Appraisal of various approaches to produce biohydrogen and biodiesel from microalgae biomass

The need for fossils fuels, including oil, coal and natural gases, has increased dramatically due to a vast expansion in human population and economic growth. The emission of greenhouse gases from fossil fuels leads to disastrous alterations in the earth's climate. In a few decades, fossil fuels will run out because of their non-renewability. Many researchers are motivated to develop new renewable energy sources to replace fossil fuels. Recent research has identified microalgae as a promising resource for the production of biohydrogen and biodiesel. Biohydrogen production affords an environmentally friendly and sustainable approach to generate clear, clean and reliable energy from renewable resources. Green microalgae use sunlight to convert water molecules into oxygen and molecular hydrogen under special conditions. Microalgae have also been reported as a promising feedstock for biodiesel production, as biodiesel is considered the best alternative to petroleum-derived diesel. In the present review, the production of biohydrogen and biodiesel from microalgae through different methods, including indirect and direct biophotolysis, transesterification and lipid synthesis, enhancement approach, is briefly discussed. This article is critical for exploring ideas for future research that can be applied in the commercialization of biohydrogen and biodiesel from microalgae biomass.Keywords: Biohydrogen; Biodiesel; Biophotolysis microalgae; Transesterification