The available energy can be effectively upgraded by adopting smart energy conversion measures. The biodegradability of biomass can be improved by employing pretreatment techniques; however, such methods result in reduced energy efficiency. In this study, microwave (MW) irradiation is used for green algae (Enteromorpha) pretreatment in combination with iron oxide nanoparticles (NPs) which act as a heterogeneous catalyst during anaerobic digestion process for biogas enhancement. Batch-wise anaerobic digestion was carried out. The results showed that MW pretreatment and its combination with Fe₃O₄ NPs produced highest yields of biogas and hydrogen as compared to the individual ones and control. The biogas amount and hydrogen % v/v achieved by MW pretreatment + Fe₃O₄ NPs group were 328 mL and 51.5%, respectively. The energy analysis indicated that synergistic application of MW pretreatment with Fe₃O₄ NPs produced added energy while consuming less input energy than MW pretreatment alone. The kinetic parameters of the reaction were scientifically evaluated by using modified Gompertz and Logistic function model for each experimental case. MW pretreatment + Fe₃O₄ NPs group improved biogas production potential and maximum biogas production rate.

Demand for clean energy has increased due to the proliferation of climate change impact from excessive emission of greenhouse gases (GHG) from the combustion of fossil fuels. H₂ is a clean energy source since water vapor is the only byproduct after its combustion. Growing microalgae offers a promising low-energy and low-cost approach for bioH₂ production. In this study, a bibliometric analysis was performed for the production of H₂ using microalgae to evaluate the conceptual, intellectual, and social structure of the dataset. In addition, a scoping review of articles was conducted to highlight recent advancements and identify future research recommendations. A total of 184 relevant publications over 23 years (2000–2022) were retrieved from the Scopus database for analysis. The results demonstrated an exponential increase in citations from 283 to 996 in the last decade, indicating the interest in bioH₂ production from microalgae. Results also revealed that the International Journal of Hydrogen Energy accounted for more than 25% of the published articles, of which China contributed almost 28%. Oxygen sensitivity of the H₂ase enzyme and sulfur deprivation were highlighted as the main limiting factors of bioH₂ production using microalgae. It was also evident that the most widely studied microalgae species were green algae, especially Chlamydomonas and Chlorella. Effective process modifications, particularly hybridizing microalgae with bacteria consortium and implementing oxygen regulating strategies, were shown to give up to a 10-fold increase in H₂ yield. This study also discusses recent developments in technologies, strategies, microalgal species, and optimizing controlling factors affecting bioH₂ production.