Slow pyrolysis of Ulva lactuca (Chlorophyta) for sustainable production of bio-oil and biochar

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

The potential of sustainable biogas production from macroalgae in Indonesia

Indonesia is the second world's major macroalgae producer after China, contributing to 28% of the global macroalgae production. Indonesia increased its macroalgae farming output from less than 4 million tons in 2010 to over 9.9 million tons in 2019. It is expected to continue rising to 13 million tons by 2024. The contribution of macroalgal products is quite significant, 60.7% of the total national aquaculture production. To achieve sustainable energy development goals in many developing countries, including Indonesia, biomass to energy technology such as the production of biogas form macroalgae has been considered one of the best options. Therefore, we aim to investigate the potential application of biomass to energy technology via the production of biogas from macroalgae as an alternative source of local power generation. Indonesia's energy mix and several issues regarding macroalgae production are comprehensively reviewed. Additionally, we also discussed the process of macroalgal biogas production

Green algae to green fuels: Syngas and hydrochar production from Ulva lactuca via sub-critical water gasification

Biomass-derived energy is gaining more attention due to environmental issues and increasing energy demand. To ensure the sustainability of fossil energy substitution using biomass, diversification of sources, including marine organisms, is vital. Among various types of marine biomass discussed in the literature, the utilization of green algae Ulva lactuca for energy generation is still rare globally. Therefore, this study aims to investigate the potential of green fuel (syngas and hydrochar) production from U. lactuca (Chlorophyta) via sub-critical water gasification (SbWG). The experiments were conducted using a batch reactor at varying temperatures (300, 350, and 400 °C), reaction times (30, 60, and 90 min), and feedstock concentrations (1 and 5 wt%). The effect of temperature on gas composition was examined in detail. The results revealed that increasing temperature from 300 to 400 °C leads to an increase in the H2 content significantly from 2.21 % to 8.09 % within 90 min. However, increasing feedstock concentration from 1 to 5 wt% reduces the H2 fraction due to suppression of the steam reforming and water-gas shift reactions. Based on the ultimate analysis, the high severity of operating conditions leads to lower O/C and H/C atomic ratios owing to dehydration and decarboxylation reactions. It was confirmed by scanning electron microscope (SEM) analysis that more void structures existed in hydrochar than the algal feedstock. The SbWG process at varying temperatures and times can increase the energy contents of U. lactuca by over 47 %. Intriguingly, hydrochar obtained at 400 °C exhibited higher HHVs (i.e., 21.75–22.93 MJ kg−1) than typical low-ranked coals, making hydrochar more potential to be used as solid fuels. Finally, a reaction model was deduced, and the decomposition of U. lactuca was confirmed to follow the Arrhenius behavior