Oil extraction from microalgae for biodiesel production

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.     

Fatty acid profiling and molecular characterization of some freshwater microalgae from India with potential for biodiesel production

We determined the fatty acid compositions of six species of freshwater microalgae belonging to the Chlorophyta, which were isolated from freshwater bodies in Assam, India. All six microalgae -Desmodesmus sp. DRLMA7, Desmodesmus elegans DRLMA13, Scenedesmus sp. DRLMA5, Scenedesmus sp. DRLMA9 Chlorella sp. DRLMA3 and Chlorococcum macrostigmatum DRLMA12-showed similar fatty acid profiles 16:0, 16:4, 18:1, 18:2, and 18:3 as major components. We also compared fatty acid compositions during the late exponential and stationary growth phases of D. elegans DRLMA13 and Scenedesmus sp. DRLMA9 in BG11 medium. We observed enhanced percentages of total saturated and monounsaturated fatty acids with a concomitant decrease in polyunsaturated fatty acid content upon the prolonged cultivation of both microalgae. Distinct morphological features of microalgal isolates were determined by scanning electron microscopic (SEM) studies. An ornamented cell wall was found in D. elegans DRLMA13, which is characteristic of small spineless species of Desmodesmus. The isolated microalgae were further distinguished through analysis of internal transcribed spacer 2 (ITS2) secondary structures and compensatory base changes (CBCs). Analysis of CBCs showed the relatedness of Chlorella sp. DRLMA3 with other Chlorella-like organisms, but it does not belong to the clade comprising Chlorella sensu stricto, which includes Chlorella vulgaris. The CBC count between Scenedesmus sp. DRLMA9 and other species of Scenedesmus provides evidence that this isolate represents a new species.     

Oil production from five marine microalgae for the production of biodiesel

Marine microalgae were studied as potential resources for the production of biodiesel. Five marine microalgae, Tetraselmis suecica, Phaeodactylum tricornutum, Chaetoceros calcitrans, Isochrysis galbana, and Nannochloropsis oculata were cultured in f/2 media, 12:12 L:D cycle at 20 ± 1°C with a light intensity of 36.3 μmol/m²/sec using a 15-L circular cylindrical photobioreactor. The dry cell weight, specific growth rate, biomass productivity, oil content and fatty acid composition of palmitic acid, stearic acid, oleic acid, linoleic acid, and linolenic acid of microalgae were determined. T. suecica, I. galbana, and N. oculata showed high dry cell weights of 0.58, 0.57, and 0.57 g/L, respectively. The culture period of T. suecica to reach the stationary phase was 9 days. On the other hand, N. oculata showed the longest culture period of 28 days to reach the stationary phase. T. suecica absorbed nitrate at the initial stages of cell growth, decreasing the nitrate concentration to 0.5 mg/L on day-7 of the culture. The highest oil contents were observed in P. tricornutum with a 25.31% dry cell weight and I. galbana with a 23.15% dry cell weight on day-9 after the stationary phase. I. galbana showed 417.33 mg of palmitic acid per g oil and T. suecica showed 235.61 mg of oleic acid per g oil. Stearic acid, linoleic acid, and linolenic acid did not exceed 30.02 mg/g oil in any of the microalgae. T. suecica showed the shortest culture period of 9 days to reach the stationary phase. Therefore, the highest biomass production of 0.58 g/L was obtained and I. galbana showed high biomass production of 0.57 g/ L and oil content of 23.15% of dry cell weight. Therefore, T. suecica and I. galbana can be selected as a potential candidate for the production of biodiesel.     

Extraction of oil from microalgae for biodiesel production: A review

The rapid increase of CO(2) concentration in the atmosphere combined with depleted supplies of fossil fuels has led to an increased commercial interest in renewable fuels. Due to their high biomass productivity, rapid lipid accumulation, and ability to survive in saline water, microalgae have been identified as promising feedstocks for industrial-scale production of carbon-neutral biodiesel. This study examines the principles involved in lipid extraction from microalgal cells, a crucial downstream processing step in the production of microalgal biodiesel. We analyze the different technological options currently available for laboratory-scale microalgal lipid extraction, with a primary focus on the prospect of organic solvent and supercritical fluid extraction. The study also provides an assessment of recent breakthroughs in this rapidly developing field and reports on the suitability of microalgal lipid compositions for biodiesel conversion.     

An alternative strategy for enhancing lipid accumulation in chlorophycean microalgae for biodiesel production

Oleaginous microalgae are considered as important feedstocks for production of biodiesel. Under nutrient stress conditions, microalgae have the ability to accumulate higher amount of lipids, which can be transesterified for the production of biodiesel. In the present investigation, four different phosphate application strategies were examined in five green microalgae (Tetradesmus obliquus, Tetradesmus lagerheimii, Chlorella vulgaris, Chlorella minutissima, and Chlamydomonas sp.) to achieve higher lipid productivity. Effects of those strategies such as phosphate-sufficient (Control), phosphate-starved approach (PSA), biphasic phosphate-starved approach (BPSA), and sequential phosphate addition (SPA) were studied under batch culture mode. The BPSA emerging as the best in terms of lipid productivity consisted of two biomass harvesting phases, which would lead to an increase in the overall cost of biodiesel production. On the other hand, the SPA with a 1/200th dose of N 11 medium, i.e., 0.4 mg L^?1 of phosphate application in 3-day intervals, also resulted into higher lipid productivity which was equal to BPSA. Fatty acid composition of the biodiesel obtained from the microalgae was analyzed and the fuel characteristics were also evaluated. A profound (~14-fold) reduction in phosphorus requirements under the SPA mode with higher lipid productivity ensured qualitative biodiesel production and a lesser amount of phosphorus release, thus making the process eco-friendly.     

Methods of downstream processing for the production of biodiesel from microalgae

Despite receiving increasing attention during the last few decades, the production of microalgal biofuels is not yet sufficiently cost-effective to compete with that of petroleum-based conventional fuels. Among the steps required for the production of microalgal biofuels, the harvest of the microalgal biomass and the extraction of lipids from microalgae are two of the most expensive. In this review article, we surveyed a substantial amount of previous work in microalgal harvesting and lipid extraction to highlight recent progress in these areas. We also discuss new developments in the biodiesel conversion technology due to the importance of the connectivity of this step with the lipid extraction process. Furthermore, we propose possible future directions for technological or process improvements that will directly affect the final production costs of microalgal biomass-based biofuels.     

Evaluating new isolates of microalgae from Kazakhstan for biodiesel production

New microalgal strains that are native to South-East Kazakhstan were isolated and characterized with a view to identifying suitable candidates for biodiesel production. Six strains of chlorophyte algae (named K1–K6) were recovered from environmental samples as axenic cultures, and molecular analysis revealed that five (K1–K5) are strains of Parachlorella kessleri, whereas K6 is a strain of Chlorella vulgaris. A third isolate from Uzbekistan (termed UZ) was also identified as a separate strain of P. kessleri. All strains show high growth rates and an ability to utilize acetate as an exogenous source of fixed carbon. Furthermore, under conditions of nitrogen depletion, all three strains showed a significant accumulation of neutral lipids (triacylglycerides). P. kessleri K5 and C. vulgaris K6 therefore represent promising autochthon strains for large-scale cultivation and biodiesel production in Kazakhstan.     

Heterotrophic cultivation of microalgae for production of biodiesel

High cell density cultivation of microalgae via heterotrophic growth mechanism could effectively address the issues of low productivity and operational constraints presently affecting the solar driven biodiesel production. This paper reviews the progress made so far in the development of commercial-scale heterotrophic microalgae cultivation processes. The review also discusses on patentable concepts and innovations disclosed in the past four years with regards to new approaches to microalgal cultivation technique, improvisation on the process flow designs to economically produced biodiesel and genetic manipulation to confer desirable traits leading to much valued high lipid-bearing microalgae strains.     

Evaluation of halophilic microalgae isolated from Rabigh Red Sea coastal area for biodiesel production: Screening and biochemical studies

In the present study, different water samples from Red Sea coastal area at Rabigh city, Saudi Arabia were studied for their dominant algal species. Microalgal isolation was carried out based on dilution method and morphologically examined using F/2 as a growth medium. Dry weight and main biochemical composition (protein, carbohydrates, lipids) of all species were performed at the end of the growth, and biodiesel characteristics were estimated. Nannochloropsis sp., Dunaliella sp., Tetraselmis sp., Prorocentrum sp., Chlorella sp., Nitzschia sp., Coscinodiscus sp., and Navicula sp. were the most dominant species in the collected water samples and were used for further evaluation. Nannochloropsis sp. surpassed all other isolates in concern of biomass production with the maximum recorded dry weight of 0.89 g L^?1, followed by Dunaliella sp. (0.69 g L^?1). The highest crude protein content was observed in Nitzschia sp. (38.21%) and Dunaliella sp. (18.01%), while Nannochloropsis sp. showed 13.38%, with the lowest recorded lipid content in Coscinodiscus sp. (10.09%). Based on the growth, lipid content, and biodiesel characteristics, the present study suggested Dunaliella sp. and Nitzschia sp. as promising candidates for further large-scale biodiesel production.     

Biodiesel production with microalgae as feedstock: from strains to biodiesel

Due to negative environmental influence and limited availability, petroleum-derived fuels need to be replaced by renewable biofuels. Biodiesel has attracted intensive attention as an important biofuel. Microalgae have numerous advantages for biodiesel production over many terrestrial plants. There are a series of consecutive processes for biodiesel production with microalgae as feedstock, including selection of adequate microalgal strains, mass culture, cell harvesting, oil extraction and transesterification. To reduce the overall production cost, technology development and process optimization are necessary. Genetic engineering also plays an important role in manipulating lipid biosynthesis in microalgae. Many approaches, such as sequestering carbon dioxide from industrial plants for the carbon source, using wastewater for the nutrient supply, and maximizing the values of by-products, have shown a potential for cost reduction. This review provides a brief overview of the process of biodiesel production with microalgae as feedstock. The methods associated with this process (e.g. lipid determination, mass culture, oil extraction) are also compared and discussed.     

Culture of microalgae Chlorella minutissima for biodiesel feedstock production

Microalgae are among the most promising of non‐food based biomass fuel feedstock alternatives. Algal biofuels production is challenged by limited oil content, growth rate, and economical cultivation. To develop the optimum cultivation conditions for increasing biofuels feedstock production, the effect of light source, light intensity, photoperiod, and nitrogen starvation on the growth rate, cell density, and lipid content of Chlorella minutissima were studied. The fatty acid content and composition of Chlorella minutissima were also investigated under the above conditions. Fluorescent lights were more effective than red or white light‐emitting diodes for algal growth. Increasing light intensity resulted in more rapid algal growth, while increasing the period of light also significantly increased biomass productivity. Our results showed that the lipid and triacylglycerol content were increased under N starvation conditions. Thus, a two‐phase strategy with an initial nutrient‐sufficient reactor followed by a nutrient deprivation strategy could likely balance the desire for rapid and high biomass generation (124 mg/L) with a high oil content (50%) of Chlorella minutissima to maximize the total amount of oil produced for biodiesel production. Moreover, methyl palmitate (C16:0), methyl oleate (C18:1), methyl linoleate (C18:2), and methyl linolenate (C18:3) are the major components of Chlorella minutissima derived FAME, and choice of light source, intensity, and N starvation impacted the FAME composition of Chlorella minutissima. The optimized cultivation conditions resulted in higher growth rate, cell density, and oil content, making Chlorella minutissima a potentially suitable organism for biodiesel feedstock production. Biotechnol. Bioeng. 2011;108: 2280–2287. © 2011 Wiley Periodicals, Inc.     

Life cycle assessment of biodiesel production from microalgae in ponds

This paper analyses the potential environmental impacts and economic viability of producing biodiesel from microalgae grown in ponds. A comparative Life Cycle Assessment (LCA) study of a notional production system designed for Australian conditions was conducted to compare biodiesel production from algae (with three different scenarios for carbon dioxide supplementation and two different production rates) with canola and ULS (ultra-low sulfur) diesel. Comparisons of GHG (greenhouse gas) emissions (g CO₂-e/t km) and costs (¢/t km) are given. Algae GHG emissions (−27.6 to 18.2) compare very favourably with canola (35.9) and ULS diesel (81.2). Costs are not so favourable, with algae ranging from 2.2 to 4.8, compared with canola (4.2) and ULS diesel (3.8). This highlights the need for a high production rate to make algal biodiesel economically attractive.     

Scenedesmus sp. NJ-1 isolated from Antarctica: a suitable renewable lipid source for biodiesel production

Microalgal lipids are promising alternative feedstocks for biodiesel production. Scenedesmus sp. NJ-1, an oil-rich freshwater microalga isolated from Antarctica, was identified to be a suitable candidate to produce biodiesel in this study. This strain could grow at temperatures ranging from 4 to 35?°C. With regular decrease in nitrate concentration in the medium, large quantities of triacylglycerols accumulated under batch culture conditions detected by thin layer chromatography and BODIPY 505/515 fluorescent staining. Scenedesmus sp. NJ-1 achieved the average biomass productivity of 0.105?g?l^?1?d^?1 (dry weight) and nearly the highest lipid content (35?% of dry cell weight) was reached at day 28 in the batch culture. Neutral lipids accounted for 78?% of total lipids, and C18:1 (n-9), C16:0 were the major fatty acids in total lipids, composing 37 and 20?% of total fatty acids of Scenedesmus sp. NJ-1 grown for 36?days, respectively. These results suggested that Scenedesmus sp. NJ-1 was a good source of microalgal oils for biodiesel production.     

Lipid productivity and fatty acid composition-guided selection of Chlorella strains isolated from Malaysia for biodiesel production

The need to develop biomass-based domestic production of high-energy liquid fuels (biodiesel) for transportation can potentially be addressed by exploring microalgae with high lipid content. Selecting the strains with adequate oil yield and quality is of fundamental importance for a cost-efficient biofuel feedstock production based on microalgae. This work evaluated 29 strains of Chlorella isolated from Malaysia as feedstock for biodiesel based on volumetric lipid productivity and fatty acid profiles. Phylogenetic studies based on 18S rRNA gene revealed that majority of the strains belong to true Chlorella followed by Parachlorella. The strains were similarly separated into two groups based on fatty acid composition. Of the 18 true Chlorella strains, Chlorella UMACC187 had the highest palmitic acid (C16:0) content (71.3?±?4.2 % total fatty acids, TFA) followed by UMACC84 (70.1?±?0.7 %TFA), UMACC283 (63.8?±?0.7 %TFA), and UMACC001 (60.3?±?4.0 %TFA). Lipid productivity of the strains at exponential phase ranged from 34.53 to 230.38 mg L^?1 day^?1, with Chlorella UMACC050 attaining the highest lipid productivity. This study demonstrated that Chlorella UMACC050 is a promising candidate for biodiesel feedstock production.     

Life-cycle analysis on biodiesel production from microalgae: Water footprint and nutrients balance

This research examines the life-cycle water and nutrients usage of microalgae-based biodiesel production. The influence of water types, operation with and without recycling, algal species, geographic distributions are analyzed. The results confirm the competitiveness of microalgae-based biofuels and highlight the necessity of recycling harvested water and using sea/wastewater as water source. To generate 1 kg biodiesel, 3726 kg water, 0.33 kg nitrogen, and 0.71 kg phosphate are required if freshwater used without recycling. Recycling harvest water reduces the water and nutrients usage by 84% and 55%. Using sea/wastewater decreases 90% water requirement and eliminates the need of all the nutrients except phosphate. The variation in microalgae species and geographic distribution are analyzed to reflect microalgae biofuel development in the US. The impacts of current federal and state renewable energy programs are also discussed to suggest suitable microalgae biofuel implementation pathways and identify potential bottlenecks.     

Progress on lipid extraction from wet algal biomass for biodiesel production

Lipid recovery and purification from microalgal cells continues to be a significant bottleneck in biodiesel production due to high costs involved and a high energy demand. Therefore, there is a considerable necessity to develop an extraction method which meets the essential requirements of being safe, cost‐effective, robust, efficient, selective, environmentally friendly, feasible for large‐scale production and free of product contamination. The use of wet concentrated algal biomass as a feedstock for oil extraction is especially desirable as it would avoid the requirement for further concentration and/or drying. This would save considerable costs and circumvent at least two lengthy processes during algae‐based oil production. This article provides an overview on recent progress that has been made on the extraction of lipids from wet algal biomass. The biggest contributing factors appear to be the composition of algal cell walls, pre‐treatments of biomass and the use of solvents (e.g. a solvent mixture or solvent‐free lipid extraction). We compare recently developed wet extraction processes for oleaginous microalgae and make recommendations towards future research to improve lipid extraction from wet algal biomass.     

The effect of temperature on growth and lipid and fatty acid composition on marine microalgae used for biodiesel production

Cultivation temperature is one of the major factors affecting the growth and lipid accumulation of microalgae. In this study, the effects of temperature on the growth, lipid content, fatty acid composition and biodiesel properties of the marine microalgae Chaetoceros sp. FIKU035, Tetraselmis suecica FIKU032 and Nannochloropsis sp. FIKU036 were investigated. These species were cultured at different temperatures (25, 30, 35 and 40 °C). The results showed that the specific growth rate, biomass and lipid content of all microalgae decreased with increasing temperature. With regards to fatty acids, the presence of saturated fatty acids (SFAs) in T. suecica FIKU032 and Nannochloropsis sp. FIKU036 decreased with increasing temperature, in contrast with polyunsaturated fatty acids (PUFAs). Moreover, Chaetoceros sp. FIKU035 was the only species that could grow at 40 °C. The highest lipid productivity was observed in Chaetoceros sp. FIKU035 when cultivated at 25 °C (66.73 ± 1.34 mg L^?1 day^?1) and 30 °C (61.35 ± 2.89 mg L^?1 day^?1). Moreover, the biodiesel properties (cetane number, cold filter plugging point, kinematic viscosity and density) of the lipids obtained from this species were in accordance with biodiesel standards. This study indicated that Chaetoceros sp. FIKU035 can be considered as a suitable species for biodiesel production in outdoor cultivation.     

Mixture design as a potential tool in modeling the effect of light wavelength on Dunaliella salina cultivation: an alternative solution to increase microalgae lipid productivity for biodiesel production

Abstract

For a feasible microalgae biodiesel, increasing lipid productivity is a key parameter. An important cultivation parameter is light wavelength (λ). It can affect microalgal growth, lipid yield, and fatty acid composition. In the current study, the mixture design was used as an alternative to model the influence of the λ on the Dunaliella salina lipid productivity. The illumination was considered to be the mixture of different λ (the light colors blue, red, and green). All experiments were performed with and without sodium acetate (4?g/L), as carbon source, allowing the identification of the impact of the cultivation regimen (autotrophic or mixotrophic). Without sodium acetate, the highest lipid productivity was obtained using blue and red light. The use of mixotrophic cultivations significantly enhanced the results. The optimum obtained result was mixotrophic cultivation under 65% blue and 35% green light, resulting in biomass productivity of 105.06 mgL^?1day^?1, a lipid productivity of 53.47 mgL^?1day^?1, and lipid content of 50.89%. The main fatty acids of the oil obtained in this cultivation were oleic acid (36.52%) and palmitic acid (18.31%).     

Biofuel production from microalgae as feedstock: current status and potential

Algal biofuel has become an attractive alternative of petroleum-based fuels in the past decade. Microalgae have been proposed as a feedstock to produce biodiesel, since they are capable of mitigating CO₂ emission and accumulating lipids with high productivity. This article is an overview of the updated status of biofuels, especially biodiesel production from microalgae including fundamental research, culture selection and engineering process development; it summarizes research on mathematical and life cycle modeling on algae growth and biomass production; and it updates global efforts of research and development and commercialization attempts. The major challenges are also discussed.