Ulva Lactuca is a fast-growing algae that can be utilized as a bioenergy source. However, the direct utilization of U. lactuca for energy applications still remains challenging due to its high moisture and inorganics content. Therefore, thermochemical processing such as slow pyrolysis to produce valuable added products, namely bio-oil and biochar, is needed. This study aims to conduct a thorough investigation of bio-oil and biochar production from U. lactuca to provide valuable data for its further valorization. A slow pyrolysis of U. lactuca was conducted in a batch-type reactor at a temperature range of 400–600 °C and times of 10–50 min. The results showed that significant compounds obtained in U. lactuca’s bio-oil are carboxylic acids (22.63–35.28%), phenolics (9.73–31.89%), amines/amides (15.33–23.31%), and N-aromatic compounds (14.04–15.68%). The ultimate analysis revealed that biochar’s H/C and O/C atomic ratios were lower than feedstock, confirming that dehydration and decarboxylation reactions occurred throughout the pyrolysis. Additionally, biochar exhibited calorific values in the range of 19.94–21.61 MJ kg⁻¹, which is potential to be used as a solid renewable fuel. The surface morphological analysis by scanning electron microscope (SEM) showed a larger surface area in U. lactuca’s biochar than in the algal feedstock. Overall, this finding provides insight on the valorization of U. lactuca for value-added chemicals, i.e., biofuels and biochar, which can be further utilized for other applications.

Indonesia is a maritime country with a coastline length of more than 95 thousand km, and the ocean area exceeds 3 million km² covering almost two third of the nation. With the vast ocean area, Indonesia has a large potential for maritime organisms, such as macroalgae or popularly called seaweed. Indonesia has more than 500 species of seaweed, but only a few that has been utilized, and mainly as food or pharmaceutical resources. Whereas Indonesian macroalgae potential as an energy feedstock is still not much explored. In this study, we assessed the potential of less-utilized macroalgae species from Indonesia, namely Padina sp., as feedstock to produce hydrochar in comparison with other species. The proximate and ultimate characteristic of macroalgae as feedstock was investigated, and its potential to generate hydrochar was discussed.