Roberto Rana, University of Foggia
In recent years the rapid economic development of some emerging countries like China, India, etc.. has led to increasing consumption of fossil fuels and, consequently, has accelerated their depletion and increased atmospheric concentration of carbon dioxide. So many governments worldwide, to address these serious risks have initiated detailed studies on renewable energy sources and proven technologies that can "sequester" the greenhouse gases. Among the solutions proposed that envisages the use of biomass seems to be the best as organic matter, through the reaction of photosynthesis, carbon dioxide traps the radiation and converts light into energy available for human activities. In this way, in fact, the plants, when burned directly to produce heat used for space heating or cooking food, or if processed by physical, chemical or biochemical processes, provide biofuels such as bioethanol (extracted mainly from sugar cane and corn) and biodiesel (made primarily from palm oil from rapeseed and soy), respectively, used as substitutes for petrol or diesel fuel in the means of locomotion.
The undisputed benefits of using biofuels (for example, a low environmental impact, energy self-sufficiency, a balance between emission and fixation of carbon dioxide is practically zero, etc..) Conducted in recent decades, which an increase in their production in 2009 reached almost 90 million tonnes. Thus, despite the improvements economic and ensuing environmental scientists have argued that the production of these goods is unsustainable because of negative effects on natural ecosystems, food supply, especially in developing countries, etc..
These issues, therefore, have stimulated researchers to seek new technologies to produce biofuels with less environmental and social impact. So, inspired by the theory of organic origin of oil and by surveys in the last fifty years, have been identified algae as a feedstock to produce biofuels such as biodiesel, by squeezing and subsequent reaction of trans-esterification, ethanol, fermentation of starchy component, biogas, anaerobic decomposition, a mixture of liquid fuels, solid and gas fractionation pyrolysis and hydrogen through cultivation of "dedicated" to produce this gas.
The marine plant biomass is represented mainly by two major groups: macroalgae and microalgae. The first, large, are used worldwide mainly as food, fertilizer or for the extraction of substances used in cosmetics or pharmaceutical industry, and the latter, however, are mostly single-celled organisms used in the fish nutrition in aquaculture and production of food supplements or adittivi such as β-carotene el'axantina.
Although you can get from biofuels from microalgae and macroalgae, since 2000 studies have focused on those plants and, in particular, the production of biodiesel, because: they reproduce rapidly (doubling their weight within a few hours ), showing high yields of biomass (up to 70 t / ha per year), contain a large amount of fats (up to 50% of their dry weight) can be grown on marginal land so as not to jeopardize agricultural production intended for human consumption.
According to some estimates it would take only 6 million hectares of land (equal 0.4% of world agricultural land) in microalgae grown to meet the global demand for biodiesel.
The first studies on the possibility of growing algae for energy back in the late forties of last century, when Hans Gaffron spotted a microalgae of the genus Scenedesmus , can produce hydrogen under anaerobic conditions. A few years later were discovered other microalgae (Chlamydomonas spp.) And marine organisms ( Rhodospirillum rubrum) can perform the same process. Research continued, and some scientists observed that the algae could accumulate large amounts of oil and that it was possible to obtain biogas dalla loro fermentazione anaerobica. Tuttavia, il basso costo dell’energia ottenuta dai combustibili fossili relegò queste indagini ai soli laboratori scientifici.
Il rinnovato interesse per queste scoperte avvenne durante la prima crisi energetica dei primi anni Settanta del secolo scorso quando il ministero americano dell’energia (DOE – Department of Energy) mediante i suoi laboratori (SERI - Solar Energy Research Institute, oggi NREL - National Renewable Energy Laboratoy) avviò uno specifico programma di ricerca (Aquatic Species Program – ASP) che, rifacendosi agli studi pregressi, impiegava i reflui urbani per la crescita delle microalghe che erano poi trasformate in biogas. Gli esiti positivi di questo esperimento and the discovery of large quantities of oil contained in the SERI microalgae led scholars to use the marine biomass for obtaining biodiesel. Despite the success obtained (about 3000 species were selected rich in fat, improved farming technologies, etc.). The project was suspended in 1996 because the funds for these investigations were transferred to new research on the production of ethanol from cellulose.
The results achieved in the ASP program have, however, represented a valuable source of information for scholars who have subsequently addressed these issues.
Today, worldwide projects have been launched for the construction of installations for the intensive cultivation of microalgae and extracting oil, although, unlike in the past, individuals also actively involved with research to improve production technologies. There are, in fact, national and international companies that supply biodiesel "sea" or who build and / or market instruments for the growth of these microorganisms. However, due to high capital costs and plant management has not yet started the commercial production stage. The development of these technologies on an industrial scale will help reduce dependency on non renewable energy sources in many countries and promote the spread of biofuels really sustainable.
The main characteristics of microalgae and the types of plants growing
As mentioned, the single-celled marine algae are plant organisms (phytoplankton) with dimensions generally less than 30 micron which have good yields of biomass (50-70 t / ha) due to their high speed dubbing (the doubling of the weight is within 12-24 hours depending on the species, while the cells are able to make cell division in 3.5 hours). From a taxonomic point of view they can be broken a three main groups: green algae Chlorophyta , who prefer to live in fresh water, the diatoms (Bacillariophyta ), which live in marine environments and are characterized by a silica coating; coccolithophores from the calcareous shell and a high concentration of lipids (30-50% of dry weight).
Commonly these organisms have a protein, carbohydrate and fat varies greatly depending on the species and the environment in which they grow lipids, for example, be a minimum of between 1% and a maximum of 40 % of their dry weight. These amounts may vary depending on the conditions of preparation of the crop and the temperature and salinity of the water so when the single-celled algae grow in situations of nutrient deficiency (such as nitrogen, silicon, etc..) or in an aqueous medium rich in sodium chloride, can increase the oil yield over 70% of their dry weight. It is the very high yields of oils and fats that make these plants more competitive than traditional oil crops, for example, while a hectare of palm oil, higher-yielding oilseed crop in fat, it is possible to recover approximately 6,000 gallons of product, from the same acreage of microalgae can be obtained nearly 20,000 gallons of oil.
The first experiments of "intensive cultivation" of algal biomass occurred in the fifties of the twentieth century when researchers published several scientific works on crescita delle microalghe in impianti pilota che, collocati all’aperto, utilizzavano i reflui urbani come fonte nutritiva. Da questi importanti studi si è poi sviluppata la tecnologia di coltivazione degli open pond, attualmente in uso negli Stati Uniti d’America, Cina, India, ecc., per la produzione commerciale della “spirulina”, una microalga usata come integratore alimentare in tutto il mondo. Gli impianti sono costituiti da una o più vasche di forma ellittica (con una estensione che può raggiungere i 5000 m2 e una profondità tra i 15-30 cm) collegate tra loro. Per alimentare le alghe s’impiegano sali minerali oppure reflui urbani e/o gas (in particolare anidride carbonica e ossidi di azoto) emessi da a power plant or a cement places a few meters away. Microalgae grown in this way, I'm a real "ecological reservoir of carbon dioxide that can transform CO2 2 kg in 1 kg of plant biomass. In addition, a propeller, on the move, avoiding the accumulation of algae on the bottom, ensuring a sufficient amount of light to perform photosynthesis. Similar structures are raceway ponds, reservoirs of greater breadth and depth of open ponds, in which the algal cells follow similar paths in circular channels.
These installations although they consist of simple tools are the inconvenience to keep changing environmental parameters such as temperature, salt concentration and the presence of dissolved gases. For example, the volume of water can increase or decrease due to evaporation to precipitation, while the temperature can follow the daily and seasonal temperature changes. Productivity, then, can be reduced to the activity of certain predators or parasites that contaminate the waters: to overcome this problem often microalgae are grown in environments with high salinity. This will, however, while it avoids competition with other aquatic species on the other hand limits the variety of algae that can essere impiegate nel processo e rende salsi i terreni su cui sorgono gli impianti.
Così, per ottenere rese in biomassa più elevate, coltivare anche varietà algali che prediligono concentrazioni saline più basse, mantenere costanti le variabili ambientali ed impedire la contaminazione di altri microrganismi sono stati proposti i fotobioreattori, strutture chiuse e trasparenti nelle quali il fitoplancton non è a contatto diretto con l’ambiente esterno e la radiazione luminosa raggiunge i microrganismi acquatici attraverso le pareti oppure mediante fibre ottiche o “collettori solari” (particolari specchi che convogliano la luce sui fotobioreattori) in forma concentrata.
Attualmente sono disponibili different models, although all the bioreactors can be traced to four basic types, such as: a column (bubble columns), large cylinder placed upright, made of glass or Plexiglas tube (tubular reactor), similar to the above but featuring a smaller diameter pipes, arranged horizontally or obliquely, in panels (flat panels), in glass tanks with a face much larger than the other and placed in succession; bag (plastic bags), large transparent plastic bags of varying form. These structures can be placed in interior spaces (indoor), such as greenhouses, or placed outdoors (outdoor) directly on the ground or on special platforms.
The first prototypes of photobioreactors have been built in the early fifties of the twentieth century in Japan and the United States of America (USA). Among the best known of these is installed on the roof of the Massachusett Institute of Technology (MIT) in the USA, composed of polyethylene pipes lying on the floor where growing algae of the genus Chlorella . However, the high cost of construction and operation of the plant, in addition to low yields in biomass, did not allow the development of this technology.
Thirty years later, however, the photobioreactors were replicated with a few fundamental changes (such as an internal recycling of water) that have improved performance (increased production, reduced risk of contamination of parasitic species, more accurate control of chemical and physical parameters of the culture medium, etc..), making these facilities more efficient than ever before. A prototype of this type have been relocated, forty years later, on the roof of the renowned U.S. research center. It consists of thirty polycarbonate tubes, of circular cross section (10-20 cm diameter) arranged in a triangle, in which the algae grow in an appropriate saline solution. The two shorter sides are placed in the shade, while the longer one is exposed to sunlight, so that the biochemical reactions of photosynthesis.
The gaseous effluent, rich in CO2 and nitrogen oxides from the plant and adjacent thermoelectric, are released from the bottom to allow the continuous movement of plant biomass, which reached the maximum density growth, is collected and sent to the extraction phase oil. The remaining algal mass is subjected to drying, heat rejection by the plant, only to be used as solid fuel in the same power plant. In addition, to avoid reaching a high concentration of oxygen inside the tubes, thus affecting the production of plant biomass, the photobioreactor is equipped with a degasser. This plant è in grado di ridurre l’86% degli ossidi di azoto e l’82% dell’anidride carbonica dalle emissioni gassose provenienti dall’impianto termoelettrico e di produrre giornalmente circa 400 kg di biodiesel (pari a oltre 450litri) e meno di 1 t di biomassa secca.
Nonostante i miglioramenti tecnici apportati ai fotobioreattori essi continuano ad avere un elevato costo e una gestione più complessa e dispendiosa rispetto agli open pond. I diversi impianti commerciali costruiti nel mondo (paese: Israele, specie coltivata: Haematococcus pluvialis, merce ottenuta: astaxantina; paese: Germania, specie coltivata: Chlorella spp., merce ottenuta: integratore alimentare; paese: Cina, specie coltivata: Spirulina platentis, goods produced: food supplement), in fact, have failed precisely because of the technical and economic problems.
The oil extraction and biodiesel production from microalgae
Once the growth phase, therefore, organisms are collected and centrifuged to separate one part water and still recover the other biomass plant for the extraction of lipids. In some cases, to save money and energy may be confined to a simple filtration or biological filters suitable mesh sieve with very narrow. The water removed, yet rich in nutrients, was postponed in the tanks or photobioreactors for the cultivation of new biomassa algale.
Segue la fase di estrazione vera e propria, dalla quale si ottiene da una parte l’olio e dall’altra un panello (cake), costituito dalle microalghe ormai prive della componente grassa. Questa operazione può avvenire semplicemente per spremitura a freddo, con recupero del 70-75 % di olio oppure con un adatto solvente (benzene, etere di petrolio, cicloesano, ecc.) immiscibile in acqua, con rese fino al 100%. Poiché il cake non trattato con solvente è ancora ricco dei preziosi acidi grassi polinsaturi (ω-3 e ω-6), delle proteine e dei carboidrati può essere venduto alle aziende agricole come mangime per il bestiame; quello trattato con solvente, invece, avendo una qualità more nutrient poor, can be subjected to anaerobic treatment, to obtain biogas (with yields of 0.15 to 0.65 m3/kg dry biomass), or aerobic to produce ethanol.
Since the phases of separation have a major impact on the final cost of fuel are being studied technical solutions such as ultrasonic extraction of lipids, with electrical pulses (Live ™ Extraction) or electromagnetic (Quantum FracturingTM), which allow to economize the entire process. With technology live extractionTM, for example, the release oil is by sending weak electrical currents in solutions containing algal cells: in this way the micro-organisms sea \u200b\u200bare not affected and can continue to grow and reproduce (for details see the website http://www.originoil.com).
oil once extracted can be used as it is in conventional diesel engines, although, generally, to improve performance and make similar, if not better, the biodiesel standard is subjected to a process of trans-esterification (in practice does react the oil with an alcohol).
The cost to produce biodiesel from algae is estimated, in 2009, depending on the technology used in about $ 3 per liter and $ 8 per liter. These values \u200b\u200bare much higher than what you spend to get palm oil (a little more of $ 0.6 per liter), considered the cheapest on the market at present, therefore, biodiesel from microalgae is still not economically viable, although the realization of a "biorefinery" could help reduce the price. In this case, the phytoplankton, as well as for producing biodiesel, could be used to purify the gases emitted by power plants and waste water from residential areas.
also by-products of the extraction processes (cake), you may obtain substances for cosmetics, pharmaceutical and feed industries, etc. .. The technique of genetic engineering could help to make profitable the production of "biodiesel marine environment", attraverso la “creazione” di specie ingegnerizzate in grado di incrementare la resa in biomassa e olio, di migliorare la resistenza dei microrganismi alle temperature estreme, di accrescere la produzione di biomassa anche in vasche densamente popolate e di favorire il processo di bioflocculazione. Ad esempio, per accrescere la produzione della biomassa vegetale marina si sta studiando la possibilità di introdurre la via metabolica degli acidi crassuleici nel genoma delle alghe unicellulari: in questo modo le microalghe sarebbero capaci di fissare l’anidride carbonica anche di notte.
Sebbene, però, alcuni esperimenti di manipolazione genetica siano in fase di sviluppo, per il momento non è possibile ottenere con questa tecnologia algal strains with high biomass yield and oil, due to the lack of complete knowledge of genes that regulate these mechanisms that lead to the synthesis of lipids within the algal cells. It must be stressed, however, that the future development of genetically modified micro algae with high productivity could prove dangerous as an accidental release into the environment might "choke" the lake habitat all over the world because of the excessive growth.
Currently, most companies involved in the sale of photobioreactors and the production of biodiesel from microalgae are American although several European companies are using le potenzialità energetiche offerte da questi microrganismi. L’Olanda, ad esempio, è una delle nazioni che negli ultimi tempi ha fatto “passi da gigante” in tal senso, l’impresa olandese Algaelink N.V., che commercializza fotobioreattori e dispone di stabilimenti di produzione di microalghe in Spagna, ha firmato un accordo esclusivo con la compagna aerea “Air France-KLM” per avviare un progetto pilota sullo sviluppo di un “jet fuel” ottenuto dalla miscelazione del biodiesel “marino” con il carburante convenzionale. In Italia è presente la “Fotosintetica & Microbiologica S.r.l.” un’azienda nata da uno spin-off tra l’Università di Firenze e una society, Sogesca Srl of Padua, whose principal activities are the technical advice and the sale of microalgae photobioreactors and inocula.
In our country especially the southern regions, thanks to the mild climate and the shape of the coastline, can become an ideal venue for the energy production of unicellular algae. ENI for example, has recently built in Sicily, a pilot plant that uses microalgae for wastewater treatment for municipal and biofixation of CO2 emitted by some oil refineries in the area, at a later stage of the research, ' company will consider converting the plant biomass in marine bio-diesel and / or other biofuels.
In the province of Lecce, a few years ago, another private company has proposed the installation of plastic tunnels on about 5,000 acres in which to grow these marine microorganisms and then used as fuel in thermal power plant at Brindisi. The unsustainability of the project and the opposition of most local public opinion have blocked the project. The following proposed plan by the same company, which involved the production of biodiesel from microalgae in the vicinity of existing power stations in the region, has failed.
Apulia, in spite of the negative goodwill, has the potential to become a district for the production of bio-energy marine biomass, for example, the many lagoons that characterize this region like Hvar and Varano or Margaret of Savoy are areas in which to develop the cultivation of microalgae. The cake residue, could then be used for the extraction of some important substances used in the pharmaceutical and food industries, as well as feed for livestock. Moreover, much of the marine biomass is not used, such as microalgae Dunaniella spp. present in saline Margherita di Savoia or the macroalgae Gracilaria verrucosa, which creates problems of anoxia in the lake of Hvar, could be raw materials for the production of biofuels as biogas or ethanol.
The production of biofuels from microalgae, it seems, therefore, be a viable alternative to dedicated energy crops, as more sustainable and higher biomass yields. However, it would be interesting to know whether the technology is sustainable, and it involves a real "energy advantage" for example, you could calculate the index EROEI (energy returned on Energy Invested), which assesses whether the energy contained in one kilogram of " marine biodiesel "is greater than the cost to produce it. The challenges for the near future are, therefore, improve the technology for species with higher yields in biomass and oil, the resolution technical problems relating to the operation of the plant (fouling, contamination of culture medium, control of operating parameters, etc..) and the commercial exploitation of by-products. This will reduce capital costs and management by allowing large-scale production of biofuels from microalgae, such as biodiesel, to be used for transport or air transport.
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