The cultivation of seaweed as a feedstock for third generation biofuels is gathering interest in Europe, however, many questions remain unanswered in practise, notably regarding scales of operation, energy returns on investment (EROI) and greenhouse gas (GHG) emissions, all of which are crucial to determine commercial viability. This study performed an energy and GHG emissions analysis, using EROI and GHG savings potential respectively, as indicators of commercial viability for two systems: the Swedish Seafarm project's seaweed cultivation (0.5 ha), biogas and fertilizer biorefinery, and an estimation of the same system scaled up and adjusted to a cultivation of 10 ha. Based on a conservative estimate of biogas yield, neither the 0.5 ha case nor the up-scaled 10 ha estimates met the (commercial viability) target EROI of 3, nor the European Union Renewable Energy Directive GHG savings target of 60% for biofuels, however the potential for commercial viability was substantially improved by scaling up operations: GHG emissions and energy demand, per unit of biogas, was almost halved by scaling operations up by a factor of twenty, thereby approaching the EROI and GHG savings targets set, under beneficial biogas production conditions. Further analysis identified processes whose optimisations would have a large impact on energy use and emissions (such as anaerobic digestion) as well as others embodying potential for further economies of scale (such as harvesting), both of which would be of interest for future developments of kelp to biogas and fertilizer biorefineries.

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 large-scale 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.

Interest to harvest wild cyanobacteria exists due to the environmental and socioeconomic risks during cyanobacteria blooms coupled with demands for nonterrestrial-based alternatives for biofuel sources. This research, therefore, sought to estimate the wild cyanobacteria harvesting potential using Nodularia spumigena, and using the Baltic Sea as the case study. Data from literature provided during years 2003-2009 were used to perform estimations. Additional benefits of harvesting were also assessed by estimating the nutrient removal and biogas production potentials from the harvested biomass. Results indicate that one boom unit has the potential to harvest approximately 3 to 700 kg dry weight of N. spumigena per hour depending on the algae concentration of the bloom. Results also suggest that nutrient removal and biogas production potentials provide substantial additional incentives to the harvesting operation during years of extensive and highly concentrated blooms. However, during nonextensive or nonconcentrated blooms such potentials are low.

Coastal areas around the world are experiencing environmental problems such as climate change and eutrophication. These, in turn, lead to emerging challenges with excessive amounts of biomass that impact coastal communities. Developing utilisation strategies for marine biomass is therefore highly relevant and forms part of the blue growth research field. In response to environmental concerns, as a waste management strategy and as part of blue growth research initiatives, several Baltic Sea coastal projects have been initiated in recent years to study utilisation of maritime biomass. However, the sustainability of these utilisation strategies has not been critically appraised. Therefore, the work presented in this thesis explored some key sustainability aspects of two Baltic Sea case studies utilising common reed (Kalmar, Sweden) and mass-occurring filamentous macroalgae (Trelleborg, Sweden) for biogas and biofertiliser recovery. Energy analyses suggested that both case studies could provide a positive energy balance and have the potential to achieve nutrient recovery. Moreover, a contingent valuation study in Trelleborg demonstrated considerable welfare benefits of biomass utilisation. These findings indicate that marine biomass utilisation strategies highlight potential to contribute to environmental and welfare benefits of these coastal communities.

Several ongoing projects are harvesting maritime biomass from the Baltic Sea for eutrophication mitigation and utilisation of the recovered biomass. Some of this biomass comprises common reed (Phragmites australis), one of the most widespread vascular plants on Earth. Reed utilisation from eutrophied coastal areas needs to be evaluated. Therefore, a system analysis was performed of reed harvesting for biofuel and biofertiliser production. The specific objectives of the analysis were to: investigate the methane yield associated with anaerobic co-digestion of reed; make a primary energy assessment of the system; quantify Greenhouse Gas (GHG) savings when a fossil reference system is replaced; and estimate the nutrient recycling potential of the system. The results from energy and GHG calculations are highly dependent on conditions such as system boundaries, system design, allocation methods and selected indicators. Therefore a pilot project taking place in Kalmar County, Sweden, was used as a case study system. Laboratory experiments using continuously stirred tank reactor digesters indicated an increased methane yield of about 220 m(3) CH4/t volatile solids from co-digestion of reed. The energy balance for the case study system was positive, with energy requirements amounting to about 40% of the energy content in the biomethane produced and with the non-renewable energy input comprising about 50% of the total energy requirements of the system. The net energy value proved to be equivalent to about 40 L of petrol/t reed wet weight. The potential to save GHG emissions compared with a fossil reference system was considerable (about 80%). Furthermore an estimated 60% of the nitrogen and almost all the phosphorus in the biomass could be re-circulated to arable land as biofertiliser. Considering the combined benefits from all factors investigated in this study, harvesting of common reed from coastal zones has the potential to be beneficial, assuming an appropriate system design, and is worthy of further investigations regarding other sustainability aspects.

The interest in harvesting biomass from the Baltic Sea has increased in recent years. However, there is a lack of available data on macroalgae biomass and of cost-effective methods for site-specific quantification of macroalgae. In this study, macroalgae biomass has been quantified in Trelleborg and thus the nutrient reduction that could be achieved by harvesting on a regional scale. The biomass was estimated on the basis of existing inventories of macroalgae, photic zone distribution and bottom substrata. An independent model for estimating the potential of macroalgae growth was applied where factors affecting the growth of macroalgae, for example nutrients, light and temperature, were considered. The estimated summer stock of macroalgae biomass along the 58 km coastal stretch in Trelleborg amounts to 19 000 tonnes dry weight (dwt) red filamentous algae. If 10-30% of this summer stock were to be harvested, a nutrient reduction of 50-150 t of nitrogen could be achieved. The model for estimating biomass proved promising and worthy of further investigation.

Eutrophication and global warming have created major problems with decaying macroalgae on Baltic Sea beaches. A considerable amount of this biomass is retrieved, only to be returned to the sea when the tourist season ends. It is therefore essential to implement systems whereby the retrieved biomass is utilised. One potential system is anaerobic digestion for biogas and biofertiliser recovery, but knowledge about non-market benefits is lacking. This study estimated the willingness-to-pay (WTP) for algae retrieval and utilisation in a case study area and examined methods for incorporating preference uncertainty information into WTP estimates. This was done by gathering data using two different methods and comparing the results. In addition, results obtained from an open-ended interval (OEI) format were compared with those from a payment card. A substantial mean WTP was found. The two elicitation formats produced similar mean WTP estimates. However, the OEI format produced weaker results, with a significantly higher level of stated preference uncertainty and an elevated zero response rate. Comparisons of preference uncertainty information gathered with two different methods yielded unexpected results and to some extent contradicted findings on interval size in the OEI format as a good measure of preference uncertainty.