https://www.massey.ac.nz/~ychisti/Biodiesel.pdf

Biodiesel from microalgae.

Sustainable production of renewable energy is being hotly debated globally since it is increasingly understood that first generation biofuels, primarily produced from food crops and mostly oil seeds are limited in their ability to achieve targets for biofuel production, climate change mitigation and economic growth. These concerns have increased the interest in developing second generation biofuels produced from non-food feedstocks such as microalgae, which potentially offer greatest opportunities in the longer term. This paper reviews the current status of microalgae use for biodiesel production, including their cultivation, harvesting, and processing. The microalgae species most used for biodiesel production are presented and their main advantages described in comparison with other available biodiesel feedstocks. The various aspects associated with the design of microalgae production units are described, giving an overview of the current state of development of algae cultivation systems (photo-bioreactors and open ponds). Other potential applications and products from microalgae are also presented such as for biological sequestration of CO 2 , wastewater treatment, in human health, as food additive, and for aquaculture.

/pdf/microalgae-for-biodiesel-production-and-other-applications-a-54vmwufrsu.pdf

Microalgae for biodiesel production and other applications: A review

Sustainability is a key principle in natural resource management, and it involves operational efficiency, minimisation of environmental impact and socio-economic considerations; all of which are interdependent. It has become increasingly obvious that continued reliance on fossil fuel energy resources is unsustainable, owing to both depleting world reserves and the green house gas emissions associated with their use. Therefore, there are vigorous research initiatives aimed at developing alternative renewable and potentially carbon neutral solid, liquid and gaseous biofuels as alternative energy resources. However, alternate energy resources akin to first generation biofuels derived from terrestrial crops such as sugarcane, sugar beet, maize and rapeseed place an enormous strain on world food markets, contribute to water shortages and precipitate the destruction of the world's forests. Second generation biofuels derived from lignocellulosic agriculture and forest residues and from non-food crop feedstocks address some of the above problems; however there is concern over competing land use or required land use changes. Therefore, based on current knowledge and technology projections, third generation biofuels specifically derived from microalgae are considered to be a technically viable alternative energy resource that is devoid of the major drawbacks associated with first and second generation biofuels. Microalgae are photosynthetic microorganisms with simple growing requirements (light, sugars, CO 2 , N, P, and K) that can produce lipids, proteins and carbohydrates in large amounts over short periods of time. These products can be processed into both biofuels and valuable co-products. This study reviewed the technologies underpinning microalgae-to-biofuels systems, focusing on the biomass production, harvesting, conversion technologies, and the extraction of useful co-products. It also reviewed the synergistic coupling of microalgae propagation with carbon sequestration and wastewater treatment potential for mitigation of environmental impacts associated with energy conversion and utilisation. It was found that, whereas there are outstanding issues related to photosynthetic efficiencies and biomass output, microalgae-derived biofuels could progressively substitute a significant proportion of the fossil fuels required to meet the growing energy demand.

/pdf/biofuels-from-microalgae-a-review-of-technologies-for-1t1wwr5e69.pdf

Biofuels from microalgae—A review of technologies for production, processing, and extractions of biofuels and co-products

https://oatao.univ-toulouse.fr/2771/1/joannis-cassan_2771.pdf

Commercial applications of microalgae

The use of fossil fuels is now widely accepted as unsustainable due to depleting resources and the accumulation of greenhouse gases in the environment that have already exceeded the “dangerously high” threshold of 450 ppm CO2-e. To achieve environmental and economic sustainability, fuel production processes are required that are not only renewable, but also capable of sequestering atmospheric CO2. Currently, nearly all renewable energy sources (e.g. hydroelectric, solar, wind, tidal, geothermal) target the electricity market, while fuels make up a much larger share of the global energy demand (∼66%). Biofuels are therefore rapidly being developed. Second generation microalgal systems have the advantage that they can produce a wide range of feedstocks for the production of biodiesel, bioethanol, biomethane and biohydrogen. Biodiesel is currently produced from oil synthesized by conventional fuel crops that harvest the sun’s energy and store it as chemical energy. This presents a route for renewable and carbon-neutral fuel production. However, current supplies from oil crops and animal fats account for only approximately 0.3% of the current demand for transport fuels. Increasing biofuel production on arable land could have severe consequences for global food supply. In contrast, producing biodiesel from algae is widely regarded as one of the most efficient ways of generating biofuels and also appears to represent the only current renewable source of oil that could meet the global demand for transport fuels. The main advantages of second generation microalgal systems are that they: (1) Have a higher photon conversion efficiency (as evidenced by increased biomass yields per hectare): (2) Can be harvested batch-wise nearly all-year-round, providing a reliable and continuous supply of oil: (3) Can utilize salt and waste water streams, thereby greatly reducing freshwater use: (4) Can couple CO2-neutral fuel production with CO2 sequestration: (5) Produce non-toxic and highly biodegradable biofuels. Current limitations exist mainly in the harvesting process and in the supply of CO2 for high efficiency production. This review provides a brief overview of second generation biodiesel production systems using microalgae.

https://www.springer.com/cda/content/document/cda_downloaddocument/BioEnergyResearch_Second+Generation+Biofuels+High-Efficiency+Microalgae+for+Biodiesel+Production.pdf?SGWID=0-0-45-1347846-0

Second generation biofuels: high-efficiency microalgae for biodiesel production

The red-tide dinoflagellate Protoceratium reticulatum is shown to be protected against turbulence-associated damage by the use of the additives Pluronic F68 (PF68) and carboxymethyl cellulose (CMC) in the culture medium. Relative to agitated controls, these additives had a dose-dependent protective effect at concentrations of up to 0.4 and 0.5 g L−1 for CMC and F68, respectively. In static cultures, these additives inhibited growth directly or indirectly at a concentration of >0.5 g L−1. Compared to CMC, PF68 was a better protectant overall. Cell-specific production of yessotoxins was enhanced under elevated shear stress regimens so long as the turbulence intensity was insufficient to damage the cells outright. Shear-induced production of reactive oxygen species and direct effects of turbulence on the cell cycle contributed to the observed shear effects.

Carboxymethyl cellulose and Pluronic F68 protect the dinoflagellate Protoceratium reticulatum against shear-associated damage

A concentration process for polyunsaturated fatty acids (PUFAs n-3) stearidonic (18:4 n-3), eicosapentaenoic (20:5 n-3) and docosahexaenoic (22:6 n-3) from cod liver oil using urea method has been thoroughly studied. The influence of urea/fatty acid ratio and crystallization temperature have been studied on both fatty acids recovery yield and fatty acid concentration. Methanol and ethanol have been used as urea solvent. The use of methanol and an urea/fatty acid ratio of 4:1, and 4°C were found to be the best conditions for SA (concentration 8,5%, yield 71,6) and DHA (59,8% and 100%, respectively). However, 28oC was found to be the best temperature for EPA (28,7% and 75,6%, respectively). At temperatures below -12oC, PUFAs also developed adducts compounds, mainly adducts derived from EPA. A variance analysis showed the urea/fatty acid ratio as the main factor affecting fatty acid concentration. At the same time, high urea/fatty acid ratios resulted in increased influence of the solvent used, being more favorable for methanol.

/pdf/obtencion-de-concentrados-de-acidos-grasos-poliinsaturados-34a7xo5jnj.pdf

Obtención de concentrados de ácidos grasos poliinsaturados por el método de los compuestos de inclusión de urea

This work studies the simultaneous extraction and fractionation of saponifiable lipids into neutral saponifiable lipids and polar lipids (phospholipids and glycolipids) from the microalga Nannochloropsis sp. (41.9% neutral saponifiable lipids, 58.1% polar lipids, 32.5% eicosapentaenoic acid, EPA) to obtain EPA-rich polar lipid fractions, using green techniques. Several two-step extraction processes were studied, combining CO2 supercritical fluid extraction, pressurized lipid extraction, and ethanol-gas (CO2) expanded extraction. Extraction at atmospheric pressure, including the Soxhlet extraction method, was used as the reference. Firstly, a lipidic fraction rich in neutral saponifiable lipids (80.4% of total saponifiable lipids), was obtained using hexane and the Soxhlet extraction method; this extract contained 85.8% of the biomass neutral saponifiable lipids. Subsequently, in the second extraction step using ethanol, an EPA-rich polar lipid extract with 89.2% polar lipids and up to 39.6% EPA was obtained. This SL extract contained 80.1% of the glycolipids, 96% of the phospholipids and 67.8% of the EPA from the Nannochloropsis sp. biomass. Good results were obtained combining the CO2 supercritical fluid extraction and pressurized lipid extraction techniques as alternative green processes. Firstly, a lipidic fraction rich in neutral saponifiable lipids (70.3% of the total extracted saponifiable lipids) was obtained using supercritical CO2 with 10 wt% ethanol as the co-solvent, at 35 MPa, 50 °C, 8 g CO2/min for 8 h; this extract contained 81.7% of the biomass neutral saponifiable lipids. Then, in the second extraction step with pressurized ethanol, at 10 MPa, 125 °C and three extraction cycles of 5 min, an EPA-rich polar lipid extract with 85.1% polar lipids and up to 39.2% EPA was obtained. This saponifiable lipid extract contained 76.9% of the glycolipids, 71.1% of the phospholipids and 61.9% of the EPA from the Nannochloropsis sp. biomass. 

Supercritical fluid extraction and pressurized liquid extraction processes applied to eicosapentaenoic acid-rich polar lipid recovery from the microalga Nannochloropsis sp

The simultaneous effect of temperature and photon flux density on microalga Chlorella sp growth was analysed by response surface methodology of two consecutive full factorial designs Maximum specific growth rate was 0128 h-1 at 35°C and 2400 μmol photon m-2s-1 A photoinhibition effect was observed at high photon flux densities with temperatures far below the optimum Temperature was the main factor affecting specific growth rate

Optimization of light and temperature for growing Chlorella sp. using response surface methodology

This paper focuses on modelling the growth rate and exopolysaccharides production of Anabaena sp. ATCC 33047, to be used in carbon dioxide removal and biofuels production. For this, the influence of dilution rate, irradiance and aeration rate on the biomass and exopolysaccharides productivity, as well as on the CO(2) fixation rate, have been studied. The productivity of the cultures was maximum at the highest irradiance and dilution rate assayed, resulting to 0.5 g(bio) l(-1) day(-1) and 0.2 g(eps) l(-1) day(-1), and the CO(2) fixation rate measured was 1.0 gCO(2) l(-1) day(-1). The results showed that although Anabaena sp. was partially photo-inhibited at irradiances higher than 1,300 μE m(-2) s(-1), its growth rate increases hyperbolically with the average irradiance inside the culture, and so does the specific exopolysaccharides production rate. The latter, on the other hand, decreases under high external irradiances, indicating that the exopolysaccharides metabolism hindered by photo-damage. Mathematical models that consider these phenomena have been proposed. Regarding aeration, the yield of the cultures decreased at rates over 0.5 v/v/min or when shear rates were higher than 60 s(-1), demonstrating the existence of thus existence of stress damage by aeration. The behaviour of the cultures has been verified outdoors in a pilot-scale airlift tubular photobioreactor. From this study it is concluded that Anabaena sp. is highly recommended to transform CO(2) into valuable products as has been proved capable of metabolizing carbon dioxide at rates of 1.2 gCO(2) l(-1) day(-1) outdoors. The adequacy of the proposed equations is demonstrated, resulting to a useful tool in the design and operation of photobioreactors using this strain.

E. Molina Grima

Papers

Carboxymethyl cellulose and Pluronic F68 protect the dinoflagellate Protoceratium reticulatum against shear-associated damage

Obtención de concentrados de ácidos grasos poliinsaturados por el método de los compuestos de inclusión de urea

Supercritical fluid extraction and pressurized liquid extraction processes applied to eicosapentaenoic acid-rich polar lipid recovery from the microalga Nannochloropsis sp

Optimization of light and temperature for growing Chlorella sp. using response surface methodology

Utilization of Anabaena sp. in CO2 removal processes