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

A simple actinometric method was evaluated formeasuring the photosynthetically active incidentphoton flux on outdoor photobioreactors. The method isbased on uranyl sulfate catalyzed photodecompositionof oxalic acid in presence of light. The uranyl–oxalate chemical actinometer absorbs radiation ofwavelengths below 535 nm. In the present work, thephotobioreactor wall material did not transmit lightenergy of wavelengths below 350 nm and the effectiveabsorptivity method was used to evaluate the photonflux between 350–535 nm. The standard solar spectrumof the American Society for Testing and Materials(ASTM) was employed for estimating the ratio betweenthe photosynthetically active radiation (400–700 nm)and the solar radiation in the 350–535 nm range. Thisratio (2.21) was taken to be equal to the quotientbetween the photosynthetically active radiation (PAR)and the incident photon flux on the photobioreactor'ssurface (for the solar radiation between 350–535 nm).PAR measurements with 4π spherical and 2πquantum sensors were used to validate the method.

Assessment of the photosynthetically active incident radiation in outdoor photobioreactors using oxalic acid/uranyl sulfate chemical actinometer

Marine microalgae are presented as alternative sources for polyunsaturated fatty acids production. A macronutrient optimization method for culture media commonly used for Isochrysis galbana growth is discussed. This microalga has been reported as a good RUFA producer. The optimization was conducted applying the response surface technique, parameters tested being nitrate, phosphate, ferric citrate and manganese chloride concentrations and the suplementary CO 2 in the bubbling air. The results show the evidence of growth limitation with the initial culture media and it is proposed a second optimization step considering as design variables the different ratios between media components.

https://grasasyaceites.revistas.csic.es/index.php/grasasyaceites/article/download/1022/1031

Estudio de macronutrientes para la producción de PUFAs a partir de la microalga marina Isochrysis galbana

Challenges in microalgae biofuels

A priority of the industrial applications of microalgae is the reduction of production costs while maximizing algae biomass productivity The purpose of this study was to carry out a comprehensive evaluation of the effects of pH control on the production of Nannochloropsis gaditana in tubular photobioreactors under external conditions while considering the environmental, biological, and operational parameters of the process Experiments were carried out in 30 m3 tubular photobioreactors under outdoor conditions The pH values evaluated were 60, 70, 80, 90, and 100, which were controlled by injecting pure CO2 on-demand The results have shown that the ideal pH for microalgal growth was 80, with higher values of biomass productivity (Pb) (016 g L−1 d−1), and CO2 use efficiency (
$$E_{\text{CO}_{2}}$$

) (746% w w−1); 
$$R_{\text{CO}_{2}}$$

/biomass value obtained at this pH (242 
$$\text{g}_{\text{CO}_{2}}$$

 gbiomass−1) was close to the theoretical value, indicating an adequate CO2 supply At this pH, the system was more stable and required a lower number of CO2 injections than the other treatments At pH 60, there was a decrease in the Pb and 
$$E_{\text{CO}_{2}}$$

; cultures at pH 100 exhibited a lower Pb and photosynthetic efficiency as well These results imply that controlling the pH at an optimum value allows higher CO2 conversions in biomass to be achieved and contributes to the reduction in costs of the microalgae production process

Bioprocess strategies for enhancing the outdoor production of Nannochloropsis gaditana: an evaluation of the effects of pH on culture performance in tubular photobioreactors

The adsorption equilibria are discussed for fatty acids 16∶1n−7, 16∶2n−4, and 20∶5n−3 (eicosapentaenoic acid, EPA). These fatty acids are major components of a polyunsaturated fatty acid concentrate from the microalga Phaeodactylum tricornutum. The solvents used were methanol/water (1% acetic acid) mixtures of different compositions, and the adsorbents used were chromatographic reversed-phases octylsilyl C8, octadecylsilyl C18, and dodecylsilyl C22 of different particle and pore sizes. The kinetic studies showed that equilibrium was attained instantaneously, suggesting an absence of mass transfer limitations. The equilibrium data were fitted by the Freundlich isotherm. The separation efficiency of EPA from 16∶1n−7 and 16∶2n−4 in all the adsorbent-solvent systems was compared in terms of the separation factors αEPA/16:2n-4=KEPA/K16:2n-4 and α16:1n-7/EPA=K16:1n-7/KEPA, where Ki is the fatty acid distribution ratio between the stationary and the liquid phases. The EPA separation from 16∶1n−7 and 16∶2n−4 by liquid chromatography could be predicted using the Craig model for the various solvent-adsorbent combinations. The best adsorbents for purifying EPA were: C18, PEP, 8 μm, 100 A, and C22, 10 μm, 100 A, and the best solvent was methanol/water (1% acetic acid) 75∶25, w/w.

E. Molina Grima

Papers

Assessment of the photosynthetically active incident radiation in outdoor photobioreactors using oxalic acid/uranyl sulfate chemical actinometer

Estudio de macronutrientes para la producción de PUFAs a partir de la microalga marina Isochrysis galbana

Challenges in microalgae biofuels

Bioprocess strategies for enhancing the outdoor production of Nannochloropsis gaditana: an evaluation of the effects of pH on culture performance in tubular photobioreactors

Adsorption equilibria of fatty acids between methanol/water and reversed-phase chromatographic adsorbents