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

https://www.massey.ac.nz/~ychisti/EPA%20Review.pdf

Recovery of microalgal biomass and metabolites: process options and economics

Urban, industrial and agricultural wastewaters contain up to three magnitudes higher concentrations of total nitrogen and phosphorous, compared with natural water bodies.1 Normal primary and secondary treatment of these wastewaters eliminates the easily settled materials and oxidizes the organic material present, but does not remove the nutrients which will cause eutrophication of the rivers or lakes into which these wastewaters may be discharged. Tertiary treatment of the effluent is therefore required, and both chemical and physical methods which are used are very expensive. Oswald2 estimates that the relative cost of tertiary treatment to remove PO 4 3− , NH 4 + and NO 3 − is about 4 times the cost of primary treatment. Higher orders of treatment, such as quaternary treatment required to remove refractory organics and organic and inorganic toxicants and quinary treatment to remove inorganic salts and heavy metals, are 8 to 16 times as expensive as primary treatment. Algae can be used as a biological alternative tertiary treatment and also for the removal of heavy metals and possibly other toxic substances.3,4 The possibility exists that the algae produced in these systems can be used as animal feed supplements,5,6 or be composted. The use of waste-grown algae may ultimately also have application in closed cycle life-support systems,7,8 or may be used in conjunction with power stations, not only to treat wastewaters, but also to act as a CO2 sink for the amelioration of the impact of greenhouse gases.9–13

Limits to Growth

One major challenge to industrial microalgal culturing is to devise and develop technical apparata, cultivation procedures and algal strains susceptible of undergoing substantial increases in efficiency of use of solar energy and carbon dioxide. Despite several research efforts developed to date, there is no such thing as "the best reactor system"- defined, in an absolute fashion, as the one able to achieve maximum productivity with minimum operation costs, irrespective of the biological and chemical system at stake. In fact, choice of the most suitable system is situation-dependent, as both the species of alga available and the final purpose intended will play a role. The need of accurate control impairs use of open-system configurations, so current investigation has focused mostly on closed systems. In this review, several types of closed bioreactors described in the technical literature as able to support production of microalgae are comprehensively presented and duly discussed, using transport phenomenon and process engineering methodological approaches. The text is subdivided into subsections on: reactor design, which includes tubular reactors, flat plate reactors and fermenter-type reactors; and processing parameters, which include gaseous transfer, medium mixing and light requirements.

/pdf/microalgal-reactors-a-review-of-enclosed-system-designs-and-4satxmahtc.pdf

Microalgal Reactors: A Review of Enclosed System Designs and Performances

Microalgae are a major natural source for a vast array of valuable compounds, including a diversity of pigments, for which these photosynthetic microorganisms represent an almost exclusive biological resource. Yellow, orange, and red carotenoids have an industrial use in food products and cosmetics as vitamin supplements and health food products and as feed additives for poultry, livestock, fish, and crustaceans. The growing worldwide market value of carotenoids is projected to reach over US$1,000 million by the end of the decade. The nutraceutical boom has also integrated carotenoids mainly on the claim of their proven antioxidant properties. Recently established benefits in human health open new uses for some carotenoids, especially lutein, an effective agent for the prevention and treatment of a variety of degenerative diseases. Consumers’ demand for natural products favors development of pigments from biological sources, thus increasing opportunities for microalgae. The biotechnology of microalgae has gained considerable progress and relevance in recent decades, with carotenoid production representing one of its most successful domains. In this paper, we review the most relevant features of microalgal biotechnology related to the production of different carotenoids outdoors, with a main focus on β-carotene from Dunaliella, astaxanthin from Haematococcus, and lutein from chlorophycean strains. We compare the current state of the corresponding production technologies, based on either open-pond systems or closed photobioreactors. The potential of scientific and technological advances for improvements in yield and reduction in production costs for carotenoids from microalgae is also discussed.

https://moritz.botany.ut.ee/~olli/b/DelCampo07.pdf

Outdoor cultivation of microalgae for carotenoid production: current state and perspectives

Cell fragility — The key problem of microalgae mass production in closed photobioreactors

Apparatus for the intensive, controlled production of microorganisms by photosynthesis. This apparatus comprises at least one photobioreactor (6) to be placed on an expanse of water (8), which has first group of flexible tubes (38), which are transparent to light and in which circulates the culture medium and a second group of inflatable tubes (62), disposed and maintained beneath the first group by means of detachable Y-shaped interpolated members (70), which are regularly spaced. At least one two-column carbonator (12) connected to the photobioreactor intake (43) for charging the liquid medium with the CO 2 necessary for photosynthesis is provided. Two degassing means (36) connected to the two ends of the photobioreactor are provided for eliminating the oxygen produced by the microorganisms from the liquid medium. There is at least one expansion tank (2) connected to the photobioreactor (6) for reducing possible volume variations in the photobioreactor (6).

Apparatus for the intensive, controlled production of microorganisms by photosynthesis

Modelling of growth of Porphyridium cruentum in connection with two interdependent factors: Light and temperature

The invention relates to an apparatus for the purification of a liquid effluent containing pollutants, particularly metals and/or radionuclides, as well as to a process for purifying the effluent. An object of the invention is to provide a continuously functioning purifying apparatus. This object is achieved with the aid of an apparatus incorporating a confinement enclosure containing a support in which are immobilized living cells of photosynthetic microorganisms. The support is made from a material transparent to light rays. The apparatus also incorporates a mechanism for introducing and circulating the effluent to be treated and a culture medium within the enclosure.

Apparatus for purifying a liquid effluent containing pollutants

Ce dispositif comprend au moins un photobioreacteur (6) destine a etre place sur une etendue d'eau (8), comportant un premier ensemble de tubes (38) souples, transparents a la lumiere, dans lesquels circule le milieu de culture et un second ensemble de tubes (62) gonflables, disposes et maintenus sous le premier ensemble au moyen d'intercalaires (70) amovibles en Y, regulierement espaces ; Said device comprises at least one photobioreactor (6) intended to be placed on an expanse of water (8), comprising a first set of tubes (38) flexible, transparent to light, in which circulates the culture medium and a second tube assembly (62) inflatable disposed and maintained under the first set by means of spacers (70) movable in Y, regularly spaced; au moins un carbonateur (12) a deux colonnes raccorde a l'entree (43) du photobioreacteur pour charger le milieu liquide en CO₂ necessaire a la photosynthese ; at least one carbonator (12) with two columns connected to the input (43) of the photobioreactor for charging the liquid medium with the CO₂ necessary for photosynthesis; deux degazeurs (36) raccordes aux deux extremites du photobioreacteur pour eliminer du milieu liquide l'oxygene produit par les micro-organismes ; two getter (36) connected to both ends of the photobioreactor to remove the liquid medium the oxygen produced by the microorganisms; et au moins une cuve d'expansion (2) raccordee au photobioreacteur (6) pour amortir les variations eventuelles de volume dans le photobioreacteur (6). and at least one expansion tank (2) connected to the photobioreactor (6) to absorb any variations in volume in the photobioreactor (6).

Daniel Chaumont

Papers

Cell fragility — The key problem of microalgae mass production in closed photobioreactors

Apparatus for the intensive, controlled production of microorganisms by photosynthesis

Modelling of growth of Porphyridium cruentum in connection with two interdependent factors: Light and temperature

Apparatus for purifying a liquid effluent containing pollutants

Device for controlled intensive production of microorganisms by photosynthesis