Microalgae a sustainable resource for valuable compounds and energy

Transcription

1 Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB Microalgae a sustainable resource for valuable compounds and energy

2 1 2 3 Production of valuable compounds with microalgae Photosynthesis is the only process using sunlight as the energy source and CO 2 as the carbon source for the production of biomass. Especially the potential of microalgae photosynthesis for the production of valuable compounds or for energetic use is widely recognized due to their more efficient utilization of sunlight energy compared with higher plants. Microalgae can be used to produce a wide range of metabolites, such as proteins, lipids, carbohydrates, carotenoids or vitamins for health, food and feed additives, cosmetics and for energy production. Why microalgae? Their growth rate is 5 to 10 times higher than that of higher plants. Essential for growth are sunlight, CO 2, and inorganic nutrients like nitrogen and phosphorous. Carbon dioxide emitted from combustion processes can be used as a source of carbon for algal growth (1 kg of dry algal biomass requiring about 1.85 kg of CO 2). Microalgae can be cultivated in seawater or brackish water on non-arable land, and do not compete for resources with conventional agriculture. Microalgae biomass can be harvested during all seasons. The biomass is homogenous and free of lignocellulose. The biochemical composition of the algal biomass can be modulated by varying growth conditions resulting in secondary metabolites such as carotenoids or lipid or starch accumulation. Microalgae grow in an aquatic medium, but need less water than terrestrial crops. Net energy production is possible. However, at present these advantages are offset by the fact that algae production plants have high investment costs and, depending on the type of photobioreactor used, high operating costs, too. Irrespective of the type of energetic application, any further utilization strategies necessitate a net energy yield from the algal biomass production. Net energy production in this case is the difference between the energy input needed for the cultivation of the algal biomass and its ensuing energy content, i.e. the light energy fixed in the biomass by photosynthesis. Valuable compounds from microalgae The Fraunhofer IGB is concentrating its activities on two markets in the food supplement sector: natural astaxanthin, a red pigment with antioxidative properties, and highly unsaturated fatty acids (omega-3 fatty acids), which play an important role in human cardiovascular and inflammatory diseases. Haematococcus pluvialis is the organism with the highest natural content of astaxanthin, which is taken up by fish via the marine food chain. Astaxanthin is used as a pigment in aquaculture in order to enhance the pink color of shrimp, salmon and trout meat as well as in cosmetics. Because of its antioxidative potential and beneficial properties for both the cardiovascular system and human eye function, it is also used as a dietary supplement. Eicosapentaenoic acid (EPA) belongs to the omega-3 fatty acids and amounts to as much as 30 percent of all fatty aids in the micro-algae Phaeodactylum tricornutum. EPA is essential 2

3 O OH HO O 4 5 COOH for humans: malnutrition with EPA results in a greater risk of diseases of civilization such as heart attack and stroke. The inflammation inhibitory effects of EPA are used pharmaceutically in rheumatoid arthritis and multiple sclerosis therapy. In Fraunhofer IGB processes for the production of astaxanthin and EPA were developed under outdoor conditions. Process parameters such as light intensity, CO 2 and nutrient concentrations, as well as the cultivation method, were optimized. Recovery of algal products Supercritical fluid extraction, a natural and green way of achieving product extraction, has received increased attention as an important alternative to conventional separation methods because it is simpler, faster, more efficient and avoids the consumption of large amounts of organic solvents, which are often expensive and potentially harmful. Within a project funded by the Deutsche Bundesstiftung Umwelt (DBU) a process for the recovery of polyunsaturated omega-3 fatty acids (eicosapentaenoic acid EPA; 20:5 n-3) will be developed. Depending on the algae strain, galactolipids can be extracted with ethanol from the biomass. Using transesterification, the fatty acid esters can be purified by means of supercritical CO 2. So far, cell disruption is not necessary for the strain Phaeodactylum tricornutum. In order to keep the process economical without any drying step requiring high energy consumption it is also possible to use wet biomass. Furthermore, in the next step it will be necessary to study the transesterification of the galactolipids. Useful substances contained in algae Pigments / Carotinoids β-carotene, astaxanthin, lutein, zeaxanthin, canthaxanthin, chlorophyll, phycocyanin, phycoerythrin, fucoxanthin Polyunsaturated fatty acids DHA (C22:6), EPA (C20:5), ARA (C20:4), (PUFAs) GAL (C18:3) Antioxidants catalases, polyphenols, superoxid dismutase, tocopherols Vitamins A, B1, B6, B12, C, E, biotin, riboflavin, nicotinic acid, pantothenate, folic acid Other antifungal, antimicrobial and antiviral agents, toxins, amino acids, proteins, sterols, MAAs for light protection MAA: Mycosporine-like Amino Acid (absorb UV). 1 Phaeodactylum tricornutum. 2 Haematococcus pluvialis. 3 Chlorella vulgaris. 4 Haematococcus pluvialis with red pigment astaxanthin. 5 Photobioreactor with Haematococcus pluvialis. 6 Chemical structures of astaxanthin and EPA respectively. 3

4 1 2 novel photobioreactor The most important process parameter in the mass cultivation of microalgae in photobioreactors is the availability and intensity of light. This determines the biomass productivity and thus the growth rate and cell concentration of the algae in the reactor. For achieving high cell concentrations the light availability for every individual cell in the photobioreactor has to be increased. Due to mutual shading in dense algal cultures an efficient and directed intermixing has to provide the uniform distribution of light to all the cells. Therefore the primary task of intermixing is to transport algal cells in short intervals to the reactor surface for intercepting high light intensities. The photobioreactor system developed and patented 1 at the Fraunhofer IGB and scaled-up by the Fraunhofer spin-off Subitec GmbH takes these parameters into account. Airlift-driven intermixing combined with static mixers offers efficient distribution of light with a low energy input for intermixing and low shear forces taking effect on the algal cells. Due to the static mixers, uprising gas bubbles induce definite vortices in the interconnected reactor compartments. In these definite vortices algal cells are transported in short intervals to the reactor surface to intercept high light intensities and then transported back to the dark. Sufficient CO 2 and O 2 mass transfer for unlimited growth is ensured by the combination of airliftdriven principle and static mixers. The flat panel airlift (FPA) reactor is well-suited for small-scale and large-scale production of microalgae. The reactor itself is inexpensively made from two deep-drawn plastic sheets including static mixers, manufactured by twin-sheet technology 1 Patent number: WO ; EP Photobioreactor scale-up In scaling-up processes, energy efficiency is the most important criterion in ensuring subsequent economical production. The crucial factor here is the energy input for algal biomass production for intermixing and light distribution resulting in high cell growth rate and high cell concentrations. In a scaleup process the volume of the FPA reactor was increased from 5 liters lab scale to 30 liters and finally to 180 liters by Subitec GmbH. The scale-up step to a pilot plant consists of linking several reactor modules (each 180 litres). In effect, this resulted in a reduction of the energy input per reactor volume necessary for possible net energy production. Currently Subitec GmbH operates two pilot plants with a volume of 1.3 and 4.5 m³ in an outdoor pilot plant using carbon dioxide containing waste gas for algae biomass production. 1 Flow profile. 2 Photobioreactor. 3 Pilot plant with 180 liter reactors. Thomas Ernsting 4

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6 energy algal biomass products: pigments ω-3-fatty acids vitamins H 2 0 CO 2 light reactions O 2 ADP + Pi + NADP + ATP + NADPH + H + calvin cycle CH 2 O CO 2 NH 4 / PO 4 recycling per kg algal biomass produced 1.85 kg CO 2 are fixed biogas CHPS digestion/ codigestion 8 MJ electricity 12 MJ heat per m 3 biogas Energetic use of microalgae biomass Use of storage lipids Sustainability by recycling of nutrients Many microalgae have the ability to produce substantial amounts (e.g percent dry cell weight) of triacylglycerols (TAGs) as a storage lipid when under stress and growing slowly, and simultaneously high light intensities are available. Besides, there are also some strains that produce polyunsaturated fatty acids (up to 5 percent of dry cell weight) in the growth phase. In screening tests at the Fraunhofer IGB various algae were tested for their ability to produce storage lipids under the conditions of a flat panel airlift (FPA) reactor. Lipid content increased up to 70 percent of dry cell weight in 4 to 6 days. Under these conditions mainly monounsaturated fatty acids with 16 and 18 carbons were synthesized. Lipid productivity was not specific for a certain strain but depended largely on the light intensity per cell. Therefore lipid production in FPA reactors was severely light limited. In future one challenge is locating the production facilities in areas with suitably high sunlight incidence to achieve maximum lipid production. Fraunhofer IGB is developing sustainable, resource-efficient and ecologically friendly production processes for the production of valuable products and the energetic use of microalgae combining the use of flue gas from combustion processes as the carbon source (combined heat and power stations with biogas or natural gas). Our intention is first to recover valuable products from microalgae followed by digestion of the residual biomass to biogas. Carbon dioxide is recycled to the algal cultivation process. For a positive net energy balance the use of waste gas as the carbon source is a must for photoautotrophic microalgae biomass production. Additionally, recycling of nitrogen and phosphorous from anaerobic digestion effluents is possible. 6

7 1 2 3 range of services and contact Screening for microalgae and cyanobacteria Development of photoautotrophic processes for microalgae and cyanobacteria in flat panel airlift reactors from laboratory to technical plant scale Process optimization for improving productivity and biomass yield Development of processes for the isolation, separation and purification of algal products contact Dr. Ulrike Schmid-Staiger Phone ulrike.schmid-staiger@igb.fraunhofer.de Prof. Dr. Walter Trösch Head of Department of Environmental Biotechnology and Bioprocess Engineering Phone walter.troesch@igb.fraunhofer.de successful cooperation: subitec and Fraunhofer IGB 1 Biomass from lipidcontaining algae after harvesting. EnBW 2 Ascending gas bubbles. 3 Photobioreactor, detail view. Fraunhofer IGB and Subitec GmbH are working together to develop new algae processes for the utilization of microalgae to produce substances and energy. The screening and the process development for new algal strains are carried out in flat panel airlift lab reactors at Fraunhofer IGB. The scaleup of the processes developed in this way is done in the FPA reactors of Subitec GmbH, including outdoor pilot produc- tion batches in their own photobioreactor plants. Thus sufficient algal biomass can be produced for the extraction of the algal substances at Fraunhofer IGB and for industrial partners. 7

8 Fraunhofer Institute for Interfacial Engineering and Biotechnology IGB (Fraunhofer-Institut für Grenzflächen- und Bioverfahrenstechnik IGB) Nobelstrasse Stuttgart Germany Phone Fax Director Prof. Dr. Thomas Hirth Phone Fraunhofer IGB brief profile The Fraunhofer IGB develops and optimizes processes and products in the fields of medicine, pharmacy, chemistry, the environment and energy. We combine the highest scientific quality with professional expertise in our fields of competence Interfacial Engineering and Materials Science, Molecular Biotechnology, Physical Process Technology, Environmental Biotechnology and Bioprocess Engineering, as well as Cell and Tissue Engineering always with a view to economic efficiency and sustainability. Our strength lies in offering complete solutions from laboratory scale to pilot plant. Customers benefit from the constructive cooperation of the various disciplines at our institute, which is opening up novel approaches in fields such as medical engineering, nanotechnology, industrial biotechnology, and wastewater purification. The Fraunhofer IGB is one of more than 80 research units of the Fraunhofer-Gesellschaft, Europe s largest organization for application-oriented research.