Utilizing beach-cast seaweed for biochar production in Gotland : A study of energy and carbon balances of algal biochar
Abstract: With global warming, rising environmental issues, and increased beach-cast production, climate change mitigation efforts are important for the future of the planet. Carbon dioxide removal technologies are now deemed essential to reach the Sustainable development goals and keep the temperature rise under 1.5 or 2 degrees °C. Biochar produced from beach-cast seaweed has great potential as a fuel or as a means of carbon sequestration, while also proposing a way of dealing with unwanted beach-cast at public beaches. This study compares the alternative methodologies for performing carbon- and energy balances of the production of biochar from beach-cast seaweed. The methodologies differ in the accounting of emissions and energy consumption, either only accounting for consumed energy, including energy embodied in materials, or including avoided emissions. The viability of producing biochar from beach-cast seaweed is assessed while trying to answer if the biochar is best used as a fuel or as a means of carbon sequestration. Furthermore, the effect of pyrolysis peak temperature on the pyrolysis products is assessed. The study provides evidence that waste products such as beach-cast seaweed can be a valuable resource both in the field of power production and for climate mitigation. Beach-cast has the potential to mitigate climate change by offsetting 0.5 kg CO₂e per kg of dry beach-cast. Using the full potential of Gotland, this would mean a carbon capture potential of 1 600 tonnes CO₂e per year. Furthermore, the energy balance suggests a best-case scenario of 4.5 proving that biochar production from beach-cast is viable as a fuel. However, the results vary depending on the methodology used for the assessment. If energy bound in materials is included, the carbon balance is not good enough for carbon sequestration while including avoided emissions leads to a more optimistic result. The study shows that a peak temperature of 500°C is optimal for producing biochar with a high energy content and that natural drying should be included in the drying process to reduce CO₂e emissions and energy consumption in the production process.
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