Harvesting of drifting filamentous macroalgae in the Baltic Sea: An energy assessment

Abstract

Red seaweed derived polysaccharides, a novel marine resource for bio-ethanol production J. Renewable Sustainable Energy 6, 033122 (2014); 10.1063/1.4880515 Multifrequency species classification of acoustic-trawl survey data using semi-supervised learning with class discovery Eutrophication combined with climate change has caused ephemeral filamentous macroalgae to increase and drifts of seaweed cover large areas of some Baltic Sea sites during summer. In ongoing projects, these mass occurrences of drifting filamentous macroalgae are being harvested to mitigate eutrophication, with preliminary results indicating considerable nutrient reduction potential. In the present study, an energy assessment was made of biogas production from the retrieved biomass for a Baltic Sea pilot case. Use of different indicators revealed a positive energy balance. The energy requirements corresponded to about 30%-40% of the energy content in the end products. The net energy gain was 530-800 MJ primary energy per ton wet weight of algae for small-scale and largescale scenarios, where 6 000 and 13 000 tonnes dwt were harvested, respectively. However, the exergy efficiency differed from the energy efficiency, emphasising the importance of taking energy quality into consideration when evaluating energy systems. An uncertainty analysis indicated parametric uncertainty of about 25%-40%, which we consider to be acceptable given the generally high sensitivity of the indicators to changes in input data, allocation method, and system design. Overall, our evaluation indicated that biogas production may be a viable handling strategy for retrieved biomass, while harvesting other types of macroalgae than red filamentous species considered here may render a better energy balance due to higher methane yields. V C 2014 AIP Publishing LLC.

Seaweed resources of the Baltic Sea, Kattegat and German and Danish North Sea coasts

“…A number of pilot projects in the Baltic Sea area have tested methods to produce biogas from beach cast. For instance, the Swedish municipality Trelleborg tested biogas production through anaerobic digestion in a customized biogas plant, using the residue as biofertilizer in agriculture (Risén et al 2014). The results show that it is possible to achieve a positive energy balance for the biogas production (Risén et al 2014), but also that there are considerable practical challenges including handling of the sand mixed in with the seaweed and the high salt, sulfur and sometimes cadmium levels in the biomass that limit its usefulness as fertilizer.…”

“…For instance, the Swedish municipality Trelleborg tested biogas production through anaerobic digestion in a customized biogas plant, using the residue as biofertilizer in agriculture (Risén et al 2014). The results show that it is possible to achieve a positive energy balance for the biogas production (Risén et al 2014), but also that there are considerable practical challenges including handling of the sand mixed in with the seaweed and the high salt, sulfur and sometimes cadmium levels in the biomass that limit its usefulness as fertilizer. The Danish municipality Solrød recently constructed a biogas plant that was specifically designed for anaerobic degradation of beach cast seaweed mixed with manure and carrageenan and pectin production waste.…”

A Review on the Valorization of Macroalgal Wastes for Biomethane Production

“…The collection or harvesting of marine macroalgae from aquatic environments requires efficient, simple and affordable methods. Marine macroalgae can be harvested in different ways, either manually or mechanically, depending on the biomass linkage and whether they are accumulated on the beach or floating in open or shallow waters [ 53 , 146 , 161 ]. Macroalgae cultivation facilities represent a source of experience regarding macroalgae harvesting from water.…”

Fermentative hydrogen production using algal biomass as feedstock

“…The energy analysis for whole process of hydrogen fermentation (combined dark and photo fermentation) from algal biomass has been rarely reported. A recent study by Risen et al indicated the whole process of biogas production from waste macroalgae in the Baltic Sea consumes 30-40% of energy content in biogas [157]. More studies on mass, energy and economical balances of the whole process should be carried out in the future.…”

“…A pilot project in Sweden has been established to harvest drifting filamentous macroalgae from shorelines in Baltic Sea. The harvested macroalgal biomass may be used for biogas production [157].…”