Chemical composition and bioenergy potentials of eleven species of macroalgae harvested in Danish
and Greenland seawaters
Anne-Belinda Bjerre1, Annette Bruhn2, Michael Bo Rasmussen2, Peter Daugbjerg Jensen1, Bodo Sake3,
Jürgen Puls3
1 Danish Technological Institute, Gregersensenvej, 2630 Taastryp, DENMARK; 2Aarhus University, National Environmental Research
Institute, Vejlsøvej 25, 8600 Silkeborg, DENMARK;3 vTI-Institute for Wood Technology and Wood Biology, Leuschnerstr. 91 b, D21031 Hamburg, GERMANY
Background and purpose: Macroalgae represent a huge unexploited bio-resource of the sea including
several thousand species. The production of macroalgae relies on sunlight for energy and assimilation of
CO2 and nutrients, in particular N (nitrogen) and P (phosphorus) for biomass, with a production potential of
more than 4-10 times that of land based crops. Macroalgae thus, serve as a sink to assimilate CO2, N and P,
minimizing their influence to the environment and converting them back into valuable carbohydrate,
proteins and lipids. Protein and carbohydrate content of species vary over the year and shows diverging
tendencies due to the growth strategy of these organisms. The main constituents of macroalgae are sugar
polymers of both C5 and C6 sugars. In their mono-saccharide form, those can serve as substrate for fuel
ethanol, butanol and biogas (methane) production. The purpose of this work was to harvest different
species from the Danish and Greenland coastal waters and analyze their chemical compositions of
carbohydrates and protein in order to estimate their bioethanol, butanol and biogas potentials as well as
their potentials in production of value added protein feed. Enzymatic hydrolyses of the dried untreated
samples were done to evaluate the need of pretreatment before fermentation trials.
Approach and results: Ten species of macroalgae were harvested from natural populations in Danish or
Greenland seawaters. Their potential for utilization in future biorefineries for the production of animal feed
and energy carriers was investigated. Five species of brown algae (Saccharina latissima, Laminaria digitata,
Agarum clathratum, Laminaria longicruris, Ascophyllum nodosum), five species of red algae (Palmaria
palmata, Odontalia dentata, Delesseria sanguinea, Cystoclonium purpureum, Dilsea carnosa) and one green
algae, (Ulva lactuca) were used. The elleven species were analyzed for their contents of C5 and C6 sugars,
protein and salts. Enzymatic hydrolyses were carried out on selected species for sugar hydrolysis. Based on
the results, the bioethanol, butanol and biogas potentials were calculated, and the protein fraction was
estimated, which could be a potential feedstock or supplemental protein source for fish feed.
Scientific innovation and relevance: The interest for using macroalgae for energy purposes and feed supply
has increased significantly during the last decades. Some of the macroalgae have a great potential for
bioethanol production by means of simple yeast fermentation due to a significant glucose content, but
other microorganisms can be used for butanol and biogas production. The results indicate that less severe
pretreatment conditions is needed for improved enzymatic hydrolysis than seen for lignocellulosic plant
residues.
Main conclusions: The carbohydrate composition of the analyzed macroalgae varied between 9 to 59% of
dry matter, some with high content of glucose others with high content of xylose and galactose. The
ethanol, butanol and biogas potentials for some algae were in the range of terrestic plant materials like
wheat straw, however the results indicates that additional enzyme will be needed due to different
carbohydrate compositions and linkages. The protein contents were up to 20% of dry matter, with indicates
that some macroalgae could serve as feedstocks for animal feed.