Mohiodin Nazemi

Recurrent influxes of pelagic Sargassum seaweed along Caribbean coastlines pose growing environmental and socio-economic challenges while offering an underutilised renewable biomass resource. This study examines the feasibility of converting Caribbean Sargassum into a solid biofuel through pelletisation, focusing on energy performance and process efficiency. Pellets were produced at laboratory scale using four feedstock compositions containing 0–100% Sargassum, providing the first systematic experimental assessment of full-range Sargassum co-pelletisation combined with an energy balance. Pellets were characterised for density, mechanical strength, moisture and ash contents, and higher heating value, and an energy balance was developed for the full processing chain, including collection, preprocessing, drying, and pelletisation. Results show that Sargassum can be densified into mechanically robust pellets with high particle and bulk densities. However, increasing Sargassum content sharply increased ash content and reduced heating value, with pure Sargassum pellets exhibiting ash contents near 47% and heating values below 8 MJ kg−1. Drying was the dominant energy consumer, rendering net energy returns marginal for 100% Sargassum pellets. Co-pelletisation with woody biomass at 50–75% Sargassum provided a more favourable balance between energy yield and biomass utilisation. Overall, Sargassum pelletisation is best suited to industrial-scale renewable and waste-to-energy systems integrated with efficient drying strategies.

Intermittent drying (ID) is often reported to be more energy-efficient than continuous drying (CD), although prior studies frequently lack consistent comparison conditions. A recent meta-analysis suggested a probable correlation between material thickness, initial water content, and the specific energy savings of ID. The present study was conducted to experimentally validate these findings under controlled and comparable conditions. Drying experiments were performed using a porous sponge model, with thicknesses ranging from 12 to 48 mm and initial water contents from 30% to 70% (wet basis), while maintaining identical operating conditions and total drying time for both ID and CD. Results show that the energy advantage of ID is condition-dependent rather than universal. For thin or low-moisture samples, the specific energy consumption ratio (ĒCD/ĒID) remained close to unity (~0.97–1.00), indicating negligible differences. In contrast, for thicker (≳36 mm) and wetter (≳60%) samples, the ratio reached ~ 1.05, corresponding to energy savings of up to 4–5%. These findings support a threshold-like behavior governed by internal moisture redistribution during tempering. The study provides experimentally validated criteria for selecting drying strategies and highlights the importance of fair comparison under equal drying duration

Seaweed can be a desirable source of renewable energy or fuel after it has been processed by combustion, thermochemical conversion by gasification, pyrolysis, or hydrothermal liquefaction (HTL) or biochemical conversion routes like anaerobic digestion (AD). This work explores how well the measured properties of seaweed pellets match the specifications for the various fuel and energy conversion options listed. Blends of hay, wood chips, sawdust, and seaweed were pelletized. Eight pellet blends with dominant seaweed content and minimum acceptable mechanical strength and stability were produced and their physical and chemical properties were reported. The seaweed pellets had an energy content of around 14 MJ/kg, and each pellet could withstand almost 200 N of compression force. Their water content was around 5% or less and their ash content was around 20–34%. According to the results, a higher wood content increased the energy content of the pellets. Among those properties measured in this project, none of them contradicted the typical specifications of combustion, HTL, and AD. However, the low water content and low strength of some pellet types were unable to meet the specifications for certain types of gasification and pyrolysis.