Balancing quality and yield of biofuel and biochar in the pyrolysis of industrial macroalgae sludge: future perspectives with a circular economy approach in the EU FLEXBY project

The accumulation of algal bio-waste, particularly in the form of solid waste from industrial processing of macroalgae, poses significant environmental and human health challenges. The presence of large quantities of untreated algal waste can lead to ecosystem imbalances such as oxygen depletion in aquatic environments, harmful algal blooms and the release of greenhouse gases during decomposition. In addition, inappropriate disposal of bio-waste contributes to soil and water pollution, which can affect marine biodiversity and local fisheries. From a public health perspective, decomposing algae can release toxic compounds and unpleasant odours, posing a risk to air quality and public well-being. Given the increasing global production of macroalgae for food, pharmaceuticals and bio-based materials, it is imperative to implement sustainable strategies to manage and reuse these wastes (Pardilhó et al., 2021). The valorisation of algal bio-waste into valuable bio-based products and energy sources offers a promising solution to mitigate its negative environmental impact, while supporting the transition towards a circular bio-economy, and has shown a high potential for bio-energy production (Anacleto et al., 2025).

The purpose of this work was to examine the feasibility of using industrial macroalgae sludge as a potentially valuable resource. This analysis was carried out with the aim of obtaining, through thermal pyrolysis processes, bioenergy and bioproducts, thus avoiding the need for landfill or incineration. In accordance with the guidelines of the EU FLEXBY Project, the experimental variables of conventional pyrolysis will be optimised to maximise the bio-oil and gas yield.