The search of sustainable and environmentally friendly alternatives to obtain compounds for different industrial sectors has grown exponentially. Following the principles of biorefinery and circular bioeconomy, processes in which the use of natural resources such as macroalgae biomass is prioritized are required. This review focuses on a description of the relevance, application and engineering platforms of hydrothermal systems and the operational conditions depending on the target as an innovative technology and bio-based solution for macroalgae fractionation in order to recover profitable products for industries and investors. In this sense, hydrothermal treatments represent a promising alternative for obtaining different high value-added compounds from this biomass; since, the different variations in terms of operating conditions, gives great versatility to this technology compared to other types of processing, allowing it to be adapted depending on the objective, whether it is working under sub/super critical conditions, thus expanding its field of application.
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Marine macroalgae Enteromorpha prolifera, one of the main algae genera for green tide, was converted to bio-oil by hydrothermal liquefaction in a batch reactor at temperatures of 220−320 °C. The liquefaction products were separated into a dichloromethane-soluble fraction (bio-oil), water-soluble fraction, solid residue, and gaseous fraction. Effects of the temperature, reaction time, and Na2CO3 catalyst on the yields of liquefaction products were investigated. A moderate temperature of 300 °C with 5 wt % Na2CO3 and reaction time of 30 min led to the highest bio-oil yield of 23.0 wt %. The raw algae and liquefaction products were analyzed using elemental analysis, Fourier transform infrared (FTIR) spectroscopy, gas chromatography−mass spectrometry (GC−MS), and 1H nuclear magnetic resonance (NMR). The higher heating values (HHVs) of bio-oils obtained at 300 °C were around 28−30 MJ/kg. The bio-oil was a complex mixture of ketones, aldehydes, phenols, alkenes, fatty acids, esters, aromatics, and nitrogen-containing heterocyclic compounds. Acetic acid was the main component of the water-soluble products. The results might be helpful to find a possible strategy for use of byproducts of green tide as feedstock for bio-oil production, which should be beneficial for environmental protection and renewable energy development.
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A PDF on SINTEF's "Hydrothermal gasification of seaweed: a promising technology to biofuels production" Power Point.
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A process for isolation of three products (fatty acids, chars and nutrient-rich aqueous phases) from the hydrothermal carbonization of microalgae is described. Fatty acid products derived from hydrolysis of fatty acid ester groups in the microalgae were obtained in high yield and were found to be principally adsorbed onto the char also created in the process. With the highest lipid-containing microalga investigated, 92% of the fatty acids isolated were obtained by solvent extraction of the char product, with the remaining 8% obtained by extraction of the acidified filtrate. Obtaining the fatty acids principally by a solid–liquid extraction eliminates potential emulsification and phase separation problems commonly encountered in liquid–liquid extractions. The aqueous phase was investigated as a nutrient amendment to algal growth media, and a 20-fold dilution of the concentrate supported algal growth to a level of about half that of the optimal nutrient growth medium. Uses for the extracted char other than as a solid fuel are also discussed. Results of these studies indicate that fatty acids derived from hydrothermal carbonization of microalgae hold great promise for the production of liquid biofuels.
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Hydrothermal carbonization is a process in which biomass is heated in water under pressure to create a char product. With higher plants, the chemistry of the process derives primarily from lignin, cellulose and hemicellulose components. In contrast, green and blue-green microalgae are not lignocellulosic in composition, and the chemistry is entirely different, involving proteins, lipids and carbohydrates (generally not cellulose). Employing relatively moderate conditions of temperature (ca. 200 C), time (<1 h) and pressure (<2 MPa), microalgae can be converted in an energy efficient manner into an algal char product that is of bituminous coal quality. Potential uses for the product include creation of synthesis gas and conversion into industrial chemicals and gasoline; application as a soil nutrient amendment; and as a carbon neutral supplement to natural coal for generation of electrical power.
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Photosynthetic bacteria utilize hydrogen as electron donor for autotrophic CO2 assimilation. Many of these organisms also evolve hydrogen under dark anaerobic conditions and, in large quantities, anaerobically in the light in the absence of ammonia and molecular nitrogen. Hydrogen photoproduction in photosynthetic bacteria is largely or completely associated with the action of nitrogenase. It is not inhibited by CO, an inhibitor of hydrogenase and is dependent on ATP. The conventional hydrogenase catalyzes the reversible reaction H2⇄2H++2e-.It seems however that in photosynthetic bacteria this enzyme catalyzes mainly hydrogen uptake in vivo. It has been suggested that a function of hydrogenase is to reutilize the hydrogen which is evolved as a byproduct of the nitrogenase reaction, retaining reducing equivalents for N2 or CO2 reduction1. In contrast to aerobic bacteria, energy conservation in a Knallgas reaction is not possible for photosynthetic bacteria growing anaerobically in the light2.
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A variety of microorganisms can evolve H2 according to the following equation:2H+ + 2e +z H2. These include strict or facultative anaerobic bacteria, aerobic bacteria, blue-green and green algae. In aerobic bacteria and in blue-green algae H2 formations are restricted to N2-fixing species. Strict and facultative anaerobic bacteria as well as green algae (Chlamydomonas, Scenedesmus, Chlorella) form the gas only under O2 exclusion in the cultures. There is no clearcut demonstration for Hrformation by mosses, ferns and higher plants. Lists of the Hrforming organisms are compiled in Mortenson and Chen I and Schlegel and Schneider2. Since the redox potential of the couple 2H+ /H2 is -413 mV at pH 7.0, a low potential reductant is required for H2-formation to proceed in the cells. The reaction is also enzyme mediated. Cells may contain 3 clearly distinguishable enzymes catalyzing either uptake or evolution of H2 under physiological conditions (for a more detailed account and the references see Bothe and Eisbrenner3).
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The world diet in 2062 or 2112 will be as unfamiliar to most people today as our own cosmopolitan diet of fast food and ethnic cuisines would be to our great grandparents in 1912. The new foods will be the result of fierce demand and resource pressures on food worldwide, astonishing new technologies, and emerging trends in diet, farming, healthcare and sustainability.
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The contemporary uses of seaweed in Ireland are many and various. Seaweed is gathered as food, processed and used as fertiliser, forms an ingredient in many cosmetics and spa treatments, and is the subject of biotechnological and pharmaceutical research.
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Biofuel From Algae?(CTSA Meeting)•Demand for high quality, fresh algae inbulk quantities•Effluenttreatment ofsewage, nutrientremoval•CO2removal•Treatment of industrial wastes–changesquality
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200 W. Kawili st., HI 96720, USA
Contact: Marine.Agronomy.Group@gmail.com
Funding for this web portal is provided by the World Wildlife Fund and the University of Hawaii-Hilo.