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Macro algae: An energy source with multiple benefits

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fredag 20. april 2012

FACT BOX

Facts on algae

Algae are aquatic organisms that, like plants, live off of fotosynthesis. Through the process of photosynthesis, energy from the sun, CO 2, and water are transformed into carbohydrates and oxygen. Algae are divided into macro and micro algae in accordance with their size. There are more than 30,000 species of algae. This article focuses on macro algae.

Macro algae (seaweed)
Multi-celled organisms that live in sea water. Between 2 mm to 30 m in size. This article focuses on macro algae because they grow in sea water, making them a good prospect for offshore renewables.

Macro algae are harvested for consumption (sushi, seaweed snacks, and algae starch), fertilizer, biomedicine, etc. When looking into producing renewable energy, it is the carbohydrate content that is of relevance. On an industrial scale, macro algae will be cultivated on ropes in sea water, as is done at clam farms.

Micro algae (phytoplancton)
Single-celled organisms. Between 2 micrometer and 0.5 mm in size. At present, these are cultivated for bioplastics, biomedecin, colourants, Omega3 oils, and improvement of water quality. Typically cultivated in tubs and basins.


Joint project on algae: Extracting energy from the macro algae, Ulva Lactuca.

One project in particular has paved the way for new interest in offshore macro algae as a source of energy. Large players in the technological world participated in the project: Danish Technological Institute (GTS Institute), DONG Energy, Technical University of Denmark, and National Environmental Research Institute.

The project’s goal was to research the potential of the macro algae Ulva lactuca, also called sea salad, as a renewable energy resource.

Important project conclusions:
Energy production must be combined with other uses: Many high-value products can be extracted The yield: 45 tons of dry matter per hectare sea salad Sea salad is not suitable for combustion due to its high salt and ash content The carbohydrate content is around 60%, making it a potentially useful crop for producing biogas.

Also explore:
www.algecenterdanmark.dk
www.enalgae.eu

Positive results from large-scale research projects have heightened interest in algae as a source of offshore renewable energy. The researchers and industry agree: Combined use of the crop is necessary. However, a series of challenges must first be overcome before algae can realistically become part of the energy mix.

By Anne Korsgaard
The 30,000 species of algae offer a multitude of potential advantages: Renewable energy generation, extraction of healthy and useful proteins, and cleaning of the world’s oceans. Historically, macro algae has been used for feeding livestock, insulating houses, and much more. However, researchers are taking it to the next level in a Danish project that is revealing the great potential as well as the major challenges of using algae to create energy.

Taking a two-step approach to algae seems to make sense according to Peter Daugbjerg Jensen, Head of the Centre for Renewable Energy and Transport at the Danish Technological Institute, who has participated in Denmark’s largest project on algae for biomass:

“What makes working with macro algae so interesting is the many potential advantages: Several high-value products can be extracted before using the algae for energy production. One can, for example, extract the high-priced colourant astazanthin, proteins for use in functional foods, that can alleviate the problem of feeding the growing world population, and anti-inflammatory substances that can be used for medicinal purposes. Also, the yield of biomass from algae is much higher than terrestrial agricultural crops.”

Nature’s own cleaning lady
Yet another positive side effect to growing algae is that they clean the environment of CO 2 and nutrients as they can be fed slurry and waste water. Algae are thus excellent bioremediation agents, with the potential to absorb massive amounts of CO 2 and play an important role in sewage and wastewater treatment.

“Algae can grow practically anywhere, in water tanks and in marine areas, ensuring that there is no competition with the farmland for regular food crops. Algae also grows quickly and can double its own weight in two to three days,” says Peter Daugbjerg Jensen.

Future prospects for the blue biomass
Much more research and development will be necessary before offshore algae can become part of the energy mix:

Anne-Belinda Bjerre, Senior Researcher at The Technological Institute, who specializes in biomass, says: “What we are looking into at present is the opportunity to extract energy carriers (e.g. bioethanol and biogas) from the algae through a bio-refinery process. By this, I mean converting the algae to fermentable sugars and then into, for instance, bioethanol and in combination with other products. In order to produce for example bioethanolis, we need to know the algae chemical construction i.e. sugarpolymers to determine the right enzymes for dissolving the algae to sugar and following turning the hydrolysed sugars into a useful substance by fermentation. In addition, down-to-earth practical solutions must be developed, such as methods for cultivating, harvesting and pretreatment including dewatering, drying and pelletizing the seaweed for storage and transportation. What keeps us going is algae’s enormous potential. Imagine extracting proteins, beta-glucan, carageenan, ulvan, and other sugar molecules for the food and medical industries, antioxidants for pharmaceuticals, and much more on top of extracting sugars for energy carriers.”

The advantages and potential uses are numerous. But so are the challenges.

DONG Energy, a major Danish utility, has an overarching objective to reduce the use of fossil fuels and increase renewable energy. Biomass will play a key role in this transition. DONG Energy has in the past looked into algae’s potential for combustion:

“We have primarily investigated opportunities for using macro algae for the combined production of heat and electricity. The conclusion is that, at present, we need significant technological breakthroughs, with associated cost reductions, before algae as power plant fuel will be technically feasible, economically competitive and available in sufficient scale. We would need large amounts of the algae in order for it to be relevant for our plants, and it is not yet proven that algae can be cost-effectively cultivated on a large scale on lines or ropes in the sea,” says Jeppe Bjerg, Senior Innovation Manager at the Center for Innovation at DONG Energy. He elaborates:

“We still consider algae an area of great potential in the long run, but at present, we are primarily looking into options for using algae as a feedstock within an integrated biorefinery. We are revisiting the algae business case within this context and have special focus on synergies in integration with existing biorefinery platforms like Inbicon , REnescience and advanced biogas."


Collecting natural sea salad. Next step is to cultivate it on ropes anchored to the sea bed. Photo: Karin Svane Bech

A chain of challenges
Many specialized fields of knowledge are required to solve the problems that lie ahead for researchers in terms of extracting competitive energy from algae in a combination with other products.

Peter Daugbjerg Jensen agrees that challenges come in bundles:

“The entire chain – from the cultivation and harvesting methods through to preparation of the algae for combustion, gasification, production of bioethanol and biogas. And then the final challenge of the dried out algae containing too much alkali (salt) and ash to be useful for combustion. They all pose new challenges. And we need to develop the entire chain. For one thing, we need to identify the right heat treatment and combine it with the adding of the right enzymes,” says Peter Daugbjerg Jensen. He continues, “And in a completely other direction, we have to solve the whole production and processing apparatus challenge. That is why we look into every link in the chain: Cultivation on ropes in the sea, vessels for harvesting the macro algae, and much more. Taking into account that 85% of the seaweed is water, we need facilities for extracting most of that water at sea, increasing the amount of dry seaweed in each shipment. We have touched on these challenges in our joint project with Dong Energy, the Technical University of Denmark, the National Environmental Research Institute, and the Danish Technological Institute, but there is a long way to go.”

The chemical composition of algae is very complex and poses several challenges. Peter Daugbjerg Jensen has a clear desire for future discoveries within the field of algae:
“We have to find a method of chemically decomposing the algae – splitting up the carbohydrates and the proteins and the other substances of the biomass. If I could choose freely which challenge to solve, I would develop a method of extracting the protein fraction from the algae, and then I would develop a preparation method that enables us to make biofuel from the algae.”

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