated their ability to withstand acidic pH. • Both the acclimated strains yielded good amounts of biomass and neutral lipids. • FTIR analysis confirmed accumulation of more triacylglycerols in NAM strains. • First report on biodiesel production in good amounts by NAM strains at pH 3.0. Abstract The overwhelming response towards algal biodiesel production has been well-recognized recently as a sustainable alternative to conventional fuels. Most microalgae cannot grow well at acidic pH. The present study, therefore, investigated whether non-acidophilic microalgae Desmodesmus sp. MAS1 and Heterochlorella sp. MAS3 can be acclimated to extreme-acidic pH for sustainable production of biomass and biodiesel. Growth analysis indicated that both the microalgal strains possessed a passive uptake of CO 2 at pH 3.0 with biomass production of 0.25 g dry wt. L−1 in Desmodemus sp. and 0.45 g dry wt. L−1 in Heterochlorella sp.. Flow-cytometry analysis for reactive oxygen species, membrane permeability and neutral-lipids revealed the capabilities of both strains to adapt to the stress imposed by acidic pH. Lipid production was doubled in both the strains when grown at pH 3.0. In-situ transesterification of biomass resulted in 13–15% FAME yield in the selected microalgae, indicating their great potential in biofuel production. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Microalgae incubation after PEF-treatment improves water-soluble components release. • Microalgae incubation after PEF-treatment improves lipid extraction yields. • With 20 h of incubation, energy of PEF-treatment can be reduced to 0.25 MJ/kg DW. • Incubation is also efficient at 4 °C but less than at 25 °C. Abstract Pulsed Electric Field (PEF) pre-treatment, applied on fresh microalgae Auxenochlorella protothecoides, induces spontaneous release of a substantial water fraction and enables subsequent lipid extraction using ethanol-hexane blends. In this study, fresh microalgae suspensions were treated with PEF and incubated under inert conditions. Incubation promotes the release of ions and carbohydrates and increases the yields of subsequent lipid extraction thus enabling a considerable reduction of PEF-treatment energy. With a 20 h incubation period at 25 °C, almost total lipid extraction is achieved with a specific PEF-treatment energy of only 0.25 MJ/kg DW. Incubation on ice remains beneficial but less efficient than at 25 °C. Additionally, incubating microalgae cells in suspension at 100 g DW /L or in a dense paste, was almost equally efficient. Correlation between the different results suggests that spontaneous release of ions and carbohydrates facilitates more successful lipid extraction. A direct causality between the two phenomena remains to be demonstrated. [ABSTRACT FROM AUTHOR]

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

Heterotrophic microalgae, capable of converting organic carbons to biofuel, as well as assimilating nutrients, have a great prospective in wastewater treatment. Meanwhile, the knowledge about heterotrophic microalgae is still far less than the autotrophic conterpart. Hence, in this study, 20 heterotrophic microalgal strains were isolated from a domestic wastewater treatment plant, and identified according to morphology and partial 18S and 23S rRNA gene sequences. Further, their biological traits were assessed in terms of N, P, TOC removal efficiencies, growth parameters, self-settleability and lipids production, expressed through a comprehensive selection index. By such, the optimal strains were chosen and applied back to treat the real wastewater, with or without pretreatment of sterilization. An organic-adaptable strain, i.e., Botryococcus sp. NJD-1, was ultimately recommended to achieve the concurrent biofuel production (up to 61.7% lipid content) and pollutants removal (up to 64.5%, 89.8% and 67.9% for N, P and TOC) in pristine wastewater. [ABSTRACT FROM AUTHOR]

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

Microalgal starch and lipids, carbon-based storage molecules, are useful as potential biofuel feedstocks. In this work, cultivation strategies maximising starch and lipid formation were established by developing a multi-parameter kinetic model describing microalgal growth as well as starch and lipid formation, in conjunction with laboratory-scale experiments. Growth dynamics are driven by nitrogen-limited mixotrophic conditions, known to increase cellular starch and lipid contents whilst enhancing biomass growth. Model parameters were computed by fitting model outputs to a range of experimental datasets from batch cultures of Chlamydomonas reinhardtii . Predictive capabilities of the model were established against different experimental data. The model was subsequently used to compute optimal nutrient-based cultivation strategies in terms of initial nitrogen and carbon concentrations. Model-based optimal strategies yielded a significant increase of 261% for starch (0.065 gC L −1 ) and 66% for lipid (0.08 gC L −1 ) production compared to base-case conditions (0.018 gC L −1 starch, 0.048 gC L −1 lipids). [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]

The lipid extraction from the microbial biomass is a tedious and high cost dependent process. In the present study, detergent assisted lipids extraction from the culture of the yeast Yarrowia lipolytica SKY-7 was carried out. Response surface methodology (RSM) was used to investigate the effect of three principle parameters (N-LS concentration, time and temperature) on microbial lipid extraction efficiency % (w/w). The results obtained by statistical analysis showed that the quadratic model fits in all cases. Maximum lipid recovery of 95.3 ± 0.3% w/w was obtained at the optimum level of process variables [N-LS concentration 24.42 mg (equal to 48 mg N-LS/g dry biomass), treatment time 8.8 min and reaction temperature 30.2 °C]. Whereas the conventional chloroform and methanol extraction to achieve total lipid recovery required 12 h at 60 °C. The study confirmed that oleaginous yeast biomass treatment with N-lauroyl sarcosine would be a promising approach for industrial scale microbial lipid recovery. [ABSTRACT FROM AUTHOR]

A one-stage cultivation process of the microalgae Scenedesmus obtusiusculus with medium based on natural water sources was developed to enhance lipids and carbohydrates. A medium based on artificial sea water, Baltic Sea water and river water with optimized nutrient concentrations compared to the standard BG-11 for nitrate (−75%), phosphate and iron (−90%) was used for cultivation. Although nitrate exhaustion over cultivation resulted in nitrate limitation, growth of the microalgae was not reduced. The lipid content increased from 6.0% to 19.9%, an increase in oleic and stearic acid was observed. The unsaponifiable matter of the lipid fraction was reduced from 19.5% to 11.4%. The carbohydrate yield rose from 45% to 50% and the protein content decreased from 32.4% to 15.9%. Using natural water sources with optimized nutrient concentrations could open the opportunity to modulate biomass composition and to reduce the cultivation costs. [ABSTRACT FROM AUTHOR]

Taxonomy and phylogeny of twenty two microalgal isolates were examined using both universal and newly designed molecular primers. Among the isolates, Scenedesmus bijugus , Coelastrella sp., Auxenochlorella protothecoides , and Chlorella sp. were particularly promising in terms of producing lipids as measured by fatty acid methyl esters (FAME) analysis and significant concentration of carotenoids. A comparative experiment showed that S. bijugus and Chlorella sp. were the most promising candidates (L − 1 d − 1 , with biomass) 174.77 ± 6.75, 169.81 ± 5.22 mg, lipids 40.14 ± 3.31, 39.72 ± 3.89 mg, lutein 0.47, 0.36 mg, and astaxanthin 0.27, 0.18 mg respectively. The fatty acids produced by these microalgal isolates were mainly palmitic, stearic, oleic, linoleic, and linolenic acid. The freshwater microalgal isolate S. bijugus be the most suitable isolate for producing biodiesel and carotenoids, due to high productivity of biomass, lipids, metabolites, and its suitable fatty acid profile. [ABSTRACT FROM AUTHOR]

This study presents gravimetric enrichment of mixed culture to screen starch and lipid producing species separately in a sequencing batch reactor. In the enriched starch-producing mixed culture photobioreactor, the starch content at the end of steady state batch became 3.42 times the beginning of depletion. Whereas in the enriched lipid-producing photobioreactor, the lipid content at the end of steady state batch became 3 times the beginning of famine phase. The obtained results revealed that the gravimetric enrichment is a suitable screening method for specific production of storage compounds in none-sterile large-scaled condition. [ABSTRACT FROM AUTHOR]

The aim of the present study was to find out the optimum sodium bicarbonate concentration to produce higher biomass with higher lipid and carbohydrate contents in microalgae Scenedesmus sp. CCNM 1077. The role of bicarbonate supplementation under different nutritional starvation conditions was also evaluated. The results clearly indicate that 0.6 g/L sodium bicarbonate was optimum concentration resulting in 20.91% total lipid and 25.56% carbohydrate along with 23% increase in biomass production compared to normal growth condition. Addition of sodium bicarbonate increased the activity of nutrient assimilatory enzymes, biomass, lipid and carbohydrate contents under different nutritional starvation conditions. Nitrogen starvation with bicarbonate supplementation resulted in 54.03% carbohydrate and 34.44% total lipid content in microalgae Scenedesmus sp. CCNM 1077. These findings show application of bicarbonate grown microalgae Scenedesmus sp. CCNM 1077 as a promising feedstock for biodiesel and bioethanol production. [ABSTRACT FROM AUTHOR]

Extracting lipids from oleaginous microbial cells in a cost effective and environmentally compatible manner remains a critical challenge in developing manufacturing paradigms for advanced liquid biofuels. In this study, a new approach using microbial growth inhibitors from lignocellulose-derived feedstocks was used to extract lipids efficiently from wet cell mass of the oleaginous bacterium Rhodococcus opacus MITXM-61. Nine common lignocellulose-derived inhibitors for treatment of cells prior to solvent extraction were used and evaluated for their efficiency of lipid extraction from the cells. When the inhibitors were individually examined, formic acid and furfural showed the highest extraction efficiency of lipids from wet cell mass. Multiple extractions of lipids with methanol from wet cell mass pretreated with combined common inhibitors or hardwood hydrolysate comprising lignocellulose-derived inhibitors resulted in lipid recovery of greater than 85% of total lipids, a 1.7-fold increase of lipid extraction as compared to those in the absence of the inhibitors. [ABSTRACT FROM AUTHOR]

Methods to convert microalgal biomass to bio based fuels and chemicals are limited by several processing and economic hurdles. Research conducted in this study modified/optimized a previously published procedure capable of extracting transesterifiable lipids from wet algal biomass. This optimization resulted in the extraction of 77% of the total transesterifiable lipids, while reducing the amount of materials and temperature required in the procedure. In addition, characterization of side streams generated demonstrated that: (1) the C/N ratio of the residual biomass or lipid extracted (LE) biomass increased to 54.6 versus 10.1 for the original biomass, (2) the aqueous phase generated contains nitrogen, phosphorous, and carbon, and (3) the solid precipitate phase was composed of up to 11.2 wt% nitrogen (70% protein). The ability to isolate algal lipids and the possibility of utilizing generated side streams as products and/or feedstock material for downstream processes helps promote the algal biorefinery concept. [ABSTRACT FROM AUTHOR]

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

[Display omitted] • Water-plasma was first employed to disrupt microalgae cell walls. • Water-plasma was extremely effective at disrupting cell walls. • Combined water-plasma and TPP were able to recover 74.34% lipid within 10 min. • Proposed process prevented drying step of biomass and reduced energy consumption. Traditional methods for lipid extraction from microalgal biomass usually involve harsh reaction conditions or the use of contaminant reagents, which lead to enormous energy consumption and wastage. Hence, a novel strategy was presented, which combined water-plasma and three-phase partitioning (TPP) techniques. Benefiting from its unique advantages such as rapid and low cost, water-plasma strategy can disrupt microalgal cell wall and can thus greatly affect lipid extraction. As a result, assisted with the TPP method, excellent performance lipid recovery (74.34%) was obtained at 200 W in 10 min. The performance was superior to that achieved through cell disruption via water-plasma pretreatment. Importantly, the whole process of lipid extraction prevented the drying of microalgal biomass, contributing to reduced energy consumption in large-scale biodiesel production. Moreover, the high fatty acids content suggested that the extracted lipids are great potential candidate for biodiesel production. [ABSTRACT FROM AUTHOR]

[Display omitted] • Intrinsic interactions between lipid feedstocks and lipid-based biofuels. • Advancements in lipid-associated biofuel technology. • Properties and applicability of various lipid sources for biofuel production. • Biotechnology and progress in lipid production for advanced biofuels. The expanding use of fossil fuels has caused concern in terms of both energy security and environmental issues. Therefore, attempts have been made worldwide to promote the development of renewable energy sources, among which biofuel is especially attractive. Compared to other biofuels, lipid-derived biofuels have a higher energy density and better compatibility with existing infrastructure, and their performance can be readily improved by adjusting the chemical composition of lipid feedstocks. This review thus addresses the intrinsic interactions between lipid feedstocks and lipid-based biofuels, including biodiesel, and renewable equivalents to conventional gasoline, diesel, and jet fuel. Advancements in lipid-associated biofuel technology, as well as the properties and applicability of various lipid sources in terms of biofuel production, are also discussed. Furthermore, current progress in lipid production and profile optimization in the context of plant lipids, microbial lipids, and animal fats are presented to provide a wider context of lipid-based biofuel technology. [ABSTRACT FROM AUTHOR]

The growth, lipid production, and carbon use efficiency of two oleaginous yeasts, Rhodosporidium babjevae and Rhodosporidium diobovatum , were compared under nitrogen-limiting conditions with glycerol as the carbon source. Final biomass concentrations of R. babjevae and R. diobovatum were 9.4 ± 0.80 g/L and 12.0 ± 0.82 g/L, respectively, after 120 h of growth. Final lipid accumulation in for R. babjevae and R. diobovatum were 34.9 ± 3.0% cell dry weight (cdw) and 63.7 ± 4.5% cdw, respectively. Biomass production increased to 9.9 ± 0.2 g/L for R. babjevae and 14.1 ± 0.2 g/L for R. diobovatum in medium containing biodiesel-derived waste glycerol, but lipid accumulation decreased in both species. In a 7 L bioreactor with biodiesel-derived glycerol as carbon source, R. diobovatum produced 13.6 ± 0.4 g/L biomass and accumulated lipids to 50.7 ± 2.2% cdw, matching flask experiments. [ABSTRACT FROM AUTHOR]

Microalgal biofilms grown to evaluate potential nutrient removal options for wastewaters and feedstock for biofuels production were studied to determine the influence of bicarbonate amendment on their growth, nutrient uptake capacity, and lipid accumulation after nitrogen starvation. No significant differences in growth rates, nutrient removal, or lipid accumulation were observed in the algal biofilms with or without bicarbonate amendment. The biofilms possibly did not experience carbon-limited conditions because of the large reservoir of dissolved inorganic carbon in the medium. However, an increase in photosynthetic rates was observed in algal biofilms amended with bicarbonate. The influence of bicarbonate on photosynthetic and respiration rates was especially noticeable in biofilms that experienced nitrogen stress. Medium nitrogen depletion was not a suitable stimulant for lipid production in the algal biofilms and as such, focus should be directed toward optimizing growth and biomass productivities to compensate for the low lipid yields and increase nutrient uptake. [ABSTRACT FROM AUTHOR]

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

This study presents experimental measurements of the biochemical methane production for whole and lipid extracted Nannochloropsis salina . Results show whole microalgae produced 430 cm 3 -CH 4 g-volatile solids −1 (g-VS) ( σ = 60), 3 times more methane than was produced by the LEA, 140 cm 3 -CH 4 g-VS −1 ( σ = 30). Results illustrate current anaerobic modeling efforts in microalgae to biofuel assessments are not reflecting the impact of lipid removal. On a systems level, the overestimation of methane production is shown to positively skew the environmental impact of the microalgae to biofuels process. Discussion focuses on a comparison results to those of previous anaerobic digestion studies and quantifies the corresponding change in greenhouse gas emissions of the microalgae to biofuels process based on results from this study. [ABSTRACT FROM AUTHOR]

Renewable fuels and energy are of major concern worldwide and new raw materials and processes for its generation are being investigated. Among these raw materials, algae are a promising source of lipids and energy. Thus, in this work four different algae have been used for lipid extraction and biogas generation. Lipids were obtained by supercritical CO 2 extraction (SCCO 2 ), while anaerobic digestion of the lipid-exhausted algae biomass was used for biogas production. The extracted oil composition was analyzed (saturated, monounsaturated and polyunsaturated fatty acids) and quantified. The highest lipid yields were obtained from Tetraselmis sp. (11%) and Scenedesmus almeriensis (10%), while the highest methane production from the lipid-exhausted algae biomass corresponded to Tetraselmis sp . (236 mL CH 4 /g VS added ). [ABSTRACT FROM AUTHOR]

Highlights: [•] Mixotrophic mode of cultivation induces higher biomass and lipid productivities. [•] Maintenance of light:dark cycle is crucial for efficient glucose uptake. [•] Low carbon is needed for growth whereas high carbon for lipid synthesis. [•] High nutrient removal was achieved and process can be easily scaled-up. [•] Increasing glucose concentrations affects FAME composition of lipids. [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: [•] A novel combined hydrolysis was developed for fungal lipid fermentation. [•] Detoxification and pH adjustment were minimized for lignocellulosic biofuel production. [•] Lipid accumulation on hydrolysate had a comparable performance with the control. [ABSTRACT FROM AUTHOR]

Highlights: [•] SMP for whole microalgae were better than lipid-extracted microalgae residues. [•] The control of I/S ratio during BMP could overcome pH drop and LCFA inhibition. [•] No signs of VFA or ammonia inhibition occurred when digested at I/S⩾1.0 ratio. [•] Higher methane production was not related to species but to lipid content of biomass. [Copyright &y& Elsevier]

Highlights: [•] A dual strategy for wastewater treatment and biofuel feedstock production. [•] Mine wastewater increased the nutrient removal efficiency of M. reisseri. [•] Mine wastewater improved the growth and lipid productivity of M. reisseri. [•] Concentrated municipal wastewater supported the algal autoflocculation. [ABSTRACT FROM AUTHOR]

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

Highlights: [•] Ethanol had a positive effect on biomass accumulation of Scenedesmus sp. [•] Maximum increment of lipid and fatty acid content were 1.34 and 3.14 times. [•] Ethanol concentration at 0.6mL/L inhibited lipid content accumulation. [•] Negligible 14C-ethanol was transferred to fatty acids used as biodiesel feedstock. [•] Promising method for feedstock production of algae biodiesel. [ABSTRACT FROM AUTHOR]

Highlights: [•] Yeasts were selected using a qualitative technique by staining with Sudan Black B. [•] We evaluated the lipid production by Candida sp. using pure and raw glycerol. [•] The profile of fatty acids produced using raw glycerol was similar to vegetable oils. [•] The yeast Candida sp. was able to accumulate about 56% of lipids. [ABSTRACT FROM AUTHOR]

Abstract: The potential for biodiesel production from microalgal lipids and for CO2 mitigation due to photoautotrophic growth of microalgae have recently been recognized. Microalgae biomass also has other valuable components, including carbohydrates, long chain fatty acids, pigments and proteins. The microalgae-based carbohydrates consist mainly of cellulose and starch without lignin; thus they can be ready carbon source for the fermentation industry. Some microalgae can produce long chain fatty acids (such as DHA and EPA) as valuable health food supplements. In addition, microalgal pigments and proteins have considerable potential for many medical applications. This review article presents comprehensive information on the current state of these commercial applications, as well as the utilization and characteristics of the microalgal components, in addition to the key factors and challenges that should be addressed during the production of these materials, and thus provides a useful report that can aid the development of an efficient microalgae-based biorefinery process. [Copyright &y& Elsevier]

Abstract: In this work, 30 microalgae strains from 17 genera were investigated in regard to biomass productivity in photoautotrophic growth conditions, lipid amount, lipid quality and biomass degradability. Six strains could be identified with robust phototrophic growth properties and high biomass productivities equal or above 300mgl−1 day−1. Anaerobic fermentation of the algal biomass was most efficient for the marine members of the genera Dunaliella and Navicula, while biogas production with the freshwater strains generally resulted in lower methane yields. Monoraphidium contortum was identified as promising candidate for liquid biofuel production, characterized by high biomass productivity during maximum growth (maximum increase of 896mg dry biomass weight (DW) l−1 day−1) and a promising lipid profile. Neutral lipid production was strongly induced in M. contortum by nitrogen deficient conditions and accumulated to up to 20.4±2.2% of DW. [Copyright &y& Elsevier]

Abstract: Microalgae can grow rapidly and capture CO2 from the atmosphere to convert it into complex organic molecules such as lipids (biodiesel feedstock). High scale economically feasible microalgae based oil depends on optimizing the entire process production. This process can be divided in three very different but directly related steps (production, concentration, lipid extraction and transesterification). The aim of this study is to identify the best method of lipid extraction to undergo the potentiality of some microalgal biomass obtained from two different harvesting paths. The first path used all physicals concentration steps, and the second path was a combination of chemical and physical concentration steps. Three microalgae species were tested: Phaeodactylum tricornutum, Nannochloropsis gaditana, and Chaetoceros calcitrans One step lipid extraction–transesterification reached the same fatty acid methyl ester yield as the Bligh and Dyer and soxhlet extraction with n-hexane methods with the corresponding time, cost and solvent saving. [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: A switchable hydrophilicity solvent (SHS) was studied for its effectiveness at extracting lipids from freeze-dried samples of Botryococcus braunii microalgae. The SHS N,N-dimethylcyclohexylamine extracted up to 22wt.% crude lipid relative to the freeze-dried cell weight. The solvent was removed from the extract with water saturated with carbon dioxide at atmospheric pressure and recovered from the water upon de-carbonation of the mixture. Liquid chromatography–mass spectrometry (LC–MS) showed that the extracted lipids contained high concentrations of long chain tri-, di- and mono-acylglycerols, no phospholipids, and only 4–8% of residual solvent. Unlike extractions with conventional organic solvents, this new method requires neither distillation nor the use of volatile, flammable or chlorinated organic solvents. [Copyright &y& Elsevier]

Abstract: Future micro-algal biofuels will most likely be derived from open-pond production systems. These are by definition open to “invasion” by grazers, which could devastate micro-algal mass-cultures. There is an urgent requirement for methodologies capable of early detection and control of grazers in dense algal cultures. In this study a model system employing the marine alga Nannochloropsis oculata was challenged by grazers including ciliates, amoebae and a heterotrophic dinoflagellate. A FlowCAM flow-cytometer was used to detect all grazers investigated (size range <20–>80μm in length) in the presence of algae. Detection limits were <10cellsml−1 for both “large” and “small” model grazers, Euplotes vannus (80×45μm) and an unidentified holotrichous ciliate (∼18×8μm) respectively. Furthermore, the system can distinguish the presence of ciliates in N. oculata cultures with biotechnologically relevant cell densities; i.e. >1.4×108 cellsml−1 (>0.5gl−1 dry wt.). [Copyright &y& Elsevier]

Abstract: Microalgae have significant potential to form the basis of the next biofuel revolution. They have high growth and solar energy conversion rates. Furthermore, their osmotolerance, metabolic diversity and capacity to produce large amounts of lipids have attracted considerable interest. Although there are a handful of commercially successful examples of the photoautotrophic mass-culture of algae, these have focused on the production of higher value products (pigments, health-foods etc.). The technical and commercial challenges to develop an economically viable process for biofuels are considerable and it will require much further R&D. In this paper the biological constraints, with a particular focus on strain selection are discussed. [Copyright &y& Elsevier]

Abstract: Three different strains of colonial green alga Botryococcus bruanii Kutz. AP103, AP104 and AP105 were isolated from the freshwater lake Kolleru, Andhra Pradesh, India. The morphological features of these three isolates were studied under laboratory conditions. Molecular identification of the strains was carried out using 18S rRNA analysis and their systematic position was confirmed to species level as B. braunii. Among these isolates, B. braunii AP103 recorded highest biomass concentration of 1.7±0.12gL−1, 17% lipids, 17% proteins, 32% carbohydrates and 13% hydrocarbons under laboratory condition. Under open raceway pond AP103 produced a biomass concentration of 1.8±0.13gL−1, 19% lipids, 33% carbohydrates, 18% proteins and 11% hydrocarbons. The hydrocarbons profile showed the presence of heptadecane (34%) and hexadecane (12.5%). Oleic (25.7%), linolenic (34.26%) and palmitic (9.42%) acids were the major fatty acids present in the lipids extracted from AP103. [Copyright &y& Elsevier]

Abstract: Synechocystis sp. PCC6803 exhibited a high degree of variation in biomass and lipid production rates in response to temperature changes in a photobioreactor. Compared with an optimal temperature of 30–33°C, a higher temperature of 44°C and lower temperatures of 22°C and 18°C severely inhibited the specific growth rate (up to a 66% decrease), biomass production rate (up to a 71% decrease), nutrient utilization rates (up to a 77% decrease), and lipid production rate (up to a 80% decrease). Temperature stress triggered changes in the relative percentage of individual fatty acids (mainly for C16:0 and C18:3), and degree of unsaturation significantly changed: 0.87 at 30°C, 0.62 at 44°C, and 1.29 at 18°C. Although PCC6803 survived temperature stress and maintained its predominate position in the culture, it could not fully recover from long-term temperature stress. Thus, avoiding prolonged exposure to extreme temperature is crucial for using PCC6803 as feedstock for biofuel production. [Copyright &y& Elsevier]

Abstract: The aim of this work was to investigate the potential conversion of Chlamydomonas reinhardtii biomass harvested after hydrogen production. The spent algal biomass was converted into nitrogen-rich bio-char, biodiesel and pyrolysis oil (bio-oil). The yield of lipids (algal oil), obtained by solvent extraction, was 15±2% w/wdry-biomass. This oil was converted into biodiesel with a 8.7±1% w/wdry-biomass yield. The extraction residue was pyrolysed in a fixed bed reactor at 350°C obtaining bio-char as the principal fraction (44±1% w/wdry-biomass) and 28±2% w/wdry-biomass of bio-oil. Pyrolysis fractions were characterized by elemental analysis, while the chemical composition of bio-oil was fully characterized by GC–MS, using various derivatization techniques. Energy outputs resulting from this approach were distributed in hydrogen (40%), biodiesel (12%) and pyrolysis fractions (48%), whereas bio-char was the largest fraction in terms of mass. [Copyright &y& Elsevier]

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

Abstract: Effects of nitrate feeding on the cell growth and lipid accumulation of marine microalgae Isochrysis zhangjiangensis were investigated. When nitrate was supplied at interval of 24h, instead of 72h, a high lipid content of 40.9% and a biomass density of 3.1gL−1 were obtained. To confirm whether I. zhangjiangensis accumulates lipid during nitrogen-repletion, a two-stage cultivation method was applied. This algal strain had a high lipid content during sustained nitrate addition and showed a high carbohydrate content under nitrate-depletion conditions. These results revealed that this algal strain can accumulate lipids under nitrogen-repletion conditions and accumulate carbohydrate under nitrogen-depletion conditions. When cultured in an extremely high nitrate concentration, 9gL−1 at 24h intervals, the growth of algal cells was suppressed, but the highest lipid content of 53% was attained. This special characteristic of lipid accumulation makes I. zhangjiangensis an ideal candidate for producing biodiesel using N-rich wastewater. [Copyright &y& Elsevier]

Abstract: The scalability of microalgae growth systems is a primary research topic in anticipation of the commercialization of microalgae-based biofuels. To date, there is little published data on the productivity of microalgae in growth systems that are scalable to commercially viable footprints. To inform the development of more detailed assessments of industrial-scale microalgae biofuel processes, this paper presents the construction and validation of a model of microalgae biomass and lipid accumulation in an outdoor, industrial-scale photobioreactor. The model incorporates a time-resolved simulation of microalgae growth and lipid accumulation based on solar irradiation, species specific characteristics, and photobioreactor geometry. The model is validated with 9weeks of growth data from an industrially-scaled outdoor photobioreactor. Discussion focuses on the sensitivity of the model input parameters, a comparison of predicted microalgae productivity to the literature, and an analysis of the implications of this more detailed growth model on microalgae biofuels lifecycle assessment studies. [Copyright &y& Elsevier]

Abstract: Production of biofuel from algae is dependent on the microalgal biomass production rate and lipid content. Both biomass production and lipid accumulation are limited by several factors, of which nutrients play a key role. In this research, the marine microalgae Dunaliella tertiolecta was used as a model organism and a profile of its nutritional requirements was determined. Inorganic phosphate and trace elements: cobalt (Co2+), iron (Fe3+), molybdenum (Mo2+) and manganese (Mn2+) were identified as required for algae optimum growth. Inorganic nitrogen in the form of nitrate instead of ammonium (NH4 +) was required for maximal biomass production. Lipids accumulated under nitrogen starvation growth condition and this was time-dependent. Results of this research can be applied to maximize production of microalgal lipids in optimally designed photobioreactors. [ABSTRACT FROM AUTHOR]

Abstract: In vivo determination of neutral lipids with Nile red fluorescence has been used as a rapid screening method for certain types of microalgae, but has been unsuccessful in others, particularly those with thick, rigid cell walls that prevent penetration of the fluorescence dye into the cell. To solve the problem, a microwave-assisted Nile red staining method for microalgal lipid determination was developed. In a two-step staining protocol, 50 and 60s were selected as the optimal microwave times for the pretreatment and staining process, respectively. Moreover, several calibration methods for quantitative analysis of neutral lipids in microalgae were investigated and compared with conventional gravimetric methods. Factors that affected the in vivo quantification of cellular neutral lipids were also investigated. Application of the new method for detection and quantification of neutral lipids in a number of green microalgae was demonstrated. [ABSTRACT FROM AUTHOR]

Abstract: This article proposes a dynamical model of microalgal lipid production under nitrogen limitation. In this model, intracellular carbon is divided between a functional pool and two storage pools (sugars and neutral lipids). The various intracellular carbon flows between these pools lead to a complex dynamic with a strong discrepancy between synthesis and mobilization of neutral lipids. The model has been validated with experiments of Isochrysis aff. galbana (clone T-iso) culture under various nitrogen limitation conditions and under nitrogen starvation. The hysteresis behavior of the neutral lipid quota observed experimentally is accurately predicted. [ABSTRACT FROM AUTHOR]

Abstract: Photosynthetic carbon partitioning into starch and neutral lipid was investigated in the oleaginous green microalga Pseudochlorococcum sp. When grown under low light and nitrogen-replete conditions, the algal cells possessed a basal level of starch. When grown under high light and nitrogen-limited conditions, starch synthesis was transiently up-regulated. After nitrogen depletion, starch content decreased while neutral lipid rapidly increased to 52.1% of cell dry weight, with a maximum neutral lipid productivity of 0.35gL−1 D−1. These results suggest that Pseudochlorococcum used starch as a primary carbon and energy storage product. As nitrogen was depleted for an extended period of time, cells shift the carbon partitioning into neutral lipid as a secondary storage product. Partial inhibition of starch synthesis and degradation enzymes resulted in a decrease in neutral lipid content, indicating that conversion of starch to neutral lipid may contribute to overall neutral lipid accumulation. Biotechnological application of Pseudochlorococcum sp. as a production strain for biofuel was assessed. [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: We describe a methodology to investigate the potential of given microalgae species for biodiesel production by characterizing their productivity in terms of both biomass and lipids. A multi-step approach was used: determination of biological needs for macronutrients (nitrate, phosphate and sulphate), determination of maximum biomass productivity (the “light-limited” regime), scaling-up of biomass production in photobioreactors, including a theoretical framework to predict corresponding productivities, and investigation of how nitrate starvation protocol affects cell biochemical composition and triggers triacylglycerol (TAG) accumulation. The methodology was applied to two freshwater strains, Chlorella vulgaris and Neochloris oleoabundans, and one seawater diatom strain, Cylindrotheca closterium. The highest total lipid content was achieved with N. oleoabundans (25–37% of DW), while the highest TAG content was found in C. vulgaris (11–14% of DW). These two species showed similar TAG productivities. [ABSTRACT FROM AUTHOR]